Interior Conference Rooms

[pegboy]

I'm new. I Love this forum and think its a good spot to throw ideas around.

This is probably an age old problem. I run into this on almost all my office space projects. The dreaded interior conference room. The cooling loads for these spaces are always way low, and the ventilation requirements are way high. The room I'm working on right now requires 350 CFM of cooling and 300 cfm of OA! Seems like these areas always screw up my ventilation for my central air handling units, requiring a high percentage while the rest of the building takes ~15% overall (via IMC 2000 code standards). I implement the Multiple Spaces calculation (IMC 403.3.2), but the fraction of OA is still too high (around 50%).

Seems crazy ($$$) to me to put in a dedicated unit for this area which would be almost 100% OA, and this solution will leave me open to criticism from clients and contractors alike.

I'm sure this is a common problem. Anybody got the common solution?

 

[walkes]

We often put in a ceiling exhaust fan with a wall-mounted speed switch. This allows the occupants to vary the flow if they feel the space is getting stuffy, drawing fresher air into the room.

In your calculations are you assuming that the space is occupied the entire time? You probably have the same occupancy throughtout the day in the overall building, with people migrating to the conference area. The conference room is essentially flushed with ventilation air when it is not occupied and there should be somewhat of a lag between when it is occupied and when the air in the space is no longer providing sufficient ventilation.

 

[pegboy]

Yes, I'm using ceiling diffusers and a VAV system with series fan powered boxes. It seems to me that the outside air required for this room by code only comes from the central air handler, and thus through the primary air. Given the requirements in the code, how do I convince a code official that I'm meeting the requirement with a transfer fan or even a fan powered box which recirculates plenum air?

How does one implement a dual duct box to meet ventilation? Aren't these used in hot/cold deck applications?

I like the idea of a transfer fan with a wall switch, but do code officials buy this design? Do I ignore the specific ventilation required for this area in my vent index?

I suppose I could even control the transfer fan with a CO2 sensor and make it completely automatic.

 

[DRWeig]

Pegboy,

I have personally done the CO2-controlled transfer fan / exhaust fan deal. Worked great, and the local code folks said it was OK too.

Good luck with it!

Old Dave

 

[cme]

ashrae 62-89 allows you to take 1/2 the ventilation demand if the space is occupied less that 3 hours

 

[darkvibe]

The ventilation of multiple spaces calculation in ashrae will combine those two OA ratios and set the outside air requirement at your unit.

 

[carlosgw]

I like the transfer fan also. In the old days (>15 yrs), conference rooms always had an exhaust fan. I always assumed it was for smoking. But now I think it may have been to allow the occupants to draw in more cooling air. Any "old timers" around that can answer that? Anyway, I would use a transfer fan and use the ASHRAE standard.
I would like to meet the code official who looks for ventilation air.