new thermostat from usa

[davidjonknight]

I wish to replace my home thermostat with one from usa. they have sent me the following instructions:
Example picture will be attached: Just an example. The attachment below is a classic example. Try not to associate color with the letter but in most cases R-is power or (Rh), W-is heat, Y-is the compressor, G-is for fan, C- can be common. Rc- can be jumped to Rh sometimes. Aux is for The auxiliary heat will only turn on below the auxiliary lockout temperature regardless of the Time to Temperature estimate. O/B is a change over valve. It can reverse heat and cold in both directions depending on what wire you have going to from the controller board. Nest does not support Line voltage 110V, Proprietary, and Milivoltage thermostats at this time. Maybe in the future.
I hope this will help you a little. I don't know how the U.K. standards are but at least you know have an idea of how we do installation here in the U.S.


Will this work in UK?

David

 

[ericmark]

I am sure it makes sense to you but sorry without the pictures it makes no sense to me.

Thermostats in general in this country can be split into:-
1) Those requiring a neutral. A compensating heater is included.
2) Those which will work with heating and cooling.
3) Those which include time as well as heat.

The 1) would be useless if designed for USA as the heater would be wrong voltage and with postage considered would be just thrown in the bin.

Most modern UK thermostats will work with open or closed contacts so why import from USA.

The battery driven thermostat like the one shown at £24 will not only set temperature but will alter the temperature according to time of day and I can't see any advantage that a simple USA thermostat can really have over this?

The X10 system which is a PLC designed for domestic use could I will admit have advantages over the standard UK system but to debate as to pros and cons one would have to declare what one wanted it to do.

So to start with what will the USA thermostat do which a standard UK one will not? Even the one I have linked to will work both AC and heating and I fail to see why anyone would want to mess around with a USA system.

So to start with what do you want it to do?

 

[Paul_C]

The milllivolt thermostat uses a thermocouple to provide a very small control voltage to the electronics in the heating or cooling unit. Line-voltage thermostats are typically used to switch a heater directly, and for residential work come in both 120 and 240V versions, so the latter would be suitable for use in the U.K.

The majority of North American central heat/air systems use 24-volt controls. The basic connections (both terminal letters and corresponding wiring color) mentioned in your quote are fairly standard now: Red (R) for 24V feed, white (W) for heating call, yellow (Y) for cooling call, and green (G) for fan control. The other connections for auxiliary controls to reverse heat pumps, control second-stage heating/cooling and so on tend to vary somewhat more between manufacturers, but black is often used as the 24V common where power is needed for a digital, programmable thermostat or the like. The Rc and Rh connections mentioned are just where there is a separate feed to the cooling and heating contacts respectively, i.e. Rh is connected to W to call for heat and Rc is connected to Y to call for cooling, instead of both sharing a single R feed.

So as the supplier indicates that the make you are considering doesn't support line-voltage or millivolt thermostats, it's almost certainly designed for the normal American 24V control system.

So to start with what will the USA thermostat do which a standard UK one will not?

Give readings in degrees Fahrenheit for one. Many of the U.K. models are now centigrade only.

 

[ban-all-sheds]

So to start with what will the USA thermostat do which a standard UK one will not?

Ah.

I can help you there.

..... Nest .....

http://www.nest.com


I wouldn't have realised the significance of that if I hadn't been looking at their site only a few hours earlier....

 

[Paul_C]

Ah, one of those fancy "learning" thermostats. Looking at the website confirms that it's for conventional 24V control systems. You could use it here, but you'd need to fit a suitable transformer and controlling relay in the system since British central-heating systems generally switch 240V directly.

 

[davidjonknight]

thanks

 

[davidjonknight]

Thanks for all your help.
Would the 'suitable transformer and controlling relay' dwarf the thermostat or could it hide behind it?

What price are they? Have you got a link you can show me of one?

David

 

[ericmark]

So to start with what will the USA thermostat do which a standard UK one will not?

Ah.

I can help you there.

..... Nest .....

http://www.nest.com


I wouldn't have realised the significance of that if I hadn't been looking at their site only a few hours earlier....

Thank you an interesting read. However it seems that they are not as yet released in UK so the internet weather report bit will not work. Not sure if USA use condensing boilers? The problem as I see it is we have moved on from the single thermostat to heat whole home. We have thermostats on every radiator so one would need to replace every radiator thermostat with a motorised valve and it would need one of the units in every room for it to control our system.

It could possibly work in a house like mine which is open plan, but we have to remember how our boilers work to start with. Unlike the old boiler which would switch on until the output water gets too hot the modern boiler senses the return water and adjusts the flame height according to the return water temperature.
This is in turn controlled by the radiator thermostatic valves (RTV) as each one turns off the bypass valve opens and returns non cooled water the flame hight is reduced.

Once the flame is reduced beyond a limit then the boiler turns off and with the expensive types it also has some anti-cycle software which if it turns off quickly increases time before it re-tried and if it takes a long time reduces time between tries i.e. it learns how often to try to heat house.

The electric thermostat is only there to turn off the system in the summer so stopping the cycle testing done by boiler altogether.

Some simple things can assist controlling the boiler like positing the thermostat so it's heated by morning sun so on a nice day the heating does not start. What we don't want is for the central heating to heat up the house in the morning to a point where once the sun comes out the house is too hot latter in the day. So using a thermostat with built in timer so cooler in morning than in evening does make sense.

Now it seems the USA type is connected with internet to forecast so when cold out side it can restart the heating ready for home coming earlier than when warmer outside. Great idea. However since we are not in USA likely that will not work.

We do have same thing in UK when working in "Next" they had a central computer system controlling the shop temperatures throughout the UK.

But in most homes I have visited the main problem is the installers don't commission correctly leaving lock shield valves wide open for example. So as a result the boiler turns off too early and so the house holder compensates by switching on heating earlier so waisting energy. Also not fitting RTV's to every radiator because in old days one left one near thermostat without a RTV they still do the same which with new system is wrong.

So to conclude although a good idea not sure if they will work in the UK with our system. By time one has built a relay bank and fitted all the motorised valves it will be super expensive. I have considered a PLC and SCADA link but just can see it being justified?

 

[Paul_C]

Thanks for all your help.
Would the 'suitable transformer and controlling relay' dwarf the thermostat or could it hide behind it?

You would need to fabricate a suitable unit containing the required components - A general purpose 24V transformer and a suitable relay with a coil which will operate on 24V AC and 240V rated contacts to provide the switching to your existing boiler controls. Something like these:

http://www.rapidonline.com/Electrical-Power/Chassis-Transformer-230v-20va-24v-24v-88-3436
http://www.rapidonline.com/Electronic-Components/24v-Ac-3PDT-11-pin-Power-Relay-60-1647

There would be the relay base, an enclosure, and miscellaneous connections, fuse etc. to add to the list. You wouldn't want to mount it by the thermostat, but by the boiler (there might be space inside the existing boiler controls enclosure for them, if you weren't worried about voiding any existing warranty).

However, there are the issues which have been mentioned above regarding how the existing system is arranged, what your existing thermostat actually switches, and so on. Without wishing to rain on your parade, I think your questions indicate that you would be rather out of your depth trying to tackle this project by yourself.

It could possibly work in a house like mine which is open plan, but we have to remember how our boilers work to start with. Unlike the old boiler which would switch on until the output water gets too hot the modern boiler senses the return water and adjusts the flame height according to the return water temperature.

While hot-water radiators systems are still to be found, remember that a very large proportion of the central-heating systems in American homes today are forced air from a furnace, with the same ductwork and fans being used for cooling systems as well.