Hospital interstitial space

[mauricestoker]

I am currently working on a renovation in a hospital, original design from the 70's. I'm taking over design from a prior mechanical enegineer, as the HVAC portion has failed. This design included taking substantial amounts of supply and return air from the interstitial space. The interstitial space has supply and return from four different AHU's on the floor, and rebalance of all four units is not within the contracted scope.

I am not familiar with any criteria, ICC, ASHRAE, AIA, etc, that dictates the amount of air to and from the interstitial space, other than common sense need for moisture control. Interstitial is obviously different than mechanical, not included in ASHRAE 62.1-2007 for allowable recirculation. Any recommendations or criteria source that can be provided would be greatly appreciated.

 

[DonPhillips]

I am not familiar with the term 'interstitial space' in regard to HVAC design. Are you refering to a plenum? I have seen in large applications a fresh air intake plenum and an exhaust plenum that are used by multiple air handlers - in the 100,000 cfm range.

The IMC Chapter 4 gives you minimum outside air requirements that the plenum could supply for each air handler and the exhaust plenum can be used for relief air to keep the building slightly positive and prevent exterior doors from standing open.




Don Phillips

http://worthingtonengineering.com

 

[GMcD]

Don: the interstice space is basically an accessible walk-around "ceiling space" containing all the services - HVAC, electrical, Comms, med gases, plumbing distribution, etc. It's like a large flat mechanical room, with very little occupancy, so likely little need for fresh air ventilation, but should at least have some basic ventilation. I'm from Canada, so our specific Hospital Codes generally require almost all exhaust, return air and supply air to be ducted directly to rooms in acute care facilities for room and zone air pressure control, as well as minimizing cross-contamination from/to the interstice space.

Given the fact that the interstice space carries a number of other services, I'd sure want avoid using the space as any kind of open air plenum which might mix air to/from the occupied spaces below, and would likely want to keep it at a slight nagative air pressure to insure that any leaks of services (med gases, plumbing) are contained within the interstice space, and not able to contaminate the clean occupied spaces below.

 

[DonPhillips]

Thanks for the clarification. I agree with GMcD. If you need specific references in the IMC, let us know.

Don Phillips

http://worthingtonengineering.com