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How often are the text books up-dated, and who reads the new books?

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Born 1951, only one house in local streets had central heating, as a lad I remember being shown the boiler in the cellar, but can't even remember what fuelled it.

My parent's first central heating was rather basic, a radiator added to the DHW supply in one bedroom, then a proper boiler to replace the Aga, it was designed to warm the house before anyone got up to light the fires, ran on the C Plan, and had a single wall thermostat in the hall, no TRV's and no thermostat on the DHW tank.

The big change was the condensing boiler, designed to extract latent heat from the flue gases, the big change was to do that, the boiler had to modulate, (turn down) and this resulted in needing analogue thermostatic control, until that point on/off was good enough, it also required a by-pass valve, and was why the TRV became the main control rather than the wall thermostat, but the control systems that went with these new boilers were rather expensive, like the Honeywell Evo Home, the price of which has not followed inflation so today we forget how expensive the Evo Home was on its release.

But the home has also changed, with double glazing and then improved double glazing, and the need for radiators under a window is now not there, but we tend to not have furniture in front of windows, so it is still somewhere a radiator can go, and not stop putting furniture against other walls.

The whole idea of central heating was all rooms warm, however today we look more to warm as and when required, the boiler may be central, but the heating is individual for each room, and the old Evo Home idea is now being done by so many more firms, with the likes of Drayton Wiser, but this has also resulted in some problems integrating with older installations.

My parents put in a whole new central heating package, part paid for with a grant, and to put it bluntly, it did not work. I did get it working near enough A1 in the end, but as installed it was a mess. Some clear errors, like a power shower from a combi-boiler, that actually broke the law. Which shows what a bunch of cowboys fitted it. But the other problems were more shuttle. All lock shield valves wide open, so that was the start point.

But this is where I had a problem, as I did not really understand what goes on, so getting the water to flow through all radiators OK, but control was a real problem. I had read the books, saying do not put a TRV on the radiator in the room with the wall thermostat, I know now that's not the case, but I tried to adjust the hall radiator again and again, and either hall OK and rest of house cold, or rest of house OK and hall cold, so at this point it was a clutch as straws point, and in spite of what the books said, I fitted a TRV on hall radiator, Bingo as sister Boniface says, at last it worked.

Sitting back and thinking about it, the TRV allowed the radiator to heat up fast and recover the area temperature from very low to nearly comfort fast, but then closed, so nearly comfort to actually comfort took a lot longer, so it kept the boiler running longer, and allowed it to heat whole of the house, and for the first time we got warm radiators rather than hot or cold radiators, as the TRV's were doing their job, and the boiler was actually modulating, and gaining the latent heat as it should, and the rooms were within a degree of their setting, by this time electronic TRV heads fitted, as part of the earlier attempt to get it running, they also helped to set the lock shield valves, if the current exceeded the target clearly they needed closing a tad. And the hysteresis had near enough vanished, the only problem was the TRV anti-hysteresis software was OTT, so 7 am set to 22ºC and at 8 am set to 20ºC to counter the software built into the Energenie TRV heads.

At last, sorted, however, moving to new house same method did not work, and it became clear, I needed multi-thermostats, the main problem was the hall cooled too slowly, so adding a second thermostat to living room, helped, no good simply moving existing one, as open fire in living room, and lighting that for the ambiance would mean rest of house cooled down.

But still one cold bedroom, with North facing walls, so thought simple, new Wiser hub can have multi-thermostats, either TRV or wall, so swap the eQ-3 TRV for a Wiser one, but yet another problem I had not considered, the radiator is against the North wall, so the TRV on the radiator until heating is running, records a temperature lower than the room in general. Wall thermostat will cure that, if I decide it need curing, as the wife likes the bedroom cool, so it may not be a problem, we will find out this year.

But again nothing in the books to say with the use of TRV's radiators are better fitted on an internal wall. It seems the books have not kept up with the changes as to how we heat our homes, but there are it seems two very different methods, heat rooms as and when required, or heat the whole home even if rooms not used, the latter I could not afford, but it does seem to be the method used with heat pumps.

Due to living through the winter of discontent, I would not want heating which relies on grid electric supply again. My central heating is battery backed, and with solar, we stand a good chance of not needing to light an open fire with a power cut, and want it to stay that way.

The size of back-up generator required to run a heat pump, puts heat pumps out, plus the cost, specially now need Derv not 35 sec gas oil for generators, so government has priced heat pumps off the market as a result. Not worked out how a generator is a diesel engined road vehicle?
 
The big change was the condensing boiler, designed to extract latent heat from the flue gases, the big change was to do that, the boiler had to modulate, (turn down) and this resulted in needing analogue thermostatic control, until that point on/off was good enough, it also required a by-pass valve, and was why the TRV became the main control rather than the wall thermostat
I don’t think that is quite right. I have a condensing boiler (Ideal minimiser SE50) 25 years old and non-modulating. No bypass valve. It’s W-plan with fairly typical ratio of rad area/boiler output, and in CH mode it never reaches control-stat setting (70-75°C), so it wouldn’t modulate even if it were that type. Most rads have TRVs (non-smart), roomstat in the hall. No noticeable variation of room temperature. The boiler only reaches control-stat setting in HW mode, when it cycles 2-3 times before the cylinder stat is satisfied.

I’ve noticed in several threads references to need for a large turndown ratio, even to the extent of implying the system won’t work properly without. I’m sceptical and don’t think it makes more than a marginal improvement.
 
I don’t think that is quite right.
I am an electrician, not a heating engineer, so could have made an error. However, back to basics of the condensing boiler. The steam in the flue gases is turned into water and in doing that the return water is pre-heated. So the return water needs to be quite cool.

So the sequence of events is as follows.
All TRV's fully open and the boiler fires up, the water is even distributed due to the lock-shield valves being set correctly.
Water returns, having been cooled by the radiators, so moisture in flue gases condenses, releasing the latent heat.
As the room heats up, the TRV's start to close, and water is diverted to those still open.
The pressure increases as more and move valves close, so the by-pass valve starts to lift, allowing hot water to return to the boiler.
The boiler senses the return water getting hotter, so it turns down the flame height (modulates) until it can't turn down any more.
At this point, the boiler uses a mark/space ratio turning the boiler off/on/off etc, further reducing the output.

But it can't turn the boiler fully off, so we have a wall thermostat in a room with no alternative heating, no doors to outside and on the lower floor, to turn the boiler fully off on warm days. However, once the wall thermostat turns the boiler fully off, when it turns back on again it does so at full output, so the return water will be too hot, and until the boiler has readjusted the output, it will not be gaining the latent heat.

So this can be improved by using an analogue thermostat, which turns the heat output up/down rather than on/off, like the OpenTherm, but then the algorithms are well over my ken.

However, I am sure you can see, unless the boiler can modulate, it can't work as a condensing boiler. In this house, my boiler does not modulate, it is either on or off, the main problem with that is the hysteresis it causes, but oil boilers can't be controlled in the same way as gas, they can modulate, but not to the same extent, so the TRV's don't work quite as well with oil boilers, but they do still work.
 
What has that massive diatribe got to do with text books?

Oh I see, it's the first chapter in yours Eric? :)
 

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