Points out that multizone air handling units were popular for nearly 25 years and many are still in service today. The degree of mixing of outside air and return air in these units depends to a great degree on the manner in which the outside air is ducted into the return air system. States that tests conducted during the described study demonstrate that there can be a 600% variation in outdoor air quantity from one zone to another. This can result in very uneven outside air distribution within the building, which can be bad or good, depending on the requirements of the individual zones.

KEYWORDS: Ventilation. efficiency, ducts, outdoor air, return air, mixing, designing, testing, air handling units