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.
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.
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.
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.
Have to agree with the NP. 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.
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)
The legislation does not support that level of detail. That is not to say that implementing a room thermostat is not a good practice, but I can find nothing more than a recommendation suggesting that one is a good idea.
In my mind the question is, what constitutes a demand for heat? TRVs typically reduce the flow to radiators rather than closing it off completely unless the radiator is grossly over sized and the room temperature overshoots from it or a heat gain from another room or perhaps solar gain. Good temperature control in the rooms where TRVs are fitted would be achieved by their reducing the water flow to the radiators such that the heat output balances the heat loss at the required room temperature.
The heat output of the radiator in the location containing the room thermostat where one is used has to be reduced to ensure that the rooms equipped with TRVs have reached their set point.
Once that has been achieved, the boiler is turned off if a room thermostat is used with a simple boiler which delivers zero or full output only.
There are, of course, room thermostats with proportional control which turn the boiler on and off on a relatively short time constant to control the average heat output so that it is reduced as the set point is approached; and thus it is possible, even with a basic boiler to limit temperature overshoot which is said to be a significant energy waster.
As I understand it, though, there is an overhead in terms of efficiency for each on/off cycle of a simple boiler which does full power or off. Presumably, this is not substantial in comparison with energy saved by the overshoot not happening otherwise there would be no point.
I think that that may be taking too simplistic a view.
Given that the plumbing and heating industry is still very conservative and persists in installing non condensing non-modulating boilers, a room thermostat may well make an energy saving with it. I rather suspect though, that this has more to do with limiting the size of the temperature overshoot that can happen with oversized radiators and TRVs, than of whether there are short burns of the boiler.
One of the referenced good practice guides,
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the fitting of room thermostats as part of an interlock scheme, yet mentions boiler energy management, modulating and condensing boilers only in passing, even though it is relatively recent. It seems to me that this is really an attempt to put a stick in the ground with the industry and to say that a room thermostat is part of good practice with a simple boiler.
However, modulating boilers, condensing or not are rapidly appearing, and even for the die-hard installer has some appeal because there is less commissioning to do.
It's also worth pointing out that it is quite easy for fairly sophisticated control capabilities to be built into the boiler as well. Most of this can be implemented in the firmware of the controller so from a manufacturing cost perspective is not a large additional factor. I suspect that the reason that more isn't done is because UK manufacturers have not had people with the skills to do the work.
For example, my own boiler has a very comprehensive set of controls and can have a number of additional sensors apart from those within the case.
On the input side, as a minimum it measures flow and return temperatures. On the output side, the microprocessor can control the burn rate from 3 to 25kW or off and the pump from 20-100%. Even with nothing else electrically connected, it will make a pretty good attempt at maximising its efficiency. If the heat demand is above the minimum 3kW then it will modulate the pump and burner anyway, so the issue of turning off altogether doesn't arise. In the range where some heat, but less than 3kW is required, it will come on for a short period, initially once per hour, measure the water temperatures and run until the heat demand reduces, then going off. The on period is remembered and adjusted so that the boiler is not coming on too much earlier or late than need be. I have seen the time between burns go out to as much as three hours with this hookup. During a normal day, it will have done a hot water cycle during this period anyway.
This is a fairly reasonable control system as it stands, but the manufacturer includes an outside temperature sensor anyway, which is placed on a north wall. It is then factored in as an input term to the controller, in effect providing a prediction based on the outside temperature. With this connected and operational, the control becomes rather better with an ability to adjust output before the house temperature changes.
Note that this is achieved with no room thermostat. From logs of burner operation, pump operation, water temperatures and internal house temperatures, the set points are achieved rapidly and without significant overshoot of inside temperature mainly through the modulating behaviour of the pump and burner.
I have added a room controller which is made by Siemens specifically for this boiler. Apart from time functions it has a temperature sensor for inside the house so that the boiler is presented with this information rather than just an on and off. The effect of adding this is mainly the convenience of a remote temperature control and even less temperature overshoot - now almost nothing. There is an installer setting whereby one can alter the relative sensitivity of this term and the outside temperature (loop gain controls if you like). In fact the defaults seem to work the best anyway.
So, I think that I could make a strong case to anybody who wanted to enquire that even without a room thermostat, I can achieve better energy use than a simple boiler with a simple thermostat because the minimum power output is very low and the boiler's built in algorithms do a pretty good job on their own.
The Approved Document and the referenced Good Practice Guide really only present *a* simple solution using a room thermostat for basic installations. Neither presents it as the *only* solution, and with increasing capability of boilers' own algorithms becoming increasingly part of mass market products, I suspect that these guidelines will need to be updated.
On Sat, 13 Dec 2003 18:20:50 -0000, "stuart noble" that the boiler doesn't know what the hell it's doing.
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.
[snip praise of technology way beyond the comprehension of most Plumbers!]
Andy, I didn't realise your MAN Micromat boiler was so clever. If only the UK industry would drag itself into the 21 century with some decent control technology. The cost of implementation is next to FA, a mid-range PIC or similar could do the job for a few quid. Even I could knock something together in a week or so's work, and I only dabble with PIC's and software occasionally. Mind, can you imagine your average Corgi optimising the PID parameters of the controller ;)
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.
The controller is manufactured by a Dutch company called Encon who appear to supply them to a number of German and Dutch condensing boiler manufacturers. I am not sure whether they also write the firmware but the copyright notices on the controller and the PC software to link to it has MAN Heiztechnik and Encon listed. You can monitor and log all of the inputs and outputs including the temperatures, pump rate, fan speed (relates to burn rate), motorised valve outputs and so on.
There are engineer's menus in the PC software for checking faults like ignition failures, running times, etc. and you can make changes within limits to some of the operating parameters than can't be reached from the front panel, but nothing that would compromise safety.
Exactly. I haven't looked in detail at the electronics but it is not sophisticated in terms of what's on the board.
The mechanical design is good in the sense that the major components like the pump, condensate drain, heat exchanger and internal pressure vessel plug onto the back panel and can easily be removed when necessary. Likewise the materials and build quality are of a very high standard and I suspect that that is where the main cost is.
Don't forget though that this part of the Building Regulations only apply when a new boiler is fitted either into an existing property or a new one.
My description of my own system was by way of illustration more than anything else.
My conclusion from looking through the Approved Document and the Good Practice Guide is that they are aimed at practitioners in the trade who are still installing conventional simple boilers and simple room stats because a) they understand them and b) they are cheap.
Therefore, given that that is the status quo, the point that struck me was that the authors are suggesting the marriage of the two as good practice because realistically that is what is often installed. They even refer to this as a minimum set of controls. With a simple boiler firing to full output or off and with simple bimetal thermostats, short cycle firing as a result of TRVs being virtually closed down is going to use some amount of energy which can easily be saved by hooking up a simple room stat.
However, even with a relatively simple modern condensing boiler is modulating to quite a low level and most that I have seen fire up at a level according to the amount of heat demand as referenced by the water temperatures. After all 3kW firing up for a minute once an hour is actually less than the pump uses.
My point was really that it strikes me that the Approved Document and Good Practice Guide make a point about the interlock thing because it can be easily achieved with what is often still installed today not that the authors are prescribing what *must* be done.
The legislation requires only that reasonable provision is made to save energy.
Once modulating and condensing boilers become the norm as it is suggested that will be the case within two years, the energy to be saved by interlocking the controls with a room stat is likely to be a lot less significant to the point where I suspect that using one will not make a whole lot of difference.
I am assuming here that time controls will indeed remain as they are which is to fully shut down the boiler and pump (notwithstanding overrun) when the heating period has finished.
Remember that with burner modulation the heat output goes down to a few kW to balance the heat loss so the residue of what we would be talking about would be on days when for *part* of the heating period boiler heat is required, but because of rising temperatures outside not for all of it. The number of days a year when that scenario happens in such a way that a very low burn rate of a few kW once or twice an hour is too much is very small. From an engineering standpoint at that stage it becomes very much a corner case to worry about switching everything off.
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.
The modve away from single stat installations to TRV'ed installations is there to reduce unwanted heating of unused or little used rooms, and allow better control of house temperature. The gains are potentially considerable.
Keeping a single stat is a complete nonsense, excepat in the one case mentioned - some idiot who runs his heating in the summer. In which case one would likley set the stat above the level where it would ever come on in winter, to make sure the TRV'sd actually do their work.
The short bypass loop TRV solution is IMHO arguably better than no TRV's, and in practice no worse than a single stat would up - and indeed may be better, because if the single stat is wound up with no bypass, the bloody pump will stall.
I am not aware how the flow swiych thing actually works, because no one has explanied how the flow switch senses deamand when the pump is stopped. And if it simply cuts the boiler, not the pump as it were, then its no different from using the boiler internal stat.
Precsiely. In the same way that I was able to install single glazing in a new build, by demonstrating overall energy efficiency.
The spirit of the regulations is to avoid uncessary boiler firing, not uneccessary pump action. Addong a single stat doesn't do anythung ecept in the case where the whole house is already warmer than the heating could actually make it, and the bozo has left the heating on..
Yup. All I can say is that teh gains from 'single stat in the kitchen' to 'all TRV's and turn teh stat up to max' were significant for me. It wasn;t ideal, but it worked pretty well for a few years.
I couldn't even use a single stat on my fan heaters now, because they heating requirements for each room and the heat flow between then is far too complex. AND they don't shut the flow down, because the stats control the fans, not the flow, unlike TRV's.
One does the best one can with available technology.
Ideally one would have a stat in every room, and a zone valve, and some temp sensors outside...and build a bigger version of what my car has - they call it 'climate control - but as yet, no one makes such a control box.
The cost to me to install, to save a piddly 50 quid of oil a year, would be immense. Not least in terms of wioring, which would be equivalent to a complete new lighting installation in complexity. Better savings are assured by simply turning the whole heating system off when not required. when I need heat, I simply slap the system on, overriding the time clocks, and in summer its set to 'always off' and I simply punch it on when the odd cold day turns up.
That depends on how much the house is insulated and draught free. You could fit an outside stat in a weatherproof box on the north wall. When above 15C (in your case) the heating is off. Then you have an interlock.
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