Heatpump + thermal store on economy 7.

rogerblack

I'm at the moment ripping up my floors to install insulation, as part of a project to properly insulate my house.
I've come to the conclusion that the cheapest possible (per kWh) way to heat is with a very large thermal store, and a heatpump, running on economy 7, leading to underfloor heating.
This can hit well under 2p/kWh.

Does anyone have a similar system?

(And yes, the thermal store will be large - several tons of water)

grahamc2003

rogerblack wrote: »

I'm at the moment ripping up my floors to install insulation, as part of a project to properly insulate my house.
I've come to the conclusion that the cheapest possible (per kWh) way to heat is with a very large thermal store, and a heatpump, running on economy 7, leading to underfloor heating.
This can hit well under 2p/kWh.

Does anyone have a similar system?

(And yes, the thermal store will be large - several tons of water)

I'm a bit dubious that it could work (without any non-e7 use). My storage heaters are in total about 21 kw, so a heat stprage capacity of around 130kwh fully charged (for a large house). Even then, IK expect it wouldn't maintain anything like 20 degrees if it dropped below zero ouitside during the day.

I'd obviously need a heat pump working at around 21kw for the 7 cheap hours to store the same (inadequate to some if very cold outside) level of heat. Not sure if they sell those in the domestic market. If I had a 10kw system, then that would be totally inadequate for my house under your proposal.

Also, running overnight, you're going to hit cold temperatures, whent the cop drops off anyhow, and icing may be a serious issue. Check the temperature the max power is taken at (probably 7C IIRC), and realise that below that, you won't even get the max power quaoted, and may get much less, all the way down to negative values during defrost.

rogerblack

The points you raise are valid, and I've considered them.
The (air-air) heatpump would be used in conjunction with an earth tube, to boost the input temperature somewhat in the cold months, which would be fed warm(er) air from a solar collector (basically a greenhouse I have and don't use) during days it's worth it.

Currently this is at the 'couple of sheets of A4' stage - I need to do proper costings of everything, as well as more detailed sums based on historical temperature and sunlight.

whasup

Roger, A colleague of mine moved into a house in the Cotswolds about this time last year. It had a very large thermal store running off ordinary E7 tarif. The fact is it was hopeless. The heat loss curve is slow to begin with (as you would expect) but when it gets going it drops like a stone. All warmth was gone by mid to late evening at best. You would obviously be better off cost wise with the heat pump (I haven't actually worked that out but assuming you would be) but I would be very doubtful you could store enough water to make it practical.

Why not just run fan coils off the heat pump? That would be efficient.

anselld

Might work better with Economy 10 tariff.