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First 5 Steps to Troubleshoot an Operation Room Out of Pressurization Compliance

(EC 2 5 1 – 15 – OR Critical Pressure)

Operating Room Humidity control and building energy solutions commissioning

When the Joint Commission presented this past fall, the 9th most common violation in Pennsylvania was EC 2 5 1 -15 – OR Critical Pressure. If that unfortunate day comes where you get a BAS alarm that one of your Operating rooms is having pressurization issues, we thought we’d share some Tips and Tricks to troubleshoot the issue quickly and calmly.

First 5 Steps to Troubleshoot an OR out of Pressurization Compliance:

  1. Check your flow sensor calibration
    a. When was the last time it was cleaned/calibrated? If the sensor isn’t properly calibrated annually, it may look like it’s getting the right flow, but it isn’t.
  2.  Are your doors completely closing/staying closed?
    a. This one is easy to check. Obstruction? Staff Operation? Stuck?
  3.  Are your VAVs “Starved”?
    a. Fully open: starved
    b. Fully closed: broken

OR Critical Pressure

 Figure 1: The exhaust VAV box associated with this flow sensor was 100% open. There is very little chance of a sensor in this condition providing an accurate reading.

4. Return/exhaust fan not running when you think it is
a. For fans not running, a known good vav box not reading any flow.
b. Visually inspect to make sure a belt didn’t break, and that the fan is actually running.

OR Critical Pressure

Figure 2:This fan motor is technically running, but the belt has snapped. https://www.americanfireprevention.net/wp-content/uploads/2019/05/099-Fan-Belt-4.jpg

5. “Ok, who messed with the balancing dampers?”
a. Often adjusted without record in response to pressure or temperature issues
b. Can break loose from vibration

** If you can’t target the issue, don’t be afraid to call an RCx Engineer **

Story Time:

A recent client desired to stabilize the OR air handlers in one of their Pavilions. The major issue was identified as return fan over-volt trips due to the return fan being dragged by the supply fan. The initial investigation began in April 2021. Equipment cleaning and calibrating was performed, and the systems were tuned to improve stability. Controls recommendations were made to ensure OR pressures are maintained even if flow sensors fail. In addition to improvements to the air handler and ORs, the OR suite was re-balanced to ensure proper pressure cascade. Sub-sterile corridors were set from negative to positive as per code.

Existing Conditions:

After further investigation, 3 are fed pre-conditioned outside air from an energy recovery unit into the mixing boxes. The remaining 2 units are fed energy recovery air upstream of the return fan. These units were susceptible to return fan over-volt trips since the full airflow of the unit passed through both supply and return fans. Combined with supply and return fan resets and associated instability, return fans would frequently trip. An initial stop-gap measure was performed which artificially loaded the return fans by throttling return air dampers. Unfortunately, this had the side effect of causing the system to relieve return air. On 2 AHUs, the return air was pre-mixed with conditioned outside air. To make up the difference, the economizers were opened slightly. This solution wasted the pre-conditioned outside air and utilized unconditioned outside air in its place.


Envinity Recommendations:

  • Clean and calibrate all VAV boxes
    • Return boxes wide open due to buildup of lint on flow grids
    • Many boxes reduced by 50% or more
  • Clean and calibrate all pressure sensors
    • These sensors are susceptible to dirt and debris
  • Reduce OR air changes to 21.5
    • Reduced airflow will slow down both supply and return fans
    • Reduced fan speed allows room for load to be shifted from the supply fan to the return fan
  • Modify Unoccupied mode (operator override)
    • The reduced airflow caused instability in the systems
    • Near zero return air starved the return fans
    • modify so that all rooms are occupied by a set morning time (e.g. 5am) and they are locked in occupied during the normal hours of surgeries (e.g. 5am – 6pm M-F) to minimize pressure transients. Occupancy sensors should be used as proof of vacancy allowing rooms to go to lower airflow after hours.
  • Disable supply and return pressure resets (operator override)
    • Resets caused instability in the system
    • Constantly changing fan speeds and pressure made balancing the load across the two fans nearly impossible
  • Implement an AHU unoccupied supply pressure setpoint
    • For future unoccupied modes
    • Slow down AHU speed when all ORs are unoccupied
  • Limit return damper positions
    • Return VAVs require frequent cleaning and calibration. When not maintained, there is a risk that ORs will lose pressure
    • Limits on return damper position will reduce the risk of ORs losing pressure due to dirty VAVs
    • Settings for occupied and future unoccupied mode
  • Adjust VVO flow from energy recovery to ensure at least 0.5”wg DP across return fans
    • Reduce OA
    • Excess is not used, just relieved
    • Affects return airflow.
  • Disable economizers (operator override)
    • Economizer mode creates instability during switchover
    • The benefit of economizer is minimal due to energy recovery efficiency
  • Balance ORs to ensure supporting space pressures are correct

OR Critical Pressure

Figure 3:  OR 9 Before and after. Note that the exhaust damper went from 100% to 63%.

Contact us today at [email protected] if you need any help troubleshooting an Operating Room Pressurization issue.