Abstract: The present invention is an economizer that is capable of mixing outside air and inside air while incurring a significantly low pressure drop across the return air damper. In one embodiment, the economizer comprises a mixing chamber, a return air vent, and an outside air vent. The economizer further comprises a plurality of curved return air dampers moveable from an open position to a closed position to control the flow of return air to the mixing chamber. The economizer further comprises a plurality of straight dampers moveable from an open position to a closed position to control the flow of outside air to the mixing chamber. During operation of the economizer, a significantly lower pressure drop exists across the curved return air dampers than in conventional economizers thereby reducing the amount of energy needed to operate fans to maintain the desired air flow.

Abstract: An interlocking joint or fastening means is provided wherein one fastening member is provided integral to a panel member to be fastened to another panel member. A second fastening member is provided having a tongue that intrudes into an opening provided by the integral fastening member.