Managing an oversized boiler...

grrrdot

Alright, One-pipe steam, 6-story NYC. Weil-McLain LGB-10 Series 2 on MPC Platinum Heat-Timer.

Boiler is oversized and will build pressure faster than the building can condense during cold-weather calls.

During cold snaps while there is still a call for heat, the boiler hits the operating pressure limit and the burner drops out for ~2 minutes until pressure falls to cut-in.

The MPC continues timing the cycle and has no awareness the burner is off on pressure. So, during cold snaps the system under-heats unless the heat adjustment is increased. Once weather moderates the boiler does not hit the cut-out and then it over-heats until adjustment is reduced.

Boiler replacement isn’t an option…
So, I come up with short cycling on purpose or raising pressure? Between those two which is better? Or is there another option I'm missing?

Thanks for any help!

-G

dabrakeman

Did you consider the L-H-L gas valve option which is available for that boiler?

Pressure is always the worst option.

ethicalpaul

Pardon this question from a non-professional, but have you ever considered blocking one or more burners to reduce the BTUs being generated? A combustion analysis could be performed in conjunction with that work to ensure acceptable values.

dabrakeman

Do you know how oversized you are? I imagine there would be a lot of radiators to total sqft up but maybe you have done so? I too will defer to the professionals regarding interaction with your outside air temperature heat timer.

Captain Who

Have you made all the appropriate adjustments to tell the system what the heat loss characteristics are of your building?

"During the Cycle-ON period, the MPC Platinum will keep the steam source activated. The length of the ON part of the cycle is dependent on the outdoor temperature, the Day/Night setting, and several user selectable adjustments that can be tuned to the specific heat loss characteristics of the building."

Also, there is this in the manual:

Space Sensor Feedback (Available with Internet Control Only)

• For better control and much more energy saving capabilities you can add wireless or wired space sensors to the MPC Platinum to fine tune its operation and increase the system's overall efficiency. When you add space sensors to the space average, the MPC Platinum checks the space average before the beginning of each cycle to determine if the building is sufficiently heated. See "Space Lockout" on page 28.

grrrdot

Thanks for all the responses! This is great.

Do you know how oversized you are?

That's a good question. It's a 28 unit building and I've not been into every apartment to measure out the radiators. I'll see if I can do this maybe something else is a-foot.

Did you consider the L-H-L gas valve option

I'll explore this. I could use the feature with a vaporstat, it might hunt a little but that seems better than short cycling or higher pressures.

Space Sensor Feedback (Available with Internet Control Only)

Another good option that I missed. Right now we run with an outdoor sensor and a system sensor on the dry return. Will need to do some research to see what it would take to enable this.

have you ever considered blocking one or more burners to reduce the BTUs being generated

I thought heating the block unevenly was bad, would pulling out burner tubes do that?

-G

EBEBRATT-Ed

You can install a time delay relay so when the boiler shuts down on pressure you delay it from restarting. This cuts down the short cycling and give the radiation a chance to give off some heat. Usually a 8-10 min time delay works.

4GenPlumber

https://forum.heatinghelp.com/discussion/comment/1887816#Comment_1887816

This used to be very common in my part of NJ. Over-size the boiler for the internal water volume but removing and plugging outside burners to decrease BTU's. I've never done it but you can probably just do the math but you would need to find the actual output needed and the chimney minimum. It would probably also do some weird stuff between the sections.