DEMAND FLOW PUMPING

• US 20110022236A1
• Filed: 07/23/2009
• Published: 01/27/2011
• Est. Priority Date: 07/23/2009
• Status: Active Grant

• Current Assignee: Siemens Industry Incorporated (Siemens AG)
• Original Assignee: Siemens Industry Incorporated (Siemens AG)
• Inventors: Higgins, Robert
• Granted Patent: US 8,275,483 B2
• Time in Patent Office: Days
• US Class Current: 700/282
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/83 by controlling the supply of heat-exchange fluids to heat-exchangers
• CPC Class Codes: F24F 11/84 using valves
• CPC Class Codes: F24F 11/85 using variable-flow pumps
• CPC Class Codes: F24F 2110/00 Control inputs relating to air properties
• CPC Class Codes: F24F 5/0003 Exclusively-fluid systems

Abstract

Demand Flow operates chilled water plants at substantially improved efficiency, regardless of plant load conditions. In general, Demand Flow utilizes an operating strategy which controls chilled and condenser water pumping according to a constant Delta T line, which is typically near or at design Delta T. This reduces or eliminates Low Delta T Syndrome and reduces energy usage by chilled and condenser water pumps for given load conditions. Operation of chilled water pumps in this manner creates a synergy which generally balances flow rates throughout the plant, reducing undesirable bypass mixing and energy usage at air handler fans and other components of the chilled water plant. At plant chillers, application of Demand Flow increases the refrigeration effect through refrigerant sub-cooling and superheating, while preventing stacking. Demand Flow includes a critical zone reset feature which allows the constant Delta T line to be reset to adjust to changing load conditions.

Claims

1. A method for efficient operation of a chilled water plant comprising:

setting a chilled water Delta T comprising a chilled water entering temperature and a chilled water leaving temperature at one or more components of the chilled water plant;

controlling chilled water flow rate through the one or more components to maintain the chilled water Delta T across the one or more components, wherein the chilled water flow rate is controlled by one or more chilled water pumps; and

performing a critical zone reset to adjust the chilled water Delta T when one or more triggering events occur, wherein the chilled water Delta T is reset by an action selected from the group consisting of adjusting the chilled water entering temperature and adjusting the chilled water leaving temperature;

wherein the control of chilled water flow rate through the one or more components to maintain the chilled water Delta T reduces Low Delta T Syndrome at the chilled water plant.

2. The method of claim 1, wherein opening of a chilled water valve of an air handler unit beyond a particular threshold is at least one of the one or more triggering events.

3. The method of claim 1, wherein an increase in temperature of the chilled water in a bypass of the chilled water plant is at least one of the one or more triggering events.

4. The method of claim 1, wherein a decrease in temperature of the chilled water in a bypass of the chilled water plant is at least one of the one or more triggering events.

5. The method of claim 1, wherein a change in flow rate of a tertiary pump beyond a particular threshold is at least one of the one or more triggering events.

6. The method of claim 1, wherein the chilled water Delta T at the one or more chilled water plant components is maintained by increasing the chilled water flow rate to reduce the chilled water Delta T and decreasing the chilled water flow rate to increase the chilled water Delta T.

7. The method of claim 1 further comprising:

establishing a condenser water Delta T comprising a low condenser water entering temperature and a condenser water leaving temperature at a condenser, wherein the condenser uses the low condenser water entering temperature to provide refrigerant sub-cooling; and

maintaining the condenser water Delta T by adjusting condenser water flow rate through the condenser, wherein the condenser water flow rate is adjusted through one or more condenser water pumps.

8. The method of claim 7, wherein maintaining the condenser water Delta T occurs by controlling the condenser water leaving temperature, wherein the condenser water leaving temperature is controlled by adjusting the condenser water flow rate through the one or more condenser water pumps.

9. A method for operating one or more pumps of a chilled water plant comprising:

pumping water at a first flow rate through a chiller with a first pump;

adjusting the first flow rate to maintain a first Delta T across the chiller, wherein the first Delta T comprises a chiller entering temperature and a chiller leaving temperature which provides refrigerant superheat at an evaporator of the chiller regardless of chilled water plant load conditions;

pumping the water at a second flow rate through an air handler unit with a second pump; and

adjusting the second flow rate to maintain a second Delta T across the air handler unit, wherein the second Delta T comprises an air handler unit entering temperature and an air handler unit leaving temperature which provides a desired cooling output at the air handler unit regardless of the chilled water plant load conditions;

wherein the first Delta T and the second Delta T comprise values which balance the first flow rate and the second flow rate to reduce bypass mixing at a bypass of the chilled water plant.

10. The method of claim 9, wherein the first Delta T and the second Delta T are the same.

11. The method of claim 9 further comprising increasing the second flow rate by resetting the second Delta T when a water valve of the air handler unit opens beyond a particular threshold, wherein increasing the second flow rate increases cooling output at the air handler.

12. The method of claim 9 further comprising:

pumping the water through a distribution loop of the chilled water plant to the second pump at a third flow rate with a third pump;

adjusting the third flow rate to maintain a third Delta T;

increasing the third flow rate by resetting the third Delta T when the second flow rate provided by the second pump is beyond a particular threshold, wherein increasing the third flow rate increases cooling capacity at the air handler.

13. The method of claim 9 further comprising:

pumping condenser water at a fourth flow rate through a condenser of the chiller with a fourth pump; and

adjusting the fourth flow rate to maintain a fourth Delta T at the condenser, wherein the fourth Delta T comprises a condenser water entering temperature and a condenser water leaving temperature which provides refrigerant sub-cooling and prevents refrigerant stacking regardless of chilled water plant load conditions.

14. The method of claim 13, wherein the condenser water entering temperature is lower than a wet bulb temperature for the condenser water.

15. A controller for controlling one or more pumps of a chilled water plant comprising:

an input configured to receive sensor information from one or more sensors;

a processor configured to control a flow rate provided by the one or more pumps to maintain a Delta T across a component of the chilled water plant, wherein the processor increases or decreases the flow rate to maintain the Delta T based on the sensor information and generates one or more signals to control the flow rate provided by the one or more pumps, the Delta T comprising an entering temperature and a leaving temperature.

an output configured to send the one or more signals to the one or more pumps;

16. The controller of claim 15, wherein the processor is configured to perform a critical zone reset by lowering the Delta T in response to sensor information indicating additional cooling capacity is desired at the component.

17. The controller of claim 16, wherein the sensor information is operating information selected from the group consisting of air handler chilled water valve position, VFD Hz, pump speed, chilled water temperature, condenser water temperature, and chilled water plant bypass temperature.

18. The controller of claim 15, wherein the processor is configured to maintain the Delta T by controlling the leaving temperature of the Delta T, wherein the leaving temperature is controlled by adjusting the flow rate through the component of the chilled water plant.

19. The controller of claim 18, wherein adjusting the flow rate comprises increasing the flow rate to lower the leaving temperature and decreasing the flow rate to raise the leaving temperature.

20. The controller of claim 15, wherein the Delta T is similar to a design Delta T for the component.