Pump speed and heat pump eficiency

[kupermanp]

Getting ready to heat my pool up for an event. I have a variable speed pump (intellispeed) and was wondering which will heat the pool up faster.

1) Using just enough flow to trip the heat pump flow meter (I'd assume the water would be heated the most but the volume of water running through the pump would be less)
2) Run at a high speed so the maximum volume of water goes through the pump (I assume the water will not get as hot as it spend less time in the heat pump, but more total water gets heated by the pump).

Just curious. Thanks

Paul

 

[JasonLion]

The highest theoretical efficiency is at higher flow rates. Heat transfer is most efficient when the temperature difference between the hot and cold sides are maximized. A slower flow rate allows the water (the cold side) to reach a higher temperature, which lowers the efficiency.

However, heat pumps won't work correctly at too high or too low of a flow rate for other reason, and in that practical flow rate range, the difference in efficiency is actually quite small. So it doesn't end up making much difference what the flow rate is, as long as it is within the flow rate range the heater was designed to support.