3-wire proportional thermostat

[jimmycooker]

Hi,

I was hoping someone could help me, I have on / off thermostats in my house and I would like to replace them with proportional controllers so my new gas boiler which can modulate from 2.8kw output upto 28kw output does not cycle on and off, but instead stays on and modulates the heat output depending on the required load.

First of all, im not even sure this is going to work the way i think it is, but my idea is to put a 0-10v actuator on the existing on / off zone valve or thermostatic valve so that it opens and closes based on the output of a proportional thermostat.

Because the existing stats are connected with 2 or 3 wires I cannot install a 4 wire controller (24V in / 10V control out) in place so was wondering if these mechanical (3 wire) old school honeywell thermostats would do the same thing and do a good job at maintaining the temperature setpoint at all times.

Also, these units are very expensive, so any other 3 wire alternatives would be great.

Thanks,
James.

http://www.pexsupply.com/Honeywell-T921A1183-135-Ohm-Proportional-Thermostat-13-C-to-29-C

 

[Kidblue]

Hi Jimmy,

Try Titan Products, I've found them very reasonable for various proportional temperature monitoring sensors...

http://www.titanproducts.com/categories/1_10/Outside_Temperature_Sensors.html

We've used the above device several times for reporting plant room temperature back to the PLC...

Hope this helps.

Rob

 

[jimmycooker]

Thanks for your reply, I know this is the plc forum but I do not want to report back to a plc, I want a wall unit that can control a proportional valve / actuator head directly...I was hoping someone on here might have some experience of this type of mechanical room stat or an alternative, and also be able to confirm that what I'm trying to achieve is possible.

Thanks,
James.

 

[jimmycooker]

http://danfoss-randall.co.uk/PCMPDF/REP24.pdf

Would it be possible to wire this danfoss thermostat up using 3 wires (having the neutral wire common for both the supply and the proportional outpu)?

Thanks.

 

[JesperMP]

Baed on what you write, I think you have a boiler that self-regulates to keep a certain set water temperature.
And in you house you have a number of radiators. How are these used to be regulated ? Or where they not regulated at all ?
How does the old thermostat come into the picture ?
Make a sketch.

I also have a boiler and radiators, 7 in all.
I am beginning to replace the old water-regulating thermostats (mounted on the radiators) for electronic thermostats with integral timers. I can set the temperature and time schedule individually for each thermostat. These electronic radiator thermostats are dropping in price rapidly and they are getting better and better. And you can simply exchange the old thermostats for the new without tools or major changes to the installation.

 

[jimmycooker]

Hi,

I have a similar system to the one you describe. I have local mechanical thermostatic valves on all the radiators which regulate the flow based on the surrounding temperature. These TRV's are adjusted locally and work on the principle of melting wax expanding and closing the pin at higher temps and opening it proportionally to the surrounding temps.

The newer domestic boilers out there can sense the return flow water temps and modulate the heat output down once your house is upto the required temp and supply just enough heat to keep it there. This means you don't get on / off cycling of the boiler and you get a flat line temperature trend, not an up / down fluctuating temp.

Most of the modern timer stats today use time or chrono (tpi) control to intelligently calculate the required heat based on the temperature and they schedule the on / off supply from the boiler to reduce boiler cycling and give a steadier heat trend, however this is still on off.

My problem is my house is full of copper pipe which wasnt properly sleeved under my floor boards, it mskes a lot of noise when it's heating up and cooling down, so I want to keep the temp in the pipes as steady as possible.

My plan is to use a 10v proprtional room stat to control a 10v proportional valve actuator head, which I will install on the zone valve to each area. I'm hoping that this will then take over the job of the TRV's located on each of the rads which I don't think do a very good job.

Thanks,
James.

 

[JesperMP]

I see what you mean.
I use the new electronic regulators to regulate the room temperature according to the demand. This to save on the heating expenses which are high now, and getting even higer in the future.
I also have some problems with noise when the piping expands or contracts. So my trick is to switch to high before the "customers" arrive, and switch to low after they have left. Its not perfect, but I am also not prepared to rip up all the floor boards