Es TresidderWe've got a full year of monitoring for heating & hot water in our #Passivhaus EnerPHit retrofit. Our total electricity usage, for heating and hot water, between 14th November 2023 and 14th November 2024 was just £175!
Before we moved in I estimated we'd be at around £250 per year just for space heating, and a significant amount on top of that for water heating, so how come we're so much lower than the already excellent numbers I expected?
I think the A2A is more efficient than the SCOP of 3 I guessed it would be. I can't monitor heat output, but comparing modelled heat demand & electricity usage I think we're getting a SCOP of 4 or 5. Much <4 would imply unbelievable fabric efficiency and much >5 would be stretching thermodynamics.
We've got a higher occupancy density (5 people in 105m2 treated floor area) than PHPP assumes for certification on a house of this size, this will reduce our space heating demand somewhat.
We've been able to demand shift quite successfully. 52% of the electricity used by the air to air heat pump was in the middle four hours of the night when the electricity is just 9 p/kWh (although the rest was at 29 p/kWh).
Our hot water demand is low because we have shower-water heat recovery, very efficient (radial 10mm) distribution and 6l/min showers. Surprisingly the showers are among the nicest I've used.
The hot water heat pump has a reasonable efficiency all year round, since it is 'stealing' heat from the house at ~20°C.
Relatively low hot water usage for now, I expect this to change as the children get older!
The last three points mean that our hot water reheat times are quick enough that all the hot water heating is during the 4 cheap hours per night.
Total space heating electricity usage (some of which is actually heat for the hwhp): 756 kWh
Total water heating electricity usage: 336 kWh
Total hot water usage: 18,000 litres (about 50 per day). Mostly at 52°C, but we boost to 60°C when we have visitors and need the extra capacity.
Total water heating electricity usage: 336 kWh
Total hot water usage: 18,000 litres (about 50 per day). Mostly at 52°C, but we boost to 60°C when we have visitors and need the extra capacity.
In fact, our house was recently recognised as having the lowest heating costs on the heatpumpmonitor.org site, which raises an interesting question, could we have the lowest heating costs in the UK?
Chuffed though I am, I doubt it. A moderately sized new build Passive House with a heat pump working reasonably well should certainly use less electricity for space heating than we do, so it would just need an efficient hot water system as well. Get monitoring your systems people!
milkb0at@EsTresidder That’s fantastic stuff. Well done. And on top of all the numbers, you have a house that’s pleasant and comfortable to live in, all year round.
djvd@EsTresidder Thanks for the updates Es. I followed it with great interest and miss your building updates now it is finished.
david M brooke@EsTresidder
Thanks; it's good to have an update on how impressively your house is performing.
Out of curiosity, do you separately track the energy usage / running cost of the MVHR unit?
There's an argument for including this in the 'heating' costs, on the basis that the excellent air tightness which is important to deliver the thermal performance *requires* the use of MVHR to maintain the air quality.
Thanks; it's good to have an update on how impressively your house is performing.
Out of curiosity, do you separately track the energy usage / running cost of the MVHR unit?
There's an argument for including this in the 'heating' costs, on the basis that the excellent air tightness which is important to deliver the thermal performance *requires* the use of MVHR to maintain the air quality.