In an earlier contribution to this discussion,
Michael Chare wrote:
"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Danny wrote:
Hi all,
I've a couple of questions that I was hoping someone could help me
out with.
I currently leave my central heating system on - constantly (during
winter). When I'm out of the house I turn the room thermostat down
to 20 degrees, when I return I pop it back up to 22-23 degrees, at
night I put the system back down to 20 degrees.
My theory is that because the water (in the system) is actually
already at temperature and the house never goes below 20 degrees and
that this is a more efficient way to heat my house and keep the
bills down. When the room thermostat is not calling for heat the
boiler only comes on every now and then for approx 30 seconds, I
assume just to keep the water which flows through the HW cylinder
at the required temp.
Would anyone agree with this?
This question may seem silly but if my central heating system is
switched off all day the house temp drops to approx 15-16 degrees,
this takes quite some time to get to 22-23 degrees and I guess alot
of gas also!
Also, if the above holds true, would it be more economical if I
close the valve to the HW cylinder and just use the electric
immersion heater and a timer for the required hot water?
Thanks in advance
If your system is wired correctly, it should *never* come just to
keep the boiler hot - unless either the room stat or cylinder stat
is calling for heat.
According to the instructions for my Danfoss TP9 Programmable
Timer/Thermostat.. if you have a gravity hot water system and pumped
central heating you may well not have
a H/W tank thermostat. Basically the boiler operates as you describe.
If you have Honeywell C plan then the boiler would only function when
either the C/H or H/W require.
http://content.honeywell.com/uk/home...20C%20Plan.pdf
One advantage of the TP9 is that it only supplies power to the boiler
when either the C/H pump is on
or the H/W timer is on.
With a conventional programmer the boiler is trying to keep itself
warm whenever the timer says the C/H is on which in your case would
be always.
The other advantage of the TP9 is that you can make the C/H follow a
temperature profile with 6 changes per day. - different at weekends
if you want.
The heating system has to replace the heat lost through the walls, ,
windows, roof and floor. The hotter the building, the greater the
heat loss. It is always more efficient to allow the building to cool
down when you don't need it to be hot - but better still if you have
very good insulation so that it only cools very slowly when the
heating is off.
It is *never* more efficient (cost-wise rather than energy-wise) to
heat water with an on-peak electric immersion heater rather than by
gas.
When I was a school I recall 'rate of loss of heat is proportional to
the excess temperature'. i.e. the warmer your house is compared to
its surroundings, the more heat it will loose.
The problem in practice is that can take a while for the house to
heat up and cool down - as you mention!.
Michael Chare
I admit I was assuming that the OP had some control over hot water
temperature - either a Y-plan or S-plan. If he's got gravity hot water, it's
BAD NEWS unless he also has a motorised valve in the circuit to make it into
a C-plan.
I think that what you are remembering from your schooldays is "Newton's law
of cooling" which, as you say, states that the *rate* of heat loss is
proportional to the excess temperature. But the rate is *also* dependent on
the level of insulation.
The secret of stopping the house cooling too much when the heating is off is
to ensure that the insulation is good. It's then not too hard a job to
re-establish comfortable temperatures after a period of no heating.
I agree that a programmable room stat is a good idea in that it enables
different temperatures to be programmed at different times of the day to
suit your lifestyle. It also enables the heating to be turned OFF when the
house is not occupied - and this facility should be used, particularly if it
also has a feature to re-establish a target temperature by a specified time,
as some do.
--
Cheers,
Set Square
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