On Wed, 14 Jan 2004 10:38:59 +0000, The Natural Philosopher
wrote:

Andy Hall wrote:

On Tue, 13 Jan 2004 23:00:11 GMT, Harry Bloomfield
wrote:


It is never more efficient to leave the heating on for a period than to
turn it off.


It can be, depending on the thermal behaviour of the house and the
control system. Systems with setback, optimum start and outside
temperature compensation can result in little or no temperature
overshoot at the wrong times and more accurate temperature control
than where a simple thermostat and timer is used.



That is what I am finding - not that I have the gubbins.- but where huge
thermal masses are involved..

See if this makes sense.

You have a well insulated house but with a big slab of concrete floor.

In order to feel warm in this house not only does the air in the house
have to be warm, but the floor has to get warm too. In the meantime to
compensate for the cold floor the air in the house has to be warmer than
it otherwise needs to be. During this period it loses MORE heat per unit
time than it does once everything is up to temperature.

If this extra heat loss exceeds the savings by having it overall cooler
at might/during the day etc, then you have a net loss.

In my case, it seems to make very little difference which way I play it
to fuel consumption.

This was my point. You have a complex system in the house itself and
then external influences are added to it such as weather change. In
most systems it is then controlled by a very simple control loop
arrangement with large hysteresis (bimetal thermostat). Then you add
in the vagaries of the boiler.

Added to all of this you put in humans and there are a whole ton of
factors in feeling warm or not there. As you say, if the human then
does something to the heating arrangement in order to feel comfortable
like winding up the thermostat or adding other heat sources, then the
simple control system is going to do a poor job anyway.

Given all of that, it is way too simplistic to say that turning the
heating off always leads to greater efficiency. Even on a simple
control basis and ignoring the humans, it may well not.




..andy

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