Standard 62.1 – 2013
Ventilation for Acceptable Indoor Air Quality


ASHRAE Standard 62.1-2013, Ventilation for Acceptable Indoor Air Quality, specifies minimum outdoor air ventilation rates based on space use, occupancy and floor area. The Standard also requires that outdoor airflow rates exceed exhaust airflow rates (net positive mechanical exfiltration) during periods of dehumidification (cooling) to limit the infiltration of high dew point outdoor air. The infiltration of high dew point outdoor air will result in poor humidity and temperature control and may lead to mold growth in the building envelope. Proper pressurization also reduces unfiltered dirt and dust in the outdoor air from entering a building. Intake flow rates should be monitored with permanently mounted airflow measuring devices to assure minimum compliance with the Standard for ventilation and building pressurization.



Outdoor air intakes are traditionally very low velocity (<<400 FPM) and have limited straight ductwork or a plenum between an intake louver and control damper. Pitot arrays and other differential pressure measuring devices as well as vortex shedders cannot be properly applied on most outdoor air intakes because of the low flow rate and space limitations. Thermal dispersion technology, as manufactured by EBTRON, is well suited for the direct measurement of outdoor airflow measurement. EBTRON pioneered direct outdoor air intake flow measurement in the late 1980's.

Depending on the level of sophistication of the controls on the air handling system, the monitored outdoor air intake flow rates may be used as an input to a control device for output to modulating control damper actuators and/or variable speed fans to maintain the desired intake flow rate. For more information on control strategies for minimum outdoor air intake control refer to the section on this web site for Control Strategies or contact EBTRON's application engineering department or your local EBTRON representative.

If outdoor airflow rates are not controlled, they should be setup for worst-case ventilation rates in accordance with the Ventilation Rate Procedure (VRP) of ASHRAE 62.1. The use of a low flow alarm is recommended and a requirement of IEQ Credit 1 (1 point) of LEED v3 2009, it is mandatory with LEED v4 2015. Outdoor Air Monitoring on VAV systems is a prerequisite for certification. Airflow measurement is also in the mandatory provisions of ASHRAE Standard 189.1-2012, Standard for the Design of High Performance Buildings. Standard 90.1-2013 has multiple requirements for multi-speed or variable supply fan control, while deferring to 62.1 for ventilation requirements. Combined, Section 6 on HVAC is forcing designers to conclude that airflow measurement is the best solution for satisfying both requirements.

Benefits of continuous monitoring/control of outside air intake flow rates include:

  • Compensation for pressure variations on the intake system including wind and stack effect and changes in mixed air plenum pressure on VAV systems. {tech bulletin coming soon}

  • Compensation for (or detection of) control damper issues including linkage hysteresis, seal deterioration and binding. {tech bulletin coming soon}

  • Maintenance of proper building pressure. {tech bulletin coming soon}

  • Optimized CO2 demand controlled ventilation (DCV). {tech bulletin coming soon}

Link to

Link to ASHRAE Standards

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