On Tue, 31 Aug 2004 11:09:41 +0100, Kalico wrote:

On Sun, 29 Aug 2004 16:47:17 +0100, Andy Hall
wrote:

[snip]

You can get calculator programs from radiator manufacturer web sites
to do the sums.,

Do you know of a good site for sizing rads Andy?

TIA
Rob


Replace 'spam' with 'org' to reply

Rob,

I've emailed you a copy of the Myson one.
It's not up on their site at the moment.

It does give correct results, but do check the U values against those
in the Building Regulations Approved Documents (www.odpm.gov.uk). I
found that a couple were wrong in the program.

None of the on line sites that I have tried give correct results and
at least one was out by a factor of 4.

When using the Myson one (and looking at data sheets for radiators),
don't forget to look at the derating factors. If you are going to run
your system at the traditional 82degree/70 degree temperatures then
the published radiator outputs have to be reduced by 11% - i.e. a
nominal 1000W radiator really gives 890W at these temperatures.
If you are doing an entirely new system with a condensing boiler, you
can run it at 70degrees flow/50degrees return. In this case, you
need to derate the radiators by 40%. You can't really mix the two
scenarios.

You begin by calculating the room heat losses at -3 degrees and then
divide by 0.6 or 0.89 as appropriate.

Even if you have to run a condensing boiler system at nominal 82/70
degrees it is still worth doing because the calculations are for worst
case. During spring and autumn the boiler will run at lower
temperatures anyway.







..andy

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