Hydronic cooling of the thermal mass on house dwellings

Chapter III – Energy Efficiency 606 HYDRONIC COOLING OF THE THERMAL MASS ON HOUSE DWELLINGS 1 Calderón Castillo, D.C. 1 Programa de Maestría y Doctorado en Arquitectura. Campo de conocimiento Tecnología Universidad Nacional Autónoma de México, Circuito Interior s/n Ciudad Universitaria, México. e-mail: [email protected] ABSTRACT This article features an analysis of the active radiant hydronic system as a thermic mass cooling system of concrete and the time which this cooling process is being made on the sub-humid mild climate temperature (Mexico City, Mexico) and the warm humid climate temperature (San Pedro Sula, Honduras). The research develop two concrete prototypes, a hydronic system and the another one as a reference to compare the system functionality. On Mexico City’s weather, the concrete thermic mass diminishes 6.73 °C in comparison with the environment temperature. At San Pedro Sula, the concrete thermic mass diminishes 3.32°C in comparison with the environment temperature as well. Reason why this system’s functions works better on sub-humid mild climate temperature because of the high dew temperature is lower than the warm humid climate temperature, so that the water temperature circulation is lower, leveling up the heat absorption from the concrete thermic mass. Keywords: radiant cooling; hydronic system; energy save; thermal mass; thermal comfort; hot and humid weather. Proceedings of the II International and IV National Congress on Sustainable Construction and Eco- Efficient Solutions 607 1.- Introduction In Honduras, as other Latin American countries on development, uses an energetic matrix dependent to Oil. San Pedro Sula, located in the north part of the country, is considered as an industrial city because of the amount of textile industries in the city, making it the second city on importance from its country. On the last years, an energetic crisis is being happened due to the rising demand of electric energy, leaving to its maximum capacity the power plants that supply with electricity the cities; the main consequence is the constant power rationing. One of the reasons of the increasing of this demand of energy is the excessive use of air conditioning equipment because of the high temperatures and humidity from the city and due to the bad design of buildings, not caring of the weather just copying models from other cities without noticing the climate specifics. Lozano (2008) explain that the facade is one of the most important components that the use of energy affects, the gain and the loss of heat is given through the –skin of the building; this represents a significant percentage in the demand of electric energy consume from 40%. Due to the effort that the equipment requires to generate comfort in the space interiors. As a consequence, the following questions appear: the thermic mass of the ceiling can be cooled in order to diminish energetic consume generate b the use of air conditioning systems? Is it possible to accomplish this cooling using water, as a heat absorption element of the thermic mass? Europe, Asian countries and United States uses the hydronic system as a complement of air conditioning systems in order to acclimatize interior spaces, this represent energy savings from 25% to 40% in comparison with the spaces that only utilize the air conditioning system. This saving depends of the climate conditions of the place. Hydronic cooling system is refer as a pipe net made of PEX attached to a cement layer which is below the surface of the building where the cold water flows. This research goal is to diminish mass thermic temperature of concrete with the use of the hydronic system to minimize the heat transference from the exterior to the interior. Among the objectives of the research is to analyze the percentage of the concrete mass thermic cooling according to weather conditions, the analysis of the required time to cool the thermic mass and to avoid condensation within the skin of the building The experimental part of the research consist to develop two scale prototypes with high thermic mass, the chosen material was concrete. One prototype will have installed a pipe system in its interior to leave cool water to pass under it; the other prototype will be used as a reference. This stage’s goal is to analyze the hydronic system functionality to get to know the cooling percentage of the concrete thermic mass and the time in which this process develop in the sub humid mild climate temperature (Mexico City, Mexico) and the warm humid climate temperature (San Pedro Sula, Honduras). The experiment will take place in the postgraduate unity building in the Mexican Autonomous National University, due to its facilities are capable and efficient to develop the experiment and the lab measure materials; and in the San Pedro Sula city, Honduras, because is the case study. 2.- Radiant hydronic system Among the active radiant systems that uses water as a acclimatize system, the most utilized are the warm systems. These systems have being evolved until the time they can be hybrid systems, warming and cooling accordingly to the season of the year. It defines as a pipe web system attached to a concrete layer located on the surface of the building. This pipe system leaves hot and cold water to circulate, so the heat and the cold from water transmit through the pipes to the concrete, and at the same time Chapter III – Energy Efficiency 608 the concrete give up and leave the heat and cold to pass to interior space from the building [1]. Fig. 1 “Radiant hydronic system scheme on the floor”. Source: the author. This system has its basis on the roman warm system called “Hypocaust” and the Korean system “Ontol”, which consisted in a series of conduits under the surface of the floor where hot water circulated (that was generated in stoves) and the warm air was transmitted to the ground and then to interior space [2]. The basic principle of the system is that water is 832 times denser than air, so that the energy density has a direct relation with the material density and can be captured and canalized quicker with water than air. The process is similar to the human body functionality, due to the radiant transfer that the body uses to change most of the thermic energy, that’s why it is a thermally active system that can change from warm to cold with the transference of energy through skin. Modified buildings under this logic change its energetic consume and human comfort patterns due to its high energy saving potential rather than the convective air conditioning systems. Common system installation consists in high density PEX pipes which finds under the concrete slap. The system can be configured to make the flow of water be constant, at the same time it can change the water temperature according to the environment temperature [4]. To make the system works it require a bomb, a mixer valve to get different temperature from water and hot/cold water suppliers systems to get the system functioning. Fig. 2 “Cooling system and radiant heating scheme”. Source: the author. 2.1.- Condensation One of the problems from this system is the condensation generation in concrete. There are strategies to avoid condensation, one of the most important consist in supply cold water to an elevated temperate than the dew temperature on the space [5]. On warm humid climate temperatures, the differential between dew temperature with the environment temperature is lower, contrary case from the dry climate temperature; that’s the reason of the limitations of the system to diminish the temperature of the concrete thermic mass on this climate types. Another strategy to avoid condensations is to diminish the filtration of the humidity from exterior to interior, because there is a high range of filtrations that can make the sensitive heat to increase, leveling up the dew temperature, so the security margin of the temperature decrease to condensation happen. To decrease the filtration is important to isolate the dwelling of the building. Other strategy is to put an air dehumidifier on the entrance [6]. PEX pipe system Reinforce d concrete Floor Water cooling methods: -Subterranean water. -Night air. -Underground collector. -Chiller. -Heat bomb. Collector Pipe system PEX Cooling or heating source Proceedings of the II International and IV National Congress on Sustainable Construction and Eco- Efficient Solutions 609 2.2.- Design There is different software to simulate the radiant system, these allow to evaluate the different alternatives of finishes to know its behavior, slab depth, temperature combinations, water flow and heat absorption quantity. Before calculation, is important to understand the building thermic behavior where this radiant system will be installed, to know how much heat will be needed to eliminate or absorb form interior to generate desire comfort. The system design criteria say that the PEX pipe circuit must be distributed with a maximum wide of 6 inches (150 mm). The rank of separation is from 8 to 10 inches (200 mm to 250 mm) with the objective to have an optimal economic balance with the required pipe. To cheap the cost of the system, many countries use pipe with low diameter, between ½” to 5/8” (12mm to 15mm) with the separation of 6” (150 mm) [7]. 2.3. - Advantages and disadvantages Between the advantages and disadvantages that the system has, we introduce and short abstract of them [8]: Advantage Disadvantage Lower maintenance costs (because of inherent system simplicity— no space conditioning equipment is needed in outside walls, and a common central air system can serve both interior and perimeter zones). The system don´t move the air around the space. The manipulation of the concrete thermal mass to cool it and slow the transfer heat to the spaces. Lower the water temperature too much can create discomfort to the people (feet too cold and head too warm) or cause condensation in the surface. Better indoor air quality (because ventilation air is not recirculated and there are no wet surface cooling coils, thereby reducing the likelihood of bacterial growth). The inappropriate installation of the system and/or the wrong design can create different temp erature in the surface or don´t get the enough cooling capacity to cold the space. The facility to use the hydronic system with others systems. The limited experience in the installation and the lack of the knowledge of how the system works. Table 1 “Advantage and disadvantage of hydronic system”. Souce: Olsen, 2008. 3.- Comparison of the cooling of the hydronic system of thermic mass The first part of the experiment took place in the postgraduate unity building of the UNAM in Mexico City, with a sub humid mild climate temperature. To analyze the hydronic system as a mass thermic cooling system were develop 2 concrete prototypes of 30 cm in length x 30 cm in width x 15 cm in thickness. On one of the prototypes is installed the internal pipe system to water flowing and the other prototype is being used as a reference. The concrete prototype has a PEX pipe of a half inch with a separation of 15 cm between pipes. Chapter III – Energy Efficiency 610 Fig. 3 “Concrete prototype with hydronic system scheme”. Souce: the author. To take measurements, thermistors register temperature from prototypes and the in/out water temperature. The measurements took place from the 21 and the 27 of November of 2014 inside the lab to analyses the system functioning in interior spaces. Then, measurements were taken from 24 and 25 of January of 2015 and from 2 to 6 of March of 2015, on the roof of the building to analyses the sun radiation incidence on the system; the results are shown choosing a significant day. To this phase of the experiments is used a water flow from 1 litter per minute. Because of the lack of water cooling equipment, the process is manual, so that the water is cooled stabilizing it with a differential degree, from 1°C to 2°C over the dew temperature. Fig. 1 “Experiment on the roof. Source: own elaboration”. On March 5 of 2015, the hydronic system worked from 10:30 am to 6:00 pm. Sensors check the temperature from the block’s interior surface, to compare the temperature from the superior surface (the one that receives full solar radiation), interior temperature and the temperature from the lower surface of the block. To get the superficial temperature from all the block’s faces, the faces are divided in six parts, the lateral surfaces: north, south, east and west; and the superior surface of the block in 9 parts. Measurements took place every ten minutes per hour with FLUKE infrared thermometer en every division, to get the average temperature on every surface and compare them with the thermistor temperature (see fig. 5) Block A, hydronic system Block B, Reference Water input Water output Proceedings of the II International and IV National Congress on Sustainable Construction and Eco- Efficient Solutions 611 Fig. 2 “Location of the sensors and the Surface división on the face of the block”. Souce: the author. On graphic 1, is shows the environment temperature, the relative humidity and the dew point temperature that feature the day 5 of March of 2015. The environment temperature rounds between 13.30°C and the 28.84°C; the relative humidity rounds between 23.34% and 68.47% and the range of dew point temperature stays between 3.76°C and 9.29°C. Maximum radiation shows at 12:48 pm with W/m², on graphic 2 we observe that after 1:30pm is cloud so that the radiation diminishes. Graphic 1 “Temperatura ambient, relative humidity and dew point temperatura on March 5, 2015”. 0 10 20 30 40 50 60 70 12:00:00 12:55:00 1:50:00 2:45:00 3:40:00 4:35:00 5:30:00 6:25:00 7:20:00 8:15:00 9:10:00 10:05:00 11:00:00 11:55:00 12:55:00 1:50:00 2:45:00 3:40:00 4:35:00 5:30:00 6:30:00 7:25:00 8:20:00 9:15:00 10:10:00 11:05:00 °C, % Temperatura ambiente Humedad relativa Temperatura punto de rocío 1 4 2 5 3 6 3 6 9 Thermistor 2 1 4 5 7 8 Thermistor Chapter III – Energy Efficiency 612 Graphic 2 “Solar radiation on March 05, 2015”. Table 1 “Test results on March 05, 2015”. On table 2, it shows that the reference block presents a maximum temperature in the interior of the block with 30.73°C. at 3:25pm, at the same time, the hydronic system block has a 22.88°C temperature at the interior, having a difference between both blocks of 7.85°C. The temperature from the inferior surface of the reference block in that time was 30.078°C so that there is a difference of 0.65°C between the interior temperature and the lower surface. On the hydronic system block, in that hour the temperature at the interior of the block was 22.88°C and the inferior surface temperature was 24.45°C, with a difference of 1.57°C. The interior temperature of the block is lower due to the water circulation of the hydronic system. The maximum difference between the temperatures of the interior from both blocks was 8.14°C (see graphic 4), it was given at 4:25pm; with the following results: - Block of reference - Interior temperature: 30.42°C - Inferior surface temperature: 29.70°C - Difference between both temperatures: 0.72°C - Block with hydronic system: - Interior temperature: 22.28°C - Inferior surface temperature: 23.89°C - Difference between both temperatures: 1.61°C The difference between the inferior temperatures from both blocks was 5.81°C at 4:25 pm, so that the hydronic system reduces the heat transference to the extreme side of the block, showed on graphic 4. In the fig. 6 we can see the block heat flux and the different areas according to the temperature, having as a result the inferior surface lower temperature than the superior. 0 100 200 300 400 500 600 700 800 900 1000 12:00:00 0:58:00 1:56:00 2:54:00 3:52:00 4:50:00 5:48:00 6:46:00 7:44:00 8:42:00 9:40:00 10:38:00 11:36:00 12:34:00 13:32:00 14:30:00 15:28:00 16:26:00 17:24:00 18:22:00 19:20:00 20:18:00 21:16:00 22:14:00 23:12:00 W/m^2 Radiation Mínimo 13.305 23.348 3.76 12.58 14.489 12.70 14.282 4.94 6.18 Máximo 28.841 68.471 9.29 30.733 30.407 23.94 25.683 15.22 18.66 Promedio 18.97 44.21 6.07 20.71 24.25 18.19 20.99 2.62 12.57 Temp, °C RH, % Punto de rocío, °C Bloque referencia Bloque hidrónico °C agua entrada °C agua salida Superficie inferior bloque referencia Superficie inferior bloque hidrónico 986 W/m² 12:48 pm Proceedings of the II International and IV National Congress on Sustainable Construction and Eco- Efficient Solutions 613 Graphic 3 “Comparison of the temperature inside the blocks”. Graphic 4 “Comparison of the temperature of the bottom surface of both blocks” . Fig. 3 “Thermal image of the reference block”. 10 15 20 25 30 35 12:00:00 1:00:00 2:00:00 3:00:00 4:00:00 5:00:00 6:00:00 7:00:00 8:00:00 9:00:00 10:00:00 11:00:00 12:00:00 1:05:00 2:05:00 3:05:00 4:05:00 5:05:00 6:05:00 7:10:00 8:10:00 9:10:00 10:10:00 11:10:00 °C Temperatura bloque referencia Temperatura bloque hidrónico 10 15 20 25 30 35 12:25:00 12:55:00 1:25:00 1:55:00 2:25:00 2:55:00 3:25:00 3:55:00 4:25:00 4:55:00 5:25:00 5:55:00 6:30:00 7:00:00 7:30:00 8:00:00 8:30:00 9:00:00 9:30:00 10:00:00 10:30:00 11:00:00 11:30:00 °C Temperatura superficie inferior bloque referencia Temperatura superficie inferior bloque hidrónico Solar radiation Heat transfer by the thermal mass of concrete to the lower surface. Surface warmer due to solar radiation Thermistor Thermistor Temperature measurements with the infrared thermometer FLUKE every 10 minutes on the upper surface Chapter III – Energy Efficiency 614 Fig. 4 “Thermal image of the blocks”. On Fig.7 there’s a thermic image from both blocks at 12:30pm, block B presents a bigger area with lower temperatures at its center than block A, which happen due to the hydronic system cold water flow. Table 2 “Average temperature in the faces of the blocks”. Graphic 5 “Temperature compared on the reference block on March 5, 2015”. Graphic 6 “Temperature compared on the hydronic system block on March 5, 2015”. On table 3, we see the average temperatures in an hour; the measurements were taken every 10 minutes on the different divisions on the faces of the blocks with FLUKE infrared thermometer. On graphic 5 and 6 shows a comparison, between 12:30 pm and 1:30 pm, of the temperature behavior between superior surface, Superior Norte Oeste Este Sur Superior Norte Oeste Este Sur 12:30:00 p.m. 43.48 25.68 26.17 33.72 34.87 42.83 26.92 26.70 33.88 34.65 12:40:00 p.m. 44.21 25.20 25.38 32.78 34.62 43.17 24.83 25.60 32.15 34.37 12:50:00 p.m. 43.98 23.47 24.95 31.28 34.03 40.31 30.03 26.27 30.03 31.20 01:00:00 p.m. 44.00 24.77 26.02 31.10 34 44.27 25.25 25.80 31.83 33.93 01:10:00 p.m. 43.01 24.90 25.83 29.65 34.57 42.00 24.75 25.48 30.65 34.62 01:20:00 p.m. 43.28 24.30 25.67 29.23 35.70 41.02 24.50 25.60 28.60 35.00 01:30:00 p.m. 43.24 24.62 25.95 29.18 36.22 42.17 25.58 26.62 28.83 35.60 Temperatura superficies Bloque referencia Temperatura superficies Bloque hidrónico Hora 24 29 34 39 44 49 12:30:00 12:35:00 12:40:00 12:45:00 12:50:00 12:55:00 1:00:00 1:05:00 1:10:00 1:15:00 1:20:00 1:25:00 1:30:00 °C Temperatura de contacto de la superficie inferior bloque de referencia Temperatura de contacto del interior bloque de referencia Temperatura superficial de la superficie superior 20 25 30 35 40 45 50 12:30:00 12:35:00 12:40:00 12:45:00 12:50:00 12:55:00 1:00:00 1:05:00 1:10:00 1:15:00 1:20:00 1:25:00 1:30:00 °C Temperatura superficie inferior del bloque hidrónico Temperatura interior bloque hidrónico Temperatura superficie superior Bloque B, hydronic system Block A, reference