RE: Re: Controlling Heating

["Kevin Hawkins" <lists@xxxxxxx>]

    Thermostats and motorised valves work quite well but tend to oscillate a little due to hysteresis. The effect is that the room tends to warm and cool alternately - if you have heavy radiators egg cast iron then the effect is worse as the radiators continue to pour out heat after the flow is turned off.

    A way around this is called proportional control - this is effectively not using just valves that are open or closed but ones that can be partially open. The motorised heads that go on valves can also be supplied as proportional versions. Indeed you can replace the heads with proportional ones and keep the same valves They operate by opening proportionally (that word again) to the voltage applied so on say a 24v version with 12V applied it would be half open. Accompanying these you also use proportional thermostats that give out a voltage the varies depending on how far away from the setpoint you are - egg set to 21degrees and reading 20 gives say 3 volts out but if the temp dropped to 19 it might give say 10V out. At setpoint it falls to near zero. This gives a system that settles to a point where the flow through the radiators is reduced to the volume that is required to maintain the temperature in the room - it is more expensive and complex but produces a better result. You can simulate proportional thermostats using say the Dallas sensors and some programming in a HA controller to output through a D/A converter. HomeVision can do this for example. Getting the levels (ramp rates) right is really a case of trial and error, - or that's how I did it.

 

    Kevin

-----Original Message-----
From: Paul Gordon [mailto:paul_gordon@xxxxxxx]
Sent: 12 April 2002 11:26
To: ukha_d@xxxxxxxSubject: RE: [ukha_d] Re: Controlling Heating

Nik,

I haven't done any of this stuff, but I'm sure there are motorised valves
that use either 12V or 24V. - I guess in that case you can use a single LV
cable for both power and signal....

Check out the Honeywell Smartfit stuff on www.comfort.org.uk as well...

Paul G



>From: "Nikola Kasic" <nikola@xxxxxxx>
>Reply-To: ukha_d@xxxxxxx>To: <ukha_d@xxxxxxx>
>Subject: RE: [ukha_d] Re: Controlling Heating
>Date: Fri, 12 Apr 2002 11:09:30 +0100
>
>Stuart,
>One general question:
>If I want to control central heating in each room individually, each
>radiator has to have some kind of valve which is operated remotely.
>I asume that they will need power, so each radiator will need two cables,
>one for power and one for control signal.
>Is there any way to reduce that cabling, so we don't need to rewire house?
>Also, putting power socket into bathroom is against regulations, I think.
>Nik
>   -----Original Message-----
>   From: stuartgrimshaw [mailto:stuart@xxxxxxx]
>   Sent: 12 April 2002 00:51
>   To: ukha_d@xxxxxxx>   Subject: [ukha_d] Re: Controlling Heating
>
>
>   Hi Marc,
>
>   I just got my connection back after a month, and I was scanning the
>   stuff I missed, and I noticed no-one replied to your mail, that's
>   the problem on a list where the signal to noise ratio is so low.
>
>   Anyway ... I beleive what you want to do is use a Universal Module
>   (http://www.laser.com/?laserlink=SGUM506) unit to drive a larger
>   relay to do the switching.
>
>   I know there are a couple of people use this or a similar method,
>   and Keith D should be able to give you more precise advice.
>
>   Also, have a look at "How do I automate...." in the FAQ, there's a
>   link on there to Keiths site and info on how he did something
>   similar.
>
>   --- In ukha_d@y..., "Marc Mosthav" <marc@m...> wrote:
>   > Hi all,
>   >
>   > I would like to control my heating from my HA computer. I do have
>   a Dallas temp. sensor and would like to control the connection which
>   is usually connected to the thermostat. My problem is that the
>   b****rd thing is 30VAC / 1A and that all the X10 relay devices are
>   rated at xVDC. Am I thinking the wrong way 'round, am I stupid or do
>   I have to do something totally different???
>   > BTW nobody answered my question about all my broken TM13's so I
>   assume that they work fine for everybody else? Mine are just
>   switched off and are not responding to anything.
>   > Any help on either question would be greatly apreciated.
>   >
>   > Marc
>
>
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