When using the PEARL, the economizer and mechanical cooling sequence of operation is more advanced than simple staging:
If all parameters are met for economizer to be active, the outdoor damper will open and mechanical cooling will be held off (the minimum hold of time is 10 minutes). The thermostat will monitor the room’s temperature rate of change. If the room is cooling adequately (0.7°F over 10 minutes) no mechanical cooling will be used and the mechanical cooling hold of timer will be reset for another 10 minutes. If the thermostat determines that the economizer is unable to maintain the cooling rate, mechanical cooling will be enabled (Click here, for an explanation of the number of mechanical cooling stages that will be enabled).
If both mechanical cooling and economizer are active the supply temperature will be monitored and the outdoor damper will modulate to make sure the supply temperature does not go lower then the Economizer Low Limit (click here, for more information) configuration.
With these sequences it is possible to have only economizer, only mechanical cooling, or both active at the same time.
What will you see on a thermostat's history graph?
On the graph you will see a green shaded area when the economizer is active. You will see a light blue shaded area when mechanical cooling is active. And you will see the green and blue shading overlapping each other if both are active.
For two stage mechanical cooling equipment, you will see a single grey bar at the bottom of the light blue shaded area when first stage is enabled and two bars (one stacked on-top of the other) when first and second stage are enabled.
