jimboflint19 Posted March 29 Share Posted March 29 Morning! I had Aira come out yesterday to discuss putting a ASHP in, but I’m wondering if anyone can help me. I know that I used 18500kw/h of gas heating the house in 2023, so considering they suggested an 8kw heat pump, is there anyway of making a rough calculation on how much electricity it would use over a year? I can’t decide if I’m trying to calculate something that’s impossible to know, or if I’m missing a very simple calculation? Any guidance would be welcome! Thanks! Link to comment Share on other sites More sharing options...
Gary68 Posted March 29 Share Posted March 29 For a rough estimates divide by 2900 so yours would be 6.3kw so your looking for a 7 or 8kw heat pump Link to comment Share on other sites More sharing options...
SteamyTea Posted March 29 Share Posted March 29 (edited) Welcome While it depends on many other things i.e. how well set up, you can use the Seasonal Coefficient of Performance (sCoP) number to get a very rough idea. But always remember that running a low temperature heating system is not like running a high temperature combustion heating system. 38 minutes ago, jimboflint19 said: 18500kw/h Some other will laugh at this, but it is kWh, a measure of energy. Not kw/h which is a nonsense unit. To satisfy that 18500 kWh of energy, an 8 kW heat pump would be running for roughly 2300 hours/year (but only at full power, which it will not). A lot of that will depend on how well your original boiler was working though. If the efficiency was, in real life, only 70%, then you only need 13,00 kWh. Edited March 29 by SteamyTea Link to comment Share on other sites More sharing options...
MikeSharp01 Posted March 29 Share Posted March 29 18 minutes ago, jimboflint19 said: 18500kw/h of gas heating Does this include Domestic Hot Water? Link to comment Share on other sites More sharing options...
HughF Posted March 29 Share Posted March 29 Similar gas numbers to us… two heat loss calcs came up within 200w of each other at ~7kW at -4. I fitted a 9kW unit. Hard to say what the running costs are , but they’re no more than we spent on gas and the house is warmer, and has been extended. Link to comment Share on other sites More sharing options...
MikeSharp01 Posted March 29 Share Posted March 29 8 minutes ago, SteamyTea said: Some other will laugh at this, but it is kWh, a measure of energy. Not kw/h which is a nonsense unit. @jimboflint19 Steamy is one of our most diligent sources of support in energy matters, indeed almost anything involving algebra, and as he will point out, I fell over this last week - and I should know better, if it is a unit named after a person then it is capatalised when used as a unit - so watts (not capitalised in a sentence unless it starts the sentence), because it is named after James Watt, otherwise it is generally not. Hence 24kWh = Twenty four kilowatt hours. More here: https://www.nist.gov/pml/owm/writing-si-metric-system-units#:~:text=NOT 250 mms.-,Capitalization,modifier "Celsius" is capitalized. Link to comment Share on other sites More sharing options...
sharpener Posted March 29 Share Posted March 29 3 hours ago, jimboflint19 said: I know that I used 18500kw/h of gas heating the house in 2023, so considering they suggested an 8kw heat pump, is there anyway of making a rough calculation on how much electricity it would use over a year? 3 hours ago, Gary68 said: For a rough estimates divide by 2900 so yours would be 6.3kw so your looking for a 7 or 8kw heat pump Depends quite a lot on your emitter setup. If you have (or fit) rads suitable for a 45C flow temp then from this table a 5kw Arotherm plus would do the job down to -2 OAT (southern England). Further north you would defo need the 7kW unit. With a SCoP of 3.77 your 18500 kWh would require 4907 kWh of electricity to generate, which is what you originally asked, multiplied as @SteamyTea says by maybe 70% to account for the (in)efficiency of the boiler. Depending on yr HW usage (which I assume is included in the 18500) you may also need to make a correction for the fact that producing HW will be at a lower CoP, I do not know if this is included in the SCoP formula. The 7kW unit has a higher SCoP so would use less, the downside would be more cycling in warmer weather, unlike a gas boiler they only modulate down to about 50% rated output, then they cycle. Link to comment Share on other sites More sharing options...
John Carroll Posted March 29 Share Posted March 29 aroTHerm seem to have a strange way of sizing their units, I generally see them specked to the standard 7C/35C, air/water, the output then falls at lower air temps or/and higher water temps. I wonder what standard, air/water, are they using?. Link to comment Share on other sites More sharing options...
sharpener Posted March 29 Share Posted March 29 (edited) Yes, rated more generously than many other mfrs. Hence I have been quoted for a 12kW Vaillant unit in place of a 15kW Stiebel Eltron. Full performance tables (in Czech) are here starting at p34. Extract for 5kW unit at 40 - 45C flow temp (modulation is better than I thought): Edited March 29 by sharpener Link to comment Share on other sites More sharing options...
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