Low Temperature Air Source Heat Research Articles

Low-temperature air source heat pump system for heating in severely cold area: Long-term applicability evaluation

Air source heat pumps (ASHPs) have gained popularity in cold regions without central heating owing to their higher energy efficiency when compared with fossil energy sources. Although studies have shown that the short-term performance of ASHPs may meet the heating demand at an ambient temperature of −20 °C, long-term performance under actual variable meteorological conditions needs further investigation. In this study, to comprehensively evaluate the long-term performance of an ASHP system in cold climates, a three-month field test was conducted in Daqing city, which is the coldest region in China. The ambient temperature fluctuated from −24.7 °C to 15 °C during the test. The test results showed that the system coefficient of performance (COP) was related to the outdoor temperature (r = 0.8955), and when the supply water temperature increased by approximately 6 °C under an outdoor temperature of −5 ± 1 °C, the corresponding COP decreased by 14.2%. Apart from the frost temperature of −5 ± 1 °C, the relative humidity (RH) had a slight effect on the system COP. Moreover, during the three coldest days when the ambient temperature ranged from −24.7 °C to −15.0 °C, the heat produced met the heating demand, and the system ran smoothly. Compared with other common heating methods, ASHPs have the advantages of high energy conversion efficiency and low pollutant emissions. From the field test results, it can be inferred that the low-temperature ASHP system is a clean and energy-efficient heating method that is well suited for severely cold regions.

Investigation on the efficiency degradation characterization of low ambient temperature air source heat pump under partial load operation

The heating capacity of air source heat pump increases with the increase of ambient temperature, coupled with the heating demand decreases, resulting in a prolonged partial load operation. The partial load operation of low ambient temperature air source heat pumps applied in cold region is particularly serious. With that also comes an efficiency degradation, taking into consideration that the characterization method of current product standards is not uniform in different countries. In this paper, the mechanism of partial load efficiency degradation was analyzed firstly, the explicit relationship between cycling losses and cyclic time was derived, and a partial load factor characterization method of air source heat pump by coupling start-up loss and stand-by loss was proposed. Secondly, the cycling losses of 3 sets of low ambient temperature ASHPs with different configurations were tested under different ambient conditions by using the intermittent ON-OFF cycles tests method. The magnitude of start-up loss is 2.0%∼17.3% for test ASHPs, and the stand-by loss rises sharply from 4.2 to 8.9% for the test ASHPs as the PLR drops from 0.2 to 0.1. The accuracy of the PLF characterization method was verified, and especially that of the load rate below 0.2 was improved.

Performance investigation and design optimization of a vapor injection rotary compressor without check valve in injection path

• The reason for the backflow of injection compressor is analyzed. • The optimal start and end of injection rotation angles are proposed. • The optimal design of the injection port increases the heating capacity by 22–45%. • The optimal design of the injection port increases the COP by 3.06–5.15%. • The operating strategy is optimized based on the CFD results. In recent years, low-temperature air source heat pumps using vapor refrigerant injection technique, which can effectively improve the performance and heating capacity of the rotary compressor heat pump systems in cold regions, have become more and more widely used. The injection rotary compressor without a check valve in the injection path has a great manufacturing advantage compared to that with a check valve. Improper position of the injection port will cause serious backflow during compression, which will greatly affect the performance of the heat pump. In order to study and correct the backflow in the injection process of the compressor, this paper analyzes the refrigerant flow characteristics of the compressor with a circular injection port without a check valve based on experiments and computational fluid dynamics. Through the analysis of the cause of backflow, the optimal position of the injection port is proposed, which has effectively solved the problem of refrigerant backflow caused by the injection. In addition, the operating strategy is optimized based on the results of computational fluid dynamics. The simulation results indicate that at low ambient temperatures, the optimal design of the injection port structure has increased the heating capacity 21.75%–45.3% over the traditional compressor without injection, and the coefficient of performance for heating also has been increased by 3.06%–5.15%.

Application and analysis of low temperature air source heat pump heating system in Cold Area

A low temperature air source heat pump (ASHP) heating system of residential building in cold area was designed and tested. The operating characteristics of the low temperature ASHP heating system in the typical day, typical month and the whole heating season were analyzed. The system energy saving performance in the whole heating season was also calculated. The results showed that the low temperature ASHP system operated stably in cold area and has energy-saving effect.

Application of Low Temperature Air Source Heat Pump Technology

Application of Low Temperature Air Source Heat Pump Technology

Experimental and simulation study of air source heat pump for residential applications in northern China

Air source heat pumps are vital for the implementation of coal-to-electricity policies in northern China. However, majority of the low-temperature air source heat pumps operate under a single and fixed mode, which maynotbesuitablefor residential applications in regions with variedclimates. Therefore, herein, a multimode single-fluid cascade air source heat pump (MSC-ASHP) is proposed, which includes the following modes: cascade compression heating, single-stage compression heating, and single-stage compression regeneration modes. To investigate variable-speed characteristics and control strategy of the two heating modes, the experiments and simulations are performed at different evaporating temperature and lower-stage compressor speed. The results demonstrate that the heating capacity in two modes can be enhanced effectively by adding the lower-stage compressor speed. The coeffinient of performance (COP) of cascade compression heating mode increases first and subsequently decreases along with the increasing of the lower-stage compressor speed. Under a condensing temperature of 46 °C and evaporating temperature of −35 °C, the COP is higher than 1.8, the discharge temperature is lower than 120 °C, and the compression ratio in each stage does not exceed 5.0, indicating this system functions safely and steadily in cold climates. The control strategies for the compressor speed and mode switch are summarized synthetically based on the simulation and experimental results. New heat pump system prolongs the year-round applications period of the low-temperature air source heat pump.

Enhancing Heating Performance of Low-Temperature Air Source Heat Pumps Using Compressor Casing Thermal Storage

Air source heat pumps (ASHPs) are widely recognized as energy-saving and environmentally friendly heating and air-conditioning equipment with broad applications. However, when conventional ASHPs are operated at a low ambient temperature, they suffer from problems such as high discharge temperature and low heating efficiency. To address these problems, this study designed a new type of dual evaporator combined with a compressor casing thermal storage heat pump system (DE-CCTS) on the basis of a low-temperature air source heat pump water heater with enhanced vapor injection (EVI). The proposed DE-CCTS used thermal storage phase change material (PCM), which was filled in the secondary evaporator (the thermal storage heat exchanger), to recover the waste heat of the compressor casing. Unlike that in the original system under different ambient temperatures, the suction temperature increased by 0.1–1 °C, the discharge temperature decreased by 0.1–0.5 °C, and the coefficient of performance (COP) of DE-CCTS increased by 0.85–4.72% under the proposed system. These effects were especially evident at low temperatures.

Study on the influence factors of energy efficiency ratio of low temperature air source heat pump

In this paper, through the experimental study of two heating seasons, it is found that the heat pump installation position and orientation, circulating pump work/frequency conversion, frosting conditions, etc. have a greater impact on the heat pump unit energy efficiency ratio. According to the actual operation data and theoretical derivation, the analysis shows that the energy efficiency ratio increases by 2.4% when the installation position and orientation increase the air temperature by 1K. The circulating water pump can save 78% of the power consumption in the period by changing the power frequency to frequency conversion. The frosting condition diagram can make a reasonable configuration and operation prediction for the heat pump system.

Public acceptance of environmentally friendly heating in Beijing: A case of a low temperature air source heat pump

China has long suffered from severe pollution due to coal consumption in rural areas. One possible solution is the promotion of a new electric heating system, low temperature air source heat pump (LTHP) technology. This paper explores the possibility that the public will accept LTHPs for electric heating. We assess people's willingness to adopt (WTA) as well as willingness to pay (WTP) for LTHP technology and sociodemographic and perception information by conducting field surveys in rural Beijing and empirically characterize the determinants of public acceptance. The analysis reveals that income, science literacy and local environmental concern positively affect WTA and WTP, whereas global environmental concern does not. Contrary to our initial expectation, people in mountainous areas express the highest WTA and WTP, followed by those in hilly and plains areas. These findings suggest that efforts to promote this technology could begin in mountainous areas and move to hilly and then to plains areas, thereby advancing public education on local environmental concerns and science literacy. The adoption of such a plan has the potential to promote electric heating systems in the lowest-cost manner and ensures a cleaner environment through the shift from coal to electricity in rural Beijing.

Research on the Clean Energy Heating Systems in Rural Beijing

Fog and haze weather has seriously affected many important aspects of human life and physical fitness. In order to improve air quality, local government has transformed coal-fired heating into clean energy heating in Beijing rural areas. This paper introduces three typical clean energy heating systems which are low temperature air source heat pump (LTASHP), thermal storage heater (TSH) and wall-mounted gas furnace (WGF), researches and tests the practical operation situation of three heating systems in the field. To compare technical and economic feasibility of three heating systems, the paper takes such residence where energy-saving standard of building palisade structure is approximately 50% as the research object, and establishes technical and economic mathematical analysis models, compares primary energy consumption and carbon dioxide emissions of three heating systems. This paper adopts annual cost approach, comprehensively takes into account power capacity increasing tariff and gas pipe network construction fee, and compares initial investment, operation cost and annual cost of three heating systems respectively from the perspective of users and government. The results show that LTASHP is the most energy-saving and its annual cost is lowest in the three heating systems. LTASHP is the most suitable alternative solutions to coal-fired heating in the three heating systems in rural Beijing.

Techno-economic analysis of air source heat pump applied for space heating in northern China

To meet the demand of clean heating in cold regions of northern China, high efficiency and environment-friendly low temperature air source heat pump heating system has been proposed and applied. In this paper, the technical feasibility and economical applicability of low temperature air source heat pump heating mode were studied and compared with conventional heating systems. A mathematical model of technical and economic analysis of different heating modes was established. With the mathematical model, different heating systems were compared with their primary energy consumption, pollution emissions, initial investment and annual running cost. The results showed that the low temperature air source heat pump heating system can stably and reliably meet the demand of space heating in residential buildings when outdoor air temperature is −15°C. In terms of energy efficiency, the primary energy consumption of low temperature air source heat pump heating mode is lower than coal-fired boiler, gas boiler, direct electric heating mode, but higher than combined heat and power generation. Comparing the pollution emissions, low temperature air source heat pump heating mode move the pollution source from residential areas to power plant, and has the relative low dioxide pollution emissions. Comparison results also show that the low temperature air source heat pump heating system is the most economical way among the candidates.

Suitability Analysis of the Heating Method of Low Temperature Air Source Heat Pump Applied in North China

The low temperature air source heat pump was a highly efficient and clean heating method. It has been gradually developed and applied in the north of China. In order to analyze the suitability of the low temperature air source heat pump in the cold region, a typical residential building in Beijing was chosen as a research object. The differences of the primary energy consumption, the carbon dioxide emissions, the initial investment and the running costs between the low temperature air source heat pump and the other traditional heating methods in North China were investigated and compared by means of simulation method. Results showed that compared with traditional heating methods, the low temperature air source heat pump heating method applied in appropriate situation has obvious energy saving and environmental protection advantages.

Simulation and optimization study on a solar space heating system combined with a low temperature ASHP for single family rural residential houses in Beijing

A pilot project of the solar water heating system combined with a low temperature air source heat pump (ASHP) unit was established in 2014 in a detached residential house in the rural region of Beijing, in order to investigate the system application prospect for single family houses via system optimization design and economic analysis. The established system was comprised of the glass heat-pipe based evacuated tube solar collectors with a gross area of 18.8m2 and an ASHP with a stated heating power of 8kW for the space heating of a single family rural house of 81.4m2. The dynamic thermal performance of the pilot system was measured for continuous 20days under typical cold climate conditions and the test data was used to validate the TRNSYS simulation model established. On the basis of model validation, system optimizations of both the existing pilot household and the typical rural house with good building insulation were undertaken to figure out the system economical efficiency in the rural regions of Beijing. The results show that the payback periods of the solar space heating system combined with the ASHP with the collector areas 15.04–22.56m2 are 17.3–22.4 years for the established pilot household on the current electricity price level of 0.5RMB/kWh, comparing with the reference condition of the fully ASHP space heating. It is further found that the equivalent solar heat price per kWh is too high under the current solar market cost price and collector technology. To put forward the integrated solar space heating for reducing carbon emission, it is suggested that the Beijing municipal government should offer some financial subsidy to compensate the equivalent solar heat price per kWh.

The Heating Coefficient Experimental Analysis of Solar Water-Assisted Low Temperature Air Source Heat Pump System

In winter,Many families use air source heat pump because of the low evaporation temperature of the system, resulting in lower heating efficiency of system. To solve this problem, the low temperature solar assisted hot water was added to the project which is on the basis of air source heat pump, and the system has been tested. After analysis of the collection efficiency of solar collectors at low temperatures and comparative analysis of the temperature cycle, pressure, energy consumption of the low-temperature solar-assisted systems and air source heat pump system, the optimal collector temperature and law of heat pump refrigerant cycle changes of the system were obtained. Theoretically, comparative analysis of low temperature air source heat pumps and solar hot water secondary air source heat pump compression ratio and COP. It gives the key parameters affecting the compression ratio and COP, pointing out ways to improve the heat pump COP. Finally, a key measure to improve the thermal performance of the unit system is proposed, to provide a reference for future practical applications and research. Foreword Air source heat pump in ambient air contains rich low grade solar potential as a source of heat, it has inexhaustible characteristics [1] . The main reason for restricting the use of air source heat pump in northern area of our country is when the outdoor air temperature is low in winter, the outdoor coil frost severe heating efficiency air source heat pump is greatly reduced. Martinez suggested experimental study on the application of solar radiant floor heating systems , solar water temperature is 50-60°C, low efficiency, especially when overcast snow lower system efficiency [2] .In view of the outdoor coil frosting problem, direct expansion solar assisted heat pump water heater system using the proposed by Li Yuwu, from a certain extent alleviated the problem of heat in winter for coil winter fros, improving the heating coefficient and improved the operating characteristics of the unit. However, this system requires the direct absorption of heat in air tube, and the specific heat of air is small, difficult to heat storage, illumination by solar radiation impact, unstable system operation [3]. Based on the above issues, for the low-level office building , the new rural residential , this study presents low temperature solar auxiliary air source heat pump system , the device uses low-temperature solar hot water heat pump system as low , both full use of solar energy , but also eliminates the original system frost problems and improve the efficiency of solar collectors and heat set to improve the evaporation temperature of the evaporator , thereby increasing the compression ratio of the heat pump unit .

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.