Outside temp two boiler control

Mike T., Swampeast MO

Boilerpro:

Is the the difficulty with balancing particularly difficult using this scheme with 1PS due to frequent poorly sized radiation with the requirement that they not only be well balanced among themselves, but properly sized to the load based on the condition of the shell? If so, would it be correct to assume that TRVs wouldn't be very helpful because they can't do anything to correct for the steam volume imbalance in the system?

steve_173

I'm still finalizing my boilers. The plan is to do a 3 and 5 section G8. It has been suggested that rather then regulate the on/off of the 3 section with a lower steam pressure, I should regulate the 3 section with the outside temperature. The person claimed this is simpler and will work better (what ever that means).

What would be appropriate system steam pressures to shut off the 3 section and to shut off the system?

What would be an appropriate outside temp to turn on the 3 section? Would this even work as I need both boiler to get adequate sq ft of steam in the system?

Al Letellier_9

steam boilers

Unless you are zoning your system and use boilers accordingly, I don't see this scenario working very well. You still have to fill the system with steam and if that 3 section won't produce enough steam to do the job, you will still run both boilers all the time. I prefer to see the boilers full size and staged with a cycling control. That way you have full redundency in case of a burner problem, lead lag capabilities and cycling with outdoor reset. For multiple boilers, Heattimer makes the best controls on the market(in my humble opinion). Why two boilers?

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steve_173

Splitting the system into two boilers serves two purposes. 1) I can use the G8 (they don't make one big enough). 2) I gain some efficiency if the system is set up right.

This forum so far has suggested initially firing the 3 and 5 section and then shutting the 3 off at a lower steam pressure and letting the 5 run until the temperature is satisfied.

I think your are suggesting using two full size boilers with staged guns and/staged firing. Why is this better than the plan so far?

Al Letellier_9

boiler set up

This set up will work and is the recommended way to stage steam boilers, but why a 3 and a 5. I have been off the wall for a while and didn't see other posts. I guess I don't understand exactly why two different sized boilers.

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steve_173

I think is was Steamhead and others that suggested a 1/3 and 2/3 of needed capacity arrangement. If you go 50/50 the second one will run longer than in a 33/67 setup, using more fuel.

Why would you suggest a 50/50 arrangement?

Which setup are you saying will work? outside temp control? or steam pressure control? both?

The Steam Whisperer (Formerly Boilerpro)

I suspect the 1/3, 2/3 set up is because

when the system is up to temp, the pick up factor drops out...about 1/3 the capacity. Also, if you have a very well balanced steam system and the radiation is well matched to the heating load, on a typical winter day a 2/3 capacity boiler would fire about continuously at very high efficiency and very closely match the heat loss. The key to making this work well is excellent system balance,which is much easier to accomplish on a orifice type vapor system or a two pipe system. One pipe systems can be a greater challenge.

Boilerpro

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steve_173

Very interesting. I should have realized that the 1/3 matched the pickup factor. No point in heating the pipes over and over again. Using this logic (2/3 boiler net output times 1.33 times 240 divided by house square footage), does 54 btu/sq ft sound right in a 1920 stucco/plaster home with original windows (w/storms) and no insulation (just attic)?

Any tips on balancing a single pipe system with such a setup? Can one set a vaporstat to 12 oz? I think this is what was previously proposed on the forum. What should the overall system pressure be?

How crucial is this 1/3, 2/3 balance? Assuming the radiation load is correct (which with some convectors is not easy) the 1/3 to 2/3 balance is actually 0.35/0.65 and 0.38/0.71 as a fraction of net boiler output and required sq ft of steam respectively. I think this means that the 2/3 boiler can maintain the house and has a little reserve for minor piping losses. I think this is better than being under the 0.66 mark where the smaller boiler might have to keep cycling.

As a side why would anyone do this setup with one big boiler? Net cost isn't that much greater for two smaller ones.

Al Letellier_21

two vs. one

You may think that the cost is relatively the same looking at two small boilers vs. one large one, but you will be in for a big $urpri$e when the bill comes in. The added piping, labor, staging controls, insulation and other stuff can drive that price up in a hurry. I am a big fan of two boilers sized at 100% with staged burners and cycling control. But then again I dream a lot. Not too many folks are willing to pay to do it the ideal way.

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steve_173

What is an example of how you would ideally run a steam system using two full size boilers? When I spoke with Powerflame about their staged guns they said most staged guns don't go much below my full system capacity of about 300 MBH. Maybe Riello makes something.

Large knockdown versus two packaged is about the same other than the auto feeder cost. At least this is what my plumber is saying.

steve_173

As a follow-up to that, what sort of problems can one run into when building insulation is added to a single pipe steam system? Does the system run and shut off or is it simply too hot? Are there any tricks short of resizing the radiators? What would you advise if there is a possibility for insulation in the future?

As an idea, could you paint part of the radiator with a ceramic reflective paint like Supertherm to insulate a portion of the radiator? Would you paint the supply or air valve side? Since this would reduce the EDR would the boilers then be oversized?

The Steam Whisperer (Formerly Boilerpro)

One pipe balancing

As with all steam, it appears to be all in the venting. It seems to be very important that the radiators are not over vented, because if they are, the steam will travel to the radiators first and not fill the complete steam main. According to the venting charts, the Hoffmans allow the smallest venting, so I try to use these. This way, you hold back the steam from filling a radiator until the whole main is full (using big main vents) then the radiators begin to fill. Since you are not directly metering the steam, but only the vented air, I think you could get into trouble easier with one pipe, than two. You end up havding to balance the radiators against each other, rather than metering the steam from the main into the radiator ( like orifice vapor systems). The steam potentially could see the full radiation load, but I suspect that ounce steam is distributed to each rad, the condensing steam will then pull more steam into the radiator. Its just important to get it moving in the right direction and the right quantity from the start.

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