UFH Zone control and HA

["David Chapman" <david@xxxxxxxxxx>]

AutomatedHome UK DiscussionI'm coming to the end of a big renovation
project (3 bed bungalow to 5 bed house) with "wet" UFH used
throughout. House is around 260SqM and has 800M of 16mm pipe split in to 19
zones to cover the 13 rooms.  Each zone has a Danfoss regulator which is
really just a 240v on/off switch for the flow of water in the pipe. There
is a seperate manual valve to control flow out and that is used to balance
the circuit.

System is run from a thermal store that keeps water at around 50c so in
terms of control the decision needs to be what zones are on and what times.
There are up to 3 zones per room so some are linked meaning there are 13
"decisions" to make.

The original design was quite complex with fallback settings on the
thermostats, external temp reading, occupancy links etc. However, having
lived with it in a "lashed up" state for two winters whilst other
jobs took priority we have now decided that  level of control is not
necessary.

For instance the idea of the fallback is that each thermostat has a second
setting (normally 16c) and whatever the room thermostat is set to if temp
drops to 16c the zone turns on - but that just doesn't need to happen and
may not always be required - also although the outside link is a nice idea
it is quite complex converting this in to accurate control of the inside
temperature.

In the last couple of weeks we have finished the revised design for the
controls, each of the 13 rooms will have it's own thermostat but just a
simple mechanical knob type that closes a pair of contacts to open the
Danfoss regulator(s) when temp drops below whatever they are set to,
probably 20c.

Then there will be two x three period timeswitches, one for upstairs, one
for downstairs and these will be used to determine when the thermostats
have power, these will also control the UFH pump. The pump is self
regulating so not a problem if it is on when all the thermostats have
turned off as rooms are warm enough. We were going to link this in to the
alarm system but decided not to as UFH has a lag of at least a few hours to
bring things back up to temp and so feel that based on time works best and
is simpler to understand.

Generally it will be set with all zones on in morning then upstairs off and
downstairs on through day and then quick boost of upstairs mid evening. If
going out for the day then downstairs will be same as upstairs. If away for
a few days then both time switches will be set to holiday mode which turns
on the heating for an hour a day which will stop the house getting too cold
in the winter.

The only thing we haven't decided is bathroom thermostats. The bathrooms
have additional towel rails running from the hot water circuit so really
need a way to limit upper temperature and wouldn't work well
"slaved" off the hall but remote control thermostats are
expensive so will probably just fit a thermostat in the well vented
"airing cupboard" in each bathroom instead as it should be
responsive enough and yet still meets electricity regs as it is behind a
door and so outside zone 3

Hope that helps someone,

David C


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