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Cheap but effective central heating controller?
QUESTION:Instructions for the CM6x and TP75 suggest setting the cycles/hour
to 6 for use with motorised valves.
I'm going to have to dig out the installation instructions for my
TP75, I'm sure they said words the effect of "it's not a good idea".
You think that's too much?
Well it's 6 cycles/hour during heating demand, where with proportional
control turned off it's one cycle until the demand is satisfied. It
may well depend on the thermal inertia of the house and the efficiency
of the heating system. The thermal inertia of this place is quite high
and the heating not that good so on a still day we might manage 2C/hr
rise but if it's a bit windy that drops to 1C/hr.
I haven't seen lifecycle data for standard motorised valves, but I
would be surprised if they are *that* bad......
But if you are operating them say twice as often the duration of
service life is reduced by 50%, regardless of wether they are rated
for 5,000 or 5,000,000 operations. The valve lasts 5 years instead of
10 etc
Even if this were a problem, it would not be that hard to organise
wiring such that heating motorised valves remained open during the
heating time period
A "heating time period" doesn't really exist with a programmable
thermostat, you leave the heating "on" all the time and let the stat
control the temp.
ANSWER: I suppose this really takes us to the realisation that there's a limit
to what the familiar S/Y/W plan components will let you do unless
you're prepared to hack around with relays and other components.
I was doing a bit of research into controllers today and discovered
that there is an internal proportional thermostat/programmer that
will go with my boiler. Basically, it pulse-width modulates a
signal to the boiler which winds up and down accordingly.
A bit more research revealed that it isn't made by the boiler
manufacturer, Man Heiztechnik, but by Landis and Staefa (now part of
Siemens). It turns out that this programmer, the QAW20, is part of a
system normally used in apartment buildings with a central boiler and
where the individual programmer controls a proportional water valve,
regulating total heat supply to the apartment. There is then an
optional central controller which can be used for logging and billing
use.
OK, so the application is different to the single family dwelling
typical in the UK, but I can't help thinking that we are stuck with 30
year old technology for the most part in controlling our heating
systems.
We shouldn't be too dejected though. On a recent trip to the U.S.
and the obligatory wander around Home Deeepo, I can report that
heating equipment is very primitive. Water heaters especially look
like something that Noah might have installed......
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