Direct Expansion Solar Assisted Heat Research Articles

Exergy analysis of direct-expansion solar-assisted heat pumps working with R22 and R433A

In this paper, the exergy performance of direct-expansion solar-assisted heat pump systems working with R22 and R433A (mixture of R290 and R1270, 70:30 by mass) was experimentally assessed. The experiments were carried out under the metrological conditions of Calicut in India. (Longitude and latitude of location are $$75.78 ^{\circ }\hbox {E}$$ and $$11.25^{\circ }\hbox {N}$$ , respectively.) The artificial neural network model was developed for simulating the performance of a direct-expansion solar-assisted heat pump system to have realistic performance comparison. The experimental data observed during the year 2016 were used for training and testing the performance of network. The results showed that the network predicted exergy performance of a direct-expansion solar-assisted heat pump was found to be closer to the experimental results with a maximum fraction of absolute variance, minimum root-mean-square values and coefficient of variance. The system exergy destruction of R22 and R433A was found to be 1.36 and 1.25 kW, respectively. Moreover, R433A is identified as an energy-efficient and environmental-friendly alternative to phase out R22 in solar-assisted heat pump systems.

Experimental studies of a variable capacity direct-expansion solar-assisted heat pump water heater in autumn and winter conditions

A variable capacity direct-expansion solar-assisted heat pump (DX-SAHP) system was studied experimentally under the meteorological condition of Qingdao located in the East China area. It was mainly made up of a solar collector/evaporator, a variable-frequency rotary-type hermetic compressor, a micro-channel condenser, and an electronic expansion valve. A series of experiments were carried out, in order to evaluate the performance of the DX-SAHP system during the autumn and winter period, including the system coefficient of performance (COP), the electric power to the compressor, the evaporating and condensing pressures, and the discharge temperature of the compressor. Experimental results showed that for the base case considered in this study, under the sunny and overcast day conditions in the autumn, the average COP was higher than 4.0 and 3.0, respectively. Even in the extreme weather of the winter conditions, the average COP was also higher than 2.5. In general, with the increase of water temperature, the compressor speed increased gradually, and the corresponding electric power of the compressor increased sharply. The condensing pressure also increases, as does the discharge temperature of the compressor, while the evaporating pressure remains a relatively low level with smaller variations.

Experimental performance analysis of a direct-expansion solar-assisted heat pump water heater with R134a in summer

A direct-expansion solar-assisted heat pump (DX-SAHP) system for domestic hot water supply was built and tested, which mainly consisted of a bare flat-plate collector/evaporator with a surface area of 2.1 m2, a variable-frequency rotary-type hermetic compressor, a hot water tank with the volume of 0.2 m3 surrounded by a micro-channel condenser, and an electronic expansion valve. A series of experiments were carried out to test the system performance under typical summer weather conditions in Qingdao, China. The effects of various parameters, including solar radiation intensity of 258–634 W·m−2, ambient temperature of 28–34 °C, compressor speed of 2500–6000 rpm and final water temperature of 50–60.3 °C, on the system performance are analyzed. Experimental results show that the system coefficient of performance(COP) could be enhanced with the increase of the solar radiation intensity or the ambient temperature, and with the decrease of the compressor speed or the final water temperature.

Performance studies of R433A in a direct expansion solar-assisted heat pump

ABSTRACTEnergy assessment of a simple direct expansion solar-assisted heat pump system has been experimentally assessed with R433A as a possible alternative to R22. An artificial neural network integrated genetic algorithm model was developed to assess the performance system. The data obtained from the experimentation at different ambient conditions are used as the training data for the ANN network. The back propagation learning mechanism with variants Lavenberg-Maguardt with 20 neurons in the hidden layer were used in modelling of ANN. The values obtained from the analysis using ANN are optimised further by integrating the ANN procedure with GA. The results indicated that R433A has 6.4% and 1% lower instantaneous compressor power consumption and heating capacity compared to R22. Energy performance ratio of R433A was found to be about 5.67% higher compared to R22. The results confirmed that R433A can be used as a possible alternative to R22 DX-SAHP systems.

Control strategy and experimental analysis of a direct-expansion solar-assisted heat pump water heater with R134a

A direct-expansion solar-assisted heat pump (DX-SAHP) system was designed and built in Qingdao China, which was used to supply domestic hot water. The system mainly consisted of a bare solar collector/evaporator with area of 1.56 m2, a rotary-type hermetic compressor with rated power of 400 W, an electronic expansion valve (EEV) and a micro-channel aluminum flat tube condenser with single surface area of 0.435 m2 surrounding a 0.195 m3 water tank. The system was charged with 800 g of R134a. Based on the degree of superheat at the outlet of the solar collector/evaporator, a control strategy for the system was developed and tested over a wide range of operating conditions, which proved that it could regulate the degree of superheat in range of 5–10 °C effectively. Then the thermal performance of the system was experimentally studied under various operating conditions. Experimental results showed that for most of the time in 2016, when the 0.195 m3 water was heated to the temperature between 55 °C and 60 °C, the coefficient of performance (COP) of the prototype device was higher than 3.0. As the solar radiation intensity or ambient temperature increased, the COP of the system increased, and the heating time decreased.

Low-temperature solar-plate-assisted heat pump: A developed design for domestic applications in cold climate

Solar energy and wasted heat in buildings are capable of supplying enough energy to answer the total demand of energy in dwellings. However, fluctuation in fuel prices and gas emissions are the main driving forces behind efforts. In this experimental study, a direct expansion solar-assisted heat pump system (DX-SAHP) using a bare ternary “retrofitted collectors with black paint” is investigated at the laboratory with a solar simulator and tested for domestic hot water (DHW) and space heating under quasi-static conditions. Unglazed solar collector absorber plates are used as an evaporator, and these are composed of two aluminium plates which are placed externally whilst another plate is mounted internally in the loft space of the house, where operating liquid from the heat pump is directly evaporated. The influence of outside temperature, solar irradiation and/or waste heat on the heating performance of DX-SAHP is investigated. The impact of the parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid is also assessed. Preliminary results elucidate that the refrigeration cycle can be a promising substitute for space heating and hot water when compared to the heat pump systems. This design technique results in higher solar collector/evaporator efficiency and lower system losses due to low evaporating temperature.

Thermodynamic analysis of a direct expansion solar assisted heat pump water heater

In this paper, the thermodynamic performance of a direct expansion solar assisted heat pump (DX-SAHP), which is used to heat domestic water from 20˚C to 45˚C, is theoretically investigated. The system includes a 3m2 single-cover flat plate solar collector, 0.150m3 water tank and 70m tube immersed in the water tank as a condenser. The effect of various parameters such as radiation on the collector surface, compressor speed and the ambient temperature on the coefficient of performance (COP) are calculated. Results show that obtained COP is considerably more than that of a conventional heat pump water heater when radiation on the collector is high. Also, increasing collector area and reducing compressor speed enhance COP. The same occurs when the ambient temperature increases. For instance, at an ambient temperature of 15˚C and 450 w/m2 irradiation on collector surface, the calculated COP was 6.37.

Modeling evaluation of a direct-expansion solar-assisted heat pump water heater using R410A

A direct-expansion solar-assisted heat pump (DX-SAHP) system by using R410A as refrigerant is described, which can supply domestic hot water during the whole year. Based on the distributed parameter and homogeneous flow models of collector/evaporator and condenser, the lumped parameter models of compressor and electronic expansion valve, and the refrigerant charge model, a numerical model is developed to estimate the thermal performance of the system. Given the structure parameters, meteorological parameters, initial and final water temperatures, for a fixed superheat degree, the effects of the refrigerant charge quantity on the performance parameters of the system are analyzed, such as compressor power, heat gain of collector, heating time, collector efficiency and system COP. Furthermore, for a fixed refrigerant charge quantity, the effects of various parameters, including solar radiation, ambient temperature, compressor speed and initial water temperature, have been simulated and analyzed on the thermal performance of the system.

Assessment of R290 as a possible alternative to R22 in direct expansion solar assisted heat pumps

Assessment of R290 as a possible alternative to R22 in direct expansion solar assisted heat pumps

Effects of Ambient Parameters on the Performance of a Direct-Expansion Solar-Assisted Heat Pump with Bare Plate Evaporators for Space Heating

Research on the direct-expansion solar-assisted heat pump (DX-SAHP) system with bare plate evaporators for space heating is meaningful but insufficient. In this paper, experiments on a DX-SAHP system applying bare plate evaporators for space heating are conducted in the enthalpy difference lab with a solar simulator, with the ambient conditions stable. The independent effects of ambient temperature, solar irradiation, and relative humidity on the system performance are investigated. When ambient temperature changes as 5°C, 10°C, and 15°C, COP increases as 2.12, 2.18, and 2.26. When solar irradiance changes as 0 W m−2, 100 W m−2, 200 W m−2, 300 W m−2, and 500 W m−2, COP of the system changes as 2.07, 2.09, 2.14, 2.26, and 2.36. With ambient temperature of 5°C and solar irradiance of 0 W m−2, when relative humidity is 50%, no frost formed. Whereas with relative humidity of 70% and 90%, frost formed but not seriously frosted after 120 min of operating. Frost did not deteriorate but improved the heating performance of the DX-SAHP system. The change of relative humidity from 70% to 90% improves the evaporating heat exchange rate by 35.0% and increases COP by 16.3%, from 1.78 to 2.07.

Theoretical analysis on a new direct expansion solar assisted ejector-compression heat pump cycle for water heater

This paper proposes a new direct expansion solar assisted ejector-compression heat pump cycle for water heater which can efficiently utilize the solar energy and air energy. The new cycle has two operation modes to be chosen according to the solar radiation intensity. The energetic and exergetic performance of the new cycle is analyzed based on the built simulation model. Under the given conditions, the new cycle outperforms the basic ejector enhanced cycle in the heating coefficient of performance (COP) and heating capacity aspects by up to an average of 13.78% and 20.41%, respectively. The simulation results indicate that the operation mode A is more suitable for the low/zero solar radiation condition, while it’s preferable to choose the operation mode B for the high solar radiation condition. The increase of the solar radiation intensity significantly benefits the performance of the new cycle, but decreases the system exergy efficiency. The exergy analysis also reveals that although the exergy destruction percentage of the solar collector increases with increasing the solar radiation intensity, the total exergy destruction percentage of other components decreases. The increase of the solar collector area always contributes to the performance improvement of the new cycle, but it should be kept in a proper range to guarantee the excellent performance and normal operation of the system.

Parametric Studies of a Simple Direct Expansion Solar Assisted Heat Pump Operating in a Hot and Humid Environment

In this paper the theoretical and experimental studies were carried out on a direct expansion solar assisted heat pump (DX-SAHP) under the metrological condition of Calicut located in the southern peninsula of the India continent. The system mainly includes a flat-plate solar collector of total are 2 m2, acting as an evaporator with refrigerant R22, a hermetically sealed reciprocating type compressor, an air cooled condenser and an electronic expansion valve. These performance parameters such as energy performance ratio, power consumption, heating capacity, solar energy input ratio and compressor discharge temperature of a DX-SAHP obtained from the experiment confirmed that, the experimental values were agreed well with simulation predicated results with average error of 1-2%. And The system COP is found to be vary from 1.8 to 2.8, power consumption from 1098 to 1305W, heating capacity from 2.0 to 3.6kW respectively. The effect of various parameters such as solar insolation, ambient temperature, collector area, wind speed has been theoretically analysed in order to understand the system performance.

Parametric Studies of a Simple Direct Expansion Solar Assisted Heat Pump Using ANN and GA

Abstract This paper reports the use of artificial neural network (ANN) integrated with genetic algorithm (GA) to predict the performance of direct expansion solar assisted heat pump (DX-SAHP), in Calicut (Latitude of 11.15 0 N, longitude of 75.49 0 E), India. The performance parameters such as power consumption, heating capacity, energy performance ratio and compressor discharge temperature of DX-SAHP obtained from the experimentation at different solar intensities and ambient temperatures are used as training data for the network. The back propagation learning algorithm with variants Lavenberg–Marguardt (LM) with 10 neurons in the hidden layer and logistic sigmoid transfer function were used in the network to predict the performance of DX-SAHP. Then those values obtained from the analysis using ANN are optimized further by integrating the ANN procedure with GA. The resulting computations confirmed that the use of ANN integrated with GA gives better optimized values compared to the value obtained from ANN for the performance prediction of DX-SAHP.

Simulation analysis on dynamic performance of a combined solar/air dual source heat pump water heater

This paper investigated a combined solar/air dual source heat pump water heater system for domestic water heating application. In the dual source system, an additional air source evaporator is introduced in parallel way based on a conventional direct expansion solar-assisted heat pump water heaters (DX-SHPWH) system, which can improve the performance of the DX-SHPWH system at a low solar radiation. In the present study, a dynamic mathematical model based on zoned lump parameter approach is developed to simulate the performance of the system (i.e. a modified DX-SHPWH (M-DX-SHPWH) system). Using the model, the performance of M-DX-SHPWH system is evaluated and then compared with that of the conventional DX-SHPWH system. The simulation results show the M-DX-SHPWH system has a better performance than that of the conventional DX-SHPWH system. At a low solar radiation of 100W/m2, the heating time of the M-DX-SHPWH decreases by 19.8% compared to the DX-SHPWH when water temperature reaches 55°C. Meanwhile, the COP on average increases by 14.1%. In addition, the refrigerant mass flow rate distribution in the air source evaporator and the solar collector of the system, the allocation between the air source evaporator and the solar collector areas and effects of solar radiation and ambient air temperature on the system performance are discussed.

Frosting characteristics and heating performance of a direct-expansion solar-assisted heat pump for space heating under frosting conditions

Direct expansion solar-assisted heat pump system (DX-SAHP) is promising in energy saving applications, but the performance of DX-SAHP under frosting conditions is rarely reported in the published literatures. In this paper, a DX-SAHP system with bare solar collectors for space heating is designed and experimentally investigated in the enthalpy difference lab with a solar simulator. The system is tested under a range of frosting conditions, with the ambient temperatures from 7°C to −3°C, the relative humidities of 50%, 70% and 90% and the solar irradiances of 0W/m2, 100W/m2, 200W/m2 and 300W/m2. The conditions when the DX-SAHP system frosts are studied. Results show that solar irradiance as low as 100W/m2 can totally prevent frosting when the ambient temperature is above −3°C and the relative humidity is 70%. Besides, the frosting process is observed to be slower than that of fin-and-tube heat exchangers. The evaporator is not seriously frosted and the system performance is not significantly influenced after 360min of continuous operating. Moreover the effects of ambient parameters, including the ambient temperature and the relative humidity, especially solar irradiation, on the system performance are studied and analyzed. Solar irradiation can effectively prevent or retard frosting, and also improve the heating performance of the DX-SAHP system. The DX-SAHP system is proved to be applicable under frosting conditions.

Exploitation of humid air latent heat by means of solar assisted heat pumps operating below the dew point

Nowadays, the exploitation of environmental exergy resources for heating purposes (solar energy, convection heat transfer from ambient air, moist air humidity condensation) by means of properly designed heat pump systems is a possible opportunity. In particular, the use of direct expansion solar assisted heat pumps (DX-SAHP) is investigated in this study, when a bare external plate (the solar collector) is kept at temperatures lower than the dew point temperature of ambient air, so that condensation takes place on it.The potential of this technology is settled and an instrumented prototype of a small DX-SAHP system is used to verify the actual performance of the system, in terms of specific thermal energy delivered to the user, efficiency and regulation capabilities. Results clearly show that the contribution of the condensation is significant (20%–30% of the total harvested energy) overnight or in cloudy days with very low or no solar irradiation, and must be taken into account in a system model devoted to describe the DX-SAHP behavior. During daytime, the percentage gain decreases but is still consistent. By investigating along these lines, the heat due to condensation harvested by the collector is found to be a function of the dew-point temperature alone.

Performance Comparison of Direct Expansion Solar-assisted Heat Pump and Conventional Air Source Heat Pump for Domestic Hot Water

Abstract In this work, performances of conventional air source heat pump water heater (ASHPWH) and direct expansion solar-assisted heat pump water heater (DX-SAHPWH) under various operating conditions are analyzed to make comparison between the two systems. The DX-SAHPWH system in this study uses a plate type roll-bond solar collector with optimized flow channel as the evaporator, which can take both solar energy and ambient air as the heat source. Performances of both systems are investigated experimentally and numerically. The influences of operating conditions (air temperature, water temperature, solar radiation intensity, et al) are analyzed, and performance comparison under various operating conditions is made between the two systems. Results show that, in clear day conditions, the COP of DX-SAHPWH is obviously higher that of ASHPWH because the solar energy can improve the evaporating temperature of the heat pump obviously; in overcast day conditions (without frost formation), COP of both systems are almost the same; and in night conditions, especially in clear night conditions, the DX-SAHPWH shows poor performance because of the poor convectional heat exchanging performance of the solar collector/evaporator and the radiative heat loss to the night sky. And annual performance analysis shows that the average COP of the DX-SAHPWH system is remarkably higher than the conventional ASHPWH system, especially in winter season.

Analysis of solar desalination system using heat pump

This paper investigates a pilot desalination system which consists of a direct expansion solar assisted heat pump (DXSAHP) coupled to a single-effect evaporator unit. The working fluid used is R134a and distillate is obtained via falling film evaporation and flashing in the unit. Experiments have been conducted in both day and night meteorological conditions in Singapore and the effects of solar irradiation and compressor speed have been studied against the system performance. From the experiments, the Performance Ratio (PR) obtained ranges from 0.43 to 0.88, the average Coefficient of Performance (COP) was 8 and the highest distillate production recorded was 1.38 kg/h.

Effects of refrigerant charge and structural parameters on the performance of a direct-expansion solar-assisted heat pump system

The direct-expansion solar-assisted heat pump (DX-SAHP) is widely studied as a refrigeration system, which can supply hot water for domestic use during the whole year. The system refrigerant charge and structure parameters are believed to have a great effect on the cycling thermal performance. The refrigerant mass charge including two-phase and single-phase in heat exchangers and pipes is calculated with distributed and lumped parameter approach mathematical models, respectively. Based on the system simulation program, the refrigerant distribution characteristics and system performance under varied structural parameters are obtained. The mathematical calculation results show that the 70%–80% refrigerant charge exists in the condenser and collector; the optimum refrigerant charge, solar collector area, condenser pipe length and condenser internal diameter for the system are 1.65–1.75 kg, 6.0 m2, 70 m and 9 mm, respectively. In the optimum parameters, the better system performance and feasible cost can be achieved.

Thermal Performance Analysis and Optimization of Solar Assisted Heat Pump Water Heater

The main objective of this paper is to analyze the thermal performance of direct expansion solar assisted heat pump DX-SAHP(A) by numerical simulation in MATLAB and comparing it with the thermal performance of DX-SAHP(B) which has an optimized collector area and mass flow rate. Optimization is performed for high exergy efficiency using Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC) optimization technique. The flat plate collector of solar water heater is used as the evaporator with refrigerant (R22).With the optimized value of mass flow rate as 0.055 kg/sec, width as 0.03 m and diameter of riser tubes as 0.021 m the performance of the optimized system has a maximum COP of 6.85 which is greater than the COP of DX-SAHP(A) and the final water temperature of is obtained 100 minutes earlier in the optimized system i.e. DX-SAHP(B) with compressor work less than the system A