Outside walls

Hi all,

This post may seem ridiculous. I'm currently researching a new boiler and radiators for my flat. In order to complete the calculations, I need to know what the construction of the outside walls in my block is. I haven't got a clue - is there any way that I can make an educated guess (using your education!)?

Here are some "clues": the block was purpose-built in 1986. It has a concrete internal structure. The outside is finished in red brick. Windows are double-glazed with aluminium frames (not sure if they have thermal breaks - this is something else I need to establish).

Lastly, when I moved in, with all the household paperwork, there was some sort of certificate saying something like the property had been built to highly energy-efficient standards, and the heating thermostat could be left on around 18. (I have found this last point to be true, and I like it warm!) Naturally I binned the certificate, so can't quote verbatim. :(

Antony

Reply to
Antony Gelberg
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This is going to be, at best, reasonable guesswork.

You would really need to know the construction of the inner leaf of the wall. You mention concrete... DOes this mean a concrete beam structure or ??

I would suggest find an unobtrusive place on an outside wall and removing a small piece of plaster or plasterboard. Then see what is behind it by way of blocks and ideally the cavity depth and whether it's filled with insulation. If you drill a hole and push a piece of metal tube into it and into the cavity, if there is insulating material then you should pick up a lump of it; plus you can measure the cavity depth.

Assuming that it is a cavity wall, aerated blocks and insulated, then from the Building Establishment tables, under best conditions the U value would be 0.35 W/m^2.K A more typical value is around 0.45 to

0.5

Without cavity insulation, it could be as much as 0.9; so you really need to know about insulation. On a place of that age, there should be insulation.

You could assume worst case and overdesign, but that would be a bit wasteful.

For the windows, double glazing in aluminium frames without low-E glass or gas filling (reasonable assumption here), the U value is 3.4

You then need to account for floors and ceilings. For a ground floor on concrete, the loss is reasonably easy to estimate, as it is if you are the top floor and have to calculate for the roof. It's more awkward for the floor/ceiling to another flat because you then have to make some assumptions about heatloss to those.

If you post some details, I can look uo the tables for you. To calculate for a ground floor, the dimensions are needed to determine an effective U value because the perimeter dimensions come into it.

Once you have all the U values, the basis for calculation is to measure the areas in square metres and multiply them by the U value and the temperature difference through the surface. That gives you the heat loss in watts for that element. You then add up the elements for a room to determine the total heat loss through surfaces.

After that, there are heat losses due to air changes. There are industry standard assumptions for these which are reasonable for heating calculation purposes and to use them you need the room volumes in cubic metres.

The two values are then added to get the heat loss for the room, which determines radiator output requirement from which you can size the radiators. Finally you add these numbers together, add a margin of

10-20% to determine the boiler requirement. Note that this is usually not too critical because most boilers are adjustable (range rated) or automatically modulate to an appropriate output.
Reply to
Andy Hall

Whilst this is perhaps the 'IDEAL' way to do it, simply laying your hand on the wall will give you a tactile measurement of heatloss.

Single brick walls in winter are ICY. Double brick with no airgap are BLOODY COLD Cavity without insulation are COLD Cavity with insulation are COOL

Remember, to size radiators all you have to do is determine peak output required. And exceed that by a margin. No one died of too large radiators.

Likewise an oversize boiler will simply spend a lot of its time off.

If you take Andys lower limit estomates of U values, and size for that, you will have a more than adequate heating system.

Lets face it, ultimately its the thermostat that controls the temperature.

Reply to
The Natural Philosopher

The regs requirement for external walls was 1.0 from 1975 to

1990, 0.6 from 1990, 0.45 from 1995 and 0.35 from 2002. Yours may of course be better than the minimum, or just could be worse if one of the trade-off provisions was used. For places built at the time the regs changed it's probably wise to assume the higher figure as the plans were probably approved pre-change.
Reply to
Tony Bryer

As it was recent, contact your local Building Control (or Planning)and ask if they can look at the drawings and let you know.

Reply to
dg

Are they guaranteed to have them? I have already had problems up to _here_ getting plans of the flat when the engineer came to survey the wall I wanted to remove. He said if there were plans it would be a lot easier, rather than go around looking for clues. The "management" company (who required the engineer in the first place) was useless - "We didn't get any plans from the builders".

Eventually he poked up through a ventilation duct and hit the concrete. I was most displeased when he told me that of course it would be fine as the building was of concrete construction as long as I didn't knock through any concrete (as if!). Did the fricking management company not know that already? In a building with around 100 flats, I doubt I'm the first person to remove a wall.

Anyway I'll do some more research and post my findings.

Reply to
antgel

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