Zoning Steam Systems

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Zoning Steam Systems

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Steam95

I've been fascinated by steam heat for years, ever since I first saw it when I was about 12. I'm 23 now, and it hasn't died, in fact I dream of owning a nice Victorian home with steam heat, especially if it has an old boiler.

In a theoretical scenario where:
A. The boiler is set to maintain a certain pressure (very low of course), rather than fire with a call for heat.
B. A two pipe system is used, with steam fed into the top of the radiator, and the trap at the bottom with a check valve after the trap to prevent backflow of condensate into the radiator when the zone valve closes.
C. Well insulated pipes, with traps where needed in the risers to drain any condensate.

Would there still be an issue with water hammer or water leaving the boiler if zone valves are used? As zone valves open and close, the pressure will rise and fall slightly, causing the burner to fire or shut off. I can't see why there'd be a problem, but have no experience to go off of either.

Thanks for your thoughts,
Nick

Jamie Hall

To answer @Steam95 's question... there would still be an issue. Sorry about that. However, not to in any way contradict Dan -- who has forgotten more about steam that I'll ever know! -- there is a way to divide a steam system into zones if it really necessary without using the bypass (which is the easiest way to do it, by far, and is the best way if all of the spaces in question remain heated and above freezing). The approach is to valve the system so that whether the zone valves are open or closed it still functions as an intact steam system, and to change the configuration only when the boiler is off. Basically, this means valves operating simultaneously on the mains, the dry returns, and the wet returns. It also involves vents or crossover traps on the hot side of any steam main valves, and drips on both the hot and cold side of the steam main valves and the dry returns. Is this worth the effort? It might be, in some situations -- but it's a lot of valves and piping...

And doesn't solve the other problem, which is the boiler being wildly oversize when a zone is cut off.

In my humble opinion if you have to zone for some reason, you would be better off with two or more independent systems, boilers and all, all properly piped and sized, of course.

Steam95

@Jamie Hall

It certainly wouldn't be necessary, only slightly convenient to zone the system. In a situation where one room would be heated by another source (such as a kitchen when baking, or a living room when a fire in the fireplace or stove is desired.)

Mentioning the bypass, would that essentially be a pipe from the steam to a trap (essentially using the pipe as a very low surface area radiator)?

Would modulating the boiler based on the number of thermostats calling for heat help? Something like an orifice and solenoid valve for each zone, feeding more or less gas to the burner based on heat load. Or opening/closing the damper a certain amount if the boiler is wood or coal fired.

Thank you,
Nick

Jamie Hall

With a two pipe system, the best way to control just one or two problem rooms such as you describe is to use the inlet valve on the radiator(s) themselves -- or if they are pesky (often are) to place another valve -- full port ball valve -- on the riser to the radiator valve. You can also use TRVs in the same sort of way. That way you are only shutting off the one radiator, and right at the radiator -- any steam slipping by gets out through the trap.

As for modulating the boiler, unless it is specifically designed for modulation (gas) you will through the gas to air ratio way off if you close one or more burners. There are two stage burners, however, which can be modulated on pressure. Not at all sure it's worth it unless you are going to be closing a large chunk of the system. Wood or coal fired boilers can be modulated, as you suggest, with their dampers -- but the combustion efficiency really gets bad, as well as emissions...

Steam95

@Jamie Hall

Say it's Thanksgiving, and I'm cooking like crazy in the kitchen, and have a fire in the parlor stove, and a fire in the fireplace. Potentially half (the whole downstairs) could be closed off. Not sure if it'd be worth it, but for now this is an entirely hypothetical exercise, so why not right?

You're saying that if I put the valve right at the radiator it won't be a problem? I should have mentioned this, but in any of the above scenarios I described, any zone valves would be right before the radiator inlet valve. I know dead legs are a no-no.

I'm fairly used to modulating burners (oil though), it would have to be custom built for this. Options include a 3 ring cast iron burner, each ring having a separate orifice and air mixer, or a series of jet burners such as those used in wok burners.

The 3 ring burner is 120kBTU, 60k outside ring, 40k middle ring, and 20k inner ring. Would then add 4 20k single ring burners in the corners for a square firebox, all piped together for an 80k burner. Then you have a 200kBTU staged 20k, 40k, 60k, 80k for 4 stages. Relatively robust and not horribly complicated.

The wok burner style is far more granular, at 10k btu per jet. 2 jets are usually directed at each other for a fan flame, so lets say it's totally modular at 20k per stage. Each jet burner has its own orifice and air mixer, so all that's needed is gas piping to each set of two. The downside is that the jets are small, so more prone to getting gummed up over time. Could easily have a 10 stage 200kBTU burner, but that's probably overkill.

Regardless, a multi position damper, or series different sized dampers would be required to open/close based on how many/ which burners are firing to prevent too much excess air.