Ground Source Heat Pumps

lovesgshp

I think you should be asking this question on the ASHP sticky. They are 2 different systems. The electricity cost would be same with either system.
I cannot comment on UK costs, as I do not live there, so hope someone will get back to you. Supply the house size, heat pump size, room temp settings, make of pump, rads or UFH and you may get some realistic answers.

edwh

I'm looking at heat pumps, and posted on this thread a while back.

This is an old property in rural Lancashire, which is currently on fuel oil, with two separate boilers feeding two separate heating systems. There's no mains gas.

The existing fuel tank needs replacing fairly soon, one boiler is on its last legs, and the other will need replacing in a few years. So we need to do something.

We've recently got a 10KW PV array, done loft insulation and cavity wall where possible. The only remaining insulation measures would be fitting insulation to the interior or exterior walls, which is difficult given the complicated and uneven layout, and not desirable aesthetically. Floor insulation will be possible over time, but not immediately without too much expense.

I'm looking at several options:
1) Replace the oil boilers with new oil boilers - either two separate ones as at present, or a single one (which would require plumbing work).
2) Air Source Heat Pump. No ground works requirement, but will need plumbing work to unify the two separate systems.
3) Ground Source Heat Pump. Better COP, but more expensive ground works also requires unification, and needs a triple phase supply.

There is a brook which we have land on both sides of, but the flow and drop are not great, so I can't see any kind of hydro system working.

I'm quite aware that heat pumps are not ideal for older buildings, and I'm therefore quite concerned about the costs - there is obviously a high up-front cost, and potentially high running costs.

I've done some calculations based on:
- Upfront costs of the different options
- RHI payments
- Offsetting of some of the electrical demand with the solar panels.

This last one gets hairy - I've done a seasonal curve for demand and generation. The idea would be to configure the compressor to run during the day to buffer heat for the evening (which looks to be possible from control manuals I've seen).

I'm considering things in today's prices - guessing future oil and electricity prices is too hard, though on balance I'd expect fuel oil prices to rise more than electricity costs.

It's not looking like the heat pump option would make sense financially. It's a shame that the RHI is only 7 years. Seasonal heat storage would be a wonderful thing.

In case there's anyone geeky who wants to review this, here's the spreadsheet, open to comments. It might be of use to other people looking at these kinds of options.

h t t p s://docs.google.com/a/ehibbert.org.uk/spreadsheets/d/1pQbrl-d8PHD-bjM0GIyMlQz8F9U5VeGQzjohUAtibPk/edit?usp=sharing

Has anyone got any experience of the widgets which divert excess PV which would otherwise be exported into immersion heaters?

lovesgshp

Welcome
Can you give some idea of the house size, plus the age?
Presume you only have radiators.

edwh

The house is in two parts; the older part is around 1740, the newer part is from 1970. The total area is 3200 square feet, about two thirds in the older part. The newer part is not much used and heated in winter only at a background level.

Yes, it's just radiators.

lovesgshp

Thanks.
Under 300 m2 so probably a 17Kw output GSHP. You can shut down 30% of the output to the rads, if you do not need the heating in that area.

edwh

The quote I've got is for a 17KW + 8KW.

Undersizing the heat pump based on not needing much heating in some of the property would mean that we weren't eligible for the RHI subsidy, which is significant over the first 7 years.

lovesgshp

edwh.
I do not know how the RHI operates in the UK, but if you have a 17kw heat pump, it also has a up to 9kw electrical immersion type heater as well. We have houses of over 350 m2 of the same age working on 17kw units.

albyota

A consideration would be a hybrid system, whereby, using a heat pump for say 85% of the winter 15% oil boiler, yes you would have to replace the oil boiler, but a good amount of the electricity to run the heat pump in autumn / spring would be covered by the solar PV, perhaps just December and January using oil, that way a 16kW air source heat pump would be a cost effective solution.
You would have to have the heat metering package to enable you to claim the RHI. the DNO would need to be notified if you were to have a heat pump, ground or air.

edwh

Lovegshp - doesn't it kill you on the operating costs if you're using the immersion heater?

Albyota, what's the heat metering package? I've not considered a hybrid system but that would mean replacing the oil tank too, so the cost might be quite high.

albyota

edwh wrote: »

Lovegshp - doesn't it kill you on the operating costs if you're using the immersion heater?

Albyota, what's the heat metering package? I've not considered a hybrid system but that would mean replacing the oil tank too, so the cost might be quite high.

Yes a new oil tank, but only a 1000 L would do, take a look at the OFGEM https://www.ofgem.gov.uk/key-term-explained/domestic
And https://www.ofgem.gov.uk/environmental-programmes/domestic-renewable-heat-incentive/about-domestic-rhi/metering-domestic-renewable-heat-incentive

Good luck