Airflow Measurement is Critical!


Outside air (OA) is required to dilute contaminants generated within a building. Those contaminants are the result of both the occupants and the building itself.


Providing too much outside air during minimum intake mode is costly since it wastes energy; too little results in unacceptable air quality.


A healthy indoor environment

High-quality air requires that harmful contaminants be maintained below threshold levels. Diluting supply air with outside air is often the only way to reduce harmful contaminants to acceptable levels.

ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality, the International Mechanical Code (IMC) and many local codes specify dilution (outside) airflow rates for acceptable IAQ.

The ventilation rates prescribed are required to dilute both human bioeffluents and space borne contaminants. Dilution airflow rates also play a significant role in building pressurization and have a significant effect on envelope moisture and mold growth.

Failure to provide proper dilution airflow rates to occupants places owners and engineers at significant and unnecessary risk. Occupants exposed to poor indoor air have shown both an increase in health problems and a reduction in productivity.

A properly designed and operated building can be healthy, sustainable and energy efficient.

Reduce Contaminants and Provide Outside Air

Whether your building uses small unitary ventilators or large built-up systems, failure to assure that adequate outside air is provided by each air handler will result in a poor indoor air environment. Simply setting the outside air intake flow rates manually by setting dampers or fans cannot assure adequate dilution air is provided at the breathing zone.

External variations in wind and stack pressures, on all air handling systems, will result in widely fluctuating outside air intake flow rates. Mixed air plenum pressure variations on VAV systems intensifies the problem when the supply airflow rate changes from initial setup conditions.

Strategies that do not directly measure airflow rates cannot assure ventilation compliance and generally result in poor occupant satisfaction and health. Failure to provide proper dilution air increases both owner and designer liability.

Minimize Moisture

A pressure differential across the building envelope can transport a significant quantity of moisture into interstitial wall cavities and results in mold and fungal growth. Such growth is becoming an increasing concern and is evidenced by insurance companies’ “mold exclusion” clauses in both commercial and residential policies.

Systems must be designed to control building pressure and have adequate capacity to remove moisture from properly supplied outside air.

Reduce Energy

Everyone is concerned about rising energy costs. However, energy accounts for less than 2% of the total operating cost of a building while employee wages account for more than 80%. The key is to balance energy and productivity.

Implement a system that will provide proper rates of outside air (no more, no less) and select a control strategy that minimizes fan energy to get the benefit of improved IAQ while minimizing energy consumption.

Comply with Codes

The IMC specifies outside air ventilation rates for compliance. It is based on the ridged interpretation of the Ventilation Rate Procedure of ASHRAE Standard 62.

ASHRAE Standard 62 defines acceptable IAQ as air in which “a substantial majority (80%) of the people exposed do not express dissatisfaction.” Failure to provide active control of outdoor air at each intake will result in a significant percentage of the occupants being dissatisfied with the building’s indoor air quality.


  • Measure outside air intake airflow rates at each AHU and into each “critical” zone
  • Measure supply and return airflow rates into each building pressure “compartment”
  • Use a “sequencing” control strategy with airflow measurement to minimize pressure drop and conserve energy
  • Continuously document ventilation rates for code and standard compliance

Thermal Dispersion

Provide airflow measurement with controls to assure that harmful contaminants are removed by maintaining proper dilution airflow rates of outside air to the breathing zone. The heart of the solution is the use of EBTRON thermal dispersion airflow measuring devices to directly measure outside, supply, return and critical zone airflow rates.

When properly implemented, your facilities will meet the requirements of ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality, and comply with local building codes. Your HVAC system can assure that both human bioeffluents and space generated contaminants are maintained below threshold levels required for acceptable human productivity and health.

The measurement and control of dilution airflow rates can meet the requirements of the Ventilation Rate Procedure of ASHRAE Standard 62, with little uncertainty or risk. Methods that indirectly determine outdoor airflow rates, such as CO2 demand controlled ventilation strategies that can only detect human bioeffluents, can not assure that minimum ventilation rates of outdoor air are provided.

Provide Outside Air

Regardless of the size of the air handler, install an EBTRON airflow measuring device at each outside air intake on your building. Use your B.A.S. to maintain the airflow setpoint by modulating control dampers and/or fans. Contact your EBTRON representative regarding product selection, placement and control strategy options for your specific application.

EBTRON technology is ideal for the measurement of low airflow rates associated with outdoor air intakes. Other technologies lack sensitivity at low airflow rates and require reduced intake free area (greater pressure drop, energy consumption and system modification) for proper application.

EBTRON has been successfully installing airflow measuring devices in outside air intakes since the late 1980’s. We are the leader in outside air measurement technology!

Indoor Air Quality

Maintain Pressure

Building pressure is the result of a difference between the outside air and exhaust air mechanically forced into and out of a building. The objective is to maintain a building NET positive during periods of dehumidification (cooling) and NET neutral during periods of humidification (heating).

In some areas of the country, a 1,000 cfm negative pressurization flow can transport up to 1,000 gallons of water across the building envelope each year.

When the outdoor dew point is high, a positive pressurization flow will dry the building envelope and prevent air carried water transport, thus reducing mold.

The pressurization flow is most effectively controlled by maintaining airflow differentials within a pressure zone.

Unlike static pressure control, airflow control is stable; unaffected by changes in adjacent pressure zones or wind.


Reduce Energy

A proper control strategy is essential to optimize energy. When it comes to IAQ, control strategies using airflow measurement devices can result in significant savings.

Airflow measurement allows the sequencing of dampers and fans, thereby reducing pressure losses and fan energy. Dynamic reset of outside air intake setpoints can also be accomplished.


Comply with Codes

Existing code language does not dictate how a system must perform during operation.

By installing permanently mounted airflow measurement devices with active control, you can assure that the building meets ventilation requirements during operation and over time – something that codes don’t require, but you need, to assure a quality indoor environment.


  • Proper dilution air control results in cleaner air, improved occupancy health and productivity
  • Proper pressurization dries the building envelope and reduces mold and fungal growth
  • EBTRON airflow control strategies result in energy efficient systems
  • Code and standard compliance reduces your IAQ risk

You wouldn’t attempt to you try to control temperature without permanently mounted thermostats, so, why would you try to control ventilation rates without permanently mounted airflow measuring devices?”



Minimal Risk

By monitoring and controlling airflow rates, you will have diluted many harmful contaminants from numerous sources that create an unhealthy indoor environment. The building envelope will be dryer and your mold growth potential will be reduced. Your IAQ risk will be minimized and your building can conform to local codes and/or comply with ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality.

As for the ultimate benefit, the occupants of your building will most likely show a decrease in health problems and an increase in productivity.

Cleaner Air

Installing airflow measurement devices directly at the outdoor air intake of each air handler can assure that the ventilation rates required to dilute contaminants are maintained every hour of every day.

In a joint 2000 report, Lawrence Berkley National Laboratory and the U.S. Department of Energy estimated that improving indoor air quality could yield up to $208 billion annually through decreased health care costs and improved productivity.

Since the annual cost per square foot for employees is typically 150-250 times the cost for indoor ventilation, even large percentage increases in annual ventilation costs are quite small compared to the employee benefits.
The occupant benefit alone is worth the investment on systems and equipment for improved IAQ!


Mold and fungal growth will be minimized by controlling envelope and space moisture. Assuring proper building pressurization and providing sufficient equipment capacity to remove the moisture of the dilution air passing through the air handling systems are prerequisites to moisture management.

Liquid flow is by far the most dangerous source of moisture, about 100 times more potent than airflow, and 1000 times greater than diffusion. Gravity is a strong driving force for liquid water and air pressure differential can augment or retard water flow. Besides the physical augmentation of liquid water flow, the moisture contained in moving air as water can be properly managed through pressurization.

By providing the proper pressurization flow, the HVAC system essentially dries the building envelope in the summer and minimizes moisture accumulation in the winter.



Control of key airflow rates using airflow measurement devices permits the use of sequential control strategies that reduce pressure drops across control dampers, hence, reducing energy costs.

In addition, accurate measurement and control of flow rates result in conditioning only the amount of outside air actually required for occupant well-being and building pressure.



There is no better way to reduce your IAQ risk than to assure that your building meets ventilation codes and standards during operation.

By providing accurate airflow measurement devices and controls to maintain key airflow rates, you have the ability to document compliance and limit your liability. The bottom line benefit is “peace of mind”.



Airflow measurement may not be your lowest first-cost option, however, there are a number of “Good-$ense” reasons that you should use airflow measurement on all of your HVAC systems. Here are a few that you should know:
  1. Air-side systems are dependent on air distribution. The only way to verify that the air is being distributed properly during operation is to continuously monitor it. Not continuously measuring airflow rates to verify actual airflow is analogous to not continuously measuring temperature to verify actual temperature. Simply stated, it does not make much sense to ignore airflow rates.

    Airflow rates within a building fluctuate as a result of variations in thermal load, occupancy and stack effect. Physical changes such as filter loading, door position or partition leakage will also influence airflow rates. Air balancing can improve system performance but is often not done frequently enough. Monitor and verify key airflow rates using your B.A.S. for continuous commissioning and verification of HVAC system performance. Control critical airflow rates when conditions are likely to change over time.

  2. The only way to positively verify that the proper amount of dilution air is being brought into a building is to continuously measure it.

    Outside air intake flow rates are heavily influenced by wind and stack pressure changes. VAV systems are affected by mixed air pressure variations with changes in supply airflow. Dampers deteriorate and linkages bind over time, making it impossible to determine the airflow rate at the intake. Demand controlled ventilation schemes require airflow reset, and can fall below base ventilation requirements or go above maximum design levels without direct verification. Outside airflow rates should be controlled by modulating dampers and/or fans to maintain the desired setpoint.

  3. Airflow measurement results in stable, compartmentalized, NET positive or neutral pressure control.

    >Airflow measurement can achieve independent, compartmentalized NET pressure control. Static pressure control, on the other hand, will result in interactive pressure control (i.e. one pressure compartment influences another) and cannot assure that NET pressurization is achieved. NET pressurization is critical for envelope moisture management.

  4. Airflow measurement allows robust, sequential control strategies, that minimize pressure drops and reduce energy consumption.

    Airflow measurement moves control authority away from dampers, which are often improperly sized, actuated and maintained. As a result, dampers can be sequenced with positive feedback (the airflow rate) to assure proper operation. The result is stable, energy efficient, HVAC operation.


Today, you have many choices when it comes to measuring airflow rates. Not all airflow measuring devices use the same technology. Those that use similar technologies may have dramatic differences in performance, not always visible to the casual observer. Here are a few good reasons to always select EBTRON thermal dispersion airflow measurement devices:
  1. Thermal dispersion uses heated thermistors to determine the airflow rate. The principal is governed by the laws of thermodynamics and a large raw signal is directly proportional to the true airflow rate

    Unlike averaging pitot arrays (often disguised in airflow measuring damper systems) that have poor sensitivity at low airflow rates, EBTRON thermal dispersion technology has high sensitivity at low airflow rates. Accuracy is percent of reading, not percent of full scale and is independent of the transducer accuracy and airflow turn-down. Sensing points are independent and unlike its pitot array counterpart, can accurately determine the true average airflow, even in locations with a significant velocity profile.

  2. EBTRON uses only the highest quality, hermetically sealed, bead-in-glass thermistors that have proven stability and reliability over time.

    Unlike our competitors, EBTRON uses only the highest quality bead-in-glass thermistors. These thermistors can withstand wide changes in ambient temperature and are extremely stable over time. Thermistor materials are also matched and selected to be used in self-heat applications (i.e. thermal dispersion) where different changes in the expansion of unlike components can result in failure (as is common on diode case chip thermistors used in self-heat). Our thermistor is more expensive (up to 15 times more costly than its diode-case cousin) but in-house testing of “chip” thermistors taught us to not compromise on this critical component.

  3. EBTRON transmitter components include industrial grade (not commercial grade) surface mount integrated circuits that are selected for wide temperature ranges and long life. Periodic calibration is neither required or recommended

    Long life without the need for periodic field calibration keeps your costs down long after you have installed our equipment. Our in-house product design team has created quality, instrument grade hardware, so you can rest assured that once you turn the power switch to the “on” position, airflow measurement will not be one of the items keeping you awake at night.

  4. Our in-house application engineering department, along with over 70 local rep offices, will take you from project design to completion. Our life-time toll free customer support team will be there to assure that your project works to your satisfaction for the life of your system.

Let us show you why EBTRON should be part of your next project!

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