Heating usage? Is ASHP worth cost?

[Guest]

Hello,

I'm thinking an ICF build with UFH. However, I'm considering if an air to water ASHP would be worth it's cost, or just use electric UFH.

 

What kind of heating usage in kwh would you expect for a 100m2 bungalow? I'm in Scotland so a bit cooler.

[Bornagain]

Hi,

We built a 190m2 ICF house with triple glazing, 300mm eps underfloor, 600+mm insulation in loft, MVHR

Our house is all electric but we do have a wood burning stove.

Our heating and hotwater come from E7, heating by direct imersion a 500L thermal store, wet underfloor heating downstairs. No heating upstairs.

Total electricity demand in the last 12 months has been 7200 kWHr.  E7 overnight useage = 3800 kWHr, if you assume that the background load for all the usual bits and bobs is 250w, then the energy to provide heating and hot water is around 3100kWHr/year.    1 kWHr of E7 electricity costs around 7.2p, therefore we provide heating and hot water for about £230/yr.

If we did it all with an ASHP @ a COP of 4, then this bill would drop to around £60/yr.

This means an ASHP would save about £170/yr - and that assumes no breakdowns or maintenance.

By the time an ASHP has paid itself back, it is in the scrap bin and you need to buy a new one.

Stick to an imersion heater, much cheaper in the short term, long term, and less to go wrong.

[DamonHD]

Background/vampire continuous load of 250W would be high IMHO.  Get that down to more like 40W to cover your fridge/freezer and save > £200/y straight off!

 

Rgds

 

Damon

[A_L]

Assuming you insulate external surfaces to 0.11-0.12 with windows <1.0 and you can do infiltration to 0.6ach@50Pa (Passivhaus standard) and an MVHR  you could heat with sub 1000kWh per year. Your hot water demand will be 2000kWh/yr or more.

[eandg]

1 hour ago, Bornagain said:

Hi,

We built a 190m2 ICF house with triple glazing, 300mm eps underfloor, 600+mm insulation in loft, MVHR

Our house is all electric but we do have a wood burning stove.

Our heating and hotwater come from E7, heating by direct imersion a 500L thermal store, wet underfloor heating downstairs. No heating upstairs.

Total electricity demand in the last 12 months has been 7200 kWHr.  E7 overnight useage = 3800 kWHr, if you assume that the background load for all the usual bits and bobs is 250w, then the energy to provide heating and hot water is around 3100kWHr/year.    1 kWHr of E7 electricity costs around 7.2p, therefore we provide heating and hot water for about £230/yr.

If we did it all with an ASHP @ a COP of 4, then this bill would drop to around £60/yr.

This means an ASHP would save about £170/yr - and that assumes no breakdowns or maintenance.

By the time an ASHP has paid itself back, it is in the scrap bin and you need to buy a new one.

Stick to an imersion heater, much cheaper in the short term, long term, and less to go wrong.

You get a 10 year interest free loan with Home Energy Scotland for the capital and installation costs of an air source heat pump. And if it's in before April next year your RHI will pay for the loan. 

[Guest]

Thanks all

 

I'm planning on having an electric shower(s) so the hot water demand would be very low, just for hand washing I imagine. 

If heating requirement so low, I wonder if solar panels and battery could provide enough power but doubt it would be enough in winter so would need mains electricity connection.

 

What sort of costs would you expect for the air to water ashp? £3k? With ICF, does this mean the concrete wall needs to be drilled through?

What COP? 3.5?

 

Edited May 21, 2020 by newbuild20201

[SteamyTea]

3 hours ago, Bornagain said:

Stick to an imersion heater, much cheaper in the short term, long term, and less to go wrong.

I tend to agree that direct resistance heating heating is cheap to install and maintain.

But for a new build, and better control, it is hard to beat an ASHP these days.

3 hours ago, DamonHD said:

Background/vampire continuous load of 250W would be high IMHO

Too true.  60% of the time my house uses nothing.  worked out with our Ed Davies a while back that my fridge uses 5W, maybe double that in the summer when it gets very hot in the kitchen (actually down here that does not happen hardly at all)

1 hour ago, A_L said:

Assuming you insulate external surfaces to 0.11-0.12 with windows <1.0 and you can do infiltration to 0.6ach@50Pa (Passivhaus standard) and an MVHR  you could heat with sub 1000kWh per year.

Yes.

 

3 hours ago, Bornagain said:

300mm eps underfloor, 600+mm

Did anyone run the numbers if the 600mm was under the floor and 300mm in the loft?

[Hobbiniho]

1 hour ago, eandg said:

You get a 10 year interest free loan with Home Energy Scotland for the capital and installation costs of an air source heat pump. And if it's in before April next year your RHI will pay for the loan. 

 

it absolutely will not cover the cost of the loan, using the RHI calculator and inputting the data that @Bornagain has provided would give less than £1000 payment over 7 years, without having the exact figures from the EPC its a bit of a guess

 

When i installed an ASHP my energy demand went from 21000KWh/year to 16000KWh/year due to the change from storage heater to ASHP the only change to the house was the heating system, the water heating demand actually went up as the old setup had a very very small DHW tank and i installed a 255l despite only having 1 bathroom

[ProDave]

16 minutes ago, Hobbiniho said:

 

it absolutely will not cover the cost of the loan, using the RHI calculator and inputting the data that @Bornagain has provided would give less than £1000 payment over 7 years, without having the exact figures from the EPC its a bit of a guess

 

 

Which brings into question is it really worth paying an MCS company to install a complete system so you can claim the RHI?

 

Many of us have found it way cheaper to source the parts ourselves and self install and forget all about the RHI.  Personally I have long concluded that with the inflated MCS prices often charged, the only winners are the MCS companies.

 

My heating cost is a little over £200 per year via the ASHP.  So assuming a COP of 3, that would me more like £600 with resistance heating.  So saving £400 per year.  The price I paid for my ASHP by the end of this year, the saving in heating costs will have paid for it.

[eandg]

45 minutes ago, Hobbiniho said:

 

it absolutely will not cover the cost of the loan, using the RHI calculator and inputting the data that @Bornagain has provided would give less than £1000 payment over 7 years, without having the exact figures from the EPC its a bit of a guess

 

When i installed an ASHP my energy demand went from 21000KWh/year to 16000KWh/year due to the change from storage heater to ASHP the only change to the house was the heating system, the water heating demand actually went up as the old setup had a very very small DHW tank and i installed a 255l despite only having 1 bathroom

Sorry. Going on my consultation with Home Energy Scotland ours more or less would, though I think the model underestimated how energy efficient a modern self-build home is - haven't progressed it beyond that.