Systems and methods for adaptive capacity constraint management

1. An adaptive capacity constraint management system comprising:

a communications interface configured to receive a measured value for a thermodynamic property affected by a refrigeration circuit at actual operating conditions; and

a processing circuit coupled to the communications interface, the processing circuit comprising:

an actual state module that uses the measured value to determine an operating value for a thermodynamic property of a refrigerant used in the refrigeration circuit at the actual operating conditions;

a gain module that uses the operating value for the thermodynamic property of the refrigerant to calculate a gain factor for the thermodynamic property of the refrigerant relative to design conditions;

a capacity gain module that uses the calculated gain factor to determine a capacity gain for the refrigeration circuit relative to the design conditions;

a capacity limit updating module that applies the capacity gain to a design capacity limit for equipment in the refrigeration circuit to determine a new capacity limit for the equipment at the actual operating conditions; and

an equipment selection module that uses the new capacity limit as a constraint in an optimization routine that selects one or more devices used to satisfy a thermal energy load.

2. The adaptive capacity constraint management system of claim 1 , wherein the thermodynamic property affected by the refrigeration circuit comprises at least one of:

a measured temperature of a chilled fluid that rejects heat to the refrigerant in an evaporator of the refrigeration circuit; and

a measured temperature of a heated fluid that absorbs heat from the refrigerant in a condenser of the refrigeration circuit.

3. The adaptive capacity constraint management system of claim 2 , wherein using the measured value to determine an operating value for the thermodynamic property of the refrigerant comprises at least one of:

estimating at least one of an inlet enthalpy and an inlet entropy of the refrigerant at an inlet of an evaporator of the refrigeration circuit; and

estimating at least one of an outlet enthalpy and an outlet entropy of the refrigerant at an outlet of the evaporator.

4. The adaptive capacity constraint management system of claim 3 , wherein estimating the inlet enthalpy comprises:

using the measured temperature of the heated fluid to estimate a temperature of the refrigerant at an inlet of an expansion valve of the refrigeration circuit;

using the estimated temperature of the refrigerant to estimate an enthalpy of the refrigerant at the inlet of the expansion valve; and

using the estimated enthalpy of the refrigerant at the inlet of the expansion valve as the inlet enthalpy.

5. The adaptive capacity constraint management system of claim 3 , wherein estimating at least one of the outlet enthalpy and the outlet entropy comprises:

using the measured temperature of the chilled fluid to estimate a temperature of the refrigerant at the outlet of the evaporator; and

using the estimated temperature of the refrigerant to estimate at least one of the outlet enthalpy and the outlet entropy.

6. The adaptive capacity constraint management system of claim 1 , wherein the thermodynamic property of the refrigerant is a volumetric flow rate of the refrigerant and wherein calculating a gain factor for the volumetric flow rate of the refrigerant relative to design conditions comprises:

determining an isentropic head across a compressor of the refrigeration circuit at the actual operating conditions;

using a compressor map to determine a volumetric flow rate of the refrigerant that corresponds to the isentropic head across the compressor at the actual operating conditions; and

calculating a ratio between the determined volumetric flow rate of the refrigerant at the actual operating conditions and a volumetric flow rate of the refrigerant at the design conditions.

7. The adaptive capacity constraint management system of claim 1 , wherein the thermodynamic property of the refrigerant is a density of the refrigerant and wherein calculating a gain factor for the density of the refrigerant relative to design conditions comprises:

determining at least one of a temperature and a pressure of the refrigerant in the evaporator at the actual operating conditions;

using at least one of the temperature and the pressure of the refrigerant in the evaporator to determine a density of the refrigerant in the evaporator at the actual operating conditions; and

calculating a ratio between the determined density of the refrigerant at the actual operating conditions and a density of the refrigerant at the design conditions.

8. The adaptive capacity constraint management system of claim 1 , wherein the thermodynamic property of the refrigerant is an enthalpy rise of the refrigerant across an evaporator of the refrigeration circuit and wherein calculating a gain factor for the enthalpy rise of the refrigerant relative to design conditions comprises:

determining a first difference between an enthalpy of the refrigerant at an outlet of the evaporator and an enthalpy of the refrigerant at an inlet of the evaporator at the actual operating conditions;

determining a second difference between an enthalpy of the refrigerant at an outlet of the evaporator and an enthalpy of the refrigerant at an inlet of the evaporator at the design conditions; and

calculating a ratio between the first difference and the second difference.

9. The adaptive capacity constraint management system of claim 1 , wherein determining a capacity gain for the refrigeration circuit relative to the design conditions comprises combining a plurality of gain factors for individual properties of the refrigerant to calculate a total capacity gain.

10. The adaptive capacity constraint management system of claim 1 , wherein:

the optimization routine optimizes an amount of power consumed by the one or more devices in satisfying the thermal energy load subject to the new capacity limit; and

the amount of power consumed by the one or more devices in satisfying the thermal energy subject to the new capacity limit is less than an optimal amount of power consumed by the one or more devices in satisfying the same thermal energy load subject to the design capacity limit.

11. A method for determining a capacity limit of equipment in a refrigeration circuit, the method comprising:

receiving, at a processing circuit, a measured value for a thermodynamic property affected by the refrigeration circuit at actual operating conditions;

using the measured value to determine, by an actual state module of the processing circuit, an operating value for a thermodynamic property of a refrigerant used in the refrigeration circuit at the actual operating conditions;

using the operating value for the thermodynamic property of the refrigerant to calculate, by a gain module of the processing circuit, a gain factor for the thermodynamic property of the refrigerant relative to design conditions;

using the calculated gain factor to determine, by a capacity gain module of the processing circuit, a capacity gain for the refrigeration circuit relative to the design conditions;

applying the capacity gain to a design capacity limit for the equipment to determine, by a capacity limit updating module of the processing circuit, a new capacity limit for the equipment at the actual operating conditions; and

using the new capacity limit as a constraint in an optimization routine that selects one or more devices used to satisfy a thermal energy load.

12. The method of claim 11 , wherein the thermodynamic property affected by the refrigeration circuit comprises at least one of:

a measured temperature of a chilled fluid that rejects heat to the refrigerant in an evaporator of the refrigeration circuit; and

a measured temperature of a heated fluid that absorbs heat from the refrigerant in a condenser of the refrigeration circuit.

13. The method of claim 12 , wherein using the measured value to determine an operating value for the thermodynamic property of the refrigerant comprises at least one of:

estimating at least one of an inlet enthalpy and an inlet entropy of the refrigerant at an inlet of an evaporator of the refrigeration circuit; and

estimating at least one of an outlet enthalpy and an outlet entropy of the refrigerant at an outlet of the evaporator.

14. The method of claim 13 , wherein estimating the inlet enthalpy comprises:

using the measured temperature of the heated fluid to estimate a temperature of the refrigerant at an inlet of an expansion valve of the refrigeration circuit;

using the estimated temperature of the refrigerant to estimate an enthalpy of the refrigerant at the inlet of the expansion valve; and

using the estimated enthalpy of the refrigerant at the inlet of the expansion valve as the inlet enthalpy.

15. The method of claim 13 , wherein estimating at least one of the outlet enthalpy and the outlet entropy comprises:

using the measured temperature of the chilled fluid to estimate a temperature of the refrigerant at the outlet of the evaporator; and

using the estimated temperature of the refrigerant to estimate at least one of the outlet enthalpy and the outlet entropy.

16. The method of claim 11 , wherein determining a capacity gain for the refrigeration circuit relative to the design conditions comprises combining a plurality of gain factors for individual properties of the refrigerant to calculate a total capacity gain.

17. The method of claim 11 , wherein:

the optimization routine optimizes an amount of power consumed by the one or more devices in satisfying the thermal energy load subject to the new capacity limit; and

the amount of power consumed by the one or more devices in satisfying the thermal energy subject to the new capacity limit is less than an optimal amount of power consumed by the one or more devices in satisfying the same thermal energy load subject to the design capacity limit.

18. An adaptive capacity constraint management system comprising:

a communications interface configured to receive a measured value affected by HVAC equipment at actual operating conditions; and

a processing circuit coupled to the communications interface, the processing circuit comprising:

an actual state module that uses the measured value to determine an operating value for a variable that affects a capacity of the HVAC equipment at the actual operating conditions;

a gain module that uses the operating value to calculate a gain factor for the variable relative to design conditions;

a capacity gain module that uses the calculated gain factor to determine a capacity gain for the HVAC equipment relative to the design conditions;

a capacity limit updating module that applies the capacity gain to a design capacity limit for the HVAC equipment to determine a new capacity limit for the HVAC equipment at the actual operating conditions; and

an equipment selection module that uses the new capacity limit as a constraint in an optimization routine that selects one or more devices of the HVAC equipment used to achieve a load setpoint.

19. The adaptive capacity constraint management system of claim 18 , wherein determining the capacity gain comprises combining a plurality of gain factors for individual variables that affect the capacity of the HVAC equipment to determine a total capacity gain.

20. The adaptive capacity constraint management system of claim 18 , wherein:

the optimization routine optimizes an amount of power consumed by the one or more devices of the HVAC equipment to achieve the load setpoint; and

the amount of power consumed by the one or more devices in achieving the load setpoint subject to the new capacity limit is less than an optimal amount of power consumed by the one or more devices in achieving the same setpoint subject to the design capacity limit.