Putting the pieces together: PV, V2H, ASHP, TOU Tariff, Gas Boiler

michaels

I have been offered by my parents an unused Air-water heat pump, nominal 16kw.
I have a V2G car charger with a 11kw G99, a 24kwh EV, 3.68kw PV, a modulating gas boiler.

I'm thinking if I add a TOU electricity tariff such as Octopus GO 4 hours at 7.5p or EDF Go Electric 98 (5 hours at 4.5p) I might be able to achieve some massive savings.

Current thought is to add the heat pump in serial to the heating circuit via a heat exchanger leaving the weather comp gas boiler connected as it will only cut in when the flow temp goes too low, run the heat pump during the off peak period direct from the mains and from the car battery the rest of the time.  A fairly cheap upgrade might be to double/triple rads in the rooms needing the most heat compared to the current sizing.  Similarly time shift as much electric usage as possible to the cheap window and use the V2G to top up.  Heat the hot water tank (200l, modern insulation) to 70 degrees using the immersion during the cheap period which will do the morning hot water usage with the gas as backup for the evening if needed.  Downside seems to be that the heat pump is not heating the hot water.

In terms of usage, I reckon our peak winter day is about 150kwh gas and 30kwh electricity.  Obviously this presents a problem although hopefully we can move 20 of the electric to off peak and another 50 of the gas for hot water heating and night space heating.  This leaves 10 kwh electric and 100 kwh gas space heating.  This is a worst winter day so COP for space heating may only be 2 so the battery probably needs to prioritise the electric use and as much as can be spared for the heat pump, beyond that it becomes cheaper to use the gas rather than electric for space heating until the temp is such that the COP is above 3.  On the EDF TOU electricity tariffs you are forced to take gas that is more expensive so there is a trade off here.

I am thinking an excel model is needed to work out the total overall cost and possible savings but would welcome any initial thoughts.

Reed_Richards

That's a lot of pieces! 

If you increase the surface area of your radiators you can run your boiler and or heat pump at a lower output water temperature.  This will make a gas boiler a bit more efficient and a heat pump a lot more so.

You can buy hybrid boilers that combine a gas or oil boiler with a heat pump, DIY might be a bit tricky.  Your heat pump will run most efficiently when it's warm outside and most cost-effectively when your electricity is cheapest.  Personally I think I might struggle a bit to work out when to use the heat pump and when to use the gas boiler.   

shinytop

Some interesting ideas; I think this approach may be something that becomes more common.  Will your electricity supply be able to cope with charging an EV, a battery and running the immersion all at once?

As R_R alludes, it would be better to have clever software controlling what works when, otherwise you'll spend your whole life fiddling with spreadsheets and heating controls!  ASHP heating normally works differently (constant, slow and steady) to gas CH (can be more on/off) so it will be tricky to get them to work together.  

Reed_Richards

shinytop said:
... ASHP heating normally works differently (constant, slow and steady) to gas CH (can be more on/off) ...

In my last house I had a gas boiler with Weather and Load Compensation and that was constant, and slow and steady once the room temperature was close to the set temperature.  If you can persuade your gas CH to be constant, slow and steady it will be more efficient.  In fact gas boilers tend to have a greater range of modulation than heat pumps so slow and steady should actually be easier with gas!

michaels

Thanks. 

Hood news the boiler is a slow and low weather comp model so can leave it circulating amd if the heat pump keeps rhe return hot enough then the gas just wont cut in.
If the heat pump is connected via a heat exchanger then van use smart controller to turn on ans off heat pump and iys circuir pump nased on oitside temp, (car) battery level time of day etc

michaels

Main problem may be permitted development, can't put the heat pump whwre makes plumbing sense as it is within 1m of boundary. 

Reed_Richards

I would have thought what you want is for the heat pump to stop and the gas boiler to start once the return water gets hot enough.  So the heat pump takes the water from cold to "lukewarm" and the gas boiler takes it from lukewarm to hot as necessary.  It's not clear to me that you have the same idea.  

michaels

Reed_Richards said:

I would have thought what you want is for the heat pump to stop and the gas boiler to start once the return water gets hot enough.  So the heat pump takes the water from cold to "lukewarm" and the gas boiler takes it from lukewarm to hot as necessary.  It's not clear to me that you have the same idea.  

Nope, my thought was that the heat pump runs all the time and the gas only cuts in if the HP water temp is not high enough.  Does that make sense?  Of course it might be that the HP then starts cooling the water in which case one would want to to go off.  Otherwise it could be on all the time unless the outside temp (and thus COP) and the gas/electric prices made gas cheaper.  So basically the boiler weather comp would never turn on the boiler if the HP was outputting enough energy so no need for any other controls on the boiler.

Hot water is on a separate circuit (diverter valve in boiler) so am thinking that using HP to help with that too would be tricky to implement - and not as obviously a saving over immersion/gas due to the higher temps.

michaels

Anyone think I could put the HP at the front of the house under a 'louvre cover' and get away with it re planning?  Could add sound insulation on the back of unit wall next to the house (to reduce reflected sound) and the side facing the neighbours.  Have seen such covers so presumably they don't hit efficiency too badly?

gefnew

Heat pumps need a certain amount of clean air to work .

michaels

gefnew said:

Heat pumps need a certain amount of clean air to work .

I guess it could be quite a large'box' - idea of the cover would be to reduce noise and make it less obvious on the front wall....