Thermal Imaging (Case One)
Case One: High Rise Cold Complaint
Building Type: 40+ Floors Office Building
HVAC System: Air handler serving variable air volume (VAV) boxes with electric reheat.
Complaint: The lower floors of the building are very cold and drafty.
Complaint Type: Comfort, energy, productivity.
Effects: High energy consumption. Poor space comfort. Low productivity.
Cause: The initial response was typical. Why are the vav boxes not working? As it turns out the boxes were working properly. In an effort to provide more heat in the space, additional heat was added to the vav boxes. The space was still cold. Alternately, there was a request to add additional heat to the space.
I explored the space with thermal imaging. Image pair 1 below shows that adding additional heat to the vav boxes did add more heating capacity to the space, but in turn increased the stratification of the space.
Image Pair 1
Digital Image of Wall
Thermal Image of Wall
Where is the cold being introduced into the space?
Next was to look at the envelope. Image pair 2 shows infiltration of very cold air (approx. 17 degrees F) into the space through the envelope. You can assume that frost is forming in the walls.
The stratification is a result of major infiltration of very cold air. The infiltration was a result of the space being negatively pressurized relative to the outside. But why, is it the air balance ratio between return and supply air of the air handling equipment? The air balance report showed a slight positive pressure (trust but verify). The test and balance report was validated.
Image Pair 2
Digital Photo of Office Wall
Thermal Image of Wall
The major problem is on the lowest floor. The air handler serves several floors, including this one.
As it turns out, the negative pressure in the lower floor was being caused by the stack effect taking place in the elevator shaft. This, in turn, was caused by a failed elevator shaft pressurization fan and poorly performing gaskets on the elevator doors.
Solutions: Repair of stairwell pressurization fan. Replacement and adjustment of elevator door gasket material.
