What heating source?

[JohnMo]

We have a 32kW combi boiler it's min turndown is 6kW, hence the big buffer.  But with our set up we can do multiple showers at the same time and back to back and never run out of hot water.

 

For context, we have 193m2 of UFH. Our walls, floor and roof have slightly better u valves than yours, but we have lots of glass (triple glazed), one of our windows is about 21m2, so our heat input is about the same as yours on a cold day.

 

The 12kW ASHP, looks to be well over sized, your problem will be getting it to turn down low enough not to short cycle when in heating mode.  It's not the coldest days that are the issue, it's at any other time when the heat pump isn't being asked to work that hard.  Only requiring a couple of kW or less for CH.  Big heat pumps come with big pipes, high min flow rates, so bumps cost up and are less efficient doing there job.  With a heat pump you need one the right size.

 

I would see the central heating being on all day at very flow temperature, a 2 to 3 setback at night, so boiler is just sitting there with nothing to do, in the night charge the large cylinder with hot water, while not on central heating duty.  People on here seem to have around 300l cylinder with a heat pump for 2 to 3 person house and store the water at around 46 degC.  So cylinder sizing is something you need to get right.

 

Based on the numbers I have seen on this thread, 5 to 6kW ASHP would be a better size.  Have a read of the attached.  One is the MCS heat pump guide, Heat-Pump-Guide.pdf, the other you would out water flow rates for UFH.

 

If you do look at a gas system boiler, make sure it can run two temperatures one for hot water and for heating, something with weather compensation built in will be able to do this.  Then you can run in condensing mode when on central heating and get better efficiency.

Heat-Pump-Guide.pdf

Edited August 7, 2022 by JohnMo
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