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PROYECTO FIN DE CARRERA INGENIERÍA INDUSTRIAL CLIMATIZACIÓN DE UNA CASA UNIFAMILIAR MEDIANTE UNA MÁQUINA DE ABSORCIÓN DE TRIPLE ESTADO ALIMENTADA CON PANELES SOLARES TÉRMICOS. ESTUDIO DE VIABILIDAD ECONÓMICA Y MEDIOAMBIENTAL EN COMPARACIÓN CON SISTEMAS CONVENCIONALES. Autor: Luis Gallardo Carro Director del proyecto: Dr. Tero Tynjälä Tutor del proyecto: Dr. Jose María Marín Herrero Zaragoza, Junio 2011 Área de máquinas y motores térmicos Departamento de ingeniería mecánica CENTRO POLITÉCNICO SUPERIOR DTO. INGENIERÍA MECÁNICA Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 44 Annex Annex 1. Characteristic equations of the main equipment………………………..……46 Annex 2. Technical specifications...................................................................................49 Annex 3. Solar collector..................................................................................................51 Annex4. Propilenglicol…………………………………………………………………55 Annex 5. Heat exchanger................................................................................................57 Annex 6. ClimaDeck………………………………………………………………...…58 Annex 7. Hot water tank……………………………………………………………….60 Annex 8. Boiler…………………………………………………………………………62 Annex 9. Simulation report.............................................................................................63 Annex 10. Economic profitability analysis.....................................................................69 lo Annex A. Thermal solar energy……………………………………………………..…70 Annex B. Solar heating technology………………………………………………….…90 Annex C. Cooling technology……………………………………………………...…101 Annex D. Description of housing……………………………………………..………115 Annex E. Calculation of thermal loads………………………………………………..124 Annex F. Report (English).............................................................................................131 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 45 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 46 Annex 1. Characteristic equations of the main equipment This section contains the basic equations that define the behavior of the two main systems (Roca Calefacción, 2007) of the circuit, such as the plane collector and the heat exchanger. 1.1. Characteristic curve of equations and flat solar collector The energy balance of a flat collector is: Where: • Q1: Incident total energy (direct + diffuse + reflected). • Q: Useful Energy. • Q2: Energy lost by dissipation to the outside. • Q3: Energy stored as heat in the collector. The useful energy of the collector at a given time is depending on solar radiation and ambient temperature, being the difference between energy absorbed and the losses. The following equation shows the useful energy of the collector: Where: • S c : Area of the collector (m 2 ). • R 1 : Total incident radiation over the collector by unit of area (W/m 2 ). • τ: Transmittance of transparent surface. • α: Plate absorptance. • U L : Global losses coefficient (W/mºC). • T m : Average temperature of the absorbing plate (ºC). • T a : Room temperature (ºC). Is defined an efficiency factor of heat exchange between the plate and the solar fluid, F R , as the ratio between the energy captured and that could capture, if the plate temperature was the same that of the temperature fluid at the entrance the collector. Based on this factor, the equation of Bliss or characteristic of the collector is defined as: The new terms introduced in the equation are: • Q: useful energy captured (W). • F R (τα)n: Orderly line of the performance curve of the sensor. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 47 • F R U L : Straight slope of collector performance curve. • T e : temperature heat transfer fluid in the inlet (ºC). Characteristic curve of a flat collector The efficacy rate of the collector is defined by the ratio between the captured and received energy in a given time. Where: • F R (τα)n: Orderly line of the performance curve (dimensionless). • F R U L : Straight slope of the collector performance curve. • R l : Radiation in the plane of collector (W/m 2 ). • T e : Heat transfer fluid temperature in the inlet (ºC). • T a : Room temperature (ºC). This characteristic curve is provided by the manufacturer and it is determined through testing by the companies of approval. Basing on the curve can be deduced the operation of a collector from the thermal point of view. A collector will be better when its orderly line F R (τα)n will be highest and the slope F R U L will be lower. 1.2. Heat Exchanger When the liquid which circulates through the collector cannot be used directly for consumption, must be entered a heat exchanger between the collector (primary circuit) and the circuit of utilization (secondary circuit). This happens due to the presence of antifreeze in the circulating fluid. The exchange can be produced in a external heat exchanger to the storage tank or in the inside serpentine of the tank, both with a similar thermal behavior. Heat exchanger effectiveness The effectiveness of heat exchanger is a parameter that directly affects the determination of the collector’s surface, and its dimension describes the operation of the system. The following figure shows the evolution of temperatures in heat exchange with two flows (ṁ 1 and ṁ 2 ) which have a specific heat (C p1 and C p2 ) (Roca Heating, 2007). Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 48 Figure 17: Temperatures evolution of heat exchanger. The exchange power between the primary and secondary circuit, in ideal conditions (no losses) is: Performance of the heat exchanger is expressed in terms of effectiveness (E) and the speed minimum of heat capacity (mass flow x specific heat). Effectiveness is defined as: The real transfer of heat depends on the constructive characteristics of the heat exchanger and also of heat capacity and temperatures speeds of circulating fluids. The advantage of the concept of effectiveness is the relation between the amount of actual heat transfer and the maximum, which is relatively constant regardless of the variations of temperature; if the flows are constant (Roca Calefacción, 2007). Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 49 Annex 2. Technical specifications Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 50 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 51 Annex 3. Solar collector Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 58 Annex 6. ClimaDeck ClimaDeck hollow core slab system offers one of the most energy efficient HVAC solutions available on the market while providing top rated comfort levels. This is possible by adding a massive thermal storage to the air distribution; the building itself. ClimaDeck can be combined with all types of Air-Conditioning/Air Handling units (AHU) units. From the AHU-unit, generally placed on the roof, supply air ducts run in vertical shafts down to each floor inside the building and then to horizontal ducts placed in central corridors usually within false ceilings. Small branch ducts feed air into each slab, and the air then enters a room via diffusers fixed to the outlet of the slab. Diffusers are normally located close to external walls, or evenly spread over the ceiling in the office landscape. The exhaust air is normally transferred into the central corridor plenum and is returned to the AHU-unit in a conventional way. The main distribution ductwork in the corridor is similar in construction to that found in conventional systems. The main difference with ClimaDeck is that every individual structural hollow core slab is supplied with a small quantity of air from the main supply duct. The ClimaDeck system is different from conventional technologies because it is integrated with the heavy structure of the building. The last part of the ductwork system for the supply air consists of hollow core concrete slabs instead of traditional steel ducts. Figure 18: Air flow inside the hollow core slabs. ClimaDeck uses the thermal storage capacity of the structural mass in the building to regulate the internal temperatures. The effectiveness of the building's thermal mass is enhanced by passing supply air through the slab before it enters the room. The slabs work as heat exchangers between the supply air and the rooms, see figure 18. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 59 The floor/ceiling slabs serve many purposes: Besides from being the structural floor it also conveys fresh air into the building while serving as an energy store. The slabs are incorporated into the building and the main supply duct would normally be situated in the corridor. No ducts and therefore no false ceilings are required in individual rooms. This allows total freedom for the interior designer to locate, or re-locate in the future, the internal wall partitions. ---------------------------------------------------------------------------------------------------------- The distribution circuits depart from the supply and return manifolds. From there, the circuits are hydraulically balanced and the circulation of the water projected is regulated in accordance with the thermal needs of each space. The manifolds are placed centrally with respect to the areas to which they provide service. At least one electronic valve is necessary for every thermostat controlled space, and each manifold has a maximum of 12 circuits. For maximum comfort it is recommended to use one thermostat for each space (bedroom, kitchen, etc. For optimum temperature control the advisable circuit design is either double coil or spiral. The supply and return pipes should always be contiguous so that the warmer pipe is always next to the colder pipe. This design ensures homogenised thermal distribution and increased comfort. For heating, a separation of 20 cm between each individual pipe is considered normal, and for air-conditioning, a separation of 15 cm is necessary (except in bathrooms, with a 10 cm separation). The type of distribution pipe and the separation between pipes should remain constant throughout the entire installation. Parts 1-4 of UNE EN 1264 specify the design and installation requirements of radiant floor heating systems. Nonetheless, this standard does not cover the design of floor-based cooling systems. UNE EN 1264-2 establishes a characteristic base curve that determines the balance between thermal flow density (q) in W/m 2 and the mean temperature of the floor surface in ºC. It is applicable to all types of radiant systems. The proportion between these is established as follows: Hot floor: q = 8.92 * (T floor/ceiling – T operative ) * 1,1 Cold floor: q = 7 * (T surface – T operative ) Radiant floors are considered suitable when the heating load is less than 100 W/m 2 , and the cooling floor when the load is less than 40 W/m 2 . For the floor, the minimum temperature recommended is 18ºC, although it will always be necessary to take the dew point of the air into account so as not to generate condensation. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 60 Annex 7. Hot water tank Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 61 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares Annex 8. Boiler Climatización de una casa mediante una máquina de absorción alimentada por paneles solares Boiler Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 62 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 63 Annex 9. Simulation report Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 64 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 65 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 66 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 67 Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 74 qualitative and quantitative leap forward and, in doing so, play a more important role in achieving Spain’s objectives for 2020. In the Community of Madrid, according to Plan of Renewable Energies 2004, 56.204 m 2 of solar collectors were installed, which represented 8% of Spain total collectors, knowing that the majority was in the tertiary sector. Due to the obligation of using it in the domestic sector, it was expected that in 2010, it would exceed the 338.709 m 2 installed. Nevertheless it was not the case, since only 17.024 m 2 were installed, about half of what was scheduled. Since the appliance of the Solar Thermal Ordinance, the 10 th of November 2003, 89% of installed solar surface into the Community of Madrid in 2010, took place in residential buildings and only 3% in industrial ones. A.2. Potential of solar thermal energy As only three renewable sources (biomass, geothermal and solar) generate heat, it is crucial to clarify how these different sectors can contribute to the renewable energy target. Obviously, solar thermal systems will be needed to provide a substantial share of the low temperature heat: deep geothermal sources are limited to a few locations in Europe and shallow geothermal is considered as energy efficiency technology within this study; biomass will be used for transport fuels, electricity generation and medium to high temperature applications as well. In order to provide the European Union and its Member States with substantiated information on the solar thermal contribution to the 20% renewable energy target and its long-term potential, detailed surveys were conducted using a representative sample of five European countries - Austria, Denmark, Germany, Poland and Spain. The information gathered was then extrapolated to the 27 EU countries. Both the technical and economic potential of solar thermal technologies were examined for different applications. To determine the potential contribution solar thermal would make to the overall heat demand in the selected reference countries, a model was developed for the future demand - taking into account also energy efficiency measures. Based on this model, the future heating and cooling demand was calculated for the years 2020, 2030 and 2050. The model includes three scenarios and focuses on the following segments: - Space heating of residential buildings. - Hot water preparation in the residential sector. - Space heating in the service sector. - Industrial low temperature heat (up to 250°C). - Air conditioning and cooling in the residential and service sectors. The three scenarios (figure 23) are a “Business As Usual scenario” (BAU), an “Advanced Market Deployment scenario” (AMD), including financial and political support mechanisms such as subsidies and obligations, moderate energy efficiency measures and improved research activities, and a “Full R&D and Policy scenario” Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 75 (RDP), which includes substantial financial and political support mechanisms, energy efficiency measures and research activities. Figure 23: Development of EU-27 solar thermal capacity according to 3 scenarios (2005- 2050). (ESTIF 2010) A.2.1. Contribution of solar thermal to the EU 20% renewable energy target. (Figure 24) Assuming there is a 9% reduction of the overall final energy demand due to energy efficiency measures by 2020 (compared with the year 2006), the contribution of solar thermal to the EU 20% Renewable Energy target would be 6,3% in the RDP scenario and 2,4% in the less ambitious AMD scenario. Related to the required 11,5 percentage points increase in renewable energies (the share of renewable in 2005 was 8,5%) in the EU-27 countries by 2020, the contribution of solar thermal would be 12% according to the RDP scenario, 4,5% according to the AMD scenario and 2,9% in the BAU scenario. To reach the goals of the RDP scenario, a 26% average annual growth rate of the European solar thermal market is needed up to 2020. A 15% average annual growth rate is required to reach the goals of the AMD scenario and a 7% growth rate for the BAU scenario. The resulting total collector area by 2020 would be between 97 million m 2 (BAU) and 388 million square meters (RDP). These collector areas correspond to total installed capacities of 67,9 GW th and 271,6 GW th . Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 76 Figure 24: Total heating and cooling demand of EU-27 and contribution of solar thermal by sector according to the Full R&D and Policy Scenario (RDP). (ESTIF 2010) A.2.2. Economic effects In the figure 25, we can see that according to the RDP scenario the impact on employment would be considerable. In total, the solar thermal sector would encompass 470.000 full-time jobs in 2020, in the European Union domestic market alone. An investment of the order of EUR 214 billion would be required in the solar thermal sector to reach the 2020 goals of the RDP scenario. This includes production, engineering, trade and installation of solar thermal systems from 2006 to 2020. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 77 Figure 25: Jobs in the solar thermal sector based on the Full R&D and Policy Scenario (Calculations assume an average increase of productivity of 4% per annum). (ESTIF 2010) A.2.3. Solar thermal contribution to the energy supply and CO 2 reduction. (Figure 26) The solar yield in the RDP scenario is 155 TWh in 2020. This corresponds to an oil equivalent of 22 billion metric tons. Taking this oil equivalent into account the annual contribution to the CO 2 reduction by solar thermal systems is 69 million metric tons. Figure 26: Annual contribution to the CO 2 reduction by solar thermal systems in the respective year - according to the Full R&D and Policy Scenario (RDP). (ESTIF 2010) A.2.4. Long-term potential In 2050, the solar thermal contribution to the European Union’s (EU-27) low temperature heat demand ranges from 47% in the RDP scenario to 8% in the BAU Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 78 scenario. The corresponding annual solar yields are 1552 TWh (RDP) and 391 TWh (BAU). The collector area needed to reach these goals is between 2 m 2 (BAU) and 8 m 2 (RDP) per inhabitant in the EU-27. The resulting total collector area is between 970 million m 2 (BAU) and 3,88 billion m 2 (RDP). If solar thermal is to contribute significantly to the long-term heating and cooling demand in the EU-27 countries then the primary focus in central and northern Europe must be on systems for space heating (solar combisystem) and in the Mediterranean area on systems providing space heating, hot water and air conditioning (solar combi+ systems). If the focus remains solely on solar thermal systems for domestic hot water preparation then the solar thermal contribution to the long-term final energy demand will be limited. By 2030 the full potential for these applications will have been reached and the market would be reduced mainly to the replacement of old systems. Another important segment with considerable potential is low temperature process heat for industry. Executive Summary The European Union and its Member States have committed themselves to achieving a 20% share of renewable energy in Europe’s final energy consumption by 2020. To reach this target, the renewable heating sector will have to make a significant contribution since the demand for heating and cooling represents 49% of the total energy demand in Europe. A.3. Regional and annual variations in heating and cooling power demand In this section, for assessing the demands, I will take into consideration the demand of hot water, heating demand and cooling demand. However, I will disregard the demand of heating pool water because the ClimateWell_10 machine heats the pool water with the energy of the dissipation. Following, you will find the explanation of the method for assessing energy demands through the figure 27 which show different dependences. I will not make an accurate calculation, since the simulation program used to calculate the graphs (demands) provide you the whole information and every equation into it. If we show the energy needs for hot water production, they will be higher during the winter months (the mains water is colder) than the summer months (the water is warmer). Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 79 On the other hand, the availability of solar radiation is much higher during the summer than in winter. In the figure 27 is showing that if by overlaying the graph of monthly power generated by solar collectors with the demand of hot water production, we make out clear that if the solar system provides the total needs in the summer months, it will not do 100% during the winter. Figure 27: Hot water demand and solar contribution. (Energía Solar Térmica, guía de usuario, Junta Castilla y León) Thus, for each application, there are an optimum number of collectors depending on the energy saving produced and the cost of placing more solar panels. We will take into consideration the number of collectors recommended by the manufacturer for a correct operation of the ClimateWell machine. Depending on the house size (square meter) and the people who are living in the house, we will place one or more machines. All of these figures would be similar in applications of air conditioning indoor and indoor pool but it will be very different in outdoor pools. Thus, for heating applications (with energy demand during the winter), solar system would be used for only 6-7 months per year (less radiation), missing a part of heat provide for the solar system when more heat is generated, as we can see in the figure 28. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 80 Figure 28: Heating demand and solar contribution. (Energía Solar Térmica, guía de usuario, Junta Castilla y León) In addition, the use of solar energy for heating needs a system of heat distribution which is compatible with the solar panels used. Thus, if the heat is distributed through radiators, it is required 80-60ºC of working temperature which it cannot be provide for this system in winter. However, if the target system is radiant floor or fan-coil units, the working temperature drops to 40-30ºC which is compatible with these collectors. Therefore, it must be reached that the annual demand will be similar to the input solar energy graph, which can be done, integrating different kinds of demand in one: demand during the winter (heating) must be compensate with other demand during the summer (cool), as we can see in the figure 29. Thus, an installation of solar energy might provide energy for both applications simultaneously, using in an optimized way, the solar system (investment) during the whole year (fuel savings for each application depending on season). The development of absorption refrigeration system as well as solar thermal systems, allows to cool Establishment, displacing the pools as absorbed of waste heat in summer months. This is achieved by squaring the circle: the house is heating and cooling with the same system without any wasting of solar energy. Taking into consideration that the transmission system used for heating or cooling (radiant floor) is the same. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 81 Figure 29: Heating and cooling demands. (Energía Solar Térmica, guía de usuario, Junta Castilla y León) The percentage of energy generated by the solar system in comparison with the energy required for the system is called coverage or replacement solar. This is expressed like an annual percentage. For example, a solar system has coverage of 70% of demand. In conclusion, the best applications of thermal solar energy are hot water production, heating and cooling as is noted in the regulation. That regulation, is Code Technical of Building -CTE-(RD 314/2006 of 17 March), requires that new buildings and complete improved buildings with consumption of hot water and air-conditioning have solar thermal systems which provide part of the demand. Following, I will explain a simple method for working out the energy demand of hot water and air conditioning. A.3.1. Calculation of monthly energy demand of the building The first step in the design of a hot water production system is: Assessing the energy demand of the building (DEmo), kWh/month. 12 values are usually calculated (one per month) which unit is kWh/month, according to the following formula: DEmo = Qday * N * (T hot water - Tcw) * 1,16*10 -3 Where: • Demo: energy demand in kWh/month. • Qday: daily consumption of hot water at the reference temperature T hot water, in liters/day. • N: the number of days of the month considered, days/month. • T hot water: the reference temperature used to quantify the consumption of hot water, in °C. • Tcw: temperature of the water supply, in °C. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 82 The temperature of hot water in a house changes depending on the application (bath, sink, shower ...). Typically, values of water consumption (Qday) are related to a given temperature (T hot water), which is used for calculating energy demand. Values showed above change depending on each area, and particularly in each City Hall. Then, I will show some reference values for the consumption of hot water in houses which are used to calculate energy demand in different towns in Spain. City Hall of Barcelona Method for calculating energy demand: • Qday: 40 liters per person per day. • T hot water: 60ºC. • Tcw: 10ºC. • The number of people is worked out using a housing functional program. If this is not defined, it should be considered 2 people in each bedroom. • For community facilities in residential buildings, consumption can reduced by f value which is calculated as the number of households n as follows: f = 1 for buildings with less than 10 houses. f = 1.2 to 0.02 • No buildings 10 to 25 houses. f = 0.7 for buildings more than 25 houses. City Hall of Sevilla Method for calculating energy demand: • Qday: 40 liters per person per day. • T hot water: 45ºC. • Tcw: 10ºC. • The number of people is worked out using a housing functional program. If this is not defined, it should be considered 2 people in each bedroom. • For community facilities in residential buildings, consumption can reduced by f value which is calculated as the number of households n as follows: f = 1 for buildings with less than 10 houses. f = 1,2 to 0,02 • No buildings 10 to 25 houses. f = 0,7 for buildings more than 25 houses. City Hall of Madrid Method for calculating energy demand: • Qday: 60 ºC, 22 liters per person per day for multifamily housing. • Qday: 60 ºC, 30 liters per person per day for single family homes. • The number of people determined from the number of bedrooms, according to the following table: Houses with a single room or apartments with 1 bedroom: 1,5 persons 2 bedroom houses: 3 people 3 bedroom houses: 4 people 4 bedroom houses: 6 people Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 83 5 bedroom houses: 7 people 6 bedroom houses: 8 people 7 bedroom houses: 9 people In the event that there is no ordinance that makes require the use of a particular value for water consumption: - Qday: 30 liters per person per day for multifamily dwelling and 40 liters per person per day for single family house. - T hot water: 60ºC. The values of cold water temperature Tcw are taken from the table 12. Table 12: Values of cold water temperature [Tcw]. (Salvador Escoda S.A., 2005) However, some Municipal ordinance set as water supply temperature (Tcw) for the calculation of thermal solar energy systems which might not be similar to the table above. The table 13 is used to calculate the demands of hot water. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 90 Annex B. Solar heating technology Solar technologies can supply the energy for all of a building’s needs without the harmful effects of greenhouse gas emissions created by fossil fuels. Solar applications can be used almost anywhere in the world and are appropriate for all building types:  Single-family homes.  Multi-family residences.  Office and industrial buildings.  Schools.  Hospitals.  Other public buildings. In the agriculture sector, solar technology is being used to dry crops ranging from coffee and tea to wool and chicken manure. Companies in Europe, North America, and numerous developing countries see this technology as a cost-effective and environmentally sensitive process. The majority of the energy used in commercial and industrial processes is below 250°C, a temperature range well suited for solar technologies. Solar technologies are being used for specific industrial processes, such as food processing, textile cleaning and drying, pharmaceutical and biochemical processes, desalination, and heating and cooling of factories. The most widespread applications of this technology for buildings are: heating, cooling and hot water. Other applications include water heating for indoor or outdoor pools and emerging applications such as air conditioning by absorption cycles, which is used in our project. Very schematically speaking, the solar thermal system is working as follow: the collector or solar panel captures the solar irradiation and absorbs the energy in the form of heat. Through the solar panel passes a fluid (usually water) which transfers the absorbed heat. The fluid temperature will increase, which will be stored or directly carried to the place of consumption. B.1. Solar thermal for hot water, pool heating, radiant floor heating B.1.1. Solar thermal hot water (DHW) The hot water is typically used at a temperature of 45-60ºC. This temperature is easily reached by a solar system whatever the season. A good percentage of DHW annual coverage is approximately 60%-70%. Indeed, we save that percentage of energy to heat water. We use this percentage, so that in the period of greatest solar radiation there is no excess of energy. The other needs not provided by the sun are obtained from Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 91 an auxiliary system that usually tends to be oil, gas or electricity. With this rate of solar contribution, payback periods are much more reduced. The initial investment is higher compared to the conventional system; however, it remains cheap because it has more than 20 years of life expectancy. Thus, the installation of solar energy is more economically advantageous, since all energy obtained from the sun with solar thermal collectors, will not have to be produced. The payback period on investment can fluctuate between 5 and 12 years depending on the size of the facility, on the place where it is installed (more or less radiation) and on the important needs or not, of the user. Figure 30 shows the schematic of an installation of hot water by solar thermal panels in a single family dwelling. Figure 30: Schematic of an installation of hot water by solar thermal panels in a single family dwelling. B.1.2. Solar thermal energy for heating swimming pools For a standard pool of 25m x 12.5m at a temperature of 28°C, the energy consumption can be higher than 300.000 kWh per year, depending on the number of inhabitants. Solar energy installations for pools are economically advantageous for two main reasons: - The pool is used as energy storage. Because of it, is not necessary to use accumulators, which makes the installation is more economical. - The optimum temperature of a swimming pool fluctuates between 23ºC and 30ºC depending on the needs, so the solar collectors are able to work with a lower temperature compared with other applications, they are therefore more efficient. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 92 Outdoor pools using solar collectors can lengthen the period of bath from April to October. In these cases are used collectors of polypropylene, in which can circulate the pool water itself, thus obtaining direct systems, in which the working fluid is water heating. Figure 31 shows the schematic of a heating installation of pool water with solar thermal combined with DHW. Figure 31: Schematic of a heating installation of pool water with solar thermal combined with DHW. B.1.3. Solar energy for radiant floor heating The radiant floor heating is a plastic pipe embedded in the mortar layer that goes heating the room. This piping leads hot water (at low temperature as compared to other heating systems) is usually produced by a boiler which can have a solar support. Through the pipe, the water transfers heat to the floor, which is then transmitted to the atmosphere of the enclosure. The emergence of cross-linked polyethylene pipes has revolutionized the world of underfloor heating. As a result, it has significantly reduced the installation time, the quality and the performance of the installation. In addition, solar heating underfloor has several advantages respect to conventional heating radiator: · The temperature distribution is ideal. It is desirable to achieve a higher temperature in the floor than in the roof since the feeling of getting heat in the floor is much comfortable than receiving it in the head. · Energy savings: With the usual radiator heating, the circuit carries water at an average temperature of 80ºC. In floor heating, the water temperature is around 40-45°C. If we work with this low temperature, heat losses in pipes are generally minor. This also reduces heat loss through roofs and outside air. With all these factors, it can be assured that energy savings from radiant floor heating is about 15% compared with traditional heating systems. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 93 · Environmentally friendly: it can be combined with alternative energy such as solar or geothermal heat pump due to the low temperature required. · Uniform temperature: With radiant floor heating, a uniform temperature can be obtained in all the surface of the housing (about 22ºC) disappearing hot and cold areas, characteristics of heating radiators. The following figure, figure 32, shows the installation of radiant floor heating combined with DHW. Figure 32: Installation of radiant floor heating combined with DHW. B.2. Solar collectors Solar collectors are the heart of most solar energy systems. The collector absorbs the sun’s light energy and changes it into heat energy. In this part I will describe the different types of solar collectors used for residences. It also briefly covers the solar heating systems for which they are best suited. Solar collectors heat a fluid, either air or liquid. This fluid then is used to heat— directly or indirectly—the following: - Water for household use. - Indoor spaces. - Water for swimming pools. - Water or air for commercial use. - Air to regenerate desiccant (drying) material in a desiccant cooling system. There are several types of solar collectors used for residences. These are flatplate, evacuated-tube, and concentrating collectors. B.2.1. Flat-plate collectors Figure 33 shows the flat-plate collectors are the most common collector for residential water-heating and space-heating installations which will be chosen in my project because of the comment after. A typical flat-plate collector is an insulated metal Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 94 box with a glass or plastic cover—called the glazing—and a dark-colored absorber plate. The glazing can be transparent or translucent. Translucent (transmitting light only), low-iron glass is a common glazing material for flat-plate collectors because lowiron glass transmits a high percentage of the total available solar energy. The glazing allows the light to strike the absorber plate but reduces the amount of heat that can escape. The sides and bottom of the collector are usually insulated, further minimizing heat loss. The absorber plate is usually black because dark colors absorb more solar energy than light colors. Sunlight passes through the glazing and strikes the absorber plate, which heats up, changing solar radiation into heat energy. The heat is transferred to the air or liquid passing through the collector. Absorber plates are commonly covered with “selective coatings,” which retain the absorbed sunlight better and are more durable than ordinary black paint. Absorber plates are often made of metal— usually copper or aluminum— because they are both good heat conductors. Copper is more expensive, but is a better conductor and is less prone to corrosion than aluminum. Figure 33: Flat-Plate Collector. (DOE/GO-10096-051, March 1996). Flat-plate collectors fall into two basic categories: liquid and air. And both types can be either glazed or unglazed. B.2.1.1. Liquid collectors In a liquid collector, solar energy heats a liquid as it flows through tubes in or adjacent to the absorber plate. For this type of collector, the flow tubes are attached to the absorber plate so the heat absorbed by the absorber plate is readily conducted to the liquid. The flow tubes can be routed in parallel, using inlet and outlet headers, or in a serpentine pattern. A serpentine pattern eliminates the possibility of header leaks and ensures uniform flow. A serpentine pattern is not appropriate, however, for systems that Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 95 must drain for freeze protection because the curved flow passages will not drain completely. The simplest liquid systems use potable household water, which is heated as it passes directly through the collector and then flows to the house to be used for bathing, laundry, etc. This design is known as an “open-loop” (or “direct”) system. In areas where freezing temperatures are common, however, liquid collectors must either drain the water when the temperature drops or use an antifreeze type of heat-transfer fluid. In systems with heat-transfer fluids, the transfer fluid absorbs heat from the collector and then passes through a heat exchanger. The heat exchanger, which generally is in the water storage tank inside the house, transfers heat to the water. Such designs are called “closed-loop” (or “indirect”) systems. Glazed liquid collectors are used for heating household water and sometimes for space heating. Unglazed liquid collectors are commonly used to heat water for swimming pools. Because these collectors need not withstand high temperatures, they can use less expensive materials such as plastic or rubber. They also do not require freeze-proofing because swimming pools are generally used only in warm weather. Figure 34: Unglazed Solar Collectors . (DOE/GO-10096-051, March 1996) Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 96 B.2.1.2. Air collectors Figure 35 shows air collectors are simple, flat-plate collectors used primarily for space heating. The absorber plates in air collectors can be metal sheets, layers of screen, or nonmetallic materials. The air flows past the absorber by natural convection or when forced by a fan. Because air conducts heat much less readily than liquid does, less heat is transferred between the air and the absorber than in a liquid collector. In some solar air-heating systems, fins or corrugations on the absorber are used to increase air turbulence and improve heat transfer. The disadvantage of this strategy is that it can also increase the amount of power needed for fans and, thus, increase the costs of operating the system. In colder climates, the air is routed between the absorber plate and the back insulation to reduce heat loss through the glazing. However, if the air will not be heated more than 17°C above the outdoor temperature, the air can flow on both sides of the absorber plate without sacrificing efficiency. Figure 35: Solar Air Collector. (DOE/GO-10096-051, March 1996) Air systems have the advantage of eliminating the freezing and boiling problems associated with liquid systems. Although leaks are harder to detect and plug in an air system, they are also less troublesome than leaks in a liquid system. Air systems can often use less expensive materials, such as plastic glazing, because their operating temperatures are usually lower than those of liquid collectors. B.2.2. Evacuated-tube collectors Evacuated-tube collectors heat water in residential applications that require higher temperatures. In an evacuated-tube collector, sunlight enters through the outer glass tube, strikes the absorber tube, and changes to heat. The heat is transferred to the liquid flowing through the absorber tube. The collector consists of rows of parallel Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 97 transparent glass tubes, each of which contains an absorber tube (in place of the absorber plate in a flat-plate collector) covered with a selective coating. Evacuated-tube collectors are modular—tubes can be added or removed as hot-water needs change. When evacuated tubes are manufactured, air is evacuated from the space between the two tubes, forming a vacuum. Conductive and convective heat losses are eliminated because there is no air to conduct heat or to circulate and cause convective losses. There can still be some radiant heat loss (heat energy will move through space from a warmer to a cooler surface, even across a vacuum). However, this loss is small and of little consequence compared with the amount of heat transferred to the liquid in the absorber tube. Evacuated-tube collectors are available in a number of designs as we can be shown in the figure 36. Some use a third glass tube inside the absorber tube or other configurations of heat-transfer fins and fluid tubes. One commercially available evacuated-tube collector stores 19 liters of water in each tube, eliminating the need for a separate solar storage tank. Reflectors placed behind the evacuated tubes can help to focus additional sunlight on the collector. Figure 36: Evacuated-Tube Collector. (DOE/GO-10096-051, March 1996) These collectors are more efficient than flat-plate collectors for a couple of reasons. First, they perform well in both direct and diffuse solar radiation. This characteristic, combined with the fact that the vacuum minimizes heat losses to the outdoors, makes these collectors particularly useful in areas with cold, cloudy winters. Second, because of the circular shape of the evacuated tube, sunlight is perpendicular to the absorber for most of the day. For comparison, in a flat-plate collector that is in a fixed position, the sun is only perpendicular to the collector at noon. While evacuatedtube collectors achieve both higher temperatures and higher efficiencies than flat-plate collectors, they are also more expensive. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 98 B.2.3. Concentrating collectors Concentrating collectors use mirrored surfaces to concentrate the sun’s energy on an absorber called a receiver. Concentrating collectors also achieve high temperatures, but unlike evacuated-tube collectors, they can do so only when direct sunlight is available. The mirrored surface focuses sunlight collected over a large area onto a smaller absorber area to achieve high temperatures. Some designs concentrate solar energy onto a focal point, while others concentrate the sun’s rays along a thin line called the focal line. The receiver is located at the focal point or along the focal line. A heat-transfer fluid flows through the receiver and absorbs heat. These collectors reach much higher temperatures than flat-plate collectors. However, concentrators can only focus direct solar radiation, with the result being that their performance is poor on hazy or cloudy days. Concentrators are most practical in areas of high insolation (exposure to the sun’s rays), such as those close to the equator. Concentrators perform best when pointed directly at the sun. To do this, these systems use tracking mechanisms to move the collectors during the day to keep them focused on the sun. Single-axis trackers move east to west; dual-axis trackers move east and west and north and south (to follow the sun throughout the year). In addition to these mechanical trackers, there are passive trackers that use Freon to supply the movement. While not widely used, they do provide a low-maintenance alternative to mechanical systems. Concentrators are used mostly in commercial applications because they are expensive and because the trackers need frequent maintenance. Some residential solar energy systems use parabolic-trough concentrating systems. These installations can provide hot water, space heating, and water purification. Most residential systems use single-axis trackers, which are less expensive and simpler than dual-axis trackers. Figure 37: Parabolic-Trough Collector. (DOE/GO-10096-051, March 1996) Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 99 B.3. Storage of solar thermal energy Thermal energy storage can contribute significantly to meeting society's needs for more efficient, environmentally benign energy use in building heating and cooling, space power, and utility applications. Thermal energy storage (TES) can aid in the efficient use and provision of thermal energy, wherever there is a mismatch between energy generation and use. Three fundamental types of thermal energy storage processes (sensible, latent, and thermochemical) can be used, and many different media are available within each type. Various subsets of these processes are being researched and developed to accelerate TES implementation, focusing on applications in building heating and cooling, industrial energy efficiency, and utility and space power systems. TES can contribute significantly to meeting society's needs for more efficient, environmentally benign energy use in these and other sectors. Perhaps the major utility of energy storage lies in its ability to couple an energy supply with a demand when the supply and demand vary independently over time. It is convenient to picture a storage system as being functionally located between an energy supply and a load. Ideally, energy is stored during a charging period and released during a subsequent discharge period in such a way that there is no net change in the thermodynamic state of the storage material. During a cycle, it is not necessary that the charge and discharge periods immediately follow one another or be of the same duration. B.3.1. Thermal energy storage mechanisms There are three types of thermal energy storage: sensible heat, latent heat, and thermochemical. With sensible heat storage, energy is stored by changing the temperature of a material. The amount of energy stored is a function of the temperature change, the mass of the storage medium, and its specific heat. Most sensible heat systems employ water, rocks, earth, or ceramic bricks as the thermal storage material and water, air, or possibly oil as the heat transfer fluid. The high heat capacity of water (4,18 kJ/KgK) often makes tanks of water a logical choice for TES systems that operate in a temperature range needed for building heating or cooling. The relatively low heat capacity of rocks and ceramics (on the order of 0,84 kJ/KgK) is somewhat offset by the large temperature changes possible with these materials and their relatively high density. In the case of latent heat storage, the storage material changes phase usually between solid and liquid. Thus, if the change in TES temperature includes the melting or freezing point of the storage material, the storage capacity is greatly enhanced by the latent heat contribution. The advantage of latent heat storage in a phase-change material (PCM) is high energy density. The advantage of latent heat storage increases as the difference between the initial and final storage temperatures is narrowed about the melting temperature of the PCM. Thermochemical energy storage involves chemical reactions. Metal hydrides have been examined for use in chemical heat pumps using hydrogen as the working Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 106 In summary, the simple absorption machine has four interconnected vessels. Two of them are located in the low pressure side (evaporator and absorber) and another two ones in the high pressure side (condenser and generator). The two pressure levels are conditioned by the temperatures of condensation and vaporization of the refrigerant. The evaporator pressure is low enough to boost the vaporization of the refrigerant. When the water temperature increases, it generates a quantity of steam coming from the cooling circuit. This steam is captured by the absorbent in the absorber, releasing heat which must be evacuated. The mixture is driven by a pump to the generator where the heat is taken from the heat reservoir. This heat makes the absorbent and the refrigerant separated once again. The refrigerant is released as steam and at a high pressure. The absorbent then returns to the absorber through the expansion valve. On the other hand, the refrigerant enters in the condenser where it is cooled and condensed. It is then expanded through the expansion valve before returning to the evaporator. An improvement to the basic cycle is to incorporate a heat exchanger between the absorber and the generator so that the concentrated stream that returns to the absorber is preheated. Figure 40 shows the different components and processes of a simple effect absorption cycle: Figure 40: Different components and processes of a simple effect absorption cycle machine. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 107 C.2.1. Simple absorption cycle (More expanded) In the cycles of absorption, figure 41, you always deal with an absorbing agent (a substance that absorbs the vapors) and a coolant or refrigerant (a substance which is evaporated and it causes the refrigeration production). Water and lithium bromide solution would be absorbents. Ammonia and distilled water, in the cooling-water absorption cycles, and in the lithium bromide-water absorption cycle, are refrigerants. The entire sequence set out in the absorption cycle will be explained below: - The high-pressure liquid refrigerant which comes from the condenser passes through an expansion valve. Here, the refrigerant pressure drops to the pressure which is in the evaporator. (Flows 8 and 9) - The liquid refrigerant is vaporized in the evaporator which absorbs the heat from the place to be cooled (cooling of the wanted environment occurs by the absorption of heat in order to change the phase). - The low-pressure steam is absorbed by an unrestricted conduit to the absorber where it is mixed with the absorbent. The refrigerant flows from the evaporator to the absorber, because the vapor pressure of the absorbent-refrigerant of the solution in the absorber is less than the vapor pressure of the refrigerant which is in the evaporator. (Flow 10) - The steam pressure in the absorber (absorbentrefrigerant of the solution) determines the pressure in the low pressure side of the system and consequently, the vaporization temperature of the refrigerant in the evaporator. In the same time, the vapor pressure of the absorbentrefrigerant of the solution depends on the nature, temperature and concentration of the absorber. Decreasing the temperature and increasing the concentration of the absorber will produce low pressure in the solution. (Absorber) - At the same time that the refrigerant vapor of the evaporator is dissolved in the absorbing solution, the volume of the refrigerant decreases (compression occurs) and heat is released from the absorption. In order to maintain the temperature and the vapor pressure of the absorbing solution at the required level, the heat released in the absorber (whose value is equal to the sum of latent heat of condensation of refrigerant vapor, and heat of dilution of the absorber) shall be evacuated to the surroundings, usually, the same heat sump or means used for condensing heat evacuated by the capacitor. In order to make the transfer of heat from the absorber to the sink, the temperature of the absorber should be higher than the one of the sump. (Flows 13 and 14) - Since the efficiency of the absorber increases when the temperature of the absorbing solution is decreasing, it results that the efficiency of the absorber depends in part, on the temperature of the available refrigerant. When the refrigerant vapor is dissolved in the absorbent solution, the resistance increases (cooling rate), as well as the vapor pressure in the solution. Therefore, a continuous reconcentration of solution is necessary so that a low level of vapor Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 108 pressure can occur, to provide low pressure and low temperature that are required in the evaporator. The reconcentration is obtained by eliminating continuously the strong absorbing solution of the absorber, making it recirculation through the generator. Here, most of the refrigerant vapor is boiled through the application of heat. In addition, the resulting weak solution returns to the absorber to absorb more refrigerant vapor from the evaporator. (Flow 6) - Since the absorber is on the low pressure side and the generator in the high pressure side, strong solution must be pumped from the absorber to the generator and thus, the weak solution will return to the absorber through an expansion valve. The increased pressure of the absorbing solution increases the pressure in the high side in the absorber. The solution is then pumped to the generator. The compression of the refrigerant will not happen in the process because it is done in the absorber chamber. Consequently, the power required by the solution pump is relatively small. (Flows 2 and 5) - Then is introduced a heat exchanger between the generator and the absorber so that the temperature of the strong solution which goes to the generator is increased while the temperature of the weak solution that goes to the absorber is decreased. On the one hand the heat exchanger will provide a reduction of heat supplied to the generator whereas on the other hand, it will provide the required cold to the absorber, improving the efficiency of the cycle. - In the generator, the refrigerant is separated from the absorbent by heating and vaporizing the solution in the coolant. The high pressure refrigerant vapor passes by the condenser, where it is condensed, giving up its latent heat to the environment. Because of this, the refrigerant is ready to circulate again in the evaporator. (Generator and flujo7) - The absorbent solution (weak) which is in the generator returned to the absorber by the return pipe as previously described. The relative strength of the weak solution is controlled by the amount of heat supplied to the generator. (Flows 4 and 5) - For a maximum efficiency in the system, the pressure differential between high pressure and low pressure sides should be as small as possible, keeping the pressure on the low side as high as possible and cooling as well as pressuring the requirements on the high side (as low as possible with the condensing means available). Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 109 Figure 41: Traditional scheme of an absorption cycle. The heat extracted from the vapor of water in the absorber and the condenser must be removed by a dissipation circuit of water. The heat from the circuit of dissipation can be removed from one of the following ways: • Aero-coolers (or heat exchanger cooled by air). • Evaporative cooling tower with open circuit. • Evaporative cooling tower with closed circuit. • Well or river or lake water, through heat exchangers. • Sea water through the heat exchanger which has appropriate characteristics. This means, that the three variables to determine its benefits should be: • The temperature of hot water which enters in the generator. • The temperature of water in the tower for heat dissipation. • The temperature of chilled water. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 110 Figure 42: Installation scheme of a simple effect cooling absorption system. All this makes the absorption refrigeration systems bulky and expensive, especially when these are designed to operate at a low temperature in the generator. This means that it is only profitable when the heat is free or very cheap, and when annual full time operating hours are high. Absorption machines can function as simple effect or double effect. The simple effect consists in basic elements, while the double effect makes the separation of the refrigerant in two phases (a first generator at high temperature and a second generator at low temperature). The second generator gets the heat from a second capacitor. The double effect machines need a generator with higher temperatures compared to simple effect machines. Besides, double effect ones are more expensive, but have however higher performance. The COP of an absorption machine of simple effect is between 0,5 and 0,7 while the COP of double effect is between 1 and 1,2. These have been developed between 1970 and 1990 and are now being introduced in the air conditioning market. Because of this, these machines capable of providing a cooling capacity of less than 100 kW are not sold a lot, knowing that this performance would be ideal for a family home. C.2.2. Couples of fluids used in absorption The refrigerant and absorbent are the two components which are always required in all cycles of absorption. Although different couples of products can be used, the most common are: 1. Water as coolant and as absorbent of lithium bromide (LiBr). 2. Ammonia as refrigerant and water as absorbent. Then will be explained with more detail both cycles, making greater emphasis on the couple of Lithium Bromide-Water which is normally used for cooling processes, as in our case, the ClimateWell machine (it does not exactly use BrLi-H 2 O but it uses LiCl-H 2 O). Finally, it will be shown a summary chart comparing the two processes. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 111 C.2.2.1. Mixture of Lithium Bromide-Water The couple LiBr-H 2 O (always appears as absorbent-coolant) is the most commonly used as mixture of work in absorption machines. It is primarily used for air conditioning although it has limited the working temperature of the evaporator approximately to 5°C because of problems with freezing the water. The working temperature of the absorber cannot be very high due to the crystallization of salt (figure 43). This makes that the difference between the temperatures of the evaporator and the absorber do not exceed 30ºC, approximately. However, as its enthalpy of vaporization is high and the vapor pressure is low, the machines can be designed with less weight because they require less thickness in the walls. Because of the crystallization, it is necessary to use heat sumps (cooling towers, pools, aerothermo...) for heat dissipation in the absorber. This makes impossible the heat pump operation mode in winter. Although Water-BrLi equipments are marketed and can meet both cold and heat needs, the heating process is limited to the transfer of thermal energy directly from the heating circuit to the generator. This doesn’t provide any kind of improvement compared to the use of a simple boiler. Figure 43: Simple effect absorption cycle H 2 O/LiBr These machines have a good acceptance in the air conditioning market because of their good thermal performance in cooling mode in spite of the low operating margin. In addition, they benefit from a very low toxicity and environmental impact rate. For this reason, numerous researches have been carried out to shift the curve of the crystallization of the dissolution towards points of higher temperature, for instance by adding salt or other substances as we can see in the figure 44. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 112 Figure 44: Plot of crystallization of LiBr. As a result of what has been explained above, some studies are being conducted with quaternary salts and sodium hydroxide, potassium hydroxide and cesium hydride ternary salt as an alternative to water-BrLi couple. The curve of crystallization of this mixture is modified, so that it can operate with a temperature in the absorber of about 50ºC and therefore makes it possible to operate at a high temperature in the generator (about 200ºC). This will provide a thermal performance similar to the previous mixture. However, its practical implementation has been currently limited due to the corrosion that causes the dissolution. Indeed, with these operating temperatures, there are problems with the materials that are used. C.2.2.2. Mixture of Water-Ammonia The Ammonia-Water machines are usually used with industrial refrigeration processes such as: frozen foods or cooling of processes which operate with evaporator temperature of -60ºC. It should be kept in mind that with this range of temperatures, the water-BrLi units are not operating (below 5ºC). The saline solution in the same operating conditions shows better thermal performance than the ammonia-water mixture because it needs an adjustment system to reduce the content of the absorbent in the evaporator. These machines work with negative temperatures, it is thus necessary to add a rectifier to the generator output with the objective to remove traces of existing water. If nothing was done, the water into the pipes would freeze and prevent the machines from working correctly. In addition, since from a security point of view, ammonia is a toxic product whose temperature inside the machine is always higher than the atmospheric pressure, the use of these machines is restricted in some countries like Japan for instance. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 113 As a summary, the following table shows the main differences between the couples used in absorption systems discussed above. Table 17: Main differences between the couples used in absorption system. Water/Lithium Bromide (LiBr ) Ammonia (NH 3 )/Water • The coolant is water and the absorbent is lithium bromide. •The lithium bromide solution is not toxic, non-flammable and odorless. • The system cannot cool below the freezing point of water (usually +5°C for safety), so the scope of these systems is the air conditioning of buildings. • Other advantage of these plants is that the pressure into the exchangers is subatmospheric and for this reason, it is not obligatory that their components are designed according to the rules of pressure vessels. • The absorbent (lithium bromide) has no own vapor pressure, making easier the task to separate the refrigerant from the absorbent. • The void means that there is a high impermeability in the system. • The coolant is ammonia and the absorbent is water. • Ammonia is a coolant with best thermodynamics properties, commonly used in industrial refrigeration (high specific heat). • It is a very toxic gas. • Mixtures of, ammonia vapor / air, are flammable and, can be explosive but only in very high concentrations (15,5 to 27% by volume). • Evaporating temperatures can be obtained until -60°C. • The scope is the industrial cooling (petrochemical, food and chemical industry) at temperatures below 0°C. • The pressures are high and all exchanges must be designed according to the regulation for pressure vessels, so that the pipes which have to be used must be thicker. • The water absorbent has a high volatility; a distillation tower is thus necessary (or rectification) to separate the refrigerant and the absorbent. • Due to high operating pressures and the necessity of an adjustment system the plants are more expensive than lithium bromide. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 114 C.2.2.3. Coefficient of performance. (C.O.P.) As mentioned above, the C.O.P. is used to measure the amount of cooling which is obtained from a machine, divided by the amount of energy required to achieve this cooling. To determine the overall performance of absorption refrigeration system, it shall be taken into consideration the necessity of mechanical energy in pumps and fans (often neglected) as well as the heat input into the generator. In absorption machines the COP is calculated as following: COP abs. cycle = (Tcapacitor – Tevaporator) / (Tevaporator – Tabsorber) = Coolant Effect / Heat input Where: - Effect Refrigerant = Cooling capacity of the absorption chiller (kJ or kW). - Heat input = Heat input in the generator of the absorption chiller (kJ or kW). The COPs expected in absorption cycles are also very low compared with mechanical compression cycles. In single stage absorption machines that use lithium bromide, the COPs will not exceed the value of 0,7. In two-stage machines, the values can reach until 1,5 times more compared with single-stage machines. This means that two-stage machines make better use of energy than simple stage. The cycles of ammonia/water which work with low temperatures get values of COP around 0,5 and maximum levels of 0,8. C.2.2.4. Available coolers by absorption There are different manufacturers of absorption machines. These machines offer a very wide power range. On the one hand the larger are used (around 200 kW) for industrial uses, on the other hand, the smaller ones for single family homes (between 5 and 15 kW). The following shows different simple effect absorption machines (COP = 0,7, Tª = 85ºC): - With P> 100 kW: Large number of options - With 35-100 kW P: Thermax, Yazaki - With 15-35 kW P: Robur - With P from 5 to 15 kW: Rotartica, Climate Well (machine used in the project), Phonix, SunInverse, EAW, Pink, AoSol, NEC, SorTech. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 115 Annex D. Description of housing D.1. Location and site Since I have to do the evaluation of a specific location, at first thought about a house in Soria, than is where I live, but after analyzing it in more detail, I came to a conclusion that it would be better if I changed the location to Madrid. I have chosen the community of Madrid for different reasons. The main reason is that there is plenty of information available about its regulations and ordinances because it is the capital city. In addition, the majority of the information and examples about the machine of Climawell talk about it. Entering the company website for searching information, I saw that during the past two years the installations of this equipment in this community have increased significantly compared to other region of Spain. The living area of the dwelling unit will be considered of 200 m 2 . There are six people living in the house. In addition, I will consider that all the occupants will live in this house throughout the summer. What will be taken into consideration is that the detached house has 4 rooms, and 6 inhabitants (according to the Ordinance of Madrid for the calculation of DHW). The house has a floor heating system to boost water at low or high temperature, depending on the temperature inside the building. The figure 45 shows a detached house in the Community of Madrid with the characteristics outlined above. Figure 45: Detached house possible in the Community of Madrid. An important part of for the implementation of this project is that the detached house has a swimming pool which will be in charge of the dissipation of the installation. This way, the heat is used for heating the pool. If the house wouldn’t have had a pool, other dissipation methods would be needed such as a vertical geothermal heat exchanger or a cooling tower. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 122 Table 23: Heat transmission coefficient of enclosure for doors. [Kcal/m 2 °C (W/m 2 °C)] D.2.3. Interior partitions Usually, the interior partition is doubled hollow brick and is then coated with gypsum. As was mentioned, these values will be high due to the fact that the heat transfer is big. These K values are usually around 3 for internal partitions; since heat transfer between rooms of the same house doesn’t matter contrary to the thickness and the saving of money that really do matter. As a result, all the available square meters (as wider walls occupy big interior space) will be used. The following figure, figure 47, displays a typical interior partition. Figure 47: Typical interior partition. In Table 24 are given the thermal resistance values of a brick enclosure of one sheet, according to the type of brick: hollow, perforated or solid, and the thickness of the enclosure, excluding coatings that could be added . Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 123 Table 24: Thermal resistance R, in m 2 h°C/Kcal [m 2 °C/W] D.2.4. Deck enclosures In this section, we will focus on differentiating the interior floors of the house, roofs and deck enclosures. - Interior floors and roofs will have K values around the unity (very low). - Deck enclosure will have K values similar to the vertical enclosures. In summary I would emphasize that internal partitions, doors and windows usually have high values regarding the heat transfer coefficient. Lower values of K (in order the heat transfer to be as low as possible and without losses) are usually set in the enclosures that separate the exterior and interior of the house. As can be noticed, all the values given in the tables above are in kcal, they will thus have to be converted into W for the calculation of K. All the tables can be found in NBE-CT -79 (Basic Rules of Construction), (Technical Code). The result of K must be less or equal to 0,91 according to Standard NBECT-79 for the considered air conditioning area. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 124 Annex E. Calculation of thermal loads E.1. Technical burdens in housing When speaking of thermal load in air conditioning, this refers to all perturbation which is capable of altering the energy in air-conditioned spaces. The perturbations are caused on the one hand, in energy sources located inside the spaces, and on the other hand, in the climatic conditions of outside space that surrounds the venue. Thermal loads are associated with determined spaces and are variable over time. The objective of the air conditioning is to cancel these loads at all times and in all spaces, so it is necessary to know how the thermal loads vary, in space and in time. There are two different ways to manifest the energy in a room which is cooled. On the one hand by convective heat fractions and on the other hand by radiant fractions of load type each. The convective fraction is transmitted instantaneously to the air of the place by convective transfer; however, the radiant fraction does not directly affect local air. It has an impact on the walls and the contents of space. Also, it is absorbed by all materials that are part of local, home or area which is air-conditioned, making the temperature increase. Then, this absorption is transferred to the air temperature by a convective mechanism. It is called gain, the energy that affects the control volume (space which is airconditioner), and load, the energy that is manifested in the air of the local. The difference between them is linked to the inertia of the enclosures and the contents of the local. In addition it is also linked to the different origins of convective and radiant fractions of thermal excitations. Then will be defined a serial of elements of buildings that are needed to know and thus be able to dimension the installations: - External load (outdoor conditions) is primarily the effect of the outside on the interior, which is modified by the enclosures of the building (which will attenuate to a greater or lesser extent the signal). It also depends on the level of isolation, because it will be responsible for slowing the signal, depending on its density or its capacity to store the conditions which separate the outside from the inside. You have to get information about the inertia and load level from outdoor for modeling the outside load. - Enclosure: as noted in the previous paragraph, it is responsible for the transmission from outside to inside. It allows different models. - The Internal loads (Internal conditions) are the elements that together with external actions will be responsible for stating the amount of energy needed by air conditioning systems to maintain comfort conditions for occupants. They are characterized by a high level of randomness, being therefore the most independent part (depending on persons, activity, internal lighting, machinery from the inside...). Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 125 - Installations: are responsible for the transit of heat/cold and the humidity in order to maintain comfort conditions inside of the place independently from the outside. The configuration and the system which are chosen will condition the control system installation. E.1.1. Indoor conditions These conditions are important for the comfort of users, i.e. the climatic conditions that satisfy their requirements when they are in a heated room. The RITE (Regulation of Thermal Installations in Buildings - 2007) tells us in the ITE 1.1, that the comfortable temperatures in summer are between 23ºC and 25ºC. In winter the comfort temperatures are between 20ºC and 22ºC. We will select in the program of simulation a comfortable temperature in the interior of 24ºC in summer and 21ºC in winter, thinking that the energy efficiency and comfort inside the home will be successful. To make the calculation, the simulation program assumed a constant occupation of the rooms, providing a constant air flow ventilation and internal heat. Due to the fact that it is a home, we can assume that these conditions are variables, but are considered as the most common that can be given, in each of the rooms. E.1.2. Outdoor conditions RITE tells us to consult the external conditions in technical articles or books that collect information from the National Institute of Meteorology (INM) for getting the external conditions which are necessary to dimension the equipment. The data are tabulated, according to the Spanish province. The data which have to be considered are: the number of hours of sunlight during the day, the nominal temperature, the thermal daily extrusion (average of daily temperature variation), altitude and latitude. These data should be considered for winter and for summer, depending on the situation of the zone where is located the house which will be heated. E.2. Calculating loads of cooling [Qc]. The formula used in the calculation is: Q c = Q sens + Q lat Where: - Qc: cooling global heat load [W]. - Qsens: cooling sensible heat load [W]. - Qlat: cooling latent heat load [W]. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 126 E.2.1. Sensible load Qs ens = Q solar + Q trans + Q inf + Q int s + Q v srn E.2.1.1. Solar gain due to the glass (Qsolar) (W) The energy that comes to the house from solar radiation and passes through transparent elements such as windows is of two types: heat transfer by convection and by solar radiation. To know the solar radiation which incidents on a surface like a window, you have to determine a month of calculation. For this calculation, it is always chosen or July 23 or August 24 because those are the moments of the year with the more solar radiation. The last indispensable factor for finding the incident radiation is the orientation of the window, which will vary depending on the room of calculation, i.e. the percentage of energy transmitted through the glass and the existence or not of blinds or curtains (Transmission of heat by solar radiation). Must be taken into consideration that the transmitted energy is converted to load and it is stored on the floors and on the walls. Q solar = Aglass · Kg · f c · f t Where: - Qsolar: solar gain due to radiation in windows [W]. - Aglass: glass area of a room in a specific orientation [m 2 ]. - Kg: coefficient of solar contribution through the single glass (Tables) [W/m 2 ] - fc: weighting. For example, for metal frame windows is 1.17. - ft: solar gain total factor through glass. For example, for double glazing with exterior blinds is 0,2 (Tables) E.2.1.2. Solar gain through the transmission of decks, interior walls and exterior walls (Qtrans) (W) The heat gains through the exterior walls, floors and decks are calculated at the time of maximum flow thermal. They are due not only to the difference between outside air temperatures and inside faces, but also to the solar heat absorbed by the outside walls, sunstroke which receives the house and the difference of temperatures inside and outside. All these variables change throughout the day, making that the intensity of the flow will be unstable. Therefore, we have used the empirical concept of "equivalent temperature difference”, which is defined as the difference between the temperatures of indoor and outdoor air, resulting from the total heat flow through the analyzed structure, which depends on variable solar radiation and on the outside temperature. This equivalent temperature difference through the structure will depend on: the different types of structures and orientations, exterior wall color, location of the building, sunstroke on it Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 127 and the conditions of the project. Because of this, we will then explain on the one hand, calculation method for external walls and decks and on the other hand the calculation method for interior walls. Solar gain by transmission of exterior walls and deck (Qtrans1) (W) When talking about radiation in walls, this refers to radiation from the sun which heats the outside walls of the local which is air-conditioned. The radiation heat is transferred by conduction through the walls and deck, generating the heating of the interior of the building. The calculation will be done by the following equation: Q trans1 = A wall · (DTE) Kc Where: - Qtrans1: solar gain transmitted on exterior walls and deck [W] - Awall: area of the outside wall of a room depending on the orientation [m 2 ] and also area of the deck in the case of the room is in contact with the outer cover. - Kc: transmission coefficient of the wall or deck (calculated in the ANNEX D of the project) [W/m 2 •°C] - DTE: equivalent difference of temperatures in °C. The equivalent difference of temperature (DTE) is referring to a jump of thermal temperature in order to take into account the effect of solar radiation (Tables). The following three parameters will be needed to find the equivalent difference of temperature of a wall: - The orientation of the wall. - The weight per square meter of the wall. - The solar time when the project takes place. To find the DTE of a deck, the parameters that must be known are: - If the deck is shaded or not. - The weight per square meter of the deck. - The solar time to which the project takes place. Solar gain by transmission (except exterior walls and deck) (Qtrans2) (W) In this part of the project, we have to consider the areas such as windows (in this case, to know the heat produced by transmission) and interior walls, provided that they are not in contact with another air-conditioned room, since in this case it would be valueless. The interior doors should not be considered. Its surface is considered as if it were a piece of wall to which it belongs. In this case the equation is: Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 128 Q trans2 = A · ∆ ∆∆ ∆T · Kc Where: - Qtrans2: Gain transmission in inside walls and floors [W]. - A: Area of inside wall, floor or roof of a room [m 2 ]. - Kc: global transmission coefficient of the wall, etc. (calculated in the ANNEX D of the project) [W/m 2 •°C]. - ∆T: It is the difference of temperature between outside and inside [ºC]. For the surfaces (walls, ceilings, etc.) in contact with an unheated room it is usually taken ∆T/2. E.2.1.3. Sensible heat due to infiltrations This part is referring to, on the one hand the heat that enters when the doors or windows are opened and on the other hand, to the heat that enters through the fissures. The calculation of this contribution is only compulsory if the doors or windows are frequently opened, like in the case of public places. E.2.1.4. Sensible internal heat (Qint sen) (W) (Internal loads) Q int sen = Q oc sen + Q el - Qint sen : sensible interior heat [W]. - Coc sen : sensible thermal load of the occupants [W]. - Qel: thermal load of lighting and machines [W]. All humans give off a certain amount of heat because our body temperature is approximately 37ºC. This heat makes the room being more or less hot, depending on the activity and the number of people that are in the room. Sensible or latent heat that a person gives off depends on the task that you are doing and the temperature of the local. These values are tabulated in tables. Multiplying the heat produced by an individual per the number of individuals, we will get the total power [W] generated local occupants. It is usually used a simultaneity factor of the people situated in the local which, as an approximation, can be taken equal to 0,75. Q oc sen = N p · Q sp Where: - N p : Number of people in the same room. - Q sp : Unity gain of sensible heat due to occupant (Tables) [W/pers] Like people, the lighting and the machines (oven, heater ...) also produce heat that will heat the local atmosphere. The heat from lighting is sensible heat, but a part of this load is due to radiation and another part due to convection, depending on the type of lighting. Again, for the instantaneous cooling load, the effect of storage will be taken into consideration in order to accurately assess their contribution to the total load. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 129 The heat produced by lighting depends on whether it is incandescent light or if it comes from a fluorescent light. In the case of incandescent lighting, it is equal to the power of illumination. But if the lighting is fluorescent, the power of illumination has to be multiplied by a zoom factor of 1,25. Fluorescent light Q el = 1,25 · I Incandescent light Q el = I Where: - I: Electrical power of illumination [W] E.2.1.5. Sensible heat of ventilation (Qv sen) (W) In the air conditioning installations, it is necessary to forecast the renewal of the air (for removing odors, etc ...) as well as the introduction of a sufficient amount of oxygen to ensure the quality of the air inside the air-conditioned room. The outside air introduced must be compensated by the same flow of air extracted or expelled through the windows and doors. Doing it, the same amount of dry air will be maintained in the enclosure. To find the amount of air that we will have to introduce inside the airconditioned room, it is necessary to look in the tables, and depending of the activity performed in the local, we will get the air flow required for the ventilation. The ventilation could be mechanical (by conduits that bring outside air) or natural (through windows or doors). With the following formula, we obtain the sensitive load of ventilation: Qv sen = q · 0,3 · (4,18 / 3,6) · (To - T i ) · ƒ ƒƒ ƒ Where: - Qv sen : sensible heat of ventilation [W]. - q: outside air flow set for the room [m 3 /h]. - To and Ti: air temperature respectively outside and inside [ºC]. - ƒ : By-pass factor (depending on the system of distribution (tables)) E.2.2. Latent load Qlat = Q OC1 + Qv1at Q OC1 = = = = N P ·Q lp Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 130 Where: - Qlat: Latent load of the occupants ( Q OC1 ) (en W). - Q OC1 : Latent thermal load of the occupants of the room [W]. - N p : Number of people who occupy the room or local. - Q lp : Unity load of latent heat due to occupants (Tables) [W/per]. Latent heat of ventilation (Qv lat ) QV lat = = = = q · 0 ,7 · (wo− −− − wi) · ƒ ƒƒ ƒ Where: - Qv lat: sensible heat of ventilation [W]. - q: outside air flow set for the room [m 3 /h]. - wo y wi: Specific humidity of respectively outside and inside air, (Tables) [g/Kg]. - ƒ : By-pass factor (depending on the system of distribution (Tables)). You can find below a summary of the three main equations for obtaining the total load of the room or stay (Q R ). Q C = Q sens + Q lat Qs ens = Q solar + Q trans + Q inf + Q int sens + Q v sens Qlat = Q OC1 + Q Vlat E.3. Calculating loads of heating [Qh] The estimation of the maximum thermal power in the case of heating is calculated in the same way as in the case of cooling, taking into account the worst possible case (minimum temperature, zero solar radiation, minimal presence of persons, and minimum light). In the case of heating, we must take into account that the loads are heat losses, to maintain an ambient temperature higher that the outside temperature, except for internal loads. I would emphasize that for this part of the project, it is necessary to use different tabulated tables. Since I have not done mathematical calculations, I thought it would be better not to put them, however, it can be found in NTE. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 131 ANNEX F. REPORT 1. Introduction, Objectives of the project and methodology 1.1. Introduction and motivation of the project The evolution of the European market of energy in recent years is marked by the progressive liberalization of different sectors and the growing concern of the impact of energy activity on the environment. The mass consumption of hydrocarbons is already producing the known greenhouse effect, which is already causing an increase in global average temperatures (+ 0,17°C per year). In addition, they are the cause of the acid rain. Currently, and despite being the air conditioning sector an emerging market in our territory (Spain), it is already considered that 12% of the electricity demand is intended for air conditioning of buildings and houses and is the main cause of the annual demand peaks in the months of July and August. Which made the electricity networks of transportation and distribution in some areas of Spain (especially in the south) to reach its limits and caused increases in the price of electricity in the market. With these teams virtually zero power consumption could be reduced and stabilize the demand. The Kyoto Protocol - drafted in the 1997 although it was not ratified until 2005 – calls upon developed countries to reduce their emissions by 5,2% in 2012 in comparison with 1990 levels. As a solution to these environmental is important to carry out efforts aimed at the replacement of conventional energy sources, such as coal or oil, for clean and renewable energy to maintain a sustainable economic growth to ensure energy supply. Currently, in Spain, due to the coming into force of Building Technical Code (CTE, 2006) the solar thermal energy is experimenting a greater implementation. According to the Basic Document HE of Energy Savings in the section "HE 4 Contribution minimum solar of sanitary hot water" (HE 4, 2004), both the new buildings and the renovated buildings must cover a part of the demand of sanitary hot water, as well as the incorporation of feedback systems, storage and utilization of lowtemperature solar energy. Likewise, also, the obligation extends to the swimming pool heating. Current cooling systems, mainly based on compression, are a technical irony. Because they radiate more heat into the atmosphere than they produce cold needed for the people. This means that if we continue to use conventional cooling systems, we will continue accelerating the spiral of global warming. System for many years offered this possibility is based on the so-called refrigeration cycle of absorption, in which the movement of fluids is achieved using Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 138 In the figure 3, we can see a drawing of the hydraulic configuration of the solar panels which will take place in our project, with the necessary sensors presented in the previous paragraph. Figure 3: Hydraulic configuration connection of the solar collectors with valves, purgers and sensor of needed temperature. These will be installed directly on the south roof deck, where the solar radiation is high if it is approximately tilted of 30º (optimum angle tilt in the peninsula) If the deck does not have this inclination, metallic structures will be placed, that will hold the solar panels with a inclination of 30º. It will be assumed in the project that there are no overlaps or leftovers. 3.2. Heat transfer fluid The fluid of heat transfer which flows through the primary circuit and through the heat exchanger is the one that transfer heat to the secondary circuit. The fluid consists in a blend of antifreeze and water, to prevent water from freezing. The fluid will have a series of none toxic legionella and corrosion inhibitors to buffer the PH, making that, with 20ºC, the PH will be maintained between 5 and 9 (as stated in technical specifications for installations of low temperature solar thermal). The antifreeze recommended by the manufacturer is propyleneglycol. This one doesn’t have toxic corrosion inhibitors and buffer the capacity of PH. In addition, the antifreeze must bear more than 170°C without being altered. After looking at the manufacturer's data which are attached in ANNEX 4, the antifreeze can bear between 184 and 189°C before boiling, meaning that it is the appropriated one. To determine the percentage of propyleneglycol that the heat transfer fluid of solar collector’s circuit should contain, it must be taken into account the registered minimum temperature in recent years in Madrid. After searching for information about minimum temperatures I have found that the lowest one for the Community of Madrid was recorded in 1963, reaching -14,8°C. Knowing the minimum temperature recorded in the site, we can determine the percentage by mass of propyleneglycol using on the table 3, which indicates the freezing temperature of heat transfer fluid according to the percentage in weight. Due to Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 139 this, we will take a 30% of antifreeze, which corresponds to a freezing temperature of - 15ºC. Table 3: Blend depending on the freezing point of propyleneglycol with water. 3.3. Heat exchanger of primary circuit The use of a heat exchanger is due to the fact that the fluid flowing through the solar collector (primary circuit), cannot be used directly in the cooling system, neither for consumption (secondary circuit) due to the presence of antifreeze in the heat transfer fluid. There are two different types of heat exchangers, depending on whether the exchange of heat in the exchanger is produced through external plates out of the tank, or inside the tank with serpentine, both being with very similar thermal behavior. The heat exchanger selected is the plate. Moreover, this will connect thermally, without mixture of fluids, the primary circuit (collector) and the secondary circuit (which feeds the hot water storage tank and the boiler). This has been chosen because the heating of DWH has to be provided in our circuit, as well as the circulation of hot water for heating, as recommended by the manufacturer. In ANNEX 1 is shown the equations for calculating of heat exchanger and for calculating its power. For this, is used the following formula: Pexchanger = ṁ 1 [Kg/s] * Cp 1 [kJ/Kg*ºC] * (Ti 1 – To 1 ) = ṁ 2 * Cp 2 * (Ti 2 – To 2 ) The hot water mass flow (ṁ), is obtained with the volumetric flow rate (Q), and its density (ρ), at the working temperature. Since the power of the heat exchanger can be calculated using the primary circuit or secondary circuit, we will use the secondary circuit, although the same liters per second will be circulated, as recommended by the manufacturer, the secondary circuit will be used because in this circuit there is only water, and the finding of its physical properties will be obtained more easily. However, if we use the primary circuit, the water is mixed with antifreeze. According to the manufacturer's recommendations, the difference of temperature between primary and secondary circuit, must be 3°C. Due to this, the temperature of the Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 140 liquid in the secondary circuit is designed for 80ºC, making that the temperature of the liquid of the primary circuit will be 83ºC. (The manufacturer of Climatewell recommended that the Tª in the secondary should be between 75 and 95ºC, always 50ºC higher than the source of heat dissipation. In addition, the mass flows in the primary and secondary circuits have to be the same). To apply the equation, it is necessary to know the specific data of the fluid that flows through the secondary circuit. The table 4 shows the thermophysical properties of water at operating temperature of the fluid in the secondary circuit of the exchanger. Table 4: Water thermophysical properties at 80ºC. (METCALF & EDDY, INC. Ingeniería de aguas residuales. Mc Graw Hill. 3ª Edición (1995)) Working temperature (ºC) 80 Density ρ(kg/m 3 ) 971,8 Specific heat Cp(kJ/Kg·ºC) 4,205 Pexchanger = 17,5 [l/min] * 1/60 [min/s] * 971,8 [Kg/m 3 ] * 1/1000 [m 3 /l] * 4,205 [kJ/KgºC] * 20 [ºC] = 23,84 kW The difference of temperature between inlet and outlet of the heat exchanger is 20ºC (manufacturer recommendation after doing the appropriate tests). The heat exchanger used is S1-9TLA of the Pilan Company. As can be seen in ANNEX 5, it can operate with a power of 26.7 kW and a maximum working volume of 26 l/min, which fits according to our design needs (17.5 l/min.) As specified by the manufacturer of ClimateWell, the heat exchanger selected should be between 20 and 30 kW and due to this, it can be said that the sizing is correct. 4. Absorption refrigeration machine (ClimateWell_10) ClimateWell_10 is an air conditioning machine that works with higher efficiency if the energy used is solar energy. It has the ability to store energy (as a chemical cell) and it provides both cooling and heating. In addition, it provides the heating of domestic hot water during winter and summer. ClimateWell 10 achieves the storage and the integration of energy-efficient, thanks to its triple technology absorption phase. It has three states of aggregation - solid, liquid and gas - allowing a continuous cooling or heating depending on the user's needs. Also, it can operate through three modes - charging, heating and cooling. It is important to emphasize that due to the availability of two similar tanks the machine can load and unload simultaneously. Because of this, it can always get heat and simultaneously supplying heat or cold (heating or cooling). The system can also simultaneously heat hot water (DHW) or a pool depending on the connection and programming or mode of operation of it. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 141 In the table 5, we can see the most important features of ClimateWell_10. It can be seen that the thermal COP is very stable; both for the supply of cold and heat, and finally, that the maximum power of cold can be doubled if the two barrels are connected in parallel, changing the operating mode (dual mode). Table 5: Technical dates of CW_10. (ClimateWell_10 producto.pdf) Mode Storage capacity(with 2 barrels) Maximum power Thermal COP Cold 60 kWh 10/20 kW 0,68 Heat 76 kWh 25 kW 0,85 As can be seen in the figure 4, the machine is formed by 3 parts: two twin barrels, each one with a reactor and condenser/evaporator that work independently. It also has a piece of plumbing that connects the two barrels with the external circuits. Figure 4: ClimateWell_10. It is making up by two identical barrels. (Thermo Chemical accumulator. pdf) Table 6 shows the electrical properties of the ClimateWell_10 machine, in which should be noted. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 142 Table 6: Electrical properties of CW_10. (Thermo Chemical accumulator. pdf) ClimateWell 10 internal components Power Each [W] Percentage operating hours Average energy consumption [kWh/year] Internal water pumps 80 20% 140 Internal LiCl pumps 80 100% 701 Internal control system 10 100% 88 Total 170 W 931 kWh/year 4.1. Operation and characterizes Three external circuits are connected to the ClimateWell_10: - Thermal heat source (solar collectors). - Air conditioning distribution system for cooling and heating (e.g. radiant floor, fan-coil units). - Heat sink for charging and discharging (swimming pool). The main features of ClimateWell_10 are: - It has internal storage in each of the two accumulators. This allows the machine to store chemical energy with a very high density. This energy can subsequently be used both for cooling and heating. It is important to emphasize that it is chemical energy, not thermal energy that is stored. - It works intermittently with two parallel accumulators (Barrel A and Barrel B). - It is designed to use relatively low temperatures and is hence optimized for usage with solar thermal collectors. It also works with a stable temperature inside the accumulators, which in turn allows for an effective use of solar thermal collectors. - Each barrel is composed of two tanks. A tank, reactor, containing lithium chloride, and another tank, condenser/evaporator, containing water. - To facilitate the process of condensation and evaporation both tanks will be empty. - It is important to emphasize that, as can be seen in the figure 5, the main difference between the use of LiCl as an absorbent and non BrLi, is that the vapor pressure in LiCl is higher, so the difference of temperature to overcome is lower (Tª). Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 143 Figure 5: Stream pressure of LiBr, LiCl and H 2 O depend on the temperature. The two barrels can work in two different ways: charging and discharged. When a barrel is charging, it is connected to the heat source and to the dissipation system, while if it is discharged, it is connected to the distribution and dissipation system. The normal operating mode means that when a barrel is discharged, the other is charging and vice versa. As a result, the machine can always receive heat, while providing heat or cold to the distribution system. 4.1.1. Charging Hot liquid from the thermal source enters the reactor heat exchanger. The manufacturer tells us that the liquid from the thermal source needs to be at least 50ºC above the heat sink temperature for charging. If the thermal source is solar collectors, then this temperature will depend on the power delivered by the solar collectors, which in turn depends on the solar irradiation, flow rate and the size and efficiency of the collectors. The figure 6 shows that when the entering heat reaches the reactor heat exchanger, it causes the LiCl solution in the reactor to boil. When boiling the LiCl returns to crystalline form. At the same time the water evaporates and steam is released to the condenser/evaporator where it condenses on the heat exchanger with the relatively lower temperature. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 144 Figure 6: Charging process of absorption machine. (Tecnología absorción ClimateWell.pdf) The figure 7 shows the energy balance during charging. Some 44 kWh are required to charge both barrels, giving the heat sink 33 kWh of energy. In winter, this energy can be sent directly to the building distribution system. Figure 7: Charging process. (ClimateWell_10 producto.pdf) Dimensioning data The maximum continuous charging temperature is 95ºC, but shorter periods (minutes) of higher temperatures, up to 120ºC are possible. Because of this, it is very important that the solar thermal panels are well dimensioned, this should not occur. If the charging power is higher than the recommended maximum power, the return temperature to the panels will increase and in consequence, the charging temperature. The two barrels can be charged in parallel, thus doubling the charging power. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 145 The typical flow rate for the solar thermal panel circuit is 15 l/min (17,5 l/min in our case). The figure 8 shows charging power (15 l/min) per barrel at 30% charging level (100% meaning fully charged) as a function of: - Hot water temperature from the thermal source. - Liquid (water) temperature from the heat sink (Ths) Figure 8: ClimateWell_10 charging performance. (ClimateWell_10 producto.pdf) We have to take in account that the maximum power is 26 kW per barrel resulting in 52 kW total if charging both barrels at the same time. For example: - If we have 80ºC from the thermal source and 30ºC from the heat sink, then the charging capacity would be 14 kW per barrel. - In terms of energy, 88 kWh is required to fully charge both barrels, thus fully charging one empty barrel would take 44 / 14 = 3 hours and 9 min. - When reaching fully charged level, typically 5ºC higher temperature is required to achieve the same charging power. 4.1.2. Discharging The discharging process can be of two types: on the one hand, the cooling to produce cold, and on the other hand, the heating to produce heat. In figure 9, it can be seen the discharging process, which will be discussed more fully below, depending on whether it is cooling or heating. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 146 Figure 9: Discharging process of absorption machine. (Tecnología absorción ClimateWell.pdf) 4.1.2.1. COOLING The water returns from the distribution system at a higher temperature than when it left the condenser / evaporator (the building has been cooled). This heat causes the water in the evaporator to boil and the steam passes down to the reactor, where it condenses, since the reactor is relatively cooler. Steam that condenses into water in the reactor will dilute the LiCl solution. The diluted LiCl solution is then pumped through the filter basket, where it mixes with the salt and regains its saturation. The saturation is needed to continuously provide a temperature difference between the condenser/evaporator and the reactor. The figure 10 below shows the energy balance during cooling. Figure 10: Energy balance during cooling. (ClimateWell_10 producto.pdf) Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 147 Dimensioning data It is important to note that low temperatures from the heat sink improve the ClimateWell_10’s cooling capacity, so selection of the type and size of heat sink is important to optimizing performance and minimizing costs. Temperature from the heat sink will depend on ambient conditions and the size and efficiency of the heat sink. If the cooling load increases in the building to a point where the maximum power of the machine is reached, the distribution circuit temperature will start to increase slowly, but still cool the building. The indoor temperature will increase, but still be lower than the outdoors. Due to, the manufacturer not recommended to have a great difference between indoor and outdoor temperature when it is very hot outside. The typical flow rate for the building distribution circuit is between 15 l/min and 20 l/min. (17,5 l/min in our case). The figure 11 shows cooling capacity (15 l/min) per barrel when fully charged as a function of: - Chilled water temperature from the machine - Liquid (water) temperature from the heat sink (Ths) Figure 11: ClimateWell_10 cooling performance. (ClimateWell_10 producto.pdf) We can see in the figure 9 that the higher the temperature to the distribution system, the more effectively the machine works in cooling mode. It is thus ideal for radiant floor applications, where flow temperatures up to 17ºC are used. If we have 30ºC from the heat sink and deliver 15ºC to the (radiant floor) cooling circuit, then the cooling power per barrel would be 9 kW. If both barrels are discharged at the same time, the cooling power would be 18 kW. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 154 7.2. Auxiliary power system As has been explained above, the installation must have an auxiliary power system in parallel to support our of ClimateWell_10 machine. Its dimensioning must be calculated for it to be able to supply the energy demand consumed in the home, in case of prolonged rainy days, without excessive light or very cold times. The chosen system will be a condensing boiler by natural gas. For the calculation of the boiler, we must consider the hypothesis that all the heat needed to heat the soil, can only be provided by the auxiliary boiler. Because the maximum heating power of our boiler is 25 kW, the chosen condensing boiler is ISOFAST 21 CONDENS F30 of the brand Dual Sauna which is attached in ANNEX 8. This condensing boiler will provide 25,7 kW of heating and 30,6 kW of DHW if necessary. 7.3. Pipes The pipe diameter is determined according to the flow requirement in each section of the circuit. In our case, we have three different circuits and because of this, three values of pipes diameters must be calculated. However, since the solar collector circuit and the distribution circuit have both the same flow, we only will calculate two different diameters. To size the pipe, we must calculate a flow rate which is between 0,5-1,5 m/s, since if it is more than 1.5 m/s, it will cause a high pressure drop in the solar circuit. If the speed is less than 0.5 m/s, it will prevent the air bubbles from arriving to the unit purged, resulting in higher heat losses. Due to this, the sizes of the pipes will be designed for a speed of 1m/s. For a pipe diameter (m) and a flow (m³/s) the flow velocity (m/s) is provided by the following expression: V = → D = D (solar collector and distribution circuit) (17,5 l / min) = 4,82 mm ≈ 5mm D (dissipation circuit) (35 l / min) = 6,81 mm ≈ 7mm The piping material used will be stainless steel because it offers efficient and reliable performance, especially in high-temperature circuits, as it is the case of solar circuit. The thickness of pipe insulation depends if the pipes are outside or inside and on the temperature of the fluid flowing through them. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 155 7.4. Circulation pumps The pumps will be responsible for the fluid circulation inside the pipes. In our circuit 5 pumps will be installed: • Solar collector primary circuit (solar collector). • Solar collector secondary circuit (on the side of ClimateWell_10). • Dissipation circuit (on the side of the pool). • Dissipation circuit (on the side of the machine ClimateWell_10). • Distribution circuit. Circulation pumps will be installed in the coldest areas of the circuit, and between two shut-off valves. Also, these will have sufficient space to allow their possible replacement or repair without having to drain the system. The functioning of a circulation pump is determined by its characteristic curve, which represents the relation between the manometric height H which provides the pump and the circulation flow Q. Due to the design of our circuit, in order the pumps to be very efficient, it is important to have high effectiveness at partial load. This is the reason why variable speed pumps will be installed. For the design of each pump, it must be taken into account the losses occurring in the circuit that depend on the circuit itself and on the quadratically flow. The calculation of all pumps will be made the same way. The only differences are the losses depending on the circuit where it is placed, and the flow circulating through them. Since our project does not reflect the distribution of pipes, we cannot calculate the losses. Nevertheless, as an explanation, we will indicate the different losses in each circuit to be able to choose the right pump. After making the balance in w.c.m. and after knowing the values of Q and H, we will choose a pump whose curve feature will be selected depending on the operating point where we want the circuit to work. Pump of solar primary circuit (solar collector) H 1 = HL pipes + HL exchanger 1 + HL solar panels Pump of solar primary circuit (on the side of ClimateWell_10) H 2 = HL pipes + HL exchanger 1 +HL ClimateWell_10 Pump of dissipation circuit (on the side of the pool) H 3 = HL pipes + HL exchanger 2 + HL (exchanger = pool) Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 156 Pump of dissipation circuit (on the side of CW_10) H 4 = HL pipes + HL exchanger 2 + HL ClimateWell_10 Pump of distribution circuit H 5 = HL pipes + HL ClimateWell_10 - H 1,2,3,4,5 : Manometric height of the pumps (water column meters) (w.c.m.). - HL pipes: Head losses in the pipes (may be lineal or singular. The first are produced in straight sections in the pipes, while the second are produced in the opposite direction.) (w.c.m.). - HL exchanger 1,2 : Head loss produced by the heat exchanger (it is provided by the manufacturer.) (w.c.m.). - HL solar panels: Head loss by the solar panels (it is provided by the manufacturer) (w.c.m.). - HL (exchanger = pool): Head losses in the pool (It is the exchanger) (w.c.m.). - HL ClimateWell_10: Head losses produced by the ClimateWell_10 machine (w.c.m.). 7.5. “Small” elements 7.5.1. Automatic air purgers In order the fluid flow not to be interrupted by the formation of air bags that prevents the correct circulation of fluid due to corrosion and high temperature points, automatic air purgers will be installed in the highest points of the circuit, one in each circuit. 7.5.2. Automatic filling valve When the circuit is discharged due to unwanted water evaporation, these elements will make the needed cold water enter automatically into the circuit to compensate the operating pressure of the circuit where it will be placed. 7.5.3. Pressure relieving valve Due to accidental causes, to prevent a sharp increase of water pressure inside the hot water tank, this valve will be installed. It acts when the pressure inside the tank exceeds 6 bars, to avoid damages to the equipment, increasing its lifetime and avoiding the possibility of accidents. 7.5.4. Pressure reduction valve In the entrance of cold water to storage tank, this valve will be installed to allow the system to work with a stable water pressure. It is necessary to ensure a sufficient flow and pressure distribution to each consumer. This way, it will avoid violent fluctuations which may cause damages to equipment components repeatedly and randomly. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 157 7.5.5. Anti waterhammer expander vessel It is vital and will be installed in the cold water inlet to the tank. Its main function is to absorb waterhammer caused by differences in density between the hot water tank and cold water entering. This installation will prevent unwanted noise in the pipes, vibration and eventual damages. 7.5.6. Non-return valve It is placed to prevent the flow of water from circulating into unwanted places. This will be installed after the pump of heat transfer circuit, so that during the stagnation, the steam does not arrive to the pump and damage it. 7.5.7. Cut-off valves These valves, usually of ball type, will be connected to all major equipment of the installation to carry out repairs or maintenance actions without emptying the rest of the circuit. 7.5.8. Expansion tank Due to changes of temperature in the working fluid, an expansion tank will be installed to absorb its dilations in all circuits in which water circulates at high temperature. To protect it, it should be installed in the coldest point of each circuit. 7.5.9. Drain valves The drain valves will enable to eliminate the water from the system to facilitate the repair or replacement processes in the circuit. These will be placed at the lowest points of the installation, in the bottom of storage tank and solar panels circuit. 7.5.10. Safety valves The main objective of the safety valves is to prevent excessive overpressure into the circuits that could damage the elements of the installation or people who manipulate it. A safety valve will be installed in the primary circuit, in the tank and in front of the expansion tank for its maintenance operations. 7.5.11. Filters The filters are placed in the automatic valves and inputs of the pumps to retain the impurities that may exist inside the installation pipes. For a complete safety, another filter is placed in the main entrance of the general water distribution of the town. 7.5.12. Expansion joint This component prevents deformations of the pipes due to dimensional differences in the tubes or other elements due to thermals causes. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 158 7.5.13. Measurement and monitoring In the solar installation, a series of measure elements are included. They have no effect on the performance of the installation but are very useful to evaluate and monitor it. In addition, it enables to quantify the real services of the installation. - Manometer: It will measure the pressure of each circuit, and will be placed in the 5 pumps of the circuit. - Temperature sensor: It will be placed at the output of solar collectors, at the input of the collectors (to see the temperature difference), at the output of solar tank (2), and a temperature probe in the return pipe of the distribution to help controlling the circuit. 8. Control and operation 8.1. Monitoring system and internal control The ClimateWell_10 control system is fully integrated with the barrels and the LCD display is situated on the front of the left barrel. The control system is based on three 8-bit microcontrollers. The system measures 7 internal temperatures, the incoming and outgoing temperatures of the 4 heat exchangers and the temperature of the charging circuit, giving in total 16 temperatures upon which all control is based. To change between heating and cooling there is a switch on the front of the control box. This procedure is not controlled by the system itself, but by the user when appropriate. ClimateWell_10 does not control the auxiliary units such as solar panels, boiler or radiant floor. Because of this, these elements must be controlled in a different way, as it will be explained later. If energy is provided to a full barrel, it will be received, processed internally by the full barrel and will be released through a heat sink. This energy is not used, but is received, thus avoiding problems with excessive heat in the solar collectors. Depending on the control strategy, ClimateWell_10 can be adjusted in different manners depending on the specific requirements of the installation. The manufacturer recommends establishing the operational strategy of ClimateWell_10 during the sizing and planning of the installation. In addition, he tells us that depending on the region of Spain where the project is implemented, the control strategies will differ. For example, in southern Spain where the cooling demand is higher, he recommends the control strategy to follow to be in dual mode. However, if the machine is installed in the central or northern of Spain, it is recommended to choose the strategy of simple mode. Because of this, and knowing that the location of our project is in the center of Spain, we will manage that our ClimateWell_10 machine work in single mode. Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 159 The following paragraphs will describe the two modes of operation which have been previously mentioned. 8.1.1. Single mode In normal operation the control strategy is set to charge one barrel and discharge the other at the same time. In this way we can deliver and charge energy continuously. As soon as one barrel is fully charged the control system automatically switches over to the second barrel and starts charging it. In order to prevent the ClimateWell_10 from switching too often, for example when both barrels are full or if we have a very high cooling demand, it has been programmed to always charge each barrel for a minimum period of 1 hour. 8.1.2. Dual mode There are situations where the single mode strategy is not optimal. By running the barrels in double mode both barrels are charged at the same time, and then discharged at the same time. This strategy is interesting when using a radiant floor system for cooling with a large inertia at a location with great difference between night time and day time outdoor temperature. 8.2. Monitoring system and externat control The temperature sensors, the motorized valves, the auxiliary system, the temperature of solar collectors and hot water tank will be united to a system of regulation, control and monitoring by a wire. This will collect information for managing the equipments and to gather significant data about the performance and energetic efficiency of the circuit. All these signals are wired to a PLC (programmable logic controller) which, after programming it, will be in charge of the acquisition and control operations of the system, deciding the opening of the valves and running or not, of the rest of the components, such as pumps. 8.3. Complete system operation Our system is designed to take in to account the following priorities: - In Winter: 1º DHW 2º CW_10 (Heating) - In Summer: 1º DHW 2º CW_10 (Cooling) 3º Pool Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 160 For a better explanation, a hydraulic circuit diagram of all the installation has been drawn with AutoCad 2010, which is shown in the figure 15 of the Spanish report. Below is explained the system operation, depending on the needs of the consumer (necessity or not of DHW) and on the system (heating or cooling). For this explanation, will be considered the position of all motorized valves, using the following table 10: Table 10: Motorized valve positioning. V1 V2 V3 V4 V5 V6 ON OFF X: The position of the valve doesn’t matter. NOT NECESSITY OF DHW (T1 ≥ 60ºC)  WINTER  Heating (Provides by CW_10). V1 V2 V3 V4 V5 V6 OFF X ON X ON OFF  Heating (Provides by the tank and/or boiler). ♦ T2 > 45ºC (The water provided by the tank does not go into the boiler to heat the floor). V1 V2 V3 V4 V5 V6 ON ON ON X ON ON ♦ T2 < 45ºC (The water that comes from the tank enters in the boiler to increase its temperature and to be able to heat the floor). Depending on whether the return of hot water after heating the floor is higher than the output water of the tank or not, the system is the following.  T3 < T2 (The water temperature of the tank is higher than the water that comes to heat the floor). V1 V2 V3 V4 V5 V6 OFF ON OFF OFF ON ON Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 161  T3 > T2 (The water that comes to heat the floor is higher than the water temperature of the tank). V1 V2 V3 V4 V5 V6 OFF OFF X ON ON ON  SUMMER  Cooling. V1 V2 V3 V4 V5 V6 OFF X ON X ON OFF NECESSITY OF DHW (T1 < 60ºC) In this point, it depends if one of the two tanks is charged or not, ie if CW_10 can provide the required demand or not, because the priority is always supplying heat to DHW.  WINTER  Heating. • Tank charged (Provides by CW_10). V1 V2 V3 V4 V5 V6 OFF OFF ON OFF OFF OFF • Tank discharged (Provides by the tank and/or boiler). ♦ T2 > 45º (The water provided by the tank does not go into the boiler to heat the floor). V1 V2 V3 V4 V5 V6 ON ON ON X OFF ON ♦ T2 < 45ºC (The water that comes from the tank enters in the boiler to increase its temperature and to be able to heat the floor). Depending on whether the return of hot water after heating the floor is higher than the output water of the tank or not, the system is the following.  T3 < T2 (The water temperature of the tank is higher than the water that comes to heat the floor). V1 V2 V3 V4 V5 V6 OFF ON OFF OFF OFF ON Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 162  T3 > T2 (The water that comes to heat the floor is higher than the water temperature of the tank). V1 V2 V3 V4 V5 V6 OFF OFF X ON OFF ON  SUMMER  Cooling (It will depend on whether the tank is changed or discharged). In this case, being in summer or winter doesn’t matter since the boiler only provides heat and not cold). V1 V2 V3 V4 V5 V6 OFF X ON X OFF OFF 9. Simulation of the system TRNSYS is a dynamic analysis tool which is used worldwide for the calculation of solar systems, energy saving systems in buildings, air conditioning systems with advanced features, renewable energy systems, cogeneration ... in conclusion, systems which require a dynamics simulation. Using the interface TRNSED (simulation software for DHW by solar energy) for TRNSYS, we will introduce the parameters of our system, to obtain the necessary results both economic and environmental. TRNSED has a database from Meteonormo. This database has all the information related to the different temperatures and climates, depending on where the project is installed. This way, the program can determine the energy to use in our system. By introducing all the values commented previously in the simulation program we will obtain a simulation report, as can be seen in the ANNEX 9. You can see that most of the parameters entered into the simulation program are included in the report. In the project we didn’t place auxiliary cooling equipment, but the program needs to know its COP value in order to be able to make the economic analysis and the corresponding comparison with the cost of fuel. After checking with the program that the variation of this value had a great repercussion on the variation of annual cost savings, we sought information about different suppliers of these devices. The chosen COP has been 2 because an average value has been selected in comparison with refrigeration equipment currently on the market. As the program does not have the option to choose the solar collector chosen in our project, we chose one of the same brand but of smaller size. This makes that the final result varies a little bit in comparison with the reality since the performance of the solar collector will be higher, as it is larger. As a result, if after calculating the project's profitability we obtain profitable results, it would even be a little more. In the graphic Climatización de una casa mediante una máquina de absorción alimentada por paneles solares 163 provided in the report, the different temperatures of solar collectors can be seen as well as the temperature inside and outside of the home, and the dissipation temperature of the pool. The pool temperature has a constant value around 23°C. As it is not more than 30ºC at any time, we can conclude that the dimensioning was appropriate. This factor is extremely important in order the machine to operate with its optimal conditions of design, especially for cooling. The temperature of the solar panels never exceeds 90ºC. Consequently, the sizing was also correct, making that, added to the sink one, both values of temperature are the two most important control parameters of the system. The temperature to the house fixed in our system is very similar to the temperature provided in the report. In addition, it offers us the different coverages both of DHW, as well as heating and cooling that are provided by the machine. The coverage of heating is only 8,1% since, as it has been commented earlier in the project; the priority is focused on DHW, making its coverage of 85,4%. Cooling coverage is 41,6%. This can be increased if the solar panels are changed by vacuum tube collectors, because of its higher performance. It should also be bear in mind that the price of vacuum tube collectors is much higher, so that the profitability of the project should be recalculated. The report provides us an annual saving which is derived from the use of this equipment. It will help us below for calculating the profitability of the project. It also offers us a series of environmental data, which will be exposed in the next paragraph. 10. Environmental Analysis The report provides us a series of environmental data to take into account. As can be seen, the consumption of 4,5 tons of CO 2 is avoided with the use of this system. This is equivalent to an area of 0.5 hectares of forest and to the emission of CO 2 when travelling around 30.000 Km with a car. To compare different buildings, we have to take into account its energy certification. It refers to a building energy qualification that reflects its energy independence. Thus it takes into account the energy savings, making a comparison with a conventional system. In order to make this comparison, the same report provides us a comparison between the energy certification of the used system and a conventional system. You can notice that the energy certification with CW_10 has improved considerably. This is especially true regarding DHW due to its high coverage providing by the system, as it has been commented previously. 11. Economic Analysis To make the economic analysis of the installation and be able to compare our system with a conventional installation, I considered the fact that not all the elements