Sensor-free optimal control of air-side economizer
View Patent ↗Systems and methods for regulating the amount of outdoor air that is introduced into a building are shown and described. These systems and methods utilize extremum seeking control logic to vary the flow of outdoor air into the building in response to cooling load determinations.
1. A cooling system comprising:
a mechanical cooling system comprising a mechanical cooling element and a mechanical cooling system controller, the mechanical cooling system controller outputting a control signal for adjusting the amount of cooling provided by the mechanical cooling element;
an economizer that provides mixed air past the mechanical cooling element to cool the mixed air prior to supplying the air to a building space via a supply air duct;
wherein the economizer includes a damper that controls the amount of outdoor air being mixed with return air in the economizer; and
an extremum seeking controller that uses the control signal output from the mechanical cooling system controller as an input, uses the input to search for an economizer damper position that minimizes the amount of cooling provided by the mechanical cooling element, and outputs a damper signal for adjusting the damper to the damper position, wherein the extremum seeking controller operates by regularly perturbing the damper position away from a previously determined optimum and sets a new damper position in response to observing the effects of the perturbations, and wherein neither a temperature setpoint nor a temperature sensor feedback are used to cause the regular perturbations.
2. The cooling system of claim 1 , wherein the mechanical cooling system is a chilled fluid cooling system, the mechanical cooling element is a chilled fluid cooling coil, and the mechanical cooling system controller is a feedback controller; and wherein the control signal output from the feedback controller is configured to cause a valve associated with the chilled fluid cooling coil to adjust the amount of cooling provided by the chilled fluid cooling element.
3. The cooling system of claim 2 , wherein the feedback controller uses feedback from a supply air temperature sensor to maintain a supply air temperature at a setpoint by changing the control signal, thereby adjusting the amount of cooling provided by the chilled fluid cooling coil.
4. The cooling system of claim 3 , wherein the extremum seeking controller does not use a sensor input to search for damper positions.
5. The cooling system of claim 3 , wherein neither the extremum seeking controller nor the feedback controller use a relative humidity sensor to conduct control activities for the cooling system and the economizer.
6. The cooling system of claim 3 , wherein neither the extremum seeking controller nor the feedback controller use an outdoor air temperature sensor to conduct control activities for the cooling system and the economizer.
7. The cooling system of claim 3 , wherein neither the extremum seeking controller nor the feedback controller use a return air temperature sensor to conduct control activities for the cooling system and the economizer.
8. The cooling system of claim 3 , further comprising:
a state machine that transitions the cooling system between a first cooling state that uses the extremum seeking controller with the mechanical cooling system to a second cooling state that uses free cooling and does not use the mechanical cooling system.
9. The cooling system of claim 8 , wherein the state machine is configured to transition from the first cooling state to the second cooling state when the control signal output from the mechanical cooling system controller is at or below a minimum value for a predetermined period of time.
10. The cooling system of claim 9 , wherein the state machine is configured to transition from the second cooling state to the first cooling state when a damper control signal exceeds a maximum value for a predetermined period of time.