Isolation room design

[mechanicaldude]

I'm sure this has been discussed several hundred times already, but here it goes anyway. I have an existing patient room that is being redesigned to be an isolation room that only needs to be negative some of the time, the rest of the time it can act as a patient room with neutral pressurization. So it seems like my options are:
A) to provide a new HEPA filter exhaust fan with a user operated switch, when the negative pressure is needed. This way you won't have to replace or clean the HEPA filter as much if you don't run it all the time. Under neutral contditions I can return the air back to the AHU.
B) run the exhaust fan continuosly but as a two speed fan. Low speed for neutral conditions and high speed for negative conditions.
C) Or as my college suggests, keep the exhaust fan constant and vary the supply air. I'm not sure why I should do it this way. If This is done how do you meet the cooling load of the room all the time. ?

Any thoughts or ideas from your experiences would be appreciated.

Thanks.

By the way this existing AHU serving this space is a constant volume hot water reheat system.

 

[GMcD]

Vary the exhaust air for room pressure control and allow the supply air to be contant volume/variable temperature. Easy if you have dual duct boxes on the supply air side, a bit harder if it's single duct VAV on the supply air.

Critical issues for medical isolation rooms:

- Untreated/Un-filtered Exhaust from the medical isolation room must go directly outside to a fume stack at least 10 meters away from any building openings, air intakes, occupied zones.

- Or, treat the exhaust air with both a HEPA filter and a UV-C germicidal lamp set, and then you can exhaust that air to the outdoors in a less stringent manner.

- Most Codes I've read do not allow the exhaust air from a medical isolation room to be recirculated back into a general air system, general exhaust, washroom exhaust or anything - the exhaust from a medical isolation room MUST be separate from all other building air systems to avoid cross-contamination potential.

- The selection and sealing of the room doors and the sealing of the isolation room itself are critical. I've done too much forensic engineering on medical isolation rooms where the lowest bidder for the doors got the job and they leaked like a sieve, so huge airflow differentials were required to maintain room design pressures, negative or positive, incurring nuisance alarms, higher fan energy use, etc.

- In my experience, there is no halfway "medical isolation room lite" design. The room and air systems have to be designed properly for medical isolation, period. The first outbreak or death of a patient or HVAC Maintenance worker where contamination was directly attributed to poor isolation room design will come back and bite the design team pretty quick. The Hospital Facilities Maintenance guys will be all over you for medically contaminated ductwork issues too.

 

[tbedford]

GMcD is correct...
there are no half-way measures.
This includes correct sealing of all mechanical and electrical intrusions thru wall membranes both above and below ceiling level.
Contaminant pathways are sometimes very insidious by their nature.
t