Heating, multiple stats on one zone

Ging Ging

Heres the scenario:
Central heating radiators zoned with motorised valves and thermostatic radiator valves on all radiators.
The problem is a thermostat in room A can signal the motorised valve to shut regardless of the whether Room B,C or D are at temperature or not.
So I was wondering if each room could have its own stat wired in parallel, all sending signals to one motorised valve? The valve wouldnt shut until all stats were satisfied.
Any problems with this?

2011

Ging Ging wrote: »

Heres the scenario:
Central heating radiators zoned with motorised valves and thermostatic radiator valves on all radiators.
The problem is a thermostat in room A can signal the motorised valve to shut regardless of the whether Room B,C or D are at temperature or not.
So I was wondering if each room could have its own stat wired in parallel, all sending signals to one motorised valve? The valve wouldnt shut until all stats were satisfied.
Any problems with this?

Yes.

Now the valve will only shut when all stats have reached/exceed their set points. Therefore the most likely scenario is that the motorised valve will effectively be controlled by the same stat all of the time. The result is that the other stats will effectively do nothing. Why not save yourself all of the hassle and only install one stat?

Clearly the best option (if possible) is to have a stat per motorised valve. When all valves are closed switch off the boiler.

Ging Ging

With TRVs on all rads this should provide localised control so individual room's radiators are shut off mechanically and therefore dont overheat that area.
What I am trying to avoid is the zone beng shut down before all rooms are at temperature.
I was looking at some electronic trv's that can call the boiler for heat but I thought the extra stats would be simpler.

2011

Ging Ging wrote: »

With TRVs on all rads this should provide localised control so individual room's radiators are shut off mechanically and therefore dont overheat that area.

I appreciate that, but do you not see that effectively only one of the stats will close the motorized valve despite the fact that you will have installed several?

Ging Ging

Yes I agree one stat will close the valve, Im not looking for an average or anything like that. Maybe under standard operating conditions it would be the same stat that usually closes the valve, but depending on heat loss or gain due to other factors like open door or solar gain it could be a different stat.
Are there temperature sensors you know of with one main master and number of slaves that could perform like this? This is a college project by the way, I have a circuit of offices and I need to control the heat in each. Maybe programmable room stats but I want to tie it into a building energy management system too.

Ging Ging

2011 wrote: »

I appreciate that, but do you not see that effectively only one of the stats will close the motorized valve despite the fact that you will have installed several?

Maybe I see what you are saying. I dont want 1 stat to shut the valve. I want the last stat to shut the valve. Whichever the last room to reach temperature is.

Bruthal

If you were to put a stat in every room, you may as well have no zone valve, as it would be likely that at least one stat would be closed somewhere, at all times, and the trv's would be doing all the regulating.

If you wanted to leave a radiator or two out of use, you would have to also turn its room stat down to min. All very messy.

A single stat per valve is better. to have each room properly controlled would in reality likely need a motorised valve zone per room.

As 2011 said, one of the multiple stats could end up controlling the zone anyway if they all managed to reach set point, for a given setup of stat settings, so close individual room control wouldn't exist any better than a single stat would provide.

Ging Ging

So its a not a viable option then. Thanks for your input lads.

Sir Arthur Daley

Ging Ging wrote: »

Heres the scenario:
Central heating radiators zoned with motorised valves and thermostatic radiator valves on all radiators.
The problem is a thermostat in room A can signal the motorised valve to shut regardless of the whether Room B,C or D are at temperature or not.
So I was wondering if each room could have its own stat wired in parallel, all sending signals to one motorised valve? The valve wouldnt shut until all stats were satisfied.
Any problems with this?

I see no problem with what you want to do here, wire the stats in series though instead of parallel and by using an additional relay/contactor this will achieve what you have proposed very easily.

frankmul

Do you usually have a trv and stat in the same room. Should you not leave one room without the trv and have the stat there. Usually the room with that will be the slowest to heat. Once all the trvs close, that room will be quick to heat, shutting off the valves

ted1

If you got rid of the main stat you could a 2 spring return valve with a thermostat on each rad, this would make each room I dependant

2011

WikiHow wrote: »

I see no problem with what you want to do here, wire the stats in series though instead of parallel and by using an additional relay/contactor this will achieve what you have proposed very easily.

If the stats are wired in series then once one stat reaches it's set point the motorised valve will close! This will result in none of the other set points being achieved. Not the way to go.

Don't try to reinvent the wheel.
Do what you know will work, one valve per zone and one stat per valve.

Bet of luck with the project

Sir Arthur Daley

If the stats are wired in series then once one stat reaches it's set point the motorised valve will close! This will result in none of the other set points being achieved. Not the way to go.

No all 4 stats would need to have reached temperature when wired in series, this will achieve what the OP wants to do very easy.

2011

WikiHow wrote: »

No all 4 stats would need to have reached temperature when wired in series, this will achieve what the OP wants to do very easy.

The drawing below shows multiple stats wired in series.

Once any of the stats reaches the desired set point it will change state (open circuit). This will cause relay R1 to de-energize, which will remove power from the motorised valve. Once power is removed from the valve motor it will close due to the spring return.

Which part of the above do you not agree with?

tomdempsey200

why would you have room stats if all rads have thermostatic valves fitted

as already said you might have one room stat for each motorized valve/timing channel for master control of heating...you'd have no trv where that's located

2011

tomdempsey200 wrote: »

why would you have room stats if all rads have thermostatic valves fitted

Thermostatic valves measure the temperature at the valve itself, whereas room stats should be positioned to measure a temperature that is representative of the air temperature in a particular zone.

In addition heating systems are often designed so that the boiler will switch off once all stats are satisfied so that the system runs more efficiently.

tomdempsey200

2011 wrote: »

Thermostatic valves measure the temperature at the valve itself, whereas room stats should be positioned to measure a temperature that is representative of the air temperature in a particular zone.

In addition heating systems are often designed so that the boiler will switch off once all stats are satisfied so that the system runs more efficiently.

thanks for stating obvious facts..
normally you don't double up room stat and trv is my point

Sir Arthur Daley

2011 wrote: »

The drawing below shows multiple stats wired in series.

Once any of the stats reaches the desired set point it will change state (open circuit). This will cause relay R1 to de-energize, which will remove power from the motorised valve. Once power is removed from the valve motor it will close due to the spring return.

Which part of the above do you not agree with?

I dont disagree with anything in the above, this is the way i would wire the installation to achieve what the OP wants to achieve.
http://i1351.photobucket.com/albums/p784/wikihow3/ink_zpsc9282f1c.jpg

2011

OK so looking at your diagram above I see you have 4 stats that are using NO contacts connected in series. So the valve is energised and therefore open until all 4 stats reach their respective set points as you said.

Using the NO contacts on a stat is not the norm, but it will work.

The problem is still the same, one stat will effectively open & close the valve. Operation of the other 3 will stats will be academic.

Why? Well suppose stat A is the last stat to reach it's set point (perhaps because it is in the coldest part of the building). The stats in the other areas will exceed their set points because the valve is still open, so stats B,C and D can do nothing to stop the heating from continuing. When stat A eventually reaches it's set point it will cause the valve to close. Most likely this will continue to be the case, one stat (in this case A) doing all of the work and the others may as well be removed or linked out.

The end user is likely to get confused also as turning down stats B, C or D does not stop the heating up of areas B, C and D. However turning down stat A does seem to make areas B, C and D cooler

2011

tomdempsey200 wrote: »

thanks for stating obvious facts..
normally you don't double up room stat and trv is my point

Normally HVAC is used in an office, but you asked