Solar Assisted Heat Pump System Research Articles

Performance analysis on the heating performance of CPV/T-air dual source heat pump system with finned microchannels heat exchanger

Solar-assisted heat pump technology is a clean building energy conserving technique with high efficiency, but it often has limitations such as large evaporator cover area and significant susceptibility to weather conditions, preventing it from being widely used. In this paper, a concentrated photovoltaic/thermal-air dual source heat pump system integrated with finned microchannel heat exchanger (CPV/T-FMC-SAHP) is proposed to solve these problems. A mathematical model for the CPV/T-FMC-SAHP system is developed, and sensitivity analysis of different environmental parameters on system performance is conducted by numerical simulation. Performance comparisons are made under dual-source and solar heating modes to explore the optimal operating conditions. The results suggest that changes in ambient temperature have a relatively minor impact, primarily attributed to the limited surface area of the evaporator. On the other hand, increased irradiance, facilitated by the concentrator, significantly improves the system's performance. In the case of solar irradiation at 600 W/m2 and an ambient temperature of 13 °C, the system's heating capacity is 1747.38 W, with a COP reaching 5.31. In comparison, the COP of existing solar-assisted heat pump systems under this condition are about 4.5, so there is an improvement of about 18 %. Furthermore, activating the air blower on the weather with bad irradiation but relatively warm can further increase the system's heating capacity. To sum up, the CPV/T-FMC-SAHP system exhibits a substantial improvement in performance and high level of integration compared to traditional solar-assisted heat pumps. Therefore, this system can provide ideas for improving the performance of heat pumps in the case of limited space. It is not only meaningful in the field of building energy conserving, but also conducive to addressing global energy challenges.

Study on long-term operation characteristics of the medium-deep ground source heat pump system with solar heat storage

Long-term heating operation of the medium-deep ground source heat pump (MGSHP) system will cause the underground temperature around the mid-deep borehole heat exchanger (MBHE) significantly lower than its initial value, which will reduce the operating efficiency of the MGSHP system. In some cases, the temperature of the circulating water in MBHE even is lower than the lowest value required by the heat pump unit, which will lead to operation failure of the unit. Attenuating the ground temperature decrease by storing heat underground during non-heating seasons is an effect way to maintain the heat extraction capacity of the MBHE. In this paper, the influence of storing solar energy underground during non-heating seasons on the long-term operating characteristics of the MGSHP system is studied. The MBHE heat transfer model which considers the heat storage process is developed and embedded in the software of TRNSYS. Based on the numerical simulation model of solar assisted mid-deep ground source heat pump (SAMGSHP) system built by TRNSYS, the long-term characteristics including the variations of the fluid temperature of the MBHE, the ground temperature distribution and the COP of the heat pump unit of the MGSHP system with heat storage during non-heating seasons are analyzed and compared with the case without heat storage. The results show that storing solar energy underground during non-heating seasons can effectively improve the ground temperature, significantly slow down the decline of the circulating water temperature of the MBHE in heating seasons and apparently increase the COP of the heat pump unit. The results can serve as a reference for engineering applications of MGSHP systems, especially those cannot completely meet the original design heating load.

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.

Improvement of energy self-sufficiency in residential buildings by using solar-assisted heat pumps and thermal and electrical storage

To reach the EU 2030 goal of reducing greenhouse gas emissions targets, many apartments within residential buildings can be equipped with rooftop or building-integrated PV systems.However, as non-programmable renewable energy sources (solar, wind) are characterized by uncertainty and fluctuation, it is very difficult to match the supply with the demand for the building’s energy needs. Thermal and electric energy storage play a fundamental role in maximizing self-consumption, reducing the difference between peaks and valleys of the energy demand, and improving the electrical system's flexibility. In this study, the performances of an energy system composed of an electric heat pump (HP) fed by a PV plant and both thermal and electric storage are investigated. An innovative logic of the charge and discharge of the two storages as a function of energy generation and demand has been developed with the aim to optimize the energetic self-sufficiency of typical residential buildings. The results of the analyses carried out evidence that the system configurations with a thermal storage of about 1.000 L and an electrical storage of 5.0 kWh allow achieving rates of self-consumption and self-sufficiency of about 80%, which are 3 times higher than that one achievable by an energy system without storage. Moreover, this system configuration reduces dramatically the power exchange with the grid. The outcomes of this study are useful to provide indications for the design of the storage in combination with a solar-assisted heat pump system avoiding the recurrent praxis of oversizing of more than 100% of the electric storage.

Ground and solar assisted heat pump systems for space heating and cooling applications in the northern region of India – A study on energy and CO2 saving potential

In the recent past, energy demand of India has increased multifold as a fast-growing developing country, due to progressive expansion of industrial and building sectors. The demand for devices that provide both cooling and heating has increased in both commercial and residential buildings. However, nearly two-thirds of electricity generation in India is obtained from fossil fuel sources such as coal, oil and gas. Hence any attempt to save electricity consumption by the conventional space heating/cooling devices will benefit the country to meet other electricity demands and will indirectly aid for reduction in CO2 emission. Ground source heat pumps (GSHP) and solar assisted GSHP are sustainable systems that consume less electricity compared to conventional devices. They can achieve cooling and heating more efficiently by exploiting the temperature difference between the deep ground and ambient during winter and summer. In this research work, a detailed analysis has been made to assess the scope for the use of GSHP and Solar Assisted Ground Source Heat Pump (SAGSHP) systems for space cooling and heating applications in ten cities located in northern region of India. Calculations on the saving of electricity and reduction in CO2 emission has been carried out by comparing SAGSHP with conventional devices such as electric heater, solar coupled heat pump system for space heating. Air-conditioners are compared with GSHP for space cooling. Implementation of SAGSHP and GSHP technologies for space heating and cooling applications will result in the saving of 151.77 GW of electricity for space heating in ten cities and 88.39 GW of electricity for space cooling in six cities respectively with forthright reduction in CO2 emission of 123.83 million ton and 144.2 million ton. For 1.5-ton capacity heating load of SAGSHP and cooling load of GSHP, the payback period is estimated as 6.8 and 4.5 years respectively.

Is solar heating an appropriate choice in rural areas of northern China? Evidence from numerical simulation and life cycle assessment

Solar heating is generally regarded as a clean and low-carbon heating method, while its high initial investment hinders its promotion in economically underdeveloped areas. With the implementation of the clean heating policy and the proposal of the carbon neutralization target, rural bulk coal heating in northern China is restricted. The Chinese government proposes to widely adopt solar heating to meet the heating demands of rural residents. In this research, the application of solar assisted heat pump systems in Beijing, Tianjin, Hebei and its surrounding areas in China is numerically simulated. A new evaluation method under the same initial investment constraint is proposed to verify its benefits throughout the entire life cycle. The results indicate that although solar thermal heating has the lowest environmental impact and carbon emissions among various heating methods, it is not the best solution to rural clean heating. The reason is that equal investment in other projects can bring much more benefits, such as roof solar photovoltaic. In contrast to the air source heat pump and photovoltaic panel scheme with the same initial investment, solar heating has obvious negative environmental impact, 53.3 % higher economic cost, 35.9 tons more carbon emissions, and 105.9 % higher roof area occupation. The sensitivity analysis of solar fraction, geographical coordinates, and energy price also supports the above findings. The recommendation is proposed to promote air source heat pumps or solar photovoltaic, rather than solar thermal collectors, so as to reduce the cost of rural clean heating and carbon emission reduction.

System optimization and mode modification of the solar assisted ground source heat pump system for primary schools in northern rural areas of China

With the increasing application of geothermal and solar energy in northern regions of China, it has become one of the main clean heating technologies for rural primary schools. However, the mismatch in equipment capacity has led to poor operating effect and economic efficiency of such systems. This paper puts forward experimental and analysis on a solar assisted ground source heat pump system in a primary school in Beijing's Daxing District. And then, to address the above issues, a TRNSYS model is established and verified to optimize the system strategy and form during 15 years period. What’ more, the main factors affecting solar collector selection are screened by sensitivity analysis. And through the step-by-step regression analysis, the collector selection correction model based on the coefficient Km is obtained. The results show that the temperature difference of the optimized collector control is 10 °C/1°C, and that of the supplementary heat is 20 °C/1°C. The applicable scenarios of the two system forms are different, and the energy efficiency of the system operation is increased by 23% and 23.4% respectively. In addition, the revised model ensures the balance of soil temperature for 15 years of operation under the condition of considering multiple elements, which provides a reference for the matching and selection of equipment for the same type of project in the future.

Performance Review of Solar-Assisted Heat Pump Systems Using Solar Collectors, PV, and PVT Technologies

Performance Review of Solar-Assisted Heat Pump Systems Using Solar Collectors, PV, and PVT Technologies

Performance analysis and multi-objective optimization of solar assisted ground-source heat pump heating system

ABSTRACT Heating through a solar assisted ground-source heat pump system is an efficient method, and optimizing its parameters can significantly improve its energy efficiency. However, the research on the impact of the start-stop temperature difference of the heat collection cycle on the system is currently limited. To address this issue, this study aims to develop a SAGSHP system model located in Tianjin using TRNSYS software, investigate the effect of parameters such as the start-stop temperature difference on the system performance, and guide the optimization process. The optimization parameters include the collector’s area, the water tank’s volume, and temperature difference during the heat collection cycle. The NSGA-II algorithm is applied to perform multi-objective optimization to enhance the system’s energy efficiency and economy. Furthermore, a sensitivity analysis is conducted to study each variable’s impact on the optimization results. The variation in temperature between the start and stop of the collection cycle has a significant impact on the system’s performance, as revealed by the study. The optimal operation scheme lies within the boundary range of parameter settings. The optimization leads to a decrease of 8.63% in the system’s annual operating cost and a reduction of 1555 kWh in the annual power consumption. The relationship between the area of the collector and the temperature difference during heat collection startup is expressed as 0.034°C/m2, and the ratio to the tank volume is 1.33°C/m3. The degree of influence of optimization parameters on optimization results is ranked as V i>A i>T s>T e.

Analysis of a solar-assisted heat pump system with hybrid energy storage for space heating

Insufficient heating capacity and low coefficient of performance have always been obstacles that inhibit the application of air source heat pump systems in cold regions. This study proposes an indirect expansion solar-assisted air source heat pump system to improve the heating performance of the air source heat pump. The indirect expansion solar-assisted air source heat pump system consists of solar collectors, a hybrid thermal energy storage tank, and a dual-source heat pump. An optimized control method is proposed to tackle the refrigerant redistribution problem for the dual-source heat pump. An experiment is carried out to study the thermodynamic performance of the indirect expansion solar-assisted air source heat pump. The experimental results indicate that the average coefficient of performance of the solar heat pump mode is increased by 50.0% compared to the air source heat pump mode due to the higher evaporating temperature. Based on the experimental results, a techno-economic and environmental analysis of the indirect expansion solar-assisted air source heat pump system for space heating is conducted in six northern cities in China. The indirect expansion solar-assisted air source heat pump system has the highest annual average coefficient of performance of 2.53 in Jinan, which is increased by 18.8% compared to Harbin. The payback period of the indirect expansion solar-assisted air source heat pump system is shortest in Xining and is reduced by 53.45% compared to Jinan. Applying the IX-SAASHP system in the northwest region is suitable for improving its energy and economic performance. The analysis results indicate that the IX-SAASHP system is beneficial for reducing carbon emissions from space heating systems in the northeast region.

Performance analysis of a novel solar assisted ground source heat pump water heating system with graded thermal energy storage

The solar assisted ground source heat pump system (SAGSHP) is recognized as an efficient, clean and economical renewable energy technology for hot water supply. However, in SAGSHP systems with an all-day hot water supply, the solar collectors can only heat the water tank with intense solar radiation, which wastes moderate and weak solar resources. In addition, as the SAGSHP system draws heat from the soil for a long time, the soil temperature around the borehole decreases, causing the performance of the GSHP to deteriorate. To solve the above problems, a SAGSHP system with graded thermal energy storage (SAGSHP-GTES) was proposed. This paper investigated the performance and feasibility of the SAGSHP-GTES system, using a case study of hot water supply in a campus dormitory in Changsha, China. Firstly, the drawbacks of solar energy utilization in the conventional SAGSHP system were analyzed. Then, the SAGSHP-GTES system was modeled by TRNSYS, and its operational performance was evaluated and compared with the conventional SAGSHP system. Finally, the feasibility and performance of the SAGSHP-GTES system in different climate zones of China were analyzed. The results showed that the conventional SAGSHP system had a poor solar energy utilization efficiency, with an average thermal efficiency of the SC (ηSC) of only around 19.4%. The long period of operation caused the soil temperature to drop from 18.1 °C to 2.78 °C, which led to a decrease in system efficiency and an increase in electricity consumption. By controlling the heat collection of the SC and the graded utilization of solar energy in the SAGSHP-GTES system, a high ηSC of around 42.7% was obtained, which improved the system efficiency while eliminating the problem of soil temperature drop. After 15 years of operation, the soil temperature increased from 18.1 °C to 19.9 °C, which led to an increase in the coefficient of performance of the system (COPsys) from 3.77 kW/kW to 3.84 kW/kW and COPGSHP from 3.45 kW/kW to 3.5 kW/kW, and a reduction in electricity consumption from 51,746 kWh to 50,735 kWh. In addition, the conventional SAGSHP system was not feasible in severe cold zones (Harbin) and cold zones (Beijing) of China, where soil temperatures fell below 0 °C and freezing of the circulating fluid occurred, while the SAGSHP-GTES system showed excellent performance in all climatic zones of China and is a feasible and efficient technology for hot water supply.

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.

Investigation of solar assisted air source heat pump heating system integrating compound parabolic concentrator-capillary tube solar collectors

Solar assisted air source heat pump heating systems are capable of achieving green heating where solar availability essentially affects its operation performance and application potentials, especially in higher-latitude regions, such as UK. Compound parabolic concentrator solar collectors can achieve high collector efficiency at high hot water temperature, benefitting to improve solar collection and corresponding thermal energy storage capacities. Though compound parabolic concentrator solar collectors have been widely investigated, application of such collector for solar assisted air source heat pump system is not studied yet. The paper reports numerical simulations of solar assisted air source heat pump heating systems that integrate compound parabolic concentrator-capillary tube solar collectors for domestic heating in the UK. The results show that, for the same seasonal performance factor, the size of the concentrated solar collector required is 12 m2 whereas the size of the flat plate solar collector required is 18 m2. This suggests one third reduction in the size of solar collector, significant reduction in cost and convenience for installation. The results also show the potential to further reduce the size of the concentrated solar collector to 9 m2 or less. The high collector efficiency of the compound parabolic concentrator-capillary tube solar collector enables much small size of solar collector, significantly lower cost and convenient for installation and wide rollout of solar assisted air source heat pump heating system to locations where solar irradiance is relatively lower.

Correction to: Thermo-Mathematical Modeling and Multi-Objective Programming of the Solar-Assisted Heat Pump System Coupled to the Multi-Criteria Decision Analysis: A Case Study in Iran

Correction to: Thermo-Mathematical Modeling and Multi-Objective Programming of the Solar-Assisted Heat Pump System Coupled to the Multi-Criteria Decision Analysis: A Case Study in Iran

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.

Numerical study on seasonal operation of solar assisted hybrid borehole heat exchange array

The combined use of solar energy and ground-source heat pump system may provide a reasonable solution to the energy crisis and low utilization efficiency of single energy. Herein, a numerical model of a solar assisted hybrid ground-source heat pump (SAHGSHP) system composed of multiple types and lengths of borehole heat exchanger (BHE) array was developed. The effectiveness of this model was validated by experimental data of a SAHGSHP system located in Tongzhou, Beijing. The verified model was used to study the performance sustainability of SAHGSHP system under different seasonal operation modes and its influence on the temperature of rock and soil. It was shown that for different types of BHEs in heat extraction periods of SAHGSHP systems, the outlet temperature decline rate decreases by an average of 2.30%, the temperature decline rate of rock and soil at the reference point under single-season operation decreases by an average of 0.78%, and the temperature increase rate of rock and soil at the reference point under double-season operation increases by an average of 0.53% compared with that of hybrid ground-source heat pump (HGSHP). The results of this study could provide a further understanding for analyzing the seasonal operation mode of SAHGSHP.

Thermo-Mathematical Modeling and Multi-Objective Programming of the Solar-Assisted Heat Pump System Coupled to the Multi-Criteria Decision Analysis: A Case Study in Iran

Thermo-Mathematical Modeling and Multi-Objective Programming of the Solar-Assisted Heat Pump System Coupled to the Multi-Criteria Decision Analysis: A Case Study in Iran

Numerical Modeming, Energy–Exergy Analyses, and Multi-objective Programming of the Solar-assisted Heat Pump System Using Genetic Algorithm Coupled with the Multi-criteria Decision Analysis

Numerical Modeming, Energy–Exergy Analyses, and Multi-objective Programming of the Solar-assisted Heat Pump System Using Genetic Algorithm Coupled with the Multi-criteria Decision Analysis

Solar assisted air source heat pump systems for campus water heating in China: Economic optimization of solar fraction design

• TRNSYS software is to simulate the solar assisted air source heat pump system . • The solar fraction design values of solar water heating systems are not economically optimal in China. • Long-term economic optimization of solar fraction design values for solar assisted air source heat pump systems is performed. • An ANN-generated proxy model is to predict the most economical solar fraction design values of solar assisted air source heat pump systems. The solar assisted air source heat pump (SAASHP) system is widely used for campus water heating owing to its cost-effectiveness and cleanliness. In the current design process of the SAASHP system, the solar collector area is determined by the solar fraction ( f ). However, it is difficult to design a cost-optimal f that can comprehensively take the atmospheric factors, device model, electricity price and initial investment into consideration. To address this issue, a SAASHP system that meets the bathing hot water demand of 480 students was established by TRNSYS software, and the cost-optimal solar collector areas and f values for 12 cities across 4 different solar resource regions in China were obtained by the TRNOPT tool of TRNSYS. Moreover, the effects of SC price, electricity price, bathing hot water demand and rated COP of ASHP on cost-optimal f values were investigated by sensitivity analysis. Finally, a proxy model was generated by the artificial neural network toolbox of MATLAB to predict the cost-optimal f values for different scenarios. The results showed that compared to the economically optimized SAASHP system, the designed SAASHP system according to the national design standards for solar heating systems in China has a larger SC area value, leading to an increase in the annual life cycle cost of the system. The difference between the optimized and designed values of solar collector area and f for the SAASHP system was minor in rich resource and sub-rich resource regions but was larger in general resource and poor resource regions. The solar collector price, electricity price, bathing hot water demand and the rated COP of the SAHP were significant factors affecting the annual life cycle cost, the cost-optimal f and solar collector area of the SAASHP system. The proxy model generated by the artificial neural network toolbox of MATLAB can accurately predict the economically optimal solar collector area and f values for SAASHP systems in different cities and system factors, providing a method for the economic design of SAASHP systems in China.