Abstract:
A method identifies at what outdoor temperature a heating or cooling system will need to operate at full capacity (e.g., 100% duty cycle) to maintain a desired indoor temperature. The tolerable outdoor temperature limit is identified by extrapolating data collected upon sampling the system&#39;s performance (e.g., duty cycle) at various loads (e.g., difference between outdoor temperature and the indoor temperature). In a similar manner, the method can also predict a best achievable indoor temperature for a given outdoor temperature. The tolerable outdoor temperature limit and best achievable indoor temperature can be displayed to indicate whether the system needs servicing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to heating, ventilating, and air conditioning systems (HVAC systems), and more specifically to a thermostat for such a system, wherein the thermostat identifies minimum or maximum tolerable outdoor temperatures for a given desired indoor temperature and/or identifies minimum or maximum achievable indoor temperatures for a given outdoor temperature.  
           [0003]    2. Description of Related Art  
           [0004]    Temperature conditioning equipment, such as gas or oil furnaces, electric heaters, air conditioners, and heat pumps are often used to control or modulate the temperature of a room or other area of a building. Although there are many ways of controlling such equipment, one common method involves cycling the equipment on and off as needed.  
           [0005]    For example, the controller disclosed in U.S. Pat. No. 4,292,813 includes an off-time counter that determines the duration of the off cycle. The counter is incremented when the measured run-time of the equipment is less than a desired minimum and is decremented when the measured run-time is greater than a desired maximum. If the measured run-time is within a desired range, then the prior off-time is maintained.  
           [0006]    As another example, U.S. Pat. No. 5,647,533 discloses a controller that varies the run-time of a heat pump. The speed of an indoor blower is adjusted whenever the operating run-time fraction of a heat cycle passes a predetermined threshold, unless the run-time fraction is sufficiently changed compared to a previous run-time fraction.  
           [0007]    Regardless of the control scheme, many factors can reduce the heating or cooling effectiveness of temperature conditioning equipment. The equipment&#39;s heating or cooling effectiveness is a function of several factors, such as the equipment&#39;s designed capacity; the cleanliness of various heat exchangers and air filters; refrigerant charge; thermal load, which can vary with the outdoor temperature and the desired indoor temperature; and mechanical condition of a compressor or blower associated with the equipment.  
           [0008]    To address diminished or otherwise insufficient capacity, some controllers include provisions for analyzing the condition of the equipment and its surroundings. For example, U.S. Pat. No. 4,574,871 discloses a diagnostic thermostat or monitor that measures run time for a heat pump compressor and compares expected run times for a particular outdoor temperature. An alarm signal identifies when the system fails to operate within expected parameters.  
           [0009]    Another example of a diagnostic thermostat is disclosed in U.S. Pat. No. 4,685,615. Here, the thermostat senses the outdoor temperature and accumulates degree-days and run-time of a heating or cooling unit. The thermostat can calculate, store, and display energy used per degree-day for a given period to indicate the performance or efficiency of the building and its heating or cooling system.  
           [0010]    U.S. Pat. No. 5,729,474 discloses another method of monitoring the effectiveness of a heating or cooling system. An efficiency value representing the system&#39;s ability to change temperature in a predetermined zone is repeatedly computed. Comparing a current efficiency value with a previous efficiency value helps identify deterioration of the system&#39;s ability to heat or cool. In response to a predetermined amount of deterioration, a control signal indicates a need for inspection of the system before the system fails completely.  
           [0011]    However, a disadvantage of current thermostats is their inability to quantify certain operating limits of heating or cooling systems. For example, conventional thermostats fail to predetermine the maximum outdoor temperature that a particular cooling system can tolerate while still maintaining the indoor temperature at its desired level. And thermostats typically fail to predetermine the minimum or maximum achievable indoor temperature for a given outdoor temperature.  
         SUMMARY OF THE INVENTION  
         [0012]    To overcome the drawbacks of current thermostats, it is an object of some embodiments of the invention to provide a method of determining a maximum or minimum tolerable outdoor temperature that a particular heating or cooling system can tolerate while still maintaining the indoor temperature at its desired level, wherein the method is based on sampling the system&#39;s performance at various loads.  
           [0013]    Another object of some embodiments of the invention is to sample a system&#39;s performance at various loads to create data through which a straight or curved line can be fitted, whereby extrapolating along the line helps identify a maximum or minimum tolerable outdoor temperature.  
           [0014]    Another object of some embodiments is to provide a method that helps determine a minimum or maximum achievable indoor temperature for a given outdoor temperature.  
           [0015]    Another object of some embodiments is to compare a system&#39;s tolerable outdoor temperature limit to an optimum or otherwise specified temperature limit to determine whether the system needs servicing.  
           [0016]    Yet, another object of some embodiments is to provide a user with feedback that indicates when a system may need servicing.  
           [0017]    A further object of some embodiments is to provide a user with feedback that indicates a system&#39;s tolerable outdoor temperature limit for a given indoor temperature.  
           [0018]    A still further object of some embodiments is to provide a user with feedback that indicates a system&#39;s best achievable indoor temperature limit for a given outdoor temperature.  
           [0019]    These and other objects of the invention are provided by method of determining a tolerable outdoor temperature limit for a temperature conditioning apparatus. The method includes sampling the system&#39;s performance at various loads to create a set of data, and extrapolating the data to identify at what outdoor temperature the system will need to operate continuously to maintain a desired indoor temperature.  
           [0020]    The present invention provides a method of determining a tolerable outdoor temperature limit for a temperature conditioning apparatus having a capacity that varies up to a maximum capacity. The method comprises determining a target indoor temperature; sensing an outdoor temperature; sensing an actual indoor temperature; repeatedly comparing the outdoor temperature to at least one of the actual indoor temperature and the target indoor temperature to determine a plurality of load values; and varying the capacity of the temperature conditioning apparatus to help maintain the actual indoor temperature within a predetermined range of the target indoor temperature. The method also comprises creating performance data by comparing the capacity to the plurality of load values; and extrapolating the performance data to the maximum capacity to predict the tolerable outdoor temperature limit at which the temperature conditioning apparatus is expected to be able to maintain the actual indoor temperature within the predetermined range of the target indoor temperature.  
           [0021]    The present invention also provides a method of determining a tolerable outdoor temperature limit for a temperature conditioning apparatus. The method comprises determining a target indoor temperature; sensing an outdoor temperature; sensing an actual indoor temperature; repeatedly comparing the outdoor temperature to at least one of the actual indoor temperature and the target indoor temperature to determine a plurality of load values; and cycling the temperature conditioning apparatus on and off to create a plurality of on-times and plurality of off-times, whereby cycling the temperature conditioning apparatus helps maintain the actual indoor temperature within a predetermined range of the target indoor temperature. The method also comprises determining a plurality of duty cycles of the temperature conditioning apparatus by comparing the plurality of on-times to the plurality of off-times; creating performance data by comparing the plurality of duty cycles to the plurality of load values; and extrapolating the performance data to predict the tolerable outdoor temperature limit at which the temperature conditioning apparatus is expected to be able to maintain the actual indoor temperature within the predetermined range of the target indoor temperature.  
           [0022]    The present invention further provides a method of determining a tolerable outdoor temperature limit for a temperature conditioning apparatus. The method comprises determining a target indoor temperature; sensing an outdoor temperature; sensing an actual indoor temperature; repeatedly comparing the outdoor temperature to at least one of the actual indoor temperature and the target indoor temperature to determine a plurality of load values. cycling the temperature conditioning apparatus on and off to create a plurality of on-times and plurality of off-times, whereby cycling the temperature conditioning apparatus helps maintain the actual indoor temperature within a predetermined range of the target indoor temperature. The method also comprises determining a plurality of duty cycles of the temperature conditioning apparatus by comparing the plurality of on-times to the plurality of off-times; creating performance data by comparing the plurality of duty cycles to the plurality of load values; based on the performance data, predicting the tolerable outdoor temperature limit at which the temperature conditioning apparatus is expected to be able to maintain the indoor temperature within the predetermined range of the target indoor temperature; establishing a specified temperature limit; comparing the tolerable outdoor temperature limit to the specified temperature limit, thereby creating a comparison; and displaying a signal that reflects the comparison.  
           [0023]    The present invention still further provides a method of determining a tolerable outdoor temperature limit for a temperature conditioning apparatus. The method comprises determining a target indoor temperature; sensing an outdoor temperature; sensing an actual indoor temperature; repeatedly comparing the outdoor temperature to at least one of the actual indoor temperature and the target indoor temperature to determine a plurality of load values. cycling the temperature conditioning apparatus on and off to create a plurality of on-times and plurality of off-times, whereby cycling the temperature conditioning apparatus helps maintain the actual indoor temperature within a predetermined range of the target indoor temperature. The method also comprises determining a plurality of duty cycles of the temperature conditioning apparatus by comparing the plurality of on-times to the plurality of off-times; creating performance data by comparing the plurality of duty cycles to the plurality of load values; fitting a line through the performance data; extrapolating the performance data via the line to predict the tolerable outdoor temperature limit at which the temperature conditioning apparatus is expected to be able to maintain the actual indoor temperature within the predetermined range of the target indoor temperature; establishing a specified temperature limit; comparing the tolerable outdoor temperature limit to the specified temperature limit, thereby creating a comparison; and displaying a signal that reflects the comparison, wherein the signal indicates that the temperature conditioning apparatus may need servicing.  
           [0024]    The present invention yet further provides a temperature conditioning apparatus having a capacity that varies up to a maximum capacity. The apparatus comprises components for determining a target indoor temperature; components for sensing an outdoor temperature; components for sensing an actual indoor temperature; and components for repeatedly comparing the outdoor temperature to at least one of the actual indoor temperature and the target indoor temperature to determine a plurality of load values. The apparatus also comprises components for varying the capacity of the temperature conditioning apparatus to help maintain the actual indoor temperature within a predetermined range of the target indoor temperature; components for creating performance data by comparing the capacity to the plurality of load values; and components for extrapolating the performance data to the maximum capacity to predict the tolerable outdoor temperature limit at which the temperature conditioning apparatus is expected to be able to maintain the actual indoor temperature within the predetermined range of the target indoor temperature.  
           [0025]    The present invention moreover provides a temperature conditioning apparatus. The apparatus comprises a device for determining a target indoor temperature; a device for sensing an outdoor temperature; a device for sensing an actual indoor temperature; and a device for repeatedly comparing the outdoor temperature to at least one of the actual indoor temperature and the target indoor temperature to determine a plurality of load values. The apparatus further comprises a device for cycling the temperature conditioning apparatus on and off to create a plurality of on-times and plurality of off-times, whereby cycling the temperature conditioning apparatus helps maintain the actual indoor temperature within a predetermined range of the target indoor temperature. The apparatus also comprises a device for determining a plurality of duty cycles of the temperature conditioning apparatus by comparing the plurality of on-times to the plurality of off-times; a device for creating performance data by comparing the plurality of duty cycles to the plurality of load values; and a device for extrapolating the performance data to predict the tolerable outdoor temperature limit at which the temperature conditioning apparatus is expected to be able to maintain the actual indoor temperature within the predetermined range of the target indoor temperature.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a schematic diagram of a thermostat and a heating or cooling system employing the subject invention.  
         [0027]    [0027]FIG. 2 is a flow chart that outlines a method according to one embodiment of the invention.  
         [0028]    [0028]FIG. 3 is a graph illustrating one aspect of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    Referring to FIG. 1, a thermostat  10  controls a temperature conditioning unit  12  for heating or cooling a room or area within a building  14 . Unit  12  is schematically illustrated to represent any temperature conditioning apparatus, examples of which include, but are not limited to, a gas or oil furnace, electric heater, air conditioner, and heat pump.  
         [0030]    Thermostat  10  is schematically illustrated to represent any system monitor or controller adapted to analyze input from a temperature sensor and provide certain feedback in response to the sensed temperature. Examples of thermostat  10  include, but are not limited to, an electronic thermostat, a computer, microprocessor, microcomputer, digital circuits, analog circuits, and various combinations thereof.  
         [0031]    In some embodiments of the invention, thermostat  10  receives an input  16  from an indoor temperature sensor  18  and an input  20  from an outdoor temperature sensor  22 . Sensor  18  senses the actual indoor temperature of building  14 , and sensor  22  senses the building&#39;s outdoor temperature. Thermostat  10  also includes an input  24  that allows a user to select or establish a desired target indoor temperature. Input  24  is schematically illustrated to represent any user interface, such as a dial, push button, keyboard, touch screen, etc.  
         [0032]    In response to inputs  16 ,  20  and  24 , thermostat  10  provides an output signal  26  that varies the capacity of unit  12  to help maintain the actual indoor temperature within a predetermined range (e.g., a few degrees or less) of the desired target indoor temperature. This process is schematically illustrated in FIG. 1 to represent all methods of varying the heating or cooling capacity of a temperature conditioning apparatus. A few examples of such methods include, but are not limited to, varying the speed of a refrigerant compressor, cycling a refrigerant compressor between different stages (e.g., a first stage providing a first refrigerant flow rate and a second stage providing a second refrigerant flow rate), throttling or cycling a valve to vary the flow of refrigerant, throttling or cycling a valve to vary the flow rate of chilled water, etc. In one embodiment of the invention, output signal  26  cycles unit  12  on and off as needed to maintain the indoor temperature at or near the desired target indoor temperature. Various on/off control schemes are well known to those skilled in the art.  
         [0033]    In addition to controlling unit  12 , thermostat  10  can calculate the tolerable outdoor temperature limit (maximum for cooling systems, minimum for heating). The tolerable outdoor temperature is the outdoor temperature at which unit  12  would need to operate at its maximum capacity in order to maintain an actual indoor temperature at or near a given desired target indoor temperature. Thermostat  10  can also determine whether unit  12  needs servicing by comparing the calculated tolerable outdoor temperature limit to a predetermined specified outdoor temperature limit. In some embodiments, thermostat  10  can also determine the minimum or maximum achievable indoor temperature for a given outdoor temperature. To do all this (in the example of an on/off control scheme), thermostat  10  follows the control algorithm outlined in FIG. 2.  
         [0034]    In control block  28 , thermostat  10  reads the outdoor temperature through feedback  20  provided by sensor  22 . In block  30 , thermostat  10  reads the actual indoor temperature as sensed by temperature sensor  18 . In block  32 , a user provides thermostat  10  with a desired target indoor temperature. Block  34  comprises a conventional on/off control scheme that cycles unit  12  on and off to maintain the indoor temperature at or near the desired target indoor temperature. Generally, the greater the difference between the outdoor temperature and the target indoor temperature, the closer unit  12  must operate at its maximum capacity of 100% (numeral  35  in FIG. 3). For an on/off control scheme, the capacity of unit  12  is in terms of duty cycle (i.e., the percentage of time that unit  12  is running: (on-time)/(on-time+off-time)).  
         [0035]    In blocks  36  and  38 , thermostat  10  determines and periodically records (e.g., temporarily stores, remembers, etc.) the capacity or duty cycle at various operating conditions. The operating conditions may be described in terms of load values (e.g., the difference between the outdoor temperature and the target indoor temperature or the difference between the outdoor temperature and the actual indoor temperature). In blocks  40  and  42 , thermostat  10  compares the various operating capacities or duty cycles to the load values to create performance data. The operations of blocks  40  and  42  are illustrated graphically in FIG. 3, wherein a Y-axis  44  represents load values (e.g., temperature differential between the outdoor temperature and the target indoor temperature), an X-axis  46  represents the capacity (e.g., duty cycle or percentage of on-time of unit  12 ), and data points  48  represent performance data plotted as load value versus capacity.  
         [0036]    In blocks  50  and  52 , a line, such as a curved line  54  or a straight line  56  can be fitted through data points  48 . Line  54  or  56  can help in extrapolating data points  48  to predict the tolerable outdoor temperature limit at which unit  12  is expected to be able to maintain the actual indoor temperature within a predetermined range of the target indoor temperature (e.g., a predetermined range of just a few degrees). For instance, if unit  12  is used for cooling with a target indoor temperature of 70 degrees Fahrenheit, then the maximum tolerable outdoor temperature is 130 degrees (70°+60°, wherein 70° is the target temperature and 60° is the indoor/outdoor temperature differential when unit  12  is operating at its maximum capacity of a 100% duty cycle). Or, if unit  12  is used for heating with a target temperature of 70°, then the minimum tolerable outdoor temperature is 10° (70°−60°). Once determined, the tolerable outdoor temperature  58  can be displayed on thermostat  10 , as shown in FIG. 1. Such a display can provide a user with an indication of how well unit  12  can handle future heating or cooling loads.  
         [0037]    It should be noted that the graph of FIG. 3 is just for illustration, and that the actual data points may lie in a much different arrangement, depending on the particular temperature conditioning unit and other factors. Although data points  48  are used for both cooling and heating examples, in reality, heating and cooling may generate completely different sets of data points. Moreover, the steps performed by blocks  36 ,  38 ,  40 ,  42  and  50  do not necessarily involve actually plotting data points  48  and physically drawing a line through the points. Rather, data points  48  can be stored as numbers or coordinates, and the step of fitting a line can be performed by deriving from points  48  an equation for a curved or straight line that when extrapolated can identify a tolerable outdoor temperature limit. Such a method of fitting a line (e.g., an equation) through a set of data points is common knowledge.  
         [0038]    In block  60 , thermostat  10  uses data points  48  to predict a best achievable indoor temperature for a given outdoor temperature. The expression, “best achievable indoor temperature” refers to the approximate expected indoor temperature that is farthest from the outdoor temperature, in the logical right direction of course. In a cooling mode, for example, if the outdoor temperature is 110°, and data points  48  indicate that at a maximum capacity or 100% duty cycle, system  12  can handle a load or indoor/outdoor temperature differential of 60°, then unit  12  should be able maintain an achievable indoor temperature of 50° (110°−60°). Using the same data points  48 , in a heating mode with an outdoor temperature of 30°, unit  12  would be expected to be able to maintain an achievable indoor temperature of 90° (30°+60°). In FIG. 1, thermostat  10  displays an achievable indoor temperature  62  to provide a user with an indication of how much extra capacity (or lack thereof) unit  12  has at a particular load condition.  
         [0039]    Block  64  illustrates the step of establishing a specified outdoor temperature limit, i.e., the tolerable outdoor temperature limit when unit  12  is new or in perfect condition. Such a limit is preferably set at the factory or by a service technician. When compared to the actual tolerable outdoor temperature limit, as performed by block  66 , the specified outdoor temperature limit provides the user with an indication of whether the performance of unit  12  has deteriorated. If so, thermostat  10  may display a signal  68  that indicates that unit  12  may need servicing, as indicated by block  70 . Signal  68  can be an on/off light or a written message.  
         [0040]    The arrows interconnecting the blocks of FIG. 2 are there to indicate that the algorithm process is repeated and ongoing.  
         [0041]    Although the invention is described with reference to a preferred embodiment, it should be appreciated by those skilled in the art that other variations are well within the scope of the invention. For example, rather than sensing temperature, other conditions such as indoor air quality, carbon dioxide level, carbon monoxide level, humidity, pressure or the like may be sensed in accordance with the invention. Therefore, the scope of the invention is to be determined by reference to the claims, which follow.