Photovoltaic Thermal Heat Pump Research Articles

Operation study of the photovoltaic thermal heat pump integrated energy system under trigeneration condition and harsh conditions

In recent years, the photovoltaic thermal heat pump has gained significant attention as a near zero-carbon energy technology, due to the comprehensive ability to provide heating in winter, cooling in summer, photovoltaic power generation and domestic hot water throughout the year. However, owing to the incomplete research on the system operating characteristics in trigeneration condition and harsh conditions, the production performance and operational stability of the photovoltaic thermal heat pump were not widely recognized. In view of the above problems, the following studies were conducted in this paper: First, the integrated energy system based on the modular photovoltaic thermal heat pump was designed and constructed. Then, the system operation in severe hot and cold season was carried out and the operational stability of the system under harsh operating conditions was demonstrated sufficiently. Afterwards, the operation of the system under the continuous trigeneration operation were analyzed. During the 7-day trigeneration operation, the average hot water output was 12.12 tons and the average photovoltaic power generation was 88.5 kWh in the daytime heating operation. Besides, the average coefficient of cooling performance was 2.32 in the nighttime cooling operation and the effective cooling-supply time of the system was approximately 4 h.

Matching analysis between the heating/cooling capacity of PVT heat pumps and the heating/cooling demand of residential buildings across various regions in China

PVT-HP (Photovoltaic-Thermal Heat Pump) is a novel type of energy saving technology. Existing researches on PVT-HP technology focuses only on its operating performance under some specific conditions, ignoring the matching of its energy supply capacity with the energy demand of buildings, which is very important for its engineering design and application. In this paper, the matching relationship between the heating/cooling capacity of the PVT-HP system and the heating/cooling demand of residential buildings in major cities of China has been analyzed. To achieve this goal, a novel prediction model used to calculate the heating/cooling performance of the PVT-HP system has been proposed. And the daily heating guarantee rate and daily cooling guarantee rate have been put forward to evaluate the matching relationship. Based on the evaluation indexes, the applicable matching relationship between the installed capacity of the PVT-HP system and the heating/cooling area of residential buildings has been analyzed. The result of case study shows that for the selected cities of Shenyang, Beijing and Wuhan, the heating/cooling area of residential building for PVT-HP system with installed capacity of 1hp should not exceed 17 m2, 31 m2 and 25 m2, respectively. Further matching analysis of major cities in China shows that the PVT-HP system is more suitable for application in hot summer and cold winter zones of China, in where the suggested heating/cooling area for the PVT-HP system with installed capacity of one horse power is within the range of 30 m2–37 m2.

Energy analysis of a direct expansion heat pump assisted by a thermal photovoltaic panel for hot water production in several regions of Brazil

This study focused on evaluating the energy performance and economic viability of a direct expansion photovoltaic-Thermal Heat Pump (PV-T/HP) system for residential heating applications in various regions of Brazil. A detailed mathematical model was implemented to compare the PV-T/HP system with other solar heating technologies, as photovoltaic with solar evacuated tubes collector (PV+TSC) and photovoltaic with electrical heat water (PV+EHW), analyzing key metrics such as electrical efficiency, thermal efficiency, and levelized cost of heat (LCOH). The study revealed variations ranging from 7.5 to 2.5 in the Coefficient of Performance (COP) of the heat pump under different solar irradiation and ambient temperature conditions, emphasizing the necessity for future optimization to enhance the system performance. Results indicated that cities with the lower ambient temperature such as Belo Horizonte and Porto Alegre exhibited favorable conditions for the PV-T/HP system, leading to increased energy generation and positive net electricity production. The study highlighted the need for tailored strategies to control system operations, limit compressor consumption, and improve overall efficiency. These findings contribute to the understanding of PV-T/HP systems in residential heating applications, showcasing their potential for sustainable energy solutions in Brazil.

Development of performance analysis model with numerical and dynamic energy modeling for an integrated PVT-HP system

This study delivers a comprehensive numerical analysis of an integrated photovoltaic/thermal-heat pump (PVT-HP) system, underscored by an innovative three-dimensional thermal energy storage (TES) model. Addressing the limitations of conventional one-dimensional TES models, which struggled with accurately simulating horizontal flows and the fluid state at various facility inlets, this research marks a significant advancement. Our development of a 3D TES model optimizes finite elements to reduce computation time and enhance accuracy, vital for precise energy analysis in buildings and air conditioning systems. The integration of this model with a network model allows for detailed analysis of flow rate changes and their impacts on heat transfer, crucial for the integrated PVT-HP system. Key findings include a 30 % increase in the temperature difference between the top and bottom layers of the TES when the flow rate is reduced from 50 LPM to 20 LPM, and a 1 % decrease in the heat pump's coefficient of performance (COP) with a 10 LPM reduction in flow rate. The study emphasizes that managing the flow rate is key to optimizing temperature gradients and system efficiency. Strategic adjustments in flow rate significantly affect thermal storage and transfer capabilities, proving essential in system performance. This research offers vital insights into optimizing PVT-HP systems, focusing on the importance of flow rate control in improving temperature management and overall system performance.

Feasibility and performance study on the novel photovoltaic thermal heat pipe/heat pump composite cycle trigeneration system in summer

Photovoltaic thermal heat pump technology with deep utilization of solar energy has great market potential to achieve “Carbon Neutrality” in the building sector. A novel photovoltaic thermal heat pipe/heat pump composite cycle trigeneration system synergetic driven by a compressor and a working fluid circulating pump was proposed and experimentally verified. On this basis, the trigeneration performance and operating characteristics of the novel system were tested and investigated in the summer. The experimental results showed that the novel system can arbitrarily switching between different cycles and has an excellent energy saving effect. The average electrical efficiency, thermal efficiency, heating COP, and refrigerating COP of the novel system were 10.1%, 40.3%, 7.02, and 2.60, respectively. During the whole day, the comprehensive COP for heating, power generation, and refrigerating of the novel system was 13.93. The heating COP and comprehensive COP of the novel system were 20%–50% and 40%–65% higher than that of the existing photovoltaic thermal heat pump trigeneration system, respectively. Furthermore, the CO2 emission of the novel system was 4042 kg CO2 in summer, which was 20%–80% lower than that of other technical solutions. The novel system represents a practical response to the need to achieve the total decarbonization of the building sector.

Thermoelectric performance analysis of the novel direct-expansion photovoltaic thermal heat pump/power heat pipe compound cycle system in summer

Photovoltaic thermal heat pump technology has outstanding cogeneration ability by utilizing renewable energy to be accepted as a decarbonization pathway in the residential sector. However, existing photovoltaic thermal heat pumps consume higher energy under better external heat source conditions. To address this problem, a novel direct-expansion photovoltaic thermal heat pump/power heat pipe compound cycle system for heating and power generation as well as refrigeration, whose core equipment was a photovoltaic thermal module with straggled honeycomb fluid channel pattern on the serpentine arrangement, was proposed, manufactured, and studied with the method of experiment. The thermoelectric performance was compared between the heat pump and power heat pipe cycle modes, investigated under typical weather conditions, and discussed in contrast to the literature. The results showed that the average photoelectric conversion efficiency and coefficient of photothermal performance of the PVT modules, as well as COP of the novel system were 10.6%, 51.0%, and 6.19, respectively, at the average ambient temperature of 27.0 °C, average solar radiation intensity of 581 W/m2 and water temperature of 18.3–55.6 °C. And daily average COPs of the novel system under sunny, cloudy, and overcast conditions were 15.12, 7.40, and 3.17, respectively. The conclusion drawn from the experimental results is that the COP of the novel system was 10.0%–60.0% higher than that in the literature under similar outdoor conditions. The payback period of the additional cost of the novel system compared with the existing direct-expansion photovoltaic thermal heat pump was within 2.5 years. The novel system represents a practical response to the need to achieve total decarbonization of the residential sector.

Superheat matching control method for a roll-bond photovoltaic-thermal heat pump system

In this paper, a superheat matching control method (SMCM) for a roll-bond photovoltaic-thermal heat pump (RB-PVT-HP) system is proposed to achieve adaptive control of the target superheat under different operating conditions. The target superheat was determined based on a comprehensive consideration of the stable running superheat and the optimally performing superheat of the system. The effectiveness of the SMCM was experimentally verified. The trigeneration performance tests of the system under the SMCM were conducted in the summer. Results show that the average deviation degrees of superheat were 0.48 °C and 2.09 °C in the heating and cooling processes, respectively. In the heating process, the average input power of the compressor, heating power and coefficient of performance of the system were 5.40 kW, 17.90 kW, and 3.31, respectively, across four days of continuous operation. The average photoelectric conversion efficiency, comprehensive energy output capacity and comprehensive performance of thermal-and-electrical generation were 14.19 %, 21.29 kW and 34.76 %, respectively, during daytime operation. In the cooling process, the average input power of the compressor, cooling power and energy efficiency ratio of the system were 3.82 kW, 7.72 kW, and 2.02, respectively, during nighttime operation.

Life cycle energy, economic, and environmental analysis for the direct-expansion photovoltaic-thermal heat pump system in China

The photovoltaic-thermal heat pump system, which integrates multiple energy technologies, can meet the building's diverse energy needs. This study evaluates the energy, economic, and environmental performance of a direct-expansion photovoltaic-thermal heat pump system for domestic hot water supply through a life cycle approach. The annual thermal and electrical outputs are estimated. On this basis, economic analysis is conducted with indicators of life cycle cost, levelized cost of heat, and investment payback time. Moreover, a detailed life cycle assessment is performed to evaluate the environmental impact, following three methods: cumulative energy demand, IPCC 2021 global warming potential, and ReCiPe 2016 Endpoint. Results show that the proposed system is highly effective, with a 9.67% increase in annual electricity output over traditional photovoltaic systems and a self-sufficient rate of 88.21%. The system also has a significantly lower environmental impact than conventional heating systems, with a life cycle environmental impact of only 3–5% compared to electric boilers. The environmental payback time ranges from 0.33 to 5.18 years, according to the three methods used in the study, which is shorter than the investment payback time of 2.49–5.21 years, suggesting the need for cost reduction for future promotion. Moreover, electricity consumption during the operation stage accounts for 32–52% of the total environmental impacts. Thus, decarbonization of the power grid and improvements in system efficiency can significantly reduce the system's environmental footprint. Overall, the photovoltaic-thermal heat pump system is an intriguing strategy for building energy conservation, offering high energy efficiency, acceptable costs, and low environmental impact.

Study on optimal allocation of solar photovoltaic thermal heat pump integrated energy system for domestic hot water

In recent years, solar photovoltaic thermal heat pump has become a highly concerned near-zero carbon energy technology for domestic hot water. In order to facilitate the optimal configuration design of the system for domestic hot water, following studies were carried out in this paper: Firstly, the photovoltaic thermal heat pump integrated energy system was established and the operation study of the system was carried out. During the operation, the average coefficient of system heating performance was 2.76 in winter, 3.55 in transition season and 4.10 in summer. Afterwards, the prediction model of system operation performance was established and hourly system performance prediction of the system in the whole year was conducted. Then, the system for domestic hot water with a total installed photovoltaic capacity of 1 MW was taking as a case study to establish the calculation model. Finally, the optimal allocation of the system was carried out with the goal of minimizing the dynamic investment payback period, then the standard cell method was proposed to facilitate the optimal allocation design. The results showed that the minimum dynamic investment payback period of the system was 3.9 years and the daily hot water supply of the standard cell was 9.2tons.

Photovoltaic Thermal Heat Pump Assessment for Power and Domestic Hot Water Generation

The efficient utilization of solar energy significantly contributes to energy efficiency in buildings. Solar photovoltaic thermal (PVT) heat pumps, a hybrid of photovoltaic and solar-assisted heat pumps, have demonstrated a significant development trend due to their multi-generational capacity for heating, power, and cooling with reliable operational performance. This research work presents and investigates a single-stage compression PVT heat pump system, along with the operation principle of the system’s heating and power co-generation throughout the winter and transitional season. The construction of the testing facility, data reduction, error analysis, and performance evaluation indices of the system are all explained theoretically. A continuous experiment research project focusing on system heating and power performance was carried out in Dalian during the transition season (November in this study) and winter season (December in this study) as part of our investigation into the potential uses for space heating, residential hot water, and power supply in northern China. The findings of the experimental research demonstrate that the proposed system can generate electricity and heat at high efficiency during the winter and transitional seasons, with long-term stable performance. The system’s average heating COPt is 5 during the transitional season and 4.4 during the winter season. Meanwhile, the average photovoltaic power efficiency under both weather conditions is 11.9% and 10.2%, with a peak value of 15.7% and 12.0%, respectively. Additionally, the system compression ratio’s variation range is 2 to 3.88, which is lower than the standard heat pump system. As a result, the entire system heating operating process remains constant.

Research on designated calibration method of fault sensor in photovoltaic thermal heat pump system based on fault detection and virtual calibration

With the increasingly serious global energy problem, clean energy sources such as solar energy have become the mainstream focus of development. Among these, solar Photovoltaic thermal (PVT) heat pump systems have promising prospects. However, incorrect data transmitted by sensors can significantly impact the operation and control of the entire heat pump system, leading to reduced efficiency. Given the specific nature of PVT heat pump systems, their internal sensors are prone to errors during operation. To address these challenges, the Autoencoder Virtual in-situ calibration (AE-VIC) is applied to PVT heat pump systems. Preliminary studies have shown that this method can effectively reduce systematic and random errors in sensors. However, the current AE-VIC method faces certain issues, including unclear calibration targets and inefficient calibration of multiple sensors simultaneously, making it difficult to implement in practical systems. In order to overcome the limitations, fault detection is integrated with AE-VIC. By combining the feature extraction capability of Autoencoder with a Softmax classifier, sensors with faults can be identified before the overall calibration process, making the calibration objective of the AE-VIC more targeted. Following fault detection, inputs of the AE model are optimized using the mRMR algorithm for the identified faulty sensors. This optimization alleviates the difficulty of calibration. Through validation with actual system, the improved method effectively diagnoses and locates faulty sensors, and subsequently calibrates them. After calibration, the sensor system error can be reduced by over 95%. The improved calibration method surpasses the original AE-VIC method in terms of both time and accuracy.

Fault detection and calibration for building energy system using Bayesian inference and sparse autoencoder: A case study in photovoltaic thermal heat pump system

Fault detection and calibration for building energy system using Bayesian inference and sparse autoencoder: A case study in photovoltaic thermal heat pump system

Research on the adaptive proportional-integral control method of a direct-expansion photovoltaic-thermal heat pump system

An adaptive proportional-integral control method (APCM) of a direct expansion photovoltaic-thermal heat pump (DX-PVTHP) system is proposed. First, the APCM was adopted and the proportional and integral factors were determined by experiments. Then, a universal engineering model combined the 10-factor model and temperature prediction model is built. The initial electronic expansion valve (EEV) opening during start-up under different working conditions is predicted and the EEV opening under dramatic irradiance changes is corrected under the APCM. Multiple experiments were conducted to evaluate the effectiveness of the APCM and test the performance of DX-PVTHP system under the APCM. The results reveal that the stability of superheat improved under typical cloudy skies and the maximum overshoot value was 3.2 °C. The overshoot time percentage of superheat was 27.54% with a decrease of 36.12% relative to the conventional control method. Moreover, the average coefficient of performance and photoelectric conversion efficiency were 3.51 and 13.25% in household mode, and 3.16 and 13.78% in commercial mode. Furthermore, the comprehensive coefficient of heating and electricity generation (CHE) is proposed to evaluate the comprehensive coefficient of the DX-PVTHP system. The CHE of the system was obtained 34.92% in household mode and 32.83% in commercial mode.

Hybrid PV/T Heat Pump System with PCM for Combined Heating, Cooling and Power Provision in Buildings

Hybrid photovoltaic-thermal heat pump (PV/T-HP) solar energy systems are promising since they can achieve a system total efficiency greater than 80%. By maximizing the output of a PV/T system for simultaneous heating and cooling, this strategy can meet over 60% of urban households’ heating needs and around 40% of their cooling needs. In this work, a novel PV/T evaporator was designed, fabricated, and an aluminium foil encapsulated hydrated salt (HS36) PCM was integrated with the PV/T evaporator of the PV/T direct expansion heat pump system (PV/T-DXHP). Energy analysis was carried out on the PV/T-DXHP system with PCM in tropical climate regions of India for achieving net zero energy buildings. The experimental study revealed that the average PV electricity efficiency was 14.17%, which is near the PV panel’s STC value. The average thermal efficiency of the system was 104.38%, and the PV/T system’s average overall efficiency was 117.58%. The heating and cooling COPs of the system were 5.73 and 4.62, respectively. It was concluded that net-zero energy buildings are possible with the help of photovoltaic heat pump systems that use PCM and solar energy to make electricity, cool spaces, and heat water.

Seasonal performance comparison analysis of the roll-bond photovoltaic thermal heat pump system in a multi-energy generation: An experimental study

Solar photovoltaic thermal heat pump systems contribute significantly to the building industry's goal of energy efficiency and “carbon neutrality” by producing multiple types of energy from the intensive use of solar energy to meet the varied and dispersed energy requirements of modern buildings. An experimental investigation of the roll-bond photovoltaic thermal heat pump system powered by a roll-bond photovoltaic thermal unit is presented in this study, together with the system's precise operating principle and the structural design of the unit. The theoretical underpinnings of experimental research are discussed, including the establishment of test platforms and error analysis, as well as the method for evaluating system performance, which includes solar power, heating, and cooling. Following that, continuous experiment monitoring under various weather conditions in Dalian is carried out throughout the year, which serves as the basis for system performance evaluation and comparison, with a focus on heating, power, and cooling. Comparison analysis results show that the heating and power generation performance in the summer season is the highest, with an average photovoltaic efficiency of 13.6% and an average heating coefficient of performance of 6.16, which is followed by the transition season and winter season, with an average photovoltaic efficiency and heating coefficient of performance of 11.9% and 6.05, 10.2% and 4.54, respectively. However, the performance of power and heating cogeneration in summer conditions fluctuates due to variations in solar radiation intensity. Furthermore, the system can run in cooling mode during the night, on overcast days, and on rainy periods to generate cooling capacity. The cooling performance is the highest during clear nighttime, followed by the overcast nighttime and overcast daytime, with an average cooling coefficient of performance of 2.99, 2.66, and 2.12, separately. Rain, as a cooling water source, significantly improves system cooling performance. The results show that the proposed roll-bond photovoltaic thermal heat pump system can generate high-efficient multi-energy under a variety of weather conditions while remaining stable over time, providing a valuable practical feasibility reference for renewable energy utilization in buildings in northern China.

Heating and power generation characteristics of the vapor injected photovoltaic-thermal heat pump system

The vapor injection compression cycle has been proved that can effectively improve the heating performance of the photovoltaic-thermal (PVT) heat pump system. In this paper, a simulation model of the vapor injected PVT heat pump system (VI-PVTHP) has been established and verified experimentally. The influence law of environmental parameters on the heating and power generation performance of the VI-PVTHP have been clarified. Results show that the coefficient of performance (COP) of the system would increase by about 0.035 under the water heating condition when the ambient temperature increases by 1 °C, and would increase by about 0.041 under the space heating condition. The COP of the system would increase by 0.12 and 0.15 with an average increase of 100W/m2 of solar irradiance under the water heating condition and space heating condition respectively. Additionally, the heating performance of the VI-PVTHP and the conventional PVT heat pump (employing single stage compression cycle) has been compared. Results show that the heating capacity and COP improvement of the vapor injected PVT heat pump system could be higher than 30% and 15% respectively. And the harsher the ambient condition is, the more obvious the heating performance advantage of the vapor injected PVT heat pump system is.

Experimental research on the vapor injected photovoltaic-thermal heat pump for heating, power generation and refrigeration

This paper presents a vapor injected photovoltaic-thermal heat pump system (VI-PVTHP), which can take advantages of the vapor injection (VI) heat pump cycle, significantly increase the heating performance of the system. Not only that, but the VI-PVTHP can also be used for refrigeration by effectively use the PVT modules as condenser of the system. As a result, the system can realize three functions of heating, power generation and refrigeration, and can be used to meet building’s heating, electricity and cooling demands. Then a prototype of the VI-PVTHP was established. Based on the test data of the prototype, the performance and operation characteristics of the VI-PVTHP were analyzed. Results show that the system has good operation reliability and considerable heating, power generation and refrigeration performance during the three working conditions of hot water production, winter space heating and summer night refrigeration. Even on cloudy winter days with ambient air temperatures as low as −8.1 °C, the system can produce domestic hot water of 50 °C with an average COP of 2.59. The VI-PVTHP prototype can continuously and stably produce hot water at the temperature of 40 °C which required for space heating, with an average COP of 2.65. The average EER of the VI-PVTHP prototype was 2.12 during the refrigeration test in summer night. The PVT modules can make good use of night sky radiation and air convection for heat dissipation and is suitable for serving as condenser for heat pump. Radiative heat dissipation to sky is the main way of heat dissipation. During the tests, the heat dissipation flux of the PVT module has reached to ∼650 W/m2.

Operation performance study and prediction of photovoltaic thermal heat pump system engineering in winter

An array arrangement strategy of photovoltaic thermal modules and a connection form of refrigerant pipeline were innovatively proposed by author’s research group. Subsequently, the photovoltaic thermal heat pump system engineering was designed and constructed, and then the performance study of system heating in continuous operation and stage operation in winter was carried out in January 2021. During the system operation, the average coefficient of heating performance of the system was 2.95 in daytime stage operating, 2.55 in nighttime stage operating and 2.07 in continuous operating. To conduct the application simulation of photovoltaic thermal heat pump system, first the prediction model of system heating performance based on back propagation neural network was established and verified according to the operational parameters, then 12 cities of typical climate zone in China were selected to conduct operation simulation and performance prediction to analyze the regional applicability of the system, finally the performance prediction of system heating under variable working conditions was carried out to guide the design calculation of engineering application of photovoltaic thermal heat pump system engineering. It can be concluded that the system was more suitable for engineering application in cities of cold zone and hot summer and cold winter zone than that in severe cold zone. Besides that, the integration and operation optimization of system should be carried out to reduce the average temperature of the circulating hot water tank so that the energy efficiency of hot water system can be improved by 42%.

The effects of multidimensional data clustering on the accuracy of virtual in-situ calibration in the photovoltaic/Thermal heat pump system

Sensor errors have a significant negative impact on the control, diagnosis, and optimisation of building energy systems. The virtual in-situ calibration (VIC) method based on Bayesian inference and the Monte Carlo Markov chain can diagnose and calibrate sensor faults without installing new sensors. In previous studies, the historical data incorporated into the VIC method were typically measured under a certain steady-state operating condition without considering the multiple operating conditions of the system. In an actual photovoltaic/thermal heat pump (PV/T-HP) system, the overall system consists of a variety of operating conditions owing to changes in solar radiation, wind speed, or temperature. A sensor under different operating conditions produces different systematic and random errors, which affect the calibration. To solve this problem, the Gaussian mixture model (GMM) based on probability is applied to pre-process the data of various operating conditions, so that each steady-state operating condition has the same Gaussian distribution to ensure the consistency of errors. To verify the validity of the GMM clustering and the accuracy of the VIC method, four operating conditions are set according to the actual working state. The results indicate that the GMM can be used to cluster these mixed working conditions well, which guarantees the selection of the following steady-state measurements. In addition, the steady-state measurements of different operating conditions are incorporated into the VIC method, the systematic and random errors are reduced by 86% and 42%, respectively. Meanwhile, the systematic error accuracy for large faults increases by 12% (from 86% to 98%) compared with that for small faults after calibration, and the random error accuracy for large faults increases by 38% (from 42% to 80%) compared with that for small faults. In general, the VIC method based on GMM broadens the scope of sensor fault repair and lays a foundation for future applications in actual systems.

Study on energy efficiency and economic performance of district heating system of energy saving reconstruction with photovoltaic thermal heat pump

Actively promoting the reconstruction of clean heating is the key direction of the “Planning for clean heating in winter in northern China (2017–2021)”. The photovoltaic thermal heat pump system was introduced in this paper to improve the comprehensive energy efficiency and reduce the operation energy consumption of the heat source system, which provided a new idea for the energy saving reconstruction of clean district heating. In order to verify the feasibility of the energy saving reconstruction by photovoltaic thermal heat pump, following studies were carried out in this paper: First, the integrated energy system engineering based on photovoltaic thermal heat pump was constructed to study the heating performance of the system in winter. Subsequently, the prediction model of heating performance based on back propagation neural network was established and optimized to simulate the heating performance throughout the year. Then, the calculation model of district heating system was established and the evaluation method of system operation energy efficiency and economic performance based on “equivalent electricity consumption of heating” was introduced. Finally, a residential area of Dalian was taking as an example to study the economic performance of energy saving reconstruction of district heating system based on three conventional heat sources by photovoltaic thermal heat pump. The results showed that after the capacity expansion and energy saving reconstruction based on photovoltaic thermal heat pump were conducted, the payback period of energy saving reconstruction investment was 5 years. Besides, with the increase of the configuration ratio of photovoltaic in the system from 1 to 2, the payback period was further shortened to 3 years.