最新刊期
卷 39 ， 期 5 ， 2018
- 摘要：The present research situation of CO2 heat pumps at home and abroad is reviewed, and the important problems in its application process are summarized in the paper. The characteristics and drawbacks of the components and systems, such as the compressor, heat exchanger, and throttle device, are introduced in detail. The latest technological means to improve the efficiency of the system are analyzed, and its development in China is forecasted. The primary reasons for restricting promotion of the CO2 heat pump is high development cost, strict processing technology, and immature, costly, dedicated compression technology. The main research content of the CO2 heat pump in the future is to improve the system, optimize the components, and to combine accurate computer control technology with the achievement of the simultaneous development of hardware and software, so that CO2 heat pump will be operated efficiently, safely, and reliably. It can be predicted that the CO2 heat pump will have promising development in China.关键词：CO2 heat pump;transcritical cycle;review;heating;refrigeration2396|3338|5发布时间：2024-07-18
- 摘要：Through the promotion policy of energy saving and emission reduction in China, space heating has been gradually transformed from the traditional small coal-fired boiler to a clean heating mode. As a key technology of clean heating, the application and development of air-source heat pump is growing rapidly due to its energy conservation, high efficiency and environment protection. However, frost occurs on the surface of the finned-tube heat exchanger when the surface temperature is below both the dew point temperature of ambient air and the freezing point temperature. Frosting on the surface of the evaporator increases the heat transfer resistance of the heat exchanger and then decreases its heat transfer coefficient and the COP of the system so that the application and popularization of the air source heat pump system is seriously limited under the clean heating policy of substituting coal with electricity in China. Thus, it is of great significance that the frosting mechanism on a cold surface is investigated to explore the defrosting technology of high efficiency and long-term-effective anti-frosting technology for the development of air-source heat pump technology and the promotion of clean heating policy. In the present paper, firstly, the research status of frosting mechanism on the cold surface is briefly described, as based on the growth law of a frost layer and its physical properties. Various factors, including air temperature, air relative humidity, air flow rate, surface characteristic, surface temperature, structure of finned-tube heat exchanger, etc., affecting the frosting process and the corresponding defrosting/anti-frosting method, such as reverse cycle, hot gas bypass, electric heater, low-frequency oscillation, hot water spray, ultrasonic vibration, electric field, magnetic field, changing the characteristics of inlet ambient air, changing surface temperature, surface treatment methods and so on are summarized. The research progresses of three kinds of common defrosting methods, including reverse cycle defrosting, hot gas bypass defrosting and electric heating defrosting are reviewed. The electric heating defrosting method can improve the indoor comfort during defrosting in comparison with the other two methods. The anti-frosting effects are analyzed based on changing air parameters, cold surface temperature, and heat exchanger structure. The research progress of anti-frosting technology is summarized for changing surface characteristics methods. Finally, the limitation of the thermal conductivity model of frost layers and the problems existing in defrosting/anti-frosting technology are pointed out. Based on the previous review and analysis, it is suggested that effects on defrosting technology of indoor comfort and energy consumption should be further studied; several measures should be taken to explore the anti-frosting technology, which can strongly inhibit different stages of frosting process, such as condensation of water vapor, condensate water freezing, frost layer melting and collapse. In addition, because of the limitation of the length of the article, research progress and existing gaps of other defrosting and anti-frosting techniques are not provided. This paper can be used for guiding the future design and system optimization for air source heat pump.关键词：air-source heat pump;evaporator;frosting;defrosting;anti-frosting2452|2373|6发布时间：2024-07-18
- 摘要：To evaluate an air source heat pump unit’s operation performance in the frosting-defrosting process efficiently and to explore its operational performance under frosting conditions, the loss coefficient of the nominal heating capacity is proposed in this paper. Lab and field tests to date are conducted to establish a loss coefficient for the nominal heating capacity model based on generalized regression neural network. The result of the research shows that the model’s correlation coefficient |r|, is higher than 0.9 and the expected error percentage (EEP) is lower than 6.5%. These results indicate that the model in this paper could be successfully used in predicting operation performance in the frosting-defrosting process of the air-source heat pump. The simulation result can be used in searching for an optimized defrosting control point under different frosting-defrosting conditions.关键词：air-source heat pump;frosting-defrosting process;evaluation of operating performance;loss coefficient of nominal heating capacity;prediction model2018|2130|1发布时间：2024-07-18
- 摘要：During the 2016-2017 heating season, the floor heating systems of a teaching building in Beijing was carried out for a field test. There are two air-source heat pump (ASHP) systems for two areas, i.e. area A and area B, in the building. The room temperature control and hydraulic balancing devices were equipped in the system of area A, and the system operation mode was divided into two periods: Period 1 with a water supply temperature of 35 °C for heating and Period 2 with a temperature of 20 °C for freeze protection. After 67 days of monitoring the indoor and outdoor temperatures, the temperature and flowrate of supply and return water, and power consumption, the operation effect of the two systems was compared and analyzed. The results show that during Period 1, the system of area A not only ensures a more suitable indoor temperature, but also a significantly lower heating capacity than area B, as well as a 24.4% energy saving effect on power consumption. In addition, the control devices do not affect the unit performance of area A. The COPs (coefficient of performance) of areas A and B were 3.56 and 3.54, respectively, and the actual operating performance of the unit was close to the performance curve. During Period 2, the thermostat setting remained unchanged, and the energy saving rate of area A decreased slightly to 16.3%. It is recommended that the thermostat should be set to match the water supply temperature for further energy savings.关键词：air source heat pump;room temperature control;floor heating;energy-saving;field test1957|2133|2发布时间：2024-07-18
- 摘要：The effect of the subcooling circuit on the cooling and heating performances of a multi-split VRF system was studied experimentally and a control strategy for multi-split VRF system with subcooling circuit is proposed in the paper. The results show that the subcooling circuit has a greater potential for improving the cooling capacity and the EER of the multi-split VRF system when the VRF system has a longer pipeline between the indoor units and the outdoor unit, a larger part-load ratio and a higher inlet water temperature of the outdoor unit, while the subcooling circuit has less influence on the heating capacity and the COP of the multi-split VRF system. Based on the results, a control strategy of the subcooling circuit is proposed, which takes the outlet subcooling degree of the outdoor unit, the compressor discharge temperature and the outlet superheat degree of the bypass stream in the subcooling heat exchanger as decision parameters and control targets of the subcooling circuit.关键词：multi-split VRF system;subcooling circuit;control strategy;pipeline length2129|2169|0发布时间：2024-07-18
- 摘要：This study develops a set of CO2 transcritical automobile heat pump air-conditioning systems, which adopts a CO2 vehicle electrical compressor, micro-channel heat exchanger, electronic expansion valve and other key components. This is to overcome technical challenges brought by CO2 automobile’s heat pump air-conditioning system such as high pressure and high exhaust temperature. The effects of the amount of system refrigerant charge on the system performance, circulation characteristics, and the expansion valve opening of the CO2 automobile heat pump air-conditioning are studied in this paper. In addition, this paper proposes a series of indoor heat exchangers to increase the heat transfer capacity of the high-pressure side in the heat pump mode, and experimentally verifies the effect of this method on automobile heat pump air-conditioning system performance. Results show that compared with the single gas cooler, the automobile heat pump air-conditioning system with series gas coolers achieves an increase in heating capacity of 17-31% and coefficient of performance（COPh）of 20-33%. The system can generate 40.4 °C gas cooler outlet air and COPh = 1.8 under the environment of﹣20 ℃ fresh air mode. Therefore, the developed CO2 automobile heat pump air-conditioning system can satisfy passenger comfort and vehicle load demand under a low-temperature environment for electric vehicles and has a very significant advantage in heating energy efficiency.关键词：automotive heat pump;heating performance experiment;CO2 refrigerant;transcritical cycle;electric vehicle2436|2443|6发布时间：2024-07-18
- 摘要：Five pairs of binary blend refrigerants with small temperature glides are proposed to be used in medium-high temperature cascade heat pumps according to the results of theoretical comparative studies, including thermophysical properties, cycle performance, environmental impact, and flammability of several potential working fluids under the refrigerants developing criterion. While R161/R1234yf and R161/R290 are found to be suitable to the sub-system of the low-temperature heating cycle, R152a/RE170, R152a/R1243zf, and R245fa/R1234zeZ are practical in the high-temperature heating cycle sub-system. Compared to the common cascade heat pump running with refrigerants R22+R134a, it is discovered that blend refrigerants that consist of R161/R1234yf+R152a/RE170 or R161/R290+R152a/RE170 possess optimal comprehensive performances. These blend refrigerants have the highest coefficient of performance （COP） of 1.58, under hypothetical working conditions for producing hot water at 80 °C. Special attention should be paid to their flammability. When using R245fa/R1234zeZ in the sub-system of high-temperature heating cycle, both the high pressure and flammability risk can be reduced significantly. In addition, the condensing temperature of system can be as high as 120 °C (about 2.1 MPa in pressure), and it would be better if using the compressor with a large working volume.关键词：refrigerant;heat pump;global warming effect;flammability2301|3024|3发布时间：2024-07-18
- 摘要：A normal heat pump air conditioner needs condensation dehumidification, leading to low energy efficiency. To improve the energy efficiency, a novel integrated dehumidification heat pump air-condition cycle, based on a desiccant-coated heat exchanger, is presented in this paper. Through the establishment of experiment table, the performance under summer condition of the novel cycle is tested and the influence of key operational parameters are analyzed. The results show that the novel integrated dehumidification heat pump air-condition cycle has good performance: the dehumidification quantity can reach 7.9 g/kg, and the coefficient of performance（COP）of the system can reach 5.2. The change in the temperature of fresh air and return air has influence on the temperature of supply air and COP. The change in humidity of the fresh air and return air has also influence on the temperature and humidity of the supply air, the dehumidification quantity, and COP.2000|2096|6发布时间：2024-07-18
- 摘要：In this study, the working principle of a heat pipe radiation heating device driven by heat pump was proposed. The prototype has been developed for testing based on a 1 HP compressor and the operating characteristics of the prototype under the working conditions of indoor temperature from 18 ℃ to 22 ℃, outdoor temperature from -15 ℃ to 0 ℃ are tested in the air enthalpy room. The experimental results showed that the heat pipe radiator can start rapidly and has a uniform temperature distribution. The optimal charge of heat pipe working fluid ratio is 0.1. The maximum heating coefficient of performance (COP) of the system can reach 4.1 under the condition of 22 ℃ indoors and﹣15-0 ℃ outdoors.关键词：heat pump;heat pipe;heating;COP1969|2308|1发布时间：2024-07-18
- 摘要：Based on the energy saving demand in operation of a ground water heat pump system (GWHP)，this study analyzes the disadvantages of the original operation strategy and proposes a new operation strategy based on indoor initial temperature. It is validated by a water supply temperature regulation experiment that the new operation strategy can save energy compared to the original operation strategy. The bypass valve closing test is carried out according to the operation status of the system. Both of these tests are carried out in late June. The results show that in similar external weather conditions and trends，the chilled water supply temperature changes from 11 to 12 °C，and the cumulative power of the system in two hours is reduced by 37.8 kW?h. The cumulative power is reduced by 7 kW?h when circulating water pump runs at 35 Hz for three hours after the bypass valve is closed.关键词：GWHP;operation strategy;bypass valve;circulating water pump;field test1911|1883|3发布时间：2024-07-18
- 摘要：The effective diffusivity is an important parameter for mass transfer research on the drying of sea cucumbers. The dependence of the effective diffusivity on temperature has been adopted in current studies, while the effects of moisture content and shrinkage have often been ignored. Therefore, in this paper, a finite element dry model is built and the diffusivity determination method based on the model is applied to study the diffusivity in sea cucumber heat pump drying. The influences of shrinkage during heat pump drying, temperature and moisture content on diffusivity have been studied and analyzed. The results show that the drying shrinkage, temperature, and moisture content affect the effective diffusivity greatly. The effective diffusivities, as determined by considering the effects of shrinkage, temperature and moisture content, are 3.9-14.6% lower than those considering the effects of temperature and moisture content The effective diffusivities determined by considering the effects of shrinkage and temperature are 8.7-14.5% lower than those only considering the effect of temperature. The effective diffusivity increases with both temperature and moisture content. Models considering drying shrinkage and influence of temperature and moisture content on diffusivity can preferably predict moisture content variation in line with the experimental values, with a coefficient of correlation higher than 0.994. The effective diffusivity decreases along the radial direction in the sea cucumber. As drying proceeds from 1 to 15 h, the difference in effective diffusivity between the center and the surface of sea cucumber reduces from 6.4 × 10-10 m2/s to 0.9 × 10-10 m2/s, and the effective diffusivity in the center decreases from 14.6×10-10 m2/s to 8.9×10-10 m2/s.关键词：heat pump;mass transfer;effective diffusivity;drying;sea cucumber1894|2161|1发布时间：2024-07-18
- 摘要：To improve the efficiency of space heating and cooling, the hybrid power-driven heat pump (HPHP) has been established. However, both the design method and operation strategy are too simplified, thus optimization is needed. In this paper, the HPHP with a gas engine and motor is put forward, and a mathematic model of HPHP is established to analyze its operation performance under a typical design (i.e., the gas engine takes 60% of the torque output under the design condition). The operation performance of the HPHP is also compared with gas engine-driven heat pump（GEHP）and electrical heat pump (EHP). The results show that the HPHP system can achieve 3-10% improvement of engine efficiency compared to the GEHP. The primary energy ratio (PER) of the optimized system is 6.9% and 5.4% higher than that of GEHP and EHP, as the ambient temperature is﹣5 ℃. The HPHP system can achieve higher energy saving potential for the whole heating season.关键词：gas engine-driven heat pump（GEHP）;air-source heat pump;hybrid power;space heating;operation strategy1827|1987|1发布时间：2024-07-18
- 摘要：This paper establishes a set of gas-engine heat pump (GEHP) experimental systems with R134a as the refrigerant and natural gas as the primary energy source to drive the open compressor. The performance of a GEHP with cooling and hot water supply were tested with evaporator water inlet temperatures ranging from 12-22 °C, ambient air temperature ranging from 24.2-35.6 °C, and gas engine speeds ranging from 1400-2000 r/min. The results show that the effects of evaporator water inlet temperature and gas engine speed on the system performance were more significant than those of ambient air temperatures. As gas engine speed varies from 1400 r/min to 2000 r/min, the COP1, COP2, PER1, and PER2 of the system increases by 15.5%, 9.9%, 18.8%, and 13.5%, respectively. Within the range of working conditions, the average cooling water outlet temperature can reach 6.7-19.3 °C, the average hot water outlet temperatures can reach 40.7-61.7 °C, and the primary energy ratio (PER2) of GEHP system can reach 1.14-1.45 considering heat recovery.关键词：gas engine-driven heat pump;cooling;domestic hot water;heat recovery;energy efficiency1856|1943|1发布时间：2024-07-18
- 摘要：In this paper, the mathematical model and experimental platform of the cross-flow heating tower are established. The effect of non-uniform liquid distribution on heat and mass transfer performance in the cross-flow heating tower is studied under different fluid flow and air volume conditions. The results show that the total heat exchange has an inverted “U” curve relation to the uniformity coefficient of liquid distribution,σ. The higher the absolute value of the uniformity coefficient of liquid distribution,|σ| is, the worse the total heat exchange performs. When the mass flow rate of the solution is 1.4 kg/s and σ=0-1, the total heat exchange capacity decreases from 13.60 kW to 12.01 kW(a decrease of 11.69%). The heat and mass transfer performance of the cross-flow heat source tower is related to the size of σ, and has nothing to do with the direction of σ.关键词：cross-flow heating tower;non-uniform liquid distribution;heat and mass transfer performance2060|1892|2发布时间：2024-07-18
- 摘要：In this study, a heat pump system with two dehumidifying and reheating modes for electric vehicles was set up, and the operating characteristics of the heat pump system were compared in two dehumidifying and reheating modes under various test conditions. Test results showed that energy consumption of the heat pump system was below 2.0 kW, and COP was above 2.0 under all test conditions. The dehumidifying and reheating mode A has better dehumidification performance with moisture extraction rate ranging from 0.41-0.83 kg/h and heating capacity ranging from 1.7-3.0 kW, while dehumidifying and reheating mode B has better reheating performance, with moisture extraction rate ranging from 0.25-0.55 kg/h and heating capacity ranging from 2.0-3.4 kW. Based on the characteristics of two modes, an energy saving strategy was proposed as a possible option for realization of energy conservation without sacrifice of thermal comfort for passengers.关键词：automotive air-conditioning;heat pump;dehumidification;coefficient of performance2078|2571|2发布时间：2024-07-18
- 摘要：Many designers simply take rated COP (coefficient of performance) and heating capacity into consideration in terms of the performance of air-source heat pumps, leading to an insufficient heating effect of heat pumps under low temperature conditions in a hot-summer and cold-winter zone. To solve this problem, this paper established three models of capacity output, energy efficiency ratio and dynamic load demand of buildings in summer and winter, and all the three models were tested in varying operation condition. Since the capacity output of heat pumps and load demand of buildings are coupled and influenced by indoor and outdoor temperature and outdoor humidity, a comprehensive analysis of factors including indoor and outdoor temperature and outdoor humidity on the heat pump performance were conducted. As a result, the paper introduced three indicators in selecting heat pumps, namely heat pump capacity output, energy efficiency ratio in the most unfavorable conditions and a stable operation conditions where the capacity output can satisfy the demand of buildings. With the operation method mentioned above, the actual performance of the selected heat pumps and the degree to which they satisfy the building load demand can be effectively predicted. Meanwhile, the selection method and evaluation standard of air-source heat pump can be greatly improved.关键词：air-source heat pump;selection of heat pump;analysis of varying operation condition;coupling model2052|2067|1发布时间：2024-07-18
- 摘要：In order to improve the energy efficiency of gas engine-driven heat pump system in low-temperature environments, a cascade gas engine-driven heat pump (CGEHP) was designed based on the gas engine heat pump and the cascade heat pump technologies. The simulation model of the CGEHP was established and researched using MATLAB. The influencing rule of the coefficient of performance (COP) and primary energy ratio (PER) were analyzed under different conditions, such as gas engine speed, ambient air temperature, and cooling water inlet temperature. The results show that when the ambient air temperature is ﹣20 ℃, ﹣15 ℃, and ﹣10 ℃, with NH3-LiNO3 solution as the working pair of absorption heat pump subsystem and the gas engine speed is 1 500 r/min, the PER of the CGEHP is 1.0, 1.02, and 1.04 respectively, which was improved by 24%, 15%, and 5% respectively, compared with the conventional air source electric heat pump system.关键词：gas engine-driven heat pump;cascade heat pump technology;low temperature environment;primary energy ratio（PER）1935|2076|0发布时间：2024-07-18
- 摘要：During operation, the energy consumption of an air conditioning system has a great influence on energy savings of the whole system. Therefore, the development of cooling water technology with a large temperature difference will help reduce energy consumption of air conditioning system. The relationship between the chiller parameters and temperature difference of cooling water is obtained through theoretical analysis and derivation in this paper. In different experimental conditions with different cooling water temperature difference, the energy consumption of the chiller and cooling water pump is analyzed. The results indicate that with an increase in the cooling water temperature difference, the energy consumption of the air-conditioning system decreases gradually, although the energy consumption of the chiller increases gradually. When the temperature difference is 8 ℃, the maximum EER of air conditioning system is 3.173. The energy saving effect of the air conditioning system is obvious when the cooling water temperature difference is 7-9 ℃.关键词：air conditioning;chiller;experiment conditions;energy saving2064|2769|0发布时间：2024-07-18
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