[sclug] Home automation - Remote central heating control?

John Stumbles john at stumbles.org.uk
Sun Dec 4 19:21:01 UTC 2005

Mark Cooper wrote:
> Is anyone aware of any 'web enabled' central heating control's? I'd like 
> to be able to turn my home heating on or off from work :)

IIRC Honeywell were promising that feature RSN on their home-auto 
offering. I was going to post a link to it but they seem to have re-( or 
rather dis-)organised their web site and totally pantsed it up so that 
links within it take you to 404s or Directory Listing Denied-s :-(

Having tinkered[1] with home automation for CH systems in my last house 
I realised when I came to sell it that there's a definite advantage to 
having something that can easily revert to a bog-standard system.

A simple approach, if you have a PC at home that's always on & connected 
to the internet, would be to use it to switch something to turn the 
heating up. For example a bit of code called by something in Apache / 
mod-perl could toggle a control line on an unused COM or parallel 
port[2] to drive an optically-isolated mains relay[3]. (There's probably 
something off-the shelf available in this department at Maplin, RS, 
Farnell/CPC etc.) The relay could switch in a room thermostat (or 
programmable 'stat) wired in parallel with the normal system programmer 
+ thermostat (or progstat). Then set the normal time & temperature 
controls to just maintain frost protection or a background temperature 
on the system and your remote-controlled override system to a normal 
system-on comfort setting.

It's tempting to think of having the HA system do all sorts of fancy 
time/temperature profiling but a fairly inexpensive programmable 
thermostat will do that for you anyway (albeit at the expense of you 
having to set it up through the controller's own interface) so if you 
only have a programmer or timer and an on-off room thermostat then 
putting in something like a Honeywell CM67 (c.?70 online) or Sunvic 
TLX6501 (c.?30 @ B&Q) will give you quite an improvement anyway - 
certainly enough to give you a feel for what a better HA system should 
offer in that department.

Unfortunately the real improvements in heating control require 
significant investments in hardware -- e.g. plumbing-in zone valves -- 
as well as software, since you really need to control rooms (or small 
groups of rooms) independently rather than having one thermostat 
controlling it all overall. Thermostatic Radiator Valves are a fairly 
crude but cheap stab at this ideal though they obviously do a poor job 
of sensing the overall room temperature and are not at all programmable. 
Honeywell have a newish system using battery-powered electrically 
operated radiator valves controlled by radio links, though the valves 
look grossly clunky and I don't know how the controllers work: you 
certaily don't want to have to go round half a dozen or more controllers 
telling them all that you're going away for n days or whatever.

Also when you start getting serious about controlling the system you 
want to start looking at things like weather compensation (feedforward 
control from outside temperature) particularly to get the best 
efficiency from condensing boilers, and even getting rid of your 
radiators and putting in underfloor heating for better confort and 
economy overall :-)

I could go on (and if you ask me at the Back Office Beyond, no doubt I 
will :-)

[1] more in theory than pracice :-)

[2] or even a used parallel port: I have an old kit and some code for 
doing this somewhere.

[3] if your boiler has volt-free contacts (as many modern ones do) then 
you could probably get away with an opto-isolator.

John Stumbles                                      mobile 0780 866 8204
plumbing:heating:electrical:property maintenance     home 0118 954 2406

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