Thermostat system having an optimized temperature recovery ramp rate

• US 5,555,927 A
• Filed: 06/07/1995
• Issued: 09/17/1996
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Shah, Dipak J.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US08/479,292
• Time in Patent Office: 468 Days
• Field of Search: 62/231, 236/46 R, 236/91 D, 236/91 R, 165/12, 364/557
• US Class Current: 165/239
• CPC Class Codes: G05D 23/1904 variable in time

Abstract

An adaptive recovery method for a setback thermostat using the intersection of the space temperature with a sloped recovery temperature line which approximates the change in temperature as a function of time during recovery of the temperature controlled space from a setback temperature, to determine the time at which recovery to the occupancy temperature should begin. The thermostat starts recovery when the current space temperature crosses the recovery temperature line. A useful feature of the apparatus and method which implement the invention, computes and constantly updates the slope of the temperature recovery line. The update of the temperature recovery line slope is based on miss time, i.e., the time between actually achieving the desired next set point temperature and the next set point time associated with the next set point temperature, the space temperature, the outdoor air temperature, the temperature recovery ramp rate during the previous recovery period, and the current and past thermal time constants. If the heating or cooling load on the space changes, the current space temperature will cross the recovery temperature line at a different time, causing recovery to start at a time more compatible with the current heating or cooling load in order to complete recovery at or near the desired time. Variables may be added to the system.

Claims

1. A thermostat system in a space having a current space temperature that changes to an occupancy temperature is achieved at an occupancy time, the changing of the current space temperature caused by a heater or cooler, having a recovery start time that occurs at a recovery time prior to the occupancy time, the recovery time being a period of time needed for the current space temperature to be changed to the occupancy temperature, the recovery time determined by an optimized recovery ramp rate of a certain amount of space temperature change per unit time, comprising:

a first temperature sensor for sensing the current space temperature;

a second temperature sensor for sensing current outdoor ambient temperature of air external but proximate to the space;

a processor, connected to said first and second temperature sensors, having a memory, instruction processor and a clock;

a space temperature changing unit having a heater and a cooler; and

a heat and cool mode selector connected to said processor and said space temperature changing unit; and

wherein;

the recovery start time is at the beginning of a period of recovery time prior to the occupancy time when the current space temperature is to be approximately the same as the occupancy temperature, the recovery time being determined by a recovery ramp rate of a certain amount of temperature change per unit time; and

the recovery ramp rate is based on (1) a difference between the current space temperature and the current outdoor ambient temperature at the recovery start time, (2) a thermal time constant based on a ratio of an average temperature difference between the current space temperature and the current outdoor ambient temperature during the recovery time when the space temperature is being changed to be approximately the same as the occupancy temperature, and of a time rate of change of the current space temperature during the recovery time, (3) a thermal time constant for a previous period of a recovery time having a similar time of day, and (4) a recovery ramp rate for the previous period of the recovery having the similar time of day.

2. The thermostat system of claim 1 wherein said processor can:

receive and store current space and outdoor ambient temperatures from said first and second temperature sensors, respectively;

send signals to said space temperature changing unit to effect or not to effect a change of current space temperature during a recovery time;

calculate and store recovery ramp rates and thermal time constants;

determine and initiate a recovery start time;

calculate and implement a recovery ramp rate; and

determine a recovery start time such that the end of a recovery time closely coincides with the occupancy time when the current space temperature becomes approximately the same as the occupancy temperature.

3. A method for optimizing a temperature recovery ramp rate of a thermostat having current space temperature and outdoor temperature sensors, a processor, connected to the temperature sensors, for calculating and comparing information, for recording and accessing information to and from an operand memory connected to the processor, for noting time from a clock connected to the processor, and for issuing operation signals, in a space having a space temperature to be controlled relative to a set occupancy temperature and occupancy time, comprising:

recording by the processor in the operand memory, space temperatures and outdoor temperatures;

setting and recording in the operand memory, at least one occupancy temperature and one occupancy time which follows a setback temperature interval;

recording in the operand memory a present time of day;

calculating and recording in the operand memory a ramp rate;

calculating and recording in the operand memory thermal time constants of a current recovery period, and a previous similar (AM or PM) recovery period, during a plant "on" period wherein a plant is changing space temperature to approach occupancy temperature;

calculating and recording in the operand memory differences between space temperatures and corresponding outdoor air temperatures;

calculating and recording in the operand memory a time rate of change of the space temperature during the plant "on" period;

calculating and recording in the operand memory a time rate of change of the space temperature during each recovery period for the day;

calculating an updated recovery ramp rate equal to a product of the temperature recovery ramp rate for the previous similar (AM or PM) recovery period and a ratio of the temperature difference between the space temperature and the outdoor air temperature at the start of the current recovery period to a temperature difference between the space temperature and the ambient air temperature at the start of the previous similar (AM or PM) recovery period and the ratio of the thermal time constant for the previous similar (AM or PM) recovery period to the thermal time constant for the current recovery period, and storing the product as the recovery ramp rate for the current recovery period in a location of the operand memory;

at the end of intervals of predetermined length, calculating a time difference equal to the difference between the occupancy time and the present time and recording the time difference in the operand memory;

after a time difference has been recorded, calculating and recording in the operand memory a ramp delta equal to a product of the latest time difference recorded and the ramp rate;

calculating and recording in the operand memory a ramp set point equal to at least one of the differences between the occupancy temperature and the ramp delta and the sum of the occupancy temperature and the ramp delta; and

comparing the ramp set point with the space temperature, and when a selectable relationship between the ramp set point and the space temperature exists, issuing an operation signal to turn the plant "on" or "off."

4. A system for optimizing a ramp rate after a setback in a space temperature and time, and the setting of an occupancy temperature and time, having a recovery period wherein the space temperature is changed by a plant that heats or cools, to the occupancy temperature at the occupancy time, the plant being controlled by a thermostat having space and outdoor temperature sensors, having heating and cooling modes, having a processor for executing instructions stored as a program and having an executive for scheduling the instructions, and having a program flow control, having a memory for storing the program and calculation results, having a clock for providing present time of day, the program having a recovery flag set at the start of a temperature recovery period and cleared when recovery period has been completed and/or at the start of each setback period, and the program having a check flag that is set when the plant is turned on and cleared when plant is turned off, comprising:

a first decision element that functions if it receives a go signal from the executive, and determines whether a current on/off status of the plant is the same as a past on/off status of the plant during a previous pass through and said first decision element outputs either a yes or a no;

a second decision element that functions if it receives a no from said first decision element, and determines whether the status of the plant has changed from an off during the previous pass through to an on, and if so, said second decision element outputs a yes and if not, a no;

a first calculation element that functions if it receives a yes from said second decision element, and calculates a difference between a current space temperature and an outdoor temperature and stores the difference in the memory, stores the current space temperature and present time of day in the memory, sets the check flag and returns the program flow to the executive;

a third decision element that functions if it receives a yes from said first decision element, and checks a status of the check flag, if the check flag is set then the program flow is returned to the executive, and if the check flag is not set, then said third decision element outputs a not set;

a second calculation element that functions if it receives a no from said second decision element, and stores the current space temperature and present time of day in the memory, calculates a time rate of change of the space temperature after a most recently completed plant on cycle, calculates a thermal time constant of the most recently completed plant on cycle, stores the time rate of change and the thermal time constant in the memory, and then clears the check flag and outputs a clear check flag;

a fourth decision element that functions if it receives a not set from said third decision element or a clear check flag from said second calculation element, and returns the program flow to the executive if a test interval has not ended and outputs a yes if the test interval has ended;

a fifth decision element that functions if it receives a yes from said fourth decision element, and tests a condition of the recovery flag, outputs a set if the recovery flag is set and outputs a not set if the recovery flag is not set;

a third calculation element that functions if it receives a not set from said fifth decision element, and calculates and stores in the memory a difference between the current space temperature and the outdoor temperature, calculates and stores in the memory a recovery ramp rate to be used in a next recovery period, calculates and stores in the memory a time difference of the occupancy time and present time of day, calculates and stores in the memory a ramp delta, and outputs a calculation completed signal;

a sixth decision element that functions if it receives a calculation completed signal from said third calculation element, and outputs a cool signal if the thermostat is in a cooling mode and outputs a heat signal if the thermostat is in a heating mode;

a fourth calculation element that functions if it receives a heat signal from said sixth decision element, and calculates a ramp set point which is the occupancy temperature minus the ramp delta, and then outputs a calculation completed signal;

a seventh decision element that functions if it receives a calculation completed signal from said fourth calculation element, and determines whether the current space temperature is less than the ramp set point, and if not, it outputs a no and returns the program flow to the executive, and if so it outputs a yes and signals the plant to turn on; and

a fifth calculation element that functions if the plan is signaled to turn on by said seventh decision element, and calculates and stores in the memory a difference between the current space temperature and the outdoor temperature, stores in the memory the current space temperature and present time of day, sets the recovery flag and returns the program control to the executive.

5. The system of claim 4 further comprising:

a sixth calculation element that functions if it receives a cool signal from said sixth decision element, and calculates a ramp set point which is a sum of the occupancy temperature and the ramp delta, and then outputs a calculation completed signal;

an eighth decision element that functions if it receives a calculation completed signal from said sixth calculation element, and determines whether the current space temperature is greater than the ramp set point, and if not, it outputs a no and returns the program flow to the executive, and if so it outputs a yes and signals the plant to turn on; and

a seventh calculation element that functions if the plant is signaled to turn on by said eighth decision element and calculates and stores in the memory a difference between the current space temperature and the outdoor temperature, and stores in the memory the current space temperature and present time of day, and sets the recovery flag and returns the program control to the executive.

6. The system of claim 5 further comprising:

an ninth decision element that functions if it receives a set from said fifth decision element, and outputs a cool signal if the thermostat is in a cooling mode and outputs a heat signal if the thermostat is in a heating mode;

a tenth decision element that functions if it receives a heat signal from said ninth decision element, and if the current space temperature is not greater than the occupancy temperature minus a control band offset then the program control is returned to the executive, and if the current space temperature exceeds the occupancy temperature minus the control band offset then a yes it outputted;

an eighth calculation element that functions if a yes is received from said tenth decision element, and calculates and stores in the memory an updated ramp rate and outputs a calculation completed signal;

an eleventh decision element that functions if it receives a cool signal from said ninth decision element, and if the current space temperature is not less than the occupancy temperature plus a control band offset then the program control is returned to the executive, and if the current space temperature is less than the occupancy temperature plus the control band offset then a yes is outputted;

a ninth calculation element that functions if it receives a yes from said eleventh decision element, and calculates and stores in the memory an updated ramp rate, and outputs a calculation completed signal; and

a tenth calculation element that functions if it receives a calculation completed signal from said eighth or ninth calculation element, and calculates and stores in the memory a thermal time constant that is a ratio of the difference of the space and outdoor temperatures at a start of recovery period to the ramp rate for the about to be completed recovery period, clears the recovery flag when the recovery period is completed, and then returns the program control to the executive.

7. The system of claim 6 wherein the updated ramp rate of said eighth and ninth calculation elements is a difference of the space temperature at the start of the recovery period and the current space temperature, divided by a difference of the ramp set point and present time of day.

8. The system of claim 6 wherein the updated ramp rate is equal to a former ramp rate plus a difference which is divided by 2 to an nth power, wherein the difference is the occupancy time minus present time of day and n is an integer from 0 to 20.

9. A thermostat system in a space having a current space temperature that changes to an occupancy temperature is achieved at an occupancy time, the changing of the current space temperature caused by a heater or cooler, having a recovery start time that occurs at a recovery time prior to the occupancy time, the recovery time being a period of time needed for the current space temperature to be changed to the occupancy temperature, the recovery time determined by an optimized recovery ramp rate of a certain amount of space temperature change per unit time, comprising:

a first temperature sensor for sensing the current space temperature;

a second temperature sensor for sensing current outdoor ambient temperature of air external but proximate to the space;

a processor, connected to said first and second temperature sensors, having a memory, instruction processor and a clock;

a space temperature changing unit having a heater and a cooler; and

a heat and cool mode selector connected to said processor and said space temperature changing unit; and

wherein;

the recovery start time is at the beginning of a period of recovery time prior to the occupancy time when the current space temperature is to be approximately the same as the occupancy temperature, the recovery time being determined by a recovery ramp rate of a certain amount of temperature change per unit time; and

the recovery ramp rate is based on (1) a difference between the current space temperature and the current outdoor ambient temperature at the recovery start time, (2) a thermal time constant for the recovery time based on a ratio of a temperature difference between the space temperature and the outdoor ambient temperature during a most recent plant "on" cycle to a time rate of change of the current space temperature during the most recent plant "on" cycle, (3) a thermal time constant for a previous period of a recovery time having a similar time of day, and (4) a recovery ramp rate for the previous period of the recovery having the similar time of day.

10. A method for optimizing a temperature recovery ramp rate of a thermostat having current space temperature and outdoor temperature sensors, a processor, connected to the temperature sensors, for calculating and comparing information, for recording and accessing information to and from an operand memory connected to the processor, for noting time from a clock connected to the processor, and for issuing operation signals, in a space having a space temperature to be controlled relative to a set occupancy temperature and occupancy time, comprising:

recording by the processor in the operand memory, space temperatures and outdoor temperatures;

setting and recording in the operand memory, at least one occupancy temperature and one occupancy time which follows a setback temperature interval;

recording in the operand memory a present time of day;

calculating and recording in the operand memory a ramp rate;

calculating and recording in the operand memory thermal time constant of a current recovery period, and a thermal time constant for a previous similar (AM or PM) recovery period, during a plant "on" period wherein a plant is changing space temperature to approach occupancy temperature;

calculating and recording in the operand memory differences between space temperatures and corresponding outdoor air temperatures;

calculating and recording in the operand memory a time rate of change of the space temperature during the plant "on" period;

calculating and recording in the operand memory a time rate of change of the space temperature during each recovery period for the day; and

calculating an updated recovery ramp rate equal to a product of the temperature recovery ramp rate determined at the end of the previous similar (AM or PM) recovery period and a ratio of the temperature difference between the space temperature and the outdoor air temperature at the start of the current recovery period to a temperature difference between the space temperature and the ambient air temperature at the start of the previous similar (AM or PM) recovery period and the ratio of the thermal time constant for the previous similar (AM or PM) recovery period to the thermal time constant for the current recovery period, and storing the product as the recovery ramp rate for the current recovery period in a location of the operand memory.

11. The method of claim 10 further comprising:

at the end of intervals of predetermined length, calculating a time difference equal to the difference between the occupancy time and the present time and recording the time difference in the operand memory;

after a time difference has been recorded, calculating and recording in the operand memory a ramp delta equal to a product of the latest time difference recorded and the ramp rate;

calculating and recording in the operand memory a ramp set point equal to at least one of the differences between the occupancy temperature and the ramp delta and the sum of the occupancy temperature and the ramp delta; and

comparing the ramp set point with the space temperature, and when a selectable relationship between the ramp set point and the space temperature exists, issuing an operation signal to turn the plant "on" or "off."