setback thermostat with freeze protection program

[bbortnick]

We are looking for programmable setback thermostats for our radiant hot water heating system in our building. Freeze control is the real driving requirement, as the rads are on the outside cold wall of the units, and have a tendancy to freeze solid with the resulant mess in winter.

To prevent that, a program that temporarily cycles the heat on is needed (for instance 1 out of every 30 minutes), in addition to the normal freeze control program that is based on ambient air temp. The heater control is a normally closed (NC) circuit, where an open circuit causes the valve to open and hot water to circulate.

Can anyone point me to programmable thermostats with all of these features?

Any help much appreciated.

Barry

[geothermaljones]

Never cared much for setback stats on scorched air units, but on radiators they don't seem to make any sense at all. How far down is your setback point that allows the units to freeze? Do you have a stat & control for each radiator, or one for a number of different spaces? It'd make some sense to put a pump exerciser on the circ pump & have it run for a minute every 15, 30, or 60 minutes just to move some water through... I think your problem has little to do with the stats.

goodluck geothermaljones

[Tom Beckner]

That's an off the shelf deal from your local supply house.

Ok.

The direct approach is maintain a space temperature via your new thermostat when the zone is unoccupied, 60 F or whatever depending on your application.

The "fail safe" convention is to use NO valves for heat.

An outdoor thermostat brings on the pump, when unoccupied, at nominal 40 F, giving freeeze protection when using NO valves. But could still be used with your NC deal in the short term as long as the setback thermostats and everything else in the control loop is working.

In addition, the convention is to reset the water temperature, basis an outdoor thermostat, with a three way diverting valve at the boiler. Your building may or may not already have that.

Your best bet is to go to a local supply house and briefly discuss your problem. Ask them to recommend a local mechanic or contractor that can come out and set the job up for you.

I could be wrong.

Tom Beckner

[bbortnick]

Thanks all for your responses; The circulating pump runs at all times, the local thermostat/valve allowing the hot water to route through the rads along the outside walls. The abient air temp may still be high (higher than the normal freeze protection temp) while the rad next to the wall experiences much colder temps and is thus subject to freezing.

These are all individual apartments, with the occupants setting their own temperatures, perhaps even leaving them off in the winter if heat from other units is enough, and/or leaving windows open in the winter (freezing air dropping down over the window sill onto the pipes) setting the stage for burst pipes.

The thermostat needs to compensate for the poor actions of tenants.