从历史上看，热泵有三大缺陷；寒冷气候下的供热能力有限，季节性性能系数通常较低，可靠性较差。自20世纪50年代热泵首次商业化以来，人们提出了许多建议，但仍有许多改进的机会。过去，提高热泵性能的常用方法主要有以下几点:5提高换热器表面的利用率，如淹没式蒸发器和无液体冷凝器。对于给定尺寸的装置，换热器面积更大。改进控制；例如除霜定时器、压力和温度限制控制器等。改进的压缩机设计，更高效的电机和阀门，更好的内部流动路径，以及更好的油循环控制。改善辅助供暖，更好地协调建筑显热储存和供暖需求，或化石燃料补充热量。 随着能源价格的上涨，实现更好性能和可靠性的新方法在经济上变得可行。其中一些新方法是:太阳能辅助热泵储热热泵多个换热器和/或多个压缩机热泵分阶段压缩热泵流量调节（容量控制）热泵以上所有这些新概念的组合都有很大的前景，每一个都应该彻底检查，以显示哪一个或哪些概念的组合是最好的。流量调节或容量控制热泵的概念要求在系统设计中进行最少的剧烈变化，因此在本研究中被选为进一步研究的对象。引文:阿什雷学报，第83卷，第2部分，哈利法克斯，北卡罗来纳州

Historically, heat pumps have suffered from three major deficiencies; limited heating capacity in colder climates, generally low seasonal performance factors, and poor reliability. Many adva~ ces have been made since heat pumps first appeared commercially in the 1950s, but there are stlll numerous opportunities for improvement. Usual approaches to improving heat pump performance in the past have centereo upon the following: 5Improved utilization of heat exchanger surface such as flooded evaporators and liquid free condensers.Larger heat exchanger areas for a given size unit.Improved controls; such as defrost timers, pressure and temperature limit controls and others.Improved compressor design, with more efficient motors and valves, better internal flow paths, and improved oil circulation control.Improved auxiliary heating, using better coordination of building sensible heat storage and heating demands, or fossil fuel supplementary heat. Newer methods of achieving better performance and reliability are becomming economically feasible as energy prices rise.Some of the new approaches are:Solar-assisted heat pumpsThermal-storage heat pumpsMultiple-heat-exchanger and/or multiple-compressor heat pumpsStaged-compression heat pumpsFlow-modulated (capacity-controlled) heat pumpsCombinations of the above,All of the preceeding new concepts hold great promise, and each should be examined thoroughly to show which concept or combinations of concepts are best. The flow-modulated or capacity controlled heat pump concept requires the least drastic changes in system design, and has therefore been chosen for further study in the present work.