Independent control of two heating zones how?

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Not put in plumbing as it's an electric question, assuming boiler is OpenTherm so the thermostats will be modulating thermostats, how do you connect two modulating thermostats to a single boiler as required now by law if house over a set area?

I can see how to use two mark/space thermostats, but they are old hat now, so how do you connect to modulating thermostats to same boiler?
 
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Assuming both modulating thermostats can be connected to one boiler

If one modulating thermostat is asking for 50% modulation and the other is asking fo 99% modulation then what modulation level does the boiler adopt.

Two modulating thermostats suggests two zones which suggests that valves may be needed.

Maybe the two zones can share the boiler using TDM ( TIme Division Multiplex )
 
I know with things like Tado and EvoHome the TRV heads tell the thermostat/hub what heat they require then the thermostat tells the boiler, however not sure if that can be regarded as independent? And also it means boiler must be OpenTherm enabled, Worcester bosch is not OpenTherm and it has a single thermostat which does not as far as I can tell connect to the TRV heads.

Hive is an odd one, does not have OpenTherm it simply switches off/on, when the TRV's need heat it sends a "heat on demand" signal that causes the wall thermostat to switch on, even if the room it is in is over the temperature set, so the set temperature on the Hive wall thermostat is really a fall back temperature and if set low then each room would be independent and the boiler would work on the return water temperature until all Hive TRV's are satisfied, as to if that would be considered independent in law is another question.

Nest is OpenTherm but has an odd connection to TRV's, it has a follow command, so if you alter the Nest dial it also alters all TRV heads set to follow, which to my mind is not independent control.

Using programmable TRV heads the rooms are independently controlled for both time and temperature as long as a wall thermostat is not fitted, as soon as you fit a wall thermostat you lose in theory the independent control, in the main the wall thermostat is only to stop cycling of the boiler, but it needs to be set to a temperature that will allow that, if used to control room and the TRV in that room is either set high or missing, it is doing a different job, so not independent.

I see no problem in complying with the law, non is there a problem in controlling the central heating, however there does seem to be a problem in economically controlling the heating and at same time complying with the law using the controls available at the moment. Unless there is a control I have missed?

I think the modulating control uses voltage to set level of modulation, so if the range was 48 volt and you have two thermostats in series both able to send out 24 volt then in theory they could work together, however they would need to be designed to work in series, and this is the point I can't find a ready made system that allows use of two modulating wall thermostats.
 
I can see how to use two mark/space thermostats, but they are old hat now, so how do you connect to modulating thermostats to same boiler?
As bernard has implied when he asked ...
If one modulating thermostat is asking for 50% modulation and the other is asking fo 99% modulation then what modulation level does the boiler adopt.
... a boiler can obviously only adopt one degree of modulation at any one time. In the situation he described, with one thermostat asking for 99% (and the other 50%), the answer would presumably be that, in order to satisfy the more demanding stat/zone, the modulation would have to be something in excess of 99% - but that would then be 'too much' for the other stat/zone.

Given that a boiler can only be 'doing one thing at a time', unless one has two or more boilers, I don't see how two or mor modulating stats could work - I suspect that (other than with multiple boilers), you would have to resort to old-fashioned on/off stats and zone valves, whatever any regs and/or 'laws' might seem to 'require'!

bernard also suggested ...
Maybe the two zones can share the boiler using TDM ( TIme Division Multiplex )
... but I'm not even sure that would really work (and one would probably have to engineer it oneself) - since you would still be stuck with the problem that, at any point in time, the water temp would be too high for one zone and/or too low for the other - so one presumably would not get anything like ideal control. Indeed, the temp in both zones would presumably oscillate.

Kind Regards, John
 
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I think the modulating control uses voltage to set level of modulation

Internally the control is ( in almost all boilers ) a voltage analog.

The controlling device can send a DC analog to the boiler but with long cable runs this can be affected by induced voltages.

Some controlling devices send a mark/space ( high frequency ) signal. Inside the boiler the mark/space waveform is converted to a DC analogue.
 
A simple solution is to have more than one boiler, one for each zone.
Too slow :) ...
Given that a boiler can only be 'doing one thing at a time', unless one has two or more boilers, I don't see how two or mor modulating stats could work - I suspect that (other than with multiple boilers), you would have to resort to old-fashioned on/off stats and zone valves, whatever any regs and/or 'laws' might seem to 'require'!

:)

Kind Regards, John
 
Some controlling devices send a mark/space ( high frequency ) signal. Inside the boiler the mark/space waveform is converted to a DC analogue.

I doubt that - why spend extra on a diode, capacitor, resistors, and use an ADC channel to end up with something that’s inaccurate...? The processor in the boiler can accurately time the on and off durations to evaluate the duty cycle.
 
why spend extra on a diode, capacitor, resistors, and use an ADC channel to end up with something that’s inaccurate...

A simple conversion from mark/space ratio to DC enables the boiler to be controled by either a DC analog level or a mark/space ratio on the input pins.
 
I doubt that - why spend extra on a diode, capacitor, resistors, and use an ADC channel to end up with something that’s inaccurate...? The processor in the boiler can accurately time the on and off durations to evaluate the duty cycle.
One thing to bear in mind is that, as one discovers if one (accurately) measures the temperature at multiple points within a room (and the wy in which those temperature change is response to changes in the heating system, is that striving for high precision in the heating control system is really nothing more than an academic exercise!

Kind Regards, John
 
I think selecting boiler size is often to satisfy DHW rather than size of house, so 50% of boilers output to one thermostat and 50% to other one would seem reasonable, so one asking for 100% other asking for 50% would be 75%, however without a device to actually combine the outputs it's all academic, in the real world we want a proprietary device designed to combine the outputs from two thermostats so boiler sees it as one, if a LABC inspector asks how have you provided independent controls for the two zones, you need to answer I have used a xxxx made by yyyy using the zzzz system. Not I have built my own device.

Law requires two independent controls, so I would assume there must be a way?
 
.... if a LABC inspector asks how have you provided independent controls for the two zones, you need to answer I have used a xxxx made by yyyy using the zzzz system. Not I have built my own device.
Law requires two independent controls, so I would assume there must be a way?
What law would this be?

Kind Regards, John
 
Well actually it's fairly simple...

A BMS controller, Both zones have modulating valves, the zone requiring the most heat has its valve to full and the boiler to the required, the lesser zone sets its valve to compensate.

It's been done for years.
 
Well actually it's fairly simple... A BMS controller, Both zones have modulating valves, the zone requiring the most heat has its valve to full and the boiler to the required, the lesser zone sets its valve to compensate. It's been done for years.
Yes, that has been done for years. However, eric seems to think that there is now some law requiring each of to zone's thermostats to simultaneously modulate the boiler - which is clearly impossible, since the boiler cannot be doing two different things at the same time.

Kind Regards, John
 
Yes, that has been done for years. However, eric seems to think that there is now some law requiring each of to zone's thermostats to simultaneously modulate the boiler - which is clearly impossible, since the boiler cannot be doing two different things at the same time.

Kind Regards, John
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.
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.
 

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