"BigWallop" wrote in message
...
"Martin Angove" wrote in message
...
Just a musing really. With the large number of digital (programmable -
but that's not really the issue) *room* thermostats now on the market at
reasonable prices, have I missed something, or is there a reason why
no-one seems to be producing a digital *cylinder* thermostat?
But why ? Do you need to check the exact temperature of the water ?
Surely with one of these you could do all sorts of clever things like...
ummm... pre-firing the boiler as hot water is drawn off but before the
tank reaches the "low" setpoint... have two sensors to allow day-period
variances (e.g. keep the top 1/3rd hot during the day, but fill the tank
in the evening)... allow user choice over "hysterisis" (or however you
spell it) so that boiler cycling is minimised... and probably loads more
that I haven't thought of.
You can have thermocouples installed around the system that feed back to a
selectable LCD display. This lets you check the temperatures at various
points around the whole system. I've only ever seen them used in
commercial
systems though.
This is the point where someone either tells me it's been done and is
available or tells me that there is no need to ditch the bimetal
thermostat because...
:-)
Hwyl!
M.
No. Can't say I've seen anything other than the bimetal strip being used
again the outside of a cylinder wall. As I said above, I've seen systems
with thermocouples placed in tanks and on pipes, that feed signals back to
a
display board. But never in a domestic system.
There is a product called a boiler manager:
http://www.deeter.co.uk/boiler.htm
which we tested for Deeter when in prototype, and have since installed in
a
few mainly local authority buildings. It checks the flow temperature from
the boiler against the return temperature, and only allows the boiler to
fire when the difference is just 3 degrees C between them. It is fitted
across the main boiler stat', so doesn't really take anything away from
the
control of the boiler. You set it manually to the top temp' and it
automatically controls the lower difference itself.
I've been told it has saved two childrens homes we visit regularly, loads
of
money on their bills over just the first years running period. I have one
fitted here in the house, and between the the first two years of having
the
heating system and the second two years after fitting the manager, we
noticed a saving of at least half on the running costs. And that's no
joking. We haven't noticed any difference in the atmosphere or the hot
water supply, so it is basically only controlling the boilers firing
cycles.
It is an expensive piece of kit to buy though, we got ours because of the
testing, but you should be able to get the outlay back withing two years
of
running the system with it attached.
Boy can I go on a bit. :-))
This is just a load compensation controller. You say it fires when the
flow/return delta T (differential) is below 3C. This would just cycle.
Having a brief read of the front page, I'm sure it does not do this.
Load compensation controls are now an integral aspect of many condensing
boilers. They do the same thing by sensing the flow and return. If for
e.g., the boilers delta T should not be more than 22c, then it will not
allow the boiler to fire until it can give a flow of 62C, if say the return
is at 40C. Also if a system is fitted to a radiator delta T of 11C then it
will not allow the flow temp to be less than 11C higher than the return.
This way the boilers heat exchanger is protected and the flow and return
delta T is never less than 11C.
That is the basics, but many makers do it differently.
Thermal stores/heat banks reduce boiler cycling when two stats are fitted to
the cylinder - preferably electronic stats. Only when approx 80-90% of the
cylinders heat is exhausted will the boiler fire, then one long, continuous,
efficient burn until the store is fully heated. Two stats can do this on a
cylinder, and with a quick recovery coil in any type of cylinder using two
stats can also promote efficiency.
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