Are room thermostats out of fashion?

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On Sun, 14 Dec 2003 02:03:09 +0000, The Natural Philosopher wrote:

Feed a bog standard boiler with mains and tell it it can fire if it wants to. As it is "cold" it will fire until it's stat says it's hot then shut down. Yes? Now have you changed the laws of physics such that this boiler will now *never* *ever* cool below the hysteris point of it's stat and fire again?
"Demand for heat" does not include keeping itself/small primary loop warm/hot.
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Or heating the outside air when heat floats through the flue when off.
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....he digeth much bigger hole for himselfeth...
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On Sun, 14 Dec 2003 11:14:42 +0000, Dave Liquorice wrote:

One of the things that so far as I known nobody has yet mentioned is the nature of the boiler that is being controlled.
With a fanned flued boiler when the burner cuts the heat exchanger is in a box which is fairly well insulated.
With a conventional or balanced flue boiler the heat exchanger then becomes a radiator fitted on the outside of the house through which the pump is pushing hot water!
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Basically, you are proposing to use yourself as the room thermostat, by manually turning off the heating when it isn't needed. However, systems should be installed to be operated by less diligent people. The room thermostat turns off the system for other people.

No it won't. It might come on at 7am, with the timer and stay on until 11am, when the outside temperature has risen on this fine winter's day and there is plenty of solar gain. Then, around 5pm, it starts getting nippy again, so the boiler fires up again. Of course, you may propose your manual controls such that you have to notice every day and turn the thing on and off. Myself, I prefer to get electronic equipment to do this for me.
Christian.
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You are confused.
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Andy Hall wrote in message ...

Thanks for the wider view, Andy. What concerns me is, I assume a room stat can't do any harm, unless of course it fights with the TRVs in such a way that the boiler doesn't know what the hell it's doing. Why the installers should bother to disconnect the old stat is a mystery. The other thing that would concern me is the reliability of the TRVs. I've never had a stat fail but I've known plenty of TRVs seize up if they're not adjusted from one year to the next.
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On Sat, 13 Dec 2003 18:20:50 -0000, "stuart noble"

Even then it won't do any harm as such. The fighting comes from a few scenarios which can be avoided:
- Room stat is in a place where the radiator(s) have TRVs. As the temperature rises, the room stat may switch off first. If this happens then there is no more heat to there or the rest of the house. Alternatively, the TRV may start to close down, effectively reducing the heat contribution into the space and preventing the room stat from operating unless the temperature goes much higher for other reasons such as solar gain or heat gain from other rooms.
- Room stat in place where there is other heating - e.g. a living room with gas fire or a kitchen. These contribute heat which is effectively outside of the control loop and the room stat will react by turning off the boiler early making the rest of the house cold.
By having the room stat where there is a non-TRV-controlled radiator you create a control loop between temperature of that space and the boiler firing. Ignoring the rest of the house for a moment, this space will attain and be maintained at the room stat setting.
When you add in the TRVs for the other rooms, the trick is to ensure that the radiator sizes and water flows are such that the TRVs are starting to shut down before the room stat cuts off the boiler.
All of this is somewhat imprecise because the radiator water flows are inter-related and of course heat passes from room to room.
You may want to think about using a radio linked room stat. These have the advantage that apart from not needing to be wired all the way, you can try different locations until happy with the results. The sensor/control piece is battery powered and the receiver is fitted near the boiler.

It doesn't make a lot of sense, although if it was an old bimetal one, using an electronic one would giver better control sensitivity.

I've always used Invensys/Drayton ones and have never had the plunger of one sieze up. I have had failures of the head part after 7-8 years but I have a couple that are still fine after 15.
.andy
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Andy Hall wrote in message ...

Interesting idea.Thanks.
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Andy Hall wrote:

Thank you Andy.

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Fine if you want the same temperature all the time the heating is on, but most don't.
I have a programmable stat in the living room which has no TRVs. Every other rad has. The house comes up to the morning temp set by a combination of the room stat and TRVs - obviously the room with the stat mustn't be the first to reach its set temperature - and when the later daytime lower temp switches in the whole house drops pretty consistently, and maintains that new temperature. Similarly with the higher evening temperature - and much lower nighttime one if I leave it on 24 hours as I do in very cold weather.
It's called balancing the system. ;-)
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Dave Plowman wrote:

Well in my house its even easier. If its cold upstairs I switch the heating on. When I go into a room, I set the wall stats (TRV equivalent) whilst I am in it, and when I am done I turn it down again.
Bedrooms that are in use are set to a preset setting that is comfortable, as are bathhrooms.
If the weather is wearm, I switch the whole zone off. In between times I have a timer that does the switching on and off for me.
The boiler does not short cycle. Neither is it always on (Except under full demand when heating first comes on or severe winter weather, when it can take a LONG tome for the underfloor to come up to temp...
Asd fars as I can tell the regulations merely say that you need some system to stop teh boiler running continuously, and that is amply provided for by a single unregulated branch in the CH system, and the boiler stat itself.
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writes

<snip>
Try www.gasman.fsbusiness.co.uk/controls - seems to have a lot a diagrams courtesy of JAG++
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On Sun, 14 Dec 2003 23:31:24 +0000, Andrew

I think that the link should be
http://www.gasman.fsbusiness.co.uk/controls.htm
I like the JAG++ label by the way. Very subtle, unlike its object.
This is not high quality information.
There are some notable errors in the text:
"Since April 2002 it is mandatory as part of the Building regulations that all new and updated systems have a room thermostat fitted preferably in the main living area and in a room with a radiator and no other source of heat"
It is not mandatory, it is only recommended as good practice.
The text in this also takes a very simplistic view of boiler operation and assumes one with a simple on/off input control that is non-modulating.
"This is because once all the rooms are up to temperature all the TRV's will be closed, but your boiler will still be producing heat at about 78 deg C."
This would only be true for a non modulating boiler.
"If you have a condensing boiler then do not fit too many TRV's, usually no more than a third of all radiators, as they will reduce the high efficiency of the boiler"
This is utter garbage.
"This also shows the actual size difference between 15mm and 8 mm which is why Small Bore (15mm) systems will always be better than Micro-Bore (8mm) as far grater volumes of water can pass through 15mm making the boiler work more efficantly making it more reliable"
This is also utter garbage.
The pasted in documents towards the bottom of the page are not from JAG++ at all, they are from TACMA, the Association of Controls Manufacturers. Unsurprisingly, they propose a long list of controls but at least mention in passing that there are other ways.
If the shoddy plumbing job with the motorised valves half way down the page is an indication of their best practice, I am not impressed.
.andy
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on
this
leaving
as
CH
It can have a flow switch on the system, but I doubt if there is one fitted.
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On Fri, 12 Dec 2003 12:34:59 +0000, stuart noble wrote:

Ours had been installed like that. I bought a Danfoss TP5 http://www.screwfix.com/app/sfd/cat/pro.jsp?id9276&tsC568 which is terrific. It beats going round 17 rads when I want to just tweak the temperature a bit. I like being able to set an 'overnight' temperature - somewhere between a froststat protection setting and the usual evening setting. So if it gets really cold overnight, the heating will come on, just enough to take the bite out the air.
Dougie
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these
It needs one by law. A control interlock to shut off the burner when the house is up to temp. Who fitted it? Tell him to get them back and fit one.
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Another drama queen . . . . .
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on
this
leaving
as
CH
Do you mean it doesn't?
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I wasn't an arrestable offence the last time I checked. It is however required by a legally enforceable statutory instrument, hardly meriting the dramatic description along with rape, murder or even carrying out gas work when not being a competent person.
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