To GSHP or not to GSHP?

[nfoote]

Sorry if this is not the right place for this, we're just desperate for some outside opinions that aren't so close to the problem and aren't trying to sell us something!

So we're pretty torn over what to do regarding installing a heat pump, probably a GSHP, or not bother, during construction of our extension, which requires moving our entire boiler/pump room anyway.

 

We've got a 300m2 1890s detached house in the South East. Empty cavity walls on the ground floor and solid walls on the first floor. Loft has been insulated. We're building an extension at ground and 1st floor to one side which will be insulated to current regs, plus the kitchen has already been extended 10 years ago to the rear. So basically 3 out of 4 elevations on the first floor remain original, while 2 out of 4 at the ground floor are original, that is to say poorly insulated.

 

We've had HP sales guys around who have done their heat lose survey and they're coming up a heating + hot water demand of 46,000kWh and us needing a HP with in excess of 17kW capacity. They're suggesting either a 22kW Ecoforest unit or a 12kW Nibe unit while keeping the gas boiler in a hybrid system (ie boiler takes over at a certain temperature when the HP won't handle the load). The Ecoforest is coming in at around £52k with £31k RHI and the Nibe at £44k with £33k RHI. The sales guys headline figures using electricity and gas pricing they've pulled out of the air come up at saving around £500pa on running costs. Not a huge amount with £10-£20k install costs remaining to pay off.

 

I've followed along on the calculations using our actual figures from last year (which don't include the new extension obviously). In 2020 we used 41636kWh of gas, basically all for space and water heating. We're currently paying basically 16p/kWh for electricity and just under 3p/kWh for gas. If the boiler is 92% efficient and a Nibe GSHP has a SCOP of 4.17 we're needing about 9100kWh of electricity instead of all that gas. All in all I'm coming up at actually costing around £300 more a year!

 

We're struggling to see what the point of installing a heat pump in the house, given its age, and retro fitting etc etc.

 

The sales guys are touting things like the Climate Change Levy coming in to tax gas thus making it far more expensive (as far as I can tell the CCL is business only tax?).
Attempts to insulate would benefit both gas and heat pump in terms of lowering running costs, although under a hybrid heat pump system the backup gas boiler would kick in less often I guess.
We've also looked at PVs (might get a 3000kWh system in, not much free energy for the install cost of around £7k) and storage batteries to work with both PVs and variable tariffs like Octopus Agile (which I worked out given a sample few days over Jan 2021 might save us an average of £1 a day, again, maybe 20 years to pay off install cost at todays prices, far in excess of their warranty).

 

On the flip side, gas prices are apparently set to rise even without taxation and we might have to install a secondary boiler in the extension (actually an annexe) anyway so there's £5k install cost anyway and more running cost.

 

Or, do we wait a few years to see if the GSHP install costs come down or the efficiencies go up? The fear there is the government subsidies might disappear.

 

Does anyone have any advice, we're pretty conflicted!?!

[Trw144]

Do you have the sales guys calculations? If you are on mains gas then I wouldn't even consider it.

[LA3222]

I'll admit I didn't read your background above, the question alone is enough for me. No. Cant say I've come across a case yet where GSHP makes economic sense.

 

ASHP yeah, GSHP nah. I did consider it very early in my planning process, swiftly dismissed.

[Trw144]

2 minutes ago, LA3222 said:

I'll admit I didn't read your background above, the question alone is enough for me. No. Cant say I've come across a case yet where GSHP makes economic sense.

 

ASHP yeah, GSHP nah. I did consider it very early in my planning process, swiftly dismissed.

Would you even swap from mains gas to ASHP. I wouldn't imagine much of a saving even in the best case scenario - and that's assuming the house is well insulated and has the low temp radiators/underfloor to make it suitable for a heat pump.

[nfoote]

3 minutes ago, Trw144 said:

Do you have the sales guys calculations? If you are on mains gas then I wouldn't even consider it.

 

Yes we have the sales guys calculations, basically they're coming up with (including the extension which they have the plans for)  heating at 37000kWh + hot water at 8000kWh using a SCOP of 3.54 at flow temp of 50 degrees, with gas at 4.5p/kWh and electricity at 12p/kWh coming in at £1746pa on a 22kW HP vs £2247 on a 92% efficient gas boiler. We seem to be running the house a bit cooler than their models predict but either way the big difference appears to be their gas and electricity pricing assumptions, we've paying far less for gas and a fair bit more for electricity, which completely wipes out their predicted £500 saving and turns it into an actual cost!

 

Yes, we're on mains gas.

 

The thing is I personal want it to work, it sounds cool and is greener etc, but the numbers at the current prices aren't stacking up. Other members of the household however seem fixated on the future, possibly rightly so, and that gas prices will rise thus creating the running cost savings the sales guy predict.

[nfoote]

5 minutes ago, LA3222 said:

I'll admit I didn't read your background above, the question alone is enough for me. No. Cant say I've come across a case yet where GSHP makes economic sense.

 

ASHP yeah, GSHP nah. I did consider it very early in my planning process, swiftly dismissed.

 

I guess the logic there is the GSHP is more efficient, under the Nibe at SCOP of 4.17 vs a max of around 3.5 on a ASHP? Plus the potential noise from a ASHP with our only placement options being right beside the lawn or on the patio doesn't seem attractive.

[LA3222]

3 minutes ago, Trw144 said:

Would you even swap from mains gas to ASHP. I wouldn't imagine much of a saving even in the best case scenario - and that's assuming the house is well insulated and has the low temp radiators/underfloor to make it suitable for a heat pump.

Nope. Everything that ever gets mentioned on here circles back to the same thing - gas is king.

 

I'm all electric, no gas available so the permutations are rigged towards heat pumps. If I could get gas, I'd have gas.

[Trw144]

Do you have a heating system that will work with 50 degree water?

 

As for gas prices, they are way off and personally I don't see them rising significantly - it would put an awful lot of people in fuel poverty if they did. I would also imagine that should their be any future increases in gas prices, we will also see similar increases on electricity.

[Trw144]

6 minutes ago, LA3222 said:

Nope. Everything that ever gets mentioned on here circles back to the same thing - gas is king.

 

I'm all electric, no gas available so the permutations are rigged towards heat pumps. If I could get gas, I'd have gas.

We're on gas here and in the same position on the next plot. Gas is 1/2 mile away and they have said it will be tens and tens of thousands so.

 

I agree that when it comes to heat pumps, the COP difference between ground and airspirce means the extra expense of gshp isn't worth it.

Edited February 1, 2021 by Trw144

[LA3222]

You have to remember, these chumps are trying to part you from your cash. The fact they are running high numbers for gas cost etc tells me all I need to know. They are rigging the game in favour of their product and hoping you don't scrutinise too closely.

[nfoote]

6 minutes ago, Trw144 said:

Do you have a heating system that will work with 50 degree water?

 

The heat survey they did including measuring the rads we already have, all but a the bathrooms and one other apparently were large enough to handle a lower temp, which seems to make sense as we don't run the thermostatic valves in most rooms beyond 3/5.

 

5 minutes ago, LA3222 said:

You have to remember, these chumps are trying to part you from your cash. The fact they are running high numbers for gas cost etc tells me all I need to know. They are rigging the game in favour of their product and hoping you don't scrutinise too closely.

 

That's what I'm feeling really. Chucking in the bit about the CCL which took all of 20 seconds on Google to determine doesn't apply to domestic didn't help their case ...

[ProDave]

Yes a GSHP is a bit more efficient than an ASHP.  But it is a LOT more expensive to install.

 

What were they proposing for a heat collector?  A borehole?  Or dig up your entire garden, lay slinky heat collector pipes and put the garden back?

 

Before you comit, forget their heat loss estimates, look up a whole years worth of gas bills and post them here so we can see how much gas you use in a year.  That will give a much better idea of how much heat you need than any estimate just by looking at the building.  That will give a better idea what size heat pump you would need.

[pdf27]

1 hour ago, LA3222 said:

I'll admit I didn't read your background above, the question alone is enough for me. No. Cant say I've come across a case yet where GSHP makes economic sense.

 

ASHP yeah, GSHP nah. I did consider it very early in my planning process, swiftly dismissed.

There are times it might come close - we're looking to build a very well insulated house which would only need a small slinky done at the same time as the groundworks and would fit in the garden. I'm figuring a GSHP would be £2-3k more expensive but that it's worth it not to have a carbuncle facing onto the back garden - once I put a value on that the two about break even.

 

1 hour ago, nfoote said:

 

Yes we have the sales guys calculations, basically they're coming up with (including the extension which they have the plans for)  heating at 37000kWh + hot water at 8000kWh using a SCOP of 3.54 at flow temp of 50 degrees, with gas at 4.5p/kWh and electricity at 12p/kWh coming in at £1746pa on a 22kW HP vs £2247 on a 92% efficient gas boiler. We seem to be running the house a bit cooler than their models predict but either way the big difference appears to be their gas and electricity pricing assumptions, we've paying far less for gas and a fair bit more for electricity, which completely wipes out their predicted £500 saving and turns it into an actual cost!

Gas cost per kWh looks a bit high and electric per kWh looks low - worth going on one of the comparison sites and checking what the actual costs would be for you. I note that their quoted gas prices are a lot higher than you're paying, and their quoted electricity price a lot lower.

 

1 hour ago, nfoote said:

I guess the logic there is the GSHP is more efficient, under the Nibe at SCOP of 4.17 vs a max of around 3.5 on a ASHP? Plus the potential noise from a ASHP with our only placement options being right beside the lawn or on the patio doesn't seem attractive.

It's more efficient for heating but less efficient for hot water - in summer the hot air gives a really nice boost to the COP for hot water. In a retrofit scenario you win significantly, less so for a new build where hot water is a bigger fraction of the total.

 

1 hour ago, Trw144 said:

As for gas prices, they are way off and personally I don't see them rising significantly - it would put an awful lot of people in fuel poverty if they did. I would also imagine that should their be any future increases in gas prices, we will also see similar increases on electricity.

At the moment there are significantly higher levies on domestic electricity than on gas, and there is a campaign going on to change that. If that happened total energy bills would presumably be about the same (assuming no change in the tax burden), but gas would become significantly more expensive and electricity quite a bit cheaper. I'm not holding my breath.

 

32 minutes ago, ProDave said:

Yes a GSHP is a bit more efficient than an ASHP.  But it is a LOT more expensive to install.

 

What were they proposing for a heat collector?  A borehole?  Or dig up your entire garden, lay slinky heat collector pipes and put the garden back?

 

Before you commit, forget their heat loss estimates, look up a whole years worth of gas bills and post them here so we can see how much gas you use in a year.  That will give a much better idea of how much heat you need than any estimate just by looking at the building.  That will give a better idea what size heat pump you would need.

At that price and heat consumption it's a borehole, and probably quite a deep one - rough rule of thumb for a slinky is 10m per kW. 17kW heat capacity is at least 170m of slinkies - so minimum of a space 50m x 25m which is a hell of a big back garden. With boreholes you're getting 25-50 W/m so for 17kW you're looking for ~300-500m of borehole which is probably two boreholes spaced apart from each other, which is where the £50k estimate is coming from (and why they hybrid system is so much cheaper).

 

Agree with everyone else, GSHP doesn't make sense for me - even environmentally, let alone financially. You'd get a much bigger carbon saving spending the same amount of money on insulation than on a heat pump.

[SteamyTea]

Do you know your winter heat loads/gas usage.  This is the important one for sizing any heat pump.

If your annual usage is 41636 kWh, and assuming that you use 4000 kWh for hot water, that leaves ~37,600 kWh for heating.

Now the coldest 4 months will use 2/3^rd of that, so ~25,000 kWh, which is about a 9 kW heat load.

It is usual to oversize a heat pump, though less so for a GSHP.  So that 12 kW Nibe ones seems, on the face of it, about the right size.

But £44,000, think about that, it is about half the price of my house.  Or a very nice Tesla Model 3, which will save you more if you do decent mileage.

This only leaves you two choices:

Improve the building

Gas

 

If you want to improve the building, look at airtightness first.

[Gone West]

In an old house with gas always stick with gas and the same with oil. If you want to spend a lot of time and money improving the fabric of an old building then an ASHP may be an option. I would only consider an ASHP if building a well insulated house and wouldn't ever fit a GSHP unless I lived somewhere like Northern Sweden.

[Jilly]

Airtightness in an 1890's cottage might not be a good idea: research interstitial condensation. 

[nfoote]

10 hours ago, ProDave said:

Yes a GSHP is a bit more efficient than an ASHP.  But it is a LOT more expensive to install.

 

What were they proposing for a heat collector?  A borehole?  Or dig up your entire garden, lay slinky heat collector pipes and put the garden back?

 

Before you comit, forget their heat loss estimates, look up a whole years worth of gas bills and post them here so we can see how much gas you use in a year.  That will give a much better idea of how much heat you need than any estimate just by looking at the building.  That will give a better idea what size heat pump you would need.

 

38 minutes ago, SteamyTea said:

Do you know your winter heat loads/gas usage.  This is the important one for sizing any heat pump.

....

If you want to improve the building, look at airtightness first.

 

Yes GSHP proposal is a borehole, the Ecoforest would be 3 holes at 125m deep while the Nibe only needs 2 holes, thus being a bit cheaper.

 

Our 2020 monthly energy usage is as follows;

	E kWh	G kWh
January	671	6903
February	553	6288
March	573	6348
April	539	3232
May	496	1603
June	502	790
July	493	716
August	492	649
September	500	919
October	567	3236
November	527	4370
December	654	6582
2020 Total	6567	41636

 

Airtightness is probably going to be hard. We're replacing most of the windows and doors but are not sure what to do regarding wall insulation. Apparently at least some of the GF cavity is filled with rubble so perhaps internal wall insulation for GF and FF is the way to go, although loath to lose the floorspace. External insulation might be hard being in a conservation area and the FF being mock tudor.

[SteamyTea]

4 minutes ago, nfoote said:

Our 2020 monthly energy usage is as follows

My guestimate was pretty close.

 

Insulation, generally, needs to be within the airtight envelope or the cold external air just penetrates and invalidates it.

This is why internal insulation is often so effective, but it is the detail between floors, extending cabling/pipework and the reduced living area, that causes problems.

But it will probably make the biggest difference.  Just sorting mine out almost halved my energy usage, and all I really did was improved the sealing of my existing windows and doors (finally sorted the front door after 16 years, almost).

If you can get airtighness sorted, then you can fit MVHR, and get an extra bonus on reduced usage.

[ProDave]

So January you use 6903 kWh that's 222kWh per day (ouch) or an average of 9kWh continuous so a 17kWh ASHP would need to be heating the house 13 hours per day to achieve that (plus the time it takes for DHW)

 

So the sizes about about right, but don't forget to allow for the increase when you build the extension