Independent control of two heating zones how?

[JohnW2]

No, of course a bolier can only run at one level which is why it will run for the highest demand and the second zones valve will compensate.

Quite so.

If such a law exists then it cannot possibly insist such an impossible task is performed. The first time it is exercised it will laughed out of court by the technical experts. ... Im sure that Eric is misunderstanding the detail of any such a law.

I strongly suspect that, in a manner which he is often guilty, eric is probably confusing Approved Document L ('guidance') with Part L of the Building Regs ('the Law), since the only (very vague - absolutely nothing about any specific detail) things that 'the Law' (Part L) says are ...

Kind Regards, John

 

[bernardgreen]

I think selecting boiler size is often to satisfy DHW rather than size of house,

That applies especially to combi boilers, as much as 48 kW to provide adequate hot water for showers and then as low as 3 kW to keep the house warm. If there is a domestic combi that can modulate down from 48kW to 3kW ( 16:1 ) I would be very surprised.

 

[ericmark]

I had indeed read the approved document, and had also noted when looking for a new house how many seemed to have two zones which seemed to be controlled with a valve which is either open or closed.

I can see the point is using a motorised valve as I have found with this house TRV's never seem to fully close, even set to 16°C I have found a radiator warm when heating DHW when the room is at 20°C. However I have also noted the natural heat transfer within a house, after my dad died my mother only used the lower floor, so heavy curtain put up around the stairs and all upper floor radiators turned off. However rooms never cooled to below 16°C the heat in lower rooms always kept them warm, plus the central heating pipes under the floor boards.

So unless insulation is placed between the floors, allowing rooms to cool when not used is rather limited. Also we lived in a semi-detached house where the neighbour failed on mortgage payments and was re-housed. The year where we had an empty house our fuel bill jumped up, again no insulation between the two houses, and even less room to room in a single house.

However I still use programmable TRV heads in the hope of reducing bills, and unused rooms are turned down, but in the last house I noted the wall thermostat was using a mark/space ratio to stop the temperature from over shooting, I was by this point sure we were moving, so did nothing but observe, but it did seem the boiler was running with very little modulation because of being turned off so frequently.

 

[JohnW2]

That applies especially to combi boilers, as much as 48 kW to provide adequate hot water for showers and then as low as 3 kW to keep the house warm. If there is a domestic combi that can modulate down from 48kW to 3kW ( 16:1 ) I would be very surprised.

I see no fundamental reason why a gas valve could not achieve that - but if there were a problem, I suppose it would be possible to have a second, much smaller, burner.

In either case, it probably would not be all that efficient to have a very small flame heating a relatively large heat exchanger (with relatively high thermal mass), but I suppose that, with two burners, each could have its own exchanger - but that would then essentially be two boilers in one case!

Kind Regards, John

 

[bernardgreen]

I see no fundamental reason why a gas valve could not achieve that

The valve can but the combustion chamber cannot operate safely unless it can reduce the area of flame.

In simple terms when the velocity of the gas and air mixture entering the combustion chamber falls below the velocity of combustion then the flame can pass back through the nozzle(s) to the mixing area. A similar action happens when the gas supply to a Bunsen burner is slowly reduced. At some point the flame "pops" down the tube and a an inverted flame burns at the end of the gas jet.

Error corrected

 

[JohnW2]

The valve can but the combustion chamber cannot operate safely unless it can reduce the area of flame. .... In simple terms when the velocity of the gas and air mixture entering the combustion chamber falls below the velocity of combustion then the flame can pass back through the nozzle(s) to the mixing area. A similar action happens when the gas supply to a Bunsen burner is slowly reduced. At some point the flame "pops" down the tube and an inverted flame burns at the end of the gas jet.

That's all true. Not only with bunsen burners, but, in a similar fashion, I imagine that most up us have seen the flame of a gas cooker 'ring' 'jump back' from where it should be (above the burner) to actually burning at the jet (albeit not 'inverted'). It was really that which made me think that 16:1 might well be ('safely') achievable, since no matter how low one turns a gas ring control (and one can usually turn them down to 'very low'), I've never seen the flame jump back to upstream of the jet orifice.

Anyway, as I also said (in the rest of my sentence, which you didn't quote) "....but if there were a problem, I suppose it would be possible to have a second, much smaller, burner." - by which I meant a much smaller jet, designed for the low velocities in question.

Kind Regards, John

 

[bernardgreen]

My error about inverted flame removed.

I've never seen the flame jump back to upstream of the jet orifice.

The flame cannnot go back past the jet orifice because, upstream of the jet orifice, there is only gas. Without air gas cannot burn

 

[JohnW2]

My error about inverted flame removed. .... The flame cannnot go back past the jet orifice because, upstream of the jet orifice, there is only gas. Without air gas cannot burn

True, provided the pressure at the upstream end of the jet is above atmospheric pressure - but suppliers and regulations appear to take on board the fact that, under certain circumstances, that may cease to be the case - in which case one will get an (as you said, before you crossed it out, "inverted") flame at the upstream end of the jet ... I imagine that, like me, you saw an experiment in school that demonstrated that air could 'burn' in an atmosphere of gas (with a flame), just as gas can burn in an atmosphere of air!

Kind Regards, John

 

[bernardgreen]

The flame detection sensor system will detect when the flame leaves the combustion chamber and it will ( should ) then cause the gas valve to shut off the gas,

 

[ericmark]

I had not thought of the simple gas ring, which can't as far as I am aware use a mark/space ratio to further reduce output, so to melt chocolate one has to use a bowl of hot water, where with the induction hob the control is far greater so you can melt chocolate direct.

However why the gas boiler can't output the fact it has had to switch off I don't know?

If the mark/space part of the gas boilers control was assessable then one could have independent on and off controls, if a thermostat turns on the boiler and limit of modulation turns it off, then it will remain running until most of the TRV's have closed modulating as intended, then remain off until the selected room has cooled enough to restart the process. There may be other methods, but aim is to get every room to selected temperature, then turn off boiler, and putting the thermostat in a room selected as average heat loss for house, heating would turn on again once there was a chance it can do a reasonable cycle.

Where the boiler is running between max and min output you want a seamless control modulating the TRV's and boiler, but once boiler is at min, it's not that cold outside so heat loss is lower and for system to turn off for a few hours is not really a problem.

Maybe restart could use time? traditionally we would light a fire, and allow it to burn out over night, on a really cold night we may bank down the fire, but in the main we allowed it to burn out, then if cold next day we would relight it. We have never tried to maintain one temperature day and night, so why do it now?

 

[JohnW2]

We have never tried to maintain one temperature day and night, so why do it now?

Quite so.

... but who is 'doing it' (or proposing to do it) 'now', and why?? Unnecessary maintenance of the same temperature 'day and night' sounds like the antithesis of 'energy conservation'!

Kind Regards, John

 

[ericmark]

When dad had central heating fitted, there were TRV's on living room, dinning room, landing, and three bedrooms, these did not have the option to set time, the kitchen and wetroom had towel rails with no TRV, and the hall had a wall thermostat and no TRV on the large radiator, and airing cupboard also no TRV.

There was a time switch which turned whole heating off/on.

So lets assume bed time 10 pm and we get up at 7 am, and we live in the main downstairs. So bedroom not used after 7 am so heating can be turned right down to say 14°C so will not take too long to warm up when required, so at 9 pm we switch the bedroom to 18°C and we can also turn the living room down to 14°C over night, dinning room can be turned down earlier say 8 pm, landing just wants chill removing so 16°C is ample 24/7.

The hall again transfer between rooms only so 16°C is ample. Setting timer to continuous, but is does not work, for rooms to heat boiler has to run, so the timer set 7 am to 8 pm and 10 pm to 5 am, this is so the hall will cool before the set times for heating to start, so when the TRV's call for heat the boiler is running. It did in a way work, but hall was either too cold or too hot, turn the lock shield valve down and rest of house warms up, but when front door opened hall cools and takes hours to reheat, and kitchen gets too hot, turn the lock shield up and hall warm but rest of house cold.

So I added a TRV in the hall set low so when front door opened the TRV would open and start to reheat hall, but before hot enough to turn the wall thermostat off, it would turn down so giving rest of house time to warm up. OK it worked within reason, but far from perfect. And when dad died and we moved in to look after mother, we wanted to live upstairs, changed the program on the TRV's but rooms upstairs tended to always be on the hot side at night, so set time switch to switch off all heating at midnight.

Rather surprised how slow the house cooled however mother living down stairs and down stairs cooled quicker than upstairs, so fitted second wall thermostat was intended to be in her bedroom, but could not get RF to work at that distance, so fitted in kitchen, most days it did nothing, but if really cold would bypass the time clock and turn heating back on.

It was never a good system, which is why I became so involved with how it worked, our own house had one programmable thermostat in centre of house, and non programmable TRV's upstairs to stop bedrooms getting too hot, it worked and had worked for 30 years, so never thought about central heating other than change the batteries start of each winter.

Dad's house has a modulating combi boiler which I don't think really modulated, the hall thermostat had built in anti hysteresis software which means as the target temperature was approached, it started to switch off/on so it did not over shoot, this resulted in the boiler not having chance to modulate. Hind sight should have used a wired thermostat which did not have anti hysteresis software, but central heating installers cut off the old wires to wall thermostat. The new Hive TRV heads would have likely worked, but they were not on the market then.

OK house now sold, so all academic, however I would still like to work out how it should have been done. Think Hive would have been best for this house, however it does not have volt free contacts so would involve relays, so went for Nest Gen 3 which had added bonus it would work with the programmable TRV's taken from dad's old house.

We were going to rent out our original house, and likely it would need the boiler changing, so was looking for what and how to upgrade that house, but now favouring selling it, saw with father-in-laws house how we spend money getting central heating running A1 and the new owners just ripped it all out, so if selling then doing nothing to central heating.

Still have daughters house to do, but two up, two down so no complex control required. Son is already using Nest Gen 2 and he will just do his own thing, other daughter seems to work OK so likely she will not change it. But would still like to learn how it all should be done.

 

[JohnW2]

So lets assume bed time 10 pm and we get up at 7 am, and we live in the main downstairs. So bedroom not used after 7 am so heating can be turned right down to say 14°C so will not take too long to warm up when required, so at 9 pm we switch the bedroom to 18°C and we can also turn the living room down to 14°C over night, dinning room can be turned down earlier say 8 pm, landing just wants chill removing so 16°C is ample 24/7.

As I said before, it's a bit ironic that, in the context of such a discussion, one should be talking about usage patterns which surely represent anything but 'energy conservation'.

I realise that 'the Law' (i.e. Part L of the Building Regs) can only consider the design and construction of a building and its heating system and that (since we don't live in a 'police state') cannot control how householders choose to use their heating system, but to leave heating 'on' (even if 'turned down' a bit) for long periods when not 'needed' (seemingly, in the case you cite, around 14 hours per day 'upstairs, and maybe 8-9 hours per day 'downstairs'), simply so that the areas do not 'take too long to warm up' when needed is surely the antithesis of 'energy conservation' and, I would have said, not really compliant with at least the spirit of the law - particularly L1(b) of Part L. If the law requires that the systems should "...ensure they use no more fuel and power than is reasonable in the circumstances", the law probably also assumes (intends, hopes!) that householders will not negate that by engaging in energy-wasting usage practices?

In my house, I have 'frost control' which will over-ride anything else if the temp in any zone falls below about 5°C but, other than that (and unless there are extremes of weather conditions), when heating in a particular zone is not required, it is turned off (not just 'down') - and it very rarely takes more than an hour or so to 'warm up' the zone when required (as you've said, under normal circumstances, temperature in a house is surprisingly well maintained, particularly 'upstairs') - and I'd be surprised if that practice doesn't use a lot less energy than would be the case if we kept zones 'warm' when they did not need to be heated.

Kind Regards, John