Andy Hall wrote:
On Thu, 30 Dec 2004 22:01:09 +0000, Dave
wrote:


I've tried a few but they seem to give wildly differing numbers (and one
gave the same answer regardless of the inputs!), can anyone suggest one
that works?




The Myson and Barlo ones are OK.

The Myson one is not on their site at present, but I have a copy and
will happily send it to you if you drop me a mail.

One of the problems with some of these programs is that they have
incorrect U values for given object types - so it's always as well to
check the numbers against the list in the Building Regulations
Approved Documents.

The other factors that can introduce error are that some programs do
not account for floor heat loss correctly. The reasonably correct
approach is based on the combination of outside wall lengths and floor
area and there are correction tables of modified U values to cope with
it. Computer programs should do all of this as well, but if not,
there will be an error. Some programs have correction factors for
whether the heating is on all day, exposure of the house and so on.
The defaults may not be sensible.

Finally, you do need to make sure that heat loss by air exchange is
reasonably accounted for. This is a big chunk of heat requirement in
most properties.



Thanks Andy, email sent.

Do you happen to know whether the U values in the myson software are
correct?
Estimating air exchange is tough, any suggestions on how to approach it?

--
Dave S
(The return email address is a dummy)