Economics and environment switching from gch to heat pump?

michaels

So our 7yo gas boiler keeps playing up and I am starting to think about whether we could replace it with an ashp or gshp.

We use about 32k kWh of gas per annum probably one third hot water, two thirds space heating.

Looks like heat pumps work better at lower temps so would probably have to replace rads with doubles (would this be enough?)

Would it make sense to continue to use gas for hot water and possibly for really cold weather for central heating too?

How do the costs of heat pump compare to the potential income from the green deal?

Lots of research for me to do but was wondering if anyone had gone down this route?

Martyn1981

I haven't looked into this in detail, as our gas consumption is pretty low, around 6k kWh pa, but some quick points.

GSHP is more expensive, but means pretty efficient use all year round as ground temps will be something like 7C (I think). ASHP cheaper to install, and daytime air temps may be higher than 7C, but cheap leccy at night with nightime winter temps could mean a larger system is needed which might have a COP of just 1 at times.

If you go for heating and hot water from the heat pump, then you can apply for RHI, which would help a lot with the costs.

I think that not only would you want larger rads, but also need to consider the pipe diameters. Most of ours is 15mm or 10mm, when you need 22mm (I think), so that would need changing too.

Dandelion Energy (in the US) have been in the news quite a bit lately promising cheaper GSHP installs, and the ability to install in any size yard so long as their drill equipment can get in, as they will do vertical loops. Note, in the US, they call GSHP's geothermal energy, though this is technically wrong as the heat harvested in the Earth's surface is from solar energy. Just mentioning this due to news coverage, and attempts to inform more folk in the US.

michaels

You suggest you can only get RHI (which is needed to make the maths work) if you go both he and CH, is this definitely the case? It just appears that hw with its higher temp requirement might be best kept on the legacy gas boiler?

Martyn1981

michaels wrote: »

You suggest you can only get FBI (which is needed to make the maths work) if you go both he and CH, is this definitely the case? It just appears that hw with its higher temp requirement might be best kept on the legacy gas boiler?

Thinking about it, I may be wrong, certainly the heat pump has to be 'to water', not 'to air', but now you say it, and made me think, I don't think DHW has to be done too, though that is also eligible. Does that make sense?

See what you find, I'd potentially consider ASHP, via multiple air to air units, installed over time, but that's definitely ineligible.

Edit - here you go, and you're right:

Must use a liquid to provide space (eg, room) heating

Heat pumps don't have to provide domestic water heating to be eligible, but may do so (They may also provide water cooling).

E7 and PV for hot water springs to mind as a simple solution for that side.

michaels

Seems like the install prices are basically the same as the FIT - ie the installers are pocketing all the subsidy. As we have mains gas and thus the savings in fuel costs are likely to be negligible the reason to do it would be if there was a decent rate of return on the investment purely from the FIT (say 5%+) and it was better for the environment.

Any thoughts on the environmental +/- of using leccy rather than gas for space heating - I guess in terms of kwh the usage should be half but then there is the 'embedded co2' in the equipment and install....

GreatApe

You are probably best off getting your gas boiler fixed or replaced especially as you use a lot of gas.
Your load on the grid is marginal load so will for all practical purposes will be powered by a gas CCGT.
While the best gas CCGTs are about 60% efficient that is in ideal conditions. The fleet average ramping up and down etc is closer to 45% knock grid losses off and your using something close to 40% efficient gas fired electricity to power a heat pump

New builds should go all electric from 2020 not 2025 but in your case it will probably be best in every way just to get your gas fixed.

Bear in mind that the cost of a system is the capital cost written down over the expected life.
So for instance if a boiler costs you £1,500 to buy and have installed and it lasts 10 years at 5% capital cost that effectively costs you £16 a month. If a heat pump system costs £10,000 and lasts 15 years that costs you £80 a month

Also there is the time and frustration of big replacements getting pipes or rads changed is not just the cost its the annoyance of maybe 3-5 days of workers in and around your home.

GreatApe

The interesting question is what happens when/if new gas boilers become illegal so all broken boilers will need to be replaced by electric systems.

In your case you would be adding 10MWh electric demand to the grid. Imagine 2 million boilers per year (which is a guess of how many break down and need replacing per year) going from gas to electric. That might be +20TWh additional annual demand which is massive additional load

If the 2050 targets are meant to be met mabye we would need to get rid of existing gas boilers starting 2030 so 2030 - 2050 is going to be quite a hell of a ramp up in demand especially if transport is also electrified during that time

2050 could be as much as twice the electricity demand as 2030 is. Good time to be an electric utility bad time to be a gas infrastructure owner

While I was quite negative about uk nuclear I do now wonder if it would be a good idea because the time frame works (if we could get one nuclear power station up and running per year from 2030 it would meet this additional load)

The alternative is to build 3.3GW of gas CCGTs per year from 2030 and about 7GW of offshore wind per year during that time and the grid infrastructure to move all that power across the ocean and inland

I still think nuclear is very unlikely but it does seem that if it is to be this is the one time it may make sense. Start building now so they come online 2030-2050. If this decision is left too late then it will have to be wind + CCGTs. Definitely someone in government should be doing some really hard thinking to see what the best outcome would be for this 2030-2050 period but like always momentum and decision paralysis and popular politics will probably win the day.

1961Nick

Martyn1981 wrote: »

See what you find, I'd potentially consider ASHP, via multiple air to air units, installed over time, but that's definitely ineligible.

I installed one 4.3kWh ASHP in our conservatory to replace 2 free standing fan heaters. The subsequent fitting of a proper roof means it's capable of heating most of the house during the day if the internal doors are left open. At 1.3kWh input the solar panels can run it a large percentage of the time. Cooling during last summer was an added bonus.

Our gas consumption had dropped by 4500kWh pa as a result.

It cost around £1200 installed.