Expansion Solar Assisted Heat Pump Research Articles

Experimental analysis of the influence of the expansion valve opening on the performance of the small size CO2 solar assisted heat pump

In a Direct Expansion Solar Assisted Heat Pump (DX-SAHP), a valuable part of the energy is provided from solar radiation. The solar radiation can fluctuate during the day affecting the performance of the system. The impact of a fixed opening in the expansion device on the system performance is not well known, especially for a small-size solar assisted heat pump. In this context, it is presented an experimental analysis of the influence of the expansion valve opening on the performance of a CO2 DX-SAHP. Experimental tests were carried out considering different solar radiations conditions. The value of the expansion device opening that leads to the maximum COP was almost the same, regardless of solar radiation. In consequence, it was concluded that, for a small CO2 DX-SAHP, using a basic cycle configuration a static expansion device as a capillary tube would be suitable, reducing the costs of this equipment.

Economic analysis and design optimization of a direct expansion solar assisted heat pump

One option to reduce the energy consumption to produce domestic hot water is to replace the electrical heaters by direct expansion solar assisted heat pumps. Although, there are many studies on the performance of this system, there are few studies on economic analysis of the equipment. In this paper, an economic analysis comparing the payback of heat pump over an electrical heater is carried out. The heat pump is modeled using lumped models for heat exchangers and a black box model for the compressor. The results show that the augment of collector size increases the COP, but it decreases the collector efficiency. The economic analysis showed that there is a collector size that minimizes the payback time. Additionally, the influence of the environmental conditions, the refrigerant, the costs and the heating capacity on the payback period and optimum collector size were investigated. The results showed that there is an economically optimum size of collector area for the DX-SAHP, which it is the same for different environmental conditions. A case study was made for three different cities and the payback time found is the range of 1.77–3.24 years.

Refrigerants selection for a direct expansion solar assisted heat pump for domestic hot water

An important step during a project of a heat pump system is choosing a more suitable refrigerant. This paper presents a comparative study among refrigerants for a small direct expansion solar assisted heat pump (DX-SAHP). The mathematical model used in this study is presented in detail and validated from an experimental setup. The R134a is the reference and the refrigerants with low GWP are R290, R600a, R744 and R1234yf. The results show that R290 has better COP than others refrigerants for solar radiation between 300 W/m2 and 700 W/m2, as well as for environment temperature between 10 °C and 35 °C. On the other hand, for solar radiation less than 50 W/m2, the R134a has better COP than R290. TEWI (Total Equivalent Warming Impact) analysis indicates that the indirect emission is the most important effect, and then, the TEWI results almost followed the COP outcome. A parametric analysis was conducted to evaluate the influence of the CO2 emission factor for producing electricity. In countries with higher emission factor, the refrigerant with the best COP has the best TEWI. The influence of wind speed and ambient temperature in COP of a DX-SAHP using R290 were more relevant in low solar radiation.

Numerical study and experimental validation of a direct-expansion solar-assisted heat pump for space heating under frosting conditions

Frosting problem restricts the wide application of heat pump, and direct expansion solar-assisted heat pump system (DX-SAHP) can be a solution. However, research on DX-SAHP for space heating under frosting conditions is rare in the published literatures, especially on numerical level. A dynamic model for a DX-SAHP system for space heating is proposed and validated in this paper. The root mean square deviations of the simulation results from the experimental data are no more than 6%, which validates the model. Based on the model, the frost characteristics are investigated and parametric analysis is conducted. Compared to the widely used air source heat pumps with fin-and-tube heat exchangers, the frost pattern of the evaporator-collector is nearly steady and the frosting rate is less. The analyzed parameters include ambient temperature, solar irradiation and relative humidity. Solar irradiation can retard frosting and improve the heating performance of the DX-SAHP system. Solar irradiance of 100 W/m2 can totally prevent frost formation as the ambient temperature and the relative humidity is −1 °C and 70%, respectively. Under the condition that the relative humidity and solar irradiance are 70% and 0 W/m2, frost is the most serious with the ambient temperature of −1 °C, with higher heating capacity and COP comparing to that under other ambient temperatures. No frost forms when the ambient temperature and solar irradiance are 1 °C and 0 W/m2, and the relative humidity is lower than 60%. When the relative humidity is over 60%, the frost thickness and the heating performance increase with increasing relative humidity. The frosting process is found to be beneficial for the heating performance of the system. The results indicate that the DX-SAHP system is applicable under frosting conditions.

Thermodynamic analysis of a direct expansion solar-assisted heat pump system working with R290 as a drop-in substitute for R22

The thermodynamic analysis of direct expansion solar-assisted heat pump system working with R290 as a drop-in substitute for R22 was carried out under the metrological conditions of Calicut, India. A prototype of a DXSAHP system consists of a compressor, an air-cooled condenser with evaporator–collector and thermostatic expansion valve. The experiments were carried during the winter months of 2016. The artificial intelligence technique artificial neural network integrated with genetic algorithm model was presented to predict energy and exergy performance of a system. The energy performance ratio of a system was found to be 5.75% higher and reduced heating capacity of about 6.8% when compared to R22. Similarly, the second law analysis (exergy analysis) of a total system working with R290 was found to be better when compared to baseline refrigerant. The selected alternative working fluid is a hydrocarbon and has zero ozone depletion and negligible global warming potential. Hence, R290 can be used as a drop-in substitute for R22 in DXSAHP systems.

Subcooling control method for the adjustable ejector in the direct expansion solar assisted ejector-compression heat pump water heater

A subcooling control method is proposed in this paper, aiming to regulate the adjustable ejector in the presented direct expansion solar assisted ejector-compression heat pump water heater. The proposed subcooling control method adopts the PID (Proportion Integration Differentiation) algorithm and aims to help the presented system track the given subcooling degree through automatically adjusting the nozzle throat area of the adjustable ejector. The proposed subcooling control method is firstly examined by dynamic simulation method. The simulation results show that the proposed subcooling control method can meet the purpose of controlling subcooling degree and reduce the power consumption by 7.95% under the considered condition. The experimental setup with and without the subcooling controller are tested for comparison, and the test results confirm the simulation conclusions. The experimental system with the subcooling controller maintains the subccoling degree in a range of 4–7 °C, and reduces the power consumption by 6.24% and 6.99% compared with those with two different ejector throat areas. Further analysis shows that the subcooling controller brings the highest ejector entrainment ratio but not evident improvement in the pressure lift ratio aspect. In brief, the proposed subcooling control method achieves satisfactory subcooling degree control precision and further improves the system performance.

Modeling and experimental analysis of the solar radiation in a CO2 direct-expansion solar-assisted heat pump

In the present work is presented the dynamic model of an evaporator of a Direct Expansion Solar Assisted Heat Pump (DX-SAHP), charged with CO2. This dynamic model was used to analyze the evaporator response to sudden variations in the solar radiation. Two strategies are used to make the system reach the steady state after the heat pump start-up. The first one is the usual balances of mass, energy and momentum. The second strategy consisted in impose an equal refrigerant mass flow rate at the evaporator inlet and outlet. Both strategies were able to conduct the system to a steady state, however, the second one required less computational effort. The mathematical model was validated using experimental data and employed to perform several simulations. The results obtained with the mathematical model revealed that a small variation of the solar radiation leads to a significant variation in the superheat, therefore requiring an immediate action of the expansion device. It was concluded that an Electronic Expansion Valve (EEV) would be better suited to meet the needs of rapid interventions on the mass flow rate at the evaporator inlet, and also because the DX-SAHP could operate in a continuous transient condition in some seasons.

Performance of hydrocarbon mixture in a direct expansion solar assisted heat pump system

The energy performance of a direct expansion solar assisted heat pump system, working with a hydrocarbon mixture (HCM) of R290/R1270, 70:30 (by mass ratio) was investigated. The experiments were carried out at a metrological condition existing near Calicut, India. The experimental system mainly consists of a compressor, condenser, thermostatic expansion valve and evaporator collector. A system simulation technique was used for modelling the system. The experimental results obtained are compared with simulation output of the system working with R22 and a mixture of R290/R1270. The selected alternative working fluid mixture showed better energy performance ratio about 5.8% higher. The parametric analysis of the system working with R22 and a mixture of R290/R1270 is investigated with the help of an established system simulation model. The effect of an evaporator (solar collector) area and solar insolation are found to be the significant influencing parameters on the system performance. Moreover, the new hydrocarbon mixture is found to be a good energy efficient and environmental friendly working fluid to phase out R22 in the solar assisted heat pump systems.

Mathematical Thermal Modelling of a Direct-Expansion Solar-Assisted Heat Pump Using Multi-Objective Optimization Based on the Energy Demand

An analytical model is proposed to evaluate the performance of a Direct Expansion Solar-Assisted Heat Pump under a given environmental condition. These thermal machines commonly employ uncovered flat plate solar collectors, and given this, the convection phenomenon is taken into account as well as the effect of the diffuse and reflected solar radiation in addition to the normal beam radiation absorbed by the tilted surface of the collectors. The heat pump cycle is modelled through a first law of thermodynamics approach in order to compute the heat yielded through condensation and the minimum heat required by the volume of water in the thermal storage unit. Consequently, the thermal capacity of the heat pump, the ratio at which the system yields heat to a given load of water, is calculated and discussed. The results of the model proposed are compared with the experimental data provided by three research papers with experiments conducted in different geographic coordinates and test rigs operating during diverse atmospheric conditions. A maximum relative error of 20% was obtained and furthermore, a statistical analysis of the data was conducted having found that there is no significant statistical difference between the analytical and experimental data samples within the 95% confidence interval. Finally, based on the thermal capacity, the performance of the heat pump is evaluated and a multi-objective optimization technique is implemented to obtain the best possible combination of factors to further enhance the performance of the heat pump.

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.

Indirect expansion solar assisted heat pump system for hot water production with latent heat storage and applicable control strategy

Integration of renewable energy with energy conversion application for hot water production is a significant technology to be studied for industrial, commercial and residential proposes. It has been further enhanced since the international energy agency (IEA) puts effort to standardize such kind of technology. In this paper, a novel study has been carried out experimentally to control an indirect solar assisted heat pump (IDX-SAHP) system integrated with a latent heat storage (PCM) tank. The PCM heat exchanger tank was designed specially and controlled automatically which allowed storing excess energy during the day and releasing it when needed. In addition, a system control strategy has been purposely designed and implemented in a Building Management System (BMS) to ensure the stable and reliable system operations. The experimental results show that the PCM heat exchanger tank installation has a significant effect on the system operation stability and can improve the COP of the IDX-SAHP system at different weather conditions and a specified hot water load profile.

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.

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

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.