Air Source Heat Pump Research Articles

A Novel solar-assisted air source heat pump system for urban renewal: Experimental test and numerical simulation

Old residential communities require novel heating solutions to meet heating demands sustainably. In Southern China, current heating systems in old communities have high energy costs and lack sustainability. A potential solution, air source heat pumps (ASHP), have evaporators susceptible to frost accumulation and poor heating performance at low ambient temperatures. This study proposes a hybrid design that uses additional solar thermal energy to improve energy gains from the air source; the innovative serial coupling design increases the air-source temperature by engineering the evaporator of the ASHP as the load-side of the heat exchanger. The novel hybrid design aims to be efficient, cost-effective, and sustainable, satisfying urban redevelopment needs. A prototype of the novel hybrid solar-assisted ASHP system was constructed; various performance parameters were evaluated, and system operation in extreme climates was simulated in TRNSYS. Results indicated that the novel hybrid system had significantly superior heating performance, delivering a 70.1% improvement in heating rate compared to single-source ASHP under lower ambient temperatures (13C). The novel hybrid system also had a high COP value between 5.7 and 6.3, significantly exceeding values of 2.3-3.5 for most air-conditioning units. It demonstrates consistent performance in all simulated climates. It is estimated that the novel hybrid system can save 1000 RMB in annual energy costs for an average Shanghai family and reduce Shanghais CO2 emissions by 4.7 million tons. The novel system addressed limitations of ASHP, optimizing performance while maintaining sustainability, offering a promising solution for urban renewal projects in China.

Experimental Study on the Combined Heat Storage and Supply of Air/Water-Source Heat Pumps

As the application of renewable energy becomes increasingly extensive, heat pump technology with renewable energy as the heat source is achieving good results. Air-source heat pumps and water-source heat pumps can be widely used in cold areas. In this work, an integrated combined storage and supply system of an air-source heat pump and a water-source heat pump was studied, and the heating characteristics of the system at the beginning, middle, and end of the heating period were examined. It was found that, when the outdoor temperature of the system was very low, the efficiency of the combined storage and supply system reached the highest value of 2.57 when the source-side water tank was kept at 30 °C, and the performance of the combined storage and supply system was better than that of the air-source heat pump and the water-source heat pump in cold regions. Meanwhile, the independent storage of the air-source heat pump and the combined storage and supply system can be used for heating at the beginning and end of the heating period.

Performance study of the rapid heating drying system based on the reverse Brayton air cycle for agricultural application

Air temperature and humidity control are important for crop storage. Current drying methods in agriculture include solar heating and air source heat pumps, whereas solar heating may lead to poor quality of the dried product and air source heat pumps may not reach the desired temperature when the environment is harsh. In this paper, a rapid heating and drying system based on reverse Brayton air circulation is proposed to obtain high temperature and low humidity air quickly by adjusting the pressure ratio to achieve an adjustable crop drying process. An improved rapid heating and drying system with a water cooler is also proposed to increase the drying efficiency of the system. The results show that the total dehumidification rate of the improved system can reach 11.51 g/s, which is 1.48 g/s higher than that of the rapid heating and drying system without a water cooler, and the dehumidification energy efficiency of the improved system can reach 1.26 kg/(kW.h), which is 0.11 kg/(kW.h) higher than that of the rapid heating and drying system without a water-cooling device.

Net-zero life cycle supply chain assessment of heat pump technologies

In this study, a comparative life cycle assessment of different heat pump technologies based on multiple supply chain scenarios according to the UK market has been conducted. In addition to conventional heat pumps – air-source heat pump (ASHP), ground-source heat pump (GSHP), and water-source heat pump (WSHP) - a novel hydrogen-source heat pump (HSHP) has been studied from an environmental aspect. Different supply chain scenarios have been developed for all technologies based on the leading supplier of heat pump components in the UK. Results showed that the manufacturing and operation of heat pumps are the main causes of the environmental impacts. Among the four technologies studied, ASHP had the highest negative environmental impacts across most categories. HSHP stands out with notably lower carbon emissions compared to other cases. However, in certain impact categories, HSHP exhibited more significant consequences, especially concerning land use and land-related pollution. Regarding CO2 emissions, ASHP is projected to achieve the most substantial reduction, with expected reductions of 23 %, 60 %, and 97 % by 2030, 2040, and 2050, respectively. GSHP, WSHP, and HSHP are also predicted to experience significant CO2 emission reductions of 94 %, 95 %, and 59 % by 2050, aligning with the UK's net-zero goal.

Modeling and operational characteristics analysis of a dual-source synergetic heat pump based on air energy and biomass waste heat

Air source heat pumps have gradually become a widely used heating solution worldwide due to their advantages of high efficiency, energy conservation, and environmental protection. However, air source heat pumps also face some challenges in practical applications, such as unstable heating and performance degradation in low-temperature environments. In order to improve these problems, based on the cascade heat technology, a new type of dual-source synergetic heat pump system is designed using air energy and biomass waste heat dual heat sources. In order to study its performance, a simulation model of the heat pump system was first constructed using distributed-parameter method. In order to verify the effectiveness of the model, an 18-kW heat pump experimental unit was constructed. By comparing the three key parameters of user side outlet water temperature, high-temperature compressor power, and system coefficient of performance (COP), the results show that the maximum error does not exceed 11 %; Secondly, in order to improve the stability and operational efficiency of the system, a three-level control strategy was designed based on considering the coordination of different grade heat sources; Finally, based on the above, the operating characteristics of the heat pump system were investigated through testing under different external input conditions. The research results indicate that by utilizing cascade heating and parallel heat exchange technology, the heat pump system can achieve stable heating even under large fluctuations in external working conditions. At the same time, compared with air source heat pumps, the COP can be improved by 69.7 % in low-temperature environments. The system results not only provide reference for the design and operation of new heat pump systems, but also provide practical and feasible solutions for the problem of decreased heat pump performance in low-temperature environments.

Ice source heat pump system for energy supply via gas pipelines – Part1: Performance analysis in residential units

This study evaluates the performance of heat pumps using water or ice as the heat source, with energy transferred via repurposed gas delivery pipes. The proposed system offers significant benefits for urban energy networks, particularly in densely populated areas. The article is divided into two main sections: the first compares the thermal efficiency of the proposed system for residential heating against similar heat pumps. The second section examines the implementation, energy transfer capacity, and water requirements of using a gas pipeline network. The study models various heating systems, including electric-resistance, air-source, water-source, ground-source, and ice-source heat pumps, in Nottingham throughout the year. The results show that switching from gas to heat pumps significantly increases electricity demand, especially during peak periods. Specifically, electric-resistance heating, air-source, water-source, and ice-source heat pumps increase peak electricity consumption by factors of 7.5, 3.2, 2.5, and 2.7, respectively, compared to a gas boiler. Additionally, electricity consumption exceeds the current peak for 89 %, 47 %, 35 %, and 39 % of the hours in the year for each respective system. These findings emphasize the proposed system's role in managing peak electricity demand and enhancing generation and transmission capacity post-natural gas phase-out.

Energy, economic and environmental analysis of a photovoltaic-thermal integrated dual-source heat pump system under a system coefficient of performance − based switching strategy

The photovoltaic-thermal integrated dual-source heat pump system can offer performance improvement by addressing the limitations of a single heat pump system, which not only improves energy efficiency and system performance but also reduces pollutant emissions. However, the operational performance of the system is significantly affected by different switching strategies between two heat sources, which has not been given adequate attention from researchers. Therefore, this study introduced a system coefficient of performance − based switching strategy, which can alternate between air-source heat pump and solar water heat pump modes to make full use of air and solar energy, to optimize the operation of the photovoltaic-thermal integrated dual-source heat pump system and compare with the conventional water temperature of the heat storage tank − based switching strategy. A TRNSYS model of the system was developed and validated, and the simulated results demonstrated the better performance of system coefficient of performance − based switching strategy in energy, economic and environmental perspectives. The average photoelectric and photothermal conversion efficiency under system coefficient of performance − based switching strategy were higher than those under water temperature of the heat storage tank − based switching strategy by 1.1 % and 4.0 %, respectively, with average modified coefficient of performance of 7.43 and 6.55. Furthermore, the system not only achieved savings of 5.63 % in annual electrical cost and 5.33 % in yearly operational cost but also reduced standard coal by 19.25 kg and total pollutant emissions by 242.55 kg per year under system coefficient of performance − based switching strategy, compared to water temperature of the heat storage tank − based switching strategy.

Does the Novel Dual Source Heat Pump (DSHP) Out-Perform the Ideal DSHP? Experimentation Versus Simulation of DSHP Based Thermodynamic Irreversibility of the Throttle Valve

Purpose: The air-source heat pumps are associated with continuous frosting problems. To ensure a more energy efficiency technology, the novel dual-source heat pump (DSHP) was developed. This article aims to confirm and compare the energy performance of the novel dual-source heat pump (DSHP) with the performance of an ideal heat pump. Methods: We applied an experimental analysis from an installed DSHP system with converters and other components to obtain the energy performance of the DSHP, while the performance of an ideal pump was obtained from simulation based on the theoretical algorithm of the basic principle of the thermodynamic irreversibility of the throttle valve. Results: We found that the Ideal (simulated) DSHP has a higher coefficient of performance (COP) than the installed (experimented) DSHP. The Ideal DSHP’s COP of 4.52 is higher than the Novel DSHP’s COP, which range from 1.78 (day 3) to 2.01 (day 1). The DSHP are power efficient, which reduces carbon emission from whatever power source that is been used. Implications: Energy efficiency in buildings has severe implications for global warmings and the need for sustainability. Because the modern ventilation system utilise energy from waste and heat recovery to power heating and cooling systems, the DSHP remains promising for future generations of building ventilation design. Originality/Value: The value of the study is because it completes an experiment that analyse the performance of the DSHP, comparing the outcomes with results from a simulation based on an Ideal system.

Impact of newer climate data for technical analysis of residential building energy use in the United States

In this study, we describe an analysis indicating the relative importance of newer hourly weather files for simulation analysis of the energy use of residential buildings in North America.Results show that older TMY3 (ending 2005) data compared with newer TMY2021 (2007–2021) data are less appropriate for the best prediction of low-energy buildings. The balance of heating and cooling is significantly altered in the more recent TMY files with potential impacts on best performing energy efficiency measures. With 64 high profile North American locations evaluated, we found heating to be approximately 11% lower with the newer data, while cooling was increased by a similar amount percentage wise. However, the dominance of space heating in North America made decreases to heating considerably larger in an absolute sense so that overall space conditioning energy fell.Small changes in annual temperature can have large impacts. For all electric homes with air source heat pumps, we found that a change of 1 °C to outdoor temperature can produce about a 19 % change in space conditioning energy. The newer data also shows increased average solar electric output from simulated rooftop photovoltaic systems, likely due to more sophisticated solar irradiance data. Water heating was about 3 % lower given rising groundwater temperatures and inlet water temperatures to water heating systems. Results also showed that the newer data tended to increase savings from comprehensive building efficiency efforts in all electric buildings. This largely takes place because higher temperatures in winter allow air source heat pumps to meet heating needs more efficiently. Generally, the direction of these influences ease pathways to reach zero energy buildings in North America.

Simulation and analysis of solar-assisted air source heat pump heating system in severe cold region

Abstract severe cold and remote areas such as the west of Inner Mongolia, due to the vast land and sparse population, the coverage rate of heating pipes is low, resulting in high non-renewable energy consumption in building heating. To diminish the reliance on pollution energy and utilize sufficient solar energy resources, this study introduces a solar-assisted air source heat pump heating system (SASHP). Using TRNSYS to simulate the SAHSP’s system performance, the result indicates a good thermal environment between 12°C and 20°C. The average solar fraction in the coldest month of January is 33.45%, with a good heat collection efficiency. Compared with a single heating system, the SASHP’s total energy consumption was reduced by 45.11%, and SEER increased by 1.4 times. Optimization analysis displays that when the collector area is 100 square meters, and the tank volume is 5.5 cubic meters, the system achieves the best energy-saving effect. An optimized system can save 10,828.46 kg of standard coal annually during the heating period.

A comparative study on the application of solar thermal collector and photovoltaic combinations to assist an air source heat pump

This study investigates the usage of photovoltaic (PV) and thermal collectors separately to assist a heat pump for supplying domestic hot water (DHW). Usage of PV and thermal collectors together to assist a heat pump and experimentally validated simulation of an air source heat pump can be considered as novelty of this study. Firstly, experimental tests were performed in a climatic room to validate the developed simulation model. Four experimental parameters, namely the coefficient of performance of the air source heat pump, average tank temperature, and heat pump inlet and outlet temperatures have been used for the validation and the highest obtained deviation was 4.5%. Simulations were carried out by adding thermal collectors and photovoltaic panels in different combinations, with a maximum of three collectors to assist the heat pump that provides DHW. For scenarios with one and two solar components (PV or thermal), applying only thermal collectors was more efficient and economical for both with a payback of 3.9 years and 4.3 years, respectively. For the scenario with three solar components, although the system supported by one thermal and two photovoltaic collectors was the most efficient option, the system supported by three photovoltaic collectors was the most economical scenario with a payback period of 4.6 years. The study found that combining thermal and photovoltaic collectors can significantly reduce energy consumption for DHW.

Dynamic modeling and defrost optimization for air source heat pumps: A deep learning and autoregression approach

Air source heat pumps (ASHPs) are celebrated for their exceptional energy efficiency and their capacity to curtail greenhouse gas emissions. However, a critical challenge in ASHPs research is the effective and accurate management of the defrosting process to preserve peak performance. The development of robust and precise simulation models is crucial yet complex for formulating and assessing defrosting strategies. To address this, our study investigates the integration of deep learning models with feature encoding to establish dynamic models for ASHPs. We evaluated various deep learning architectures, achieving a Mean Absolute Percentage Error (MAPE) of 3.5% in heating capacity predictions. Moreover, our analysis reveals that feature encoding substantially lowers the MAPE by 12%, thereby enhancing model accuracy. We employed a comprehensive suite of evaluation metrics to benchmark the performance across models, finding that the Temporal Convolutional Network (TCN) marginally surpasses others, including Transformer, LSTM, and LightGBM models. Additionally, we utilized transfer learning to boost the generalization capabilities models across different outdoor conditions (temperature and humidity), facilitating effective few-shot training. Finally, our study introduces a novel defrosting control strategy based on Heating Capacity Degradation (HCD). Using dynamic modeling, we determined optimal control thresholds (89%-94%) that ensure maximum heating efficiency during frosting conditions. This strategy improves the average heating capacity by 101-278 W compared to conventional defrosting methods. The insights from this research not only advance defrosting control but also serve as a valuable reference for dynamic modeling and control optimization in the heat pump sector. The proposed control method enhances ASHPs performance and energy efficiency, supporting efforts towards achieving carbon neutrality.

Simulation study on thermal performance of solar coupled air source heat pump system with phase change heat storage in cold regions

The development of efficient and clean heating technologies is profoundly significant for the reduction of carbon emissions in cold regions. This paper puts forth a novel solar-coupled air source heat pump system integrated with phase change heat storage technology, which is well-suited for regions with such climatic conditions. A numerical model of the components and coupled systems is established using the lumped parameter method, and an iterative method is employed for the computational solution in MATLAB software. A variety of system performance aspects are then simulated and analysed following the configuration of component structural parameters and initial operating conditions. The results of the simulations indicate that an increase in the phase change temperature interval of the phase change materials leads to a higher average heat release power. In particular, a 2 °C increase in the phase change temperature interval results in an increase in the heat release power of over 10 %. Furthermore, when the system is applied in typical cold regions, including Kunming, Hangzhou, Lhasa, and Harbin, the average coefficient of performance is 10.23, 8.87, 8.49, and 7.70, respectively. The proportion of solar energy input contributes to an increase in system efficiency across all regions. A case study of Hangzhou reveals that the incorporation of solar energy into the system results in an increase in efficiency of 70.91 %. This research provides valuable operational methods and site selection recommendations for engineering practices, laying a theoretical foundation for its widespread application in cold regions.

Study on performance of a multi-heat source heat pump coupled energy storage system for plant factory heating system

CO2 air source heat pump (CASHP) faces challenges of performance degradation caused by the high return water temperature and the low ambient temperature for building heating. This study proposed a novel multi-heat source heat pump system (MHSHP) that combined with a CO2 air source heat pumps (CASHP) and ground source heat pumps (GSHP) with the implementation of a thermal storage tank. The performance and CO2 emissions of both CASHP and MHSHP systems were investigated by applying a plant factory located in Beijing, China. The effects of user-side parameters and ambient temperature were explored with the storage water temperatures ranging from 20 °C to 40 °C. The results demonstrated that the heating performance of the CASHP improved with an increase of user water flow rate and ambient temperatures, while it decreased as the storage water temperature increased. At the flow rate of 1.1 m3/h, the increase of the compressor frequency from 40 Hz to 60 Hz led to a significant improvement in heating capacity by 53.3 %, and a reduction in COP by 23.3 %. When the user-side water flow ratio decreased or the total flow rate increased, the COP of the MHSHP system showed improvement and outperformed that of the CASHP system, with an increase ranging from 46.9 % to 61.5 %. Additionally, it exhibits reduced sensitivity to ambient temperature fluctuations, resulting in a decrease in COP variability from 33.3 % to 20.6 %. Moreover, the CO2 emissions of the system decrease as the COP increases, with significant reduction of 69.2 %.

A multi-valve flexible heat pump system with latent thermal energy storage for defrosting operation

There has been growing interest in using air-source heat pumps as an alternative to potentially replace fossil-fuel-based heating technologies for heat decarbonisation. One of the technical issues that hinders the wide uptake of air source heat pumps is the decreasing energy efficiency caused by frequent defrosting operations under low ambient temperatures. Currently, the most widely used defrosting method is the reverse-cycle defrosting but this operation would have to interrupt the heating supply during the defrosting process. The authors recently proposed, developed, and demonstrated a flexible heat pump concept that recovers partial of the subcooled heat from the hot refrigerant exiting the condenser and stores it in an integrated thermal storage. The stored heat could later be used to save compressor power and defrosting applications. In this paper, we proposed an innovative method by using a multi-valve design of the flexible heat pump to achieve the defrosting function. In this new concept, defrosting is achieved by condensing the refrigerant inside the evaporator and simultaneously ensuring uninterrupted heating during the heat storage discharge process. A model has been established to study the heat pump performance during a full charge/discharge cycle of the storage. Results indicated that with R410a, R134a and R1234yf, the proposed flexible heat pump has the potential to respectively save up to 11.2%, 10.8% and 13.2% of compressor power, in comparison with a heat pump using the conventional reverse cycle defrosting method. Concurrently with the defrosting operation, the same heating capacity is ensured without interruption by the flexible heat pump.

Experimental study on the characteristics of frost formation and defrosting water retention between vertical double surfaces with different wettability

Frost formation and defrosting water retention directly affect the heat transfer process of outdoor finned tube heat exchanger, which in turn influences the energy efficiency of air source heat pumps for building heating. Three typical wettability surfaces were prepared, including a bare copper hydrophilic surface (BCS), a hydrophobic copper surface (HCS) and a superhydrophobic copper surface (SHCS). The above three surfaces are combined in pairs to construct three different wettability combinations, which are Combination 1: HCS-BCS, Combination 2: BCS-SHCS and Combination 3: HCS-SHCS, respectively. Frosting-defrosting experiments between vertical double surfaces are carried out on the above combinations. The results illustrated that the combinations with SHCS exhibit excellent frost inhibition properties. Compared with Combination 1, the channel filling rate of Combination 2 and Combination 3 were reduced by 16.79 % and 30.09 % respectively at a frosting time of 60 min. The defrosting time of the combination is determined by the slower defrosting of the two surfaces. Compared with Combination 2, the defrosting rate of Combination 3 is improved by up to about 12.93 %. Avoiding the formation of large-sized liquid films and droplets or utilizing the “absorption” phenomenon caused by wettability differences between surfaces are important measures to reduce the possibility of bridge formation during the defrosting process. And the greater the wettability difference, the more obvious the “absorption” phenomenon became. Spherical droplets on the SHCS can be completely absorbed by the liquid film on BCS under the action of differential surface tension. Neither Combination 2 nor Combination 3 formed a liquid bridge at a surface spacing of 2 mm. The research will provide theoretical support for the selection of fin spacing and fin coating type under different working conditions in practical engineering.

Study on the Coupling of Air-Source Heat Pumps (ASHPs) and Passive Heating in Cold Regions

Air-source heat pumps (ASHPs), as an active device, are widely used in building heating and cooling processes. However, in severe cold regions, they face reduced heating efficiency and frosting problems in winter. This paper proposes a new heating solution by coupling an ASHP with passive heating systems. It combines an ASHP with passive sunrooms and heat storage systems for heating. Through software simulations and mathematical modeling, the new scheme is compared and analyzed against traditional ASHP solutions to explore the performance of this scheme in rural houses in severe cold regions of China during winter. According to simulation and calculation analysis, on the coldest day of winter, the coupling scheme can provide approximately 99.41 kWh of heat to the indoors, which exceeds the 86.67 kWh required to maintain an indoor temperature of 20 °C. The system’s power consumption is 36.96 kWh, which is 66.88% lower than that of traditional heat pump heating. The study shows that the coupling system of an ASHP and passive heating has a good heating effect in severe cold regions. For the situation of insufficient solar energy at night, the design of phase-change materials and heat storage media can meet heating needs throughout the day.

Design and analysis of thermoacoustic air source heat pump water heaters

Thermoacoustic air-to-water air source heat pumps (TAWASHP) are the eco-friendly, simple, compressor less, low cost and likely looking future substitute for the existing compressor-based heat pumps. In this work, the design optimization of the 1-kW TAWASHP with helium for the temperature difference of 15 to 70 K for pumping heat from the atmospheric air to water using the linear thermoacoustic concepts was discussed. The optimized design can fit for both cooling and water heating applications without wasting the heat rejection to the surrounding atmosphere, rather supplied to the insulated hot water tank. The optimized one-fourth wavelength resonator TAWASHP shows the coefficient of performance of 1.1 to 2.34. The theoretical results are validated with the DeltaEC software results, and the results are in concurrence with each other. The DeltaEC predicts the TAWASHP can supply 1.55 to 3.35 kW of heat to water, which is equivalent to 37.3 to 80.3 kWh of heat energy per day.

Study on photovoltaic combined air source heat pump heating system under typical meteorological conditions

Abstract This paper proposes a photovoltaic (PV) combined air source heat pump heating system for rural areas in severe cold regions of northern China, where the current clean heating methods have high costs and low efficiency. The paper uses meteonorm8 and TRNSYS software to derive the typical meteorological parameters and simulate the system performance in a guard room in Shenyang city. The paper analyzes the heat pump power consumption, PV cell power generation, and economic and environmental benefits of the system under different outdoor temperatures in the heating season. The results show that the system can meet the heating demand and maintain a comfortable indoor temperature, with an annual cost of 1603 RMB, which is 61.33% lower than a single heat pump system. The system can also reduce the emissions of carbon dioxide, sulfur dioxide, and dust by 2619.43 kg, 10.78 kg, and 6.91 kg per year, respectively, demonstrating its economic feasibility and environmental contribution.

Determination of the defrosting duration ratio for defrosting performance evaluation of air source heat pump

Defrosting performance evaluation is an important aspect for pre-delivery inspection of air source heat pumps (ASHPs). According to GB/T 25127-2020 and ANSI/AHRI 550/590–2023, defrosting duration ratio (α) should not exceed 20 % of the frosting-defrosting cycle. This value has remained unchanged for over 20 years. However, with the rapid iteration of defrosting technology, the α of new ASHPs has been decreased significantly. Hence, the applicability of this index value deserves to be deliberated. To solve this issue, a method for determining the optimal α was proposed firstly. Then, the α under different characteristic index (CICO) values at 2/1 °C and 2/0 °C were investigated at the optimal and original defrosting initiating time point (topt, tori), using twelve ASHPs from nine manufacturers. Results indicates the frosting duration (tf) is directly proportional to defrosting duration (tdf), at the same ambient air condition and CICO. For Unit C, when tf is increased from 30.0 min to 60.0 min and 90.0 min at the CICO of 10.0 × 106, tdf increases from 2.43 min to 3.20 min and 4.03 min at 2/1 °C, respectively. No matter at topt nor tori, the range of α is 1.4%–9.9 %. It is suggested that the 10 % is used as the new index for defrosting performance evaluation of ASHP.