Annual Performance Factor Research Articles

Transcritical CO2 system with two-stage throttling for supermarkets: Field tests, energy and emission performance assessment in China

Transcritical CO2 system is eco-friendly for the application of refrigeration and cooling in supermarket. To evaluate the applicability of transcritical CO2 supermarket refrigeration system in China with different climate regions, this study focuses on the field tests of a transcritical CO2 two-stage throttling system in a supermarket in Suzhou, Jiangsu Province, China. Furthermore, based on the tested data, the system energy and emissions performance models of four system configurations are also developed and validated, including the system integrated with an internal heat exchanger, a parallel compression, and mechanically assisted subcooling. In order to improve the usability of the system in different climatic zones, 40 cities were selected for calculation in China. Five representative cities (Beijing, Harbin, Xiamen, Chongqing, and Kunming) located in different climate regions of China are selected, and the annual performance factor and life cycle climate performance (LCCP) are determined to evaluate the application potential of the CO2 refrigeration systems in different climate conditions. The tested results show the operation mode of transcritical and subcritical changes occurs at an ambient temperature of about 27 °C, at which the coefficient of performance (COP), compressor discharge pressure and discharge temperature change dramatically. The simulation results demonstrate that the mechanical subcooling system shows the best performance. The annual performance factor can be improved by 18.69 % when the mechanical subcooling is adopted. For the case of the system used in Xiamen by using mechanical subcooling, the carbon emissions can be reduced by 19.3 %.

Assessment of booster refrigeration system with eco-friendly working fluid CO2/halogenated alkene (HA) mixture for supermarket application around the world: Energy conservation, cost saving, and emissions reduction potential

For the scope of commercial supermarkets, the demand for energy efficiency improvement and environmentally-friendly working fluid of the refrigeration system is necessary. In this study, supermarket booster refrigeration system by using eco-friendly working fluid CO2/halogenated alkene (HA) mixture is proposed, and the mixture used in systems with two evaporation temperatures and operating modes affected by ambient temperature are studied. The energy efficiency, economic performance and emission reduction potential of the whole life cycle are conducted to compare with the pure CO2 booster refrigeration system. Furthermore, the influence of climate condition is discussed when used in 40 typical cities around the world. The results show the coefficient of performance (COP) of booster refrigeration system can be significantly improved by using CO2/HA mixtures. As the ambient temperature is 33 °C, the CO2/R1234yf (93/7) operates with the maximum COP of 1.367, which is 11.59 % higher than that of pure CO2. Using CO2/HA mixtures in the booster refrigeration system can significantly improve the exergy efficiency of system. Moreover, the system using CO2/HA mixtures has higher annual performance factor and lower life cycle cost (LCC) than pure CO2. LCC of the system using CO2/R1234yf (94/6) is the lowest, and the reduction rate is 3.06–5.59 %. Meanwhile, the life cycle carbon emissions of systems in different climatic regions using CO2/R1234yf can be reduced by 2.39–5.21 %. The booster refrigeration system adopting CO2/HA mixtures is a promising alternative solution for commercial supermarket refrigeration and energy-saving.

Improving performance of air conditioning system by using variable-circuit heat exchanger: Based on the Chinese APF standard

For finned-tube heat exchangers, owing to the extremely different refrigerant pressure drop characteristics between condensation and evaporation processes, the optimum refrigerant circuits of these two conditions are different. However, for a typical heat pump type air conditioner, refrigerant circuit of the conventional heat exchanger (CHX) is fixed no matter what operation condition is conducted. To solve this problem, a modified variable-circuit heat exchanger (VCHX) is developed for air conditioner outdoor unit applications. The VCHX, for which the refrigerant circuit can be easily switched by using a globe valve, could provide better matching characteristics between refrigerant circuit and operation condition variations. With a developed simulation model, refrigerant circuit of the VCHX is optimized by using the entropy generation minimization theory. Then, comparative experimental works were conducted to investigate the performance of VCHX and CHX systems in detail. Experimental results show that the presented VCHX is more suitable for high heating capacity and low cooling capacity applications. Based on the Chinese APF (annual performance factor) Standard, the VCHX system yields 6.5% higher APF value over CHX system. Significantly, economic analysis indicates that the investment payback period of VCHX system is 1.46 year, which is much lower than the designed lifetime of a residential air conditioner. In general, the VCHX technique has a great application potential for improving the overall performance of a heat pump type air conditioner.

Dynamic modelling of a dual-source heat pump system through a Simulink tool

In this paper, the performance of a reversible Dual-Source Heat Pump (DSHP) system, able to exploit renewable energy from, alternatively, air and ground sources, is evaluated by using Matlab-Simulink. The actual source exploited depends on a simple control strategy on the basis of the current external air temperature. Yearly dynamic simulations have been carried out by coupling the DSHP to a detached residential building located in Bologna, in which heating and cooling loads are strongly unbalanced, and coupled to a Borehole Heat Exchangers (BHEs) field. Different case studies have been analysed in which the length of the borefield has been modified. The obtained results show that an optimal switching temperature can be determined to maximise the Annual Performance Factor (APF) for a fixed BHE field length. Additionally, it has been demonstrated that DSHPs can be very useful in order to reduce the total required length of the borehole heat exchangers and, consequently, the associated costs, and to solve the problems linked to the ground temperature drift, which can be originated by the presence of an undersized borefield and/or by unbalanced building loads. As a consequence, DSHPs can be suggested for the retrofitting of traditional ground-coupled heat pump systems in presence of undersized BHEs.

Hybrid solar energy and waste heat driving absorption subcooling supermarket CO2 refrigeration system: Energetic, carbon emission and economic evaluation in China

A novel hybrid solar energy and waste heat driving absorption subcooled carbon dioxide (CO2/R744) booster refrigeration system (SE + WH) is proposed to improve the energy efficiency of the traditional CO2 refrigeration system used in supermarkets. The thermodynamic and energy conversion model of the system is established. Then, the optimization method of the two-dimensional golden section search algorithm is introduced to optimize the system energy efficiency taking the variation of ambient temperature and solar radiation intensity into account. Moreover, considering the maldistribution of solar energy and the influence of meteorological conditions in China, eight typical cities are selected to assess the annual performance factor and life cycle carbon emissions to achieve energy saving and carbon emission potentials. The performance of hybrid solar energy and waste heat driving absorption subcooled CO2 booster refrigeration system is the best with the COP enhanced by 3.05–42.30 % at the solar radiation intensity of 1200 W/m2 and the temperature of 0–35 °C in contrast to the baseline system. In addition, the discharge pressure of the new proposed hybrid system can be reduced by 7.86 % when the ambient temperature is 34 °C. The annual performance factor of the new proposed hybrid system in Haikou can be increased by 14.47 %, and the life cycle carbon emissions are effectively reduced by 39.54 %. The payback period is also reduced by 4.01 % and 3.37 % for Beijing and Shanghai. Consequently, the novel configuration of the hybrid absorption subcooling subsystem is recommended, particular in hot or warm climate areas with rich solar energy.

Effect of reversely-variable circuitry on finned-tube heat exchanger performance in air source heat pump under annual performance factor (APF) conditions

The finned-tube heat exchanger (FTHX) in air-source heat pumps (ASHPs) shows a contradiction that the evaporator prefers more circuits while the condenser likes fewer. Hence, the reversely-variable circuity is proposed in our previous work to address this problem by incorporating the respective optimal circuits for the FTHX in both modes. In this article, the reversely-variable circuitry is adopted to maintain 7 circuits in the evaporator mode but 4-2-1 flowpath (4 circuits merging into 2 then 1) in the condenser mode of the outdoor FTHX. Compared with the original 7-circuit reversely-fixed one, the reversely-variable FTHX yields 2.1% higher annual performance factor (APF) for the ASHP due to higher capacity and COP in all 6 cooling conditions, when the outdoor FTHX is used as the condenser and the fewer circuits increases the overall heat transfer coefficient. Moreover, the performance enhancement with the reversely-variable FTHX is higher in lower-temperature ambience and part load conditions, since refrigerant flowrate is lower and the increment in overall heat transfer coefficient is more dominant. Different possible transformations of the reversely-variable circuitry is obtained with the principles of single-way valves and distributors described, so that it could be popularized to wider applications.

Optimization on annual energy efficiency of heat pumps based on maximum solving of definition functions with multi constraints

Air conditioners is expected to be the second largest source of growth in global electricity demand. To promote electrification, heat pump air conditioner is encouraged to replace natural gas furnace. Improving heat pump’s energy efficiency can help reduce global energy consumption and greenhouse gas emissions. Annual performance factor is one of the key metrics to evaluate heat pump systems’ energy performance. Seeking annual performance factor maximum belongs to an optimization problem with multi constraints. However, due to the nested variables, continuous non-differentiable and piecewise form of annual performance factor definition functions, the optimized objective function is usually based on the simplification with large errors. Meanwhile, the multi constraint boundaries are either ignored or considered but through complicated and high-cost tests. In this research, the variable iteration logic of the annual performance factor definition functions is sorted firstly. Then the above exact mathematical definitions are programmed as the objective functions without any simplification. Enumeration method is used to establish the annual performance factor maximum solution algorithm. More importantly, taking a 3.5 kW cooling capacity mini-split heat pump prototype as an example, energy performance tests are conducted to fit the multi constraints, namely using less global parameters to cover more local parameters, which greatly simplifies the test procedures and cost. Then, using our proposed method, the maximum annual performance factor is predicted and validated by experiments. The prediction accuracy is 99.6%, with a 38.4% improvement compared to the best reported value from literature. Based on the recommended variable values, the prototype’s annual performance factor achieves the maximum with a 7.71% improvement from the baseline. The proposed method can save time and experimental resources in the product development stage compared with the traditional trial and error method.

Annual energetic evaluation of multi-stage dedicated mechanical subcooling carbon dioxide supermarket refrigeration system in different climate regions of China using genetic algorithm

Supermarket is the main carbon producer due to the requirement of food refrigeration and freezing. In order to realize cleaner production, three configurations of carbon dioxide booster refrigeration system integrated with multi-stage dedicated mechanical subcooling (DMS) applied in commercial supermarkets in different climate regions of China are proposed in this study. Thermodynamic and cooling load models are established to study the energetic operation performance of proposed systems. The energy efficiency of the systems is optimized employing the method of genetic algorithm with the optimization variables of subcooling degree, discharge pressure and intermediate pressure. Meanwhile, the baseline, single-stage DMS and R404A refrigeration systems are compared with the multi-stage DMS systems. Results indicate that the coefficient of performance of the three-stage DMS system is 1.12–28.84% higher than the baseline system at the ambient temperature of 0–40 °C, and it also operates at the lowest discharge pressure. Furthermore, a switch parallel compression is added to get high energy efficiency in different ambient temperature ranges, which is compared with the R404A refrigeration system that is one of the extensively used in Chinese supermarkets. The annual performance factor of the three-stage DMS system combined with a switch parallel compression is 10.92% and 7.62% higher than the R404A refrigeration system and baseline system in Haikou, respectively. Consequently, a carbon dioxide booster refrigeration system integrated with a multi-stage DMS system can achieve a prominent performance especially for a three-stage DMS system, which can overcome the drawback of the lower efficiency of the baseline system in hot and warm regions. A multi-stage DMS system is a promising solution for commercial supermarket refrigeration and socially sustainable development.

Alternative positions of internal heat exchanger for CO2 booster refrigeration system: Thermodynamic analysis and annual thermal performance evaluation

• Three CO2 booster systems with different locations of IHX are proposed. • Thermodynamics models of booster systems are developed and annual performance is studied. • S1 is the optimal solution system to improve COP, which is enhanced by 0.6% - 6.36%. • By adding IHX, the APF of CO2 booster system can be improved significantly. • IHX can improve annual performance in subtropical and tropical climatic regions. Refrigeration systems running on transcritical CO 2 cycle are considered an alternative to phase-down the use of hydrofluorocarbons (HFCs) in response to the Kigali Amendment. Responding to the need to improve the efficiency of CO 2 booster systems and to identify optimum system designs, thermodynamic models of three booster systems are proposed with the use of an internal heat exchanger (IHX). Findings from this study suggest that placing the IHX with a low-temperature fluid side at the suction line of high pressure stage compressor and high-temperature fluid side at the outlet of gas cooler represents the most optimal approach in improving the coefficient of performance (COP) of the booster system. When operating in the transcritical conditions, the COP values can be improved by 6.35% at the IHX thermal effectiveness of 0.8 and by 6.48% at the ratio of medium temperature load to low temperature load of 6. Using IHX can significantly reduce the compressor discharge pressure, which can be reduced by 0.55 MPa at the ambient temperature of 40 °C. Furthermore, by adding IHX, the annual performance factor of CO 2 system can be improved significantly by 1.68% and the annual total power consumption can be decreased by 6.48% in the tropical climate. It can be concluded that IHX can improve the COP values of a booster system when operating in the subtropical and tropical regions.

Monitoring and aggregate modelling of an existing neutral temperature district heating network

This contribution provides preliminary modelling results and data analysis of an existing neutral-temperature district heating (NTDH) network. The word ”neutral” in this context refers to the fact that the distribution temperature is close to the ambient temperature (e.g., 15–20 °C). This type of network is coupled with decentralized heat pumps (HP), for both heating and cooling. They offer the advantage of being reversible and the possibility of integrating low-temperature waste heat. The considered case is located in Ospitaletto, Italy. The network includes two sources (industrial waste heat at about 25 °C and ground source heat from aquifer wells at about 15 °C), it is mainly built with non-insulated pipes and has a length of approximately 2 km. Decentralized HPs installed at user substations provide the proper temperature for space heating and sanitary hot water production.An approximate model was applied to analyse the network operation. This model is focused on energy balances aggregating all users as a lumped demand and explicitly includes the behaviour of HPs substations, a component not available in other district heating analysis tools. The simulation of an entire year of operation is considered, with an hourly resolution. Thermal load profiles are known and used as input to the model, while the outputs are compared with real data -a combination of weekly and hourly measurements at the users substations-which include annual heat supply, electricity consumptions, thermal losses, and seasonal performance factor (SPF). The results yield an overall deviation of 15% in the main indicators when using pre-defined data. In conclusion, even though the measured SPF is slightly lower than expected, the model reaches a reasonable agreement.

Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid

Given the large demand nowadays for domestic hot water, and its impact on modern building energy consumption, air source transcritical CO2 heat pumps have been extensively adopted for hot water production. Since their system efficiency is limited by significant irreversibility, a CO2-based mixture could offer a promising drop-in technology to overcome this deficiency without increasing system complexity. Although many CO2 blends have been studied in previously published literature, little has been presented about the CO2/R32 mixture. Therefore, a proposed mixture for use in transcritical CO2 heat pumps was analyzed using energy and exergy analysis. Results showed that the coefficient of performance and exergy efficiency variation displayed an “M” shape trend, and the optimal CO2/R32 mixture concentration was determined as 0.9/0.1 with regard to flammability and efficiency. The irreversibility of the throttling valve was reduced from 0.031 to 0.009 kW⋅kW−1 and the total irreversibility reduction was more notable with ambient temperature variation. A case study was also conducted to examine domestic hot water demand during the year. Pure CO2 and the proposed CO2 blend were compared with regard to annual performance factor and annual exergy efficiency, and the findings could provide guidance for practical applications in the future.

Analysis and determination of a seasonal performance evaluation for air source heat pumps

Performance evaluations of heat pumps play an important role in regulating energy markets and promoting energy conservation technologies. The development of air source heat pumps (ASHP) standards, especially seasonal performance factors including the annual performance factor (APF) method and integrated part-load value (IPLV) method, are reviewed for applications worldwide and in China. Based on the reviews, this study introduces and analyzes the methods of evaluating the seasonal performance of ASHPs by analyzing and proposing principles and key factors of seasonal performance evaluations, including building load models, operational period distributions (bin hours), and ASHP performance models. Then, The similarities and differences between the APF and IPLV approaches were analyzed and compared, indicating that the APF method should be applied as a seasonal performance evaluation method for ASHPs (for both air–water and air–air heat pumps). Therefore, the rules for three key factors of seasonal performance evaluations were determined, which take China as an example. The specific results and parameters were calculated according to meteorological data and simulation. Besides, the related energy efficiency limitations and comparisons of the APF index, which greatly improve the ASHP industry, were discussed. This paper provides a basic reference for other countries to formulate their own ASHP standards.

Regional suitability of heating tower heat pumps based on technical and economic performance maps

Heating tower heat pump (HTHP) technology is evolving rapidly owing to its good performance in summer and frost-free operation in winter. However, a lack of comprehensive comparisons between the HTHP and conventional methods, such as the air-source heat pump (ASHP), and the chiller and boiler, significantly limits its applications. To solve this problem, this paper analyzes the technological and economic performance of these three types of systems at 353 locations over China. The principle of energy saving and potential of the HTHP are presented, based on which a comparison of economic performance is conducted by considering the efficiency of energy conversion and cost of the three systems. The results show that the HTHP is superior to the ASHP at most locations in China, with a 10% to 20% higher annual performance factor (APF). For locations in southwest China, this improvement is less than 10% owing to the large regeneration penalty in winter, and minor differences between dry-bulb and wet-bulb temperatures in summer. The APF of the HTHP is 10% to 23% higher than the chiller and boiler system in the hot summer and cold winter zone as well as the cold zone. However, the HTHP exhibits no advantage over this system in the severe cold zone because of the low efficiency of the heat pump in winter, or in the hot summer and warm winter zone owing to the small heating load. The results are used to develop technical and economic performance maps to guide the application of the HTHP in different climatic regions.

Comparison of annual performance factors of normatively designed heat pump systems

AbstractHeat pumps play a key role in decarbonizing the heat supply for buildings. To exploit heat pump's potential in a resource‐efficient way, high coefficients of performance (COP) are required. For air‐source heat pumps, the COP is subject to outside temperature, building dynamics, and user demands. To achieve high COPs, it is necessary to design heat pumps to meet the demands and to optimize operation in terms of COP.In this study, we compare design methods according to DIN EN 15450 and VDI Guideline 4645. Based on these, heat pump systems (heat pump, auxiliary heater and thermal storages) are designed for an example building, and a controller is set up. Following VDI Guideline 4650, an Annual Performance Factor (APF) is used for comparison on the basis of dynamic simulations. For the same building, the study proves both systems to ensure supply temperatures at APFs about 3.5 to 4. In order to achieve optimal APF, a consideration of operation already in the design should be suggested.

Energy saving analysis of evaporative cooling composite air conditioning system for data centers

An evaporative cooling composite air conditioning system aimed at enhancing energy efficiency of data centers was proposed. Furthermore, the mathematical models on the base of the operation characteristics of the system were established. After verification by experiment, the energy saving performance of the system under different climatic conditions was investigated. The simulation results showed that the annual performance factor (APF) values are 5.31, 5.02, 4.75 and 4.50, respectively in severe cold zone-Shenyang (123.38E, 41.8N), cold zone-Beijing (116.30E, 39.9N), hot summer & cold winter zone-Nanjing (118.78E, 32.0N) and mild zone-Kunming (102.72E, 25.1N). The power usage effectiveness (PUE) values are below 1.40, the system has good energy saving advantages in different locations. After a water-cooled heat exchanger is used in the evaporative condenser, the APF values improve in all the four cities. The use of water-cooled heat exchanger is beneficial to further enhance energy saving of the system. A case study based on the system elaborates that it is feasible for energy saving of data centers in various climatic zones.

Chinese policy leadership would cool global air conditioning impacts: Looking East

The International Energy Agency expects the global stock of room air conditioners (RACs) to triple between today and 2050, with critical implications for energy use and greenhouse gas emissions. Because China produces approximately 70% of the world's RACs, it is in a unique position to lead a global transition to higher-efficiency RACs with substantially lower environmental impact. To date, however, Chinese policies have targeted relatively modest RAC efficiency increases. We recommend that China target production of RACs that use low global warming potential (GWP) refrigerants and are at least as efficient as the most efficient RACs produced today in China or on the global market. Specifically, we recommend that China set minimum energy performance standards for RACs at China annual performance factor (APF) 5.4 in 2025 and China APF 6.9 in 2030. This leadership would provide a longer-term policy signal to RAC manufacturers in China, enabling them to meet the efficiency targets cost-effectively by providing adequate time for investment planning. We project that full implementation of our recommended policy could result in global electricity consumption savings of 74 petawatt-hours, CO2 reductions of 49 billion metric tons, and bill savings of 6 trillion U.S. dollars (cumulative benefits 2020–2050). The policy is viable in China because of its provision of long-term certainty for manufacturers and their demonstrated ability to produce low-GWP RACs with the required efficiencies. Exploiting the parallel transition away from high-GWP refrigerants under the Kigali Amendment to the Montreal Protocol would provide manufacturing efficiencies and substantial savings opportunities.

A fast prediction method for maximum APF of heat pump type air conditioners based on a single group of experimental data

The annual performance factor (APF) is a new performance index of heat pump type air conditioners (HPACs) based on multiple testing conditions which may result in orders of magnitude larger workload in the product development for enhancing the APF to be close to the maximal value. The development process can be accelerated if the maximum APF can be predicted. The purpose of this study is to present a fast prediction method with a high precision for the maximum APF of HPACs based on a single group of experimental data. The idea of achieving fast prediction is to establish a simplified lumped parameter model for the calculation of capacities and efficiencies of HPACs, and to present a simplified approximate APF correlation by eliminating all the intermediate parameters from the complicated APF equations defined in standards of HPACs. A group of experimental data is applied in the prediction model to improve the precision of the fast prediction method. Application of this method for a typical HPAC shows that the predicted maximum APF of the HPAC agrees well with the tested maximum APF, the maximum deviation of predicted capacities and efficiencies from the experimental data is within ±1.4%; and the duration of prediction for maximum APF is within 12 s on a typical personal computer, significantly saving the time of HPAC development.

Energetic, exergetic and exergoeconomic assessment of transcritical CO2 reversible system combined with dedicated mechanical subcooling (DMS) for residential heating and cooling

A transcritical CO2 reversible heat pump-air conditioning system combined with dedicated mechanical subcooling (DMS) is proposed as an annual heating and cooling solution. A common residential building is selected as a scenario to assess the system annual performance from the viewpoint of energetic, exergetic, and exergoeconomic, and compare with traditional CO2 system (BASE). The influences of terminal type, climate condition, and energy-saving potential are discussed. The results indicate the annual performance factor (APF) of CO2 system is significantly improved by up to 6.23 ~ 22.90%. APF generally increases with the latitude, and it achieves the highest value of 3.41 by using small temperature difference fan-coil unit (STD-FCU) as terminal. The annual exergy efficiency (AEE) is promoted by 7.25 ~ 24.79%, and the throttling irreversibility can be significantly reduced by adopting DMS. From the perspective of thermoeconomic, introducing DMS to CO2 system is cost effective. The total cost, including non-exergy-related investment and cost of exergy destruction, is reduced by 16.96% for heating and 4.52% for cooling. The annual exergoeconomic factor increases with the improvement of building energy-saving potential while decreases with the compressor price reduction. To widen the application of CO2 system, it is suggested that the price of CO2 compressor should be reduced, such as with the help of government subsidies. Furthermore, the thermal insulation performance of the residential building should also be improved, especially for the severe cold and cold regions.

Improving the energy efficiency of room air conditioners in China: Costs and benefits

China is the world’s largest consumer of room air conditioners, and it contributes about a quarter of global space cooling CO2 emissions. We model the costs and benefits of recently proposed new room air conditioner minimum energy performance standards (MEPS) in China. Our results suggest that newly proposed MEPS brings accumulative CO2 emissions reductions of 12.8% between 2019 and 2050, and accumulative bill saving of 2620 billion RMB to China's consumers. The benefits of the proposed MEPS decrease with longer MEPS revision intervals and increase with shorter intervals—indicating that the intervals should be balanced to maximize benefits while accommodating constraints due to air conditioner manufacturer design cycles. We also model potential nationwide benefits from higher MEPS. Across two increasingly aggressive MEPS scenarios, China’s room air conditioner electricity consumption and CO2 emissions in 2050 are both reduced by 15–53% compared to the proposed MEPS. The highest-efficiency scenario (reaching MEPS of annual performance factor 5.4 in 2025) provides the largest long-term national benefits. These results could inform development of a Chinese regulatory regime that effectively updates room air conditioner MEPS. Because China is the world’s largest manufacturer of room air conditioners, the economic, energy, and emissions benefits resulting from higher Chinese MEPS could also have a global reach.

Study on annual energy performance of transcritical CO2 heat pump water heating systems in Shanghai

CO2 heat pump water heating is an energy-efficient technology and being widely applied in Shanghai. However, its energy efficiency after long-term operation has not been well evaluated so far. In this paper, the energy efficiency and potential issues of CO2 heat pump water heater after multi-year service are in-depth investigated. In-situ study of CO2 heat pump water heating systems in Shanghai was carried out. Operating data were collected and field test was conducted. A typical case was chosen for comprehensive analysis. The results show that the annual performance factor (APF) of the actual system is 2.57, relative to 4.12 in its perfect shape. To find out what happened to this system, a simulation model was developed, calibrated and validated with field test data and operating data. In terms of simulations, suggestions were made on the system design and control for long-term performance improvement.