Multiple boilers, two way vaporstat

Phil_17

wouldn't the setup work better like this:
1.stat calls for heat--both boilers fire
2.pressure rises to 4oz. vaporstat cuts out out one boiler 3.remaining boiler slowly builds pressure to cutout point [12 oz?]
4.if single boiler cannot maintain pressure inactive boiler is then fired by vaporstat
i think this would get the steam up quickly and then maintain it at the optimum low pressure
opportunities for tuning are in trying to find which of the 2 boilers is the ideal "maintainer" --nbc

steve_173

If you use two boilers for steam in a 1/3 and 2/3 load configuration, are there vaporstats/other controls that can shut off either one depending on the load, temperature, etc?

Could one just run a vaporstat in each direction with a valve and then shut the bigger boiler first when it is warm and the smaller boiler first when it is cold.

What other ways can the two boilers be controlled?

Any idea as to the efficiency gain with two boilers versus one larger one?

gerry gill

weve done it with

a two stage thermostat..and another with a vaporstat..as for efficiency, depends..how often is the off boiler really off..maybe the triggered boiler should just go to low fire..theres many variables to a multiple boiler set up..just keep in mind your waterlines have to be at the same height..

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SpeyFitter

If I did a two-stage thermostat I guess the up stage would be both and the down stage would be either the 1/3 or 2/3 boiler. Which configuration makes more sense? Could this be easily adjusted seasonally?

The vaporstat would control the on/off based upon the steam pressure. To me this seems more accurate as far as efficiency is concerned that the temperature. Does that make sense? Which boiler should go off first in this configuration?

Is it hard to get the water lines to be level?

gerry gill

you can get

pretty intricate with this type of set up..you can add as many controls as you see fit..the vaporstat method is perhaps the better way to go..you could then have both fire on high fire..then perhaps have the smaller go to low fire on a pressure rise..another vaporstat could even then take it off line if the pressure continued to rise..or the big boiler could then go to low fire..see the options are there for the choosing..you'd have to decide which method works best on the system your working on..what works well on house #1 may not work well on house #2..there will be a tweaking period..getting the upper water lines the same is easy..but the lower water lines more difficult..burnham independance models have the same water lines even when they reach a size that appears bigger..makes that part take care of itself..

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jp_2

pressure and Tstat

you need something like an Omron programmable ZEN relay.

set it up to fire little boiler first, then when that can't keep up switch to the larger one, then when that can;t keep up fire them both.

the piping would be harder to do I would think???

sounds like a fun project. not sure if the boilers would like to run that way though?

SpeyFitter

Any idea what sort of cost?

Anyone else know about the costs of such a setup?

SpeyFitter

Won't all boilers have the same lower and upper water level if one uses the same boiler family So two Burnham, Smith, etc. boilers have the same levels, but more sections on larger boilers.?

A problem could come up if one boiler fails and can't be replaced with an identical product. I'm gonna put the boiler on some blocks anyway. How much lower water height variations exists across product lines so I can get a sense if a different height block would work in the future?

I'm trying not to get too complex as this is already above most plumbers understanding. Is there a simpler is better apporach that should work well in most cases?

SpeyFitter

I think you are saying let the vaporstat control the on/off of one of them and the trick is which one. Can one switch which boiler is vaporstat controlled without going over to logic controllers? I guessed that it is better to cut the smaller one, but someone today said maybe cut the larger one and let the small one maintain. Or would such a setup cause the larger one to short cycle in an attempt to bring the pressure up?

Combined they still need to meet the sq ft steam requirement?

Steamhead (in transit)

Have the Vaporstat

shut down the smaller boiler at 2-3 ounces. By this time the pickup factor is satisfied, and the larger boiler just simmers along until the thermostat is satisfied.

The smaller boiler could also drive an indirect.

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SpeyFitter

This is what had previously been suggested. I've been told indirects are not worth the trouble on a steam system. Plain old water tank is the way to go.

When the weather is warmer (say >40 degrees) wouldn't it be better to shut the larger one first? Could one achieve this just with two vaporstats, some valves, and some extra pipe by controlling the steam flow through one vaporstat or the other?

gerry gill

your overthinking this i think..

using two boilers of the same make should keep all waterlines the same..bring all your wires to a terminal strip, and if you want to play around its easy then to switch wires and screw terminals..it works fine..

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