共查询到19条相似文献,搜索用时 109 毫秒
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将结霜的主要影响因素和热泵系统对结霜状况的响应这两个方面确定为机组开始除霜的输入判据。在此基础上,研究模糊除霜的控制算法,确定隶属函数与模糊集,建立模糊规则表,并且确定除霜指令和除霜效果的评判,为实现空气源热泵热水机组的实时除霜控制和提高机组的运行性能奠定基础。 相似文献
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结霜是降低空气源热泵冬季制热能力的主要因素之一,目前解决结霜问题的主要技术路线是抑霜和高效率除霜。本文通过总结国内外学者对空气源热泵抑霜除霜技术的研究工作,分析目前抑霜和除霜技术的优缺点及其适用性。研究显示:改变蒸发器进口空气参数以及改变蒸发器结构等都能够起到抑霜的作用,无能耗或仅带来较小的能耗;电热除霜以额外消耗电能为代价,在冰箱中应用较多;逆循环除霜和热气旁通除霜是目前常用的除霜方式,但只适用于小型制冷、热泵装置;蓄能除霜尚处于试验和模拟阶段;未来需要开发一种能量损失更小、持续制热且不停机的新型除霜方式。 相似文献
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为实现空气源热泵产品除霜性能测试工况的低温高湿环境,设计一种长期低温运行设备及其温度耦合控制系统,通过2套制冷系统的除霜模式与制冷模式的交替循环,解决因蒸发器结霜而导致制冷量下降问题。基于实际测试系统和研究,提出切入除霜、除霜结束的判定依据:电加热输出为零且环境测试间内干球温度高于设定值0.1℃作为切入除霜判定依据;在除霜过程中,蒸发器制冷剂出口温度高于环境测试间干球温度10℃,且蒸发器空气侧阻力小于150 Pa作为除霜结束判定依据。该方案能够解决环境测试间内因空气处理机组蒸发器除霜需求而造成的干球温度和相对湿度的剧烈波动问题,保证环境测试间内低温高湿环境工况的长期稳定,提高除霜工况的测试准确性。 相似文献
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空气源热泵机组除霜性能试验研究 总被引:1,自引:0,他引:1
为了研究不同节流机构、不同除霜方式对空气源热泵机组除霜性能的影响,在空气源热泵机组上对热力膨胀阀、电子膨胀阀作为除霜节流机构,以及采用“四通换向阀直接换向除霜”和“压缩机停机四通换向阀换向除霜”2种除霜方式,进行了试验比较研究。结果表明:采用电子膨胀阀的除霜时间比热力膨胀阀的短12s,即减少11%。笔者提出采用电子膨胀阀+压缩机停机四通换向阀换向除霜模式的结合,具备四通换向阀换向除霜的除霜强度,解决了“奔油”等部分缺陷,而且采用电子膨胀阀进行除霜可缩短部分除霜时间。 相似文献
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风冷热泵机组中的热气除霜方法 总被引:5,自引:1,他引:4
针对风冷热泵机组在制热工况下容易结霜的特性,本文论述了利用压缩机排出的热气来除霜的方法,阐述了热气除霜循环的原理和过程,并提出了除霜总负荷及除霜时间的计算方法。其中除霜总负荷包括预热负荷和除霜负荷。 相似文献
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通过对风冷热泵冷热水机组冬季制热运行时换热器结霜与除霜问题的研究,针对一种常见的逆循环除霜中旁通除霜法研究,提出了相应的减少除霜损失的措施。 相似文献
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一种新型空气源热泵除霜方式的实验研究 总被引:3,自引:0,他引:3
提出了一种新型空气源热泵除霜方式,其基本原理是在热汽旁通除霜循环的基础上将室外换热器分为前后两排,中间用毛细管节流,前后排换热管在除霜过程中分别作为蒸发器和冷凝器,利用四通阀换向分别对其进行除霜.对新循环除霜性能进行了实验研究,并与逆循环除霜方式进行了比较.实验结果表明,新型分组节流除霜方式合理地利用了除霜能量,因此除霜时间及除霜损失小于传统逆循环除霜方式.而且在除霜过程中不从室内吸收热量,对其温度波动影响较小.在除霜过程中,新除霜方式的四通阀换向次数与逆循环除霜方式相同,但系统压力的波动幅度远远小于逆循环除霜方式,因此对系统的机械冲击要小得多. 相似文献
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风冷热泵除霜过程动态特性模拟和实验研究 总被引:3,自引:0,他引:3
风冷热泵热气除霜过程动态特性的研究是风冷热泵(机组)研究的一个重要课题。在热气除霜实验研究的基础上,从基本守衡定律出发,提出了风冷热泵热气除霜过程的动态特性模型,重点模拟了这一过程中霜层侧的传热传质和制冷剂侧压力变化情况。回顾了热气除霜过程的研究现状,详细介绍了采用分布参数求解模型的过程,以及实验结果和模拟结果的比较。尽管在一定程度上这是一个理想化的动态特性模型,但实验结果和模拟结果的良好吻合证明了这一模型的有效性,可以应用于风冷热泵的全过程仿真研究。 相似文献
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Effects of fan-starting methods on the reverse-cycle defrost performance of an air-to-water heat pump 总被引:3,自引:0,他引:3
The effects of fan starting methods on the defrost performance in an air-source heat pump were investigated experimentally. Experiments were conducted on a 50 kW unitary air-to-water heat pump. The dynamic characteristics of both the coil fan pre-start and normal-start tests during the defrost cycle were discussed. The peak of discharge pressure for the fan normal-start test was up to 2595.6 kPa during defrost termination and recovery time, which was close to the discharge protection value (2650 kPa). The discharge pressure for the fan pre-start test was 742.3 kPa lower at the end of the drain time, so the peak of the discharge pressure was 687 kPa lower during the defrost termination and recovery time than that for the fan normal-start test. We found the phenomenon seemed to be related to both the small inner volume of the plate heat exchanger and larger refrigerant flow rate during the defrost termination and recovery time. Pertinent performance data (pressure, temperature, superheat, sub-cooling, etc) was plotted and discussed to determine the effects of the coil fan pre-start. 相似文献
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Frost, defrost, and refrost and its impact on the air-side thermal-hydraulic performance of louvered-fin, flat-tube heat exchangers 总被引:2,自引:0,他引:2
Y. Xia Y. Zhong P.S. Hrnjak A.M. Jacobi 《International Journal of Refrigeration》2006,29(7):1066-1079
The thermal-hydraulic performance under conditions of an initial frost growth on the air-side surface, and for subsequent ‘refrosting’ after a defrost period is experimentally studied for folded-louvered-fin, microchannel heat exchangers. In total, five heat exchangers are considered; the thermal performances during one frost-growth cycle for four different fin geometries are compared in terms of overall heat transfer coefficient, pressure drop, and j and f factors; the defrost and refrost characteristics of two heat exchangers are compared to explore geometry effects. Typically, the performance under refrosting conditions becomes periodic and repeatable after the third or fourth refrosting cycle. The allowable frost growth period (before a defrost is required), the defrost requirement, and the thermal-hydraulic performance depend on heat exchanger geometry for the specimens used in this study. 相似文献
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Hot gas defrost model development and validation 总被引:5,自引:0,他引:5
This paper describes the development, validation, and application of a transient model for predicting the heat and mass transfer effects associated with an industrial air-cooling evaporator during a hot gas defrost cycle. The inputs to the model include the space dry bulb temperature, space humidity, coil geometry, frost thickness, frost density, and hot gas inlet temperature. The model predicts the time required for a complete frost melt as well as the sensible and latent loads transferred back to the conditioned space during the defrost period. The model is validated by comparing predicted results to actual defrost cycle field measurements and to results presented in previously published studies.A unique contribution of the present model is its ability to estimate parasitic space loads generated during a defrost cycle. The parasitic energy associated with the defrost process includes thermal convection, moisture re-evaporation, and extraction of the stored energy in the coil mass following a defrost cycle. Each of these factors contribute to the parasitic load on compressors connected to the defrost return. The results from the model provide quantitative information on evaporator operation during a defrost cycle which forms the basis to improve the energy efficiency of the defrost process. 相似文献
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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. 相似文献
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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. 相似文献
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阐述了空气源热泵热水器的结霜特性,分析了热泵热水器化霜时与空调器不同的特征,提出了采用检测冷凝器温度与水温的差值来判断室外蒸发器是否结霜、检测室外热交换器盘管温度来判断除霜是否完成的两器盘管温度综合判断除霜法。 相似文献
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指出了全低压大型制氧机原解冻加热方法之不足 ,提出并详细介绍了一种新解冻加热方法 :大加热前的工作 ,大加热路线与步骤及主要优点 相似文献
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A significant advance in defrost control for ice removal in refrigerators, freezers, cold stores and heat pump cooling coils is described. This control is based on measurement of the thermal insulation effect of the ice layer, with automatic operation for defrost on demand. 相似文献