ASHP Pump Speed

[J1mbo]

Setup: 12kW Arotherm Plus, Plate Exchanger, Buffer Tank, Radiator Circuit with UPS3.

 

Radiator side has pump on fixed speed 2, seems to work OK with ~5°C drop across the circuit when everything is calling.

 

I'm not sure how to set the other two pumps. The ASHP 'auto' simply runs it at 100% providing 2,048 litres per hour through the plate heat exchanger. Whilst rated at 12kW, the heating demand is more like 9kW which would indicate a flow requirement of 1,500 litres per hour. But, when the compressor starts it runs at 45% for three minutes before adjusting to load and this can already result in overshoot mid-season which in turn causes shorter cycling than would be preferred.

 

The heat exchanger pump has three fixed speeds. There's very little resistance (28mm piping to a buffer cylinder next to it) and no way to monitor the flow.

 

I'm wondering if there are efficiency gains to be had by tuning these two pumps and if so how!

[dpmiller]

what's the flow-return Delta at the ASHP? Is the pump controlled from the ASHP or just off it's own algorithm?

[J1mbo]

7 minutes ago, dpmiller said:

what's the flow-return Delta at the ASHP? Is the pump controlled from the ASHP or just off it's own algorithm?

 

Due to the varying flow temperature requirements the simple answer is: it depends (weather and room temperature compensation means everything is continually varying). I suppose I need to spend some time measuring.

[dpmiller]

Yep, on our Cool Energy unit the main pump is under PWM control based on in-out Delta as far as I can see. Min, max, and startup speed are all configurable though.