Hot Gas Defrost
You are better off without it
Almost all pool heat pumps have a hot gas defrost. Except the Elite, the Hybrid, and the Sunriser swimming pool heat pumps. Why? To maintain higher efficiency.
A hot gas defrost works using a reversing valve just like those found in a residential heat pump. The valve is used to reverse the heat pump from cooling to heating.
In a pool heat pump, the reversing valve reverses the system to melt the frost on the evaporator. Frost prevents the air from going through where heat can be absorbed and therefore reduces efficiency. So, the quicker the frost melts, the faster the pool heat pump can return to heating the pool. Usually, frost forms below 10 Celsius or 50 Fahrenheit. The heat pump can continue heating to as low as 5 Celsius or 40 Fahrenheit. Below this temperature, there is no point in heating because the pool loses heat faster than the pool heat pump can heat it.
So, how can not having a hot gas defrost improve efficiency? The pool heat pump must reverse the heating cycle to defrost. This means that during the defrost cycle it is actually cooling the swimming pool. Remember, it is below 50F (10C) when this happens and the water is probably above 80F. (See the side for efficiency variations) Because the pool water is warmer than the air, the heat pump is highly efficient in transferring heat from the water to the evaporator. But when the defrost cycle ends and the heat pump heats the water once more, it has become less efficient because the air is cooler than the water. Even if the defrost cycle only takes 5 minutes, the heating time it takes to restore the heat loss from the defrost cycle can take up to 20 minutes. In other words, the heat pump has operated for 25 minutes without adding anymore heat than it had 25 minutes ago. That's a total loss of electricity because the heat pump has operated all this time with the compressor running.
The Elite, Hybrid, and Sunriser pool heat pumps have a ambient air defrost cycle. When frost builds up on the evaporator, the compressor stops and the fan continues to run to move air through the evaporator. The defrost cycle is will take 10 minutes which is longer than the hot gas defrost. But the advantage is that the compressor is not running. When the heat turns on again, the heat pump does not need to restore heat to the pool because it didn't cool the water like the hot gas defrost. The heating cycle has become more efficient because it produces more heat per hour than the hot gas defrost models.
If this is not enough to convince you that the Hybrid, Elite, and Sunriser heat pumps are the best. Consider that a reversing valve is a moving part. It is prone to fail. Without it, the heat pumps are more reliable.
The colder the outside air gets, the less efficient a heat pump will be. A heat pump is energy efficient because it doesn't produce heat. It transfers heat from the air and sends it to the pool after compressing this heat.
A Elite 100 pool heat pump will have a COP of 6.8 at 80F but will be reduced to 4.9 at 50F. The BTU output will also be less. The warmer the swimming pool is, the faster it loses heat. Below 40F, the heat pump cannot efficiently restore the evaporating heat back to the pool. The electronic control is set to stop the heat pump below 40F to prevent useless consumption of electricity.
What is COP?
COP is short for Coefficient of Performance. The COP number basically means how much heating value you get from every dollar of electricity you spend.
A simple way of understanding is to compare with other heating equipment.
- Electric resistance heat has a COP of 1
- Highest efficiency gas has a COP of 0.95
- Heat pumps have a COP of between 3 to 7