ASHRAE 62.1
Operation & Maintenance

Buildings that are likely to be changed or altered during their life span, should consider including a robust HVAC system design that takes into account changes in airflow rate requirements imposed by this Standard. Of course, provisions for permanently mounted airflow measurement devices and controls would significantly reduce both the cost and time associated with such changes as long as the HVAC load capacity could accommodate future requirements.

§8.4.1.7 addresses sensors. “Sensors whose primary function is dynamic minimum outdoor air control, such as flow stations…” is discussed in this section even though they were not mentioned under Section 5, Systems and Equipment. Section 8.4.1.7 requires that sensors have their accuracy verified “once every six months or periodically in accordance with the Operations and Maintenance Manual.” The Operations and Maintenance Manual for some airflow measuring devices does not recommend periodic recalibration. Permanently calibrated airflow instrumentation has a significant advantage over other airflow measuring technologies and CO2 sensors whose transmitters are subject to frequent adjustments, zeroing or regular calibrations to correct for analog electronic circuitry and sensor drift.

However, §8.4.1.8, Outdoor Air Flow Verification, only requires the verification of airflow rates “once every five years". Since external and system factors change continuously, clearly influencing outdoor airflow rates, this requirement does little to assure that proper ventilation rates are maintained under normal operation at different times of the day and the year. It effectively places the burden of verification of new building/system performance on the building operator, who is often not in a position to make such a determination.

This seemingly contradictory requirement (with §8.4.1.7) will likely be examined by the ASHRAE SSPC-62.1 committee in the near future. Permanent outdoor airflow measuring stations would provide continuous verification and the necessary control inputs to maintain ventilation requirements, automatically minimizing intake rates for energy usage and preventing other control inputs from causing a maximum intake limit from being exceeded.

Select reliable airflow measuring equipment, periodic calibration or dampers and actuators for years of trouble-free operation. Under normal operating conditions, EBTRON airflow sensors do not require maintenance