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Common Clues

Following are indicators of a possible issue with a direct-measurement building-pressurization-control system's operation:

• Return or relief fans operate near 100-percent speed most of the time.

• Building differential static pressure fluctuates widely and/or rapidly.

• Return- or relief-fan speed fluctuates widely and/or rapidly.

• Exterior doors are hard to open or do not close securely.

If any of these is noticed:

• Inspect the low- and high-port-tubing terminations. Ensure the high-port tubing terminates at a location representative of the space pressure and away from doors and that the low-port tubing terminates in an accessible location and a manner minimizing wind effects. Consider installing an outside-air-pressure-sensing device at the low-port termination to mitigate wind effects.

• Check and, if necessary, adjust the calibration of the differential-pressure sensor.

• Inspect the integrity of the tubing between the sensor and interior and outdoor spaces.

• Review the control sequences. If building differential pressure is controlling the return fan(s), consider using the signal to control the relief-air damper instead and installing a pressure sensor in the return-air plenum to control return-fan speed. The economizer-damper-control sequence would need to be modified as well.

• Ensure the outside-, return-, and relief-air dampers are sized properly.²

• Trace the return-air pathway from the interior space to the fan. Ensure return-air grilles/openings are sufficient and that the pathway is not obstructed by interior walls extending to the floor deck above (for return-air plenums), closed fire/smoke dampers, or damaged internal duct insulation.

For more information on building-pressurization-control systems, including the diagnosis of problems and testing of performance, see “Functional Testing Guide: From the Fundamentals to the Field.”⁴

Conclusion

Many large commercial buildings utilize direct-measurement building-pressurization-control systems. Optimizing the performance of those systems as part of a retrocommissioning project can yield energy savings and improved IAQ through reduced return/relief-fan speeds, reduced infiltration, and proper outside-air intake.

ASHRAE President Gordon V.R. Holness, PE, FASHRAE, has urged ASHRAE members to focus on increasing energy efficiency in existing buildings.⁵ Optimizing the performance of building-pressurization systems can be a low-cost method of doing that.

References

1. ASHRAE. (2007). 2007 ASHRAE handbook - HVAC applications (ch. 46). Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers.

2. Lizardos, E., & Elovitz, K.M. (2000, April). Practical guide: Damper sizing using damper authority. ASHRAE Journal, pp. 37-43.

3. Taylor, S.T. (2000, September). Comparing economizer relief systems. ASHRAE Journal, pp. 33-40, 42.

4. PECI. (n.d.). Functional testing guide: From the fundamentals to the field. Portland, OR: Portland Energy Conservation Inc. Available at http://www.peci.org/ftguide/ftg/index.htm

5. Holness, G.V.R. (2009, August). Sustaining our future by rebuilding our past: Energy efficiency in existing buildings — Our greatest opportunity for a sustainable future. ASHRAE Journal, pp. 16-21.

Did you find this article useful? Send comments and suggestions to Executive Editor Scott Arnold at scott.arnold@penton.com.

Dave Moser, PE, is a senior engineer for Portland Energy Conservation Inc. Focusing on commercial-building energy efficiency, he manages the technical aspects of utility retrocommissioning programs, leads in-building retrocommissioning projects, and conducts research. He can be contacted at dmoser@peci.org.