We have recently discovered probably the biggest marketing bubble in pool business for past decade.
Everywhere we see inverter pool heat pump as brand new technological innovation. COPs of 20 are claimed. Faster heating times than any other pool pump are marketed as ‘proven by tests’. We held an international conference in May where we asked professionals from 20 countries what they think about inverter pumps. Also we ran a wide variety of tests for past months with number of inverter heat pumps. Below I present you a brief conclusion of that discussion.
Before I start, I need to say that I personally have an inverter heat pump to heat my house during winter. Also I use inverter air conditioning both at home and at work. These are different types of pumps than pool heat pump, but they’re inverter.
Main issue with using inverter technology for pool heating is that water has 3278 times more heat capacity per volume and 4 times more per mass than air (in JK-1kg-1; for those who seek more info, an interesting article on Wikipedia here ). This means that your pool heat pump needs minimum 3 hours of continuous heating at 100% performance to increase the water temperature by 1°C. This applies for a properly sized heat pump. A/C system in comparison can change the air temperature in room by 1°C literally in the matter of minutes.
But inverter pool heat pump follows the marketing wave and the manufacturers needed to program the performance at some point to say that inverter ‘is more efficient’. So they programmed the pump to run at 75% when the water temperature is 3°C off desired. They go down to 25% when water temp is 1°C below required.
By 25% of heat pump’s performance you’re not looking at 3 hours heating time for 1 degree, you’re actually looking at 12 hours. Should this 12 hours ‘land’ in night, the conditions for a heat pump worsens and COP decreases while heat losses of the pool increase. So at the end of the day, not only inverter heat pump needs much more time for heating but also consumes more energy in total than fixed speed heat pump.
We at Microwell refuse inverter heat pump for a swimming pool as a technological breakthrough. Fixed speed heat pumps are better, have higher COP and overall heat faster and cheaper.