it works by induction

 

The primary air (usually the fresh air requirement) from the central air conditioning unit is discharged through nozzles at high speed. Simultaneously, it draws back-in secondary air from the room. The secondary air flows into the unit through a heat exchanger and is thus being heated or cooled. Then, the primary air is mixed with the heated or cooled secondary air inside the unit and flows into the room through an outlet grille or diffuser. OK

 

what okemechtech is talking about is called the "Coanda Effect", which is used when you have a cold air vav system (<48°F).

I believe you are talking about an induction unit? Normally used to condition the perimeter of a larger commercial building? Is this correct, or where you talking about an induction diffuser which mixes primary air with room air?

 

I’m thinking the same as oke, if this is what you have…

I have only seen this style of system on a very, very old building, at least what was describe to me as an induction system. It was heating only and setup as described above. Just a CV unit pushing air up to the rooms, each room had it’s own heating coil.


Here is a drawing that will help you see what is going on.

 

Induction VAV

Further info

Hope this is of some help.

Regards

 

That's a new one on me.

Looks like the same principle as the old school system packed into a VAV box. Shouldn’t be any different control than a fan powered VAV system, maybe tweak the AHU to run colder.

I’m curious what the min inlet static requirement is on these boxes compared to normal boxes…

 

Induction VAV

Additional info.

Engineered right, its a very energy efficient system.

Regards

 

An old hospital I've been working in lately has these induction boxes on the perimeter walls. First time I've ever seen them, not sure how well they control room temp and humidity.

Not sure what kind of temp schedule they run on the primary air, which runs constant volume thru a little 4 in. round duct into the box. A summer/winter pneumatic room stat controls a valve on the water line to the coil.

In the summer, they run some of the building's chilled water return to the coils, which is at a higher temperature than typical chilled water.

The coils in the induction boxes don't have any condensate drain pans, so if the chilled water running thru them gets too cold, I imagine condensation from the coils would be a big problem, especially if the building humidity levels get fairly high.

 

I have seen this before. Must of been popular with the designers in the 80's. And have yet to see one work very well. Like lenb said, running chilled water through the reheats is insane without condensate pans or proper insulation, its a mold factory waiting to happen, thats bad news, and in a hospital thats really really bad news. Subcool the hell out of rooms, especially inner core rooms with little natural load or losses. Maybe makes a bit of sense on the perimeter zones with huge heat gains? But other than that its crazy logic. IMO

The Chilled water has to be very cold. Seen chillers piped in series of each other to get desired temps. And this plays havoc on them as well. Creating all sorts of mechanical and staging issues with them. Overall I think its a bad idea just to save a few bucks on initial cost of install.

 

We've found above ceiling Induction Units in hospital isolation rooms....a big no-no (check AIA Table 7.1) because it invites cross-contamination between rooms and has a return. We converted them successfully to primary only.
I've seen some very old commercial buildings with them.
jogas

 

We have a system here in a building built in the 70's which worked very well, it would keep an office on the perimeter of the building i.e. 50% glass in the outside wall and OAT up to 35deg C to within 1 deg C. Chilled water at a min temp of 11 deg C ( to limit condensation) is circulated to coils in the IU units. High pressure air is sent to nozzles in the IU which induces room air over the coils and hence cools the room. The high pressure air is also cooled, this time to 5-7 deg C. There is a simple bi-metal stat which measures the air returning to the coil and will cause a damper to bypass the air from the coil.
In winter the chilled water to the IU coils was shut down and the high pressure nozzle air was now heated which provided the room heating. There are 11 of these units per side of the building and 26 floors. It was only in the 80's when PCs came on the scene and with open plan offices that the system became a problem.
The unit were manufacured by Carrier. I think I still have some brochures on the units if anybody is interested.

Gareth

 

Gareth,

Thanks for the insight .
Would be glad if I could get some brochures on the units.

Thanks
Benny

 

Induction Units

Hi

I have attached a sheet showing the basic operation of the unit. If you want more contact me direct and I can mail more sheets to you.

Gareth

 

Gentlemen,
I am reviewing a building with this system for perimeter heating and cooling. They are console type though.

Central plant heated or unheated air is fed to the unit which has chilled water coils. They appear to be the original 1970 units. The air is fed down exterior columns and these are along the whole perimeter.

They appear to be well maintained & working adequately at best; but new tenants have not been replacing them on build-outs. There have been no reports of condensation issues although there may be some not reported. No smell was noticeable.

I am concerned that the units may not properly damper correctly. On the ones that I viewed (I really didn't know that much about it when I was first looking at them), it appeared to be dumping air into the unit that then just came up behind the coils and out - I didn't realize that much air would be sucked in across the coil.

What should I really be thinking about doing with these systems?

I attached a side view of how I think this one works. I also attached a pic of the system.

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screenshot on pc

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