Programmable RF Thermostats - multiple receivers?

[Tim S]

Hello,

Interesting query: I've been looking at various of the above and found some interesting units such as the Honeywell CM67 and also units made by Danfoss and Sunvic.

What I'm considering doing with a CH upgrade is rather than setting up a 2 (or 3 or 4) zoned system, I'd rather have electric valves on each radiator (thermo-hydraulic actuators) and a local room timer-thermostat. Maximum flexibility.

Then I find the above RF capable units and think "hmmm - less wiring..." Fused spur off the ring near each rad and one receiver and actuator and I'm done...

But, I have a problem... how to turn the CH pump on or off. So I'm thinking, I wondering if any of those units can drive multiple receivers, so the second set of receivers can be wired in parallel to generate a "demand" signal which I used to control the pump.

The Honeywell unit looks the best on paper as it's using the newer 868MHz RF band and uses a short pulsed signal. So in theory one should be able to set two receivers to the same code as one thermostat unit and have it work.??

Anyone ever tried this or have an alternative idea for doing something similar?

Ta muchly

Timbo

[Andy Hall]

I haven't done this, but I am fairly certain that it would work because part of the installation is to pair up the receiver with the transmitter. You would simply do that on multiple receivers.

There is no return path to the transmitter so it would have no way of knowing.

[Lurch]

On Tue, 23 Nov 2004 16:33:13 +0000, Andy Hall strung together this:

I haven't actually used these or read the instructions but some pairing\learning processes effectively default the transmitter and receiver first. Bit of trial and error I think.

[Tim S]

[Reply to Andy and Lurch]

Yes - my feeling too - that the RF is one way only so in theory multiple receivers would work.

It would be bloody expensive to set up 10 areas this way (I found some prices) so I might compromise and control a few main areas and just have common areas (hall, kitchen, bathroom etc) "on" whenever *any* controlled area demands heat (and leave the TRVs in place). Seems like a variation on the standard system where a central clock and hall thermostat control evrything.

I think it would work quite well. Sort of S plan plus, but with more flexibility. I don't like the idea of defining zones in hard plumbing as the house in question does not lend itself to the notion that "room x = bedroom". The way it's laid out, today's bedroom could be tomorrow's secondary living room or study etc. Such is life with bungalows ;->

I emailed Honeywell and Sunvic and they are supposed to be getting a technical bloke to come back to me so I'll post their answers here if I get them.

I should contact Danfoss too - as they have an RX3B reciever that can listen on 3 channels and provide a common demand signal. Though either way, I'll be wiring their relays in parallel as I'm looking at 5 zones minimum even with my compromise solution.

If anyone has any alternative suggestions, such as a 5-10 zone central controller with extra-low voltage signal cable going between various modules, rather than RF, I'd be interested.

Sure this problem must have been solved before...

Ta

Timbo

[Tim S]

[replying to myself - first sign of madness :/ ]

There is another solution I though of... Using a manifold with lots of electric valves. Got the idea from some underfloor heating company on the web. If I don't want [afford] a timer/thermostat in every area, I could lock certain circuits on.

I could get away with one RF module per circuit, and make up my own box full of DIN mounted relays to provide the common demand signal.

As it happens the manifold would be centrally located in the house so not much difficulty with plumbing, and it would be adjacent to the boiler and pump anyway.

Hmm...

Tim

[Lurch]

On Wed, 24 Nov 2004 12:22:37 +0000, Tim S strung together this:

No doubt there will be but I think we'd be getting into industrial control solutions. I've worked on a few commercial systems and the controls aren't cheap. I think a homebrew solution is what you're after. If you're keen on the low voltage idea then you just need a low voltage link from the actuator to the a'c where that would control a relay controlling the pump. AFAIK most, (all?), RF thermostat receivers have volt free CO contacts. Obviously could be a problem if the actuators are mains voltage, as this would require more relays by the valves to switch the LV demand pair, but depending how much you're prepared to spend it might not be such a major hassle.

[Pete C]

Hi,

Another way would be to have some resistance wire in the TRV. When current flows through it the heat from the wire lowers the temperature the TRV closes at.

This could work quite well as in mild weather it's OK to turn off the rads in rooms that aren't being used, but in colder weather some background heat is still a good idea.

Or the current can be switched at different duty cycles to vary the effect, an old laptop with a parallel port interface circuit would be ideal for this.

cheers, Pete.

[Tim S]

OK - I've figured it out...

1) Sunvic did come back and say that multiple recievers *could* be keyed to one transmitter. But this has become less relevant...

What I've more or less decided to do is to:

Have the plumber install lots of spring-return-close 2 port valves with microswitches in the central location (adjacent to thermal store unit). Probably one per room. Effectively a DIY manifold with valves, but using serviceable standard parts. Run 10-15mm pipework to existing rads.

OK, that's lots, probably 10. But two port valves aren't too expensive and the fitting isn't much extra work as I need the central section of pipework for rads and hot water replaced anyway as it's rubbish.

Bearing in mind, altering plumbing later is a pain, but altering localised electrics is easy.

So I have *potentially* a 10 zone system. But the RF thermostats are expensive, so me and the missus just worked out we have 4 areas which could be grouped into zones at present.

So, 4 receivers into a wiring box driving a set of valves each. Common up all the valve microswitches and I have the demand circuit. Easy!

Plus I can trivially reconfigure the zones (I did say that zoning in Dad's house is not a given and is likely to change over time). Also I can very easily add extra programmer-thermostats + RF receivers in the future (any make, they don't need to be compatible) and create extra zones if it seems necessary.

I like this idea. Not novel, (S-Plan-Plus taken to extreme I suppose??) but it's quite practical.

Pretty bomb proof too. As long as I make sure the 2 port valves have the little manual override lever and I leave the existing TRVs in place (but normally set to max) I have a manual backup when all the complex technology blows up at the least convenient time possible, as is wont to happen.

Yep - think that's sorted - unless a learned friend here spots a fatal flaw...

Thanks for your various suggestions folks :-)

Timbo

[Andy Hall]

You can buy valve heads that do this made by Sauter, called thermal drives. RS have them as part 328-8562 or less from ControlsCenter.

I've been using Sauter's motorised variety (AXM 117S) which work from

24v ac or dc with a 0-10v control signal. THese fit on in place of the TRV head and can be set to any open or closed position from a DAC. They work quite effectively.

[Tim S]

Bit like a set-back thermostat? Good idea. I'm not quite into the old laptop idea though, as I want this to work ;-> I'm a programmer, so I know when not to depend on computers, which is most of the time if at all possible, especially if involves me getting cold :/

Always, always have a *big* manual override switch.

Cheers - I do like the first idea though!

Timbo

[Tim S]

Something similar is called a thermo-hydraulic actuator? (Heater heats liquid, moves rod to operate valve head). I was going along these lines (Danfoss ones are about 15+VAT, but driven at 240VAC) until I hit upon the idea of just centralising everything except the actual thermostat transmitters.

Timbo

[Andy Hall]

The thermal drives are effectively as you describe.

They can be controlled in a pseudo-analogue way by varying the power duty cycle but it's not very accurate.

The motorised ones have a built in servo which periodically recalibrates itself against the end stop. Thus the 10v dc voltage gives quite accurate and repeatable results.

wanted to have genuine proportional control so went for this approach.

If you wanted similar for your solution, Sauter do make similar valves that are equivalents or similar function to heating zone valves but again with analogue control. I believe they cost around £70 though :-(