Many facilities and maintenance departments do not properly maintain the flow sensors and transducers on VAV boxes due to complexity, difficulty, lack of staff, cost, etc. This results in wasted energy and incorrect airflows and improper pressurization. Whenever work needs to be performed above the ceiling, including adjusting or cleaning a VAV terminal unit, there is a long list of actions and procedures that must be followed.
An Infection Control Risk Assessment (ICRA) must be filled out, and approved by the hospital’s infection control department. The area may have to be cordoned off. Specific infection control procedures need to be adhered to, which may include disinfecting the ceiling tile before it is moved, bagging out contaminates, etc.
When VAV boxes are initially installed and balanced correct flows can be expected within the limitations of the flow cross and transducers being used for these applications. Monitoring of room pressure validates that the correct pressurization levels are being achieved. But when the exhaust sensor becomes clogged with lint and dust over time, the velocity ports on the flow cross sends a low velocity pressure signal to the controller via the transducer and interprets the wrong flow and associated reading to the BMS.
The controller responds by opening the damper more because it thinks flow is reduced. Your CFM on the exhaust side is now higher than it should be. Your supply is steady to maintain 20 ACH. But now your OR is slightly negative? A pressure monitor setup to alarm will advise the users but can lead to downtime and maintenance costs while the sensor is cleaned and recalibrated.
Venturi valves are immune to lint and dust in the airstream due to the metering concept. No pitot orifices get clogged up and minimal downtime and maintenance is required. The advantages of venturi valves are numerous, and can prove to be both cost- and energy-efficient solutions for healthcare applications.