Hospital HVAC failure cases

[seanhkim]

Am I able to find real cases where infection problems have happened due to impaired pressure relationship or due to sluggish pressure relationship restoration?

How is the performance of PID controller in the VAV terminal unit? Does it work fast enough to cope with changed pressure requirement?

When there is a high humidity in a patient room, saying because of showers or water use, what would be the best way to control the humidity instead of using dehumidifer? Instead of increasing the set point temperature, if the blower is putting more flowrate, would there be any problem? Wouldn't the moisture be transfered to other areas?

 

[quark]

There is an article in ASHRAE journal that explains studies about the threshold dP requirement to stop cross contamination. It was found to be at 12.5 Pa.

If the pressure drops by a door opening, then the pressure rise is not immediate even if you ramp up the fan. It is better to offset the pressure control till the door gets closed. My experience with such type of pressure control is half a minute (yes, it is high but can't help)

Depends upon what is the dew point and how much moisture is being added. If the temperature is increased (it only decreases RH but moisture remains same), it causes uncomfortable condition. If the flowrate is increased, then you have to cool the extra air to the required room temperature.

Why can't you exhaust the air from bath rooms separately?

 

[lilliput1]

We have problems maintaining accuracy of exhaust air valves using pitot tube type airflow measuring stations. Lint would clog them. Putting filter back exhaust grilles helped but is a maintenance issue. It would be better to use venturi type (Phoneix) exhaust & supply air valves.

I agree with quark. Using fixed CFM differential is better than active pressurization control. It would take too much airflow to compensate for open door. Even differential pressure alsrm sensors for isolation room recognize this and thus provide an adjustable time delay feature before it goes into alarm to give time for the door to close.

Main HVAC requirement for hospitals is the use of minimum 90% efficient final filters (downstream of the supply air fan & cooling coil), minimum airflow rates & outdoor air flow rates for ventilation and relative pressurization between rooms.

 

[atlas06]

Using CV means that you rely on a damper to give you years of pressure control without a VAV box is really and a good pressure monitoring station such as TSI, you really throw it up there for guess work.
Note that the Health and Human services (the governing code is published by AIA and HHS) requires the hospital to save all alrms and reactions from the monitoring system up to 5-years. with a VAV and BAS and TSI stations, you can print out all alarms and even the time that it took for the nurse to go and check and turn the alarm off.

Take a look a TSI literature, probably the best there is out there. As for ASHRAE, pleeeease, don't ever mention ASHRAE when it comes to healthcare design, especially when if you have to mention the differential set point for TB isolation rooms. In fact, no one, not even the CDCP will give you the set point for isolation rooms. The engineer is really on his own.


VAV boxes allow you all kinds of set ups even if your ductwork system is leaking, you can figure it out and compensate from the BAS resetting. With TAB, out of luck.