电动汽车热泵空调系统综述

在新能源汽车市场高速发展下,其续航里程却提升缓慢。为了降低冬季PTC(Positive Temperature Coefficient正温度系数)加热下对续航里程的影响,热泵系统是目前效率最高的方案。本文首先对于新能源汽车不同的热泵模式进行优缺点分析和比较。其次,结合国内外学者的研究,分析了在新能源汽车热泵设计中所要面对的部分难点,并给出了解决方案。最后,为热泵系统未来的发展方向提出了建议。     

Performance evaluation of a vapor injection heat pump system for electric vehicles

Battery-powered electric vehicles (EV) need an efficient electric heating system for extending the driving mileage. An air-source heat pump system offers an economical alternative for EV because it consumes less energy than a heating system using Joule heat and it can use the same components as an air conditioning system for cooling. However, its performance degradation is inevitable at very low ambient temperatures. Although vapor refrigerant injection is known as a good technology to overcome this problem in residential heat pump systems, the number of vapor injection heat pump studies for EV applications is quite limited. In this paper, considering the characteristics of EV application, the configuration of a vapor injection heat pump system for EV is introduced, and it was modeled, using a scroll compressor geometry-based thermodynamic analysis. The performance was estimated for cold ambient regions under the EV operational conditions.     

大温差空气源热泵在供暖系统中的应用

为了解决空气源热泵在供暖系统存在的末端匹配性差、系统运行费用高等问题,提出一种适应大温差高效热能输配的热泵系统。通过理论分析和试验验证,对大温差空气源热泵在供暖工程中的应用进行研究,比较大、小温差下的热泵系统的节能效果和供暖效果。研究结果表明:按照GB/T 25127.1—2020测算,采用大温差空气源热泵的制热系统全年制热季节性能系数HSPF可提升57%以上,循环水泵耗电量占比下降73%以上,室内温度变化偏差为±0.2℃,可以推广应用。     

电动汽车热泵空调冷凝器空气侧性能模拟与结构优化

电动汽车热泵空调是用于解决电动汽车冬季无法制热的问题,本文设计一种用于电动汽车热泵空调的新型平行流换热器。通过对换热器的冷凝工况进行数值模拟,得到不同入口速度条件下的换热及阻力特性,并与经验公式进行比较,验证数值模拟的正确性。分析不同的翅片倾斜角度及翅片间距下换热及阻力特性变化,得到优化的结构参数,为电动汽车热泵空调换热器设计提供依据。     

Simulation based identification of the ideal defrost start time for a heat pump system for electric vehicles

Resistance heating with PTC elements to cover the heat demand of electric vehicles reduces significantly the cruising range at low outside temperatures. Reversible heat pump systems are one of the most promising solutions for this problem. However, in heat pump mode the frost formation on the exterior heat exchanger reduces the performance and efficiency of the system. Therefore, an efficient defrost method is crucial to benefit from the heat pump also under frosting conditions. In the present paper, a transient Modelica simulation model of a reversible CO₂-heat pump system with hot gas defrost was set up in order to assess the impact of different defrost start times. The model is able to handle frost growth on the exterior heat exchanger as well as defrosting. The simulation results showed an optimal point of time to conduct defrost at chosen operating conditions in order to maximize the average COP including the frosting and defrost period.     

长沙地区空气源热泵地板采暖系统实测分析

为了了解夏热冬冷地区空气源热泵用于地板采暖系统的运行特性和实际采暖效果，本试验以长沙某栋写字楼的一套办公室为研究对象，对系统在初始运行、连续运行、间歇运行工况下的室内温度、围护结构表面温度、机组供回水温度作了测量，得出相关曲线图，测算出能耗及运行费用情况。基于实测数据。对长沙地区空气源热泵地板采暖系统进行技术经济性分析，并提出相关改进意见。     

空气源热泵辅助供热太阳能热水系统技术经济性分析

结合昆明地区的气候特征,分别以电加热热水系统与燃气热水系统为参照,对空气源热泵辅助供热的太阳能热水系统集中供生活热水进行技术经济性分析。研究结果表明,在昆明地区采用空气源热泵辅助供热太阳能热水系统,节能性与经济性均较显著,是适宜推广的生活热水系统形式。     

一种电动汽车谐振式无线供电系统的研究

针对谐振式无线供电系统初级线圈和次级线圈相对位置变化引起接收功率及输出电压变化的现象,以及二极管整流导致次级电路电流畸变和功率因数下降等问题,提出了一种基于PWM整流的电动汽车谐振式无线供电系统,即采用电压外环及电流内环的双环控制方法,以保证供电系统的单位功率因数及直流电压的恒定输出,并且利用ANSYS和MATLAB/Simulink仿真软件,分别研究电动汽车停车充电位置偏差对互感的影响及基于PWM整流的谐振式无线供电系统的性能,仿真结果验证了方案设计的有效性.     

Performance comparison between a single-stage and a cascade multi-functional heat pump for both air heating and hot water supply

Multi heat pumps have been widely used in buildings due to their higher energy efficiency. Recently, demands for multi-functional heat pumps, which can provide heating, cooling, and water heating in a building, have been increased. In this study, a cascade multi-functional heat pump, combining a multi heat pump using R410A for air heating with a water heating unit using R134a for hot water supply, was investigated experimentally. The performance of the cascade multi-functional heat pump was measured by varying the refrigerant charge amount, EEV opening, water flow rate, and water inlet temperature. Test results were compared with those of a single-stage multi-functional heat pump using R410A for air and water heating. The cascade multi-functional heat pump adopting the water heating unit showed more stable air and water heating operations and higher water outlet temperatures than the single-stage multi-functional heat pump.     

Performance of an air to air heat pump in a temperate climate

The performance of a commercial air-air heat pump installed in an occupied house in New Zealand is reported. The data cover operation both before and after the heat pump was extensively modified to improve the efficiency and reliability. The consequences of the non-optimal refrigerant charge and capillary in the original unit are illustrated and the advantages of installing a suction accumulator, crank-case heater and other improvements described. The results also show the sensitivity of the operating time to changes in the heating capacity and the difficulty in sizing a heat pump for normal residential use.     

Defrost cycle performance for a circular shape evaporator air source heat pump

Air source heat pumps have numerous advantages in many applications over other heating equipment with regard to energy efficiency. However, there are two main problems with air source heat pumps: (1) heating capacity decreases when the outdoor air temperature becomes lower and (2) when there is frost formation on the outdoor heat exchanger surfaces in humid climates. This paper will examine the defrost cycle for a residential heat pump with circular shaped evaporator coil in more detail paying special attention to the high humidity conditions encountered in maritime climates. The investigation was to optimise the efficiency of an air source heat pump operating under a range of conditions that would include defrost. Performance optimisation was achieved through a series of experiments carried out to the EN14511 test standard from which it was possible to note the best defrost initiation condition, defrost operating time and intervals between defrosts that most benefited the performance of the heat pump.     

Investigating control strategies for a domestic low-temperature heat pump heating system

Despite energy conservation regulations and efforts for improving HVAC operations, numerous domestic buildings do not perform energy efficiently and many times the indoor environment is far away from specified comfort levels. Especially in houses served from low-temperature heating systems the low ability of the heating system to respond to fast changing thermal loads is common. In such cases, the implementation of new, sophisticated controls is an important issue. In this study, we use a reference model of a domestic low temperature heat pump heating system developed in TRNSYS–EES and analyse its operation. Several methods of control strategies have been applied for specified time periods in order to keep the comfort within reasonable ranges. Prognostic climatic control and increased ventilation rates when required are some of these methods. The results depict the influence of the control method on the indoor temperature and the comfort indexes of PMV and PPD. The highest indoor temperature difference for a chosen day reaches 4 °C when there is no shading and when there is internal shading with the option of applying prognostic climatic control. Generally, the findings highlight the importance of dynamics in controlling functions and the difficulty of incorporating in models unpredictable factors as the solar radiation.     

Modelling and simulation results for a domestic exhaust-air heat pump heating system

Energy consumption in residential buildings has gained an increasing interest the latest years due to the rising demand for efficient energy use and higher comfort standards. In tight building constructions with controlled ventilation, heat recovery with exhaust-air heat pump connected to floor heating is regarded as energy efficient heating system that optimises the energy use in buildings while maintaining an acceptable level of thermal comfort. In this study, we use the computational tools TRNSYS and EES to model and analyse the performance of a residential house, its ventilation system and its floor heating system based on an exhaust air heat pump. The system analysis focuses particularly on the influence of internal and solar gains on the operation of the heating system and the thermal comfort of the house. Furthermore, the way that gains influences the performance of the floor heating system is examined. Overall, the results bring to light the impact of factors that are not easy to predict on the indoor climate and the thermal comfort.     

Defrost cycle performance for an air-source heat pump with a scroll and a reciprocating compressor

A 10.6 kW nominal cooling capacity air-source heat pump was tested according to ANSI/ASHRAE Standard 116-1983 for the frost acumulation and defrost cycle. These tests required indoor conditions of 21.1°C (70°F) dry-bulb, 15°C (60°F) maximum wet-bulb, with outdoor conditions of 1.7°C (35°F) dry-bulb, 0.5°C (30°F) wet-bulb. The unit was tested with the original scroll compressor and a reciprocating compressor that yielded similar heating performance. Heating capacity for the scroll system peaked at 8.4 kW (2.38 tons), while the reciprocating system heating capacity peaked at 8.5 kW (2.42 tons) during the frosting period. Heating capacities for the two system configurations differed by less than 1% during the frosting period. Power demand for the scroll system peaked at 2.9 kW, and the reciprocating system power demand peaked at 3.1 kW. During the frosting period, the reciprocating system power demand averaged 7% higher than the scroll system power demand. The reciprocating system completed a defrost 5% faster than the scroll system. Scroll system defrost time was 6.8 min while reciprocating system defrost time was 6.5 min. The volume of condensate produced differed by less than 3% with 1680 ml (102.5 in³) and 1640 ml (100 in³) produced by the scroll and reciprocating systems, respectively. Discharge pressures during defrost were within 3% with peak values of 1315 kPa (191 psia) and 1351 kPa (196 psia) for the scroll and reciprocating systems respectively. The reciprocating compressor produced higher levels of discharge superheat, peaking at 53°C (95°F) compared to the scroll system peak discharge superheat of 47°C (85°F). Overall, discharge superheat for the reciprocating system averaged 18% higher than the scroll system. The reciprocating system produced defrost refrigerant flowrates that averaged 3% higher than the scroll system. Refrigerant flowrates for the scroll and reciprocating systems peaked at 3.7 kg min⁻¹ (8.2 lbm min⁻¹) and 4.0 kg min⁻¹) (8.8 lbm min⁻¹) respectively.     

纯电动汽车热泵空调系统优化

针对纯电动汽车在冬季行驶过程中热泵空调系统外部换热器结冰失效的问题,提出增加主动式可调节进气格栅以及使用分层空调系统的优化设计方案,并通过整车环境模拟试验进行验证。结果表明:车辆装配主动式可调节进气格栅,运行1 h后,外部换热器的最大结霜面积不超过总面积的30%,热泵空调系统可以一直正常工作;在相同条件下,分层空调系统出风口温度较传统空调系统高5～6℃,达到设定目标温度用时更短,该方案既可增加整车续航里程,又具有较高的制热效率及整车舒适性。     

低温热水地板与热泵空调器采暖测试对比分析

通过对重庆地区一住宅内温水地板供暖系统的测试,分析对比了该系统与热泵空调器采暖方式对室内热舒适性的影响及运行费用的差别,同时对地板辐射和对流散热的综合效果进行分析,表明在长江流域等非采暖地区应用地板辐射采暖的可行性及优越性.     

CO2热泵技术在供暖系统中的应用研究

针对自然工质CO2跨临界循环存在高排气温度和温度滑移等特点,论证其在热泵热水系统方面应用的优势。开发一套CO2热泵供暖系统,对供暖系统的热负荷和供热能力进行计算,同时对系统中的制冷机组、换热器、阀件、通风系统及风道进行试验分析。实际运行结果表明,该系统性能稳定、运行可靠、各项测试精度达到要求。     

Simulation of a transcritical CO2 heat pump cycle for simultaneous cooling and heating applications

A steady state simulation model has been developed to evaluate the system performance of a transcritical carbon dioxide heat pump for simultaneous heating and cooling. The simulated results are found to be in reasonable agreement with experimental results reported in the literature. Such a system is suitable, for example, in dairy plants where simultaneous cooling at 4 °C and heating at 73 °C are required. The optimal COP was found to be a function of the compressor speed, the coolant inlet temperature to the evaporator and inlet temperature of the fluid to be heated in the gas cooler and compressor discharge pressure. An optimizing study for the best allocation of the fixed total heat exchanger inventory between the evaporator and the gas cooler based on the heat exchanger area has been carried out. Effect of heat transfer in the heat exchangers on system performance has been presented as well. Finally, a novel nomogram has been developed and it is expected to offer useful guidelines for system design and its optimisation.     

Optimization of a transcritical CO2 heat pump cycle for simultaneous cooling and heating applications

Energetic and exergetic analyses as well as optimization studies of a transcritical carbon dioxide heat pump system are presented in this article. A computer code has been developed to obtain sub-critical and super-critical thermodynamic and transport properties of carbon dioxide. Estimates for irreversibilities of individual components of the system lead to possible measures for performance improvement. The COP trends indicate that such a system is more suitable for high heating end temperatures and modest cold end temperatures. Expressions for optimum cycle parameters have been developed and these correlations offer useful guidelines for optimal system design and for selecting appropriate operating conditions.     

Residential CO2 heat pump system for combined space heating and hot water heating

A theoretical and experimental study has been carried out for a residential brine-to-water CO₂ heat pump system for combined space heating and hot water heating. A 6.5 kW prototype heat pump unit was constructed and extensively tested in order to document the performance and to study component and system behaviour over a wide range of operating conditions. The CO₂ heat pump was equipped with a unique counter-flow tripartite gas cooler for preheating of domestic hot water (DHW), low-temperature space heating and reheating of DHW.

The CO₂ heat pump was tested in three different modes: space heating only, DHW heating only and simultaneous space heating and DHW heating. The heat pump unit gave off heat to a floor heating system at supply/return temperatures of 33/28, 35/30 or 40/35 °C, and the set-point temperature for the DHW was 60, 70 or 80 °C. Most tests were carried out at an evaporation temperature of −5 °C, and the average city water temperature was 6.5 °C. The experimental results proved that a brine-to-water CO₂ heat pump system may achieve the same or higher seasonal performance factor (SPF) than the most energy efficient state-of-the-art brine-to-water heat pump systems as long as: (1) the heating demand for hot water production constitutes at least 25% of the total annual heating demand of the residence, (2) the return temperature in the space heating system is about 30 °C or lower, (3) the city water temperature is about 10 °C or lower and (4) the exergy losses in the DHW tank are small.