Performance Of Air Source Heat Pump Research Articles

Defrosting Performance Improvement of Air-Source Heat Pump Combined Refrigerant Direct-Condensation Radiant Floor Heating System with Phase Change Material

Traditional defrosting methods applied to solve frosting problems of air-source heat pumps operating in cold periods may reduce heat capacity of the system and decrease indoor thermal comfort. In order to improve the performance of air-source heat pump (ASHP) and maintain indoor temperature in defrosting conditions, an air-source heat pump combined with a refrigerant direct-condensation radiant floor heating system with phase change material is proposed and evaluated in this study. Two radiant floor heating terminals with and without composite phase change material modules were compared through experiments. A composite phase change material based on dodecanoic acid-tetradecanol-hexadecanol mixture and expanded graphite was investigated for this application. Experimental results indicate that both heat fluxes of two comparing terminals are higher than 70 W/m2 in heating condition. At the same time, the floor surface temperature, indoor air temperature, and heating capacity of the terminal with composite phase change material modules are higher than those without composite phase change material modules in defrosting condition. This suggests that the proposed system with composite phase change material modules can improve indoor thermal comfort in defrosting condition as well as satisfy the heating requirement in heating condition.

Air-source heat pump performance comparison in different real operational conditions based on advanced exergy and exergoeconomic approach

The use of air-source heat pumps (ASHP) is increasing to meet the energy needs of residential buildings, and manufacturers of equipment have permanently expanded the range of work and improved the efficiency in very adverse outdoor air conditions. However, in the time of a wide range of different technologies, the problem of using ASHP, from a techno-economic point of view, is constantly present. Exergetic efficiency and exergoeconomic cost no longer provide sufficiently reliable information when it is necessary to reduce the investment costs or in-crease the energy/exergetic efficiency of the component/system. This paper presents comparison of ASHP in different operational conditions based on an advanced exergy and exergoeconomic approach. The advanced exergy analysis splits the destruction of exergy for each individual component into avoidable and unavoidable part in order to fully understand the processes. The information of stream costs is used to calculate exergoeconomic variables associated with each system component. Irreversibility in the compressor have the greatest impact on reducing the overall system exergetic efficiency by 46.7% during underfloor heating (UFH) operation and 24.53% during domestic hot water (DHW) operation. Exergy loss reduces exergetic efficiency by 5.72% UFH and 39.74% DHW. High values of exergoeconomic cost for both operating regimes are present in flows 1, 2, 3 and 4 due to high costs of production and relatively small exergy levels. The general recommendation is to set the ASHP to operate with near-optimal capacities in both regimes and then reduce exergy of flows 1, 2, 5, 11, and 13.

Numerical study of residential Smart Dual Fuel Switching System (SDFSS) with on-site solar photovoltaic system

Building energy consumption accounts for approximately 36% of total energy consumption in the world. Since buildings are capable of on-site electricity generation and exhibiting predictive pattern of heating and cooling, the focus of this study is to investigate the Smart Dual Fuel Switching System (SDFSS), comprising a natural gas furnace and an air-source heat pump (ASHP), working in conjunction with on-site solar photovoltaic system. Base-case scenario using 1.5-ton rated capacity ASHP with 8.5 heating seasonal performance factor (HSPF) yielded only 4% cost savings and 15% greenhouse gas (GHG) emission reduction when compared to natural gas furnace space heating scenario. With an ASHP of 2-ton rated capacity and HSPF of 10 working in conjunction with solar photovoltaic (PV) system of 4.08 kWp, the cost savings of SDFSS increased to 12% and the GHG emissions reduction of 45%. SDFSS integrated with the grid is expected to yield significant benefits. It can help avoid situation of buildings drawing electricity all at once and reduce the overload on the grid. Also, it can redirect electricity generated from the solar PV system of a building for which using natural gas furnace is more economical to a building whose space heating demands can be met with this excess electricity. Higher ASHP performance and capacity, higher carbon pricing, and higher solar PV electricity generation will lead to the design of a more economical and sustainable SDFSS.

Extremum seeking control for efficient operation of an air-source heat pump water heater with internal heat exchanger cycle vapor injection

The vapor-injection (VI) technique is known effective for improving the performance of air-source heat pump (ASHP) in cold climates. Optimizing the intermediate pressure is critical for the efficiency of VI-ASHP under varying operating conditions, while model based control is cost prohibitive in practice. We propose an extremum seeking control (ESC) framework as a model-free optimal control strategy for internal heat exchanger (IHXC) based VI-ASHP, minimizing the total power consumption in real time. The ESC takes the total power as the only feedback, and the intermediate pressure setpoint as the manipulated input. A Modelica-based dynamic simulation model of an IHXC-VI ASHP water heater is developed. The water outlet temperature is regulated by the compressor capacity, while the injection-loop expansion valve regulates the intermediate pressure. Under fixed, staircase and realistic ambient temperature profiles, simulation results show that ESC can optimize the intermediate pressure for system efficiency with good steady-state and transient performance.

Air source heat pump for domestic hot water supply: Performance comparison between individual and building scale installations

Air source heat pump (ASHP) for domestic hot water (DHW) preparation under cold climatic conditions is studied by TRNSYS simulation. Emphases are focused on comparing different strategies of installation using energy efficiency performance criteria. Studied strategies include individual (apartment-scale) and collective (building-scale, centralized) installations. Different daily hot water consumption profiles are considered in the annual simulation program. Simulation results show higher annual system efficiency from individual installations than centralized system. In the latter case, pump consumption during hot water recirculation makes the overall system less efficient. Due to lower over-sizing factor, the centralized installation is more favourable to the ASHP performance than individual ones. In both the two cases, GHG emissions can be significantly reduced by 7 thanks to ASHP. This paper provides decision-making information regarding energy efficiency incentive policies of heat pumps for a more sustainable energy supply.

A New Mixture Refrigerant for Space Heating Air Source Heat Pump: Theoretical Modelling and Performance Analysis

Air source heat pump (ASHP) is becoming a substitute for small coal boilers in rural residential buildings of North China. However, the application of ASHP faces challenges of heating capacity, energy efficiency, ozone depletion potential (ODP) and global warming potential (GWP). Proper refrigerant is a key factor influences the performance of ASHP. In this paper, a new mixture refrigerant named RHR-1 is proposed, which aimed to improve energy efficiency, eliminate ODP and reduce GWP of ASHP refrigerant. The performance of RHR-1 was analyzed and compared with commonly used refrigerants including R134a, R410A, R407C and R22 in terms of heating coefficient of performance (COPh), compression ratio (CR) and discharging temperature (DT). The results show that, under the design cases, where supply water temperatures vary from 35 °C to 50 °C and outdoor air temperatures vary from −15 °C to 15 °C, the COPh of RHR-1 are in the range of 2.43–4.93. The COPh of RHR-1 is higher than other candidates when the supply water temperature is above 40 °C. The CR and DT of RHR-1 are in medium levels of the compared samples. A logarithmic regression equation was deduced to get the relationship of COPh with temperature difference between supply water and outdoor air which suggested the temperature difference should be controlled within 47.5 °C to get reasonable COPh. In addition, RHR-1 has no ODP, and its GWP is 279, which is much lower than other candidates. RHR-1 could be a reasonable refrigerant used in ASHP for space heating in North China.

Experimental investigation and evaluation of the performance of air-source heat pumps for indoor thermal comfort control

Air-source heat pumps (ASHPs) have been widely used in domestic buildings. However, the regulation performance of ASHPs for indoor thermal comfort control is influenced by the factors such as cold draft and slow response to the variation in room temperature. In this paper, a range of experiments was carried out for 14 ASHPs in an indoor environmental chamber under both cooling and heating conditions. A multi-index comprehensive evaluation model including the questionnaire survey method, the weighted scoring method and the quartile algorithm method was then adopted to analyze the tested data in order to give some intuitive indices to evaluate the regulation performance of ASHPs for indoor thermal comfort control. The results showed that unsatisfied factor of the overall thermal comfort under the cooling conditions was reached to 71 %. Besides, the precision of the temperature control was poor in both cooling and heating conditions, which manifesting ASHPs need a novel matched adjust mode and more intelligent control system to meet thermal comfort requirement. This study provided a reference basis for evaluating ASHP’s regulation performance on indoor thermal comfort.

Performance evaluation of air source heat pump under unnecessary defrosting phenomena for nine typical cities in China

Defrosting under unnecessary conditions is a typical and undesirable operating phenomenon for air source heat pump (ASHP). This paper aims to evaluate the ASHP performance under unnecessary defrosting phenomena in different regions of China. Firstly, energy loss for two kinds of unnecessary defrosting phenomena was quantified by 60 days field test. Secondly, a method was developed to predict unnecessary defrosting times. The prediction accuracy can be controlled within 10%. Furthermore, the ASHP performance of unnecessary defrosting was evaluated for nine typical cities in China. It was found that the average unnecessary defrosting rate was 53% for northern cities, 38% for mid-land cities, and 15% for southern cities during a heating season. Correspondingly, the total energy loss was 233 MJkW−1, 161 MJkW−1, and 44 MJkW−1. These results indicate that unnecessary defrosting processes should not have been ignored. It is a valuable work to improve the defrosting control method.

Performance investigations of an R404A air-source heat pump with an internal heat exchanger for residential heating in northern China

Air-source heat pumps (ASHP) have been widely used for residential heating due to its energy-saving and high efficiency characteristics. However, the performance of an ASHP reduces as the ambient temperature decreases. In order to investigate the effect of ambient temperature on ASHP performance, an ASHP with an internal heat exchanger (IHX) using R404A as refrigerant was developed and studied at low ambient temperatures. The theoretical simulation was first performed to evaluate the performance of the ASHP with IHX and compared with three different cycles. The simulation results were validated by data available from literature and experimental data in this study. The results showed that the R404A ASHP system with IHX had a good potential for residential heating. Further investigation was performed to compare the performance of the R404A ASHP with and without IHX. The comparison results showed that the performance of the ASHP with IHX was far better than that of the ASHP without IHX. As the ambient temperature decreased from 0 °C and −26 °C, the improvement of the heating capacity of the R404A ASHP with IHX increased from 5.91% to 15.92% while the COP improvement increased from 10% to 20%. This indicated that the IHX technology became more and more effective as the ambient temperature dropped lower and lower.

A techno-economic comparison of a direct expansion ground-source and an air-source heat pump system in Canadian cold climates

This study aims to compare two commonly used ASHP (air-source heat pump) and DX-GSHP (direct-expansion ground-source heat pump). There have been many debates on energy efficiency, system costs and relative payback period of DX-GSHP against ASHP systems over the past few years. In this context, and with the aim of enriching this debate, a detailed screening heat pump model previously developed is modified and used to compare the seasonal performance of ASHP vs DX-GSHP in a residential building in the cold climate city of Montreal. Further, a life cycle cost analysis is performed to account for the difference between initial and 10-year operating costs of the two systems based on the current prices in Quebec. The obtained results show that by proper sizing, energy consumption of the DX-GSHP system can be reduced by 50%. Moreover, with current borehole installation prices, the relative payback period of the GSHP (ground source heat pump) compared to ASHP is more than 15 years. However, if the borehole installation price reduced by 50% the payback period would be reduced to just a few years. Such results highlight the importance of further investigations in the area of DX-GSHPs, in order to reduce the borehole installation cost and increase its performance.

Self-optimizing control of air-source heat pump with multivariable extremum seeking

The air-source heat pump (ASHP) is widely adopted for cooling and heating of residential and commercial buildings. The performance of ASHP can be controlled by several operating variables, such as compressor capacity, condenser fan speed, evaporator fan speed and suction superheat. In practice, the system characteristics can be varied significantly by the variations in ambient condition, operation setpoint, internal thermal load and equipment degradation, which makes it difficult to obtain accurate plant models. As consequence, the model based control strategies for ASHP could limit the achievable energy efficiency. Model-free self-optimizing control strategies are thus more preferable. In this study, a multi-input extremum seeking control (ESC) scheme is proposed for both heating and cooling operation of ASHP. The zone temperature is assumed to be regulated by the compressor capacity, while the expansion valve opening is used to regulate the suction superheat at the given setpoint. The total power consumption of the compressor, the condenser fan and the evaporator fan is measured as input to the ESC, while the ESC controls the evaporator fan speed, the condenser fan speed and the suction superheat setpoint. The proposed scheme is evaluated with a Modelica based dynamic simulation model of ASHP under both cooling and heating modes of operation. Simulation results show the effectiveness of the proposed scheme to achieve the maximum achievable efficiency in a nearly model-free manner.

Performance of two-stage variable capacity air source heat pump: Field performance results and TRNSYS simulation

An investigation is reported on the performance of a two-stage variable capacity air source heat pump (ASHP) system, recently installed at the Archetype Sustainable House (ASH) in Woodbridge, Ontario, Canada. The controlled testing on the system was carried out in both summer and winter seasons for 4 to 6 weeks. TRNSYS simulation was performed and validated to model the performance of ASHP. The experimental data were extrapolated to predict the annual performance of ASHP. It was noticed for the cooling mode, the coefficient of performance (COP) varied between 4.7 to 5.7 as the outdoor air temperature changed from 33°C to 16°C, respectively. While in the heating mode, the COP varied between 1.79 and 5.0 as the temperature of outdoor air changed from −19°C to 9°C, respectively. The performance result has indicated that the use of variable speed ASHP provides an improvement in the efficiency as compared to other available options. These enhancements are due to the reduction in the operating cyclic time and relatively lower operating speeds of the device.

Improving cold climate air-source heat pump performance with refrigerant mixtures

Heat pumps (HP) are one of the most adapted heating solutions for meeting low energy consumption requirements of buildings. However, improving the performance of the heat pumps at low ambient temperatures is still an open challenge. This paper assesses the potential benefits of implementing zeotropic refrigerant mixtures in residential air-source heat pumps for cold climates, in order to increase their seasonal performance. The seasonal performance of a heating system with an air-source heat pump, supplemented with an auxiliary electric heater is studied in two cold climate cities of Montreal and Edmonton. To this aim, a detailed screening heat pump model previously developed is modified and used. Furthermore, the performance of the system with a variable composition refrigerant mixture is assessed, the main goal being to illustrate the possibility of applying environmentally friendly zeotropic refrigerant mixtures in conventional heat pumps, with minimal changes in the components, in order to improve their performance in cold climate conditions.

A thermodynamic analysis of an auto-cascade heat pump cycle for heating application in cold regions

The coefficient of performance (COP) of air-source heat pumps (ASHP) decreases toward low outdoor temperatures. This paper presents an auto-cascade heat pump system (ACHPS) with the objective to improve the heating performance of ASHP in cold climate. The auto-cascade process is achieved based on the separation of binary zeotropic refrigerant mixture consisting of pure refrigerants with different boiling points. Fluid selection for the ACHPS is carried out to validate the feasibility for potential application. Based on the performance analysis on COP, 15 qualified binary mixtures are obtained. R143a/R600 (0.8/0.2) tops the potential working fluid with a COP of 2.15. The effects of system parameters, such as circulation composition, heat transfer fluid (HTF) temperature glide and temperatures of heat source and sink on COP and exergy efficiency of ACHPS are thereafter investigated. The simulation results show that there exist a maximum COP of 2.15 and a maximum of exergy efficiency of 37.2% at the R143a mass fraction of 0.8 when the ambient temperature and heating temperature are −10°C and 50°C, respectively. Finally, by comparison with the single-stage heat pump operating with commercially available refrigerants, the proposed ACHPS shows an advantage of compressor isentropic efficiency. The compression isentropic efficiency of ACHPS could be increased by 25.5% compared to the single stage cycle working with R407c when the ambient temperature is −10°C.

Testing and simulation of a low-temperature air-source heat pump operating in a thermal buffer zone

Air-source heat pumps (ASHPs) are commonly used in temperate climates throughout Europe and Asia to provide energy efficient heating and cooling. However, ASHPs have not been widely adopted for heating in colder climates because the coefficient of performance (COP) is lower when outdoor temperatures are colder. While many researchers are working on improving the cold-temperature performance of ASHPs by altering the design of the equipment, this work examines an innovative way to improve performance by operating an existing ‘off-the-shelf’ ASHP within a thermal buffer zone. This paper shows that operating an ASHP in a thermal buffer zone (TBZ) created by an enclosed balcony space can improve the COP in cold temperatures. An ASHP operating in a TBZ was tested in a climate chamber where the performance was monitored under a variety of climatic conditions. The temperature drawdown of the TBZ and the associated impact on the COP were observed. The TBZ solar heat gain rates required to improve the COP were identified for a range of exterior temperatures. Then, a suite-based energy model was developed and calibrated to simulate the performance of the ASHP operating in the TBZ. The model provided a reasonable prediction of the ASHP performance below 10 °C.

Effect of fin types of outdoor fan-supplied finned-tube heat exchanger on periodic frosting and defrosting performance of a residential air-source heat pump

The effect of fin types—flat, wavy and louver fins—of outdoor fan-supplied heat exchanger on the periodic frosting and defrosting performance of a residential air-source heat pump was experimentally compared. Six consecutive frosting/defrosting cycles were performed for each fin type, and the frosting/defrosting durations were almost equal, about 46.6 min and 3.9 min for each fin type, due to the same defrosting control schemes. The time-average values during the third, fourth and fifth frosting/defrosting cycles were used to compare the overall frosting/defrosting performance among three fin types, and the real-time data during the fourth cycle were analyzed to compare their dynamic characteristics. The experimental results showed the flat fin had the best thermal performance of the air-source heat pump, followed by wavy and louver fins. The time-average heating capacity, COP and input power for flat fin during frosting cycle were more by 17.1%, 9.0% and 7.6%, respectively than those for louver fin. The frosting curves for flat fin increased slightly and then decreased gradually, while the curves for wavy and louver fin types increased slightly at first, then decreased rapidly and gradually at last. Meanwhile, the curves for louver fin decreased considerably earlier than those for wavy fin. The initial increases of the frosting curves were ascribed to that the positive frost effect of increased surface roughness surpassed both the negative frost effects of increased frost layer thermal resistance and reduced fan-supplied airflow rate due to frost blockage. The frosting curves for wavy and louver fin types decreased rapidly because the outdoor axial fan experienced the stall zone caused by more frost accumulation and greater air pressure drop, and decreased slightly at last after the stall zone was went through. The frosting curves for flat fin decreased always slightly because the outdoor axial fan did not experience the stall zone during the frosting duration of 46.6 min. The frosted finned-tube heat exchanger and fan characteristic should be coupled together for the optimal design.

Reducing carbon, tackling fuel poverty: adoption and performance of air-source heat pumps in East Yorkshire, UK

Deploying heating technologies, such as air-source heat pumps (ASHPs), can respond to the dual challenges of tackling fuel poverty and reducing carbon emissions from domestic energy consumption. In the UK, ASHP performance has been found to be below design levels. Elements of three strands of literature – innovation diffusion, environmental psychology and neighbourhood effects – are combined to gain insights into why the adoption and performance of ASHPs are lagging policy targets and design potential. Evidence from users, installers and area-based scheme facilitators suggests that the perceived complexity of the technology is a barrier. The level of technology maturity and the typical profile of the elderly fuel poor do not match; the target group might prefer to be late adopters or laggards in adopting technology. The role of installers is critical as the disruption from installation is a barrier to adoption and ASHPs place demands on users to change existing practices.

Research on frost formation in air source heat pump at cold-moist conditions in central-south China

A dynamic evaporator model of air source heat pump (ASHP), considering the ratio of the latent heat to sensible heat of wet air, is presented to analyze the performance of ASHP under frosting. The performance parameters, such as the heating capacity, COP and the outlet temperature of compressor, are simulated with CYCLEPAD. Then a semi-empirical correlation that predicts frost accumulation on the air-side of fin-tube heat exchanger is developed with dimensionless analysis and also modified by a test conducted under cold-moist conditions in winter. In addition, eight influence factors are considered involving the ambient conditions and structures of heat exchanger, whose effects are analyzed as well. Among them, the equivalent diameter of air flow cross-section in fin-tube deq is especially proposed. Lastly, the relationships between the ratio, the performance parameters and the frost accumulation are discussed in this paper, followed by an evaluation of an optimal defrosting time interval to improve the ASHP’s energy efficiency and operational reliability at cold-moist conditions in central-south China.

Performance analysis of air-water dual source heat pump water heater with heat recovery

A new air-water dual source heat pump water heater with heat recovery is proposed. The heat pump system can heat water by using a single air source, a single water source, or air-water dual sources. The water is first pre-heated by waste hot water, then heated by the heat pump. Waste heat is recovered by first preheating the cold water and as water source of the heat pump. According to the correlated formulas of the coefficient of performance of air-source heat pump and water-source heat pump, and the gain coefficient of heat recovery-preheater, the formulas for the coefficient of performance of heat pump in six operating modes are obtained by using the dimensionless correspondence analysis method. The system characteristics of heat absorption and release associated with the heat recovery-preheater are analyzed at different working conditions. The developed approaches can provide reference for the optimization of the operating modes and parameters. The results of analysis and experiments show that the coefficient of performance of the device can reach 4–5.5 in winter, twice as much as air source heat pump water heater. The utilization of waste heat in the proposed system is higher than that in the system which only uses waste water to preheating or as heat source. Thus, the effect of energy saving of the new system is obvious. On the other hand, the dimensionless correspondence analysis method is introduced to performance analysis of the heat pump, which also has theoretical significance and practical value.

A Study of Air-source Heat Pump Performance Analysis for Replacing Night Time Electric Heating Boiler

A Study of Air-source Heat Pump Performance Analysis for Replacing Night Time Electric Heating Boiler