On 13/11/2017 16:59, whisky-dave wrote:
On Monday, 13 November 2017 16:24:56 UTC, John Rumm wrote:
On 13/11/2017 13:58, whisky-dave wrote:

All we need is a heating engineer that knows stuff, both theory and in practice
It was 12C @ 9am, now 16C @ 13:45.

This is with 5 of 2KW heaters and 2 of 1.5KW heaters.

So if yuo wanted the demp to be 16C before the 10am class how many heaters would we need in total. ?


It seems like working out the heat loss from first principles would be a
good start:

http://wiki.diyfaq.org.uk/index.php/Heat_loss

Once you have a feel for that, you know what power input you will need
to maintain a steady state at a desired temperature. You would then need
to size the heating to be able to exceed that by enough to lift it to a
working temperature in a reasonable time frame (and what that is will
depend a bit on how the place s built - you may be able to achieve it in
a few hours, or you might need to heat it continuously if it turns out
the answer is "days").

So how would yuo go about that ?

A combination of experience with the current heating system, and some
knowledge of the construction of the building (i.e. how much thermal
mass it has, and where that mass is with respect to the insulation (if
it has any).

For buildings that are reasonably will insulated, and have their thermal
mass outside of the insulation, then conventional thermostatic
controlled stats will work ok. For more "difficult" buildings then
optimising stats that learn the response of the building and adjust the
on times automatically can work well. Some places however which have
large volumes of masonry and no insulation will frequently take days of
continuous heating to get to a sensible temperature. In those cases just
setting the heating output based on an external stat (i.e. a weather
compensating type of arrangement) is often the easiest way so that you
track the general trend in the external temperature to aim at a roughly
constant inside temp).

What are the things you need to know ?

For what, heat loss calcs? General details of the construction, and the
areas involved.

If it turns out you need 5kW to keep pace with losses on a cold day,
then you know that if you have 7kW available, you should be able to
reach the target temperature eventually. Then it becomes a question of
optimising start times and working out what your minimum setback
temperature is. If it turns out you can only gain 1 deg/hour, then you
probably want your setback temp no lower than 15 degrees, and the
heating to go to full power at say 7am to get a comfortable temp by 10am.

Think about it and you'll realise the where the biggest error would be.

Will I?

--
Cheers,

John.

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