Overheating Steam System....Boilerpro

Art Pittaway_2

Hi Dave
Undersize the boiler and balance the venting. I can see how it would work but I would like to know what the sequence is and how long it takes to get the balance right. That's the trouble with not being a "regular" on the wall, I do miss some good stuff. Art

Boilerpro

Overheating Steam System....Boilerpro

Just looked at a one pipe steam system today in a four flat and from what the owner describes it sounds like the system is overshooting. Thermostat is set at 67, and turns on heat about this temp, but can overshoot up to 80 sometimes. The boiler is an Ideal Redflash fired at 400,000 btu/hr input, about 750 EDR installed radiation (columnar). Current heat load is about 105,000 in the living spaces plus 8,000 for basement. I belive main vents are working, but may be a little small. Pressure is also set to 2 to 3 lbs. My thoughts about the source of the problem, 1) Boiler overfired, 2) Radiation oversized 3)Pressure too high 4) High internal gains of apartment buildings making problem worse. Solutions 1)Downfire boiler or install correct size new and 2)Adjust rad vents to slow down the heat up of the rads so they are not completely hot before thermostat shuts off heat 3) Reduce pressure. Any other thoughts?

Boilerpro

Art Pittaway_2

Scortched air anyone?

Hi Dave, Got your last e-mail to me ...thank's for the nice comments. It sounds to me like you might want to look into Danfoss 1-pipe vents for the radiators. The boiler can fire or not fire, but it's the radiators heat in the room that causes the overshoot. If the building has had window replacement or added insulation the rad's are oversize. Then also where is the thermostat? The heat from the rad's has to shut it down in time to stop the overshoot, so if it's down the hall and around a corner to the thermostat then the overshoot is inevitable. Remember with 1-pipe, the only limit on radiator heat is when the boiler cycles off and pulls a vacuum (it has to do that) or if the vent shuts down because it's satisfied and doesn't vent air.

Boilerpro

Hi-ya Art

Thermostat is just outside the living room in one aparment in the hall. Thermal upgrades have been made so rads are definitely oversized; load = 120,000, rads = 185,000. Had this same situation in a church...just shut off and diconnected some rads and turned down the pressure and overshoot is gone. If figure slowing the heating of the rads by cutting the firing rate of the boiler and slowing venting will allow the rads to heat only partially in milder weather, helping eliminate overshoot and effectively reducing the size of the rads. If I have the opportunity to replace the boiler, I think I would size it close to the structure heat loss or the rad load with no pick up factor added,and balance the system using the existing adjustable rad vents and put in bigger main vents. BTW the piping is all insulated. Thanks for your input!

Boilerpro

Art Pittaway_2

1-Pipes breathe...

when the boiler fires it fills the piping and rad's, then it should go to a vacuum and pull in air to the rad's and stop the heating. That's why 1-pipe vents need to have a vacuum breaker in them. Also, you mentioned the pressure, look at a steam chart that shows specific volume at pressure. 1 psi steam is 25.2 cu.ft./lb. and at 5 psi it's 20.1 cu.ft./lb., that's a 20% reduction in volume and 12 degree more temp. If it fires slower, it still has to fill all the rad's, the question is, now which rad's don't get filled on a design degree day because it's firing to slow. Find your copy of Dan's "Lost Art of Steam heating" and read page 75 to 78. Art !!

Boilerpro

I guess you missed the \"underizing\" steam boiler discussions

I have seen several steam boilers undersized to the radiation and heat very evenly. I installed one myself that was undersized in an old Moline vapor system minus the vacumn operation. If you use adjustable air vents to balance the rate at which air exits the rads, you can control the rate at which steam enters, just like two pipe. By balancing each radiator to its current heating need, you should be able to achieve partial heating of all the rads while the boiler is running full out on the coldest day of the year. Talked to Rick P. about this, and he sees no problems with it, and I even convinced Noel of Slantfin that this can work after the other guys in his office also agreed. Interesting concept, eh, that has worked for some systems for decades.

Boilerpro

Steamhead

Also install a Vaporstat

to reduce the pressure and not compress so much steam in the rads. You can also try hand-adjustable (without tools) rad vents like the Vent-Rite #1. I did a 7-unit apartment building this way and it no longer overheats.

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Boilerpro

Figured I hear from you, if you weren't out traveling

Boiler's got a nice old prsssuretrol that the owner says runs right at what the pressure guage says, so at least I can get it done at reasonable levels. She's got both of Dan's Lost Art books...great to work with someone who does thier homework! Thanks again!

Boilerpro

Steamhead

Nice Gauges to use with Vaporstats

Winters Instruments makes these low-pressure gauges- looks like they had us steam freaks in mind. Follow this link:

http://www.winters.ca/pre_lowpressure.html

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Boilerpro

Still working on it

With the Moline System (4500 sq. ft home)I worked on I just estimated....I knew the second floor needed much less heat than the first because they had just installed 12 inches insulation in the attic (none previously, and I also knew which rooms tended to overheat, so I cut back on the supply vavles for those rooms. On a one pipe system (2,200 sq. ft home)where the boiler was just adequete to meet the calculated radiation and piping load, I started up the system and adjusted vents as needed to get an even percentage of rad heating in each room. Then if some rooms were too cool, I opened vents a bit, or too warm closed than a bit. The moline system had nearly all columnar rad, however, the one pipe had a mix, so you have to compensate for the various air volumes of the different types of rads when thinking about the settings of the vents in addition to thier overall heating capacity. Overall it took a few hours for each system, and I showed the homeowner how to tweak the balance for thier own temp preferences. A suppose a more scientific approach would be to calculate the heat load for each room, figure the air volume that needs to be vented per btu of heat output for each rad, chose a time period for that air to be vented for all the rads, adjust the venting rate on each rad vent to vent that amount of air in the time alotted to get the btu's needed for each room, and install the vents and find out what happens. What do you think?

Boilerpro