Do I need an ASHP?

[Tom]

I've always thought I'd be getting an ASHP for our build and I have been dithering on pulling the trigger on one of the Cool Energy packages - unfortunately it looks like I've dithered too long as it seems their prices have just gone up by over £1k. This has made me think a bit more on whether we actually need one - and reading other's experiences on here with using a willis heater for their UFH makes me think this might be a reasonable alternative. I'm trying to work out a comparative cost for this but am struggling a bit, can anyone advise?

 

So, putting all my vital statistics in to JH's spreadsheet I get the following: total daily heat loss power for January OAT: 5677W and for the minimum January OAT 6826W - energy input at 4224kWh and 5079kWh respectively. We also will be having a wood buring stove so this could be fired up on the really cold days.

 

Hot water usage would be on the lower end of the scale. It's a 4 bed house but we take mostly showers.

 

The slightly complicating factor which is making me scratch my head is that we will be putting back the 12kW PV array that was on the barns before we knocked them down. They're on a SE/SW orientation split approx 50/50. With a willis heater we could therefore potentially utilise more of our own generation for the UFH than we could if we had an ASHP - but exactly how much the array could produce in deepest winter is probably quite low, and could probably just as easily all be dumped in to the UVC without "losing" any to export. But this is all me guessing, can anyone help with anything a bit more rooted in reasonable estimates?

 

If it seems reasonable, I'm guessing I could plumb everything in but with a willis heater in place of an ASHP, adding one at a later date if it didn't work out.

 

Any views greatly appreciated.

Tom

[Iceverge]

Direct 400l UVC for the DHW with PV divert. Should be ok all year round with 12kWp solar. 

 

Willis heater for UFH.

 

Program the diverter to heat the water first and then the slab. Your shortfall will still be 90% (quick calcs) for space heating (without the stove)  in the coldest months, but will ensure you don't export any solar. Make up the difference with the Willis on E7. A thicker (super insulated)  slab will help to buffer the heating and avoid complex control systems. 

 

Pre-plumb and wire for a cheapy ASHP when one turns up, but in the interim monitor the house performance to see what your actual usage is. 

Edited June 9, 2022 by Iceverge
clarity

[Tom]

Thanks Iceverge. The slab is 200mm with 400mm EPS beneath, so should do the job nicely. I guess I can get away without a buffer tank as well, as short-cycling wouldn't be a problem with a willis - or, thinking about it, might make sense to have one to store any excess and smoothe out the ripples with intermittent PV generation when cloudy etc.

[Tom]

The other complication is grants for ASHPs. Is there still money for ASHPs in a new build? I thouight not, but I spoke to a plumber earlier this week and he seemed to think there still was.

[Iceverge]

3 minutes ago, Tom said:

The slab is 200mm with 400mm EPS beneath, so should do the job nicely

Topps. 

 

4 minutes ago, Tom said:

I guess I can get away without a buffer tank as well, as short-cycling wouldn't be a problem with a willis - or, thinking about it, might make sense to have one to store any excess and smoothe out the ripples with intermittent PV generation when cloudy etc.

Beyond my knowledge I'm afraid but I can't see why you'd need one. 

 

2 minutes ago, Tom said:

The other complication is grants for ASHPs. Is there still money for ASHPs in a new build? I thouight not, but I spoke to a plumber earlier this week and he seemed to think there still was.

 

No idea sorry. 

[SteamyTea]

47 minutes ago, Iceverge said:

Make up the difference with the Willis on E7.

I think the big financial advantage of E7 has now gone.

EDF are charging me 33.33p/kWh Day Rate, 17.68p/kWh Night Rate and 55.1p/Day meter rental.

 

Just looked at my meter, was changed in 2006, and I have used 28% on day rate and 71% on night rate.  This works out as a unit cost, at todays prices, of 22.06p/kWh.

Last year I had changed that fraction to 17% and 83%, so 20.34p/kWh at todays rates.

So on reflection, by being very careful, it is still possible to get a decent overall rate on E7.

Edited June 9, 2022 by SteamyTea

[joth]

1 hour ago, Tom said:

The other complication is grants for ASHPs. Is there still money for ASHPs in a new build? I thouight not, but I spoke to a plumber earlier this week and he seemed to think there still was.

 

New builds are ineligible, except for self-builds which can claim the grant so long as certain evidence is provided

https://www.gov.uk/guidance/check-if-you-may-be-eligible-for-the-boiler-upgrade-scheme-from-april-2022#self-builds

 

If you own a self-build property

To be eligible, a self-build must have:

• been built mainly using the labour or resources of the first owner
• not been owned by a business or organisation

You will need to provide proof to your installer that your property is a self-build, for example a copy of the title deeds.

[jack]

1 hour ago, SteamyTea said:

I think the big financial advantage of E7 has now gone.

EDF are charging me 33.33p/kWh Day Rate, 17.68p/kWh Night Rate and 55.1p/Day meter rental.

 

I'm on Octopus Go and have just been moved onto a 34.86 p/kWh rate for 04:30-00:30, 7.5 p/kWh rate for 00:30-04:30, and about 43.12 p/day standing charge.

 

Only 4 hours on the cheap rate, but at a bit over 20% of the day rate, it takes some beating. We put everything on during that period during winter - washing machine, dishwasher, car.

 

We have a lot of PV, so we focus on using that during the day during summer and on sunny days the rest of the year, but it's nice to know there's a cheap period for when the timing doesn't work out (eg, dishwasher is full after dinner and we don't want to wait until mid-morning the next day to start a cycle).

[Tom]

So I guess I would qualify as the property will be "self-built" in that I'm project managing. Does getting an ASHP now so as to get the grant make sense? Compared to a willis based system which I would have to pay 100% for. I guess it comes down to what the plumber would charge for installing the two systems.