Interesting Iso Room Design

[dblyle]

Here's the situation: I have a small (~14x16) iso room which I am designing. To achieve the required ACH (including the anteroom, restroom, etc), I need a unit to produce 411 cfm.

Here's the problem: 411 cfm of 100% OA doesn't really work well with a DX system (Location is in Houston, Texas - 98/80 design conditions) and the closest chiller is about 600' away (requiring a pump producing 7.7 gpm at ~70' head). I have though about using some type of heat recovery, but I am not really sure that I can use potentially contaminated air to pre-treat the supply air (I know they won't mix - I am more concerned about exposure to the technicians when they clean coils, etc.).

Any suggestions on the best type of unit/combinations to used for this situation?

Thanks.

 

[trashcanman]

Use a fan-powered box (parallel) to provide the 411 CFM. Supply the box with the actual CFM you need for cooling. Sort of a face & bypass system where you are mixing supply air with room return air. You get your Air Changes/Hr without overcooling the space.

 

[tys90]

@trashcanman

According to AIA Health Care Guidlines, iso rooms are 100% exhausted unless you return the air through HEPA filters and only to the system serving that room. So to use a parallel box you'd have to add HEPA filters in the return system somehow which adds a lot of pressure loss that I'm not sure a parallel box could handle.

@dblyle

Take a look at this article:

http://txspace.tamu.edu/bitstream/handle/1969.1/4579/ESL-HH-02-05-29.pdf?sequence=1

 

[trashcanman]

Then use ceiling/attic air or interstitial space air instead of iso room air.

 

[mauricestoker]

Consider looking at the VHA criteria for USP797. The situation you are describing matches with pharmaceutical compounding under USP 797, with a 4 foot LAFW with air gap (in an ISO 7 buffer room). Under the VA criteria, chilled water is mandatory, providing redundant capacity between the dedicated chilled water unit and building system (if toxic compounding, which is implied by requirement for 100% outside air). The VHA guidance also requires consideration of desiccant for the 100% OA. Recovery is not allowed, as this is considered toxic airstream. Running the exhaust duct economically has been more of a bear than anything else.
Preferably, the exhaust fan will have all maintenace items outside of the air stream, especially the belt, backflow damper and end switch (if using the end switch for AHU shutdown). If not for toxic compounding, air can be recirculated.
I had considered using the interstitial space, but do not like to consider that equivalent to outside air (separate string, no guidance known outside of IMC). Potential for renovation work in the interstitial, and potential for ACM in older buildings, makes this shaky.
Not sure why a restroom would be included on air flow; if a renovation you'll be getting 30 ACH, if new 45 ACH, minimums, just in the ISO 7. If worried about energy, then put the restroom (or any non-regulated space) on a separate system. At 14' x 11', you must have a low ceiling to only be sending 411 cfm to make 30 ACH.

 

[cry22]

I think what trashcanman is saying: use the plenum or attic air for the decicant wheel to supply make-up air, that's another unit in the system, but it beats having a recirc unit with HEPA filters and still does not do the dehumidifying work.
That way, you only have exhaust fan HEPA filtration system.

 

[marcoh]

I had a similar project once for a small lab located in a field away from any source of chilled water. We ended up using a small Trane chiller connected to a single chilled water AHU with HEPA filtration etc. Wasn't cheap but was the only system that could deliver the required environmental conditions.

 

[dblyle]

I initially thought about doing what Marcoh did (single chiller with AHU), however the system is too small. A chiller under 5 tons will still only have 1 circuit and not unload properly.

Can anyone think of the disadvantage of an ERV connected to a RTU? The only thing I can think of is that the exhaust air would pass thru a coil before being ejected.