Stage-fired boiler controls?

vaporvac

I'm soon to be installing two (2) Slantfin TR50s with Riello G-4oo burners to be stage-fired. This is on a gravity return Trane vaporvacuum system most of which is intact and running fairly well. Many of the valves are original.

The question is which controls to use to stage-fire it. I had though to swtch between boilers, but would happily go with simpler controls for the time being to get it up and running. SF says they know some pros use Heattimer and Teckmar, but don't really advise one or the other. so no help there.



Jamie suggested using vaporstats.

see: <a href="http://www.heatinghelp.com/forum-thread/147639/Which-Vaporstat-for-stage-firind-boilers">http://www.heatinghelp.com/forum-thread/147639/Which-Vaporstat-for-stage-firind-boilers</a>

This past discussion incorporates that approach, but also adds a Tstat: <a href="http://www.heatinghelp.com/forum-thread/145847/Lead-lag-set-up-for-two-steam-boilers">http://www.heatinghelp.com/forum-thread/145847/Lead-lag-set-up-for-two-steam-boilers</a>

I found the empty boilers mentioned at the end a bit disconcerting. Wish there had been a follow-up, SF said I wouldn't need pumps and probably not even a condensate return tank.

Here are a few other posts i found of interest:

<a href="http://www.heatinghelp.com/forum-thread/95546/Boiler-Staging">http://www.heatinghelp.com/forum-thread/95546/Boiler-Staging</a>



<a href="http://www.heatinghelp.com/forum-thread/147044/1930s-VECO-Vapor-System-Boiler-change-and-system-upgrades">http://www.heatinghelp.com/forum-thread/147044/1930s-VECO-Vapor-System-Boiler-change-and-system-upgrades</a>



<a href="http://www.heatinghelp.com/forum-thread/132199/Two-Steam-Boilers-in-Parallel">http://www.heatinghelp.com/forum-thread/132199/Two-Steam-Boilers-in-Parallel</a>

<a href="http://www.heatinghelp.com/forum-thread/145847/Lead-lag-set-up-for-two-steam-boilers">http://www.heatinghelp.com/forum-thread/145847/Lead-lag-set-up-for-two-steam-boilers</a>

Does anyone have any experience with these different set-ups? I don't mind changing later, but would like to have something soon before I actually NEED the heat over here.

Thanks for all the help...almost there! I think I'll get the dubious award for having taken the longest getting my system changed out.

Colleen

Dave in QCA

The Steam Whisperer

Colleen, The Steam Whisperer, fka boilerpro, has done installs exactly like yours. You have images of one of them. I am not sure, but as I recall, it might have been a trane system too. He controlled the staging with a 2-stage thermostat. Of course, I would assume that a vaporstat is required for each boiler too. With this setup, if you turn up the thermostat, it will cause both boilers to run until the temperature is almost caught up, at which point one of the boilers will shut down allowing the other to run until space temp is satisfied. In normal operation, as soon as the temperature falls to the point that the T-stat calls for heat, it will only call for first stage heat. One boiler will operate until the call for heat is satisfied. If one boiler cannot keep up with the heat needed and the space temp falls slightly more, the second stage will come on until the space temp warms slightly, at which point second stage will shut off allowing 1st stage to continue running.



The potential problem with steaming with only one boiler is that the piping loss and pickup factor are not being met. This will normally cause steam distribution problems. The Steam Whisperer dealt with this issue by have all of the radiator valves opened only slightly. He intended to go back in the following year and install inlet orifice plates, but I don't know if that was done. If it was, it would correct steam distribution issues when firing at low fire. The orifice plates are inexpensive and easy to install.



All of that said, I have a Tekmar 279 in my building. I find it to be great, but it does not provide 2 stage control. I have a burner that does have 2-stage firing and it is controlled by a second vaporstat. My boiler is oversized so that I can put the garage and chauffer's apartment back onto the system in the future. At the present time, the system is working fine firing only on the first stage.



The advantage of the Tekmar in my situation is that the building is presently apartments. I can control off of 2 sensors and the tenants cannot adjust. The Tekmar provides very even heat with little no fluctuation in space temp. However, I would expect that a thermostat with a proper anticipator would do the same. I would also assume that a 2-stage thermostate set up on your system would also provide a very even temperature.

jumper

why two boilers?

With staged burners why not one boiler with low fire sized fairly low, say 15%? So on low rads never get cold but luke warm. Isn't that the idea of vacuum steam heat?

vaporvac

Toggling between Boilers?

Thanks for the replies. I am reviewing StWh's installs. I guess my real query was how the vstat/tstat setup toggles between the two boilers. I would like to do that at some point in the future. Of course i could just change the setting from time to time and toggle them manually every month or so. That certainly would be simpler.



I had emailed STWh directly and I think he said he never installed the rest of the orifices, but i could be mistaken. I know I had written to some Wallies about the condensate tank and, in conjunction with SF, we decided to give it a miss unless we see a need later. My system has many of the original Trane valves which do sort of the same thing as orifices. I'm hoping after the install to see about replacing those that don't with something similar or orifices. Is that what you have, Dave?



In sizing these boilers, we took the Trane valve/orifice issue into account, but there is extra capacity for sure. We may have sqeezed by with the Tr40w. While we may still need both boilers to steam initially, weprobably doesn't need them both to maintain steam, especially in the vacuum situation. Of course, on very cold days the requirements will change.



Thanks for your input, Jumper. Hopefully , the two boilers will work similarly to the two-stage firing as you described. That's the goal, anyway. However, that ship has sailed; the two boilers and burners have been sitting in my basement for a couple of months. Yikes! It really came down to price for me. My set-up was probably 1/3$ of one large boiler and two-stage burner...at least for the equipment. I'm hoping to reuse much of the piping from the old boiler and only have to buy some elbows, valves etc. We'll see if it was the best decision down the road, but it can't be any worse than what I had!

JStar

Staging

I'll take two staged boilers over one big staged burner any day. The two smaller boilers will heat up faster and add a level of redundancy for peace of mind.



Use the Vaporstats to control staged pressure, and a two-stage thermostat coupled with a TACO 2-stage switching relay to control the boilers.

jumper

ship has sailed

So it's too late. But two equally sized burners only give you 0; 50%; or 100%. Lo-Hi-Lo can provide 0; 33%; 66% or 99%. 0 can be too cold but 50% is usually too warm.



With vacuum systems steam heat can actually be more precise than hot water.

Eastman

balance

How would you balance the system?  Size the orifices for 33% at minimum vapor pressure, then increase the pressure as outdoor temperature drops?

JStar

Balance

The orifices are sized at 85% capacity. The boiler will build different pressures at different temperatures naturally. On mild days, the boiler won't have to run as long, and won't build pressure.

Eastman

Jstar

,it was a hypothetical not related to your install. But I'd love to know how you would approach  such a fire ratio.

vaporvac

How to proceed?

This is a repeat of my comments left on The Epic Trane Journey post, but I thought others might benefit from the specifics and would probably not read that post in its entirety.

The two twinned boilers have differing firing rates of 200Kbtu and 230Kbtu respectively.Currently (until Tstat wire replaced), I'm manually controlling the boiler by turning them on and off either at the switch or at the boilers.



The pressure is the most interesting thing. From a big set-back on a VERY cold day, I get 1 - 11/2lb on the 230btu boiler and a couple of ounces on the 200btu boiler. These are readings from the factory 0-30 guages, but they are always the same under similar conditions. On warmer days, there's no pressure on the 200btu boiler and maybe 1/2lb. on the 230 one. I still get between 5-7 " vacuum regularly with all the leaks in my system.



I usually shut down one of the boilers once steam hits the rads. Even on VERY cold days, the larger burner alone will continue to raise the temp with a negligible pressure, while the smaller burner will maintain temp at 0 lb. The latter actually operates in a 2" vacuum if the weather is in the 30s!!!! while still raising the indoor temp. It really highlights how useful ODR would be in maintaining a good indoor temp as that seems to be what's driving the pressures.



Interestingly, One time I thought I'd turned them both on when it was coldish to bring the house temp up. It took a bit longer than usual, but I realized that was because I was only heating with the 230Kbtu boiler. I was surprised it would heat the house at all, (although I don't think that's the most efficient way to heat long-term).



So now the question is how the heck to regulate this thing? It would be great to let it go into the vacuum to distribute the heat and maintain a steady temp. Currently the rads get hot all the way across and stay warm for a couple of hours when in vacuum. On warmer days, only the smaller burner would be needed to main temp.



I have ta 2-stage Honeywell wireless Tstat and two Vsats with a 1-5lb gauge, but am now wondering how to set that up to maximize the two differing burn rates as well as the vacuum. Can they be used with an ODR and how would that be accomplished?

Any and all thoughts are welcomed and thanked for in advance.

Colleen

nicholas bonham-carter

Final steps-the controls

I'm so glad to hear your report of good operation, even though you have to flip switches to get some heat.

Now that the boilers and burners are operational, with 2 different burn rates, I wonder how important the Taco boiler switcher is. It would be better to log the results further to see which one should be the lead boiler, and which the lag.

As I see the control strategy, when firing from cold with a two-stage thermostat, the thermostat will energize both boilers. As they fire, and the steam fills the system, the vaporstat will cut off the lag boiler at the setting you choose-from 2 ounces to 6, (if the pressure should rise that high). As the inside temperature has risen by this time, the 2-stage thermostat will probably reduce firing to 1-stage(boiler), and the lead boiler will carry the load.

During most of the winter, the temperatures are average, instead of very cold like the design temperature. Maybe these average winter temperatures can be handled by the smaller 200k boiler, and if so, that would be the lead, which will continue firing when the lag has been cut off by the 2nd stage of the thermostat, or the vaporstat.

In a vacuum system, at moderate cold temperatures, the vaporstat will rarely see the 2-6ounces of maximum pressure, so it will be up to the thermostat to do most of the controlling of the 2 boilers, while operating so much of the time at sub atmospheric pressures. Some experimental time will be needed to determine the correct setting of the CPH on the thermostat.

I'll probably be doing the same thing with my chapel Dunham project this summer, and so any observations you may have will be useful.

Keep up the good work--you are a great credit to all of us non-professionals on this site!!--NBC

vaporvac

toggle switch?

Thanks for your reply. So do you think a toggle switch would work that's similar to what Jamie suggest sin my post: http://www.heatinghelp.com/forum-thread/147639/Which-Vaporstat-for-stage-firind-boilers



" I would also be inclined to wire the assembly with a switch (four pole double throw) so that either vapourstat could control either boiler; that way you could change which boiler was lead and which was lag from time to time. Which would probably be overkill."



This way I could manually change which is the lead/lag boiler depending on general weather conditions. ie. use higher burn rate in colder weather? Would this be something to just add to the system suggested by Jstar in the above post and if so, how would it be wired, specifically. OR, is there some other way to do this automatically?

nicholas bonham-carter

2 stage controls

I think the wiring needs to accommodate not only the vaporstat connection to the lag boiler, but also the switching of the thermostat (second stage wire) to either boiler.

I am not enough of an electrician to do that, but maybe Jaimie can.

To repeat my control theory, the thermostat has 2 output paths: first stage, and second stage. The first stage will fire first, and most often, and if that lead boiler has trouble keeping up with the heating load, then the thermostat will energize the second stage, and the lag boiler will fire. The lag boiler will have the vaporstat wired in series so that when the low pressure is attained, it will cut off, even though the thermostat second stage calls for heat. Soon after a few pressure cycles, the thermostat 2 stage will be satisfied, and the system will be fed with steam from the lead boiler (still running) at sub atmospheric pressures.

In order to switch either boiler from lead to lag, and vice versa, needs some fancy wiring, and yet would be good to do as you don't know which one to choose for either job. Just make sure that the vaporstat is on the second stage output wire from the thermostat, and then connect to some sort of switcher. I don't think a vaporstat is needed on the first stage, because one boiler on its own will not produce any pressure above zero.--NBC

vaporvac

So I think my wiring question is buried in the copious text on my Epic Trane Tale: any thoughts on the following questions?

My last hurdle is wiring up the Tsats to stage them. Does anyone have a wiring diagram for that? I've yet to find anything. I know I'll have to redo the Tstat to the staged wiring (it's for single-firing now) and set the cycles to two-stage, unless I still keep it at steam/gravity. There's not alot of info on this aspect, so any help is appreciated.
p.s. the 240K boiler (vs. the 200K) does get about 4oz of pressure on its own sometimes.