Design considerations for airflow measurement

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The quality of the air we breathe in the workplace plays an important factor in our health and well-being. Ever felt tired or drowsy in a meeting room? Could not focus and head felt heavy? The air you breath indoors might be to blame.

Ventilation is the process of bringing air from outside a building inside, distributing it, and later expelling the air outside. One of the easiest and most effective ways to save energy and improve indoor air quality is to directly measure and control airflow.

Have we forgotten why fresh air is important? Outdoor ventilation can assist to reduce moisture, odours, smoke, heat, or dust from the room and replenish it with air from outside. In addition, outdoor ventilation/single pass air can also help with managing exposure risk resulting from the handling of hazardous substances in laboratories.

Mechanical ventilation offers a controllable, responsive way to provide optimal indoor air quality when natural ventilation e.g., operable windows or louvres, is not available.

  • Provide an airflow measurement station (AFMS) to validate the outdoor air intake flow (L/s) of each air handler unit (AHU)
  • Installed accuracy of AFMS: +/- 10% of set point
  • Indicate a warning alarm at the BMS when flow value varies by 15% or more from setpoint
  • Position user display of AFMS so that personnel have safe access without aids
  • Trend flow in intervals of 15 minutes for a period of no less than 12 months
  • Performance metric at the BMS of average outdoor air flow per person, during occupied hours when operating at minimum outdoor air mode.

External variations in wind, stack effect and inaccurate damper positioning on the intakes of mechanical equipment, will often result in widely fluctuating outdoor flow rates if not directly measured and controlled.

Do it right the first time. Whenever flow rates are modulated, use of measurement needs to be considered as dampers are not linear flow devices. Measurement can also be used to set a diversity limit, such as the maximum capacity of the mechanical equipment.

Measurement provides better tracking of flow rates and validates that minimum ventilation is achieved. Avoid over-ventilation and wasting energy.

Additional monitoring of population and CO2 concentrations will further optimise the process to deliver the right amount of air, at the right time and at the right location.

Outdoor damper of large air handler in hi rise building showing an Ebtron airflow measurement station.
Industry best practice
  • Replace differential pressure (DP) devices on BMS and associated ventilation systems that measure pressure drop across a mixed air chamber, louver, cooling or heating coil or obstruction
  • Each sensor node uses two (2) bead‐in‐glass thermistors and are individually factory calibrated and marked to NIST traceable standard.
  1. AS1668 Part 2 § 2.3.1 Intakes for outdoor air are located and arranged so that all conditions of operation including effects from wind and other factors do not cause the flow rate of outdoor air to be reduced below the minimum requirements.
  2. AIRAH Technical Handbook Edition 6 2021

Short courses courtesy of Ebtron. Includes the case for outdoor airflow measurement, building pressurisation and dilution ventilation for IAQ control.

For a free, no-obligation discussion of your project and needs, email John today or call 07 5619 3747.