Duty cycle control for hot water boiler

The Steam Whisperer

I have a pretty typical 196's 6 unit with a central hw cast iron boiler and unit thermostats. Since these buildings tend to need little heat due to internal gains, outdoor reset is useless since the system can heat the structure with 140F water on the design day. What I need is a simple duty cycle control, like those for steam, without the additional return sensors, etc. to prevent abuse of the "free" heat by tenants . Any ideas who makes these..remember cost is an issue since this is a very small building as are several others I am working with. This should be a very simple control.

SWEI

ICM 305/306 will do it.

The Steam Whisperer

Thanks all, but I was thinking of something fully automatic... no human interaction to reset the timer cycle lengths. Sorry, I should have been a little more descriptive....The cycle time needs to change automatically with outdoor temperature.....very similiar to heat timer steam controls.

SWEI

I was wondering about that. Your "outdoor reset is useless" line fooled me.

I could do it using a small DDC controller which would cost a bit less than half what a Tekmar 279 goes for. You'd get BACnet connectivity and a small display as part of the package.

A PLC platform (perhaps something like the Teco that @PMJ used or the Phidgets stuff @MarkS used) would probably cost half of that.

SWEI

Check out http://www.mydtcstore.com/

Brian was doing some kind of ODR when I looked at them a couple of years back.