MODEL PREDICTIVE CONTROL FOR HEAT TRANSFER TO FLUIDS

• US 20150253051A1
• Filed: 03/09/2015
• Published: 09/10/2015
• Est. Priority Date: 03/07/2014
• Status: Active Grant

• Current Assignee: Alliance For Sustainable Energy LLC
• Original Assignee: Alliance For Sustainable Energy LLC
• Inventors: JIN, Xin, MAGUIRE, Jeff, CHRISTENSEN, Dane
• Granted Patent: US 10,378,805 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F24D 19/1054 the system uses a heat pump
• CPC Class Codes: F24D 19/1063 counting of energy consumption
• CPC Class Codes: F25B 2500/19 Calculation of parameters
• CPC Class Codes: F25B 49/02 for compression type machines, plants or systems

Abstract

Model predictive control methods are disclosed which provide, among other things, efficient strategies for controlling heat-transfer to a fluid.

Claims

1. A method for controlling a temperature of a fluid, the method comprising:

defining an objective function as a function of at least a future fluid temperature set-point for a heating element configured to heat the fluid;

initializing an intermediate fluid temperature set-point;

changing the intermediate fluid temperature set-point;

solving the objective function with the changed intermediate fluid temperature set-point;

optimizing the objective function by repeating the changing and the solving; and

setting the future fluid temperature set-point for the heating element equal to the intermediate fluid temperature set-point corresponding to the optimized objective function.

2. The method of claim 1, wherein the objective function is also a function of a future fluid usage prediction, and the future fluid usage prediction is at least partially determined by historical fluid usage data.

3. The method of claim 2, wherein the historical fluid usage data are determined by

defining a first time period (T);

defining a second time period (t) by dividing T by an integer value (N) such that T is divided into N equal and consecutive time intervals (t_n), wherein T restarts and repeats upon completion of the last t_n; and

collecting consecutive measurements of actual fluid usage data (F_n) for each consecutive t_n as the historical usage data.

4. The method of claim 3, further comprising storing on a data storage medium no more than N sets of consecutive measurements.

5. The method of claim 4, wherein the historical fluid usage data comprises a measurement of at least one of a fluid flow or a fluid temperature.

6. The method of claim 2, wherein the objective function is also a function of an input energy required to heat the fluid for the future usage prediction to the future fluid temperature set-point, and the objective function is optimized to minimize the input energy required.

7. The method of claim 6, wherein the input energy required is calculated using a mass and energy balance, the calculating comprising:

defining a fluid volume comprising at least two fluid containing nodes in series, wherein each node is characterized by a fluid temperature, a first node has a maximum fluid temperature, and each subsequent adjacent node in the series has a fluid temperature less than or equal to the fluid temperature of the node immediately preceding and adjacent to it;

calculating for each node the energy required to heat the fluid of that node to the future fluid temperature set-point; and

summing the energy calculated for each node to yield the input energy required.

8. The method of claim 7, wherein the energy required to heat the fluid of each node is adjusted by at least one of an energy loss from the node to a local surrounding, an energy loss from the node to an adjacent node, an energy input into the node from mixing, or an energy input into the node by conduction from an adjacent node.

9. The method of claim 6, wherein the input energy is calculated using a state space model.

10. The method of claim 1, wherein the heating element comprises at least one of a resistive heating element or a heat pump.

11. The method of claim 1, wherein the fluid is a liquid.

12. The method of claim 11, wherein the liquid is water.

13. The method of claim 1, wherein the future temperature set-point ranges from about 0°

F. to about 500°

F.

14. A method for controlling a temperature of water, the method comprising:

defining an objective function as a function of at least one future water temperature set-point for a resistive heating element and a heat pump, wherein both the resistive heating element and the heat pump are configured to heat the water;

initializing an intermediate water temperature set-point;

changing the intermediate water temperature set-point;

solving the objective function with the changed intermediate water temperature set-point;

optimizing the objective function by repeating the changing and the solving; and

setting the future water temperature set-point equal to the intermediate water temperature set-point corresponding to the optimized objective function.

15. The method of claim 14, wherein the objective function is also a function of a future water volume usage prediction, and the future water volume usage prediction is at least partially determined by historical water volume usage data.

16. The method of claim 15, wherein the historical water usage data are determined by defining a first time period;

defining a second time period by dividing the first time period by an integer (N);

defining a third time period by dividing the second time period by an integer (I) to create N*I consecutive time intervals, wherein each time interval is about equal to the third time period; and

collecting consecutive measurements of actual water flow and water temperature data for each consecutive time interval as the historical usage data.

17. The method of claim 16, wherein the first time period equals about 14 days, the second time period equals about 1 day for an N of about 10, and the third time period is about 30 minutes for an I of about 48.

18. The method of claim 16, wherein the objective function is also a function of a calculated input energy required to heat the water for the future water usage prediction to the future fluid temperature set-point, and the objective function is optimized to minimize the input energy required, and the energy input calculation comprises:

defining a fluid volume comprising a first water containing node and a second water containing node in series, wherein both nodes are characterized by a first and second water temperature respectively, the first water temperature is a highest temperature, and the second water temperature is less than or equal to the first water temperature;

calculating for both nodes the energy required to heat the water to the future water temperature set-point; and

summing the energy calculated for both nodes to yield the input energy required.