Thread: TRV stuck
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fred fred is offline
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Default TRV stuck

In article , Autolycus
writes

The additional constraints that have made me consider this fully-zoned
system a

1) It's a bungalow: the dining room has a small kitchen directly off
it, and has a large, south-facing window, but the lounge is north-facing
with a small window on the west wall, and has previously been found to
work well with two radiators. One bedroom faces north, one south.

2) It will be occupied by an elderly couple, who may wish to use the
rooms fairly flexibly (study-bedroom, etc) and who will almost certainly
want to be able to vary the temperature in odd rooms at odd times. I
think that only the bathroom is really amenable to a normal programmable
room stat, though they could be used in the other rooms.

3) They don't really want to be crawling round faffing with trvs,
especially since most are so coarsely calibrated that you can't easily
return them to a "standard" position. Remote heads for trvs seem to
have gone out of fashion. A dial, or a display, that they can set to
21, or 18 (or even better, 70 or 65) will be much more likely to be
used.


In the system I envisage, when the room stat calls for heat, two things
will happen: the relevant valve(s) will open; and the boiler will get a
call for heat. This can be achieved using normally open actuators, and
an SPDT room stat, or by NC actuators and a bank of relays, or, easiest,
perhaps, by using conventional two-port motorised valves with auxiliary
switches. The latter have the further advantage that the boiler won't
be woken up till the valves are open, whereas with thermal actuators the
boiler will fire before there's anywhere for the hot water to go.

With full multi-zoning like this using simplified controls that don't
have synchronised demand you can find the boiler firing just to service
a call to heat for a one small room, leading to frequent boiler cycling.
When I designed my own system I plumbed it so that heat from the large
H/W cylinder could be stolen to meet light C/H demands, as with a
thermal store. The boiler would then only fire to top up the thermal
store (when operating on light loads). The extra components are a second
pump and a non-return flap valve to stop back flow through the boiler
and of course extra control to detect light loading. This phase of the
project has yet to be implemented as I have the 7 zones configured in 2
control banks (4+3) and the need for such fine control hasn't been
required. The control for the light loading would be simple logic but
proprietary.

An alternative is not to fire the boiler until either 2 or more rooms
call for heat or 1 room plus a fixed delay had timed out. The effect of
this is to try and force the zones into some sort of synchronised demand
but again this requires proprietary control.
--
fred
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