How to size a heat pump, using heat loss calculations.

[@chrismorrish130]

Your videos are a brilliant source of information. Thanks

[@fje1948]

Thank you for the video, I wish I had seen it before the heat pump installation. My heat pump is 3 kW’s too small and it felt like it - Gas boiler re-installed a week ago!

[@JamesRattray]

Goodness me, how terrible. Who did the heat pump calculations? Surely your heat pump installer would have done these calculations on your behalf.

[@fje1948]

@ A D…. Approved installer. We heat our house/DHW via a heat store as we also have a wood burning Rayburn, hence re-installing the gas was not an issue. Merry Christmas in a warm house!🎄

[@hughrattray9354]

Very sorry to hear of your poor experience. I wonder if you could report the installer to MCS

[@fje1948]

@ As a last resort I shall!

[@MentalLentil-ev9jr]

The most usual error is installing too large a heat pump, this is very unusual. My 5kW heat pump is more than sufficient for my 1960s ex council end terrace. If the heat pump was too small then it's a real shame to reinstall a gas boiler, it should just be a case of fitting a larger heat pump as all the plumbing would be done.

[@andrewcunningham1]

Hi James. Did you compare your calculation with your real world heat pump usage?

[@hughrattray9354]

I have done that in the video Microbore heat pump 12 months performance. I found that the heat loss was less than I calculated. I think this is due to the air changes per hour used in the calculations being too high.

[@andrewcunningham1]

@@hughrattray9354 Interesting. Did you recalculate to try and match your real world with a lower air change calc.?

[@hughrattray9354]

@@andrewcunningham1 I do that in the video "Microbore heat pump 12 months performance" at about 24 mins in. I found if I assumed ACH of 0.5 rather than 1 the calculation and actual were very close. I think this makes sense as we have modern door and windows in the main living area.

[@FrancisCWolfe]

How do you feel about the degree days approach to sizing?

[@hughrattray9354]

I will look into it more but on the face of it seems easier and more accurate to us the energy usage from a single cold day to get the heat transfer coefficient..

[@FrancisCWolfe]

@hughrattray9354 just to be clear, I was referring to this method kzbin.info/www/bejne/nnTImJuBlpifn68si=9clejskhcMllG9H9

[@hughrattray9354]

@@FrancisCWolfe Thanks - I have had a look at the video and it is very well explained and does seem to work well so it is a good alternative. I haven't quite got to where the formula comes from. I still feel a controlled experiment over a couple of days woul reassure me more. The house would need to be preheated to the temperature you want (not what you have put up with). The tempetaure inside needs to be measured accurately so a good average can be calculated. I will try and use this method form my house and see how it matches with the other approaches.

[@hughrattray9354]

@@FrancisCWolfe I have jus done the degree day calculation and it came out at between 4.0 Kw and 2.5Kw depending on which year I used. The lower figure did come after we had improved insulation. The figures are close to the calculation method.

[@nickmarshall7019]

How did Heatpunk compare with your spreadsheet calculation for heat loss?

[@hughrattray9354]

I found them to be very similar. It was easier with my spreadsheet to look at insulation options than on heat punk.