Central plant control system with computation reduction based on graph theory

1. A controller for an energy plant, the controller comprising:

a processing circuit comprising a processor and memory storing instructions executed by the processor, the processing circuit configured to:

identify, from a plurality of thermodynamic states affected by a plurality of heat, ventilation, and air conditioning (HVAC) devices, a reduced subset of the plurality of thermodynamic states to be predicted based on connections between the plurality of HVAC devices;

predict values of the reduced subset of the plurality of thermodynamic states; and

operate the plurality of HVAC devices based on the predicted values of the reduced subset of the plurality of thermodynamic states.

2. The controller of claim 1 , wherein the plurality of thermodynamic states include pressure values, and wherein the processing circuit is configured to identify the reduced subset of the plurality of thermodynamic states by:

identifying a subset of the pressure values to be predicted based on the connections between the plurality of HVAC devices.

3. The controller of claim 2 , wherein the processing circuit is configured to identify the subset of the pressure values by:

identifying one or more input conduits connected to inputs of the plurality of HVAC devices and one or more output conduits connected to outputs of the plurality of HVAC devices;

identifying a plurality of the input conduits or output conduits that connect to a common node based on the connections between the plurality of HVAC devices; and

removing one or more unknown pressure values associated with the input conduits or the output conduits that connect to the common node such that the common node is associated with a single unknown pressure value.

4. The controller of claim 2 , wherein the processing circuit is configured to identify the subset of the pressure values by:

identifying a plurality of nodes coupled to one or more inputs of the plurality of HVAC devices or one or more outputs of the plurality of HVAC devices;

determining whether any of the plurality of nodes are coupled to multiple of the one or more inputs or the one or more outputs; and

removing one or more unknown pressure values for each of the plurality of nodes coupled to the multiple of the one or more inputs or the one or more outputs such that each of the plurality of nodes is associated with a single unknown pressure value.

5. The controller of claim 1 , wherein the plurality of thermodynamic states include mass flow values, and wherein the processing circuit is configured to identify the reduced subset of the plurality of thermodynamic states by:

identifying a subset of the mass flow values to be predicted based on the connections between the plurality of HVAC devices.

6. The controller of claim 5 , wherein the processing circuit is configured to identify the subset of the mass flow values by:

identifying one or more nodes that connect to exactly two of the plurality of HVAC devices and are associated with multiple unknown mass flow values based on the connections between the plurality of HVAC devices; and

removing one or more of the multiple unknown mass flow values until each node that connects to exactly two of the plurality of HVAC devices is associated with a single unknown mass flow value.

7. The controller of claim 5 , wherein the processing circuit is configured to identify the subset of the mass flow values by:

applying a mass balance to one or more nodes having a known mass flow value at an input conduit or output conduit connecting to a node to pre-solve for an unknown mass flow value at another input conduit or output conduit connecting to the node.

8. The controller of claim 1 , wherein the plurality of thermodynamic states include enthalpy values, and wherein the processing circuit is configured to identify the reduced subset of the plurality of thermodynamic states by:

identifying a subset of the enthalpy values to be predicted based on the connections between the plurality of HVAC devices.

9. The controller of claim 8 , wherein the processing circuit is configured to identify the subset of the enthalpy values by:

identifying one or more nodes that connect to exactly two of the plurality of HVAC devices and are associated with multiple unknown enthalpy values based on the connections between the plurality of HVAC devices; and

removing one or more of the multiple unknown enthalpy values until each node that connects to exactly two of the plurality of HVAC devices is associated with a single unknown enthalpy value.

10. The controller of claim 8 , wherein the processing circuit is configured to identify the subset of the enthalpy values by:

identifying one or more nodes that receive a fluid from one or more input conduits and provide the fluid to multiple output conduits; and

removing one or more unknown enthalpy values associated with the multiple output conduits such that the multiple output conduits are associated with a single unknown enthalpy value.

11. The controller of claim 1 , wherein the processing circuit is configured to:

generate a weighted diagonal adjacency matrix indicating a directional property of unknown thermodynamic states, the processing circuit to identify the reduced subset of the plurality of thermodynamic states based on the weighted diagonal adjacency matrix.

12. A method for operating a plurality of heat, ventilation, and air conditioning (HVAC) devices, comprising:

identifying, from a plurality of thermodynamic states affected by the plurality of HVAC devices, a reduced subset of the plurality of thermodynamic states to be predicted based on connections between the plurality of HVAC devices;

predicting values of the reduced subset of the plurality of thermodynamic states; and

operating the plurality of HVAC devices based on the predicted values of the reduced subset of the plurality of thermodynamic states.

13. The method of claim 12 , wherein the plurality of thermodynamic states include pressure values, and wherein identifying the reduced subset of the plurality of thermodynamic states includes:

identifying a subset of the pressure values to be predicted based on the connections between the plurality of HVAC devices.

14. The method of claim 13 , wherein identifying the subset of the pressure values includes:

identifying one or more input conduits connected to inputs of the plurality of HVAC devices and one or more output conduits connected to outputs of the plurality of HVAC devices;

identifying a plurality of the input conduits or output conduits that connect to a common node based on the connections between the plurality of HVAC devices; and

removing one or more unknown pressure values associated with the input conduits or the output conduits that connect to the common node such that the common node is associated with a single unknown pressure value.

15. The method of claim 13 , wherein identifying the subset of the pressure values includes:

identifying a plurality of nodes coupled to one or more inputs of the plurality of HVAC devices or one or more outputs of the plurality of HVAC devices;

determining whether any of the plurality of nodes are coupled to multiple of the one or more inputs or the one or more outputs; and

removing one or more unknown pressure values for each of the plurality of nodes coupled to the multiple of the one or more inputs or the one or more outputs such that each of the plurality of nodes is associated with a single unknown pressure value.

16. The method of claim 12 , wherein the plurality of thermodynamic states include mass flow values, and wherein identifying the reduced subset of the plurality of thermodynamic states includes:

identifying a subset of the mass flow values to be predicted based on the connections between the plurality of HVAC devices.

17. The method of claim 16 , wherein identifying the subset of the mass flow values includes:

identifying one or more nodes that connect to exactly two of the plurality of HVAC devices and are associated with multiple unknown mass flow values based on the connections between the plurality of HVAC devices; and

removing one or more of the multiple unknown mass flow values until each node that connects to exactly two of the plurality of HVAC devices is associated with a single unknown mass flow value.

18. The method of claim 16 , wherein identifying the subset of the mass flow values includes:

applying a mass balance to one or more nodes having a known mass flow value at an input conduit or output conduit connecting to a node to pre-solve for an unknown mass flow value at another input conduit or output conduit connecting to the node.

19. The method of claim 12 , wherein the plurality of thermodynamic states include enthalpy values, and wherein identifying the reduced subset of the plurality of thermodynamic states includes:

identifying a subset of the enthalpy values to be predicted based on the connections between the plurality of HVAC devices.

20. The method of claim 19 , wherein identifying the subset of the enthalpy values includes:

identifying one or more nodes that receive a fluid from one or more input conduits and provide the fluid to multiple output conduits; and

removing one or more unknown enthalpy values associated with the multiple output conduits such that the multiple output conduits are associated with a single unknown enthalpy value.