General advice for refurb project on large property

[Jimlad]

Hi all, I'd really appreciate the input of members here on the best approach to modernising the heating setup for a fairly large property which we're just about to start the refurb on. The house is approx 385m2, dating back to early 1900's and has solid 400mm thick stone walls. A room by room heat loss calulation gave a 26kw heating load at -2c design temp and that includes the feasible fabric upgrades which we have planned. We have an existing array of 8kw solar PV which in the last 12 months generated 6400kwh of leccy. We don't currently own an EV but that's definitely a possibility on the horizon. Current heating and DHW are powered by an ancient oil boiler with open-vented cylinder (albeit with a new burner fitted in the boiler in the last 3 years) and we went through 3500 litres of oil last year (gulp), and that included a period of "just put a jumper on", when prices were at the absolute peak of madness. The hosue is hugely over specced in terms of rads (e.g. living room has a heat loss of approx 2kw but has almost 5kw of rads capacity) Priority number one is to reduce our fuel bills and it seems like a no-brainer to do as much with the fabric as possible and also have an iBoost or similar installed to dump excess PV generation into DHW. Beyond that, I'm really torn as to the best approach in term of the type of system to specify for that kind of heat load. We don't have a huge budget and there's lots of other jobs that need doing so ground source is out of the question. Ideally we'd completely remove any reliance on fossil fuels but it seems that would mean cascading multiple ASHPs to get the KW rating we need, which then becomes quite expensive. I have spotted that Cool Energy do a 3 phase ASHP which goes up to 32KW but it looks to be quite noisy (70dB) and would only just cover the load required. Another option would be the Grant Hybrid, although that would obviously still tie us to oil somewhat. 

 

Thoughts and opinions about the best way to proceed very gratefully received!

[SteamyTea]

19 hours ago, Jimlad said:

hosue is hugely over specced in terms of rads (e.g. living room has a heat loss of approx 2kw but has almost 5kw of rads capacity

Good if you want to use a lower flow temperature. 3500 litres of oil is not excessive, about 35,000 kWh. At nearly 400m², you are using about 90 kWh/m².year.  Pretty average.  I use 42 kWh/m².year in a terraced place, in Cornwall (just the heating that is). 

You could put in a simple electrical resistance heater in a buffet tank, or a Willis heater plumbed in directly to the pipework. Then dump excess PV into it. Buffer would my option as you can retain the current oil burner.

 

So work in airtightness and insulation, worry about the technology once you get your oil usage down to 18 MWh.

[JohnMo]

All the stuff mentioned above, also look at how you operate the heating.  Big thick walls take a lot of energy to heat up, if you operate the heating in short bursts all the energy goes into heating the building fabric.

 

You may be better turning the CH flow temperature down and run the boiler for long periods, stabilise the building temperature, with a small setback at night.

[joth]

On 06/06/2022 at 15:41, Jimlad said:

The house is approx 385m2, dating back to early 1900's and has solid 400mm thick stone walls

 

Large property and large walls: a couple questions come to mind:

1/ what is the usage pattern? Are all 385m2 in use 24 hours a day every day? How many occupants? Any seasonal variation? Any scope to change usage patterns?

2/ Are the 400mm walls all external, or any large internal partitions too? Any natural lines under which you can zone the system into "warm" living areas and colder transit areas (halls, corridors). And disused bedrooms etc.

 

Together, this maybe a good case for a smart control system that only heats the rooms actually used, and for the times of day/year they are used. Notwithstanding the very good point JohnMo makes above that the reheat times will be very slow given wall sizes, so this would need to be planned in a considered way.

 

Also what fabric upgrades have been planned? A friend has a similar sounding "country pile" can got a very long way by adding secondary glazing and thick insulated curtains (in addition to smart zoned controls)

 

 

[Ferdinand]

Commenting mainly on the fabric.

 

 My 2c:

 

In a large house like that with two of you I would perhaps look at External Wall Insulation, or properly done dry lining, both making sure to also manage the ventilation. And also consider things such as under-floor insulation (if necessary raise the floor if you are doing a full reno). Plus all the other usuals such as modern double glazing etc.

 

My usual cost-effective solution has been underfloor insulation and a draught sealed floor, well rated 2G, a loft fan and permanently on trickle ventilation, dry-lining all external walls (ideally 75mm celotex or more if you have large rooms), and lots of insulation in the roof. I hvae properties done like this that are fine nearly 10 years later.

 

I'd suggest a reasonable goal is a reduction of 40-50% in energy usage, which would normally mean an EPC figure of a High C or ideally a low B. That is a 75-85 number.

 

There's a thread on here called Little Brown Bungalow about one I did, which has some debate in it, and care (and advice here) is useful with things like floor builldups and the order of wall elements.

 

Was it empty for a period to get you the reduced VAT rate on reno costs (I think still available)?

 

And go through your local Energy Saving people to see if grants or free anything are available. I think you could have got your loft insulation free under ECO. Start with the SImple Energy Advice no:

 

If you’re looking for home energy efficiency advice, try the Simple Energy Advice website, or call them on freephone 0800 444 202.

 

Ferdinand

 

PS I hope you bought your heating oil at not-the-wrong-time. It's been a touch variable !