u/BerlindaBuntly

we hada a heat loss survey that said 14.19Kw and have been specced a 16kw samsung r290.

From my last years real data, the max gas usage in a single day was 260kw on 05/01/2026. This includes hot water. The external temperature was -2.5C

 This is simplistic, and doesn’t include

1. Boiler efficiency not being 100% (which would make the actual heat loss of the building lower by about 10 percent, our boiler is rated at 89 – 92% efficient)
2. Gas used for hot water (which would make the actual heat loss of the building lower)

 If we ignore the above and use worst case scenario, on the worst day, that’s 10.83kw/H

 Do we then need a 16kw heat pump or would a 12kw do?

if we still need a 16kw ASHP, what am i doing wrong on the calculations?

https://preview.redd.it/gzc7gr66h21h1.png?width=1126&format=png&auto=webp&s=a70f10fa0eb18c753e99feb12ef76885cebd5df2

hi everyone, hope you are well.

i'm trying to model what a heat pump would cost me using real world data from the last 8 months from my smart meter and the "what if" if we had a 18kw solar and 18kw battery system.

i've got estimated day by day generation data, real world day by day gas and electric consumption data. i know if the battery would need filling up that night on a cheap overnight tariff, what that would cost and have mitigated the stored energy against the electric consumption of our actual electric usage plus what i believe the heat pump would draw.

at the moment my calculations all assume that the heat pump runs at full tilt (it would be a 16kw samsung) in order to supply the equivalent gas KwH that was used on that day. I have assumed a COP of 4. (so if there was say 20kw gas used that day, then the heat pumps needs 5kw).

this is important because we use a lot of electricity anyway, so the batteries need to be able to supply the juice the heat pump needs and the extra electric that we use over and above generation anyway otherwise we end up having to buy very expensive electricity to mitigate it.

for instance, on the intelligent flux tariff, the cost of buying the extra electricity over and above what we generate and can store in the battery on a cheap overnight charge, at 32p per kilowatt, for the energy the battery cannot supply in dark cold winter months completely blows away any annual savings and costs more than gas. plus it eats energy i could sell back to the grid.

is there any way of modelling roughly what KwH rate the the heat pump would be running at on a given day if i had say outside temperatures for each day?

hello everyone, hope you are well.

looking at getting 17kw of solar and 16kw of battery.

we have water based underfloor heating in half the downstairs and 2 of the bathrooms.

trying to see if i can get a heat pump too but i cant make the numbers work. i like tech, i like the low carbon idea, i like the energy independence but i cant make the numbers worth it. i know, its not all about money for everyone, but, if im spending what will be 5 or 6k on top of the bus grant, i want to make sure its not going to actually cost me more money to run than the system I have that already works. Maybe i am missing something, and if you can point out where i'm wrong i'd love to hear it.

been quoted a 16kw samsung unit after a heat loss survey.

current prices below on UW club for gas and leccy.

electric rate 26.51p per KwH

gas rate 5.715p per KwH

electric standing charge £13 per month

gas standing charge £10 per month

real world data since last july when we moved in to today (301 days) shows

32,247 KwH gas

9213 KwH electric

if i annualise these, i know it wont be quite right because we have warmer months coming now but assume worse case, the costs are below

gas: 38,974 KwH costing £2237 including standing charges

electric: 11,171 KwH costing £2974 including standing charges

straight off the bat, if i look at the ratio between electric and gas cost per kwh, i would need a cop of 5 to break even, and thats with spending a tonne of money. ok, so theres a bit of standing charge £120 per year for gas but really thats a rounding error given the investment i'm going to need to make.

cop of 5 is unrealistic and that is just break even.

hot water heating is also by gas, but its about 12kw to heat 250 litres of water by 40 degrees c, so its not going to effect the numbers for heating very much

so im looking at different heat pump tariffs, and its a minefield "free electric from x to y this week" "3 dip periods where you get cheaper electric but you pay 50% more when you use it between this time and that" "10p below the rate in your area for x time on day z". all of these offers will change over time too, meaning i'm going to have to watch it all the time and generate spreadsheets otherwise im not going to be able to sleep at night.

it just looks like a nightmare and the wrong tariff or doing the washing at 5pm would blow any savings away. . .i dont want to be a slave to watching electric deals every week.

ok, so the batteries will help, but, with the real world data, the most we used in a day for gas in terms of kwh was 250 kwh. there is an entry for 350kwh but i think this may be nonsense, maybe the meter didnt read one day and sent the full read for 2 days possibly.

anyway, so with 16kwh of battery, even if they are fully charged, in the depths of january when we have little to no solar, its gonna run the heat pump for an hour or so.

what am I not seeing?

thanks for your time.