Abstract: An electrical circuit includes a rectifier having an input for receiving an alternating current (AC) voltage and an output for supplying a first direct current (DC) voltage. The circuit also includes a first regulator having an input electrically connected to the rectifier for receiving the first DC voltage and an output for supplying a second DC voltage. The circuit further includes a second regulator having an input electrically connected to the output of the first regulator for receiving the second DC voltage and an output for providing a third DC voltage.

Abstract: A method of determining the amount of air flowing through an outside air damper of a recirculating air heater includes the steps of sensing an amount of airflow flowing through the damper, recording the amount of airflow and a damper position value at a plurality of damper positions, and interpolating a curve relating the amount of airflow to the damper position for all damper positions between a minimum damper position and a maximum damper position. Once the amount of air flowing through the outside air damper is determined from a position on the curve, the concentration of carbon dioxide (CO2) within a building space can be calculated and/or determined to be within acceptable limits.