Bishara

A frequently asked question in Cx meetings is the best location for interior build pressure control reference; one of the things I bring up (If the location is not depicted in the design plans).    

Here are my thoughts and what I experienced as good practice.  Interior building pressure reference location is best to be located on the first floor in an open space of a multistory building, an interior door separating it from the main exterior door to the building and avoiding elevator lobby.

The intent of building pressure control is to make sure building pressure is controlled to a positive value (Acceptable control range 0.02″ to 0.06″ wc).  The definition of positive pressure building is the measurement of positive pressure value across an exterior door (Pressure differential between building interior and outdoor).

The BAS is controlling exterior door pressure differential. Therefore, interior pickup location is best closest to the variable it’s controlling by providing feedback pressure reading into the BAS logic; closest to the exterior door.

Having said that there are few items to consider when selecting the location:

A. The exterior door opening and closing may impact pressure readings, resulting in system cycling.  The following are few measures that can be done to mitigate and still achieve accuracy.

1. Install building pickup in a space separated by one interior door away from the exterior door in a big open space.  This inherently provides the system with a buffer minimizing the impact of exterior door operation.  

2. The measured building pressure value feeding into the BAS control logic is best to be a rolling average value over 15 minutes.  This is another method to stabilize building pressure control.

3. If building security with exterior door closure is a concern, interior reference can be installed in the lobby, but expect some fine tuning and adjustment during tab.  I think even with the presence of a security concern, having the interior reference separated by an interior door away from the exterior door should work with less adjustment needed.

4. The design should have accounted for an oversized transfer air opening between the lobby and the building interior, assuming the lobby a non-ducted return air path.

B. Avoid elevator lobbies as the elevator movement will impact the pressure reading.

C. Selecting a location other than the first floor, like the second floor of a multistory building, with the intent in avoiding exterior door operations is taking it to the other extreme of locating it in the lobby.  Depending on the building layout and connectivity of the first floor lobby, it may or may not work properly.  I see no value in taking this risk.