KEES air mixers use a proprietary design to mix air of different temperatures, typically outside air and return air, as it passes through an air handling unit before encountering tempering coils. This counteracts the natural air stratification process and produces air with an even temperature profile.
Sizing a KEES air mixer for an existing air handling unit is a simple mathematical equation that gives specifiers options to suit their individual needs.
What Is the Equation for Sizing a KEES Air Mixer?
The equation used by KEES to size our proprietary air mixers is as follows:
Airflow (CFM) / Air Velocity (FPM) = Dimensions (sq. ft.)
The airflow value is calculated by adding the return air stream and outside air stream of a client’s air handling unit together. For example, if the air handling unit takes in 8,000 CFM of return air and 1,000 CFM of outside air, the unit’s total CFM is 9,000.
Testing has determined that KEES air mixers achieve their best performance at an air velocity of 1,000 FPM. KEES uses as close to this value as the system design parameters will allow when sizing air mixers.
What Other Factors Go Into Sizing a KEES Air Mixer?
Air Handling Unit Size: Air mixers should be no smaller than half the overall height of the air handling unit. Filler or safing panels surround an air mixer that is smaller than the dimensions of the unit to prevent unwanted bypass of unmixed airflow.
Ductwork Connections: If the ductwork connections in the air handling unit are full width, it’s possible to use multiple air mixers side-by-side. If ductwork connections are not full width, only one air mixer can be used.
Downstream Distance: To properly swirl air, air mixers need a minimum distance between the mixer itself and the tempering coils equal to one side of a square air mixer or the average of two adjacent sides of a rectangular mixer.
Shape: KEES air mixers can be made either square or rectangular. Rectangular air mixers perform best when maintaining a 2:1 ratio of width to height.
What Is an Example of Sizing a KEES Air Mixer?
A client wants to specify a KEES air mixer for their air handling unit with full-width ductwork connections. The total airflow entering their air mixer is 9,000 CFM. By dividing this number by the KEES air mixer optimal velocity, the KEES rep can determine the client’s air mixer size:
9,000 CFM / 1,000 FPM = 9 sq. ft.
For this client, a KEES rep would suggest two air mixer configurations, both offering the same performance values:
A single square 36”x36” air mixer with a minimum downstream distance of 36”.
Two rectangular 36”x18” air mixers side-by-side with a minimum downstream distance of 27”, if downstream distance is limited.
KEES Air Mixers Solve the Air Stratification Issue Raising Your Overhead
Conditioning stratified air wastes energy and money while risking damage to tempering coils due to uneven coil loading. KEES air mixers solve the air stratification issue common to all air handling units, improving HVAC system efficiency and reducing overhead costs. We can manufacture custom-sized air mixers to fit any existing air handling unit to ensure air is mixed at the optimal velocity every time.
