Are room thermostats out of fashion?

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On Fri, 12 Dec 2003 17:04:07 -0000, "Christian McArdle"

That would work, but the advantage of my approach is that the hall rapidly gets close to temperature, then takes a long(er) while to get to final temperature. This has the effect of making it seem to warm quickly.
Your approach would result in the hall seeming colder for longer, but would work.
Tim Hardisty. Remove HAT before replying
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The problem with your system is that it requires a reasonably sentient being to operate and adjust it, which makes it fine for someone such as yourself who understands the interactions between the various valves and temperature sensing devices and knows not to fiddle after it is set up.
For an installation by an engineer for your average spod with no understanding on how central heating and TRVs work, it would be hopeless. The first thing most people do with TRVs is set them to 30C when they feel cold, as they think they are on/off/power switches.
Christian.
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On Fri, 12 Dec 2003 17:21:20 -0000, "Christian McArdle"

Over and out :-) Tim Hardisty. Remove HAT before replying
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Christian McArdle wrote:

(hint. I have done this for some considerable time. The boiler doesn't short cycle at all. Only in the case of very poorly insulated CH pipes and a fairly warm set of rooms, and very cold spaces through which the pipes run [almost impossible to achieve together with fairly warm rooms] do you get teh '5 minute burn, five minute idle' sort of cycle. You MAY get this with a fully TRV'ed system with a bypass buit even then its unlikley. The water has to cool down quiet a lot to overcome boiler stat hysteresis, and in that time its almost certain that one or more rads will have opened up the TRV's a tad and be calling for heat anyway. )

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writes

Here its a fully TRV'd system, bypass loop and NO room stat. Right now its about 10C outside, most of the radiators have gone off, a couple (mostly lounge, its the warmest setting) are running at about 40C, just feeding enough heat into the room to balance losses. One or two rads are barely warm, maybe 25C, (inlet pipe is hot), again just trickling heat into the room. Overall very comfortable, very stable temperatures. Boiler fires for about one minute in every ten.
TRV's are analogue controllers, in well designed system they can throttle heat output to match room losses. Rooms don't "reach temperature" and magically stay there, constant heat loss needs to be balanced with heat input. You can control it digitally with a stat turning the system on and off, or have a nice room by room analogue control.
I do sometimes consider fitting a room stat, probably an RF one so it can be moved around, just to experiment with the stability of the system.
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Steve


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On Sat, 13 Dec 2003 19:59:34 +0000, Steven Briggs wrote:

And in the summer?
I know you (manually) turn the heating off, but if you don't?
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its off ~May to ~October. But being a tight Yorkshireman I wouldn't be leaving the heating running unnecessarily anyway ;) The 1 hour boost button does the job on the old cold day.
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No Tim, 100% twaddle!
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On Fri, 12 Dec 2003 17:24:50 +0000, IMM wrote:

respectful disagreement (by Tim Hardisty) and something else.
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When someone is prattling twaddle, they must be told.
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It isn't.

It refers to it as a control interlock. Can be a flow switch. In short, a device to switch out the burner when the house is up to temp. A boiler is not allowed to cycle unnecessarily.

That is cycling - NOT ALLOWED.

That is because you don't understand.

Not so.

Good idea.

What if all rads have TRVs? Then the boiler cycles. So a flow switch is necessary to cut out thre burner.

Not useless, just less effective. If the room stat is in the coolest part of the house, usually the hall, and the rad is sized and balanced to give the desired room temp, then if this room is satisfied then all the others are. As it is the coolest room in the house it will demand heat before the others, so the other room will not be cool.

'fraid not! It is you who are twaddling along.
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IMM wrote:

What is wrong with letting the CH return stat do this?
That is the point.
I ran a system fuly TRV'ed with the house stat turned flat out for several years. The boiler neither short cycled nor ran continuously. It cut off when the TRV's had had enough. There was a single unregulated radiator in a well insulated airing cupboard.
I have a system now that in part is functinally equivalent, in that I have room stats on fan blown rads. Plus a few TRV equipped rads. The pump runs continously, The water circulates continuously, the fans come and go, and the boiler does the same. It burns a few minutes, and then shuts down.
Every room is set to the temperature requiertd. I don't have to mess with heat leaks - which anyway would never work, because there is no simple place to put a zone stat on this little lot. Dowqnstais hall ae on a different zone (UF) and upstairs halls/landings are unheated as they take heat from teh UF system by convection.

I beg your pardon. All boilers cycle under normal usage. They get the water up to temperature in the primary HW or CH circuits, and then shut down. That is what they are designed to do for gawds sake!

I don't think YOU do then.

No, you are confuding 'cycle' with 'short cycle' and also if yopu read back on all posts, I never said that all rads were TRV'ed without at least a bypass loop. The point is that short cycling happens when there is NO flow. With ANY flow the boiler cuts out, and the hystersis of teh boiler stat means the water cools several degrees before the next burn comes along to raise it again. Unless you have a stalled pump, that takes several minutes and more likely up to half an hour.
How quickly it heats up again of course depends on boiler stat hysteresis and how much water is actually circulating. Obviously if you stick a bypass loop by the boiler its not a huge amount. However, in my case a long pipe run to a small radiator in an airing cupboard was more than enough to mean a 2-3 minute burn was required at the minimum. And frankly, any house that has its heating on, and requires no heat input for half an hour, is wrongly timed anyway. I have been sitting here for the duration of typing this, and my boiler has not fired up, yet the pump is running all the time in the evening.

Ok, at what point will a system with all TRV'ws and a master stat become exactly the same as a system with no stat and all TRV's?
Easy. When the stat is turned up beyind the ability of the TRV'd rads to flip it.
Result, one user adjustable contol that all by itself, renders the house essentially exactly the way I ran mine. Statless.
Guess why they have stats in the boilers chaps, and make them cycle...

No. I still don't see it.
On an ALL TRV'ed system, I'll buy that a poorly designed system equipped with a very short bypass COULD in theory - but rarely in practice - short cycle. It will NOT run the boiler continuously tho. If it does the bloody thing wil explode.! Thats why teh boiler has its stat... Equipping the house with a stat does NOTHING to remedy that in my opinion. Either the stat is set too low and the TRV's never do their work, or the stat is set too high, and might as well not be there at all. Finding some arbitrary finely tuned position and temperature setting for the stat is completely beyond the average home owner, and is far more likely to result in over use of energuy as he rams the stat open in frustration, and then faffs around with his TRV's.
A non statted sytem that detects a stalled pump is good, except how does it detect a stalled pump when the pump is off? It can't. So instead of boiler short cycling we have pump short cycling.
The answer os simple. All TRV's no ghouyse stat and one radiator that is not TRV'ed that has sufficient thermal inertia and water capacity to stop short cycling. Or simply put a bypass right across the longest pipe run. Sure, the pipe run is contributing to heatinbg teh house, but the situatin where th ehouse is warm enough, all rads are shutdown and teh bozo still runs his heating every day all day seems rather remote.
Most users can cope with the 'its bloody hot today, sparrows are wilting in teh park, I'll turn my central heating off'.
The iedal is obviously a separet zone in every room coupled back to the pump and boiler. TRV's are almost that, the only difference is that you have to rely on return temperature to tell the boiler its not needed anymore.

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Many people here have attempted to educate you on this point. You clearly do not understand my old chum. So it is best you just take it as it is.
Best stop digging yourself into a deeper hole, my old chum.
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No one has actually pointed out where it is said that this is not allowable.
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My old snooty uni chum, it is best to stop now before it's embarrassing for you.
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wrote:

While not wishing to get into a debate about what works and what doesn't and what is and isn't good practice, I took a look through the statutory instrument, the approved document to part L1 and some of the good practice guides. I drew the following conclusions:
- The statutory instrument talks in very general terms about requirements using words like "reasonable provision" and essentially empowers the secretary of state to issue Approved Documents which are not part of the legislation but guidelines..
- In the introduction to the Approved Documents it is stated that they are guidance.
"Approved Documents are intended to provide guidance for some of the more common building situations. However, there may well be alternative ways of achieving compliance with the requirements. Thus there is no obligation to adopt any particular solution contained in an Approved Document if you prefer to meet the relevant requirement in some other way."
The last sentence is in heavy type.
- In section 1.37 it states "requirements would be met". If this document were prescriptive then it would say "requirements shall be met". Likewise in section 1.38 it says "A way of demonstrating", not "the way of demonstrating" and "temperature control could be" not "temperature control must be". In section 1.41, referring to interlocks the word "should" not "must" is used.
- In section 1.46, an alternative way of showing compliance is to use Good Practice Guide 302. This does indeed suggest that room thermostats be used as part of a boiler interlock arrangement but also comments on boiler energy management systems as being suitable as well.
From all of this, I would conclude that room thermostats may be good practice and used as part of demonstrating compliance with Part L1, but I can see nothing in the Approved Document that mandates them and it is certainly a long stretch to say that not having one in a new installation is specifically illegal.
.andy
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On Sat, 13 Dec 2003 14:02:27 +0000, Andy Hall wrote:

What they want is the boiler to off, really off, when there is no demand for heat. There are many ways to comply with this, hence the "loose" wording of the documents.
Leaving power to the boiler and using the boilers output temperature stat or return temp stat to switch the boiler off doesn't, IMHO, comply with Part L1. Basically if the boiler can ever fire without there being a demand for heat it does not comply.
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A very good bottom line.
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Unless the outside temperature is maybe 15C +, there is continuous heat loss from the house, therefore continuous heat demand. I glad Andy's pointed out his interpretation of part L, as I did think I was technically non-compliant having no room stat.
(I take 15C arbitrarily, the sort of the outside temp I would turn the system off anyway. Other heat sources, people, TV's, cooking, solar gain etc can be enough to keep the house comfortable)
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On Sat, 13 Dec 2003 20:23:32 +0000, Steven Briggs wrote:

Andy's setup if *very* sophisticated and in the 30th centuary compared to most heating systems in the UK. I don't doubt that with such a level of monitoring and control very good effciencies can be achieved but those levels do not exist on the vast majority of installed systems.
The test is can the boiler fire to keep itself and/or a small primary loop warm/hot, if can then then, IMHO, it fails Part L1. There are many ways, from a simple room stat or flow switch to systems like Andy's, to achieve the desired result.
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