Economizer: Free Cooling & Fresh Air

Economizer

The Economizer system utilizes the latest technology available for integrating the use of free cooling with mechanical cooling for packaged rooftop units. With controls like the Jade W7220 it can optimizes energy consumption, zone comfort, and equipment cycling by operating the compressors when the outdoor-air temperature is too warm, integrating the compressor with outdoor air when free cooling is available, and locking out the compressor when outdoor-air temperature is too cold. Demand controlled ventilation is supported. This Economizer can be used with 1 or 2 speed indoor fan motor units. The Economizer system utilizes gear-drive technology with a direct-mount spring return actuator that will close upon loss of power. The Economizer has fault detection and diagnostics, an outdoor air temperature sensor, and mixed air temperature sensor (also called supply air temperature sensor). Outdoor enthalpy, indoor (return) dry bulb or enthalpy, and CO2 sensors are available for field installation. Standard integrated barometric relief dampers provide natural building pressurization control.

During Occupied mode operation, indoor fan operation will be accompanied by economizer dampers moving to Minimum Position set point for ventilation. If indoor fan is off, dampers will close. During Unoccupied mode operation, dampers will remain closed unless a Cooling (by free cooling) or mechanical cooling demand is received. When the outside air is not cool enough for free cooling, the unit cooling sequence will be controlled directly by the space thermostat. Outside air damper position will be closed or Minimum Position as determined by Occupancy mode and fan signal. When free cooling is available as determined by the appropriate changeover command (dry bulb, outdoor enthalpy, differential dry bulb, or differential enthalpy), a call for cooling (Y1 closes at the thermostat) will cause the economizer control to modulate the dampers open and closed to maintain the unit supply air temperature. Default supply air temperature is 53°F, with a range of 38°F to 70°F. Compressor will not run. If the outside air is not cold enough to satisfy the space temperature, space temperature will rise until Y2 is closed. The economizer control will call for compressor operation. Dampers will modulate to maintain set point with Compressor 1 operation. The economizer control will lock out compressor operation when outside air temperature is below set point (default 32°F). When space temperature demand is satisfied (thermostat Y1 opens), the dampers will return to Minimum Damper position if indoor fan is running or fully closed if fan is off.

Above in a 50TCQ heat pump the blue trace is circuit Y1 as it leaves the tstat, and goes to the economizer, where it is determined if free cooling or mechanical will be used for a Y1 cooling call. Economizers are a great piece of equipment to add to a system to in controlling cost when outside temps are cool enough to use outside air to cool a building. Also with other control fresh air can be brought in if carbon dioxide levels are too high in a building. Economizers are a great benefit to the building and people inside.