Steam zoning

Steamhead (in transit)

individual thermostat control of each UH or group of UHs is all you need, there's a lot simpler way:

1. Install a strap-on, make-on-rise aquastat on the return pipe as it comes out of each UH and before the steam trap. Set it to 140 degrees or so.

2. Wire the aquastat in series with the room thermostat or relay that controls the UH fan motor.

3. Control the boiler's burner with an outdoor-reset unit such as a Tekmar #269.

4. Vent the heck out of the steam mains so the steam distributes quickly and evenly on just a few ounces pressure.

This will give tenants some control over the temperature in their spaces, while not permitting the UH fans to run unless the steam is up. The ODR will keep the building from overheating.

If lo-hi-lo firing is installed on your boiler, this will save a lot of fuel. The same can be said of using a Vaporstat as the operating hi-limit rather than a Pressuretrol.

To answer your question- no, zone valves on the returns wouldn't work well. You can't depend on air separating water from steam as you describe. Also, on shutdown, the condensing steam remaining in the coil will pull a vacuum and draw more steam towards it, filling up the coil. You sure don't want water getting trapped in the UH coils- when the valve opens and the steam comes in, you WILL get some ferocious banging!

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Jeff Perry_2

Steam zoning

My current employer has acquired a 330,000 sq ft factory building. (Actually consists of 3 buildings). These buildings all have steam heat, which was separate from the process steam that was once there. The building I am currently working on consists of a single boiler with a couple of mains that go straight to the top floor and then down-feed all the ceiling suspended unit heaters. Piped this way means that a specific branch line will feed unit heaters on all 3 floors.
We are dividing these buildings up into individual spaces and we need to zone some of the heat. We can't install valves on the branches as this will cause heaters on multiple floors in different tenant's spaces to be affected. Installing motorized valves on the 2" or 1-1/2" steam supply to each heater will be very difficult as some of these are up against the ceiling and/or very short runs from the main branch to the heater.
My question is... is there any reason we can't install zone valves on the condensate returns? If we prevent the air from being pushed in front of the steam, through the heater and the steam trap, the unit shouldn't heat as the steam should never reach the coil. If a small amount of condensate does get to the coil because of the main branch being so close, and there would potentially be steam traveling down it, I'm not sure there would be enough condensate to fill up the unit heater and cause water hammer as it backs up into the main.

Any thoughts?

Jeff Perry
Charlottesville, VA