DC Inverter Heat Pumps

[jpadie]

Hello

 

I've had a fixed power gshp for 20 years and changed a couple of years ago to a 15kW DC inverter. 

 

I'm curious about what the relationship between pump frequency and output is.  And what best practice might be.

 

What I've found is that I don't see much benefit in terms of speeding up the ufh warming or maintaining the temperature when I let the inverter ramp up to max versus keeping it at 44Hz (which correlates roughly to 11 amps at 230v). To the contrary, the power draw is close to 6kW at that point.  

 

I'm also finding that in dhw mode the heat pump errors without a fixed max frequency as the outlet inlet delta t exceeds 10C.  I think this is because the circulator used is the same for the dhw and ufh and is set too low for the short run to the water tank.  It's not a PWM controlled pump but I could upgrade.

 

For info UFH is buried in a big concrete screed with tiles on top.  House is 22 years old and located in southwest France.  Surface area of the ufh is 180sqm. Upstairs is heated by forced air and one coil from the heat pump and is very inefficient: takes hours and hours for a room to warm up). 

 

Thanks in advance 

Justin