Ducts

• Duct Work
  Most air-handling units operate with a discharge air temperature setpoint of 55 degrees F when in cooling mode. The return temperature to the unit is usually in the 75-80 F range. It makes no sense to use chilled water to force the 80 F return air back down to 55 F when the outside air is already at or below 55 F. Simply dump all the return air and bring in all the outside air that is needed to deliver 55 F air to the supply ductwork. This should be done with a mixed air temperature setpoint controller. That way the amount of outside air can be adjusted when it is very cold to be just enough to mix with the warm return air to produce the 55 F discharge air temperature.