Thermal store for heat pump?

anon_ymous

So 

I guess this means some kind of hot water tank?

If say you've got an EV, you can charge that car between 12am and 5am for 7.5p/kWh

In that same time, there's nothing stopping you from also charging up your home batteries + your hot water tank which means you only really need a COP of like 2 or so to be cheaper than gas on Octopus tracker rates

Is this something people do? What kind of thermal store do you use? Is it perhaps a Mixergy or something else? 

Reed_Richards

You would not be able to store a days worth of heat in a thermal store.  Well it wouldn't work for me, my daily use, averaged over a full 365 days is approximately 17 kWh per day.

I'm not saying that you could not make this idea work as a means of saving money.  You could certainly heat up your DHW cylinder using cheap EV/night-rate electricity and heating the hot water with your heat pump.  But if you want to also save money on your central heating then you need another cylinder of hot water (or the equivalent) for your thermal store so you need somewhere with the space and the load-bearing capacity to site this.  It will only run your central heating for a while and if sited in the wrong place (like a loft) could then go into reverse and start to leak heat out of your heating system.       

QrizB

waqasahmed said:

So 

I guess this means some kind of hot water tank?

If say you've got an EV, you can charge that car between 12am and 5am for 7.5p/kWh

In that same time, there's nothing stopping you from also charging up your home batteries + your hot water tank which means you only really need a COP of like 2 or so to be cheaper than gas on Octopus tracker rates

Is this something people do? What kind of thermal store do you use? Is it perhaps a Mixergy or something else? 

You could do it with something like Solarchaser's "wee project" but it's not exactly plug & play:

https://forums.moneysavingexpert.com/discussion/6377030/ditching-gas-going-electric-immersion-only-a-wee-project

One thing that immediately comes to mind is that, if you're limited to the typical heat pump output temperature of 60C, the amount of energy you can store in a given volume of water is going to be somewhat less than he achieves. Maybe half as much. Which means even bigger tanks.

Solarchaser

Yeah as QrizB says, this is essentially what I'm doing, but with 800L of tank at 85C and only immersion.
So I'm currently on intelligent octopus meaning I get 7.5p from 11:30pm to 05:30am with which to heat the tanks by immersion.
So running 9kw (3 x 3kw heaters) at 6 hours gives the potential for 54kwh of stored heat, but thats with PID thermostats and solid state relays (thanks QrizB and heedtheadvice) instead of the standard thermostats which didn't really like over 75C.

Really the 800L is not enough, and I'm a fairly low *gas* user at maybe 12Mwh a year these days if I had to switch back.