Interstitial Space
Interstitial Space
(OP)
I am starting on design for replacement of interstitial HVAC support space for a hospital, and have run into a problem at the onset: for U.S., State, Local and Federal complaince, I can find no basis or criteria for design. nearest thing located, which does not appear to be in ASHRAE or NFPA, is standard given by IMC for unoccupied space. Anyone availab;e that has expereince or knows criteria relating to HVAC support of interstitial? I have found lighting requirements and fire/smoke control guidance (going back to 1986 NBS criteria), nothing on HVAC.





RE: Interstitial Space
If on the other hand your interstitial spaces are more like intermediate floors of the hospital containing HVAC or other support equipment, then such a space would be considered a 'mechanical' space and fall under the requirements of your regular mechanical rooms.
Perhaps a little more information about the spaces in question would help. I.E. Where are the spaces located relative to occupied spaces? What is in the interstitial spaces?
RE: Interstitial Space
IMC 406.1 specifically includes ventilation air requirements for unoccupied space. ASHRAE 62.1 does not have a standard for unoccupied space, though the 0.06*SF would probably be closest category. Generally, they are interior zones, and need cooiling/dehumidication only, as on a cool day like today (36*F) you need to take off your coat to chase out duct or pipe runs.
I'm in favor of ventilatio air even if not mandated, as purge will be needed whenever renovation is performed to change occupancies in above or below occiped areas, and the interstitial floors include large amounts of asbestos containing material. Construction was done before ASHRAE 15 publication and includes refrigerant lines. That would probably dictate purge air, but not ventilation air.
RE: Interstitial Space
NFPA
IMC
NBS
IESNA
ASHRAE 15
Isn’t it amazing how many standards there are that prevent you from exercising your own brain power as an engineer? Codes and standards should prevent idiocracy, not dictate our every decision.
RE: Interstitial Space
The IESNA lighting requirements are for the very rare occasion people are actually in the space (once a year maybe). The lack of sprinkler requirements is because the space is not intended to be occupied on a regular basis such as a storage room.
Next time you are on the site, you may want to take a temperature measurement of these spaces and use that information in your load calculations. In Carrier's HAP there is a tab on the room input page to include partitions with unconditioned spaces.
Bill
RE: Interstitial Space
Just attaching to the existing AHU's is the problem. The customer wants to eliminate all NFPA 92 and move solely to NFPA 90A. Right now I'm thinking DOAS based on IMC 406.1 and VRV with purge to match refrigerant.
RE: Interstitial Space
RE: Interstitial Space
RE: Interstitial Space
IMC 406.1 requires an "exhaust" rate, and does not require "outside air". In other words, air leaving the unoccupied space is required to go to the outside (not returned to an AHU); however air entering the unoccupied space, the supply air (different from outside air), can be from anywhere. Think of it as you would a restroom (except EA <= SA), you don't provide a DOAS just for restrooms do you? That would be overkill.
You already know there is no cooling/heating load, so what do you think a VRV system is going to do? Other than add maintenance to the building and make your interstitial space a "mechanical room".
You can't get away from NFPA 92, so don't try. Any new duct work penetrating fire and smoke barriers will need to be appropriately protected.
You already have existing interstitial mixing boxes? This tells me you already have a means of getting air into the interstitial spaces. Then all you need is to provide some exhaust (2 CFM per 100 SF) and balance the system.
RE: Interstitial Space
Not making it tougher than is needed, and yes, you can get away from NFPA 92. That is the specific customer request. Current arrangement has 19 different hospital central AHU's providing ventilation and conditioning for three interstitial floors. If interstitial floors were defined under ASHRAE 62.1, then it might be easier to see the infectious control issues with supplying air to the interstitial and returning that air to patient support areas as is the existing. Not having a FSCS, biannual witness testing of smoke control dampers, pneumatics and controllers not having UL rating, and age of all the above (over 30-years) requires replacement in-kind or with a preferred system, and dedicated units appears to be the only way around NFPA 92.
I've read through the IMC several times, until it struck me that there is no ventilation rate per se; a mechanical system controlled to keep RH below 60% is required; no high humidity, no ventilation air. Cooling is still a separate issue, even during winter the temperature stays in high 80's/low 90's. Mold formation or worse are a concern if humidity cannot be controlled and temperature starts getting above 90*F. If mold starts growing on interstitial ductwork because of failed humidity control, much costlier issues can develop.
Yes, for exterior wall patient bathrooms, I do specify and install mechanical cooling and heating beyond transfer air.
RE: Interstitial Space