Are room thermostats out of fashion?

[IMM]

It requires the pump to turn to see if a TRV has opened up giving flow. A simplr timer can do this once every minute or so.

[IMM]

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.

[IMM]

You are confused.

[IMM]

Or heating the outside air when heat floats through the flue when off.

[IMM]

Gosh!

[IMM]

....he digeth much bigger hole for himselfeth...

[Andy Hall]

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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[IMM]

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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.

[Ed Sirett]

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.

[Ed Sirett]

Andy, the Baxi Barcelona is _such_ a poor design no ammount of tinkering 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.

[Ed Sirett]

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!

[Andy Hall]

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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[Steven Briggs]

Er yeah. Run times are gradually reduced as the weather warms up, then 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.

[Andrew]

Try

- seems to have a lot a diagrams courtesy of JAG++

[Andy Hall]

I think that the link should be

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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[Christian McArdle]

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.

[Christian McArdle]

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.

[Christian McArdle]

Yes, but this requires the occupant to turn the heating off depending on the weather/time of year (and many people won't). Why bother requiring the user to do this, when a simple electronic device can do it for them. with proper controls, you can leave your heating on 365 days a year without energy wastage. Many people do.

In any case, I really don't see the problem with adding an interlock to a TRV based system. Just put a flow switch after the bypass/always on radiator and have it cut the boiler demand power. Set the pump to run for programmer CH on. Job done.

I would be surprised if the court (or building control department) decided that a reasonable provision is a system described in the approved document with an important feature missing. OK, a totally different system not directly comparable, but not a suggested system made less efficient. The approved document describes a suitable simple modification to an all TRV system that seems perfectly reasonable, reliable and easy to implement and prevents the wastage of energy.

Christian.

[Andy Hall]

I certainly do that because it isn't necessary to turn it off. However it doesn't require a room stat to achieve that.

This was part of my point. During the heating season and during timed heating periods of the day, a modulating boiler will be supplying heat adequate to balance the heat losses from the building. The TRVs should be partly open around the set point and the boiler running continuously at a low modulating level or turning the burner off because it is producing heat at a greater rate than required. However there is still a demand for heat - just a small one. If a room stat were used in this situation, it would have to be set for a few degrees above this operating temperature or the boiler would not be able to meet the demand.

If you consider the electricity used to run the pump, it is around 80W or so. If a boiler modulating down to 3kW comes on for a minute an hour then that is less energy.

It's in the same league as a light bulb and how many people can say that they never leave lights switched on when not required.

If you also contrast all of this with a condensing boiler vs. not the energy saving is substantially greater,

My point was really that much better energy management can be achieved through the use of a modulating and preferably a condensing boiler. Given this scenario, adding a room stat is down in the noise in terms of being worthwhile.

Therefore, for it to be suggested that a room stat is mandatory is stretching the point from the legislative, economic and the ecological point of view.

In the case of conventional, full output on/off boilers, possibly. The focus is demonstrably on the wrong issues.

.andy

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[Christian McArdle]

Ah, but there is no requirement in approved doc Part L1 for a room stat, just a boiler interlock. It suggests in a non-exhaustive list that room stats and flow switches are appropriate for this use.

The addition of a flow switch interlock to an all TRV system would have absolutely no bad effect (beyond the small installation cost) and much good effect.

The pump would be running all the time, whether the flow switch was installed or not. The flow switch just causes the primary water to cool down if all the TRVs are hard off. If they are passing by at all, then the modulating boiler will be allowed to fire at the low rate. The flow switch doesn't force a modern low modulating burner to become cyclical.

The 80W from the motor can be saved by additional electronics to cause occasional pulsing every ten minutes or so, when the flow switch shows no flow (I see no requirement in Part L1 to do this, however). It would also be possible to incorporate the entire lot into a combi style boiler, although I doubt any manufacturers do.

Only if you assume that people actually turn off the system when it is warm outside. You can't make this assumption.

Christian.