Heat Pump Water Heater System Research Articles

Study on performance of direct-expansion heat pump water heater integrating uninsulated micro-channel PV/T solar collector

In this paper, a direct-expansion heat pump water heater system integrating uninsulated micro-channel PV/T solar collector is proposed. This system can realize storage for both thermal energy and electricity and complementary grade, ensuring the supply of domestic hot water. Based on the performance of the micro-channel PV/T heat pump water heater system, the theoretical models of micro-channel PV/T solar collector, hot water storage tank, compressor and electronic expansion valve are established where R134a is used as refrigerant. Theoretical simulation and analysis of system performance under different solar radiation intensities, ambient temperatures and different outdoor wind speeds are carried out with MATLAB. The results show that solar radiation intensity has the greatest influence on the system performance, followed by ambient temperature and wind speed. The basic-thermal system performance coefficient (COP) and the advanced system performance coefficient (COPpvt) will be enhanced, while the required operating time will be reduced, as solar radiation intensity and ambient temperature increase. This system removes the thermal insulation for the micro-channel PV/T solar collector that the convection heat transfer on the micro-channel evaporator is enhanced. Therefore, the system can absorb the thermal energy from the ambient air according to different solar radiation intensities, and maintain a high coefficient of performance, electric efficiency, thermal efficiency and overall energy efficiency. Even when the solar irradiation is 322 W/m2 and the ambient temperature is −18.6 °C, the thermal efficiency, electric efficiency and overall energy efficiency of UMC-PVT-SC and COPpvt can still remain at 0.718, 0.2442, 1.341 and 5.63, ensuring the heating capacity and high grade power output capacity.

Multi-objective particle swarm optimization algorithm for data acquisition and system characteristics research of phase change thermal storage heat pump water heaters

In order to understand the multi-objective particle swarm optimization algorithm for data collection and system characteristics research of heat pump water heaters, the author proposes a multi-objective particle swarm optimization algorithm for data collection and system characteristics research of phase change thermal storage heat pump water heaters. The author first introduced the working principle of the phase change heat storage heat pump water heater, and then conducted a comparative experimental study on the performance of two types of heat pump water heater systems using pure paraffin phase change heat storage and water storage. They compared and analyzed the heat storage process, condensation heat recovery rate of the heat storage box, and comprehensive energy efficiency coefficient of the system under the refrigeration and heat recovery mode of the two types of heat pump water heater systems, on this basis, measures were proposed to improve the performance of pure paraffin phase change thermal storage hot water systems. At long last, the examination of exploratory information shows that the Rx of the water warm capacity framework is around 6% higher than that of the stage change warm capacity framework, and the framework COPt is likewise 20% higher than that of the stage change warm capacity framework, from this, it tends to be seen that the stage change heat capacity box has unfortunate intensity move proficiency, prompting a lessening in the presentation of the intensity siphon water radiator framework. Contrasted and customary water stockpiling heat siphon boiling water frameworks, unadulterated paraffin stage change capacity heat siphon high temp water frameworks lessen the volume of the intensity stockpiling tank, and the framework works somewhat flawlessly during the intensity stockpiling process. However, the system?s overall energy efficiency is impacted by the heat storage tank?s poor heat exchange effect and relatively low condensation heat recovery rate. The intensity move of the intensity stockpiling box can be upgraded by finning the winding curls in the intensity stockpiling box, embedding aluminum foil, adding extended graphite, and different measures to further develop the buildup heat recuperation rate, subsequently working on the general execution of the framework.

Energetic analysis and performance improvement algorithm of transcritical CO2 heat pump water heater system

Transcritical CO2 heat pump water heaters have been widely studied by researchers for its environmentally friendly nature and energy efficiency. To analyze the impact of various operating parameters on the heating performance of transcritical CO2 heat pump water heater systems, simulation models were developed and their accuracy was verified through experiments. Results indicated that the discharge pressure and CO2 temperature at the gas cooler outlet (Tgc,out) had a significant effect on the system performance, the coefficient of performance (COP) increased notably with higher evaporation temperatures, and the optimal discharge pressure varied depending on the evaporation temperature. The system equipped with intermediate heat exchanger demonstrated a lower optimal discharge pressure and a higher COP compared to the basic system. The inclusion of an intermediate heat exchanger in a system, the maximum COP is 2.99 % to 3.83 % higher than the basic system under the same conditions. It has been observed that the introduction of intermediate heat exchanger significantly improved the system performance when Tgc,out were 35 °C, 40 °C and 45 °C, corresponding to discharge pressures lower than 10.75 MPa, 11.167 MPa and 11.625 MPa. According to the research results, the optimal discharge pressure equation was fitted and an improved algorithm was proposed. Compared to the experimental values, the improved algorithm exhibits a maximum error of 8.81 % and 7.55 % for determining the optimal discharge pressure and temperature, and the improved algorithm is effective in engineering applications. Consequently, the simulation data holds great importance in guiding the design of transcritical CO2 heat pump water heater systems.

Self-optimized efficient operation of trans-critical CO2 ejector-expansion heat pump water heater system with two-stage evaporation

In application scenarios with lower ambient temperatures and higher sink temperatures, the trans-critical CO2 heat pump water heater system using an ejector instead of a conventional expansion device offers better performance, and the higher pressure differential allows for partial pressure loss recovery through the ejector. However, the complexity of discharge pressure and ejector matching affects the further application of the system. Therefore an optimization method called Extremum seeking control method is proposed to achieve the lowest power consumption implementation under off-design conditions. The ESC controller applied to the system uses the compressor power consumption as the feedback signal and the discharge pressure is used as operating input set-point. The dynamical model of a trans-critical CO2 heat pump water heater built on Modelica/Dymola is used as the study object and optimized for three scenarios: fixed, sloped step profile, and actual ambient temperature. The simulation results show that the ESC applicable to the proposed system can optimize the matching of discharge pressure and ejector driving nozzle throat area to obtain the best performance. Compared with the benchmark system, the extremum seeking control for actual ambient temperature conditions results in a 5.7% increase in system efficiency.

Applicability evaluation of internal heat exchanger in CO2 transcritical cycle considering compressor operation boundaries

CO2 transcritical cycle has been widely promoted as a green energy utilization technology. Internal heat exchanger (IHX) is under consideration for cycle efficiency improvement. However, the interaction between IHX and compressor in CO2 cycle has not yet been fully explored. In this regard, compressor operating boundaries are introduced as constraints to IHX applicability evaluation in CO2 cycle. It indicates that considering compressor limits, IHX can either benefit or attenuate the CO2 cycle performance, depending on operating conditions. By reducing optimal discharge pressure, IHX helps CO2 cycle avoid the upper pressure limit, further improving performance by 5%. Over a wide range, however, IHX increases compressor discharge temperature, indirectly resulting in up to 50% performance degradation. The major factors affecting the duality of IHX in CO2 cycle are compressor discharge temperature limit, IHX efficiency and motor heat loss. Finally, performance-oriented IHX design guidelines for mainstream single-stage CO2 applications are provided. For automotive air conditioner, optimum IHX efficiency improves cycle performance by up to 30% in cooling mode. By contrast, IHX contribution is negligible in heating mode. For heat pump water heater and refrigeration system, both can benefit from IHX, particularly when compressor discharge temperature tolerance is high.

Experiment study on startup characteristics and operation performance of PV/T solar assisted heat pump water heater system driven by direct current variable frequency compressor

The use of renewable energy can alleviate climate warming and environmental pollution. PV/T (photovoltaic/thermal) system has been widely concerned and rapidly developed owing to its capability of generating electric and thermal energy simultaneously. In the article, a PV/T solar assisted heat pump water heater system driven by direct current variable frequency compressor was proposed to meet the growing needs of residents for domestic hot water. This system was tested in different working conditions in Lanzhou, and the startup characteristics and operation performance were evaluated. The results indicate that at the same ambient temperature, low speed is conducive to the continuity of the refrigerant cycle and improves the system performance. In this system, the initial water temperature of the water tank was 23.1 °C and after 2.5 h it reached 53 °C. The average power generation efficiency is 13.64%, the average thermal efficiency is 26.42%, the overall efficiency is 62.69% and the average COP (coefficient of performance) is 4.87. Compared with traditional PV (photovoltaic) modules, the average temperature reduction is 11.2 ℃. With the increase of solar radiation intensity, the electrical power of the system will increase and the electrical efficiency will decrease. The average daily electrical efficiency of PV/T system is 13.64%, which is 6.25% higher than that of uncooled PV panel. In addition, controlling a proper compressor speed is crucial for enhancing system performance. The PV/T collector can remarkably reduce the temperature of PV panel, improve power generation efficiency and comprehensive utilization efficiency of solar energy.

Experimental Performance Analysis of Ejector Heat Pump-Water Heater Under Transient Conditions

Net-zero energy buildings are on the agenda of international community due to reducing energy consumption in the building, thus dropping carbon emissions and negative environmental effects. One of the solutions is to utilize heat pumps to decrease energy consumption in the building. In this study, the idea of ejector utilization in a heat pump system was investigated in an experimental test facility by comparison to a conventional heat pump system (without an ejector). The experimental facility, which utilizes hot and cold water as the heat source, can operate in two modes: The ejector heat pump water heater (EHP-WH) and heat pump water heater (HP-WH). The system was tested in transient conditions and the effect of ejector utilization on the system was determined. Results indicate that EHP-WH mode (COP between 5 and 6) had an average of 5.5% higher COP value than HP-WH mode (COP between 4.5 and 5.5). Furthermore, the heating capacity obtained in EHP-WH mode was 30% higher than in HP-WH. Additionally, the water cooler loop’s water temperature was 64.5% higher in EHP-WH mode than in HP-WH. Finally, it is determined that the ejector positively impacts on the performance of HP-WH system.

Assessment of Optimal Operating Range and Case Verification of a Waste Heat Air-Source Heat Pump Water Heater Based on a Semiempirical Parametric Model

Waste heat air-source heat pump water heater (WH-ASHPWH) systems have been widely used to provide water heating in buildings due to their advantages of high efficiency and low environmental impact. It is important to determine reasonable operating conditions for WH-ASHPWH systems to improve their heating efficiency, especially for systems using industrial waste heat. In this study, a semiempirical parametric model of a WH-ASHPWH system was established to simulate heating performance under different working conditions and determine the optimum operating range of the system. A new discrete model for a tube-in-tube condenser was also generated. Taking the equipment of a pharmaceutical factory as an example, the heat exchanger model was first calibrated; then, the global model was used to study the effects of different air-side and condenser-side waste heat conditions on the heating performance of the system. According to the simulation results, the coefficient of performance (COP) reached a maximum value of 4.5 under the optimum working conditions. The deviation between the COP simulation data and experimental values was less than 8.28%, and the simulation time was less than 8 min. These metrics indicate that the model is reasonable and efficient.

A new moving-boundary algorithm to predict heat transfer rate of counter-flow water-cooled transcritical CO2 gas cooler

A new moving-boundary model was proposed for predicting steady-state heat transfer rate of water-cooled transcritical CO2 gas cooler. The new model aims to separate the CO2 gas cooler into up to three zones depending on the local thermal capacitance rate, which is significantly different from the moving-boundary models used in subcritical region, which is based on fluid phase. The experimental data from the literature were used for model validation, and the results show that the prediction accuracy of the new moving-boundary model is comparable to that of the finite volume method. The deviations between predicted and measured heating capacities are within ±5%, and the predicted CO2 outlet temperatures are within ±4°C. The averaged computation time of the model is 22% of that of the finite volume model for the 45 data points in the present study. The proposed new model is suitable for steady-state simulation of transcritical CO2 water-cooled gas cooler, either standalone or integrated into overall CO2 heat pump water heater systems.

Energy, economic, and environmental (3 E) examinations of the indirect-expansion solar heat pump water heater system: A simulation-oriented performance optimization and multi-objective decision-making

In this paper, a simulation-oriented optimization integrated with the multi-objective decision-making (MODM) model for an indirect-expansion solar-assisted heat pump (IDX-SAHP) water heater is proposed and the energy, economic, and environmental (3 E) aspects of the system are examined. The developed model is verified and its performance is scrutinized in a humid continental climate region of China. Next, the sensitivity analysis is conducted via the one-way analysis of variance (ANOVA) approach. Then, the single-objective optimization (SOO) and multi-objective optimization (MOO) are conducted via the migrating birds optimization (MBO) method to maximize the coefficient of performance (COP) and the collector efficiency (CE), singly and concomitantly. The SOO results indicate the IDX-SAHP design as per the COP-oriented optimization causes the system to operate less for about 120 hours a year in contrast to the system design as per the CE-oriented optimization. Also, the results of MOO integrated with MODM indicate that MOO gives better performance in contrast to the SOOs so that although the CE of the maximized IDX-SAHP reduces a little from 51% to 46%, its COP increases greatly from 2.5 to 7. Therefore, the overall power consumption of the system decreases about 269 hours in contrast to the initial IDX-SAHP. Besides, the environmental examination illustrates the use of IDX-SAHP in Beijing buildings can prevent the burning of 2,877, 000, 000 cubic meters of natural gas per year in the fossil fuel power plants and prevent the release of 8,055,600 tons of CO2 per year into the environment. Furthermore, the economical examination illustrates that Beijing residents may save approximately one billion USD per year on the purchase of electricity if they use the IDX-SAHP. Besides, the Chinese government can achieve about 109 billion USD per year if the equivalent electricity is exported instead of domestic consumption for Electric Water Heaters (EWHs). Moreover, the external costs decrease by 928 million USD per year if the IDX-SAHP is replaced with the EWHs. This paper discloses the significance of energy, economic, and environmental (3 E) examinations, optimization, and MODM during the IDX-SAHP design to increase the system efficiency and decrease the costs and environmental impacts by opting the most appropriate design parameters of the system.

Field Measurement of Central CO2 Heat Pump Water Heater for Multifamily Retrofit

Domestic hot water heating of multifamily buildings accounts for a substantial portion of the energy load of existing buildings. This load is made up of both the energy required to produce hot water and the energy needed to maintain the temperature of the heated water within a building’s distribution piping so that heat can be promptly delivered to building occupants as needed. Properly designed heat pump water heater (HPWH) systems have the ability to improve efficiency in both water heating and temperature control operations. Further, CO2 heat pump technology reflects a shift away from traditional refrigerants and toward refrigerants with low global warming potential (GWP). In this paper’s case study, a design consisting of multiple CO2 heat pump water heaters (commonly used in single-family homes) with a novel “swing tank” was proposed to meet the demand for domestic hot water heating and recirculation loop temperature maintenance. The proposed design was applied to the retrofit of a 60-unit, low-rise, multi-family building located in the Pacific Northwest of the United States. The purpose of this paper is to verify the performance of the system including the proposed “swing tank” in a centralized SHW system using CO2 HPWH. It also provides practical information and lessons learned from the retrofit project. Long-term monitoring data showed that the system had a coefficient of performance (COP) of three or greater and provided an average of 20 gallons of hot water per day per apartment. The results of this work indicate that residential-scale CO2 HPWH equipment and a “swing tank” design can efficiently provide domestic hot water heating and temperature maintenance for mid-sized multifamily buildings.

Energy, exergy, economic and environmental analysis of photovoltaic/thermal integrated water source heat pump water heater

The photovoltaic thermal integrated water source heat pump (PV/T-WSHP) water heater system can meet the demand for not only the domestic hot water but also the electricity production. To comprehensively analyze the benefits of the PV/T-WSHP water heater system, energy, exergy, economic and environmental analysis method was applied. A TRNSYS model of the PV/T-WSHP water heater system was developed based on the existing experimental setup, and validated by the experimental data. A combined system of single PV system and single air source heat pump water heater (PV + ASHP) system model was also built for comparison. The simulated results indicated the PV/T-WSHP water heater system had a 25.3% improvement in electrical conversion efficiency, a slightly lower EER of 3.71 and a significant reduction in annual exergy loss, comparing with the combined PV + ASHP system. In addition, the annual cost of the PV/T-WSHP water heater system was 217.7 yuan lower than the combined PV + ASHP system. The PV/T-WSHP heat water system and the combined PV + ASHP system could annually save the standard coal of 0.62 tons and 0.50 tons, respectively. This study provides an effective method to comprehensively analyze the performance of the PV/T-WSHP water heater system.

Performance analysis on parallel condensing air-source heat pump water heater system

Based on the technology of heat pumps, a parallel condensing air-source heat pumps water heater systems providing domestic hot water is proposed to improve the energy efficiency of common ASHPWH system. Considering the climate in southern China, two operating modes of system are designed to adapt to the different water temperature conditions. the simulation model was built to analyzed the factors affecting system performance. Taking Changsha, China as an example, the COP and the energy consumption of system in each month are analyzed. We can find that the parallel condensing air-sources heat pumps water heater system can effectively disperse the total heating quantity by steps heating; the average COP in summer mode increases from 5.42 to 6.44, approaching 19.00%; the average COP in winter mode increases from 4.05 to 5.45, approaching 34.68%. The system has excellent energy-saving effect especially in winter.

Numerical Investigation on the Performance of Two-Throat Nozzle Ejectors with Different Mixing Chamber Structural Parameters

In this study, the effects of the mixing chamber diameter (Dm), mixing chamber length (Lm) and pre-mixing chamber converging angle (θpm) were numerically investigated for a two-throat nozzle ejector to be utilized in a CO2 refrigeration cycle. The developed simulated method was validated by actual experimental data of a CO2 ejector in heat pump water heater system from the published literature. The main results revealed that the two-throat nozzle ejectors can obtain better performance with Dm in the range of 8–9 mm, Lm in the range of 64–82 mm and θpm at approximately 60°, respectively. Deviation from its optimal value could lead to a poor operational performance. Therefore, the mixing chamber structural parameters should be designed at the scope around its optimal value to guarantee the two-throat nozzle ejector performance. The following research can be developed around the two-throat nozzle geometries to strengthen the ejector performance.

Performance Assessment of Zeotropic Mixtures for Heat Pump Water Heaters

The subcritical cycle performances of eco-friendly pure refrigerants and zeotropic mixtures for heat pump water heater systems were performed by MATLAB programs. The results indicated that pure refrigerants are often restricted in meeting criteria such as environmental protection, efficiency, and flammability. The optimal compositions of R13I1/R161/R32, R13I1/R290/R32, and R13I1/R152a/R32 zeotropic mixtures are observed at 0.5/0.3/0.2, 0.15/0.65/0.2, and 0.3/0.5/0.2 (by mass), whose temperature glides are 6.2°C, 14.3°C, and 6.7°C under the given operating conditions, respectively. Meanwhile, the optimum heating coefficients of performance (COPs) are up to 5.04, 4.83, and 5.11, resulting in 10.5%, 5.9%, and 12.1% increments, respectively, compared to R22. However, the COP of R13I1/R1270/R32 exhibits a decreasing and then increasing trend with the rise of the R13I1 mass concentration. The volumetric heat capacities of R13I1/R161/R32 (0.5/0.3/0.2), R13I1/R290/R32 (0.15/0.65/0.2), and R13I1/R152a/R32 (0.3/0.5/0.2) blends yield 121.9%, 116.9%, and 94.1% of the R22 system, respectively. On the other hand, the mixtures are significantly superior in terms of lower pressure ratios, discharge temperatures, and irreversibilities of systems in comparison with R22. Furthermore, the operating pressures of blends are similar to that of R22. Consequently, it is concluded that these three zeotropic mixtures can be superior alternatives to R22 and R134a for heat pump water heater applications.

Transient refrigerant and oil distribution in a residential heat pump water heater system: Experiments and model

• Transient refrigerant and oil retention in a heat pump water heater are measured. • Models are built to predict refrigerant and oil retention in two heat exchangers. • Models are validated against the experimental data. This paper presents an experimental and numerical investigation of the transient refrigerant and oil distribution in a residential heat pump water heater (HPWH) system. In the experiments, R134a is paired with POE 22 oil. The quick closing valve technique (QCVT) is used to trap the refrigerant and oil in each section of the system. The trapped refrigerant mass is measured after recovered by liquid nitrogen. The retained oil mass in each section, except for the compressor, is determined by the mix and sample technique (MST). Five experiments are conducted to cover a full warm-up of five hours. The experimental data shows that most of the refrigerant is in the heat exchangers. During the water warm-up, the inventory of the refrigerant generally decreases in the evaporator, while in the condenser, it decreases in the first three hours and later increases. The measurements also indicate that most of the oil stays in the compressor and the escaped oil is mainly retained in the heat exchangers. Besides, a model is developed to predict the refrigerant and oil retention in the heat exchangers by applying the mixture vapor quality to calculate the void fraction. The developed model predicts the refrigerant inventory in the condenser with an average deviation of 7.4%, and in the evaporator, 9.1%. The average deviations in the predictions of the oil retention in the two heat exchangers are 15.8% and 10.2%.

Study on the operating characteristics of a solar heat pump water heater based on data fusion

To improve the operating performance of a heat pump system, experimental data obtained from a solar integrated air source heat pump (SIASHP) water heater system were analysed in detail. With the information integration and decision-making abilities of data fusion, the all-weather operation strategies of the system were newly proposed. These new strategies comprehensively considered the solar radiation intensity, air temperature, energy dissipation, and COP. According to the relative magnitudes of the solar radiation intensity and air temperature, the system performed reasonably in different modes, ensuring its efficient operation under all weather conditions. Then, the annual costs of the system in five cities located in regions with various solar radiation intensities were analysed and compared. It was concluded that the maximum savings achieved by the system were $86.5/yr and $225.3 per year compared with gas and electric water heaters, respectively, indicating the system is cost-efficient and promising. Furthermore, the operating performance of the switched mode was optimized based on a regression algorithm. When the solar radiation intensity was poor and the temperature of heated water rose to 34 °C, the air source evaporator was switched to a solar evaporator. In addition, the COP of the system was 3.023, equal to 97% of the COP of a solar energy heat pump (SHEP) water heater with a sufficient solar radiation intensity. Therefore, the optimized scheme can compensate for the inefficient operating conditions under a weak solar radiation.

Study on Heat Transfer Performance of Phase Change Thermal Storage Heat Pump Water Heater with Carbon Nanotubes

To explore the feasibility of applying carbon nanotubes (CNTs)/paraffin composites to heat pump water heater system, heat transfer characteristics of phase change thermal storage heat pump water heater were analyzed and discussed. It was shown that the melting and solidification rates of nanocomposite were significantly improved upon the addition of CNTs nanoparticles, and the heat pump heat water with thermal storage has good stability in heat storage and release process. There are some differences in the distribution of temperature field in phase change thermal storage system, especially in exothermic stage. Thermal “stagnation” occurs near the corner of the outlet of water medium, so it is necessary to increase the amount of materials appropriately. Compared with traditional regenerative heat pump water heater with water tank, volume of regenerator of heat pump water heater is reduced by about 1/2 with the addition of nano-composites, and the thermal efficiency can reach 86%. The running experimental results of heat pump water heater suggests the reliability of designment of the thermal energy storage and the feasibility of CNTs/paraffin using in the heat pump water heater. The temperature of CNTs-paraffin composites rises faster and the heat transfer time is shorter at higher ambient temperature. Obviously, ambient temperature has a significant impact on the property of heat pump system.

Experimental study of the thermal performance of a novel plate type heat exchanger with phase change material

The paper presents an experimental investigation of a novel latent heat thermal energy storage system. The new energy storage unit is a pillow plate type heat exchanger with multi flowing channels, while the phase change material (PCM) - sodium acetate trihydrate (SAT) works as the energy storage medium. Water as the working fluid, flows in the distributed channels inside the plates to charge or discharge the system. The thermal performance of the latent heat thermal energy storage system was evaluated, including the outlet temperature of water, thermal power and energy, effectiveness and heat transfer coefficient. Results from the experimental analysis showed that the released energy of system can reach up to 6.3 MJ with the average power 4 kW. The overall heat transfer coefficient and heat transfer area ranges from about 25 to 70 W/k from 100 to 500 L/h flow rate. The pillow plate type heat exchanger showed good thermal performance, offering high heat transfer rate under the compact structure. Also, the novel multi flowing channels designed heat exchanger provides more flexibility and adaptability for real application, it has a wide application prospect in the fields of solar water energy storage, heat pump water heater system and waste heat recovery system.

The Influence of Internal Heat Exchanger on the Performance of Transcritical CO2 Water Source Heat Pump Water Heater

The characteristics of the transcritical CO2 heat pump water heater (HPWH) system are; a lower inlet hot water temperature (Ti-hw) (sometimes this is lower than the water source temperature), and an outlet gas cooler temperature (To-gc) which is affected by the Ti-hw and often lower than the critical temperature. In order to study the effects of the internal heat exchanger (IHX) on the operational performance of the transcritical CO2 HPWH when To-gc is low, a transcritical CO2 water source HPWH experiment platform is established to conduct experimental research and comparative analysis on the operational performance of the transcritical CO2 water source HPWH, with or without IHX. It is found that, if only the coefficient of performance (COP) and heating at the optimal exhaust pressure of the transcritical CO2 water source HPWH were considered, COP and the heating of the non-IHX system would be slightly higher than those of the IHX system at the lower hot water flow and water source temperature, and this increase was not obvious. At the higher hot water flow rate and water source temperature, COP and the heating of the non-IHX system were also higher than those of the IHX system, and the increase was obvious. The experiment results showed that, near the optimal exhaust pressure, the variation range of COP and heating of the IHX system is relatively small, and the system has a relatively high stability.