HVAC Blog

The countdown has begun, and the excitement is palpable as we gear up for the highly anticipated 2024 AHR Expo taking place January 22-24 at McCormick Place in Chicago, IL. We will be alongside ONICON Incorporated showcasing our HVAC flow, energy, and airflow measurement solutions in Booth #S6334.

The AHR Expo is not just an exhibition — it’s a convergence of expertise, innovation, and collaboration, and we’re excited to be at the forefront of it all. As the world’s largest HVACR event, it draws together a diverse group of industry professionals from across the globe. The expo offers an array of educational sessions, networking opportunities, and a collaborative space, bringing together attendees to share ideas—all within a single venue. We can’t wait to meet with our sales reps, customers, and movers and shakers in the HVACR industry at the show.

“Sharing our newest innovations with attendees is always a delight, especially when we can showcase our products in action on the show floor.” – Mike Rivers, Director of Sales and Marketing

Registration is free through January 20th and once you have registered, be sure to visit our Map Your Show page to see what we will be featuring and to make sure you don’t miss out on visiting our booth while you’re there. Our booth will be staffed with dedicated HVAC flow and energy experts throughout the event, ready to assist with any questions regarding applications or products.

We look forward to seeing you in Chicago and If you missed us last year in Atlanta, be sure to check out our AHR 2023 Recap Video!

However, accurate outdoor HVAC airflow measurement can be difficult due to weather and local climate conditions, as well as the design of the air inlets. 

Climate and Weather Conditions

Outside air pumped into an HVAC system from the rooftop of a building can vary widely in temperature, moisture level, and particulate load. On top of that, the speed and direction of the wind and the barometric pressure can fluctuate from one hour to the next. All these factors can affect the accuracy of an outdoor air flow measurement system.

Duct Design Difficulties

Accurate measurement is made more difficult by the design of some outdoor air inlets, which usually have limited straight runs available to condition the airflow prior to measurement. Some systems require a certain number of upstream straight runs of the duct to reduce flow turbulence before taking measurements.

In addition to the lack of straight duct runs, HVAC inlets are often retrofitted with an economizer inlet to help meet the building’s energy efficiency goals. The addition of an economizer means that the inlet is oversized for maintaining indoor air quality. The result is very low flow velocities at the inlet most of the time, which directly affects measurement accuracy and reliability.

Rooftop packaged units are a worst-case example, as the minimum outside air and the 100% outside air economizer functions are forced into a single inlet. To make matters worse, some manufacturers combine several unit sizes into a single box/frame/control damper/hood size.

Outdoor Airflow Measurement Technologies 

The three most often used technologies for measuring outside air are thermal dispersion, Pitot array, and pressure difference across a known resistance. In this post, we will briefly look at each technology to determine the best fit for measuring outdoor air flow.

Thermal dispersion 

To get accurate air flow measurements, thermal dispersion systems typically require 2 to 8 diameters of straight duct runs both upstream and downstream – something that’s rarely available in outside air intake duct configurations. Also, thermal sensors do not tolerate any form of moisture in the air and they perform poorly in dynamic and turbulent airflow conditions, making them a poor choice for accurate outdoor hvac airflow measurement.

Pitot array technology

In this type of air flow measurement system, dynamic pressure and static pressure are measured at many points throughout the duct, and the results are averaged. The velocity of airflow is proportional to the difference in pressure, so a differential pressure (DP) transmitter is used to convert the difference into an average airflow velocity. The transmitter then converts average velocity into average airflow volume using the cross-sectional area of the duct. 

The performance and price level of airflow measurement systems that use the Pitot measurement principle can vary widely. These systems have two types of components: Pitot probes and the DP transmitter. System accuracy depends on the number of Pitot tubes required, the quality of the transmitter, and to some degree, the local air quality. Air inlets with limited straight runs available to condition the airflow require large numbers of Pitot tubes to achieve accurate flow measurements, which could make them cost-prohibitive. 

Pressure difference across a known resistance

Yet a third technology uses small differences in static field pressures created by air moving through a fixed inlet to accurately measure airflow without the need for straight ducts to condition flow. The concept is based on measuring static pressure fields that develop when air flows through any screen or louver with a known velocity vs. pressure drop curve without a significant change in the pressure drop. 

These static pressure measurements used in concert with temperature, barometric pressure measurements, and inlet size can be used to calculate the flow rate at any atmospheric condition. This type of system is nearly impervious to dust and moisture, has a high tolerance for dynamic variations in air flow velocity and direction, and requires zero straight runs of duct. 

An Accurate Solution for Airflow Measurement in Outside Air Applications 

Air Monitor’s OAM II Outdoor Airflow Measurement System uses static pressure field measurements to provide accurate airflow monitoring in this challenging application. The system consists of the OAM II Transmitter with a built-in barometric pressure sensor, one or more uni-sensors or OAM II airflow measuring stations, and one or two temperature sensors. The system has been designed to measure the actual airflow rate to within ±5% by measuring differential pressure across a fixed inlet, such as a louver, screen, or layer of expanded metal.

Precision in outside airflow measurement is essential to ensure that ASHRAE ventilation standards are met, energy consumption calculations are accurate, and proper indoor air quality is maintained for occupant health and safety. The OAM II System allows you to fine-tune the amount of outside air flow to maintain pressurization, meet energy efficiency goals, and keep operating costs low. 

Click below to learn more.