One ton of cooling requires how many CFM of air flow?

One ton of cooling requires how many CFM of air flow?

• A. 200 CFM
• B. 600 CFM
• C. 400 CFM
• D. 800 CFM

Answer: (C)

Removing heat at the rate of one ton (12,000 BTU/hr) with typical cooling coil conditions uses about 400 cubic feet per minute of air flow. This comes from the sensible heat equation Q = 1.08 × CFM × ΔT, where Q is the heat transfer rate, ΔT is the temperature change across the coil, and CFM is the air flow. With a ΔT across the coil roughly in the 28–30°F range, solving 12,000 = 1.08 × CFM × ΔT gives about 370–400 CFM. Designers use the practical rule of thumb that one ton requires around 400 CFM, so 400 CFM is the best answer. The other numbers would imply either too little or too much air for this cooling capacity given typical operating conditions.

Removing heat at the rate of one ton (12,000 BTU/hr) with typical cooling coil conditions uses about 400 cubic feet per minute of air flow. This comes from the sensible heat equation Q = 1.08 × CFM × ΔT, where Q is the heat transfer rate, ΔT is the temperature change across the coil, and CFM is the air flow. With a ΔT across the coil roughly in the 28–30°F range, solving 12,000 = 1.08 × CFM × ΔT gives about 370–400 CFM. Designers use the practical rule of thumb that one ton requires around 400 CFM, so 400 CFM is the best answer. The other numbers would imply either too little or too much air for this cooling capacity given typical operating conditions.