Zoned steam

yellowdog

What's the general consensus of having multiple zone valves on a 1 pipe steam system in a small commercial building? I was never really a fan of it due to the boiler not knowing how many valves are open and having no way of modulating output.

Jamie Hall

If all the piping is done right -- including a surprising number of drips where you might not expect them -- and there aren't too many zones and the boiler is not oversized (this is a situation where undersizing a steam boiler might not be a bad idea)... it works. The boiler is going to drive you bananas cycling, particularly if some of the zones are small, and the heat is likely to be very unresponsive, unless the boiler is controlled by an outdoor sensor and timer setup rather than a thermostat or multiple thermostats.

Mustangman

I agree with being on the light side of BTUs required. Piping is key also. When you say one pipe steam, in my mind that is a steam system without a designated return. The condensate flows on the bottom of the pipe and steam on the top. If its as described, when the zone valve shuts, you still have steam in that zone. It will condense leaving you with a considerable amount of water that will want to flood back when the zone valve opens on the next call for heat. System over filling is a concern of mine.
I actually ran into a similar system at a church 5 years or so ago. They had 3 zones, fairly large too. I was the 3rd guy in on this call. They had severe hammering. When I arrived, I could hear the hammering when I got out of my truck. I went down to the boiler room and at first glance, It appeared that the sight glass was empty. Looking a little closer, I realized the boiler was flooded. I opened up the LWCO and it ran and ran for long time until the level was in the site glass. I talked to their maintenence guy and I asked him, when does this happen. He said during sunday worship is the worst time. Then the truth came out, I asked if he was running a set back program. Their unoccupied set back was 15 degrees. Basically the long run times, with all zones calling, the condensate could not get back to the boiler fast enough. The fill valve opens and it takes in fresh water. All the sudden you start getting condensate back and you have a flooded boiler. As I looked over the piping, I see they had end of main drips with a bucket trap. Pretty easy to figure out the traps were not working. We cleaned all the strainers and traps and replaced some piping around a door that was loaded with sludge. Now we can get condensate back to the boiler much faster and life is good. This zoned system was done properly. You can't set back a steam system more than a few degrees.
Hope this helps.

jumper

When I'm trying to fall asleep my brain –against my wishes– comes up with strange stuff. For example; how about zoning with throttles versus shut off?

pecmsg

Most commercial buildings have modulating valves trying to maintain 50% open. 

EBEBRATT-Ed

It's not only the zone valves and the boiler sizing that causes issues. Condensate return becomes a problem. When the ZV closes you have no steam pressure to help the condensate back.

Most of the time with ZVs you end up with a boiler feed tank or a condensate pump. But every job is different. It can work well on some jobs. Are TRVs an option as an alternative to zoning?

jumper

pecmsg said:

Most commercial buildings have modulating valves trying to maintain 50% open. 

One pipe in commercial buildings?

EdTheHeaterMan

There is a church in Cape May NJ that has 3 steam zone valves. While installing a replacement boiler, I replaced the old Honeywell zone valves (two 4" threaded valves and one 2" threaded valve) with a less expensive brand of valve that was rated for steam. I ordered flanged valves so they can be easily removed for service. I didn't want to be married to 45 year old zone valves in this new boiler job.

To make things even more difficult the original system had the boiler located in a basement. (Cape May is already 4 feet below sea level and this church had a basement ???) So the 80 year old coal boiler was moved into the parking lot near the chimney where they build a boiler room around the boiler. The original basement setup was a one pipe. none of the radiators have traps.

From the 3 zones there were 3 wet returns based on the basement boiler location that were trapped and then went into a small condensate return tank.

I redesigned the pump on that tank to be a boiler feed pump and kept my fingers crossed that the small tank was big enough. It was. The old boiler was a coal boiler converted to fuel oil. Probably around the time they moved the boiler up 9 feet higher out of the basement. I figure a hand fired boiler could get some sea water in it and be cleaned out and made ready to accept coal more easily that a boiler that needs electrical controls to make it work on OIL.

So I called on John McGarry from Weil McLain to help me out on this new boiler Spec. He was impressed with the redesign of the 80 year old oil fired boiler and suggested the 80 series boiler (the 78 was just discontinued at the time). Just put the new boiler in like the old one you are taking out. The 6" steam main went up to the ceiling of the boiler room then dropped to below the floor where it went thru a small tunnel to the basement where the old boiler was located and was connected to the 3 different mains. followed by 3 zone valves. It worked great. But I was sweating bullets from the time I was awarded the contract until the boiler was commissioned.

I had already read about the horror stories about zoning with steam. But a dead man had already completed the homework and worked out the bugs. The new boiler was just as simple as any other replacement boiler.