Interior Exterior Air Distribution

[philgrp]

I working working on a 220,000 sq. ft. 4 story office building that will be using thermafuser type diffusers for supply air. The open office areas are 30 to 40 feet deep from an exterior wall and often run the entire length of the wall. Typically each zone has only one exterior wall. The load calculations were performed assuming exterior zones are from the exterior wall to 10 feet inward, interior zones are from the 10 feet point to interior walls. Unfortunately the diffusers were not sized for exterior and interior zones. The diffusers were sized for the total CFM in an area with slightly more air on the exterior than interior. The perimeter ductwork has reheat coils and there is also perimeter finned tube. With the current diffuser layout do you feel that there will be adequate mixing of the air between interior and exterior zones so that most everyone is comfortable or do I need to have the exterior and interior zones as per the calculations? This project is going out for bid in a couple of days, your speedy response will be appreciated.

 

[trashcanman]

Short answer: no. One thermostat/diffuser will not satisfy both interior and exterior zones.
Are some diffusers supplied by exterior ductwork and some by interior ductwork? Your question is not clear on that.
Where are the thermostats to be placed? Why where the diffusers not sized and laid out as per calculations? If so, why do the calculations?
Seems like this should have been caught early on. Good luck with the redesign (if you choose to that is).

 

[philgrp]

Thanks trashcanman,

In case you are not familiar with thermafuser each diffuser has its own thermostat (wax element) that controls space temperature. There is an exterior duct loop with reheat coils to diffusers. There is also a separate interior duct loop. Thermostats will be placed on exterior walls to control reheat coils and finned tube.

Loooooooong answer to why diffusers were not sized per calculations. But does not matter now, I just need to go on.

 

[willard3]

You should tell your client that you have new information on this system and it needs to be redesigned and it will take more time.

Meeting an unrealistic schedule by not doing the proper engineering/design is a bad idea.

 

[philgrp]

Thanks Willard3, that is exactly what we did last week, we told the client we need more time. I feel a lot better about it now, it was the right thing to do.