Energy consumption reduction of a chiller plant by adding evaporative pads to decrease condensation temperature

energies Article Energy Consumption Reduction of a Chiller Plant by Adding Evaporative Pads to Decrease Condensation Temperature Francisco J. Rey Martínez 1, Julio F. San JoséAlonso 1,* , Eloy Velasco Gómez 1, Ana Tejero González 1, Paula M Esquivias 1and Javier M. Rey Hernández 2 1Department of Energy and Fluid mechanics, School of Engineering (EII), University of Valladolid, Paseo del Cauce No. 59, 47011 Valladolid, Spain; [email protected] (F.J.R.M.); [email protected] (E.V.G.); [email protected] (A.T.G.); [email protected] (P.M.E.) 2Higher Polytechnic School, European University Miguel de Cervantes (UEMC), Padre Julio Chevalier, 47012 Valladolid, Spain; javier[email protected] *Correspondence: [email protected] Received: 16 March 2020; Accepted: 24 April 2020; Published: 2 May 2020   Abstract: The high energy consumption of cooling systems justifies the need for strategies to increase the efficiency of the facilities, in order to reduce the related CO 2 emissions. This study aims to improve the performance and reduce the energy consumption of an 8.6 MW air cooled chiller. This installed capacity is biased due to the screw compressors, of 2.98 Energy Efficiency Ratio (EER) at full load (characteristics provided by the manufacturer). The chiller unit has been modified by placing evaporating cooling pads before the condensing coils. The chiller has been monitored for three months, recording over 544,322 measurements (5 min-step data), with and without the evaporative cooling pads, to assess the performance. Data comparison has been done by selecting two days (with and without evaporative panels) with the same health care load and temperatures. Implementing the proposed strategy yields an improvement in the European Seasonal Energy Efficiency Ratio (ESEER) from 3.69 to 4.83, while the Total Equivalent Warming Impact (TEWI) decreases about 1000 tCO 2 . Energy savings of up to 32.6 MWh result into a payback period lower than 2 years. Keywords: air cooled chiller; evaporative cooling pad; adiabatic condenser; equivalent carbon dioxide emissions; energy savings 1. Introduction The building sector is responsible for 40% of the final energy consumption in the European Union [ 1 ]. For this reason, the EU promotes the renovation of existing buildings, the improvement of energy efficiency and the integration of renewable energies in buildings in order to get by 2050 a decarbonized building stock by means of getting nearly zero-energy buildings (nZEB) [2]. The increasing global temperature due to the climate change will decrease the heating energy demand and increase the cooling energy demand. In fact, simulated future weather climates for 2050 and 2080 on an existing nZEB provokes an increase on cooling energy demand around 9% for 2050 and 21% for 2080 regarding to 2020 results [ 3 ]. These results show that, in order to achieve an adequate indoor air quality (IAQ) in buildings, the focus should be on strategies for cooling demand reduction. According to Article 2(2) of the Energy Performance of Buildings Directive (EPBD) [ 4 ] a nZEB means a building that has a very high energy performance; it means that the amount of energy needed to meet the energy demand associated with a typical use of the building which includes, inter alia, energy used for heating, cooling, ventilation, hot water and lighting, is very low. However, although nZEB reduces considerably the cooling energy demand from the envelope, lighting and equipment, occupancy and Energies 2020,13, 2218; doi:10.3390/en13092218 www.mdpi.com/journal/energies Energies 2020,13, 2218 2 of 13 ventilation are always non-modifiable thermal loads, as they are associated to the activity of the building and the requirements of air change in order to secure air quality for those occupants. In order to cover the cooling energy demand of a building, air conditioning systems, which use compression refrigeration cycle, are used. The efficiency of these systems varies according to the working temperatures (evaporation and condensation temperatures). The evaporation temperature in air-conditioned occupied spaces falls in a narrow temperature range because, due to comfort guidelines, air cannot be supplied at a temperature far below the body temperature. However, condensation temperature presents several options depending on the resource with which the heat is exchanged—water, earth or air. In this study, only air condensation is considered. The water heat exchange requires an aquifer and earth heat exchange implies an important investment. Condensation temperature (T c ), when the air is used as a heat sink, directly depends on the local climate conditions of the placement of the building. There are two options, using the dry bulb temperature (T DB ) or the adiabatic saturation temperature of the moist air (T sat ) as the heat sink for the condenser [5], enabling in the latter case a lower thermal level of the heat dissipation media. Refrigeration systems permit condensation closer to T sat if we make use of the phenomenon of evaporative cooling. The difference between T DB and T sat increases, hence the potential of evaporative cooling, as the Relative Humidity (RH) of outside air decreases [ 6 ]. Condensers that apply this phenomenon may have higher levels of maintenance in order to avoid possible contamination by legionella [ 7 ], although they also allow to reduce the condensation temperature and improve the Coefficient of Performance (COP) of the equipment. Condensers that apply the phenomenon of evaporative cooling can be classified in different typologies according to: (i) the contact of the saturated airflow and the condenser; (ii) the moment when water is added and (iii) the source of the water that will be evaporated. If the same airflow in which water is evaporated passes through the condenser, it is called direct; otherwise is indirect. If water is evaporated within the air before the condenser, it is called “dry”; but if water is supplied on the condenser, it is called wet evaporative condenser. If the water source comes from a loop, it is a recirculation water system; otherwise is referred as “lost water” system. Direct-dry systems are commonly called “adiabatic condenser.” Table 1gathers these possible configurations of evaporative condensers (EC). Condensation temperature is function of the minimum temperature of the environment, which is usually the T sat in the direct-dry recirculated water configuration and the water temperature (T w ) in the direct-dry lost water case. The processes of mass and heat transfer at the condenser determines the condensation temperature of the refrigerant. Table 1also indicates the condensation temperature according to the minimum temperature of the process. Many studies have been carried out on this type of condenser in order to improve the efficiency of refrigeration systems. Wei et al. [ 8 ] study a direct wet EC using recirculated water. They propose a numerical model validated with experimental data, obtaining a 30% increase in the COP on an equipment that condenses at T DB . Chien et al. [ 9 ] study the water spraying on a direct wet EC using recirculated water in order to avoid the dragging of water drops and improve the air saturation process. They propose the optimal type and separation of nozzles in each case. This study is of interest as it is focused on one of the disadvantages of EC—the deterioration of the condenser by dragging drops and salts. Fiorentino and Starace [ 10 , 11 ] studied a direct dry EC using recirculated water. They present an experimental study where the evaporation process is evaluated, concluding that an increase of 6% in relative humidity implies a reduction of 30% in the dry temperature. They also highlight the importance of the air speed when it crosses the saturator. Harby et al. [ 12 ] carried out a study on different systems and collected research on vapor compression cooling systems using EC, presenting a lot of experimental data on different technologies. Energies 2020,13, 2218 3 of 13 Table 1. Evaporative condenser types and condensation temperature over saturation temperature or spray water. Type of Evaporative Condensers (EC) Configuration Condensation Temperature (Tc) Indirect Energies 2020, 13, x FOR PEER REVIEW 2 of 14 although nZEB reduces considerably the cooling energy demand from the envelope, lighting and equipment, occupancy and ventilation are always non-modifiable thermal loads, as they are associated to the activity of the building and the requirements of air change in order to secure air quality for those occupants. In order to cover the cooling energy demand of a building, air conditioning systems, which use compression refrigeration cycle, are used. The efficiency of these systems varies according to the working temperatures (evaporation and condensation temperatures). The evaporation temperature in air-conditioned occupied spaces falls in a narrow temperature range because, due to comfort guidelines, air cannot be supplied at a temperature far below the body temperature. However, condensation temperature presents several options depending on the resource with which the heat is exchanged—water, earth or air. In this study, only air condensation is considered. The water heat exchange requires an aquifer and earth heat exchange implies an important investment. Condensation temperature (Tc), when the air is used as a heat sink, directly depends on the local climate conditions of the placement of the building. There are two options, using the dry bulb temperature (TDB) or the adiabatic saturation temperature of the moist air (Tsat) as the heat sink for the condenser [5], enabling in the latter case a lower thermal level of the heat dissipation media. Refrigeration systems permit condensation closer to Tsat if we make use of the phenomenon of evaporative cooling. The difference between TDB and Tsat increases, hence the potential of evaporative cooling, as the Relative Humidity (RH) of outside air decreases [6]. Condensers that apply this phenomenon may have higher levels of maintenance in order to avoid possible contamination by legionella [7], although they also allow to reduce the condensation temperature and improve the Coefficient of Performance (COP) of the equipment. Condensers that apply the phenomenon of evaporative cooling can be classified in different typologies according to: (i) the contact of the saturated airflow and the condenser; (ii) the moment when water is added and (iii) the source of the water that will be evaporated. If the same airflow in which water is evaporated passes through the condenser, it is called direct; otherwise is indirect. If water is evaporated within the air before the condenser, it is called “dry”; but if water is supplied on the condenser, it is called wet evaporative condenser. If the water source comes from a loop, it is a recirculation water system; otherwise is referred as “lost water” system. Direct-dry systems are commonly called “adiabatic condenser.” Table 1 gathers these possible configurations of evaporative condensers (EC). Table 1. Evaporative condenser types and condensation temperature over saturation temperature or spray water. Type of Evaporative Condensers (EC) Configuration Condensation Temperature (Tc) Indirect Tc = (Tw + 20) °C TA = (Tw + 5 + 5 + 5) °C (Tw + 5 + 5) °C (Tw + 5) °C (approach) Tref = Tw Direct Dry Recirculation TC = (Tsat + 15) °C TA = (Tsat + 5 + 5) °C Tsat + 5 °C (approach) Tref = Tsat Lost water TC = (Tw + 15) °C TA = (Tw + 5 + 5) °C Tc =(Tw +20) ◦C TA=(Tw+5+5+5) ◦Cv (Tw+5+5) ◦C (Tw+5) ◦C (approach) Tref =Tw Direct Dry Recirculation Energies 2020, 13, x FOR PEER REVIEW 2 of 14 although nZEB reduces considerably the cooling energy demand from the envelope, lighting and equipment, occupancy and ventilation are always non-modifiable thermal loads, as they are associated to the activity of the building and the requirements of air change in order to secure air quality for those occupants. In order to cover the cooling energy demand of a building, air conditioning systems, which use compression refrigeration cycle, are used. The efficiency of these systems varies according to the working temperatures (evaporation and condensation temperatures). The evaporation temperature in air-conditioned occupied spaces falls in a narrow temperature range because, due to comfort guidelines, air cannot be supplied at a temperature far below the body temperature. However, condensation temperature presents several options depending on the resource with which the heat is exchanged—water, earth or air. In this study, only air condensation is considered. The water heat exchange requires an aquifer and earth heat exchange implies an important investment. Condensation temperature (Tc), when the air is used as a heat sink, directly depends on the local climate conditions of the placement of the building. There are two options, using the dry bulb temperature (TDB) or the adiabatic saturation temperature of the moist air (Tsat) as the heat sink for the condenser [5], enabling in the latter case a lower thermal level of the heat dissipation media. Refrigeration systems permit condensation closer to Tsat if we make use of the phenomenon of evaporative cooling. The difference between TDB and Tsat increases, hence the potential of evaporative cooling, as the Relative Humidity (RH) of outside air decreases [6]. Condensers that apply this phenomenon may have higher levels of maintenance in order to avoid possible contamination by legionella [7], although they also allow to reduce the condensation temperature and improve the Coefficient of Performance (COP) of the equipment. Condensers that apply the phenomenon of evaporative cooling can be classified in different typologies according to: (i) the contact of the saturated airflow and the condenser; (ii) the moment when water is added and (iii) the source of the water that will be evaporated. If the same airflow in which water is evaporated passes through the condenser, it is called direct; otherwise is indirect. If water is evaporated within the air before the condenser, it is called “dry”; but if water is supplied on the condenser, it is called wet evaporative condenser. If the water source comes from a loop, it is a recirculation water system; otherwise is referred as “lost water” system. Direct-dry systems are commonly called “adiabatic condenser.” Table 1 gathers these possible configurations of evaporative condensers (EC). Table 1. Evaporative condenser types and condensation temperature over saturation temperature or spray water. Type of Evaporative Condensers (EC) Configuration Condensation Temperature (Tc) Indirect Tc = (Tw + 20) °C TA = (Tw + 5 + 5 + 5) °C (Tw + 5 + 5) °C (Tw + 5) °C (approach) Tref = Tw Direct Dry Recirculation TC = (Tsat + 15) °C TA = (Tsat + 5 + 5) °C Tsat + 5 °C (approach) Tref = Tsat Lost water TC = (Tw + 15) °C TA = (Tw + 5 + 5) °C TC=(Tsat +15) ◦C TA=(Tsat +5+5) ◦C Tsat +5◦C (approach) Tref =Tsat Lost water Energies 2020, 13, x FOR PEER REVIEW 3 of 14 (Tw + 5) °C (approach) Tref = Tw Wet Recirculation TC = (Tsat + 10) °C (Tsat + 5) °C (approach) Tref = Tsat Lost water Tc = (Tw + 10) °C (Tw + 5) °C (approach) Tref = Tw Condensation temperature is function of the minimum temperature of the environment, which is usually the Tsat in the direct-dry recirculated water configuration and the water temperature (Tw) in the direct-dry lost water case. The processes of mass and heat transfer at the condenser determines the condensation temperature of the refrigerant. Table 1 also indicates the condensation temperature according to the minimum temperature of the process. Many studies have been carried out on this type of condenser in order to improve the efficiency of refrigeration systems. Wei et al. [8] study a direct wet EC using recirculated water. They propose a numerical model validated with experimental data, obtaining a 30% increase in the COP on an equipment that condenses at TDB. Chien et al. [9] study the water spraying on a direct wet EC using recirculated water in order to avoid the dragging of water drops and improve the air saturation process. They propose the optimal type and separation of nozzles in each case. This study is of interest as it is focused on one of the disadvantages of EC—the deterioration of the condenser by dragging drops and salts. Fiorentino and Starace [10,11] studied a direct dry EC using recirculated water. They present an experimental study where the evaporation process is evaluated, concluding that an increase of 6% in relative humidity implies a reduction of 30% in the dry temperature. They also highlight the importance of the air speed when it crosses the saturator. Harby et al. [12] carried out a study on different systems and collected research on vapor compression cooling systems using EC, presenting a lot of experimental data on different technologies. Martínez et al. [13] studied the improvement of a direct dry EC using recirculated water, due to the integration of an evaporative cellulose pad to the condenser of an Split Unit, obtaining an increase of 10.6% in the COP. In addition, they present a table with a compilation of previous researches on EC, organized by the type of analysis carried out, the equipment used and the results obtained. This paper shows the results obtained by installing cellulose evaporative pads, with lost water humidification, before the airflow goes into the condensers, so a direct-dry lost water configuration, also known as adiabatic condenser. The air-conditioning system of the building under study has an installed cooling capacity of 8.70 MW and the strategy applied on the use of the evaporative pads consisted of an ON/OFF mode of the water supply pump to the cellulose pad, depending on the time, being ON from 3pm to 10pm and the remaining hours on standby. 2. Case Study TC=(Tw+15) ◦C TA=(Tw+5+5) ◦C (Tw+5) ◦C (approach) Tref =Tw Wet Recirculation Energies 2020, 13, x FOR PEER REVIEW 3 of 14 (Tw + 5) °C (approach) Tref = Tw Wet Recirculation TC = (Tsat + 10) °C (Tsat + 5) °C (approach) Tref = Tsat Lost water Tc = (Tw + 10) °C (Tw + 5) °C (approach) Tref = Tw Condensation temperature is function of the minimum temperature of the environment, which is usually the Tsat in the direct-dry recirculated water configuration and the water temperature (Tw) in the direct-dry lost water case. The processes of mass and heat transfer at the condenser determines the condensation temperature of the refrigerant. Table 1 also indicates the condensation temperature according to the minimum temperature of the process. Many studies have been carried out on this type of condenser in order to improve the efficiency of refrigeration systems. Wei et al. [8] study a direct wet EC using recirculated water. They propose a numerical model validated with experimental data, obtaining a 30% increase in the COP on an equipment that condenses at TDB. Chien et al. [9] study the water spraying on a direct wet EC using recirculated water in order to avoid the dragging of water drops and improve the air saturation process. They propose the optimal type and separation of nozzles in each case. This study is of interest as it is focused on one of the disadvantages of EC—the deterioration of the condenser by dragging drops and salts. Fiorentino and Starace [10,11] studied a direct dry EC using recirculated water. They present an experimental study where the evaporation process is evaluated, concluding that an increase of 6% in relative humidity implies a reduction of 30% in the dry temperature. They also highlight the importance of the air speed when it crosses the saturator. Harby et al. [12] carried out a study on different systems and collected research on vapor compression cooling systems using EC, presenting a lot of experimental data on different technologies. Martínez et al. [13] studied the improvement of a direct dry EC using recirculated water, due to the integration of an evaporative cellulose pad to the condenser of an Split Unit, obtaining an increase of 10.6% in the COP. In addition, they present a table with a compilation of previous researches on EC, organized by the type of analysis carried out, the equipment used and the results obtained. This paper shows the results obtained by installing cellulose evaporative pads, with lost water humidification, before the airflow goes into the condensers, so a direct-dry lost water configuration, also known as adiabatic condenser. The air-conditioning system of the building under study has an installed cooling capacity of 8.70 MW and the strategy applied on the use of the evaporative pads consisted of an ON/OFF mode of the water supply pump to the cellulose pad, depending on the time, being ON from 3pm to 10pm and the remaining hours on standby. 2. Case Study TC=(Tsat +10) ◦C (Tsat +5) ◦C (approach) Tref =Tsat Lost water Energies 2020, 13, x FOR PEER REVIEW 3 of 14 (Tw + 5) °C (approach) Tref = Tw Wet Recirculation TC = (Tsat + 10) °C (Tsat + 5) °C (approach) Tref = Tsat Lost water Tc = (Tw + 10) °C (Tw + 5) °C (approach) Tref = Tw Condensation temperature is function of the minimum temperature of the environment, which is usually the Tsat in the direct-dry recirculated water configuration and the water temperature (Tw) in the direct-dry lost water case. The processes of mass and heat transfer at the condenser determines the condensation temperature of the refrigerant. Table 1 also indicates the condensation temperature according to the minimum temperature of the process. Many studies have been carried out on this type of condenser in order to improve the efficiency of refrigeration systems. Wei et al. [8] study a direct wet EC using recirculated water. They propose a numerical model validated with experimental data, obtaining a 30% increase in the COP on an equipment that condenses at TDB. Chien et al. [9] study the water spraying on a direct wet EC using recirculated water in order to avoid the dragging of water drops and improve the air saturation process. They propose the optimal type and separation of nozzles in each case. This study is of interest as it is focused on one of the disadvantages of EC—the deterioration of the condenser by dragging drops and salts. Fiorentino and Starace [10,11] studied a direct dry EC using recirculated water. They present an experimental study where the evaporation process is evaluated, concluding that an increase of 6% in relative humidity implies a reduction of 30% in the dry temperature. They also highlight the importance of the air speed when it crosses the saturator. Harby et al. [12] carried out a study on different systems and collected research on vapor compression cooling systems using EC, presenting a lot of experimental data on different technologies. Martínez et al. [13] studied the improvement of a direct dry EC using recirculated water, due to the integration of an evaporative cellulose pad to the condenser of an Split Unit, obtaining an increase of 10.6% in the COP. In addition, they present a table with a compilation of previous researches on EC, organized by the type of analysis carried out, the equipment used and the results obtained. This paper shows the results obtained by installing cellulose evaporative pads, with lost water humidification, before the airflow goes into the condensers, so a direct-dry lost water configuration, also known as adiabatic condenser. The air-conditioning system of the building under study has an installed cooling capacity of 8.70 MW and the strategy applied on the use of the evaporative pads consisted of an ON/OFF mode of the water supply pump to the cellulose pad, depending on the time, being ON from 3pm to 10pm and the remaining hours on standby. 2. Case Study Tc=(Tw+10) ◦C (Tw+5) ◦C (approach) Tref =Tw Mart í nez et al. [ 13 ] studied the improvement of a direct dry EC using recirculated water, due to the integration of an evaporative cellulose pad to the condenser of an Split Unit, obtaining an increase of 10.6% in the COP. In addition, they present a table with a compilation of previous researches on EC, organized by the type of analysis carried out, the equipment used and the results obtained. This paper shows the results obtained by installing cellulose evaporative pads, with lost water humidification, before the airflow goes into the condensers, so a direct-dry lost water configuration, also known as adiabatic condenser. The air-conditioning system of the building under study has an installed cooling capacity of 8.70 MW and the strategy applied on the use of the evaporative pads consisted of an ON/OFF mode of the water supply pump to the cellulose pad, depending on the time, being ON from 3pm to 10pm and the remaining hours on standby. 2. Case Study The case study is a chiller plant installed in a hospital building. The building has 115,354 m 2 built area, around 3000 employees and 600 beds. The chiller plant has a cooling capacity of 8.70 MW and is composed by 6 TRANE chillers, R series, model RTAC 400, with a cooling capacity of 1442 kW/each Energies 2020,13, 2218 4 of 13 and a COP of 2.89. Each chiller has four screw compressors, enabling partial cooling capacity of the chiller. Figure 1shows the chiller plant at the roof of the hospital. Energies 2020, 13, x FOR PEER REVIEW 4 of 14 The case study is a chiller plant installed in a hospital building. The building has 115,354 m2 built area, around 3000 employees and 600 beds. The chiller plant has a cooling capacity of 8.70 MW and is composed by 6 TRANE chillers, R series, model RTAC 400, with a cooling capacity of 1442 kW/each and a COP of 2.89. Each chiller has four screw compressors, enabling partial cooling capacity of the chiller. Figure 1 shows the chiller plant at the roof of the hospital. (a). Secondary group of pumps Primary gr oup of pumps Cooled water By passed water Returned water (b). Figure 1. (a) Chiller plant at the roof of the hospital; (b) Scheme of principle. The produced cooled water by the chiller plant is distributed by a double ring system with inverted return that covers the whole building and enables the water supply to the installed 200 Air Handling Units and 1500 inductors (the inductors are installed at offices and meeting rooms). The temperature of the supply water is 7 °C and 12 °C for the returned water. Figure 1. (a) Chiller plant at the roof of the hospital; (b) Scheme of principle. The produced cooled water by the chiller plant is distributed by a double ring system with inverted return that covers the whole building and enables the water supply to the installed 200 Air Handling Units and 1500 inductors (the inductors are installed at offices and meeting rooms). The temperature of the supply water is 7 ◦C and 12 ◦C for the returned water. Energies 2020,13, 2218 5 of 13 The SCADA system of the chiller plant, provided by siemens, measures and allows to display several operating parameters, due to the SITRANS sensors installed. Figure 2shows a screenshot with all the data provided by the control system for each chiller. •Partial load ratio, based on the electric energy consumption (Row 1), • Temperature of the refrigerant at the condenser and the evaporator, in both circuits of each chiller (Rows 2–5), •Inlet and outlet water temperature to the chiller (Row 6–7), •Outdoor temperature in each chiller (Row 8), • Data about the performance state of each chiller (Row 9–10)—presence of evaporative pad and operation of the chiller (On/Off). Energies 2020, 13, x FOR PEER REVIEW 5 of 14 The SCADA system of the chiller plant, provided by siemens, measures and allows to display several operating parameters, due to the SITRANS sensors installed. Figure 2 shows a screenshot with all the data provided by the control system for each chiller. • Partial load ratio, based on the electric energy consumption (Row 1), • Temperature of the refrigerant at the condenser and the evaporator, in both circuits of each chiller (Rows 2–5), • Inlet and outlet water temperature to the chiller (Row 6–7), • Outdoor temperature in each chiller (Row 8), • Data about the performance state of each chiller (Row 9–10)—presence of evaporative pad and operation of the chiller (On/Off). All measurements of the sensors were checked with calibrated equipment, verifying the accuracy of the results. Figure 2. Screenshot of the Control System of the chiller plant. Before the research, the chiller plant produced peaks of power consumption, which exceed the maximum contracted electrical power during the peak hours of cooling demand in summer. This situation caused additional costs and overheating in the transformers of the electrical system. Figure 3 shows the electricity consumption curve in one year and the average trend line for the year from data taken from the SCADA system. Figure 2. Screenshot of the Control System of the chiller plant. All measurements of the sensors were checked with calibrated equipment, verifying the accuracy of the results. Before the research, the chiller plant produced peaks of power consumption, which exceed the maximum contracted electrical power during the peak hours of cooling demand in summer. This situation caused additional costs and overheating in the transformers of the electrical system. Figure 3shows the electricity consumption curve in one year and the average trend line for the year from data taken from the SCADA system. After observing the high power consumption, the proposed strategy was reducing the condensation temperature by installing evaporative pads before the condensation batteries. The decrease in the condensation temperature would mean an improvement in the COP and in the ESEER [ 14 ] of the system, taking into account that the chillers are located in a location where the dry bulb (T DB ) and wet bulb (T WB ) temperatures of the moist air are 33.2/19.1 ◦ C respectively, at a percentile level of 1% [ 15 ]. The introduction of evaporative pads before the condensers allows to reduce 14 ◦ C the condensation temperature, which would mean an increase in the EEC and in the ESEER. An evaporative pad was selected from the MUNTERS company, model CELdek 7060-15, which is made of corrugated cellulose with different striation angles, with a 60-degree inclination (colored in pink at Figure 4) and another pad below with a 30-degree inclination (colored in blue at Figure 4), glued together to achieve a high evaporation efficiency and a very low pressure drop. Figure 4and Table 2show the characteristics of the evaporative pad. Energies 2020,13, 2218 6 of 13 Energies 2020, 13, x FOR PEER REVIEW 6 of 14 Figure 3. Power consumption of the building in one year, without changes in the cooling system. After observing the high power consumption, the proposed strategy was reducing the condensation temperature by installing evaporative pads before the condensation batteries. The decrease in the condensation temperature would mean an improvement in the COP and in the ESEER [14] of the system, taking into account that the chillers are located in a location where the dry bulb (T DB ) and wet bulb (T WB ) temperatures of the moist air are 33.2/19.1 °C respectively, at a percentile level of 1% [15]. The introduction of evaporative pads before the condensers allows to reduce 14 °C the condensation temperature, which would mean an increase in the EEC and in the ESEER. An evaporative pad was selected from the MUNTERS company, model CELdek 7060-15, which is made of corrugated cellulose with different striation angles, with a 60-degree inclination (colored in pink at Figure 4) and another pad below with a 30-degree inclination (colored in blue at Figure 4), glued together to achieve a high evaporation efficiency and a very low pressure drop. Figure 4 and Table 2 show the characteristics of the evaporative pad. Figure 4. Evaporative cooling pad CELdek 7060-15. Table 2. Characteristics of the installed evaporative cooling pad, the selected cooling pad is highlighted with the grey background color. CELdek 7060-15 Thickness (mm) 100 150 200 300 Input temperature (°C) 33.1 33.1 33.1 33.1 Adiabatic saturation temperature (°C) 19.1 19.1 19.1 19.1 Saturation efficiency (%) 68 81 88 96 Pressure drop (Pa) 4 6 8 12.5 Output temperature (°C) 23.6 21.8 20.8 19.7 0 500 1000 1500 2000 2500 3000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec MWh Power consumption Figure 3. Power consumption of the building in one year, without changes in the cooling system. Energies 2020, 13, x FOR PEER REVIEW 6 of 14 Figure 3. Power consumption of the building in one year, without changes in the cooling system. After observing the high power consumption, the proposed strategy was reducing the condensation temperature by installing evaporative pads before the condensation batteries. The decrease in the condensation temperature would mean an improvement in the COP and in the ESEER [14] of the system, taking into account that the chillers are located in a location where the dry bulb (T DB ) and wet bulb (T WB ) temperatures of the moist air are 33.2/19.1 °C respectively, at a percentile level of 1% [15]. The introduction of evaporative pads before the condensers allows to reduce 14 °C the condensation temperature, which would mean an increase in the EEC and in the ESEER. An evaporative pad was selected from the MUNTERS company, model CELdek 7060-15, which is made of corrugated cellulose with different striation angles, with a 60-degree inclination (colored in pink at Figure 4) and another pad below with a 30-degree inclination (colored in blue at Figure 4), glued together to achieve a high evaporation efficiency and a very low pressure drop. Figure 4 and Table 2 show the characteristics of the evaporative pad. Figure 4. Evaporative cooling pad CELdek 7060-15. Table 2. Characteristics of the installed evaporative cooling pad, the selected cooling pad is highlighted with the grey background color. CELdek 7060-15 Thickness (mm) 100 150 200 300 Input temperature (°C) 33.1 33.1 33.1 33.1 Adiabatic saturation temperature (°C) 19.1 19.1 19.1 19.1 Saturation efficiency (%) 68 81 88 96 Pressure drop (Pa) 4 6 8 12.5 Output temperature (°C) 23.6 21.8 20.8 19.7 0 500 1000 1500 2000 2500 3000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec MWh Power consumption Figure 4. Evaporative cooling pad CELdek 7060-15. Table 2. Characteristics of the installed evaporative cooling pad, the selected cooling pad is highlighted with the grey background color. CELdek 7060-15 Thickness (mm) 100 150 200 300 Input temperature (◦C) 33.1 33.1 33.1 33.1 Adiabatic saturation temperature (◦C) 19.1 19.1 19.1 19.1 Saturation efficiency (%) 68 81 88 96 Pressure drop (Pa) 4 6 8 12.5 Output temperature (◦C) 23.6 21.8 20.8 19.7 Using the technical characteristics presented in Table 2, a 100 mm thick pad was installed in order to introduce the least pressure loss at the condenser and ensure that no water drops reaches the condenser, as the low saturation percentage of the pad does not allow the air to leave saturated, so the water drops released from the pad are evaporated in the airgap. The increase in the pressure loss due to the evaporative cooling pad was bearable by the fans without increasing the energy consumption; otherwise the frequency variator would be adjusted. The distance between each chiller, in order to avoid air bypassing, allows the introduction of the evaporative cooling pads between them. The panels were placed before the condensing coils and were humidified by lost water. Figure 5 shows the before (a) and after (b) of the installation of the evaporative panels before the condensers of the chillers of the Hospital. Energies 2020,13, 2218 7 of 13 Energies 2020, 13, x FOR PEER REVIEW 7 of 14 Using the technical characteristics presented in Table 2, a 100 mm thick pad was installed in order to introduce the least pressure loss at the condenser and ensure that no water drops reaches the condenser, as the low saturation percentage of the pad does not allow the air to leave saturated, so the water drops released from the pad are evaporated in the airgap. The increase in the pressure loss due to the evaporative cooling pad was bearable by the fans without increasing the energy consumption; otherwise the frequency variator would be adjusted. The distance between each chiller, in order to avoid air bypassing, allows the introduction of the evaporative cooling pads between them. The panels were placed before the condensing coils and were humidified by lost water. Figure 5 shows the before (a) and after (b) of the installation of the evaporative panels before the condensers of the chillers of the Hospital. (a). (b). (c). Figure 5. Chillers without (a) and with (b) evaporative cooling pads, (c) Schematic diagram. 3. Analysis and Results Figure 5. Chillers without (a) and with (b) evaporative cooling pads, (c) Schematic diagram. 3. Analysis and Results The operating parameters of each chiller, shown in Figure 2, were recorded every five minutes from July to August, “without” and “with” the evaporative cooling pads, getting a total of 544,320 data. In order to compare the chiller plant “without” and “with” the evaporative cooling pad, two days were selected, one when the system was operating “without” and other when it was operating “with” the evaporative cooling pad, fulfilling: (i) similar weather conditions, same external temperature and relative humidity; (ii) same evaporation temperature and (iii) similar equipment load ratio. The selected days were August 10th for operation without the evaporative cooling pads and August 17th for operation with them. Figure 6shows the outside temperature on both days and an average of both. Energies 2020,13, 2218 8 of 13 Energies 2020, 13, x FOR PEER REVIEW 8 of 14 The operating parameters of each chiller, shown in Figure 2, were recorded every five minutes from July to August, "without" and "with" the evaporative cooling pads, getting a total of 544,320 data. In order to compare the chiller plant "without" and "with" the evaporative cooling pad, two days were selected, one when the system was operating "without" and other when it was operating "with" the evaporative cooling pad, fulfilling: (i) similar weather conditions, same external temperature and relative humidity; (ii) same evaporation temperature and (iii) similar equipment load ratio. The selected days were August 10th for operation without the evaporative cooling pads and August 17th for operation with them. Figure 6 shows the outside temperature on both days and an average of both. Figure 6. Outside temperature on August 10th and 17th and the average temperature. The operation of the evaporative cooling pad was programmed to run from 3:00 pm to 10:00 pm, which corresponds to the consumption peaks of the building. Figure 7 shows the evolution of the inlet air temperature at the condenser with and without the evaporative cooling pad and the condensation temperature with and without the evaporative cooling pad. In the case "Without" the refrigerant condenses at 45 °C and "With" the refrigerant condenses at 30 °C. (a). Figure 6. Outside temperature on August 10th and 17th and the average temperature. The operation of the evaporative cooling pad was programmed to run from 3:00 p.m. to 10:00 p.m., which corresponds to the consumption peaks of the building. Figure 7shows the evolution of the inlet air temperature at the condenser with and without the evaporative cooling pad and the condensation temperature with and without the evaporative cooling pad. In the case “Without” the refrigerant condenses at 45 ◦C and "With" the refrigerant condenses at 30 ◦C. Energies 2020, 13, x FOR PEER REVIEW 8 of 14 The operating parameters of each chiller, shown in Figure 2, were recorded every five minutes from July to August, "without" and "with" the evaporative cooling pads, getting a total of 544,320 data. In order to compare the chiller plant "without" and "with" the evaporative cooling pad, two days were selected, one when the system was operating "without" and other when it was operating "with" the evaporative cooling pad, fulfilling: (i) similar weather conditions, same external temperature and relative humidity; (ii) same evaporation temperature and (iii) similar equipment load ratio. The selected days were August 10th for operation without the evaporative cooling pads and August 17th for operation with them. Figure 6 shows the outside temperature on both days and an average of both. Figure 6. Outside temperature on August 10th and 17th and the average temperature. The operation of the evaporative cooling pad was programmed to run from 3:00 pm to 10:00 pm, which corresponds to the consumption peaks of the building. Figure 7 shows the evolution of the inlet air temperature at the condenser with and without the evaporative cooling pad and the condensation temperature with and without the evaporative cooling pad. In the case "Without" the refrigerant condenses at 45 °C and "With" the refrigerant condenses at 30 °C. (a). Energies 2020, 13, x FOR PEER REVIEW 9 of 14 (b). Figure 7. (a) Inlet air temperature and (b) condensation temperature "with" and "without" evaporative cooling pad. The comparison of the performance of the chiller plant was made on the basis of: (i) the COP at partial loads and the ESEER in the summer period, (ii) the TEWI [16] carbon emission reduction and (iii) the economic analysis. 3.1. COP and ESEER analysis In order to calculate the average COP of the chiller plant the operating values are collected from the SCADA system every five minutes, operating "with" and "without" the evaporative cooling pad and are introduced in the following Equation (1): COP= 󰇗∗∗∆ ∗ 󰇗 , (1) where ṁw is the cooling water flow of the equipment (kg/s); cpw is the specific heat of water (4.18 kJ/kg°C); ΔTw is the difference between the outlet and inlet water temperature of the equipment (°C); φ is the chiller load factor; Ẇmax is the power consumption when the chillers work at full load (kW). Figure 8 shows the calculated COP values for each load factor when the chiller plant operates "with" and "without" the evaporative cooling pads and the linear regression of each group of values. Figure 8. Determination of Coefficient of Performance (COP)"with" and "without" of refrigeration systems in service. Figure 7. ( a ) Inlet air temperature and ( b ) condensation temperature “with” and “without” evaporative cooling pad. Energies 2020,13, 2218 9 of 13 The comparison of the performance of the chiller plant was made on the basis of: (i) the COP at partial loads and the ESEER in the summer period, (ii) the TEWI [ 16 ] carbon emission reduction and (iii) the economic analysis. 3.1. COP and ESEER analysis In order to calculate the average COP of the chiller plant the operating values are collected from the SCADA system every five minutes, operating “with” and “without” the evaporative cooling pad and are introduced in the following Equation (1): COP = . mw∗Cpw∗∆Tw ϕ∗ . Wmax , (1) where ˙ m w is the cooling water flow of the equipment (kg/s); cp w is the specific heat of water (4.18 kJ/kg ◦ C); ∆ T w is the difference between the outlet and inlet water temperature of the equipment ( ◦ C); ϕ is the chiller load factor; ˙ Wmax is the power consumption when the chillers work at full load (kW). Figure 8shows the calculated COP values for each load factor when the chiller plant operates “with” and “without” the evaporative cooling pads and the linear regression of each group of values. Energies 2020, 13, x FOR PEER REVIEW 9 of 14 (b). Figure 7. (a) Inlet air temperature and (b) condensation temperature "with" and "without" evaporative cooling pad. The comparison of the performance of the chiller plant was made on the basis of: (i) the COP at partial loads and the ESEER in the summer period, (ii) the TEWI [16] carbon emission reduction and (iii) the economic analysis. 3.1. COP and ESEER analysis In order to calculate the average COP of the chiller plant the operating values are collected from the SCADA system every five minutes, operating "with" and "without" the evaporative cooling pad and are introduced in the following Equation (1): COP= 󰇗∗∗∆ ∗ 󰇗 , (1) where ṁw is the cooling water flow of the equipment (kg/s); cpw is the specific heat of water (4.18 kJ/kg°C); ΔTw is the difference between the outlet and inlet water temperature of the equipment (°C); φ is the chiller load factor; Ẇmax is the power consumption when the chillers work at full load (kW). Figure 8 shows the calculated COP values for each load factor when the chiller plant operates "with" and "without" the evaporative cooling pads and the linear regression of each group of values. Figure 8. Determination of Coefficient of Performance (COP)"with" and "without" of refrigeration systems in service. Figure 8. Determination of Coefficient of Performance (COP) “with” and “without” of refrigeration systems in service. Table 3shows the average values for each load factor in order to get later the European Seasonal Energy Efficiency Ratio (ESEER). Table 3. Average COP values for each load factor of the chiller plant. % Load “Without” Cooling Pad “With” Cooling Pad 100 2.67 3.45 75 3.22 4.2 50 3.78 4.95 25 4.33 5.7 Applying the definition of ESEER, the result is that “without” the evaporative cooling pads, the ESEER is 3.69 and “with” them, the ESEER is 4.83. The improvement in the ESEER is 30.89%.