I’m learning that my (oversized) heat pump has a minimum output between 4 and 6 kW, depending on the outside temperature. If the radiators can’t emit that all that energy then the flow temperature will keep on rising. Meanwhile, the heat loss of the property is only 4 kW at 4C, which is less than the minimum output of the (11 kW) heat pump. (I’ve see it go as high as 14 kW!)
(MCS calculated peak load of 9.5 kW at -3C. I’m seeing actual load of 6 kW)
- HeatingEnergy (W) is the measured heat output from the heat pump
- EmitterOutput (W) is computed the wattage of all radiators for the flow temperature
- HeatLoss (W) is computed based on inside - outside temperature x heat loss coefficient
When HeatingEnergy is below EmitterOutput (assuming all TRVs are open), the flow temperature will stabilise, and the HP will run for a long cycle. Otherwise, the flow temp creeps up and up until the HP stops for a breather.
Also, as HeatingEnergy is often above the HeatLoss of the building, the average temperature of the whole house is either increasing (when it’s on) or decreasing (when it’s off). Like a good ole gas boiler. /sarcasm
So, during milder days (i.e. above freezing) my HP is doomed to cycle, either bouncing the flow temp or the house temp. I don’t know if fiddling with flow speed will help, or I need to add more radiators. Probably needs a smaller heat pump.
On the other hand, the house is warm, and it’s still cheaper to run than gas, so I should be content with that.