Air,scource heat pumps

[Lorraine]

Renovating traditional Irish Stone Cottage

Grants available for air scouce heat pumps, would appreciate feedback re insulation in respect of performance?? and efficiency ie cost savings?,

 

[fernicarry]

and efficiency ie cost savings

Anecdotally (my mate installs them), ASHP's can be 4 times, or bit more, efficient than gas boilers. In technical jargon the COP is about 4 to 4.5. But that is in new builds expressly built to a spec that makes them suitable. The COP drops the harder the pump has to work. The less efficient the building the harder it will have to work.

Currently electricity is about 25 to 28 pence a unit and gas about 6 or 7p a unit. Almost exactly a ratio of 4 to 1. So in terms of running costs, at today's prices, you won't save a thing. You might be able to get your electricity price down a bit with a different tariff, some offer very low rates for a few hours a day (typically overnight), some track the wholesale price so can go very low (but also very high). These fancy tariffs generally require a smart meter.

That's the best case scenario in a building that is well insulated and air tight. Its possible to do that in a renovation but its very intrusive and the work needs to be carried out to a high standard. This will cost, as will the HP itself. The grant will cover some of this but not all. Its hard to justify on economic grounds alone and there is a risk that a badly executed renovation could leave you with a building that's still not suited to a HP.

Prices may change in the future but this country has locked itself into an energy policy that pretty much guarantees high electricity prices for years to come. The politicians will promise to tinker around the edges but don't expect that to fundamentally alter anything. Gas is a global commodity and prices can go up or down. If gas goes up a lot then the HP starts to look like a better option, but you still have to recoup the potentially 10's of thousands needed to make the building suitable before you are actually ahead.

What other fuel sources do you have available?

 

[paulc]

Having undertaking various insulating projects here, some areas are well worth doing whilst others have had very little impact.
Windows and doors, whilst expensive, have made a huge difference. I suspect mostly down to killing off cold draughts that were coming in around the badly fitted frames. Get quite a bit of solar gain from the south facing windows which is a bonus during the winter.
Loft insulation - A low cost undertaking that makes a big difference. Key is packing the stuff between the joists and making sure it goes right up to the perimeter of the outer walls without compromising loft ventilation. 300mm should be regarded as the minimum.
Solid wall insulation - I've done a few of the walls here internally, and to be quite frank, have not been able to measure any difference. However, the rooms that have had IWI added do not seem to suffer from condensation (and the attendant black mould). Insulating externally requires great attention to the finishing details around the roof line, doors/windows, and where pipes come out of the wall. Get it wrong, and water can get between the insulation & wall, causing significant damage over time.

When I replaced my heating system a couple of years back, I did some rough calculations and fitted larger radiators with the intention of using a heat pump at some point. Due to not being able to meet the requirements of the BUS grant that were in force at the time, I ended up with a gas boiler. Having the bigger radiators means I can run the heating system at a much lower temperature and push boiler efficiency to the limit. Switching to a heat pump would only require a couple of small changes, and I would jump at the chance if it were offered (depending on cost). In terms of running costs, pick the right tariff, and it should be cheaper to run. Getting rid of the gas meter would save £100 on standing charges straight away.

In the meantime, a document from Historic England to read: https://historicengland.org.uk/images-books/publications/air-source-heat-pumps-historic-buildings/

 

[Flyfisher]

The 'harder to work' thing also applies to the outside air temperature, not just the insulation effectiveness of the house, so the COP drops just as you really need it in the winter.

I've no actual experience of living with an ASHP but I seriously considered them (and GSHP) when planning a new heating system as we had nothing other than open fires and a very old oil-fired Rayburn. It was all looking feasible, compared to oil or LPG, until I discovered I could connect to mains gas for £300 at which point all the other options went out of the economic window. As fernicarry rightly pointed out, a 400% efficiency figure sounds attractive until you remember that mains gas is about 4x cheaper than electricity, so the running costs end up about the same but the installation costs remain much higher. Of course, if you can't have mains gas then things are somewhat different.

Another thing to consider is investing in PV and a home battery system. This won't directly heat your house of course but it can significantly reduce the cost of electricity to the point where conventional electric heating costs about the same as mains gas. Current price for electricity is about 29p/kWh but my monthly grid consumption is priced at about 7.5p/kWh by a combination of PV generation during the day and using the home battery at other times, which has been charged either by excess PV during the day or at the 7p/kWh overnight rate. Basically, I use hardly any grid energy outside of the cheap rate periods.

I also have underfloor heating in some areas and am very pleased with it. It's a 'wet' system but I imagine it would work equally well as an electric system and might work out more economical than an ASP if the electricity cost is 7-8p/kWh. Another advantage of electric UFH is that it can use the 'free' PV during the day to heat up and will, depending on slab thickness, remain warm throughout the evening and into the night - basically it's just one big storage heater.

 

[L_Bow]

Hi Lorraine, certified Heat Geek here! There's a lot of misconception around heat pumps. There's no need for a home to have a special level of insulation to be efficiently kept warm using a heat pump. I keep my own 1900 house with uninsulated solid walls comfortable with one, and my bills are a little below the national average.

The main factor which determines heat pump efficiency is flow temperature - this is the temperature of the hot water circulating in the radiator (or underfloor) system. It's often beneficial to upgrade radiators during the installation (for example to double convector type) so that they'll keep the home warm at lower flow temperature - your installer should carry out a heat loss survey and calculate the need to upgrade any radiators. But same as a boiler, a heat pump can be sized for whatever level of insulation the home has, and the efficiency is not directly affected by insulation.

As for running costs, it's all about tariffs really. On a standard tariff, running costs are likely to be similar to gas, though you can save on the gas standing charge if you also go electric for cooking. Special tariffs like Ovo's heat pump tariff can save you a solid 40% or so against gas. The Ovo tariff only works with specific heat pumps. Octopus also have a HP tariff which works with any of them, though the savings are a bit less. If you're on oil, then you'll avoid all the hassle of oil deliveries and eventual tank replacement.

Since you mention renovation, you'll want to make sure the installer designs the system for the level of insulation you're expecting to have when it's finished. And if the central heating is being overhauled anyway, then taking advantage of the grant might come out cheaper overall, with the benefit of being future proofed, and saving the cost of converting further down the line. Converting to a heat pump sometimes involves changing pipework as well as radiators, so renovation is an ideal time to get that messy work out the way.

 

[jamest]

One thing that hasn't been considered much so far and which could contribute significantly to costs, depending on your existing set up, is the size of your current pipework. It's not just the flow temperature that matters for HP efficiency, the flow rate matters too and to get decent flow rates you need wide bore pipes. So you might find you need to upgrade your pipes, especially if you currently have any microbore pipework. With a small house, 15 mm pipework might be OK, but the thing to do is have a heat loss survey done so that your installer can properly specify the system you need, as L_Bow recommends (you can even do it yourself, it's not that hard - Heat Geek have some good youtube videos that are worth a look). Obviously, if you're renovating, you have the opportunity to upgrade insulation, pipework and radiators as needed to get the best bang for your buck. You'll not know how much you'll save (or conversely, how much you'll lose) until you know exactly what system you need.

 

[fernicarry]

In winter I run my heating at 65' flow temperature so a delta of 45. Actually closer to 47 because the room won't get above 18' on the coldest days. I have 3 huge cast iron radiators in the living space. In order to get the flow temperature down to 40' (delta of 20-ish) then I'd need over twice the radiator area. Bigger again for a more desirable flow of 35'. Its just not practical, although once I've burned the furniture to keep warm there will be plenty of space for radiators...

So whilst I fully appreciate that a property with sort of middle of the road thermal performance can be made to work with a well executed HP installation (I read the blogs and watch the videos too) it would be misleading to suggest that the same is possible with the long tail of properties with quite poor thermal performance which tend to be the ones we discuss on here.

I'd be suspicious of tariffs that only work with certain makes of HP's or EV's. That tends to suggest that there is a back channel to the supplier that allows them to switch it on and off remotely when it suits them (i.e. turn it off when they aren't making enough money from the tariff). Whilst you might have a bit of flexibility in when your EV charges you don't with your heating. If the wind doesn't blow you still need to be warm. And if they really can afford to give HP/EV owners some amazing deal then why not everyone?

 

[Lacan07]

In winter I run my heating at 65' flow temperature so a delta of 45. Actually closer to 47 because the room won't get above 18' on the coldest days. I have 3 huge cast iron radiators in the living space. In order to get the flow temperature down to 40' (delta of 20-ish) then I'd need over twice the radiator area. Bigger again for a more desirable flow of 35'. Its just not practical, although once I've burned the furniture to keep warm there will be plenty of space for radiators...

So whilst I fully appreciate that a property with sort of middle of the road thermal performance can be made to work with a well executed HP installation (I read the blogs and watch the videos too) it would be misleading to suggest that the same is possible with the long tail of properties with quite poor thermal performance which tend to be the ones we discuss on here.

I'd be suspicious of tariffs that only work with certain makes of HP's or EV's. That tends to suggest that there is a back channel to the supplier that allows them to switch it on and off remotely when it suits them (i.e. turn it off when they aren't making enough money from the tariff). Whilst you might have a bit of flexibility in when your EV charges you don't with your heating. If the wind doesn't blow you still need to be warm. And if they really can afford to give HP/EV owners some amazing deal then why not everyone?

took the words right out my mouth

 

[Lacan07]

I looked into Air source very briefly last year but not really in much depth, I thought about installing an external unit with under floor ducting. The COP just isn't god enough for older properties and as Fernicarry has already pointed out even when it is (new builds) its not really any more efficient cost wise than a gas boiler, so why bother?

I also got the impression that in comparison to gas it'll be slow, unresponsive, (you'll likely need it on 24/7), and there was a very real issue with maintenance in terms of cost and finding engineers.

 

[Robola]

Fernicarry has already pointed out even when it is (new builds) its not really any more efficient cost wise than a gas boiler, so why bother?

To access renewable energy and to not have an explosive gas piped into your home.

 

[Lacan07]

To access renewable energy and to not have an explosive gas piped into your home.

Gas explosions are extremely rare