Zone valves on steam

Patrick_North

Here’s the scenario.

A church steam boiler which serves two buildings- one very large (the church itself) the other (a meeting hall- essentially one room) quite small. Electrically controlled valves have been added to restrict steam flow to either building if only one thermostat is calling for heat. It seems that the boiler was sized for the entire load, NOT one building or the other. You can probably see where this is headed.

The huge (1600+ sq. ft. steam) boiler hums along at about 6oz when both buildings are calling for heat and about 8oz when only the church calls for heat, but the pressure skyrockets to about 4-5# when only the smaller building is calling for heat. Short cycling on pressure, noisy operation, the works. Fuel bills are quite high.

Both buildings are heated above a setback for a few hours each Sunday morning, but the smaller meeting hall is used once or twice throughout the week when the church is unoccupied. I guess this was the original rationale for zoning the buildings this way, right or wrong.

In the long term the church would like to uncouple the heat source for the two buildings, but in the meantime is of course interested in mitigating waste. Would you say that there’s clear rationale for keeping or ditching the zone valves, or is it more complex than that?

(yes, this is the same setup with the “first it’s a dry return then it’s a wet return” in another thread.)

 

Thanks,

Patrick



**UPDATE**- for what it's worth, the boiler is rated at 1645 sq.ft. steam. The church (larger building) has a total EDR of about 1000. The meeting hall (smaller building) has an EDR of about 460.

Dave in QCA

turn the pressure limit down!

If you say the buildings heat well when the boiler is producing 8 oz of steam, but the pressure skyrockets when only the smaller buidling is calling for steam, have you tried lower in the pressure limit control?  Is it a pressuretrol or a vaporstat?  If a pressuretrol, you probably won't get it to work at a setting much lower than 2 psi, perhaps 1.5 if you're lucky.



What kind of boiler is this?  Does it have a 2 stage burner?

Patrick_North

Correction!

Good catch, Dave- I should have clarified. I turned the pressuretrol up just as an experiment to gauge operating pressure and see what was happening. I found that the pressure goes up this high very quickly- well before steam starts closing vents . With the pressuretrol dialed back, it just  cycles like mad. And no, it's not a vaporstat.

I believe this is a Weil-McLain LGB-6- 1645 sq.ft. steam. No power burner, so I assumed that meant no 2-stage was possible, but I'm ignorant in this realm. Regardless, it's of a vintage where the church hopes to limp along for a few more years and will not be replacing this boiler as is.

Thanks,

Patrick

The Steam Whisperer (Formerly Boilerpro)

Very Easy, Very Good Fix...

LGB's come from the factory with a two stage gas valve.  I would first just run the boiler on low fire all the time for a few weeks to see how it performs.  If you are having problems, connect high fire and and use vaporstat to control high fire.

Patrick_North

AWESOME!

This is great news!

I'll report back... and I'm sure I'll check in with more questions. Thanks for the invaluable tip!



Best,

Patrick

Dave in QCA

Steam Whisperer Stole my Thunder!

When I asked what type of boiler you have, I was hoping in the back of my mind that it might be an LGB, because the LGB-6 and larger have two stage firing already built in.  All you need to do is add the controller, But Dave (Steam Whisperer) beat me to it!

To keep it on low fire, simply pull the red wire off of the MV terminal on the electronic module. 

Patrick_North

Shared props.

Then let me double my thanks! The Wall never ceases to amaze me.

Thanks, guys!

Patrick

Patrick_North

UPDATE- it just couldn't be easy...

I’d appreciate some additional help guys as I’m now starting to doubt my sanity.

 

Had a service tech out. Told him we have two zones and want to set up two-stage firing such that when only the small zone is calling for heat and system pressure rises, the pressuretrol activates low fire.

 

The boiler currently has two pressuretrols, so I told him I wasn’t sure if one was a “backup,” or if it had been wired originally to control the low fire but was not working. Could he check this out?

This is a Weil McLain LGB-6 equipped (as I understand it) with hi-lo firing capability.

 

A full two hours later and I’m not sure he understood me. He says the lo-fire is used to test the pilot, and that he doesn’t think what I’m proposing is possible with my setup. (I’m wondering “what do you think hi-lo firing is for?”)

 

Thankfully he didn’t seem to think I was crazy, and I’m guessing he felt a bit out of his depth (doesn’t work much on steam) so he called his boss. Unfortunately, the boss also doesn’t seem to understand the situation- maybe because it was relayed through the tech. We both agreed I should email the boss with the details of what I want to accomplish in black and white and see if that clarifies things. Frankly, I don’t know how to explain things any clearer.

 

I’m attaching some pix of the wiring panel and gas valve in the hopes that someone can confirm that YES, this is possible with this boiler and maybe offer some tips on communicating this to the service company?

 

Thanks,

Patrick

Dave in QCA

Probably no 2-stage on this Boiler

This valve is not a two stage valve.  Is it the only gas valve, or are there two?  I am guessing that this boiler was built prior to the decided to put on 2-stage control.  The terminal strip does not look like 2 stage either, unless there is an additional terminal strip that you didn't photograph.



Sorry that we sent you barking up a tree that isn't there.

Patrick_North

Aw crud.

Think a retrofit would be possible? And I know we don't discuss pricing, but would it be pricy?

Thanks,

Patrick

SWEI

from the wiring colors

It looks like there might be two separate pilot modules.

Patrick_North

What does that indicate?

Maybe I should have taken more pictures. What would two pilot modules suggest?

Thanks,

Patrick