We get calls from customers often during the winter months asking why their heat pump is suddenly running really loudly. What most people don't know or maybe forget, is that heat pumps come equipped with a defrost cycle that is designed to remove frost from the coil.
When a heat pump is operating in the heating mode or heat cycle, the outdoor air is relatively cool and the outdoor coil acts as an evaporator. Under certain conditions of temperature and relative humidity, frost might form on the surface of the outdoor coil. The layer of frost will interfere with the operation of the heat pump by making the pump work harder and, therefore, inefficiently. The frost must be removed. A heat pump has a cycle called a defrost cycle, which removes the frost from the outdoor coil. A heat pump unit will defrost regularly when frost conditions occur. The defrost cycle should be long enough to melt the ice, and short enough to be energy-efficient. In the defrost cycle, the heat pump is automatically operated in reverse, for a moment, in the cooling cycle. This action temporarily warms up the outdoor coil and melts the frost from the coil. In this defrost cycle, the outdoor fan is prevented from turning on when the heat pump switches over, and the temperature rise of the outdoor coil is accelerated and increased. The heat pump will operate in the defrost cycle until the outdoor coil temperature reaches around 57° F. The time it takes to melt and remove accumulated frost from an outdoor coil will vary, depending on the amount of frost and the internal timing device of the system.
So next time when it gets really cold outside and you hear your heat pump sounding louder than usual, odds are it's just going into defrost mode. Hopefully this will give you some insight into the workings of your heat pump and maybe save you some money so you won't have to pay a service technician to come out and tell you that your heat pump is fine and is just going into defrost mode. Environmental wishes you all a happy holidays!
-Nickadeemus
919-535-8422
www.enviro-nc.com
