An economizer is another means of energy saving. In its simplest form it consists of two sets of dampers, one set controlling the amount of return air that is directed either to exhaust or back to the air handler and a second set controlling the amount of outside air routed to the air handler.

Cooling Season: When the outside air (OAIR) has a lower enthalpy than the return air (RAIR), then the OAIR is directed to the coils and the RAIR is routed to the exhaust. By routing the lower enthalpy air (OAIR), the coil requires less energy to provide cooling. If the enthalpy of the RAIR is lower than the OAIR, then the RAIR is routed to the coil and only the minimum amount of OAIR is routed to the coil. OAIR is still required in order to maintain the proper amounts of fresh air to the occupants.

HVAC Economizer for the Mechanical PE Exam