Performance study of a photovoltaic solar assisted heat pump with variable-frequency compressor – A case study in Tibet

The performance of a photovoltaic solar assisted heat pump (PV-SAHP) with variable-frequency compressor is reported in this paper. The system is a direct integration of photovoltaic/thermal solar collectors and heat pump. The solar collectors extract the required thermal energy from the heat pump and at the same time, the cooling effect of the refrigerant lowers the working temperature of the solar cells. So this combined system has a relatively high thermal performance with an improved photovoltaic efficiency. To adapt to the continuously changing solar radiation and ambient temperature conditions, the refrigerant mass flow rate should match the heat gain at the evaporator accordingly. A variable-frequency compressor and an electricity-operated expansion valve were used in the proposed system. Mathematical models were developed to evaluate the energy performance of the combined system based on the weather conditions of Tibet. The simulation results indicated that on a typical sunny winter day with light breeze, the average COP could reach 6.01, and the average electricity efficiency, thermal efficiency and overall efficiency were 0.135, 0.479 and 0.625 respectively.     

Experimental study of photovoltaic solar assisted heat pump system

A novel photovoltaic solar assisted heat pump (PV-SAHP) system has been proposed in this study. Performance tests with a range of condenser supply water temperature were conducted on an experimental rig. The dynamic performance of this PV-SAHP system in a 4-day period with very similar weather conditions was analyzed and the influencing factors were identified. The results indicate that this PV-SAHP system has a superior coefficient of performance (COP) than the conventional heat pump system and at the same time, the photovoltaic efficiency is also higher. The COP of the heat pump was able to reach 10.4 and the average value was about 5.4. The average photovoltaic efficiency was around 13.4%. The highest overall coefficient of performance (COP_p/t), bringing into consideration both the photovoltaic and thermal efficiency, was about 16.1.     

Simulation of a photovoltaic/thermal heat pump system having a modified collector/evaporator

A new photovoltaic/thermal heat pump (PV/T-HP) system having a modified collector/evaporator (C/E) has been developed and numerically studied. Multi-port flat extruded aluminum tubes were used in the modified C/E, as compared to round copper tubes used in a conventional C/E. Simulation results suggested that a better operating performance can be achieved for a PV/T-HP system having such a modified C/E. In addition, using the meteorological data in both Nanjing and Hong Kong, China, the simulation results showed that this new PV/T-HP system could efficiently generate electricity and thermal energy simultaneously in both cities all-year-round. Furthermore, improved operation by using variable speed compressor has been designed and discussed.     

Experimental performance analysis on a direct-expansion solar-assisted heat pump water heater

A direct expansion solar assisted heat pump water heater (DX-SAHPWH) experimental set-up is introduced and analyzed. This DX-SAHPWH system mainly consists of 4.20 m² direct expansion type collector/evaporator, R-22 rotary-type hermetic compressor with rated input power 0.75 kW, 150 L water tank with immersed 60 m serpentine copper coil and external balance type thermostatic expansion valve. The experimental research under typical spring climate in Shanghai showed that the COP of the DX-SAHPWH system can reach 6.61 when the average temperature of 150 L water is heated from 13.4 °C to 50.5 °C in 94 min with average ambient temperature 20.6 °C and average solar radiation intensity 955 W/m². And the COP of the DX-SAHPWH system is 3.11 even if at a rainy night with average ambient temperature 17.1 °C. The seasonal average value of the COP and the collector efficiency was measured as 5.25 and 1.08, respectively. Through exergy analysis for each component of the DX-SAHPWH system, it can be calculated that the highest exergy loss occurs in the compressor, followed by collector/evaporator, condenser and expansion valve, respectively. Further more, some methods are suggested to improve the thermal performance of each component and the whole DX-SAHPWH system.     

Experimental performance analysis and optimization of a direct expansion solar-assisted heat pump water heater

In this study, a direct expansion solar-assisted heat pump water heater (DX-SAHPWH) with rated input power 750 W was tested and analyzed. Through experimental research in spring and thermodynamics analysis about the system performance, some suggestions for the system optimization are proposed. Then, a small-type DX-SAHPWH with rated input power 400 W was built, tested and analyzed. Through exergy analysis for each component of DX-SAHPWH (A) and (B), it can be seen that the highest exergy loss occurs in the compressor and collector/evaporator, followed by the condenser and expansion valve, respectively. Furthermore, some methods are suggested to improve the performance of each component, especially the collector/evaporator. A methodology for the design optimization of the collector/evaporator was introduced and applied. In order to maintain a proper matching between the heat pumping capacity of the compressor and the evaporative capacity of the collector/evaporator under widely varying ambient conditions, the electronic expansion valve and variable frequency compressor are suggested to be utilized for the DX-SAHPWH.     

Thermal performance analysis of a direct-expansion solar-assisted heat pump water heater

A direct-expansion solar-assisted heat pump water heater (DX-SAHPWH) is described, which can supply hot water for domestic use during the whole year. The system mainly employs a bare flat-plate collector/evaporator with a surface area of 4.2 m², an electrical rotary-type hermetic compressor, a hot water tank with the volume of 150 L and a thermostatic expansion valve. R-22 is used as working fluid in the system. A simulation model based on lumped and distributed parameter approach is developed to predict the thermal performance of the system. Given the structure parameters, meteorological parameters, time step and final water temperature, the numerical model can output operational parameters, such as heat capacity, system COP and collector efficiency. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions. The effect of various parameters, including solar radiation, ambient temperature, wind speed and compressor speed, has been analyzed on the thermal performance of the system.     

Performance analysis of solar-assisted chemical heat-pump dryer

A solar-assisted chemical heat-pump dryer has been designed, fabricated and tested. The performance of the system has been studied under the meteorological conditions of Malaysia. The system consists of four main components: solar collector (evacuated tubes type), storage tank, solid-gas chemical heat pump unit and dryer chamber. A solid-gas chemical heat pump unit consists of reactor, condenser and evaporator. The reaction used in this study (CaCl2-NH₃). A simulation has been developed, and the predicted results are compared with those obtained from experiments. The maximum efficiency for evacuated tubes solar collector of 80% has been predicted against the maximum experiment of 74%. The maximum values of solar fraction from the simulation and experiment are 0.795 and 0.713, respectively, whereas the coefficient of performance of chemical heat pump (COP^h) maximum values 2.2 and 2 are obtained from simulation and experiments, respectively. The results show that any reduction of energy at condenser as a result of the decrease in solar radiation will decrease the coefficient of performance of chemical heat pump as well as decrease the efficiency of drying.     

Study on performance of solar assisted air source heat pump systems for hot water production in Hong Kong

This paper reports the investigation results on application of the solar assisted air source heat pump systems for hot water production in Hong Kong. A mathematical model of the system is developed to predict its operating performance under specified weather conditions. The optimum flow rate from the load water tank to the condenser is proposed considering both the appropriate outlet water temperature and system performance. The effect of various parameters, including circulation flow rate, solar collector area, tilt angle of solar collector array and initial water temperature in the preheating solar tank is investigated, and the results show that the system performance is governed strongly by the change of circulation flow rate, solar collector area and initial water temperature in the preheating solar tank.     

Performance analysis of an irreversible cogeneration heat pump cycle

An irreversible heat engine-driven vapour compression and absorption heat pump system is considered as a cogeneration cycle. The effects of thermal resistances and internal irreversibilities on the coefficient of performance (COP) of this cogeneration cycle were investigated using finite-time thermodynamic approach. An improved equation for the COP of the system under consideration was obtained. The results obtained here may serve as a good guide for the evaluation of existing real cogeneration heat pumps or provide some theoretical bases for the optimal design of future cogeneration heat pumps. © 1998 John Wiley & Sons, Ltd.     

Performance of a multi-functional direct-expansion solar assisted heat pump system

This paper reports on the long-term performance of a direct-expansion solar assisted heat pump (DX-SAHP) system for domestic use, which can offer space heating in winter, air conditioning in summer and hot water during the whole year. The system employs a bare flat-plate collector array with a surface area of 10.5 m², a variable speed compressor, a storage tank with a total volume of 1 m³ and radiant floor heating unit. The performance under different operation modes is presented and analyzed in detail. For space-heating-only mode, the daily-averaged heat pump COP varied from 2.6 to 3.3, while the system COP ranged from 2.1 to 2.7. For water-heating-only mode, the DX-SAHP system could supply 200 l or 1000 l hot water daily, with the final temperature of about 50 °C, under various weather conditions in Shanghai, China. For space-cooling-only mode, the compressor operates only at night to take advantage of a utility’s off-peak electrical rates by chilling water in the thermal storage tank for the daytime air-conditioning. It shows that, the multi-functional DX-SAHP system could guarantee a long-term operation under very different weather conditions and relatively low running cost for a whole year.     

Solar assisted heat pump on air collectors: A simulation tool

The heating system of the bioclimatic building of the Greek National Centre for Renewable Energy Sources (CRES) comprises two heating plants: the first one includes an air source heat pump, Solar Air Collectors (SACs) and a heat distribution system (comprising a fan coil unit network); the second one is, mainly, a geothermal heat pump unit to cover the ground floor thermal needs. The SAC configuration as well as the fraction of the building heating load covered by the heating plant are assessed in two operation modes; the direct (hot air from the collectors is supplied directly to the heated space) and the indirect mode (warm air from the SAC or its mixture with ambient air is not supplied directly to the heated space but indirectly into the evaporator of the air source heat pump). The technique of the indirect mode of heating aims at maximizing the efficiency of the SAC, saving electrical power consumed by the compressor of the heat pump, and therefore, at optimizing the coefficient of performance (COP) of the heat pump due to the increased intake of ambient thermal energy by means of the SAC. Results are given for three research objectives: assessment of the heat pump efficiency whether in direct or indirect heating mode; Assessment of the overall heating plant efficiency on a daily or hourly basis; Assessment of the credibility of the suggested simulation model TSAGAIR by comparing its results with the TRNSYS ones.     

Seasonal cooling performance of a ground-coupled heat pump system in a hot and arid climate

The goal of the present study is to validate the cooling performance of a ground-coupled heat pump system established in Fırat University, Elazığ (38.41°N, 39.14°E), Turkey. The cooling load of the test room was 3.1 kW at design conditions. The experimental results were obtained from June to September in cooling season of 2003. The ground heat exchanger was used, and it was buried with in 2 m depth trench. The average cooling performance coefficient of the system (COP_overall) was obtained to be 2.01. The results obtained from experimental measurement showed that these systems could be used safely, reliably and efficiently at the lowest possible cost for Elazığ, Turkey climatic conditions. Especially, the seasonal energy efficiency ratio (SEER) of this system is moderate at longer-term testing.     

Expanding photovoltaic penetration with residential distributed generation from hybrid solar photovoltaic and combined heat and power systems

The recent development of small scale combined heat and power (CHP) systems has provided the opportunity for in-house power backup of residential-scale photovoltaic (PV) arrays. This paper investigates the potential of deploying a distributed network of PV + CHP hybrid systems in order to increase the PV penetration level in the U.S. The temporal distribution of solar flux, electrical and heating requirements for representative U.S. single family residences were analyzed and the results clearly show that hybridizing CHP with PV can enable additional PV deployment above what is possible with a conventional centralized electric generation system. The technical evolution of such PV + CHP hybrid systems was developed from the present (near market) technology through four generations, which enable high utilization rates of both PV-generated electricity and CHP-generated heat. A method to determine the maximum percent of PV-generated electricity on the grid without energy storage was derived and applied to an example area. The results show that a PV + CHP hybrid system not only has the potential to radically reduce energy waste in the status quo electrical and heating systems, but it also enables the share of solar PV to be expanded by about a factor of five.     

Performance analysis of solar water heater combined with heat pump using refrigerant mixture

In the research presented in this paper the thermal performance of a solar water heater combined with a heat pump is studied. A solar collector was modified from corrugated metal roofing with a copper tube attached beneath. The performance of the solar water heater was tested, and models for the collector efficiency and storage tank were developed and used for the evaluation of their performance when combined with a heat pump system.     

New optimized model for water temperature calculation of river-water source heat pump and its application in simulation of energy consumption

The energy consumption calculation plays an important role in the analysis of project economic and social benefits. In order to calculate energy consumption accurately, this research presents a water temperature of condenser inlet calculation model of river-water source heat pump unit. The feasibility and calculation error of the model had been analyzed. Additionally, the new water temperature calculation model had been validated via an engineering case. The results showed that the hourly water temperature in 24 h could be replaced by daily average water temperature due to little change of the daily water temperature change. In this case, the calculation error could be less than 5%. It is found that despite water temperature has many influenced factors, there is a remarkable relationship between the daily average water temperature and daily average outdoor dry bulb temperature by data analysis (R² ≈ 0.9). The influence of river sampling location on water temperature calculation of condenser inlet could be ignored due to slight temperature changes (within 0.15 °C). The method proposed in this paper met the engineering accuracy and provided a very effective method for the engineering calculation of energy consumption of water chilling unit.     

Solar heat pump drying and water heating in the tropics

In this study, the performance of a solar assisted heat pump dryer and water heater has been investigated. A simulation program has been developed. The predicted results are compared with those obtained from experiments under the meteorological conditions of Singapore. A coefficient of performance (COP) value of 7.0 for a compressor speed of 1800 rpm was observed. Maximum collector efficiencies of 0.86 and 0.7 have been found for evaporator–collector and air collector, respectively. A value of the specific moisture extraction rate (SMER) of 0.65 has been obtained for a load of 20 kg and a compressor speed of 1200 rpm. Results suggest that the total drying time of the product decreases with the increase in drying potential. Drying potential is directly proportional to the air flow rate, drying air temperature and inversely proportional to the air relative humidity. Three important parameters that affect the system performance are solar radiation, compressor speed and the total load placed in the drying chamber. Both SMER and COP decrease with increase in compressor speed.     

Performance analysis of a closed regenerated Brayton heat pump with internal irreversibilities

This paper analyses the performance of a real heat pump plant via methods of entropy generation minimization or finite‐time thermodynamics. The analytical relations between heating load and pressure ratio, and between coefficient of performance (COP) and pressure ratio of real closed regenerated Brayton heat pump cycles coupled to constant‐ and variable‐temperature heat reservoirs are derived. In the analysis, the irreversibilities include heat transfer‐irreversible losses in the hot‐ and cold‐side heat exchangers and the regenerator, the non‐isentropic expansion and compression losses in the compressor and expander, and the pressure drop loss in the pipe and system. The optimal performance characteristics of the cycle may be obtained by optimizing the distribution of heat conductances or heat transfer surface areas among the two heat exchangers and the regenerator, and the matching between working fluid and the heat reservoirs. The influence of the effectiveness of regenerator, the effectiveness of hot‐ and cold‐side heat exchangers, the efficiencies of the expander and compressor, the pressure recovery coefficient and the temperature of the heat reservoirs on the heating load and COP of the cycle are illustrated by numerical examples. Published in 1999 by John Wiley & Sons, Ltd.     

回热器对跨临界CO_2水源热泵的影响判别式及实验研究

分析了回热器对跨临界CO2压缩循环效率等的影响,推导出回热器对系统的制热效率影响的判别式。在带回热器和不带回热器两种情况下完成了跨临界CO2水源热泵系统的实验。实验结果表明：带回热器的跨临界CO2水源热泵系统的制热效率和制冷效率略高于不带回热器时系统的效率;带回热器时热泵系统的制热效率比不带回热器系统的制热效率高约4%-8%。