Arkansas HVACR NewsMagazine May 2022

HVACR NewsMagazine May 2022

Tech News

Static Pressure –

350-400 CFM (594.65 m3/h-679.6 m3/h) per ton works in my neck of the woods. If you are in a very dry climate or at a high altitude, the CFM per ton requirements may be higher, often 450- 500 CFM ton.

Why Measure It?

This article is furnished by HVAC School: For Techs by Techs authored by Neil Comparetto.

Why measure static pressure? Because it's fun. I enjoy drilling holes in things. I rarely leave a house without drilling a hole in something. I also believe it's an essential step to commissioning and diagnosing a forced-air piece of equipment. Let me explain why. I think we all can agree that proper airflow is necessary across the indoor coil. You should set the airflow before adjusting the refrigerant charge, right? Yes. Well, how do you know what fan speed to set the blower at? Whether it's a PSC, X-13, or an ECM motor, you have fan speed options. The easiest way to set the blower speed is to measure TESP (total external static pressure); cross-reference the TESP to the manufacturer's blower chart in the installation manual, and adjust the blower speed. Sure, there are other ways of estimating or measuring airflow, but for commissioning a system in cooling, using static pressure and a blower chart is easy and accurate enough. Commissioning

Even when commissioning a furnace in heating, I like to set up my airflow first, or I at least like to know how many CFM the blower is moving. Typically, it's between 130 and 150 CFM per 10,000 input BTUH. How many times have you serviced a system installed by others, there is no evidence of airflow being measured, and the blower speed is set too high? My guess: every day.