Advice for a period property

[anthonywallace]

Hello,

I was wondering if someone would be kind enough to offer advice on a Victorian house we are thinking about buying. It has solid walls with no cavity. The house is around 3300 square feet and has an E rated EPC (but capable of going to D). Space heating is projected at 50,000 kwh and the cost for heating and lighting is around £4k per anum which I no likey! External and Internal installation are not cost effective or impossible because of the presence of very nice internal cornicing and\or the house is located in a conservation area. Having looked at the other options for heating, I liked the idea of underfloor heating from a heat pump but it seemed unlikely in a poorly insulated house there was any real benefit in taking this approach. However, I would welcome comments in that regard since I can insulate under the house and in the midfloor joists easily and cheaply. The house will be in use pretty much all day 4/7 days in the week.

It has a large south facing garden and plenty of roof space. It seemed to me that a large solar array (10 - 20 kw) might be the best I could do here. I am not particularly afraid of the capital cost and in Scotland there is a good interest free, 12 year loan scheme and some form of RHI grant.

I understand that under ECO I may qualify for solid wall insulation but it would be sacrilege to take down the cornicing which in places is almost 2 feet in overall "depth" for the sake of a projected saving of £600 per anum per the EPC.

Would anyone be able to help?

Anthony

 

[BruceB]

A couple of thoughts.

That is a large space heating requirement. It has two elements when you do the calculation: the direct heat loss through the walls and the heat loss due to ventilation requirements. The latter can easily amount to half the heating requirement. The traditional advice with solid walls is do not compromise ventilation because you will get condensation, damp and mould. However, if this is a new purchase and you have the opportunity to do some knocking around before you move in, then you should consider: insulating where you can, double glazing if not already there and really blocking up all air leaks/draughts completely and installing mechanical ventilation with heat recovery (MVHR). MVHR can transform the interior of an old solid walled, slightly damp and previously draughty property and make the interior air permanently fresh. Because of heat recovery levels of up to 90% the ventilation heat loss is greatly reduced. You do not need trickle ventilators either if you have MVHR.

Heat pump is more difficult in old properties, although I have done it in mine. I paid attention to draught proofing, had UFH throughout and added to 600 mm listed stone walls a further 100m of sprayed on aerated insulating lime plaster to provide additional insulation. You would need to do the sums carefully to see the benefit under the domestic RHI particularly as the payment calculation will assume a SPF based on the assumed flow temperature for your worst performing emitter (radiator).

There is no substitute for having someone who can put some numbers together for you to do the comparisons, or do it yourself, but that is likely to require some understanding of the field.

 

[anthonywallace]

Thanks - very helpful. I had not considered MVHR. No chance I am up to doing the numbers!

 

[Gavin A]

Because of heat recovery levels of up to 90% the ventilation heat loss is greatly reduced. You do not need trickle ventilators either if you have MVHR.

all good points Bruce, and as you've been there and done it with your house, you're definitely worth listening to on the subject.

One minor clarification needed though is that with MVHR units they recover 90% of the temperature, but usually more like 50% of the actual heat energy content of the air as most of the energy content of the air leaving the house is contained in the vapour content of that air which is only released when the vapour condenses (latent heat of evaporation / condensation). That's the extra energy an exhaust air heat pump is able to extract btw.

Pretty sure you'd be aware of that, but it's very commonly misunderstood.

 

[BruceB]

You are reminding me of my thermodynamics lectures of many years ago! Interesting point about the energy content of the moisture element. In cold weather you can get quite a lot of condensation from the MVHR units. I did look for some authoritative discussion on the point recently when I was doing a quick illustrative design and came up blank from the CIBSE stuff I had. I did not use a 90% figure but certainly nowhere near 50% (I used 80%) because I reckoned that on those occasions when there was significant moisture in the air it had not been put there by the space heating system, but incidentally by people breathing, cooking or running baths/showers. The significant point in the calculation seemed to me how much of the load of heating the incoming air had been reduced. There are different ways of looking at it though and I hope I have not over-egged the saving. Where do you get your 50% number from and have you seen some good guidance on this point?

 

[SPARTYKUS]

Thanks chaps really interesting thread

 

[Gavin A]

You are reminding me of my thermodynamics lectures of many years ago! Interesting point about the energy content of the moisture element. In cold weather you can get quite a lot of condensation from the MVHR units. I did look for some authoritative discussion on the point recently when I was doing a quick illustrative design and came up blank from the CIBSE stuff I had. I did not use a 90% figure but certainly nowhere near 50% (I used 80%) because I reckoned that on those occasions when there was significant moisture in the air it had not been put there by the space heating system, but incidentally by people breathing, cooking or running baths/showers. The significant point in the calculation seemed to me how much of the load of heating the incoming air had been reduced. There are different ways of looking at it though and I hope I have not over-egged the saving. Where do you get your 50% number from and have you seen some good guidance on this point?

I ran the calcs a year or so ago for a thread on green building forum essentially trying to work out what the maximum actual energy available was from exhaust air from an MVHR system that an exhaust air heat pump could use - this basically sets the actual upper limit on what heat energy an exhaust air heat pump can put back into the house that would otherwise have been dumped out of the MHRV unit, anything above that is just parasitic energy recycling for no good purpose, and this explains theoretically the practical experience of many householders who've had these units installed inappropriately and not had anything like this explained to them about how they work.

tbh, I doubt that 99% of those installing them or specifying them are even aware there is a theoretical limit to their use, never mind calculating what it is for any given house.

don't take the 50% as gospel though, I'm just giving that as a ball park from memory, and it depends a lot on the moisture content of the air involved going in and going out.

 

[BruceB]

Thanks. I only visit the GBF forum occasionally as iirc they wanted me to pay to be able to post. I think I saw in one of your recent posts that you want to become HP qualified. Good luck with that. You will be become very practised at doing a load of detailed heat loss and ground loop calculations to satisfy MIS3005!

 

[Gavin A]

Thanks. I only visit the GBF forum occasionally as iirc they wanted me to pay to be able to post. I think I saw in one of your recent posts that you want to become HP qualified. Good luck with that. You will be become very practised at doing a load of detailed heat loss and ground loop calculations to satisfy MIS3005!

yeah, it's somethng I'm looking at gradually getting into - don't really have an issue with doing heat loss calcs, was the best at it out of all the heating engineers on the biomass course I did, seems most heating engineers just sub that stuff out to the manufacturers or guess then add a bit for luck usually.

I've got 2 second hand 25kW heat pumps on there way now for a non MCS, non RHI install for someone who's more of a business partner than customer, so we'll jump in at the deep end with that, but not have the bother of trying to use that one for RHI. I really want to test out what sort of average COP figures we can achieve with it tbh, as well as how we can integrate it with the solar PV production on site to make the most of the 'free' energy in the day time from a 30-50kWp PV system.

Think I'll only ever install heat pumps to integrate with PV generation, as to my mind they're a complete con in carbon terms if there is a gas alternative on site, and RHI money is going to be used in huge quantities for zero net carbon benefit / possibly even a net carbon cost funding heat pumps in those situations... I want no part in that nonsense.

 

[The Solar King]

If you are in a Conservation Area or have a listed building, you are going to struggle with anything solar, PV or Thermal. There is a general (misguided) presumption against approving any planning application for these technologies. Here in Edinburgh people have just about given up applying due to the intransigence of City of Edinburgh Council. Conservation Areas cover more than one third of the city and proportionally more of the population. What makes it worse is new build in Conservation Areas is treated differently to existing properties. The presumption for approval still applies. So we have new build with solar in Conservation Areas, but nothing for retrofit unless it is completely invisible from the road side.

 

[TedM]

The permitted development regulations for Scotland are slightly different from England and Wales in this respect. In Scotland PV or solar thermal on a roof is not permitted in a Conservation Area without express planning permission, whereas in England and Wales it is OK even if visible from a road.

 

[anthonywallace]

The houses surrounding my own have solar arrays and I have spoken to the LA who tell me it should be fine.

As an interesting aside, I ran some calculations for heat loss and underfloor heating. Taking the largest room in the house, it was suggested that I would need c. 6000W to keep it warm. According to Polypipe, at 40C, the overlay system will generate only 60w m2. The room is 35m2 meaning a heat output of 2100W. I think the maximum heat output of the underfloor system is around 100w M2 which to my very simple, uninformed and uneducated way of thinking means that it will never adequately heat the room on a cold day (Polypipe quote their figures at -2C). Moreover, it presumably also means that, even if was possible on a per m2 basis, the COP from a heat pump would be very low eliminating most of the advantage?

 

[Worcester]

That sounds about right, we're just working on a specification for a 300 year old Grade 2 listed building and are seeing similar heat losses.

What you can do to keep the flow tempratures down and therefore still maintain a reasonable CoP is to supplement the under floor heating with either oversized and or oversized fan assisted radiators. Stelrad do some triple layer radiators, and in '70's built properties simply swapping a single panel radiator to a 3 panels one useually meets the heat output requirements, add fan assisted and you could well do it.
Jaga do one and Dimplex also offer the SmartRad, both are fan assisted.

Anybody that provides you with a quote will have to provide a full room by room heat loss calculation and specification of emitters (underfloor / radiators) to achieve the required heat imput to the room. Note that some will be 'lazy' and just bump up the temperature of the Heatpump, others will produce an optimised system. It is unlikely that the cheapest quote will be the best / most economical system long term. It sometimes takes us at least two days to produce a fully optimised heating design with all parameters considered.

Bearing in mind the requirement for air circulation, the win has got to be insulate, insulate, insulate as the best (and cheapest) option. Becasue of the high temperatire output, you may be beter off considered a Biomass pellet boiler - well designed ones can be semi-automatic almost maintenance free (empty the ash once a week..).

Just before Xmas 2011, we helped one of customers refurbish a typical detached Victorian property and with good insulation, 4kW Solar PV, 2 x 30 tube Solar Thermal panels, a wood burning back burner, in the open space massive through kitchen / diner / living room, a 500 litre thermal store new radiators with multiple zones (5 as opposed to the usual 1! ) and a small back up gas boiler... - the gas boiler hasn't been called into service yet, and the house is warm as toast

 

[Gavin A]

one thing to bear in mind is that with under floor heating the actual air temperature can be kept significantly lower than with just the single radiator, as the heat is evenly spread around the room, and you've no radiative heat losses from the body to the entire floor, minimal cold spots etc (especially if you keep the radiator in place below the windows as well), and no layers of cold air lower down in the room.

Biggest savings are going to be made on draught proofing, and heavyweight lined curtains on all windows IMO - do all of this first before doing the heat load calcs and sizing the heat pump, and IMO I'd assume the curtains will be closed in the coldest conditions, which I'd expect could well seriously drop the peak heat demand you're sizing for.... probably not the official way of sizing these things mind, but daft to assume you'd have the heat blasting out with all the curtains open,or that you should be sizing a heat pump for that scenario and getting paid RHI on that basis.

(not entirely sure if this is taken into account or not, I suspect not - it's long been a major failing of SAP, and probably accounts for a significant part of the failure of a recent monitored green deal pilot project to deliver anything like the expected energy savings).

 

[anthonywallace]

That sounds about right, we're just working on a specification for a 300 year old Grade 2 listed building and are seeing similar heat losses.

What you can do to keep the flow tempratures down and therefore still maintain a reasonable CoP is to supplement the under floor heating with either oversized and or oversized fan assisted radiators. Stelrad do some triple layer radiators, and in '70's built properties simply swapping a single panel radiator to a 3 panels one useually meets the heat output requirements, add fan assisted and you could well do it.
Jaga do one and Dimplex also offer the SmartRad, both are fan assisted.

Anybody that provides you with a quote will have to provide a full room by room heat loss calculation and specification of emitters (underfloor / radiators) to achieve the required heat imput to the room. Note that some will be 'lazy' and just bump up the temperature of the Heatpump, others will produce an optimised system. It is unlikely that the cheapest quote will be the best / most economical system long term. It sometimes takes us at least two days to produce a fully optimised heating design with all parameters considered.

Bearing in mind the requirement for air circulation, the win has got to be insulate, insulate, insulate as the best (and cheapest) option. Becasue of the high temperatire output, you may be beter off considered a Biomass pellet boiler - well designed ones can be semi-automatic almost maintenance free (empty the ash once a week..).

Just before Xmas 2011, we helped one of customers refurbish a typical detached Victorian property and with good insulation, 4kW Solar PV, 2 x 30 tube Solar Thermal panels, a wood burning back burner, in the open space massive through kitchen / diner / living room, a 500 litre thermal store new radiators with multiple zones (5 as opposed to the usual 1! ) and a small back up gas boiler... - the gas boiler hasn't been called into service yet, and the house is warm as toast

Thanks - all very helpful. I was intrigued by your suggestion of supplementing the UFH with low flow radiators. I looked on the Jaga website and in particular the Strada DBE Boost Type 21. With a custom EN244 of 35/25/20, it would appear that two bigger radiators in that range would provide the heat output. I chose 35C on the basis that I will get the best COP from a heat pump. However, even with an increase to 45C, the COP is still acceptable.

Now the cost of installing radiators is far less than the cost of retrofitting UFH by a considerable difference. Assuming I can live with more radiators in a room that I would ideally like, is a GSHP a realistic option for me (303m2 house)? From my position of relative ignorance, it would seem that it is but no doubt I am missing something. To be clear, I know that I would need to have proper SAP\room calcs done but from what I can make out, if you are prepared to accept more surface area emitting heat, GSHPs seem to be fine for any house, poorly insulated or otherwise?

I looked at Biomass and discounted it for various reasons, not least laziness - even if cleaning is required once a week! Also, wall insulation is a no go for me because of the cost of taking down cornicing and reinstalling (Best guess £3k per room based on some of the quotes I have on a like for like basis).