Modulating steam boiler staging controls

The Steam Whisperer

Any suggestion for this application? Looking for lead/lag and maybe parallel modulation of the burners.

Timothy77

Tekmar.

nicholas bonham-carter

Use a 2-stage thermostat, with the second stage wired through a second Vaporstat to the second boiler. Make the first boiler capacity the same as the heat loss, and the second the difference between that, and the EDR.
When the thermostat calls for heat, from a setback, it will energize both boilers. As the pressure builds in the system, (8 oz.), the vaporstat will cut out the smaller lag boiler.
When the thermostat calls for a top up of heat, the thermostat will only fire the lead boiler.--NBC

SWEI

He said modulating. What kind of burner controls? I'd probably start there if it's one of the major players.

The Steam Whisperer

NBC---Yep, I've done that before for simple home systems with 2 on/off boilers. However, this is 2 big, modulating steam boilers about 6 million btu/hr each feeding 4 zones of a vacuum system in a 13 story building. They currently have a $100,000.00 or more Johnson controls setup, which, of course is all proprietary to the point that the building engineer can't even make any adjustments without calling out Johnson to run any changes through their lap tops. And when the system goes down mid winter, it is often a week before they can get out. That system certainly needs to go. I suspect the new Burnham will accept the typical 4-20 MA, 2-10 v, 0-10 mod input. The old Kewanee with an old Power Flame may still have a resistance control set up. Sadly, they greatly prefer running the old Kewanee, it just runs a lot better. I believe either boiler can mod off its internal controls, so just a lead/lag control may be all that is really necessary, though parallel mod would probably provide a boost in efficiency and reduced stress on the boilers.....less cycling and lower operating temps, less water carryover. However, Jacket losses would be higher.

Timothy 77, I don't believe Tekmar makes any staging controls for Steam. They only work with Hot water, except the single stage steam control.

ratio

How complicated do you want the controls to be? Check out the new Honeywell T775 series, they have a number of different models, including analog I/O & a pump controller that will IIRC do lead-lag & round robin scheduling. I've used a number of them in the past, they're reliable & simple to program.

If that's not flexible enough, there're a number of simple PLC's (called programmable relays or something) that are used by some on The Wall. One of those should allow you to do whatever you want, at the expense of learning how to program them. Search for "PLC" above right.

hvacfreak2

Heat timer . And even Bacnet into your existing JCI N2 system if that will help with the sell.

heat-timer.com/mpc-steam/