Direct Expansion Solar Assisted Heat Research Articles

Experimental study on the operating characteristics of multiple collector direct expansion solar-assisted heat pump

Solar thermal application is one of the most important ways to replace fossil energy. The discontinuous heating character and low heating efficiency are two key factors that limit the large-scale promotion of solar thermal application. Large-scale direct expansion solar heat pump systems (DX-SAHP) can provide high efficiency and low-cost continuous heating. However, the characteristics of multiple collector arrays and the system's performance still need more research and exploration. In this paper, a DX-SAHP system with multiple solar collectors was constructed and the work process of the system under different operation conditions was expressed. An experimental platform with two DX-SAHP system was built and studied, and each system contained a 10HP compressor, 16 set solar collectors and one fin evaporator in parallel. The results show that the coefficient of performance (COP) of the system running with solar collectors was nearly 30 % higher than that with the fin evaporator under constant frequency mode, and nearly 45 % under variable frequency mode, indicating that such a system has better performance under variable frequency operation mode. The refrigerant in the collector/evaporators were distributed uniformly in equal-path connection mode, which was beneficial in promoting the system's performance. The heating performance of the system under sunny and cloudy weather conditions was analyzed and discussed, respectively. The test results indicated that the COP of the system on sunny or cloudy days was higher than 4.0, and the maximum hourly COP can reach 11.3 and the maximum hourly heating capacity was 27 kW.

Control strategy calibration of a direct-expansion solar-assisted heat pump

As known, the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) is affected by environmental and operational parameters significantly, and the variable capacity system has distinct advantages. The calibration of the control strategy will be very useful for the thermal performance improvement of DX-SAHP systems. Based on the test rig which is used to supply domestic hot water, the original variable capacity control strategy has been calibrated with the quasi-dynamic mathematical model under different conditions. The calibration results show that the optimum range of the degree of superheat is 7–12 °C. For winter and spring/autumn conditions, the optimum range of operation duration are 360–420 min and 300–360 min, and the corresponding optimum range of average compressor speed are 3750–4500 r·min−1 and 2750–3750 r·min−1, respectively. Experiments prove that the actual operation parameters can be maintained at the optimum range well and the average coefficient of performance (COPm) during the whole heating process has been improved further. For winter and spring/autumn, the average operation duration and compressor speed are 395 min and 3970 r·min−1, 345 min and 3066 r·min−1, respectively. Moreover, the values of COPm could reach 3.44 and 4.67, respectively. Even at solar radiation intensity of 577.6 W·m−2 with ambient temperature of −9.1 °C, the COPm could reach 2.38.

Optimal high-pressure correlation for transcritical CO2 cycle in direct expansion solar assisted heat pumps

Heat demand may be met sustainably by a solar-assisted heat pump that CO2 as a refrigerant. This is made possible by the employment of an ecologically benign refrigerant and a renewable energy source that enhances system performance. At the ideal high pressure, the CO2 heat pump running in a transcritical cycle will function at its highest coefficient of performance (COP). In that way, this study aims to present correlations for calculating the optimum high pressure in a CO2 direct expansion solar assisted heat pump (DX-SAHP). In this study a mathematical model for compressor, solar evaporator and gas cooler was developed and validated experimentally. The mean difference between the mathematical model and experimental results are −3.9%. Two new equations are proposed to calculate the optimum high pressure in a CO2 DX-SAHP. The first one considered environment temperature, water outlet temperature and evaporating temperature, which are easy to measure. These facilities the use of correlation to control the heat pump. The second one considered environment temperature, water outlet temperature and solar radiation, which are more suitable for designing CO2 DX-SAHP. A data base with 100 optimum points was used to curve fitting. Another data base with 50 optimum points was used to compare the results obtained from curve fitting and correlations for the optimum high pressure available in the literature. The proposed correlations shown a maximum error lower than 10.2% despite of the correlations available in the literature from which the errors are about 30%.

Performance of a direct-expansion solar-assisted heat pump for domestic hot water production in Algeria

The focus of this study is to investigate the energy performance of a direct-expansion solar-assisted heat pump water heating system (DX-SAHPWH). The system consists of an unglazed solar collector-evaporator, which can absorb heat from solar energy and air ambient simultaneously, a condenser in the form of a coil immersed in a hot water storage tank, a thermostatic expansion valve and a hermetic reciprocating compressor. The performance of the heat pump system is evaluated using a developed mathematical model under Matlab code. The modelling method is based on lumped and distributed parameter approach of different system components. Numerical calculations were carried-out to study the influence of different parameters, such as ambient temperature, solar radiation intensity and polytropic index on the system performance. Additionally, in order to evaluate the long-term system performance, the system’s model was applied on a case study of a single-family building located in Djelfa (Algeria), which represents the coldest arid region of the country. The results showed that the solar radiation intensity and ambient temperature have significant effects on the heat pump performance. A COP of 5.9 and a collector-evaporator efficiency of 1.9 were obtained at high solar radiation of 850 W/m2 resulting in lower heating time (29 min). In addition, results revealed that the system can operate even at lower ambient temperature due to its ability to take advantage of heat from the ambient air. The results from the case study gave a COP ranging from 2.3 to 3.8, which enhance the promising adoption of this system in domestic hot water production to respond to people daily life needs with clean, abundant and renewable energy.

Investigation of the thermodynamic performance of a direct-expansion solar-assisted heat pump under very cold climatic conditions with and without glazing

This study investigates the long-term thermodynamic performance of a direct-expansion solar-assisted (DX-SAHP) system for hot water production in an average Canadian household. Performance is evaluated using realistic time-varying demand profiles and DX-SAHP with and without glazing under cold climatic conditions. A mathematical model for determining the system's long-term thermodynamic performance based on the first law of thermodynamics and heat transfer fundamentals is developed and thoroughly validated. The solution is implemented in MATLAB®. The CoolProp® database is coupled with MATLAB® and used to determine the working fluid's thermal physical properties. Besides, the thermodynamic performance of the DX-SAHP throughout the year, operating with low global warming potential (GWP) and class A safety refrigerants, was evaluated. Moreover, the influence of solar irradiation and ambient air temperature on the DX-SAHP's thermodynamic performance is studied. Results indicate that the monthly average coefficient of performance (COP) varies between 2.5 and 3.8, while the monthly average energy consumption of the system varies between 170 and 275 kWh. The obtained figures for COP and power consumption demonstrate the high-efficiency potential of the DX-SAHP system, making it an attractive alternative to reduce energy costs and CO2 emissions in residential water heating. In addition, results show that R1233zd gives the highest COPs, followed by R152a, R1234ze, R134a, R1234yf and R32. Besides, the long-term simulation results indicate that the DX-SAHP water heater without glazing has superior thermal performance compared to one with glazing. Also, results show that the COP rises as the ambient temperature or solar radiation level increases.

Experimental performance analysis of evacuated tube type direct-expansion solar-assisted heat pump system

ABSTRACT The direct-expansion solar-assisted heat pump (DX-SAHP) have proven to be one of the strategies in reducing energy consuming for domestic hot water supply. The poor pressure resistance of the collector, high heat loss from radiation for the traditional bare-plate type DX-SAHP limits its popularization and application. To solve this problem, a DX-SAHP system using evacuated tube type collector-evaporator was proposed in this post. System optimization can not only reduce operating costs, but also results in energy savings. Thus, a DX-SAHP prototype was established and tested under various running conditions to obtain the optimal running parameters. Based on experimental data, the impacts of refrigerant charge, solar radiation intensity, and ambient temperature on the performances of evacuated tube type DX-SAHP system are investigated and evaluated. The outcome indicates that this system coefficient of performance (COP) increases by 73.4% with the decrease of charge amount of refrigerant in the range of 5.66–6.67 kg. And, the average collector efficiency is 0.71 with a refrigerant charge of 5.66 kg. And, the optimal COP of this presented system is 5.27 when an ambient temperature, solar radiation intensity, and refrigerant charge are 26.3°C, 954.37 , and 5.56 kg, respectively.

Direct-expansion solar-assisted heat pump coupled with crystallisation-controlled supercooled PCM for shifting building electricity demand

This paper proposes a novel approach for improving the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) system by integrating a crystallisation controllable phase change material (PCM) and building energy demand shifting strategy. The proposed system aims to reduce buildings' energy consumption while utilizing solar energy efficiently. Sodium acetate trihydrate (SAT) as the crystallisation controllable supercooled PCM has a promising feature of releasing the stored latent heat when it is externally triggered, allowing the user to control the stored heat whenever needed. In the study, the PCM can store the thermal energy generated by the DX-SAHP during peak solar hours in an efficient way. This stored energy can be released when solar energy is unavailable, but the heating is requested. This approach not only reduces the load on the heat pump system but also makes efficient use of the stored thermal energy by crystallisation controllable PCM. A detailed controlling methodology of the system is given, and heating output is controlled considering the level of solar irradiance. The proposed system was modelled and simulated using MATLAB, and the results show that the integration of crystallisation controllable PCM and building demand shifting strategy can significantly reduce the energy consumption of the buildings. On the low solar radiation day, the COP improvement compared to the air source heat pump system was found 9.4%, this improvement value can reach 77% on high solar radiation days. The system can also effectively utilize solar energy and reduce the overall carbon footprint of buildings.

Exergoeconomic Analysis of a Direct Expansion Solar Assisted Heat Pump for Humid and Tropical Climates

A direct expansion solar assisted heat pump (DX-SAHP) is a heating water technology that convey a conventional solar heating system with a heat pump. This technology with great potential should overcome economics aspects to be available commercially soon. An exergoeconomic analysis of a DX-SAHP has been performed for three collector configurations and three compressor displacement capacity under the meteorological condition of Portoviejo city in Ecuador, a location with a tropical and humid climate. The present work is aimed to study the relationship between exergoeconomic data under various operations conditions. In addition, the exergy destruction, exergetic efficiency, cost rate per exergy unit product and fuel, cost rate associated to exergy destruction, exergoeconomic factor for each component of a DX-SAHP are evaluated. The exergoeconomic factor is found lowest for the solar collector for all the configurations, with estimated values of 5 to 21%. The component that needs more improvement for a tropical and humid climate is the solar collector based on exergoeconomic factor. On the basis of the present study, it can be concluded that a solar collector area of 1,5 m2 and a rotational displacement capacity of 1350 rpm performs better in all respects.

Energetic, exergetic, environmental and economic (4E) analysis of a direct-expansion solar-assisted heat pump with low GWP refrigerant

The main objective of this study was to develop, validate and apply a mathematical model for analysing the performance of a Direct-Expansion Solar-Assisted Heat Pump (DX-SAHP) based on the energetic, exergetic, environmental, and economic (4E) analysis. The DX-SAHP produces domestic hot water using the low-global-warming-potential (GWP) refrigerant R290 which is the best candidate for energy, environmental, and logistical performance among six previously evaluated candidates (R152a, R744, R1234yf, R1234ze(E), R170, R290). Environmental and economic analysis are founded, respectively, on Total Equivalent Warming Impact (TEWI) and payback. The proposed model was validated using an experimental test bench developed for this study. Using the validated model, simulations were conducted to investigate the influence of geometric parameters (evaporator area and condenser length) on the system's performance. The results show that increasing the evaporator area yields the greatest increase in COP (117 and 80.4%) and the greatest decrease in TEWI (53.8 and 44.5%) for final water temperatures of 45 and 65°C, respectively. However, this also leads to a drop in collector efficiency (58.7 and 60.8%) but results in a shorter payback time (6.06 and 3.87 years) for final water temperatures of 45 and 65°C, respectively. The greatest increase in exergy efficiency (11.5 and 14.1%) occurs with an increase in condenser length for final water temperatures of 45 and 65°C, respectively.

Experimental and numerical analysis of a CO2 dual-source heat pump with PVT evaporators for residential heating applications

Multi-source energy systems are a promising solution to lower the environmental impact of the heating and cooling sector and enhance the exploitation of renewable energy sources. In this context, dual-source solar-assisted heat pumps exploit solar energy and air as the low-temperature heat sources. However, the efficiency of solar-based systems is strictly related to weather conditions, location, and time. Therefore, there is a need for accurate models to be used in dynamic simulations of these systems and perform detailed performance analyses and study the involved energy flows.This paper presents an experimental and numerical investigation of a direct-expansion solar-assisted heat pump (DX-SAHP) operating with CO2 as the refrigerant. The heat pump prototype can work with an air-finned coil heat exchanger or photovoltaic-thermal (PVT) solar collectors as the evaporator. The solar-mode configuration allows the exploitation of the heat from solar radiation to evaporate the refrigerant and to improve the photovoltaic electricity production due to the cooling of the cells up to 8%.A numerical heat pump model, integrated with novel gas-cooler and PVT collectors models, has been developed and implemented as a TRNSYS type for dynamic simulations of the system. The model has been validated with continuous measurements during the heat pump operation in solar and air modes. The proposed model can be used for performing seasonal simulations of a heat pump operating with a transcritical CO2 cycle. Moreover, the outcomes of the analysis show how the configuration of a CO2 heat pump with a direct-expansion air-finned coil heat exchanger or PVT can be used to enhance the performance of the heat pump and increase the electrical efficiency of the photovoltaic cells.

Energy performance of direct-expansion solar heat pump integrated with thermal network

Direct-expansion solar-assisted heat pumps (DX-SAHP) are increasingly used in heating applications owing to their high efficiency. In this study, the energy performance of a DX-SAHP for a distributed thermal prosumer in a thermal network was investigated. A thermal network for supplying hot water, established in the eco-friendly energy town of Jincheon, was selected as the test site, and a daycare center was selected as the pilot building. A control logic for serving produced thermal energy to the thermal network was developed as an operation of thermal prosumer. Experiments were conducted during the cooling and heating seasons, and the results of three operation cases showed that the proposed prosumer operation can transfer the thermal energy within the thermal network. The daily load of domestic hot water was approximately 50–100 kWh, and the daily coefficient of performance of the DX-SAHP ranged from 2.0 to 5.0. The coefficient of performance of the DX-SAHP was found to be strongly dependent on the outdoor air temperature, solar irradiation, and outlet water temperature. During the operation, the DX-SAHP contributed to achieving over 66% savings in the operating energy compared with a conventional electric heater.

Development, experimental validation through infrared thermography and applications of a mathematical model of a direct-expansion solar-assisted heat pump with R290 based on energy, exergy, economic and environmental (4E) analyses

The application of renewable sources, such as solar energy, and the use of ecological refrigerants in refrigeration and heating systems contribute to more sustainable development and the reduction of global warming. With this perspective, the main objective of this work is to develop, validate and apply a mathematical model based on the energetic, exergetic, environmental, and economic analysis of a Direct-Expansion Solar-Assisted Heat Pump for the production of Domestic Hot Water operating with R290. Environmental analysis is based on Total Equivalent Warming Impact and economic analysis is based on payback. The proposed mathematical model was validated on an experimental bench with R290 through infrared thermography applied to evaluate the temperature distribution in the evaporator. The influence of environmental parameters on the system with R290 is investigated through simulations. Among the environmental parameters investigated, solar irradiance was the parameter that most contributed to the increase in energy (69.3 %) and exergy efficiency (8.72 %). In addition, the increase in ambient temperature contributed more to the reduction of greenhouse gas emissions (88.6 %) but promoted the longest payback time for the system. Finally, in the tests performed, heating the water at a lower temperature (45 °C) compared to the higher temperature (65 °C) increased energy (25.0 %) and exergy efficiency (2.86 %), contributed more to the reduction of emissions, but increased the payback time.

Experimental Validation Through a Parallel Computation Algorithm for Evaluation Uncertainty of the Mathematical Model of Direct Expansion Solar Assisted Heat Pump

This paper presents the development of a mathematical model for a direct-expansion solar-assisted heat pump (DX-SAHP) operating in steady-state. The mathematical model was implemented using the scientific software EES and using a code written in Python. It was utilized a lumped parameter model for the heat exchangers and a semi-empirical model for the compressor. The mathematical model was validated using experimental data of a DX-SAHP running with R134a. Two hundred simulations were made combining different correlations for estimating the convective heat transfer coefficient in the evaporator/collector. The Mean Absolute Deviation (MAD) and the Mean Deviation (MD) between the theoretical and experimental values for the COP were 2.6±1.8 % and 0.9±1.8 %, respectively. The MAD and MD between the discharge temperature were 1.56±0.16 % and -1.45±0.16 %. The mean difference between the results using EES and Python were 1.4 %. The use of Python with parallel computing for uncertainty analyses, reduced the simulation time in 88 % if compared with EES. The model in Python is available as open-source through the platform Google Colaboratory.

Evaporation temperature prediction of a direct-expansion solar-assisted heat pump

As known, evaporation temperature is critical for the thermal performance of a direct-expansion solar-assisted heat pump (DX-SAHP), which is subjected to environmental parameters. It is significant to explore the effect of environmental parameters on evaporation temperature and system performance for the optimal design of DX-SAHP systems. An experimental study on the affecting factors of evaporation temperature in DX-SAHP is firstly implemented, and an evaporation temperature prediction model is constructed by multiple linear regression method and validated, which uses solar radiation, ambient temperature and wind speed as independent variables. Based on this, the effect of environmental parameters on evaporation temperature is compared and analyzed. Results show that evaporation temperature is most affected by solar radiation, followed by ambient temperature and wind speed. The weights of solar radiation, ambient temperature and wind speed are 47.6 %, 43.1 % and 9.3 %, respectively. Furthermore, evaporation temperature will have a 1.80, 0.58 and 0.94 °C increase for a 100 W·m−2 increase in solar radiation, a 1 °C increase in ambient temperature and a 1 m·s−1 increase in wind speed, respectively. The prediction model obtains satisfactory accuracy under different conditions and would be helpful for optimal design and thermal performance improvement of DX-SAHP systems.

Thermodynamic investigation of a direct-expansion solar assisted heat pump with evacuated tube collector-evaporator

Direct-expansion solar-assisted heat pump (DX-SAHP) system has proven to be an effective energy-saving application. In view of the low output temperature and large radiant heat loss in the conventional flat plate type DX-SAHP, this paper proposed an evacuated tube type DX-SAHP system to realize performance enhancement. Then, an experimental prototype of the proposed system was originally designed and constructed in laboratory. Moreover, the thermodynamic performance of the system was thoroughly investigated and analyzed under different operating conditions. The results indicate that the thermodynamic performance of the proposed system is sensitive to the solar radiation intensity and collector area. About every 100 W m−2 increase of solar radiation intensity, the COP increases nearly 1.70% and the heat collection efficiency decreases nearly 8.44%. Increasing collector area (from 1.5 m2 to 3 m2) results in 8.81% increase of COP and 22.47% reduction of the system exergy efficiency. A higher circulating water temperature can effectively improve its exergy performance and higher ambient temperature can enhance its energetic performance. Additionally, the optimization of the evacuated tube collector-evaporator should be preferential to improve the system due to large exergy destruction and low exergy efficiency.

Mass flow characteristics of CO2 operating in a transcritical cycle flowing through a needle expansion valve in a direct-expansion solar assisted heat pump

An expansion device is one of the key components of heat pump systems. Although in the literature there are several studies that analyze the effect of opening the expansion valve on heat pumps, none of them reported this effect for heat pumps that operate with solar energy. In this study, the mass flow rate characteristics through an expansion device in a direct-expansion solar assisted heat pump (DX-SAHP) operating with CO2 is investigated. With experimental data, a new correlation is proposed. A statistical method is used to determine the dimensionless Π-groups that most influences the mass flow rate. The parameters selected to compose the new correlation are: outlet and inlet pressures of the expansion device, geometric (cross-section area) and fluid viscosity. The proposed correlation shows good agreement with the measured data with average and standard deviations of 0.77% and 10.4%, respectively. The maximum relative deviation of all predictions of mass flow rate is less than ±30% and approximately 90% of mass flow rate experimental data are within ±20% of the predictions. In addition, for a same needle expansion valve opening, the mass flow rate increases with the augment in the solar radiation flux.

An Installed Hybrid Direct Expansion Solar Assisted Heat Pump Water Heater to Monitor and Modeled the Energy Factor of a University Students’ Accommodation

This paper focused on the performance monitoring and modeling of a 6.0 kW, 2000 L hybrid direct expansion solar assisted heat pump (DX-SAHP) water heater used for the production of hot water in a university students’ accommodation with 123 females. The data of total electrical energy consumed, volume of hot water consumed, ambient temperature, relative humidity, and solar irradiance were obtained from the data acquisition systems and analyzed in conjunction with the energy factor (EF) of the system. A multiple linear regression model was developed to predict the EF. The EF of the hybrid DX-SAHP water heater was determined from the summation of the coefficient of performance (COP) of the heat pump unit and the solar fraction (SF) of the solar collectors. The operations of the hybrid energy system were analyzed based on three phases (first phase from 00:00–08:00, second phase from 08:30–18:30, and third phase from 19:00–23:30) over 24 h for the entire monitoring period. The average EF of the hybrid energy system per day during the second phase of operation was 4.38, while the SF and COP were 0.697 and 3.683, respectively. The developed multiple linear regression model for the hybrid DX-SAHP water heater accurately predicted the determined EF.

Influence of refrigerant charge and condenser area on direct-expansion solar-assisted heat pump system for radiant floor heating

As known, the refrigerant charge and condenser area have important influence on the thermal performance of a heat pump system. A test rig of a direct-expansion solar-assisted heat pump (DX-SAHP) system for radiant floor heating has been built, and the quasi-dynamic mathematical model of the system has also been established, which uses propane (R290) as the refrigerant. The deviations between the simulated results and experimental data are within 7.1 %, showing a good agreement. The analysis reveals that, when the refrigerant charge of the DX-SAHP system increases, the condensing pressure and the subcooling degree in the condenser increase, while the evaporating pressure decreases, resulting in the increase of the effect heat gain and the compressor power. The system coefficient of performance (COP) first increases to a maximum and then decreases with the refrigerant charge, and remains at a relative high level within a certain range near the optimal refrigerant charge. The optimal refrigerant charge is independent of solar insolation and ambient temperature, and decreases with initial water temperature in the hot water storage tank, while the corresponding subcooling degree is always in the 6–9 °C range. Furthermore, the system COP is also influenced by the condenser area. Both the maximum COP and corresponding optimal refrigerant charge are found to increase with the condenser area. As the condenser area increases from 0.553 to 1.393 m2, these two parameters increase by 8.95 % and 27.91 %, respectively.

Investigation on transient response of the direct expansion solar assisted ejector-compression heat pump cycle for water heater

Aiming to provide data support for the control-oriented design and practical application, the transient response characteristics of the direct expansion solar assisted ejector-compression heat pump cycle for water heater is investigated in this study. The dynamic simulation model of the presented system is built, and relevant experimental items are also conducted to verify the simulation model. The experimental and simulation results during a typical water heating process show satisfactory agreement, and the maximum forecast error of four main operation parameters is less than 6.6%. The system transient responses under the step change of the expansion valve opening degree are explored by both simulation and experimental methods, and the simulation model still appears high forecast precision. Thereinto, the maximum simulation error of the refrigerant flow rates is less than 5.2%. The system dynamic responses under the sudden changes of the ejector nozzle throat area and solar radiation intensity are further evaluated based on the verified model, and the coupling relation of the system pressure and refrigerant flow rate is further revealed. In addition, further simulation research proves that substituting R134a with R1234yf and R1234ze(E) in the present system has little impact on the system dynamic characteristics.

Numerical investigation on the factors influencing the temperature distribution of photovoltaic/thermal (PVT) evaporator/condenser for heat pump systems

Due to a high solar energy utilizing efficiency, Direct-expansion Solar-Assisted Heat Pump (DX SAHP) system has been a research hotspot for many years, especially for the system using PV/T module as the evaporator. The heat transfer throughout the PVT evaporator is an important factor for either electrical or thermal performance. We have developed and analyzed numerically the temperature distribution of a multi-source PVT heat exchanger of serpentine shape to fit a function as evaporator/condenser for Direct-expansion Photovoltaic/Thermal-Heat Pump (DX PVTHP) system. The suitability of the developed model was based on the calculated results of the efficiency factor and simulated results of temperatures of heat exchanger and working fluid as well the working fluid pressure drop. During the numerical simulations, we have considered different temperature influencing factors such as the refrigerant and refrigerant flow rate, spacing between the adjacent tubes of the heat exchanger, backside convection and radiation effect and finned heat exchanger. Simulated results showed that the serpentine PVT heat exchanger with fins and small space between tubes (62.5 mm) at 0.02 kg/s flow rate could achieve better results in terms of uniform temperature distribution, smaller fluid pressure drop (0.078 bar) and the highest efficiency factor (0.9873) which make it recommended as the best option for suitable evaporator/condenser. The average PV temperature reached by cooled and uncooled PVT evaporator at 0.02 kg/s flow rate was 47.81 °C and 71.11 °C, respectively. It was 40.99 °C and 37.07 °C at the flow rate of 0.035 kg/s and 0.05 kg/s, respectively, and 44.44 °C for PVT evaporator with smaller space between tubes at 0.02 kg/s. The average PV temperature reached by the PVT evaporator with fins was 40.734 °C at the flow rate of 0.02 kg/s while it was 53.956 °C when the unit is insulated.