Thermostat for radiators (for the engineers)

[jziegler]

This is a questions mostly for the other engineers out there.

I have old cast iron radiators that heat my house. They work great, but the typical Home Depot special programmable thermostat that I have controlling them leaves a lot to be desired for radient heat. It would be great for forced air, but not as good with the radiators due to their large thermal mass. It turns on a little later than it really should, and sometimes runs long enough that the room temperature can reach 2-3 degrees above the setpoint half an hour after the heat turns off.

So, the question is does anyone know of thermostats designed for radient systems? If not, why couldn't a PI or PID control loop be used for something like this, which might minimize some of the problems with the typical thermometers. I've even thought that a second sensor to monitor the temperature of the radiator itself could be useful. Just some random thought that I've had in the last few cold days.

Jim

[mleichtle]

I have a similar situation, radiant convectors, like short baseboards. Our thermostat has a temperature swing thats programable up to 5 degrees or so, to keep the furnace from kicking on too often, but it doesn't work, I imagine cause the furnace/boiler doesn't have the proper connections that a forced air system would. So what you would want is a temp. swing that works in reverse. And I'm sorry, but I have no knowlege of such a product. I have read of a product that moniters the outside air, and adjusts the the boiler so it doesn't work as hard on warmer days. Another thought, fixing the problem you describe, could cause more problems by causing your circulating pump or boiler to short cycle.

[Tequila]

Manual thremostats typcally have an adjustment slider hidden behind the controls to allow exactly the sort of adjustment you're talking about. If you can track down the manual for your programmable one, it might have a similar adjustment hidden somewhere.

[TheRic]

I have a hot water boiler. When I put in a new thermostat, I looked for one that would would work with hot water boilers. A forced Air thermostat turns on the heat and fans at the same time. One designed for a boiler heats the water a couple of minutes before the pumps kick in. It stops heating the water a few minutes before the pumps kick off.

Got mine at Lowe's or Home Depot a couple of years ago. It was not the bargain basement version. It cost around $80 if I remember correctly. I tell it what time and temp I want the room. It determines how long before it needs (from past history) to turn everything on /off to meet that demand. When I have been home I have noticed it is off a little if there is a large swing in temp from one day to the next, least of my worries.

[jziegler]

Thanks for the pointers. I guess I'll need to check the stores again sometime. So far, I have never seen any for boilers. Of course, the wiring that I have currently doesn't have seperate wires for the burner and the pump, just a wire for the pump. But, if it looks at past temperatures, it still might work better than what I have.

Thanks again for the pointers.

Jim

[jcrenick]

I am in the process of designing my new heating system which will replace a 20 year old boiler.
A lot of reading has lead me towards a modulating boiler with TRVs. (Thermostatic Radiator Valves) These valves are fitted to each radiator and allow you to control the temperature of each radiator.

Look them up on the web it may be of interest to you.