Automatic Flue Dampers in High Rise Buildings

Carl_21

...very possible. The draft controls do indeed appear to be very old, e.g., Bakelite gauges, switches on carbon blocks. We already have thermostatic control valves on our radiators. Hot water is supplied from a completely separate system installed only 5 years ago. For the boiler control system we have better than a heat timer; we have a JC FX controller interfaced to a parallel positioning combustion controller. If there is any benefit to be had from such a device in the first place, the flue damper could be interfaced to our controller.

Carl_21

Automatic Flue Dampers in High Rise Buildings

I am on the building committee of a 1920's era, 16 story coop apartment building in Chicago. My building is heated by a true 2 pipe steam heating system that has been well maintained and upgraded as new fuel and control technology has become available. I have recently learned that what I thought was a properly functioning automatic flue damper on our boilers has, in fact, not been functioning for decades (well before I moved in to the building). My question is whether or not it is worth replacing. Searching this forum, I sense that people have realized underwhelming efficiency gains from automatic flue dampers, but as far as I can tell, these discussion threads concerned smaller systems than ours. To give some general parameters, our boiler's furnace burns ~850 therms of natural gas on a typical 10 degree F winter day and vents into a large steel stack that I estimate is around 5' diameter and perhaps 180' high, running through the interior of the building. The boiler breach to that stack looks like it's around 3' diameter, but the stack is larger because it used to vent 3 such boilers -- we now run only one at a time. Air intake is from the boiler room, no external supply. The boiler itself is the original, 3 pass, steel, fire tube boiler built on-site circa 1925 to run on coal, since converted to natural gas. The system's current steady state efficiency during a heating day is around 70%. (Burner efficiency is over 80%, the 70% figure comes from an I/0 analysis of actual heat delivery. Seasonal efficiency is probably circa 60%; we've not calculated this yet.) How much efficiency gain might we realize from installation of an automatic flue damper? On this forum and searching the internet generally, I see wildly varying figures and further, these reports do not seem to apply to systems like mine.

seabee570

big old boilers

your existing 'flue damper' that has been disconnected may be left over from the coal days.This may have been used to control and balance the draft when firing coal.I have not really seen auto dampers on large boilers.best bet is to install individual thermostatic control valves on rads,and possibly a control such as a heattimer to control boiler.You might also look at lowering pressure at boiler,otherwise,look at replacing the boilers.How is the building domestic hot water heated?

Carl_21

Pressure

Oh, and we run 0.5 PSIG at the boiler header and -2 PSIG at the condensate receiver which has a vacuum pump.

GusHerb

heat

this system sounds very interesting can you post some pics?

RonWHC

Give this a try.

http://clevelandcontrols.com/Actuators & Regulators.htm

Carl_21

Exactly

That is the supplier being recommended to us. I've read their "Why is Draft Control Recommended?" white paper and it certainly makes sense. Significantly for me, it states, "High-rise building design, which provides a naturally high stack influence, amplifies the need for accurate draft controls." Further, since my building is on Lake Michigan, the wind at the top of our stack can vary tremendously (70mph is extremely common as measured by our building's anemometers)...further amplifying our draft variance. So I am sold on the theory. But I am wondering if anybody on the forum can speak to actual, realized efficiency gains -- a ballpark estimate.

Carl_21

I don't have any right off

...but I'll get some eventually. It would seem to help discussions like this. Cheers.

RonWHC

Mighty big ballpark

Most of the stack dampers discussed here are fully open during burner operation. Not referring to Barometrics. As you know, the Cleveland will respond to draft based on the burner's modulating input & what's happening in the stack. That feature is at least as important as closing off @ end of combustion cycle.

Why have a 3' diameter breech opening when your 3:1 burner only needs 1/3 (or less) of that area in low fire? Additionally, how much fuel could be saved if it were easier to tune the burner, w/ a stable draft, through the entire firing range?

The answer(s)? It depends. Not an enganer (sic on purpose) & not a fan of the up to xx% savings. But, I wouldn't think of selling new combustion equipment on a steam system, w/ a 160+' stack, w/o recommending a fully automatic damper. Makes too much sense. $$? Pick a number.

Carl_21

Like I said, I am sold

I am an engineer, although electrical and not mech/civ/arch/HVAC. I am doing my best to remember my one course in thermo from college as I learn about steam! If it were up to me alone, I would proceed for the price that I have been quoted on the general principles we have been discussing. But I am in a cooperative that houses everything but engineers: mainly lawyers, traders, doctors, and accountants. (Other than myself, I think there is only one other technically trained individual ...unless you count the doctors which took chemistry about as long ago as I took thermo.) So my issue is selling the expense to my community. I think I can swing it on the basis of a Minnesota govt. report I found that advocates draft control as an energy saving upgrade. But my intuition + one Googled report (and a suspiciously optimistic one at that)...I am seeking more numbers if there are any to be had.

Carl_21

Oh and the vendor's value proposition

Add Cleveland's value prop to my ammunition and the contractor's opinion that recommended them. But a skeptical resident will say that they both have an interest in advocating sales. That same resident will say that Minnesota group sounds like they are sponsored by Al Gore. And they will at least politely listen to my opinion. But I can get this funded more easily if I have more supporting points of view. I will, of course, share the transcript of this discussion thread.

Carl_21

That \"Minnesota Report\" I refer to

Authored by a local utility and funded by Minnesota state grants: http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/95/950909.html Directly on point, but the range of savings quoted seem very high. Perhaps this is due to their testing upgrades on steam heating systems that have not been upgraded or less well maintained or generally in poorer condition than ours is to begin with?

Rich Kontny_3

How much heat is lost?

I question the need for a flue damper on a power burner and a three pass boiler. The resistance of a cold boiler and the tall chimney negate the need for a flue damper.

A positioning type damper may be neeeded if you are modulating the firing per load(s).

Carl_21

I think this was my misuse of terms

"Automatic draft control" is what I should have said. We are modulating the firing with a Honeywell RM7800 combustion controller and this interfaces with a JC FX controller that monitors the condensate return lines to determine demand. It all works very well and substantially improved our fuel efficiency and heating comfort. Since we have that, my question was whether or not a draft controller would enhance our fuel efficiency significantly. For us, anything greater than about 1% would justify our installing one.

RonWHC

Yep.

W/ the auto damper, the opening to the flue will also follow what's happening w/ the burner. Draft controller would interlock w/ the modulating circuit controlled by the RM7840.

FX tells the 7840 to trim firing rate - interlocked draft controller tells damper what's happening. Precision draft control is a lovely thing.

seabee570

cleveland control

I remember an old large coal boiler converted to gas that had a cleveland control on it tied into burner.It seemed to work ok but you have to watch where the small cleveland motor is mounted to damper.I recall that it should be as close as possible to avoid stress on the tiny fractional hp motor.(premature motor failure).I am not sure on the savings,but it might help a little in keeping the heat in the boiler a little bit longer.good luck