Re: c-bus and hot water/boiler control

["simon_haslam" <simon_haslam@xxxxxxxxxxx>]

I'm at a similar stage of specifying a new CH system, albeit with rads and
only a couple of UFH zones.

To run your boiler most efficiently (comparable to using weather
compensation) you'll want some way of setting the output according to heat
required. There's a standard called OpenTherm (http://www.opentherm.eu/) which a
number of European boilers comply with. This includes how a controller
specifies the amount of heat output from the boiler. The trouble is in the
UK many boilers have a lower spec to cut down the price so not many are
OpenTherm compatible - the more common ones I've found are Viessmann
Vitondens 100-W (with an adaptor lead) and Keston. I'm waiting back to hear
from Vaillant. I don't think Worcester (Bosch) are.

Otherwise each manufacturer has its own means of controlling output - from
a 0-10V voltage (e.g. some Keston I think) to a PWM signal. I think most
also have an on/off control for backwards compatibility. Finally I think
most modern condensing boilers measure the return temp to modulate the flow
temp.

Whether it's worth trying to control DHW separately I'm not sure - many
newer boiler controls have a temperature sensor or two on the cylinder so
can adapt flow temp accordingly.

By the way, I'm interested to see you chose Clipsal/c-bus for HA. I posted
a question about the most appropriate technology a couple of weeks ago but
didn't get any responses:
http://groups.yahoo.com/group/ukha_d/message/159854

I think I am leaning towards Clipsal too - they seem to be fairly popular
and provide plenty of choices. It's a shame you're locked in to one vendor
though.

HTH


Simon

--- In ukha_d@xxxxxxx, Kieran Broadfoot <kjb@...> wrote:
>
> Hi there,
>
> I am currently planning a c-bus installation and was prompted to
consider controlling an underfloor heating installation using clipsal
thermostats.  Single zone thermostats seem appropriate coupled with a 12ch
relay unit to control the manifold actuators but I am less sure how to
drive hot water generation from my boiler.  I am planning on installing a
bosch system boiler and unvented cylinder.  Has anyone trodden this path
such that they could provide some advice to me regarding
configuration/cabling etc?  Did you use an additional thermostat (or a zone
on a 4-zone unit) to control the circuit?
>
> If anyone could provide some advice it would be very much appreciated.
>
> All the best
> kieran
>




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