Can anyone point me at some heat loss info?

[Martin Angove]

I know there is software out there which could do this sort of thing, but as I only need one calculation I wondered if anyone could give me a few ballpark figures to help me guestimate the heatloss from a badly underheated building?

It's a prefabricated church hall - built in those concrete slot-together slab things that you sometimes see used for garages. The wall construction appears to be concrete slab (maybe 100mm thick?) then a "cavity" of sorts with battening, then an internal layer of fibreboard, about 15mm thick perhaps. There may once have been a small amount of insulation between the two layers, but there's no evidence of it at the moment.

The building is one large hall, a couple of toilet rooms, a kitchen and a small meeting room. At the moment I'm only interested in the hall.

The hall is about 12m by 6m and is open to the underside of the roof which is some kind of corrugated material on the outside, thin insulation, fibreboard again. At the apex the roof is maybe 5m above the floor which is Marley tiles on a concrete slab. There are four windows down each of the long sides (i.e. eight total), single glazed metal framed units of perhaps 3ft by 4ft.

The main door (double wooden door) is in one of the short sides and the other rooms lead from a corridor in the centre of the other short side. The toilets and kitchen are the adjoining rooms, and neither has any form of heating at all. Vague ASCII:

+-----------+ | smr | +----+/+----+ | T / \ | +----+ + K | | T / | | +----+/+----+ | | | | | | | hall | | | | __ | +---/ \----+

As you might guess, the heating has always been completely inadequate in this building and as there is no mains gas (though it is available in the two next-door houses which are mere meters away) the church has relied on Calor heaters and electric heaters. The current crop of electric heaters in the hall is failing and they were never adequate between about November and February anyway, so I'm looking to start from scratch with a decent idea of how much heat a building like this will consume in the winter in order to be able to make an intelligent recommendation about the type and quantity of new heaters to install.

If it makes any difference, the southern side is on the left in the above diagram, but is shaded almost completely by a thick hedge and mature trees.

I have a few prejudices, but I'll leave those for now.

Any sensible advice greatfully received. There is not a big budget for this, but if we're going to come up with a loss figure of 20kW then maybe there is a case for installing gas :-)

Hwyl!

M.

[John Rumm]

There is a reasonable starting page here:

It's a prefabricated church hall - built in those concrete slot-together

That sounds like it is going to be no better than a solid 9" brick wall. So a u value of about 2 perhaps.

You neglected to mention the height of the walls, but I suppose we can guess at about 2.5m if we assume a roof pitch of 40 degrees.

That gives a total wall area of about 6 x 12 x 2.5 = 180m^2 (ignoring any gable)

Pobably no insulation in the floor... so assume 72m^2 at a u value of 0.8

Sounds like about 10m^2 at a u value of 5.8 so a wall area of 170m^2 at a u value of 2 ish

We can probably ignore this as it won't be that much worse than the walls.

For the moment lets just treat them as "outside" then

A design temperature is something else you will need. It may be unrealistic to get it to "house" levels of comfort, but perhaps 16 degrees would be a fair target. Lets work on a worst case outside of 0 which is not quite as onerous as you would use for a house design (typically -3). So that gives us a delta of 16.

So no solar gain worth mentioning then...

Quick sums suggest:

16 * 170 * 2 + 16 * 10 * 5.8 + 16 * 72 * 0.8 = 7.2kW for the walls.

Roof is a bit trickey not knowing what it is made from. You could take the "pitched with felt and 50mm insulation" figure of about 0.6 and make it a bit worse - say 0.8 If we assume a total area of about 96m^2 we get

16 * 96 * 0.8 = 1.2kW

So about 8.6kW before considering any air changes...

If we work on 1 per hour, and total air volume of 90m^3 for the pitched roof, and 180m^3 for the rest of the hall thats about 270m^3. Equivilent u value of 0.36

16 * 270 * 1 * 0.36 = 1.5kW

Well check my figures, but I make that about 10kW to get it to "a bit chilly" in cold but not the worst conditions. If you worked on getting it to house type temperatures and assumed a -3 worst case then you would be well over the 20kW.

In a word it sounds like the thing you *really* need is insulation. At those sorts of losses you get a rapid payback on the capital costs. Even sticking 50mm of PIR foam under the fibreboard would make a big difference.

Also remember that if you stick 100 people in there then you have another source of 5kW of heat!

[owdman]

Just a detail but we've found that heating impossible spaces is better with radiant heat - oil filled electric radiators, or other radiant forms. This way some of the heat may hit the room occupants, whereas hot air will simply go straight up from the source and out through the roof.

cheers

Jacob

[Martin Angove]

[snip fantastic advice]

That would tally with the present situation; they currently have 12kW of fan heaters in there, only 6kW of which works reliably. Don't forget that, being a church hall, 16C is going to be more than "a bit chilly" for the grannies' knitting club :-)

Agreed. In fact what they *really* need is to knock the place down and start again. They have been speaking to an architect with the intention of getting the toilet block up to DDA scratch and apparently that was the first thing he suggested too! The hall has other problems apart from the heating; it wasn't particularly well built to start with. In common with many churches though, this kind of budget really isn't available.

The other issue is that the hall isn't in constant use. I was told that during the colder months it averages about once a week (the small meeting room is used more often). In other words, between uses the floor in particular becomes *very* cold and the place, even with all four fan heaters working and Calor heaters too, could take three or four hours to get up to a "useable" temperature. Given that most hall use is likely to be a couple of hours at most, this seems very wasteful. The other complaint they have is that people tend to feel stuffy at head height but have numb feet.

Thanks for the help so far.

Hwyl!

M.

[Martin Angove]

The thought had occurred to me too, though I *detest* those "infra red" type heaters. A possible advantage of panel or panel/convector radiators would be that you could have more of them at a slightly lower power output, thus spreading the heat around better without necessarily increasing the total power drawn. At the moment they have 4x3kW fan heaters at just above head height (yes, the walls are going to be about

2.5m). For a similar heat input with no moving parts they could be replaced with 8x1.5kW panel/convectors.

The big problem with this is that they have a lot of benching in the hall which is all stored around the outside walls to keep the central part free. Thus any such source placed in the usual position - thigh height - is going to be blocked from radiating directly to occupants. Also at about 6m wide, those in the middle (say) third of the space aren't going to benefit much from the radiant heat anyway.

As a variation on the radiant theme I've seen "Heat Profile" skirting radiators which are available as water or electric and claim 150W per element meter. Presuming this means 300W per meter of product (there are two element chambers), this could give 7kW or so on the long walls alone... but I haven't seen a price, and it'll be at floor level... hmmm...

Hwyl!

M.

[Set Square]

I was wondering about that when I read your first post. This is often the case, compared with a house, which needs to be heated all the time.

The problem this presents is that you need a very much higher transitional heat input to get it up to temperature for each use compared with the steady state input to maintain the temperature. One possible solution is to use an industrial type calor-powered heater to get it up to temperature before each use. These are noisy, so would need to be turned off when the meeting started - but a much lower rate of heat input from panel heaters or whatever should then be able to maintain the temperature.

As others have said, it is *well* worth while investing in better insulation.

[Owain]

I agree too about insulation. Redoing the battening with a thicker gap, insulation and plasterboard may be feasable on a diy basis (or at least by getting a handyperson in) without having to go through the rigmarole of planning and building regs.

The plasterboard would be inherently more fire resistant than fibreboard, and I am concerned that your Kitchen and SMR only appear to have exit through the main hall.

Another thing that would help might be to put a porch on the main doors to provide an airlock.

Joisting and flooring the SMR should also be feasable on a moderate budget.

What's it used for - it might be cheaper hiring a venue during the winter, or even the upstairs room at the pub (on-sales facilities might make PCC meetings a little more lively :-) )

The other option is that all those broken old heaters might catch fire resolving the problem for you :-)

Owain

[Martin Angove]

Not sure what kind of manpower the church has, but it is certainly something that could be suggested.

Sorry, didn't show the external doors. There is an additional external door in both the kitchen and the small meeting room.

They're already inset slightly. All that would be needed would be an external door. As others have said though, compared with the likely loss through walls and roof, this is somewhat secondary.

Interesting...

Yeah. The church is 100 yards away from the local college which is very likely to have spare rooms. They could flog off the land - it would make a very nice site for a self-build house :-)

I wondered about that; there is some evidence of the plastic grills metlting, but on further inspection each fan has two in-series thermal cutouts (both bimetal) and so the chance of that happening in reality is rather low.

The heaters don't look all that old. Some 10 years apparently. Screwfix do an identical-looking (and specified) model - 60720 - for an incredible £125, and I've not found them significantly cheaper elsewhere. Had we been looking at £20 or £30 then we probably wouldn't be having this discussion, but the thought of replacing £500 worth of heaters that don't really do the job anyway really doesn't sit well with me. £500 would go a long way towards getting a proper "wet" system installed were it not for the lack of on-site gas.

Hwyl!

M.