NATE Air Conditioning and Heat Pumps Practice Exam

The appropriate air volume flow rate of recirculated indoor air that equals one ton of cooling load on the evaporator is 400 cubic feet per minute (cfm). This value is derived from the general formula used in HVAC systems to determine the relationship between air flow and cooling capacity.

One ton of cooling is equivalent to 12,000 BTU/hr. In air conditioning systems, a rough rule of thumb is that it takes approximately 400 cfm of air to transfer 1 ton of cooling. This estimation is based on the temperature rise through a standard air conditioning coil where the air is cooled by typically around 20°F, which results in the necessary cooling effect to achieve one ton of cooling.

The 400 cfm figure is widely accepted in the industry, making it crucial for HVAC professionals to understand when calculating air flow rates necessary for proper system performance. An error in this value could lead to insufficient cooling or inefficient operation of the air conditioning system, emphasizing the importance of using the correct airflow rate.