"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.
"at least half". Have you took measurements? data over periods when fitted
and not fitted? What type of boiler do you have. On a condensing boiler I
can see big gains. On a regular boiler, gains in that only boiler dry
cycling is reduced. In a regular boiler you don't want the return temp to
drop low as condensation may occur. Anti-cycling can be achieved via a
simple electrical timer. Just delay re-firing for may 5,6,7 mins or so.
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.
A Savastat is £175 + VAT which I think is steep for domestic. The Savastat
only has a return pipe sensor, relying on sensing "rate of temp change" to
judge the load of the system. The Savastat will work well with basic
commercial systems, which is its main target market.
The Deeter has a sensor on the flow and return which is more encouraging.
But it depends on how they have programmed it. How much is this unit?
I can see both of the above giving gains with a modulated burner boiler that
modulates to maintain a set flow temp, as do combi's. Just keep it on full
temp and let the load compensator stat do the rest. That also includes
combi's. But there must a way of cutting out the load compensator to allow
full heat for DHW. Fitting one on a boiler that already had load
compensation built-in is needless.
With a simple cheap condensing boiler, I would go for an outside weather
compensator. The Danfos model is £166 +VAT from discountedheating. This is
a good unit and takes into account the cylinder stat and that the boiler
needs to be on full heat when re-heating water. It senses the return pipe
temp to keep the boilers return in key with the outside weather.
Better units than the Randall, although more expensive, have inside
temperature influence, in that if the room temp is being approached it drops
the return temp even further and if over room setpoint by a degree or so
cuts out the burner. Anti-cycle control is also built-in. Very effective.
I know I have one like this.
http://www.danfoss-randall.co.uk/prod_bem5000.htm
BEM 5000 Boiler Energy Manager
The BEM 5000 is a sophisticated electronic domestic boiler energy manager
which when added to almost any central heating system. new or existing, will
reduce unnecessary boiler cycling. improve boiler seasonal efficiency and
reduce running costs.
The BEM 5000 integrates the operation of the heating system and domestic hot
water systems and includes a pump overrun.
The unit is a weather compensator which during periods of heating demand
varies the temperature of water flowing to the radiators as a function of
the outside temperature The technique which is well established in the
commercial market. adds significantly to system efficiency and reduces
running costs in the process. During periods of hot water demand. the
weather compensation function is cancelled to enable the cylinder to be
reheated as quickly and efficiently as possible
The BEM 5000 is an all electric solution which can be installed without the
need to drain down the system, making it an ideal system upgrade option
Improves system efficiency
Provides electronic boiler interlock
Low cost weather compensator
Provides HWS priority
Built-in pump run-on control
User adjustable
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