Old schools

[Kman0923]

This is my first post, been lurking on here for a few months. I was excited to see somewhere to discuss T&B.

Here are my questions. Im in the Chicago area and have been doing a fair amount of work in Chicago Public Schools (CPS). Most of these schools are close to 100yrs old or over. These types of schools have the concrete air tunnels in the basement to distribute flow to the classrooms and relief vents to the attic. What im curious to know is what is this type of system called?

Im also hoping someone else understands these type of schools to help me understand what I have experienced. It was explained to me by a building engineer that class room doors need to be closed for the system to work properly. What I noticed on a different school after a teacher explained to me her room was always cold, I took 2 readings in that room. One with door open and one with door shut. The supply for the room was 19x70" and to just get a good idea of what was happening I got an average from 4 velgrid readings. With door open my average was almost 0, and with the door shut the average was around 44fpm. Keeping the door shut appeares to pressurize the room like a baloon. Trying to keep this simple, this is just the tip of the iceberg for issues on this school.

Any thoughts?

[hvacker]

I can understand why the room is cold. Your not moving any air to speak of. You didn't say how big the room was but this amount of air is enough for a small space like 400 square ft. aside from other conditions. I don't understand why the air dropped when the door was open. Kinda backwards.
First, is air available. Filters, belts, dampers, all that stuff. Work from there to see where the air is going. Check to be sure this isn't a ventilation system and the room is heated by other means.
BTW those tunnels were often used for piping. Sometimes asbestos was used to insulate them. One school I worked in didn't remove the asbestos and just posted a warning near the access. Because of the warning I was shown an access w/o one. A bit pi$$ed when I discovered there attempt to subject me to that environment w/o saying anything.

[Poodle Head Mikey]

How are the "air ducts" arranged? Are the runs lined up under the rooms?

I ask because I have worked on a couple of buildings with concrete (and red brick) underfloor 'air ducts' - but the primary heating intent was Floor Radiant - not forced air. You could not set them back because the huge thermal mass of the floor was intended to be warm all the time. The air venting out the 'registers' is not the primary heating source for the space.

PHM
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This is my first post, been lurking on here for a few months. I was excited to see somewhere to discuss T&B.

Here are my questions. Im in the Chicago area and have been doing a fair amount of work in Chicago Public Schools (CPS). Most of these schools are close to 100yrs old or over. These types of schools have the concrete air tunnels in the basement to distribute flow to the classrooms and relief vents to the attic. What im curious to know is what is this type of system called?

Im also hoping someone else understands these type of schools to help me understand what I have experienced. It was explained to me by a building engineer that class room doors need to be closed for the system to work properly. What I noticed on a different school after a teacher explained to me her room was always cold, I took 2 readings in that room. One with door open and one with door shut. The supply for the room was 19x70" and to just get a good idea of what was happening I got an average from 4 velgrid readings. With door open my average was almost 0, and with the door shut the average was around 44fpm. Keeping the door shut appeares to pressurize the room like a baloon. Trying to keep this simple, this is just the tip of the iceberg for issues on this school.

Any thoughts?

[heatingman]

This is my first post, been lurking on here for a few months. I was excited to see somewhere to discuss T&B.

Here are my questions. Im in the Chicago area and have been doing a fair amount of work in Chicago Public Schools (CPS). Most of these schools are close to 100yrs old or over. These types of schools have the concrete air tunnels in the basement to distribute flow to the classrooms and relief vents to the attic. What im curious to know is what is this type of system called?

Im also hoping someone else understands these type of schools to help me understand what I have experienced. It was explained to me by a building engineer that class room doors need to be closed for the system to work properly. What I noticed on a different school after a teacher explained to me her room was always cold, I took 2 readings in that room. One with door open and one with door shut. The supply for the room was 19x70" and to just get a good idea of what was happening I got an average from 4 velgrid readings. With door open my average was almost 0, and with the door shut the average was around 44fpm. Keeping the door shut appeares to pressurize the room like a baloon. Trying to keep this simple, this is just the tip of the iceberg for issues on this school.

Any thoughts?

You say attic vent. Is that for every room?

When you closed the door you noted air movement, door shut, you noted nearly none.

That would indicate to me that the motive force for flow was not air pushing into register, but perhaps something pulling a negative on the room, and dragging air from the register.

Im in Chicago. Ive worked in many schools, but most are not CPS. I cant say Ive ever seen the sort of system your describing. Ive seen quite a few large multizone hot deck/cold deck sorts of systems.




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[WAYNE3298]

The first problem you have is using the velgrid for measuring velocity (airflow). It was designed to read the airflow entering the AHU air filters. To use it the way you did you need a correction factor which is obtained by comparing a duct traverse to the velgrid reading and correcting the velgrid to agree with the traverse. Your operating manual tells you this.
The second problem you have is you need to determine the intent of design and see if the system is operating per design. You need to know why the room heats with the door to the classroom closed. Is the attic vent just an open duct or does it have a barometric relief damper. There are a lot of other questions that need answers. Too many to ask at this time.
The systems you alluded to were normally designed with huge very low pressure fans that delivered air at a very low velocity. The air for lack of a better term got to the diffuser and fell out. A lot of these systems were steam and were basically designed to over power building leakage and etc. in order to heat the building.
There is a lot you need to know but redesign of the system and addressing building leakage will have an attractive payback if the building fits what I have described.