【作者】 董建锴；

【导师】 姚杨； 姜益强；

【作者基本信息】 哈尔滨工业大学 ， 供热、供燃气、通风及空调工程， 2012， 博士

【摘要】 空气源热泵在结霜区运行时，室外换热器壁面存在结霜现象。霜层的生长导致了机组供热性能的下降。为保证空气源热泵机组的高效运行，需要周期性除霜。目前，逆循环除霜是应用最广泛的除霜方法之一。逆循环除霜过程中，室外换热器变为冷凝器，室内换热器变为蒸发器。机组从室内环境取热融化霜层，造成了室内环境的恶化。另一方面，为了防止向室内吹冷风，除霜过程中室内风机关闭，除霜能量主要来源于压缩机做功和室内换热器盘管蓄热。因此造成了除霜能量的不足，从而造成较低的吸气压力，较长的除霜时间、较低的室内环境温度。为了改善空气源热泵机组结霜区的供热性能，提高除霜效率，本文在延缓结霜、过冷蓄能除霜，以及除霜控制方法等方面开展了理论和实验研究工作。针对不同研究内容，在两个人工模拟环境小室中设计并搭建了三套实验台。选取了热泵机组及数据测量和采集系统，确定了模拟室内外环境的控制策略，计算了实验台误差。结果表明所搭建实验台的测量误差在可接受的范围内。在研究空气源热泵结霜机理和室外换热器气流组织对结霜影响的基础上，提出了一种延缓空气源热泵结霜的新方法，即通过室外风机换向，在供热运行时，将室外换热器由常规的负压区变为紊流正压区，从而利于霜层脱离室外换热器壁面，并达到延缓结霜的目的。通过改变室外换热器风向及风量，对新型延缓结霜方法进行了实验研究，分析了其延缓结霜效果和机理，最终验证了首次提出的延缓空气源热泵结霜新方法的可行性和可靠性。为了缩短除霜时间，减少除霜能耗，提高除霜效率，在室内风机开启状态下，对空气源热泵单个逆循环除霜过程中除霜能量的来源和能耗分配进行实验研究。分析了除霜能量的来源及各自的份额，研究了除霜能耗的用途及各自分配，计算了系统的除霜效率，提出了提供充足除霜能量，减少除霜能耗和提高除霜效率的方法，为进一步改善空气源热泵逆循环除霜过程中的系统性能提供支持。为了提供充足的除霜能量，提出了空气源热泵过冷蓄能除霜新系统，分析了过冷蓄能除霜系统的系统原理，针对该系统的全新关键部件相变蓄热器，采用表冷器中肋片效率的思想，计算了相变过程中的肋片效率，建立了有翅片和无翅片情况下相变蓄热器模型，模拟分析了使用有机和无机两种相变材料时，相变蓄热器的蓄热和释热特性，为其结构形式的优化设计奠定了基础。针对提出的过冷蓄能除霜系统，设计了相变蓄热器，选取和测试了相变材料，实验研究了系统在过冷蓄能和蓄能除霜过程中的系统特性，结果表明：该过冷蓄能除霜新系统不仅实现了节流前制冷剂过冷，保证了系统的安全运行，同时为除霜提供了充足热量，有效地缩短除霜时间，很好地改善除霜时室内供热环境，提高热舒适性。提出了一种基于最小稳定过热度的空气源热泵除霜控制新方法。实验研究了以毛细管为节流机构，采用定时除霜方法时热泵机组结霜过程中的系统性能，分析了室外换热器出口制冷剂过热度变化，提出了基于最小稳定过热度的除霜控制方法。另外，在以固定开度电子膨胀阀作为节流机构，采用定时除霜方法的热泵机组上开展了结霜过程系统性能实验，并验证了新型除霜控制方法的科学性和合理性，提出了采用新型除霜控制方法的后续研究工作，为实现按需除霜和热泵机组性能优化提供支持。本文的研究工作以及后续工作将为改善空气源热泵除霜过程中系统性能，实现合理除霜，以及达到延缓结霜的目的，甚至在供热周期内实现不除霜，提供了理论基础和技术储备。更多还原

【Abstract】 For a space heating air source heat pump (ASHP) unit, when its outdoor coilsurface temperature is below both the air dew point and the freezing point of water,frost will form on its outdoor coil surface. Frost affects its operational performanceand energy efficiency. Therefore, periodic defrosting is necessary. During a reversecycle defrosting operation, the indoor coil in an ASHP unit actually acts as anevaporator while the outdoor as an condenser. Therefore, there is no heatingprovided and hence indoor air temperature in a heated space can drop. At the sametime, the indoor fan is turned off during defrosting operation to avoid cold air fromindoor coil. And hence the defrosting energy is mainly from input power intocompressor and energy stored in indoor coil metal. As a result, there is insufficientenergy to melt and drain the frost on outdoor coil surface, which leads to lowsuction pressure, prolonged defrosting period and deteriorated indoor environment.To improve the system performances under frosting condition and increasedefrosting efficiency, some experimental and theoretical work about retarding frost,energy storage defrosting based on sub-cool energy of refrigerant and defrostingcontrol method were conducted in this paper.Firstly, three test-rigs were built in two artificial environment chambers. Firstof all, the experimental ASHP units and parameter measurement and data acquisitionequipment were chosen, and then control strategies of simulated indoor and outdoorenvironments were determined. Finally, test error was calculated, which resultsshowed that the built test-rigs were enough accurate for the following experiments.Secondly, a novel method of retarding frost on outdoor coil surface for anASHP unit was presented based on the study of frost mechanism and the effect ofoutdoor air distribution on frost. Using which, the air pressure of outdoor coilchanged from negative zone to positive by changing the operation direction ofoutdoor fan, which facilitated the frost remove from coil surface and finally retardedfrost accumulation. In this study, the novel retarding frost method by changingoutdoor fan direction and air flow rate was experimentally studied, and then themechanism was analyzed. The experimental results indicated that it couldeffectively retard frost accumulation on outdoor coil surface by using the providednovel method.Thirdly, the experimental study on defrosting heat supplies and energyconsumptions during a reverse cycle defrost operation for an ASHP unit wasconducted when the indoor fan was turned on. The sources of heat supplies andrespective amounts, the purpose of energy consumptions and respective amount were respectively measured. And then the defrosting efficiency was calculated.Finally, methods of providing enough defrosting energy, reducing energyconsumption and improve defrosting efficiency were suggested, which was in favorof perfecting the system performances during defrosting operation.Fourthly, the energy storage defrosting method using sub-cool energy ofrefrigerant for an ASHP unit was presented to provide enough defrosting energy. Inwhich the phase change material-heat exchanger (PCM-HE) was importantequipment. In this paper, the energy storage and release process in the PCM-HEwere simulated and analyzed. The fin efficiency in PCM-HE was calculated duringphase change process. And then the energy storage and release process under withand without fins were simulated, and the simulation results were analyzed.Fifthly, the experimental study on energy storage and defrosting using thenovel method was measured. During normal heating operation, the refrigerantleaving indoor coil flowed to PCM-HE first, before passing through the capillarytube. In this way, the sub-cool energy of refrigerant was absorbed by the PCM andstored in the PCM-HE. At the same time, the safe system operation could be ensuredbecause further sub-cooling of refrigerant reduced the likelihood of liquidrefrigerant flashing and suction refrigerant over-superheating. When defrost becamenecessary, the heat stored in the PCM-HE could be used so as to provide sufficientthermal energy to melt the frost off the outdoor coil surface. In this study, the novelsystem form was provided, and then the PCM-HE was designed and appropriatePCM was chosen and measured. Finally, system performance during heating anddefrosting were measured.Sixthly, a novel defrost control method based on degree of refrigerant superheatwas provided. A conventional experiment was carried out on an ASHP unit withcapillary as throttle device under simulated frosting and defrosting conditions basedon time control defrosting method, and its experimental result was analyzed,especially the degree of refrigerant superheat. And then the novel defrost controlmethod was provided. To validate the provided novel defrost control method,another experiment was conducted on ASHP unit with fixed opening electronicexpansion valve (EEV) as throttle device under simulated frosting and defrostingconditions, and its experimental results validated the correctness of the providedmethod. Further study on this novel control method could achieve defrostingoperation when it was needed and performance optimization for an ASHP unit.Accomplished work in this paper and further study was in favor of achievingretarding frost and defrosting when it was needed, so far as to no defrostingoperation during heating cycle.更多还原