MERV vs Motors

September 12, 2022

Motor Minute™ Technical Tip – MERV vs. Motors

Hi, Chris from Regal Rexnord here with your Motor Minute technical tip. Helping you become an HVAC motor pro one minute at a time.

Today’s motor minute topic is MERV vs. Motors.

In last month’s Motor Minute™ Tech Tip (Genteq® Evergreen® DS Motors), I stated that replacing lower MERV (Minimum Efficiency Reporting Value) rated air filters with higher MERV rated air filters, without increasing the area of the filter, will increase the resistance to the flow of air, measured as static pressure or pressure drop. This month I want to briefly discuss how this will affect airflow based on the type of motor in the HVAC system.

HVAC systems built with Permanent Split Capacitor (PSC) and constant torque ECM motors exhibit similar airflow performance. When Total External Static Pressure (TESP) increases, airflow decreases. Notice the difference in CFM from 0.3 – 0.9 TESP. (See Chart A below)

If proper airflow cannot be achieved with the higher MERV rated filter, increasing the area of the filter will lower its pressure drop, thus lowering the TESP and increasing airflow in HVAC systems built with PSC or constant torque ECM motors. (See Chart B below)

HVAC systems built with constant airflow (variable speed) ECM motors will maintain airflow performance when TESP increases. However, if they are continuously operated at the limit of their design, the life expectancy of these motors will decrease. Notice the amperage difference between 0.3 – 0.9 TESP. (See Chart C below)

Increasing the area of the filter will lower its pressure drop, thus lowering the TESP and the amperage in HVAC systems built with constant airflow (variable speed) motors. (See Chart D below)