1900s Thermal Chimney

Brad White_198

Glad it helps.

Yes, room by room is probably how I would go regarding the relief. But keep in mind that what may not originally have had fusible link fire dampers before may require them now. (Nothing Is Easy). I would get ahold of the architect and ask what the ratings of the shafts are. Fire dampers can often be installed behind the grilles and the grilles can have dampers.

Another thought on pressure control: "What If" you could have a top-of-shaft master damper which would use the same Delta-Pressure principle to maintain a certain setpoint behind a damper at the top of the shaft? Cap and safe-off the top of the shaft with sheetmetal, then cut in a damper sized to allow some back-pressure. Top the shaft with a rain hood and you could be done.

It may not be "room by room" but you know what? Those older buildings are pretty leaky and the air will find it's way out. At least as a group you will relieve. The only reason you want to make sure you relieve is that too much back-pressure (too little outflow) reduces your UV inflow which is where it counts. Make sense?

Ah! I see you found the pull chain locations.

As far as disconnecting the radiators, if they are isolated and the pipes can just be cut, I would not be too concerned about removing them unless gross demolition presents the opportunity. You could spend a lot of money on demolition and patching (most likely tile, glazed brick, terra cotta and other masonry), remove the radiators for what purpose? At least now they slow the airflow somewhat.

My $0.02 anyway!

Jeremy Scott

Trying to figure out an old school building in MA. Originally built with steam radiators in the classrooms. Each classroom has a vent in an interior wall for ventilation. When we opened the vents to see why we could see daylight through the grills...we found that it was part of a chimney system with no dampers! Needless to say this building uses twice as much energy as you would expect. We figured these chimneys were designed as thermal chimneys using stack effect to exhaust air. To our surprise we found just above the vent in each classroom (each vent has a dedicated flue in the chimney) there was a steam radiator! I'm guessing these were used to increase the stack effect but there is no control on these radiators! Literally all of the heat is going up the chimney!

Now these classrooms have unit ventilators. We would still need to use the chimneys to relieve the pressure created by the UVs. Just need to add some automatic dampers. None of the chimneys have caps either so water fills the bottoms.

What a crazy design...anyone ever see this before?
Jeremy

Brad White_194

Extremely common, Jeremy

Perhaps too much so.

Many old schools, hospitals but mostly schools had such systems. Typically they terminated on the roof with a brick curb covered with a raised shed roof made of -drumroll please... copper (!) Ever wonder why your shafts have no caps? I have an answer for you, -in my truck. My brother-in-law found them, honest...

The principle was simple but energy-intensive in the days before electricity and fans being widespread. You nailed it, exactly, how they were intended to work. Double the energy? Much higher. Airflow rates are uncontrolled. Out of sight.

Large pin type radiators or standing radiators in concentration would be installed in a sheetmetal plenum the base of a supply system. 100% outside air was drawn by convection over these radiators, pre-heating but moving the air. Such air was delivered low in the rooms, usually. Look up "indirect air heating"; this is the same thing.

On the exhaust side, similar "accelerator" radiators moved air upward from the base of the exhaust "chimney", thus inducing room air to follow. These room exhaust inlets were usually high in the classroom and opposite corner if possible from the inlet.

A variation of this was to install just the exhaust side and allow operable windows to do the intake work but conditioned by the room radiators instead. "Iffy" in that it required human intervention, but then, humans have very good stuffy-sensors.... I suspect that this is what you have, exhaust-side only operation.

They often did have chain-operated or cog-operated dampers in large stamped grilles for some control, but these may have been removed.

Good news is that the shafts make great pathways for ducted systems and can be insulated and capped.

For pressure relief especially during economizer operation, I set up dampers to respond to a delta-P (differential pressure) signal, indoors to outdoors, of about 0.05" WG.

The relief damper modulates to maintain positive pressure indoors so that the airflow is always outward. I even do this when I relieve excess return air to ventilate a mechanical room.

I started doing this when gymnasiums with high relief dampers above the bleachers would allow light snow and misty rain onto spectators. By assuring an outflow the problem was solved. Cost-effective for a large space but may be costly on a classroom by classroom basis.

Incidentally, with unit ventilator jobs, I always wished for a way to really use energy recovery wheels. Sure, you can pre-condition some outside air with recovered exhaust energy but you need a place to put it. An auditorium or corridors are good bets at least.

What I do like are the small classroom size HRVs and ERVs to take the edge off. For example, a 1,000 CFM unit ventilator bringing in say 400 CFM normally (15 CFM for 27 people depending). If you use one of these ERVs or HRVs, you can exhaust and introduce maybe half your OA or more, leaving less to be actually conditioned by the UV.

Sorry to ramble, but yes, you nailed just what you have. I would make sure that the radiators are disconnected though, in case a freeze happens. I do suppose they are drained by now.

Mark Eatherton

Wow....

Thanks for the heating history lesson Brad...

I learned a LOT today :-)

ME

Darin Cook_8

Brad - You are a real smartie!

How did you get so damn smart? Here, I thought that I was pretty good to be able to stand upright and having opposing thumbs. Standing next to the black obelisk, hearing the funny vibrations, and picking up a leg bone to use as a club was just a big bonus.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

JJ_4

Reverse in Southwest

I have heard (but not seen for myself) of passive evaporative cooling chimneys in NM and AZ. No fan, just a ring of misters near the bottom of the chimney that creates a downdraft and cools air as it enters the house. I suppose you could use the same chimney for fires the winter (tho you would have to give it a good cleaning prior to summer!)

Jeremy Scott

Interesting...

Brad, very helpful! Sounds like we have an exhaust only system as you suggest with operable windows. I was trying to figure out how to provide exhaust for the UVs using the chimneys but was thinking the stack effect would still create too much flow even with the radiators disabled. I like the idea of operating dampers based on differential pressure. I guess this would have to be done on a room by room basis?

Still trying to figure out how to disable the radiators. The custodians had no clue they were there. The lines enter the chimney to serve the radiators with no valves. Plus we can't find where the pipes come from...even getting into the chimneys to cut out the radiators would be tricky...its like they installed the radiators as the chimneys were being constructed. Nearly impossible to get at them...I can't wait for the boilers to fire up so we can see if the radiators are still live!

The old grates have stamped on them "pull chain to close damper". Of course all of the dampers are gone. Luckily they have a control system for the UVs and boilers or else the energy usage would probably be double what it is now.

Jeremy

Bob Bona_4

I guess

MA people are just more advanced than us NY and CT goobers

Brad White_198

Nah

We just keep our old systems so we can oooh and ahhh once in a while. We talk a good game on energy but in the end, someone else is paying

It seems that way sometimes!

bob young

how about some photos, please

for prosperity. very interesting tale, bro

Jeremy Scott

Pictures

Here are some pictures of the building. Notice how large the chimneys are on the roof!

Not sure if capping the chimneys and installing one damper would accomplish adequate pressure control, would it? Each classroom has it's own shaft and the hallways share shafts on each side of the building. It would be more expensive to go to each classroom but wouldn't provide better control?

If we can find shutoffs for the radiators that will be the way to go. Hopefully we can...other option would be to install a new hot water system but that would be a little extreme...

thanks so much for you insight!
Jeremy

Brad White_198

It would seem

that if each classroom runs express to the roof, you might not need fire dampers. Only your architect can determine that, or the code officials and this depends on the wythes of brick between the shafts and what fire rating is deemed to be between the shafts. Still, better than a ganged shaft.

Given the individual nature though, the relief should also be individually done. There does not seem to be a common plane which would allow sharing of the relief via a common control.

Another idea: Poor Man's Relief, I would call it. Counter-weighted dampers set in the shafts or at the grilles. The arms could be adjusted to only open when the room pressure got to such a point. (Could be as high as 0.10").

Regardless, you need some control, even if the relief air is "wasted". When the UV's do not run, you really do have several open doors' worth of uncontrolled leakage.

Yet another thought: Two-Position Dampers, small enough to back-pressure, (1 square foot or so, even less), interlocked to open during occupancy and close at the end of the school day. As the simplest low-cost fix, that is what I would do.

Where in MA is this school? Are you the contractor or engineer/designer?

Jeremy Scott

Brad, I am an engineer trying to figure out how to save energy in the building. Controlling these chimneys should have a very quick payback. Thanks again for your insight!
Jeremy