虽然基于燃烧的供暖系统在寒冷地区得到了广泛的应用，但空气源热泵由于其提供的高能效，作为替代性供暖设备受到了广泛的关注。然而，传统的空气源热泵以前需要间歇运行，以在室外空气温度较低的环境中加热时融化加热系统室外机上形成的霜。由此产生的室温下降最终会让居民感到不舒服。为了解决这个问题，过去有人提出了一种制冷剂回路，用于执行连续加热。该回路涉及在室外机内安装热气旁通阀。 然后，室外热交换器分为两个平行部件，其中一个用于加热，另一个由压缩机排出的高温气体制冷剂供应，用于除霜。然而，出现了一个问题:使用气体制冷剂产生的显热产生的热量较低，这意味着除霜需要较高的制冷剂流速。这将导致用于室内供暖的制冷剂短缺，室内排热空气温度下降。提高加热能力的有效方法是尽可能降低除霜用制冷剂的流速，并确保室内加热用制冷剂的高流速。 因此，重点放在利用制冷剂冷凝产生的潜热进行除霜，以开发新的制冷剂回路和用于控制制冷剂压力的新技术。具体而言，在热交换器的上游和下游安装了两个压力调节阀，以进行除霜。制冷剂回路的配置方式是，用于除霜的制冷剂通过热交换器（用作蒸发器）的上游部分返回主流。此外，控制制冷剂压力，以使气体制冷剂在高于霜熔点的温度下冷凝。 因此，除霜所需的制冷剂流速降低到传统方法的1/6（包括利用制冷剂的显热）。当室外空气温度为36°F（2°C）时，除霜期间的加热能力提高了30%，这是因为供应给室内机的制冷剂流速增加了。此外，已经证实，即使温度低于冰点，也可以进行连续加热，这在使用传统方法时是不可能的。引文:2021篇虚拟会议论文

While combustion-based heating systems have been in widespread use in cold regions, air source heat pumps have been gathering attention as alternative heating devices owing to the high levels of energy efficiency they provide. However, conventional air source heat pumps had previously required intermittent operation to melt the frost forming on the outdoor unit of the heating system during heating within environments characterized by lower outdoor air temperatures. The resultant room temperature drops would end up making residents uncomfortable.To solve this problem, there has been proposed in the past a refrigerant circuit serving to perform continuous heating. This circuit involves the installation of hot gas bypass valves within the outdoor unit. The outdoor heat exchanger is then divided into two parts in parallel, with one being used for heating and the other supplied with high-temperature gas refrigerant that is discharged from the compressor for defrosting. However, an issue arose: sensible heat resulting from the use of a gas refrigerant presented low amounts of heat, which meant that defrosting would require a high flow rate of the refrigerant. This would result in a shortage of refrigerant to be used for indoor heating and a drop in terms of the warm discharge-air temperature indoors.An effective means to improve heating capacity is to reduce the flow rate of the refrigerant used for defrosting as much as possible and to ensure a high flow rate in terms of the refrigerant used for indoor heating. Therefore, a focus was placed on utilizing the latent heat generated by the condensation of the refrigerant for defrosting to develop a new refrigerant circuit and a new technology which serves to control refrigerant pressure. Specifically, two pressure-regulating valves have been installed at the upstream and downstream portions of the heat exchanger to be subject to defrosting. The refrigerant circuit has been configured in a manner which has the refrigerant used for defrosting returning to the mainstream via the upstream portion of the heat exchanger (which works as an evaporator). Furthermore, the refrigerant pressure was controlled in order to have the gas refrigerant become condensed at a temperature above the melting point of the frost. As a result, the flow rate of the refrigerant required for defrosting was reduced to 1/6 of that seen with the conventional method (which involves the utilization of the sensible heat of the refrigerant). Heating capacity during defrosting was improved by 30% when the outdoor air temperature was 36 °F (2 °C) as the result of an increase in the flow rate of the refrigerant supplied to the indoor units. Additionally, it was confirmed that continuous heating was possible even when temperatures were below freezing, which was not possible when utilizing the conventional method.