udarrell
03-07-2009, 11:14 PM
Quick Check for Sizing Units to enough Airflow
Actually, even on service calls where there are cooling problems the ductwork should have a quick Manual D performed.
Then take the ESP static pressure & compare to blower graph or chart, also take the FPM duct velocity.
Then do a quick estimate of airflow per equipment tonnage.
To find area of a round duct; Duct diam is 7"; 7"X7"= 49-sq.ins., X's .7854 = 38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's FPM Velocity 550-FPM = 160.35246-CFM X30 = 4,810.5738 each 7" run X's 6 branch runs = 28,863-BTUH, or airflow for 2.4-ton.
That would also be good for 2-ton; at 550-FPM velocity X's 0.2672541= 147-CFM X 30 = 4,410-BTUH each run X 6-runs = airflow for 26,460-BTUH.
Never sell units requiring more airflow than the duct system & blower will support! - udarrell
Actually, even on service calls where there are cooling problems the ductwork should have a quick Manual D performed.
Then take the ESP static pressure & compare to blower graph or chart, also take the FPM duct velocity.
Then do a quick estimate of airflow per equipment tonnage.
To find area of a round duct; Duct diam is 7"; 7"X7"= 49-sq.ins., X's .7854 = 38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's FPM Velocity 550-FPM = 160.35246-CFM X30 = 4,810.5738 each 7" run X's 6 branch runs = 28,863-BTUH, or airflow for 2.4-ton.
That would also be good for 2-ton; at 550-FPM velocity X's 0.2672541= 147-CFM X 30 = 4,410-BTUH each run X 6-runs = airflow for 26,460-BTUH.
Never sell units requiring more airflow than the duct system & blower will support! - udarrell