空气源热泵机组除霜性能试验研究

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。     

复叠式空气源热泵蓄能除霜与常规除霜特性实验研究

针对复叠式空气源热泵在冬季寒冷地区供热运行中遇到的结霜和除霜问题,本文提出增设蓄热器的蓄能复叠式空气源热泵除霜系统,通过实验研究了该系统间断制热蓄能除霜及不间断制热蓄能除霜两种除霜模式下的除霜特性,并与常规复叠式空气源热泵采用的低温级热气旁通除霜方式进行对比分析。结果表明:采用蓄能除霜方法的除霜时间较旁通除霜减少71.4%~77.6%,系统除霜能耗降低65.1%~85.2%,机组除霜运行更稳定、可靠。     

一种新型空气源热泵除霜方式的实验研究

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.     

一种新型分部除霜系统的试验研究

针对现有逆向除霜的不足,提出一种新型空调器除霜系统,其原理是在热气旁通除霜的基础上将室外换热器分成2个独立回路,利用电磁三通阀切换和单向阀导流,先后对2个回路除霜。对新型分部除霜方式与逆向除霜方式进行对比试验研究,结果表明,分部除霜方式除霜耗时少,除霜过程中室内换热器仍能提供部分热量,室内温度受除霜影响小,舒适性更好;系统排气压力波动幅度小于逆向除霜方式,可靠性高。新型分部除霜方式在单周期除霜洁净度上存在不足,而采用2种除霜方式相结合的"3+1模式"可以获得良好的除霜效果。     

风冷热泵旁通除霜问题的研究

本文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方法。     

采用相变蓄热模块多联式空调（热泵）系统除霜过程的试验研究

空调采用传统除霜方法对系统性能带来不利影响。本文通过试验研究采用相变蓄热模块的多联式空调（热泵）系统除霜过程的动态特性,并与常规的逆循环除霜方法进行对比。试验结果表明：在除霜、大湿度除霜和低温制热3种工况下,蓄热除霜的制热量比常规除霜时略高,整机的消耗功率基本相同,室内换热器的制热周期基本一致,但除霜期间室内机停机时间缩短一半;蓄热除霜除霜期间室内换热器盘管温度比常规逆循环除霜高20-25℃,蓄热除霜除霜期间室内换热器出风口温度比常规逆循环除霜高13-17℃,大大提高室内环境的舒适性。这表明相变蓄热除霜空调（热泵）系统除霜性能优于传统逆循环除霜空调（热泵）系统。     

多联机空气源热泵相变蓄能除霜特性试验研究

为了解决多联机空气源热泵常规除霜时间长、室内环境恶化等问题,提出多联机热泵相变蓄能除霜方法。针对提出的新方法,设计系统流程和试验方案,并在模拟室内外环境条件下完成试验研究。相对于常规除霜,新的除霜方法可以有效缩短33.7%的除霜时间,显著改善机组的除霜性能和室内供热环境。     

空气源热泵热水机组模糊除霜控制器的研究

设计了空气源热泵热水机组模糊除霜控制的方案,从输入量模糊化模块、模糊推理模块、除霜控制模块、除霜监控、规则调整模块等方面对模糊除霜控制器进行了深入研究。构建了完善的控制流程,并进行了实验研究;研究结果表明模糊除霜控制器有助于空气源热泵热水机组除霜性能的改进和提升,同时也提高了机组在低温、高湿工况下运行的稳定性和对环境的广泛适应性。     

房间空调器热气旁通法除霜分析及实验研究

通过对不同阻力的旁通电磁阀除霜进行实验研究,热气旁通法除霜可以较大程度地改善室内舒适性,旁通电磁阀的阻力大小直接影响着换热器除霜时间和除霜效果。经分析表明,采用电子膨胀阀和旁通电磁阀组合除霜不仅有良好的节能效果,还可较大程度地缩短除霜时间;压缩机吸气管温度大于０℃可作为结束除霜的判据之一。     

不常采用的冷库蒸发器除霜方法

本文介绍了适用于小型系统的热气除霜、气动除霜和超声波除霜的基本原理和应用范围。以较大篇幅介绍了天津商业大学提出的液体冷媒除霜方法的实验研究状况和相关参数的变化规律,总结了该除霜方法的控制逻辑和优、缺点。     

Hot gas defrost model development and validation

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.     

Optimal defrost cycle for the air cooler

By constructing a computer model of a frosted air cooler equipped for periodic defrost it has been possible to define a cooler efficiency parameter η_Q.Optimising η_Q leads to the conclusion that proper determination of the defrost initiation value may considerably increase the capacity of the air cooler. The model gives a better understanding of the processes occuring during defrost. Further development of this model will make the proper control of defrost initiation possible.     

Effects of fan-starting methods on the reverse-cycle defrost performance of an air-to-water heat pump

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.     

风冷热泵除霜过程动态特性模拟和实验研究

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。     

Optimal defrost cycle for the air coolerCycle optimal de dégivrage d'un frigorifére

By constructing a computer model of a frosted air cooler equipped for periodic defrost it has been possible to define a cooler efficiency parameter η_Q.Optimising η_Q leads to the conclusion that proper determination of the defrost initiation value may considerably increase the capacity of the air cooler. The model gives a better understanding of the processes occuring during defrost. Further development of this model will make the proper control of defrost initiation possible.     

Frost, defrost, and refrost and its impact on the air-side thermal-hydraulic performance of louvered-fin, flat-tube heat exchangers

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.     

Selecting the size of pipes carrying hot gas to defrost evaporators

The selection of correct pipe size for carrying hot gas to defrost evaporators is an important factor in conserving energy by such practices as maintaining low condensing pressures. The correct size will ensure that the resultant increase in specific volume of the hot gas that occurs at low pressures does not cause prohibitive pressure drops in the pipes. The way in which hot gas flow rates during defrost affects the pipe size selection is discussed together with the influence of saturation temperature.     

冷库热气融霜与电热融霜的对比分析

通过一个实际案例从能耗方面对冷库中的热气除霜和电热除霜进行对比分析,并从实验和理论方面进一步讨论,说明热气除霜的优越性。以往冷库中常用定时除霜,针对定时除霜的缺陷进行改进,采用时间温度法进行控制。     

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.