Are room thermostats out of fashion?

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writes

Very few condensing boiler now do not have load compensation control, at modulates the burner. The problems is that when you want full output at all times, as when heating a thermals tore or quick recovery cylinder, most can't do it. Some boilers do have terminals that when switched the modulation is turned on or off. Some boilers, the Baxi is one and see current thread on this, can either be full power or modulate, by only be removing 3 jumpers from the control board.

Not in a million years. They need idiot proof controls. This is where well specced combi's score well. They thinking is done for them and they just connect up the pipes.

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All of which is very disappointing. If the boiler is going to have a board of electronics with a microprocessor to read the temperatures and control the modulation, then with virtually zero extra cost it could directly monitor the cylinder temperature or cylinder stat and operate the motorised valve. Given that, the boiler could be wound up to full power for the hot water/thermal store cycle and back down to modulating for the heating circuit when this is complete. All of this can be accomplished with the controls available today, and simple ones at that. In an existing property, there is almost certainly wiring that will handle it all as well.

.andy
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writes

That is the idea. Some boilers have this function, but only a few.

One way of fooling the boiler to ramp up to full power, is to parallel up two wires from the return pipe thermostat temp sensor at the terminals at the board. Find out what temps = what resistance. Then switch over to either full resistance or none, whichever tells the board that the return temp is cool when it isn't. Then the boiler us full on, and should not interfere with the control logic of the safety circuitry. But the makers would probably not like this.
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On Sun, 14 Dec 2003 16:57:44 +0000, Andy Hall wrote:

with the electronics could redeem it.
I went to one the other week: The customer was reporting smell of un/burnt gas/gas fumes in their utility room. Turned out the the drain plug on the condensate trap had split in half and was hanging off. Damp flue gasses were filling the room. [How the f**k did they manage to get CE or GC type approval?] There was no water on the floor because these boilers don't actually produce condensate, which is just aswell since when they do (at start up) it finds it way out by every route _except_ the trap.
Such boilers (chosen by a large installation company) have held/put back the industry many years.
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Ed Sirett - Property maintainer and registered gas fitter.
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On Sun, 14 Dec 2003 18:52:12 +0000, "Ed Sirett"

I'm amazed by this.
Clearly whoever designed this or more realistically selected the off the shelf components for it just didn't pay attention to detail.
I would have thought that since the prime requirement is safety, any component that is, in effect in the flue pathway or can become so, should be thoroughly checked for suitability. Probably this component has a cost of a penny or two.
In looking through manufacturer installation guides when boiler selecting I found one (can't remember who now) who has the electronics board near the top of the appliance close to the heat exchanger. Great idea for reliability.
I was distinctly underwhelmed by the build quality of the Glow Worm Fuelsaver that I had before the present boiler. After removing the inside cover around the burner to replace the thermocouple, the remaining metalwork has razor sharp edges and corners. That's just sloppiness and there is no excuse for it.
Clearly the manufacturers are not employing the best from the engineering profession......
.andy
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On Sat, 13 Dec 2003 22:24:27 +0000, Steven Briggs wrote:

Right now most of the combi market have modulating burners and some sort of anti-short cycling control as standard, so do all most condensing models and many system boilers. Installing middling and low tech boiler which only just scrape into Part L compliance is not part of my game. (Eg. potterton Profile 'L'/Kingfisher IIs etc)
In one or two installs for older people I have not tried to upgrade to a programmable thermostat because user confusion would undoubtedly cost more energy (mine and my van's fuel) that what it might save. However these installs have most/all TRVs and a boiler with in built anticycling controls.
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Although the approved documents propose methods that are not totally set in stone, you still have to implement a suitable level of compliance to the original intent. If the approved document says that you need a boiler interlock, then you can implement a system without one provided you can prove with calculation or measurement that your alternative system has the equivalent level of safety/energy efficiency or whatever. I don't see anyone proposing to install joists with less that those specified in the approved documents without further calculation. There are plenty more approved documents with suggestions that no-one would contemplate breaking, so why are people thinking that Part L1 is optional. No-one states that the SEDBUK 'D' boiler restriction in Part L is optional, so why the interlock? Yes, the approved documents are optional. No, you can't just ignore their contents without implementing their intent in another way.
In order to get the building regulations approval, you need to get your alternative system examined and passed by the building control department.

I would suggest that mostly closed off TRVs are still counted as a demand for heat. However, there are situations when there is absolutely no demand for heat. This can occur during the middle of the day in marginal conditions, or in the summer. The control systems should be sufficient to prevent boiler firing during these times. You can't rely on some spod to do it for you (who may have limited mobility or understanding of the system), when it can be done so easily by electronics.
Christian.
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On Mon, 15 Dec 2003 09:23:27 -0000, "Christian McArdle"

.. but it doesn't - it merely suggests it as good practice.

That's simple enough to do.
If the boiler manufacturers were doing their job properly, it would be a non issue anyway.

Of course not, because there are sound engineering reasons to back up the practice or the use of calculation.

I didn't say that it was optional. However, some of the methods described as "best practice" fade into inignificance if a properly designed modulating boiler is used. The best practice has been thought out assuming the simplest and least efficient boiler is used. Even the slothful UK heating industry is gradually moving beyond that point and the return from using systems appropriate for older technology heating equipment becomes less and less.

True, but there is no specific legislated requirement. It states that very clearly at the start of the Approved Document.

One can always refer back to the statutory instrument.

The boiler is going to fire numerous times during the day anyway at full power output to recover the hot water cylinder, even in the summer.....
In comparison to everything else that can be done, preventing a boiler from firing for a minute or two an hour on a few days of the year is not a big winner in terms of energy saving.

.andy
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I still don't understand the objection to adding a simple flow switch to the radiator circuit. It costs very little, makes the system explicitly compliant with approved document L1, is simple to wire and prevents your primary circuit being hot 24/7/365. (Unless you sit by the controls and act as a manual room stat, turning your system on when it gets cold outside).

I read the document as being suggestions of what might be considered reasonable provision, rather than best practice. You are required to make reasonable provision. If it considers system 'A' explicitly with feature 'B' to be reasonable, then I can't see how system 'A' without feature 'B' or an alternative to it can be considered reasonable.
The system without this feature depends on user intervention to remain efficient. This appropriate user intervention may not be apparent when you sell the house to someone else. It relies on the user to understand that the system uses considerable energy even when the house is not being heated.
Christian.
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On Mon, 15 Dec 2003 10:47:18 -0000, "Christian McArdle"

Easily. If I can demonstrate that I can substantially exceed the energy saving of adding room stats to old technology boilers by using a newer technology boiler, then that is more than reasonable.

That assumes that the boiler is a simple on/off type which is the assumption of the whole document and those referenced by it.
If the game is changed by using a newer and better technology, then those assumptions are no longer the case in the overall scheme of things.

It's only considerable in the case of an older style simple on/off boiler.

.andy
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I don't get that assumption at all. Why do you think that turning off the boiler when no heating appliance requires heat is specific to an on/off type boiler? It is simple to do, cheap and effective to turn off the burner when no heat is required, whether it is a modulating type or not. OK, an old open flue boiler suffers more from short cycling than a modulating condensing fanned flue boiler, but the primary circuit losses are the same for both.
Obviously, with analogue TRVs and a modulating boiler you have the advantage that the system can modulate down and bumb along nicely. However, there are still savings to be made when the system really doesn't require heat, and by a very simple, cheap and effective system, too. The cost of a flow switch is very small, and it is wired up in the same way as a room stat, just requiring to be inserted into the correct bit of pipe. (i.e. after the bypass). The pulsing pump system is optional (but could save quite a lot of cash, if you run an 80W pump 24/7).
Christian.
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On Mon, 15 Dec 2003 12:33:09 -0000, "Christian McArdle"

I didn't say that it was specific, only that it is much more worthwhile.
On a conventional on/off boiler, especially one with large thermal mass heat exchanger and with natural draught flue, there are numerous inefficiencies:
- It isn't modulating - It isn't condensing - Heat convects through the flue after firing - There is a lot of hysteresis in the water temperature coming up once the burner starts. - It operates at a consistently high temperature.
All of these add up to an overhead each time the boiler is fired up, so I agree that for that scenario, preventing firing when there really is no heat demand is desirable because the energy saved may be significant.

They are not because the operating temperatures are different.
During the winter heating season the system will be operating in a condition when some level of heat is required to compensate the building heat losses during the timed heating period. There is always a demand for heat, so there is no reason to interlock firing. The burner may turn off because its minimum heat output is less than required, but there remains a demand. At this stage, the flow temperature may well be in the 40s.
During the spring and autumn the duty cycle of on time gets less and less as the heat requirement reduces and with a properly designed modulating boiler you end up with very short burning periods and very low circuit temperatures except during hot water cycles.

Exactly.
There are still *some* savings perhaps, but I think that it is a matter of keeping these things in proportion. There is really no point in saving 50W of energy if there are other factors that result in the waste of hundreds of watts or more elsewhere.

Flow switches are cheap, I agree, but they are not very accurate or sensitive. If you consider that TRVs around the set point should be partly open because they should be allowing some amount of water through how do you determine the cut off point? A bypass around the switch could be used, but I still wonder about the sensitivity.
I suppose a flow sensor would be better, but then that's a lot more expensive. In any case, the boiler should be able to deduce the flow because it knows how much energy is going in and the temperature drop across the heat exchanger...

.andy
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Certainly, if the boiler can work it out in software, all the better.
Christian.
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Not if my shower pump was anything to go by. The flow switch activated even for a couple of drips. For the CH application, you would want it at the sensitive end, to take full advantage of the TRV's analogue nature.
The alternative is to put the flow switch on the bypass. However, I reckon this wouldn't be as good. Firstly, it makes the control wiring more complicated. Secondly, a correctly configured bypass would actually operate slightly when TRVs were mostly closed, in order to reduce noise in the system. You wouldn't want to cut the burner under these conditions.
Christian.
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Christian McArdle wrote:

Ok, given that I have very few TRV's, and instead a series of fan assisted convectors, how do you think I should control THAT lot :-)
Wire OR all the room stats together to control the pump? And then what about the rads with TRV's on?
Blimey, the installation cost in both cash and energy would exceeed savings over the lifetime of the system...

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I'd have thought that fan convectors would have simplified matters.

If I had several fan convectors and several TRVs and didn't want a room stat in the radiator part of the house, I would:
1. Have a programmable room stat for each fan convector (basically because you can, and it gives separate timing for rooms likely to be used differently, such as kitchens and conservatories, where such heaters are typically installed).
2. Put all the convectors on a separate convector zone (or unzoned, if the convector has an internal valve to prevent water circulation when off).
3. Put all the TRV radiators on the unzoned circuit, with flow switch. Any bypass is before the radiator circuit
4. Run boiler when either HWC or convector zone valve (internal or external) opens, or when flow switch activates.
5. Run pump either continuously, or when any zone valve or flow switch opens and pulsed every ten minutes when not.
Alternatively, if the convectors have internal valves, an alternative is to just treat them like a TRV radiator, in that they would cut the flow when off and can activate the boiler using the flow switch, just like the radiator. This would be very simple to wire, as the signalling to the central heating from the convector is simply through the water pipework. No electrical connection is needed.
Christian.
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Christian McArdle wrote:

No, they re installed throughout. They all have stats, but not on teh water. On the fans :-)

They are on a seprate zone, altho it has some TRV rads as well.

Flow switch won't work. They don't cut the flow, just the fans :-)

Thats what happens now. HWC or that zone comngh in starts boiler - but its purely on timoimg for convector/TRV zone...

Pump is run continously. But that is what you said was a nono?
Right now, the water curculates all teh time, and teh boiler jts cuts in when its temp drops.

Well ... they don't have internal valves..

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Obviously, flow switch will only work directly on the convectors if they have internal valves.

You could increase efficiency by having boiler connected to a TRV zone flow switch or'ed with the convectors when any heater is active (either from the thermostats via a relay, or any output contacts provided by the heater).

I can't find anything that says the pump needs an interlock, only the boiler. It is sensible to stop the pump, if possible, though. I'm not sure I'd want mine on all the time. Electricity is four times the cost of gas, as well. However, stopping the pump would require some electronics, or it won't be able to start again. The electronics just consist of a device to pulse for two seconds every ten minutes. Then the pump will run for 2 seconds every 10 minutes OR whenever the boiler pump output is active.
Christian.
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I should, perhaps, reiterate that the pulsing will only affect the radiator circuit, in that it will look to see if TRVs have opened during the pulse. In the event of the fan convector (or HWC) demanding heat, the boiler and pump will start immediately. The TRVs (and hence boiler) will modulate down in normal action, so only when the demand for heat has dropped very considerably, will the flow switch close and revert to the pulsing pump action. In this event, large amounts of heat are unlikely to be rapidly required, and the 10 minute period is unlikely to be problematic.
Christian.
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Dave Liquorice wrote:

The boler can never fire without demand for heat if its equipped with a thermostat. I know of none that are not.

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