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What is the best strategy for operating a very oversized heat pump?

 
Air Source Heat Pumps (ASHPs)
Last Post by Tim441 1 hour ago
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 JamesPa
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Topic starter 10/03/2025 9:21 am  

As the title really.  There are at least three live threads currently where its obvious that a part of the problem is a heat pump oversized by a factor of 2 or more, and I would guess that a fairly significant proportion of the threads have this somewhere at their centre.  As we get into the shoulder season, the 'problem' will rear its head more frequently.

So whats the best strategy and why?  Im assuming that the heat pump is operated on weather compensation obviously

1. Operate on WC and leave it open loop (no external controls).  Trust the heat pump controller do its job

2. Operate on WC and batch heat by timed operation, accepting the variation in IAT.  Adjust the number of on/off cycles according to the thermal time constant of the house

3. Operate on WC and modulate on and off using a thermostat

4. Something else

All are in fact cycling, so all will suffer the thermodynamic/COP penalty of cycling, perhaps to a greater or lesser extent depending on the resulting flow temperatures.

What's the best strategy and why?  Any answers?

 

This topic was modified 3 hours ago by Mars

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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 Tim441
(@tim441)
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10/03/2025 11:23 am  

Something else... that works for some people...

LG has "Quiet/silent mode" that is normally intended where noise is an issue (say at night or proximity to neighbours etc). When using that mode the compressors operate at lower rate than normally called by WC. 

Some people use very effectively for oversized heat pumps to reduce cycling etc. It means operating at less than optimal efficiency for size of pump but if oversized that may suit.

I guess many other heat pumps have a similar option. Maybe called something else.

Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
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