A new method of defrosting evaporator coils
A new method of defrosting evaporator coils
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DOI：
10.1016/j.applthermaleng.2012.01.033
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发表时间：
2012-06
影响因子：
6.4
通讯作者：
G. Mader;C. Thybo
中科院分区：
文献类型：
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作者：
G. Mader;C. Thybo
提出了一种使用空气作为热源的热泵蒸发器盘管除霜的新方法。在室外温度较低时，蒸发温度会降至水的冰点以下，空气中的水蒸气会在盘管的外表面上冻结。这增加了空气侧压降并降低了蒸发器盘管的传热能力，导致系统效率降低。霜积聚时间过长会导致蒸发器盘管部分或完全堵塞，导致系统无法运行。因此，为了保持系统的功能，有必要定期除霜。对于可逆空调系统，这通常是通过反转系统的流动来完成的。在相反的模式下，室外盘管充当冷凝器，从而融化盘管表面的霜。然而，这些除霜循环中的每一个都进一步大大降低了系统效率。新方法使用主动分配阀，能够单独向平行蒸发器通道供料。使用该阀可以定期关闭单个蒸发器回路。虽然闭合回路中没有制冷剂蒸发，但盘管表面温度会升高，只要空气温度高于 0°C，周围空气的流动就足以对蒸发器的这一部分进行除霜。实验结果表明，在标准结霜条件下，蒸发器可以保持无霜，即使在恶劣条件下，也可以避免大多数效率低下的系统反转。从而系统效率显着提高。
A new method is presented to defrost evaporator coils of heat pumps using air as a heat source. At low outdoor temperatures the evaporation temperature can drop below the freezing point of water, the water vapor in the air then freezes on the outer surface of the coil. This increases air side pressure drop and reduces the heat transfer capability of the evaporator coil, leading to a decrease in system efficiency. Long frost build-up times would lead to a partly or totally blocked evaporator coil, rendering the system inoperable. To maintain the functionality of the system it is therefore necessary to remove the frost regularly. For a reversible air conditioning system this is typically done by reversing the flow of the system. In the reversed mode the outdoor coil serves as a condenser, hereby melting the frost on the coil surface. Each of these defrost cycles however further reduces the system efficiency substantially. The new method uses an actively distributing valve which is able to feed parallel evaporator passes individually. With this valve single evaporator circuits are regularly shut off. While no refrigerant is evaporated in a closed circuit, the coil surface temperature increases and the flow of the ambient air is sufficient to defrost this part of the evaporator as long as the air temperature is above 0 °C. Experimental results show that under standard frost conditions the evaporator can be kept frost-free and even under severe conditions most of the highly inefficient system reversals can be avoided. Thereby system efficiency is increased significantly.