Heat pump for new build

[deuce22]

Hi.

 

I am trying to get some info on installing a ASHP on a new build. I have just spoken with a company and they have suggested a twin 16kw-8kw with a 400l water tank.

 

The floor area is roughly 350m2 over 3 floors. A friend who is a heating engineer (but doesn't have much experience with ASHP) advised installing UF heating as it runs off a much lower temperature to radiators and also combine it with solar (so in theory heating and hot water would very cheap).

 

I don't really have a clue about heat pumps and solar at the moment, but will educate myself on both. I just wanted to check if these are actually worth installing as another person said it will take him a very long time to recoup the cost of it.

 

Thanks.

[SteamyTea]

Have you had a proper heat loss calculation done.

That is the very first part.

Just knowing the size of a property is of little use.

[JohnMo]

Solar, good electric production in summer, but much lower in winter.  Don't bank on it doing much to lower heating bills, unless you have a huge amount of PV installed.  In spring, summer and autumn most of your hot water production should come from solar.

 

How well insulated and airtight is the house?  Your house is just under twice the size of ours and we have a heat load of around 3kW at -5 degC.

 

You need to get the sizing of the heat pump right, that is the first thing, they are not as forgiving as say a gas boiler for being oversized.

 

UFH is better, but radiators can also be done, with oversized radiators.

 

UFH needs a well insulated floor, otherwise you loose too much heat downwards, and have to run the UFH hotter to compensate...

 

What stage is your build at?

What is your current wall, floor and roof buildup with respect insulation?

[PhilT]

1 hour ago, deuce22 said:

A friend who is a heating engineer (but doesn't have much experience with ASHP) advised installing UF heating as it runs off a much lower temperature to radiators

To be clear - much lower than gas boiler fed radiators. I considered UFH but in the end went for properly sized rads with my heat pump, and I'm very glad I did, they work brilliantly, always within a temperature range of 35 - 50degC, similar to UFH.

Edited July 18, 2022 by PhilT

[deuce22]

I've had the SAP calculations done, but not heat loss, I'll look into it. 

 

The property is an ICF build. I'm just about to start framing the roof and will have doors and windows fitted soon as well. I'll bo doing a warm roof with 150mm PIR on top and mineral wool in between 8x2 rafters.

[PhilT]

2 hours ago, deuce22 said:

I just wanted to check if these are actually worth installing as another person said it will take him a very long time to recoup the cost of it.

It is absolutely definitely worth installing. Heat pumps are key to solving the energy crisis AND saving cost.

My stats. MCS heat loss 16,213kWh p.a.

Energy consumption in previous year before ASHP was 21,134kWh gas plus 3,274kWh electricity = 24,408kWh total.

Energy consumption with ASHP in first full year was 200kWh gas (cooking only) plus 6,533kWh electricity = 6,733kWh total i.e. a whopping 72% reduction in energy consumption!

ASHP gave rise to additional 3,259kWh electricity which, simplistically and very roughly, gives a SCOP of 5 - seems almost absurdly good but them's the numbers!

This translates into actual savings for me of at least £600p.a. at current energy prices, on a net outlay of £6,000, so simple payback = 10 years.

[Conor]

You'll be pretty well insualted and airtight by the sounds of it. 16kW sounds way too much. 

 

We built a 345m² ICF house. We installed a 2-9kW coolenergy heatpump. Not used it in winter yet but it's coping well heating the 300l tank. Our modelled peak heat load is 5kW.

 

Today, its cooling the house through the UFH. Consuming about 3kW to do this, so less than what our PV is generating. Very happy and wouldn't consider anything else.

[SteamyTea]

1 hour ago, deuce22 said:

I'm just about to start framing the roof

Have you considered roof integrated PV, similar price to some roofing materials.

[PeterW]

43 minutes ago, PhilT said:

Heat pumps are key to solving the energy crisis AND saving cost.

Insulation is far more important, as is properly designed glazing. Heat pumps do not solve energy issues in winter as they essentially become resistance heating when CoPs are considered. 

[Adrian Walker]

11 minutes ago, PeterW said:

Insulation is far more important, as is properly designed glazing. Heat pumps do not solve energy issues in winter as they essentially become resistance heating when CoPs are considered. 

Totally agree. a fabric first approach is the way forward 

[SuperJohnG]

52 minutes ago, SteamyTea said:

Have you considered roof integrated PV, similar price to some roofing materials.

I'd recommend this highly just now. I didn't do it last year when I was getting my roof slated and regret it heavily. 

 

Midsummer wholesale and get the GSE in roof trays - do it now and you save the roofing material cost. 

[SteamyTea]

31 minutes ago, PeterW said:

Heat pumps do not solve energy issues in winter as they essentially become resistance heating when CoPs are considered. 

How cold do you think the UK usually is in winter?

Not many of us live in the frozen north.

Very really below 5°C, 20% of a year, 73 days)

Only 0.75% is -3 or below, 2.7 days. (Central England Temperature data set)  So a fan heater can sort that out, but ASHPs still have a greater than unity CoP at that temperature.

 

[PhilT]

4 minutes ago, PeterW said:

Insulation is far more important, as is properly designed glazing. Heat pumps do not solve energy issues in winter as they essentially become resistance heating when CoPs are considered. 

To the first point - not in the context of the original post - it's a new build so safe to say a good standard of insulation and glazing will already have been planned, so the question then becomes is it worth getting a heat pump? Answer yes absolutely compared to other forms of heating such as gas. To the second point, in the 3 coldest months Dec/Jan/Feb my heat pump used 1,674kWh compared to gas the same period one year earlier of 9,779kWh so that's where the energy saving is actually most impressive.

[SteamyTea]

32 minutes ago, PhilT said:

To the second point, in the 3 coldest months Dec/Jan/Feb my heat pump used 1,674kWh compared to gas the same period one year earlier of 9,779kWh so that's where the energy saving is actually most impressive.

Say electricity is 28p/ kWh, then £468.72.

Gas at 7p, £684.53.

Gas would need to be 0.04793p/kWh.

[PhilT]

6 minutes ago, SteamyTea said:

Say electricity is 28p/ kWh, then £468.72.

Gas at 7p, £684.53.

Gas would need to be 0.04793p/kWh.

the point at issue was about energy saving not cost saving. Which supplier gives you 28p - I'll be switching to them!

Edited July 18, 2022 by PhilT

[SteamyTea]

3 minutes ago, PhilT said:

Which supplier gives you 28p

Isn't that the price cap before tax?

[JohnMo]

But why were you using so much gas, was the boiler oversized with no buffer, multiple zones, so continuously in short cycle?

 

Using your figures if the same input heat, you getting a CoP of close to 6 in the coldest months!  Which points to the gas system not performing correctly.  Manufacturers would be shouting from the roof tops if you could get a CoP that good.

 

 

[SteamyTea]

57 minutes ago, JohnMo said:

Using your figures if the same input heat, you getting a CoP of close to 6 in the coldest months! 

How do you work that out from the annual figures?

The overall CoP may be 5.9, does not take into account seasonality changes.

Though it does seem very high.

[JohnMo]

41 minutes ago, SteamyTea said:

How do you work that out from the annual figures?

The overall CoP may be 5.9, does not take into account seasonality changes.

Though it does seem very high.

 

3 hours ago, PhilT said:

 To the second point, in the 3 coldest months Dec/Jan/Feb my heat pump used 1,674kWh compared to gas the same period one year earlier of 9,779kWh so that's where the energy saving is actually most impressive.

So 9779/1674 = 5.84=CoP or very close too.

[SteamyTea]

4 minutes ago, JohnMo said:

 

So 9779/1674 = 5.84=CoP or very close too.

Ah, I missed/forgot the winter 3 months.

 

Would be interesting to see CoP by areas. I wonder if the dryer east of the country gets better results than the warmer, but wetter, west.

[jack]

6 hours ago, PhilT said:

To be clear - much lower than gas boiler fed radiators. I considered UFH but in the end went for properly sized rads with my heat pump, and I'm very glad I did, they work brilliantly, always within a temperature range of 35 - 50degC, similar to UFH.

 

I run my UFH at 25, and it's only that high because I can't turn it lower. I have a small amount of weather compensation dialed in - from memory, I think it starts kicking in at about 7 or 8 degrees outside temp, and ramps the outlet temp to 28 or 29 degrees at around 0 degrees outside temp. 

 

I'm sometimes curious about what it would have been like to have radiators rather than UFH in an airtight and well-insulated house. That said, I certainly don't miss having big lumps of metal all over the walls! 

[PhilT]

3 hours ago, JohnMo said:

But why were you using so much gas, was the boiler oversized with no buffer, multiple zones, so continuously in short cycle?

 

Using your figures if the same input heat, you getting a CoP of close to 6 in the coldest months!  Which points to the gas system not performing correctly.  Manufacturers would be shouting from the roof tops if you could get a CoP that good.

 

 

Agreed it was bad! 16/21 = only 76% efficiency. The CoP for those 3 winter months theoretically would be 16/21 x 9,779 = 7,450, divided by 1,674 = 4.4. I suspect many/most gas households have this issue so the claim of potentially huge energy savings is still valid, IMO.

Edited July 18, 2022 by PhilT

[deuce22]

I've got somebody coming on the weekend to do a heat loss calculation and let me know exactly what I need. 

 

Thanks for all the advice.

[ProDave]

4 minutes ago, deuce22 said:

I've got somebody coming on the weekend to do a heat loss calculation and let me know exactly what I need. 

 

Thanks for all the advice.

If this is a new build then you should know exactly the wall floor and roof make up and U values and be able to accurately calculate the heat loss using Jeremy's spreadsheet.  Has nobody involved in the design of the building done this for you?

[deuce22]

I didn't have any detailed drawings or any other details.

 

I have had SAP calculations completed, so would the info I need be in there?