Generating and implementing thermodynamic models of a structure

• US 9,910,449 B2
• Filed: 04/19/2013
• Issued: 03/06/2018
• Est. Priority Date: 04/19/2013
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google LLC (Alphabet Inc.)
• Inventors: Matsuoka, Yoky, Malhotra, Mark, Minich, Allen J., Ruff, Joseph A.
• Primary Examiner(s): Ciric, Ljiljana
• Assistant Examiner(s): COX, ALEXIS K
• Application Number:
  US13/866,602
• Publication Number:
  US 20140312128A1
• Time in Patent Office: 1,782 Days
• CPC Class Codes: F24F 11/52 Indication arrangements, e.g. displays
• CPC Class Codes: F24F 11/58 using Internet communication
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 17/02 electric
• CPC Class Codes: G05B 2219/2614 HVAC, heating, ventillation, climate control
• CPC Class Codes: G05B 2219/2642 Domotique, domestic, home control, automation, smart house
• CPC Class Codes: G05D 23/1917 using digital means

Abstract

Thermostats disclosed herein are operable to control an HVAC system. In controlling the HVAC system, a need to determine an expected indoor temperature profile for a particular schedule of setpoint temperatures may arise. To make such a determination, a thermodynamic model of the structure is used. The thermodynamic model may be generated by fitting weighting factors of a set of basis functions to a variety of historical data including time information, temperature information, and HVAC actuation state information. The set of basis functions characterize an indoor temperature trajectory of the structure in response to a change in HVAC actuation state, and include an inertial carryover component that characterizes a carryover of a rate of indoor temperature change that was occurring immediately prior to the change in actuation state.

Claims

1. A thermostat for controlling a heating, ventilation, and air conditioning (HVAC) system in a structure, the thermostat comprising:

HVAC control circuitry operable to actuate one or more elements of the HVAC system;

a communications component;

one or more sensors for measuring characteristics of the structure; and

a processor coupled to the HVAC control circuitry and the one or more sensors that is configured to perform operations including;

storing temperature information from the one or more sensors and time stamps for the temperature information;

causing the HVAC control circuitry to actuate an HVAC function to transition a temperature inside the structure from a first temperature to a second temperature;

populating a thermodynamic model that predicts a temperature trajectory of the temperature of the air inside the structure in response to actuation of the HVAC function, wherein;

the thermodynamic model comprises a plurality of basis functions that together characterize the temperature trajectory of the air inside the structure in response to the actuation of the HVAC function;

the thermodynamic model comprises a plurality of weighting factors corresponding to the plurality of basis functions; and

the plurality of basis functions comprises a basis function comprising an expression that models an effect of a rate of temperature change that was occurring in the structure prior to actuating the HVAC function and which exponentially decays from a time that the HVAC function is actuated until a time when steady-state activity overcomes early-cycle activity;

fitting the plurality of weighting factors of the thermodynamic model to a portion of the temperature information and time stamps for the temperature information corresponding to times when the HVAC function was actuated; and

predicting the temperature trajectory of the air inside the structure using the thermodynamic model.

2. The thermostat of claim 1, wherein the processor is further configured to create the thermodynamic model where the plurality of basis functions further comprises a basis function for a current stage effect component that characterizes an effect that a current stage has on the temperature trajectory of the air inside the structure.

3. The thermostat of claim 2, wherein the processor is further configured to create the thermodynamic model where the current stage effect component begins at zero, reaches a maximum after a certain period of time, and diminishes thereafter.

4. The thermostat of claim 1, wherein the processor is further configured to fit the plurality of weighting factors using weather forecast and a clock signal received through the communications component.

5. The thermostat of claim 1, wherein the processor is further configured to cause the HVAC control circuitry to actuate the HVAC function by switching the HVAC function from a first state characterized by a relatively low energy consumption, to a second state characterized by a relatively high energy consumption.

6. The thermostat of claim 1, wherein the expression used by the processor that models the effect of the rate of temperature change that was occurring in the structure prior to actuating the HVAC function comprises:

7. The thermostat of claim 6, wherein the processor is further configured to create the thermodynamic model where the current stage effect component begins at zero, reaches a maximum at 2×

t^steady-state, and diminishes thereafter.

8. The thermostat of claim 1, wherein the plurality of basis functions further comprises a basis function characterizing an effect of a difference between an outdoor temperature and an indoor temperature.

9. The thermostat of claim 1, wherein the operations the processor is configured to perform further include estimating a temperature of the structure by:

setting an initial temperature of the structure to an indoor temperature at a first time; and

for each of a plurality of times after the first time, determining the temperature of the structure as a weighted combination of a previous indoor temperature and a previous outdoor temperature.

10. The thermostat of claim 1, the wherein the plurality of basis functions further comprises a basis function characterizing an effect of a difference in a temperature of the structure and an indoor temperature.

11. The thermostat of claim 1, wherein the plurality of basis functions further comprises a basis function characterizing an effect of a time-of-day approximating an effect of sunlight.

12. The thermostat of claim 11, wherein the basis function characterizing the effect of the time-of-day approximating the effect of sunlight comprises a sinusoidal term having a period of 24 hours.

13. The thermostat of claim 1, wherein the plurality of basis functions further comprises a basis function comprising a constant representing energy changes not affected by environmental factors.

14. The thermostat of claim 1, wherein the operations the processor is configured to perform further include:

using a required level of specificity for the thermodynamic model.

15. The thermostat of claim 14, wherein the operations the processor is configured to perform further include:

searching a plurality of existing thermodynamic models for one or more candidate thermodynamic models that satisfy the required level of specificity for the thermodynamic model.

16. The thermostat of claim 15, wherein creating the thermodynamic model that predicts the temperature trajectory of the air inside the structure in response to the actuation of the HVAC function comprises:

failing to identify one or more candidate models; and

in response to failing to identify the one or more candidate models, generating the thermodynamic model.

17. The thermostat of claim 1, wherein the processor is configured to predict the temperature trajectory of the air inside the structure by calculating a time-wise series of temperature changes beginning at a current indoor temperature.