Abstract:
The present disclosure describes methods and apparatus for automatically changing between heating and cooling modes of an HVAC system, sometimes using a single or common set point in both modes. In an illustrative but not limiting example, an HVAC controller may monitor the temperature of an inside space of a building, and may switch the HVAC system to a cooling mode when the temperature of the inside space rises above a high switch-point temperature, and may cool the inside space to at least below the high switch-point temperature. The HVAC controller may also switch the HVAC system to the heating mode when the temperature of the inside space falls below a low switch-point temperature and may heat the inside space to at least above the low switch-point temperature. In some cases, after switching to the heating mode, the HVAC controller may cause the HVAC system to heat the inside space to substantially the set-point temperature. Likewise, after switching to the cooling mode, the HVAC controller may cause the HVAC system to cool the inside space to substantially the set-point temperature.

Description:
FIELD 
       [0001]    The present disclosure relates generally to building control systems, and more particularly, to the control of building control systems with both heating and cooling modes. 
       BACKGROUND 
       [0002]    Heating, ventilation, and/or air conditioning (HVAC) systems are often used to control the comfort level within an inside space of a building. Many HVAC systems include an HVAC controller or other device that activates and deactivates one or more HVAC components of the HVAC system to affect and control one or more environmental conditions within the building. These environmental conditions can include, but are not limited to, temperature, humidity, and/or ventilation. Many HVAC systems have the ability to heat and cool the inside space of a building. 
       SUMMARY 
       [0003]    The present disclosure relates generally to building control systems, and more particularly, to the control of HVAC systems that have both heating and cooling modes. In one illustrative embodiment, the HVAC system may contain an HVAC controller that controls the operation of the HVAC system. The HVAC controller may include at least one set-point temperature, as well as a low switch-point temperature and a high switch-point temperature, where the low switch-point temperature is below the set-point temperature and the high switch-point temperature is above the set-point temperature. The HVAC controller may monitor the temperature of an inside space of a building, and may switch the HVAC system to the cooling mode when the temperature of the inside space rises above the high switch-point temperature and may cool the inside space to at least below the high switch-point temperature. The HVAC controller may also switch the HVAC system to the heating mode when the temperature of the inside space falls below the low switch-point temperature and may heat the inside space to at least above the low switch-point temperature. In some cases, after switching to the heating mode, the HVAC controller may cause the HVAC system to heat the inside space to substantially the set-point temperature. Likewise, after switching to the cooling mode, the HVAC controller may cause the HVAC system to cool the inside space to substantially the set-point temperature. As can be seen, and in some sense, the present disclosure may relate to methods and apparatus for automatically changing (auto changeover) between heating and cooling modes of an HVAC system, sometimes using a single or common setpoint in both modes for increased comfort. 
         [0004]    The preceding summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
     
    
     
       BRIEF DESCRIPTION 
         [0005]    The disclosure may be more completely understood in consideration of the following detailed description of various illustrative embodiments of the disclosure in connection with the accompanying drawings, in which: 
           [0006]      FIG. 1  is a schematic view of an example building including an illustrative heating, ventilating, and air conditioning (HVAC) system; 
           [0007]      FIG. 2  is a schematic block diagram of an illustrative HVAC controller that may be used in conjunction with an HVAC system; 
           [0008]      FIG. 3  is a front perspective view of an illustrative HVAC controller; 
           [0009]    FIGS.  4  and  5 A- 5 C are flow diagrams of illustrative methods of operating an HVAC controller to control an HVAC system; 
           [0010]      FIGS. 6 and 7  are graphs that help illustrate the method of  FIG. 4 ; and 
           [0011]      FIG. 8  is a graph that helps illustrate the method of  FIG. 5A-5C . 
       
    
    
     DESCRIPTION 
       [0012]    The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The description and drawings show several embodiments which are meant to be illustrative. 
         [0013]      FIG. 1  is a schematic view of an example building including an HVAC system. While  FIG. 1  shows a typical forced air type HVAC system, other types of HVAC systems may be used including hydronic systems, boiler systems, radiant heating systems, electrical heating systems, combinations thereof, and/or any other suitable type of HVAC system, as desired. The illustrative HVAC system of  FIG. 1  includes one or more HVAC components  2 , a system of vents or ductwork  4  and  6 , and one or more HVAC devices, such as HVAC controller  8 . The one or more HVAC components  2  may include, but are not limited to, a furnace, a boiler, a heat exchanger, an air cleaner, a source of hot and/or cold water, and/or any other suitable HVAC components. 
         [0014]    In the illustrative HVAC system shown in  FIG. 1 , the one or more HVAC components  2  can provide heated air (and/or cooled air) via the ductwork throughout the inside space of the building. As illustrated, the one or more HVAC components  2  may be in fluid communication with every room and/or zone in the building via the ductwork  4  and  6 . In operation, when one or more of the HVAC controllers  8  switches on the HVAC heating mode, one or more HVAC components  2  (e.g. forced warm air furnace) may be activated to supply heated air to one or more rooms and/or zones within the building via supply air ducts  4 . The heated air may be forced through supply air duct  4  by a blower or fan  9 . In this example, the cooler air from each zone may be returned to the one or more HVAC components  2  (e.g. forced warm air furnace) for heating via return air ducts  6 . 
         [0015]    Similarly, when one or more of the HVAC controllers  8  switches on the HVAC cooling mode, the one or more HVAC components  2  (e.g. air conditioning unit) may be activated to supply cooled air to one or more rooms and/or zones within the building or other structure via supply air ducts  4 . The cooled air may be forced through supply air duct  4  by the blower or fan  9 . In this example, the warmer air from each zone may be returned to the one or more HVAC components  2  (e.g. air conditioning unit) for cooling via return ducts  6 . 
         [0016]    In some cases, the system of vents or ductwork  4  and  6  can include one or more dampers  11  to regulate the flow of air. For example, one or more dampers  11  may be coupled to one or more of the HVAC controllers  8  and can be coordinated with the operation of one or more HVAC components  2 . The one or more HVAC controllers  8  may actuate dampers  11  to an open position, a closed position, and/or a partially open position to modulate the flow of air from the one or more HVAC components  2  to an appropriate room and/or zone in the building or other structure. The dampers  11  may be particularly useful in zoned HVAC systems, and may be used to control which zone(s) receives conditioned air from the HVAC components  2 . 
         [0017]    While a forced air type HVAC system is shown in  FIG. 1 , it is contemplated that any suitable HVAC system may be used. For example, it is contemplated that the HVAC system may be a fan coil HVAC system, such as often used in Hotels and/or other such buildings. In some fan coil HVAC systems, a source of hot and/or cold water may be provided to a heat exchanger of a local fan coil unit. When heating and/or cooling is desired, a fan may circulate or blow air across the heat exchanger to provide hot and/or cold air. In some cases, the hot and/or cold water may be provided pipes, but this is not required. 
         [0018]    In any event, it is contemplated that the one or more HVAC controllers  8  may be configured to control the comfort level of the building by activating and deactivating the one or more HVAC components  2 . In some cases, the one or more HVAC controllers  8  may be thermostats, such as, for example, wall mountable thermostat, but this is not required in all embodiments. In some embodiments, the one or more HVAC controllers  8  may be wired, wireless, or both. In some embodiments, the HVAC controllers  8  may be zone controllers, each controlling the comfort level within a particular zone in the building or other structure. The one or more HVAC controllers  8  may be configured to control and/or set one or more functions and/or parameters, such as, for example, schedules, set-points, switch-points, trend logs, timers, and/or other building functions or parameters, as desired. 
         [0019]      FIG. 2  is a schematic block diagram of an illustrative HVAC controller  20  that may be used in conjunction with an HVAC system  24 . The HVAC system  24  may have a heating unit  25  and a cooling unit  26 . In some cases, the HVAC controller  20  may be considered to be a thermostat, but this is not required. In the illustrative embodiment, the HVAC controller  20  includes a control module  21 , a user interface  22 , a memory  23 , and a temperature sensor  27 . Although not shown in  FIG. 2 , the HVAC controller  20  may include a wired or wireless interface so that data may be sent to and/or gathered from the HVAC controller  20 . 
         [0020]    Control module  21  of HVAC controller  20  may be configured to control the comfort level (i.e. heating, cooling, ventilation, air quality, etc.) of an inside space of a building by controlling whether the HVAC components  25  and/or  26  of HVAC system  24  are activated or not. In some instances, control module  21  may include a processor, microcontroller and/or some other controller, which can be programmed to perform certain functions. It is contemplated that control module  21  may be configured to control and/or set one or more HVAC functions, such as, for example, HVAC schedules, temperature set-points, temperature switch-points, humidity set-points, trend logs, timers, environment sensing, HVAC controller programs, user preferences, and/or other HVAC functions or programs, as desired. In some illustrative embodiments, control module  21  may be programmed to control the comfort level of at least a portion of the building using a temperature sensed by one or more local and/or remote temperature sensors  27 . 
         [0021]    Control module  21  may be configured to operate in accordance with an algorithm that controls or at least partially controls one or more components of the HVAC system  24 . In some instances, the algorithm may include or reference a number of operating parameters. Examples of components that may be controlled by control module  21  include one or more of a furnace, a boiler for hot water heat or steam heat, a heat pump, an air conditioning unit, a humidifier, a dehumidifier, an air exchanger, an air cleaner, a fan, and the like. In some instances, control module  21  may operate in accordance with an algorithm that references an HVAC schedule with temperature set-points, temperature switch-points, starting and/or ending times, and/or the like. 
         [0022]    Memory  23  may be electrically connected to control module  21 , and may be used to store any desired information, such as the aforementioned HVAC schedules, temperature set-points, temperature switch-points, humidity set-points, trend logs, timers, environmental settings, and/or any other settings and/or information as desired. Memory  23  may include any suitable type of memory, such as, for example, random-access memory (RAM), read-only member (ROM), electrically erasable programmable read-only memory (EEPROM), Flash memory, or any other suitable memory, as desired. Control module  21  may store information, such as a plurality of parameters, within memory  23 , and may subsequently retrieve the stored information from the memory  23 . 
         [0023]    User interface  22  may be any suitable interface that is electrically connected to control module  21  and configured to display and/or solicit information as well as permit a user to enter data and/or other parameters and/or settings such as temperature set-points, temperature switch-points, humidity set-points, starting times, ending times, and/or the like, as desired. In some cases, user interface  22  of the HVAC controller  20  may allow a user (e.g. owner, technician, or other person) to program and/or modify one or more control parameters of HVAC controller  20 , such as programming temperature set-points, temperature switch-points, temperature differentials or offsets, start and stop times, equipment status and/or other parameters, as desired. In some instances, the user interface  22  may include a touch screen, a liquid crystal display (LCD) panel and keypad, a dot matrix display, a computer, one or more buttons and/or any other suitable user interface, as desired. 
         [0024]    In some cases, the HVAC controller  20  may include or have access to one or more sensors, such as a temperature sensor  27 , a humidity sensor, a ventilation sensor, an air quality sensor, and/or any other suitable building control system sensor, as desired. In some cases, the temperature sensor  27  may be contained within a housing of the HVAC controller  20  itself. In other cases, the temperature sensor  27  may be separate from the HVAC controller  20 . In some cases, HVAC controller  20  may also include a data port configured to communicate with control module  21  and may, if desired, be used to either upload information to control module  21  or download information from control module  21 . Information that can be uploaded or downloaded may include values of operating parameters, settings, firmware, and/or any other suitable information, as desired. 
         [0025]      FIG. 3  is a front view of an illustrative HVAC controller  30 . In some instances, HVAC controller  30  may represent a manifestation of HVAC controller  8  of  FIG. 1  or HVAC controller  20  of  FIG. 2 , but this is not required. The illustrative HVAC controller  30  includes a display  32  that is disposed within a housing  34 . In some cases, display  32  may be at least a portion of the user interface of the HVAC controller  30 . Display  32  may be a touch screen display, a liquid crystal display (LCD) panel, a dot matrix display, a fixed segment display, a cathode ray tube (CRT), or any other suitable display, as desired. A dot matrix display is typically an LCD display that permits images such as letters, numbers, graphics, and the like to be displayed anywhere on the LCD, rather than being confined to predetermined locations such as is the case with a fixed segment LCD. Housing  34  may be formed of any suitable material, such as a polymeric, metallic, or any other material, as desired. In some cases, the display  32  may be either inset or recessed within the housing  34  as shown. In some cases, HVAC controller  30  may be configured to provide substantial display and/or programming functionality, but this is not required in all embodiments. 
         [0026]      FIG. 4  is flow diagram of an illustrative method for controlling the heating and cooling units of an HVAC system. The HVAC system may or may not be the HVAC system described in  FIG. 1 . The task of employing this method may be carried out by an HVAC controller. Such an HVAC controller may be, but is not required to be, HVAC controller  8  described in  FIG. 2  or HVAC controller  30  described in  FIG. 3 . 
         [0027]    As shown in block  500 , a set-point temperature may be identified by the HVAC controller. This set-point temperature may be stored in a memory of an HVAC controller, such as memory  23  of HVAC controller  20 . In some embodiments, the set-point temperature may be entered into the HVAC controller via a user interface, such as user interface  22 . In some cases, the set-point temperature may be set to a default setting at the factory. 
         [0028]    In block  504 , the HVAC controller may identify the values of a low and a high switch-point temperature. In one example embodiment, the HVAC controller may automatically identify the values of the low and the high switch-point temperatures based on the value of the set-point temperature. In determining the values, the HVAC controller may employ an algorithm to calculate the values, such as +/−4 degrees above and below the set-point temperature. In another example, a user may define the values of the high and the low switch-point temperatures. The user may utilize a user interface, such as user interface  22 , to program the values of the high switch-point temperature and the low switch-point temperature into the HVAC controller  20 , or to program a differential or offset such as +/−4 degrees. In some cases, the low and high switch-point temperatures may set to a default setting at the factory. 
         [0029]    In decision block  514 , the HVAC controller determines if the temperature of the inside space is less than the low switch-point temperature. The HVAC controller can, for example, determine the temperature of the inside space through the use of a temperature sensor. In the illustrative embodiment, if the temperature is less than the low switch-point temperature, the HVAC controller switches the HVAC system to the heating mode. Control loop  516  then controls the heating of the inside space. Control loop  516  directs the HVAC system to heat the inside space in the heating mode until the temperature of the inside space rises above a low shut-off temperature. Once the temperature of the inside space rises above the low shut-off temperature, the HVAC controller exits control loop  516 . Block  519  then commands the HVAC system to shut-off, at least temporarily. While not explicitly shown in  FIG. 4 , the HVAC controller may cycle the HVAC system on and off in the heating mode to maintain the temperature of the inside space at substantially the low shut-off temperature, if desired. In some embodiments, the low shut-off temperature is at least greater than the low switch-point temperature. In other embodiments, the low shut-off temperature may be substantially the same as the set-point temperature. The low shut-off temperature may be any value that is, for example, equal to or greater than the low switch-point temperature and equal to or less than the high switch-point temperature. 
         [0030]    If the temperature of the inside space rises above the high switch-point temperature, decision block  524  directs the HVAC controller to switch the HVAC to the cooling mode. Control loop  526  then controls the cooling of the inside space. Control loop  526  directs the HVAC system to cool the inside space until the temperature of the inside space falls below a high shut-off temperature. Once the temperature of the inside space falls below the high shut-off temperature, the HVAC controller exits control loop  526 . Block  529  then commands the HVAC system to shut-off, at least temporarily. While not explicitly shown in  FIG. 4 , the HVAC controller may cycle the HVAC system on and off in the cooling mode to maintain the temperature of the inside space at substantially the high shut-off temperature, if desired. In some embodiments, the high shut-off temperature is at least less than the high switch-point temperature. In other embodiments, the high shut-off temperature may be substantially the same as the set-point temperature. The high shut-off temperature may be any value that is, for example, equal to or less than the high switch-point and equal to or greater than the low switch-point. 
         [0031]      FIG. 5A-5C  show a flow diagram of another illustrative method for controlling the heating and cooling units of an HVAC system. The HVAC system may, or may not be, the HVAC system described in  FIG. 1 . The task of employing this method may be carried out by an HVAC controller. Such an HVAC controller may be, but is not required to be, HVAC controller  8  described in  FIG. 2  or HVAC controller  30  described in  FIG. 3 . 
         [0032]    The illustrative method of  5 A- 5 C begins with block  600  by identifying the set-point temperature. The set-point temperature may be stored into a memory of the HVAC controller, and may be set by a user using a user interface, such as user interface  22 . The set-point temperature may also be set to a default setting at the factory, if desired. In block  604 , the HVAC controller identifies the values of a low switch-point temperature and a high switch-point temperature. In one example, the HVAC controller may automatically determine the values of the low and the high switch-point temperatures based on the value of the set-point temperature. In determining the values, the HVAC controller may employ an algorithm to calculate the values, such as +/−4 degrees above and below the set-point temperature. In another example, a user may define the values of the high and the low switch-point temperatures. The user may utilize a user interface, such as user interface  22 , to program the values of the high switch-point temperature and the low switch-point temperature into the HVAC controller  20 . Additionally, the low and high switch-point temperatures may set to a default setting at the factory. 
         [0033]    In decision block  614 , the HVAC controller determines if the temperature of the inside space is less than the low switch-point temperature. The HVAC controller may monitor the temperature of the inside space through a temperature sensor, which may or may not be part of the HVAC controller itself. If the temperature is less than the low switch-point temperature, the HVAC controller may switch the HVAC system to the heating mode. Control loop  616  then controls the heating of the inside space. Control loop  616  directs the HVAC system to heat the inside space until the temperature of the inside space rises above the low shut-off temperature. Once the temperature of the inside space rises above the low shut-off temperature, the HVAC controller exits control loop  616 . In some embodiments, the low shut-off temperature is at least greater than the low switch-point temperature. In other embodiments, the low shut-off temperature may be substantially the same as the set-point temperature. The low shut-off temperature may also be any value that is, for example equal to or greater than the low switch-point temperature and equal to or less than the high switch-point temperature. 
         [0034]    After exiting control loop  616 , block  619  turns the HVAC system off and the HVAC controller enters a temperature control mode. One embodiment of a temperature control mode may be described by the block diagram outlined in box  630 . The temperature control mode allows for more precise control over the temperature of the inside space. Once the HVAC system switches to the heating mode and heats the inside space to the low shut-off temperature, the temperature control mode may provide for the temperature of the inside space to remain near the shut-off temperature. 
         [0035]    Decision block  631  of the temperature control mode box  630  determines if the temperature of the inside space is less than a low threshold temperature. If the temperature is not less than the low threshold temperature, decision block  632  determines if the temperature of the inside space is greater than the high switch-point temperature. If the temperature of the inside space is not greater than the high switch-point temperature, the HVAC controller loops back to decision block  631 . At decision block  631 , if the temperature of the inside space is less than the low threshold temperature, the HVAC controller directs the HVAC system to turn on and heat the inside space until the temperature of the inside space rises above the low shut-off temperature. The low threshold temperature is preferably lower than the low shut-off temperature, but higher than the low switch-point temperature. In one embodiment of the invention, the low threshold temperature is 1 degree F. less than the low shut-off temperature, providing a small dead band below the low shut-off temperature. In another embodiment, the low threshold temperature is 0.5 degrees F. less than the low shut-off temperature. Other values for the low threshold temperature may be used as well. In at least some embodiments, the low threshold temperature may not be less than the low switch-point temperature. Note, while in the temperature control mode  630 , if the temperature of the inside space should rises above the high switch-point temperature, the HVAC controller switches the HVAC system to the cooling mode and control loop  626  begins to control the cooling of the building. 
         [0036]    Referring back to decision block  614 , if the temperature of the inside space is not lower than the low switch-point temperature, decision block  624  determines if the temperature of the inside space is greater than the high switch-point temperature. If the temperature of the inside space is not greater than the high switch-point temperature, then the HVAC controller loops back to decision block  614 . This loop may continue until the temperature of the inside space rises above or falls below the high or low switch-point temperatures. 
         [0037]    If, at decision block  624 , the temperature of the inside space is greater than the high switch-point temperature, the HVAC controller switches the HVAC system to the cooling mode. Control loop  626  then controls the cooling of the inside space. Control loop  626  directs the HVAC system to cool the inside space until the temperature of the inside space falls below the high shut-off temperature. Once the temperature of the inside space falls below the high shut-off temperature, the HVAC controller exits control loop  626 . In some embodiments, the high shut-off temperature is at least less than the high switch-point temperature. In other embodiments, the high shut-off temperature may be substantially the same as the set-point temperature. It is contemplated that the high shut-off temperature may be any value that is, for example, equal to or less than the high switch-point temperature and equal to or greater than the low switch-point temperature. 
         [0038]    After exiting control loop  626 , block  629  turns the HVAC system off and the HVAC controller enters a temperature control mode. One embodiment of a temperature control mode may be described by block  640 . In block  640 , decision block  641  determines if the temperature of the inside space is greater than a high threshold temperature. If the temperature is not greater than the high threshold temperature, decision block  642  determines if the temperature of the inside space is less than the low switch-point temperature. If the temperature of the inside space is not less than the low switch-point temperature, the HVAC controller loops back to decision block  641 . At decision block  641 , if the temperature of the inside space is greater than the high threshold temperature, the HVAC controller directs the HVAC system to turn on and cool the inside space until the temperature of the inside space falls below the high shut-off temperature. The high threshold temperature is preferably higher than the high shut-off temperature, but lower than the high switch-point temperature. In one embodiment, the high threshold temperature is 1 degree F. greater than the high shut-off temperature. In another embodiment, the high threshold temperature is 0.5 degrees F. greater than the high shut-off temperature. Other values for the high threshold temperature may be used as well. In at least some embodiments, the high threshold temperature may not be greater than the high switch-point temperature. While in the temperature control mode, if the temperature of the inside space falls below the low switch-point temperature, the HVAC controller switches the HVAC system to the heating mode, and control loop  616  controls the heating of the building. 
         [0039]      FIG. 6  depicts a graph of the temperature of a space versus time. In this graph, an HVAC controller is controlling an HVAC system to heat and cool a space using the method described by  FIG. 4 . The HVAC system may or may not be the HVAC system described in  FIG. 1 . The HVAC controller may be, but is not required to be, HVAC controller  8  described in  FIG. 2  or HVAC controller  30  described in  FIG. 3 . 
         [0040]    In this example, the set-point temperature  700  has been set to a temperature of 70 degrees F. As described above, set-point temperature  700  may be set at any suitable temperature, and may be set in any suitable manner. The high switch-point temperature  710  has been set to 72 degrees F., and the low switch-point temperature  720  has been set to 68 degrees F. The switch-point temperatures  710  and  720  may be set at any suitable temperature, and may be set in any suitable manner. In  FIG. 6 , the high shut-off temperature  730  and the low shut-off temperature  740  have also been identified, with high shut-off temperature being 71 degrees F. and low shut-off temperature being 69 degrees F. As described earlier, the shut-off temperatures  730  and  740  may be set at any suitable temperature, and may be set in any suitable manner. In some cases, the low shut-off temperature  740  and/or the high shut-off temperature  730  may be at or substantially at the set point temperature  700 . 
         [0041]      FIG. 6  contains two regions, region  760  and region  761 , which help illustrate the functioning of an illustrative HVAC controller. In region  760 , at cooling switch-point  750 , the HVAC controller switches the HVAC system to the cooling mode and the HVAC system begins cooling the inside space. As depicted in  FIG. 6 , the system actively cools the inside space until the temperature of the inside space reaches the high shut-off temperature  730 , at shut-off point  770 . At shut-off point  770 , the HVAC controller directs the HVAC system to shut-off. After shut-off point  770 , the temperature of the inside space may be allowed to float until the temperature again crosses one of the switch-point temperatures  710  or  720 . For purposes of illustration, this happens again at cooling switch-point  751 . At cooling switch-point  751 , the HVAC controller directs the HVAC system to turn on and to cool the inside space back down to the high shut-off temperature  730 . Once the temperature of the inside space reaches the high shut-off temperature  730 , at shut-off point  771 , the HVAC controller again directs the HVAC system to shut-off. The temperature of the inside space may then be allowed to float, as indicated by region  761 . 
         [0042]    While not specifically shown in  FIG. 6 , after the HVAC system reaches the high shut-off point  770 , the HVAC controller may cycle the HVAC system on and off in the cooling mode to maintain the temperature of the inside space at substantially the high shut-off temperature  730  (which may, in some cases, be at or substantially at the setpoint temperature  700 ), rather than allowing the temperature of the inside space to float upward to the high switch-point temperature  710 . Since the HVAC system is in the cooling mode, the temperature of the inside space may be allowed to float downward to the low switch-point temperature  720 , at which point the HVAC controller may switch the HVAC system to the heating mode (see  FIG. 7 ). 
         [0043]      FIG. 7  also depicts a graph that helps illustrate the method of controlling an HVAC system as described above in  FIG. 4 . In this example, a set-point temperature  800  has been set to a temperature of 70 degrees F. A high switch-point temperature  810  has been set to 72 degrees F., and the low switch-point temperature  820  has been set to 68 degrees F. Also, a high shut-off temperature  830 , and the low shut-off temperature  840  have also been identified, with the high shut-off temperature  830  being 71 degrees F. and the low shut-off temperature  840  being 69 degrees F. 
         [0044]      FIG. 7  contains 2 regions, region  860  and region  861 , which help to illustrate the functioning of the HVAC system controller. In region  860 , at heating switch-point  850 , the HVAC controller switches the HVAC system to the heating mode, and the HVAC system begins heating the inside space. As depicted in  FIG. 8 , the HVAC system actively heats the inside space until the temperature of the inside space reaches the low shut-off temperature  840 , at shut-off point  870 . In some cases, the low shut-off temperature  840  and/or the high shut-off temperature  830  may be at or substantially at the set point temperature  800 . 
         [0045]    At shut-off point  870 , the HVAC controller directs the HVAC system to shut-off. After shut-off point  870 , the temperature of the inside space may be allowed to float until the temperature again crosses one of the switch-point temperatures  810  or  820 . For purposes of illustration, this happens again at heating switch-point  851 . At heating switch-point  851 , the HVAC controller directs the HVAC system to turn on and to heat the inside space back up to the low shut-off temperature  840 . Once the temperature of the inside space reaches the low shut-off temperature  840 , at shut-off point  871 , the HVAC controller again directs the HVAC system to shut-off. The temperature of the inside space may then be allowed to float, as indicated by region  861 . 
         [0046]    While not specifically shown in  FIG. 7 , after the HVAC system reaches the shut-off point  870 , the HVAC controller may cycle the HVAC system on and off in the heating mode to maintain the temperature of the inside space at substantially the low shut-off temperature  840  (which may, in some cases, be at or substantially at the setpoint temperature  800 ), rather than allowing the temperature of the inside space to float downward to the low switch-point temperature  820 . Since the HVAC system is in the heating mode, the temperature of the inside space may be allowed to float upward to the high switch-point temperature  810 , at which point the HVAC controller may switch the HVAC system to the cooling mode (see  FIG. 6 ). 
         [0047]      FIG. 8  is a graph of the temperature of an inside space versus time that helps illustrate the method of  FIG. 5A-5C . In this example embodiment, a set-point temperature  900  has been set to a temperature of 70 degrees F. A high switch-point temperature  901  has been set to 72 degrees F., and the low switch-point temperature  902  has been set to 68 degrees F. A high shut-off temperature  903  and the low shut-off temperature  904  have also been identified, with the high shut-off temperature  903  being 70.5 degrees F. and the low shut-off temperature  904  being 69.5 degrees F. Also, a high threshold temperature  905  has been set at 71 degrees F., and a low threshold temperature  906  has been set at 69 degree F. The values of the high and low threshold temperatures  905  and  906  are meant as examples only. 
         [0048]      FIG. 8  contains a number of regions including regions  940 ,  941 ,  942 ,  943 ,  944 ,  945 ,  946 , and  947 , which help to illustrate the functioning of this example HVAC controller. At cooling switch-point  910 , the HVAC controller switches the HVAC system to the cooling mode and directs the HVAC system to cool the inside space. Region  940  depicts a time period where the HVAC system is actively cooling the inside space. In the example shown, once the temperature of the inside space reaches the high shut-off temperature  903 , at shut-off point  920 , the HVAC controller directs the HVAC system to shut-off. The HVAC controller then enters a temperature control mode. One example of a temperature control mode has been described with reference to  FIG. 5A-5C . After entering the temperature control mode, the temperature of the inside space may be allowed to float within a restricted temperature range. Region  941  of the graph shows the temperature of the inside space floating. When the HVAC controller enters the temperature control mode after cooling the inside space to the high shut-off temperature  903 , the temperature of the inside space is only allowed to rise up to the high threshold temperature  905 . Once the temperature reaches the high threshold temperature  905 , such as at threshold point  930 , the HVAC controller turns the HVAC system on and directs the HVAC system to cool the inside space back down to the high shut-off temperature  903 , such as at shut-off point  921 . Region  942  depicts a time period during where the HVAC system is actively cooling the inside space. After shut-off point  921 , the temperature of the inside space is again allowed to float but not above the high threshold temperature  905 . Region  943  illustrates the temperature of the inside space floating. After actively cooling the inside space to the high shut-off temperature  903 , the temperature of the inside space is only allowed to fall as far as the low switch-point temperature  902 . 
         [0049]    Once the temperature of the inside space reaches the low switch-point temperature  902 , such as at switch-point  911 , the HVAC controller directs the HVAC system to switch to the heating mode, and to heat the inside space up to the low shut-off temperature  904 . Region  944  depicts a time period where the HVAC system is actively heating the inside space. Once the temperature of the inside space reaches the low shut-off temperature  904 , at shut-off point  922 , the HVAC controller turns the HVAC system off. The HVAC controller then enters a temperature control mode. After entering the temperature control mode, the temperature of the inside space is allowed to float within a restricted temperature range. Region  945  depicts the temperature of the inside space floating. When the HVAC controller enters the temperature control mode after heating the inside space to the low shut-off temperature  904 , the temperature of the inside space is only allowed to fall to the low threshold temperature  906 . Once the temperature reaches the low threshold temperature  906 , such as at threshold point  931 , the HVAC controller turns the HVAC system on and directs the HVAC system to heat the inside space back up to the low shut-off temperature  904 , such as at shut-off point  923 . Region  946  depicts a time period where the HVAC system is actively heating the inside space. After Shut-off point  923 , the temperature of the inside space is allowed to float but not below the low threshold temperature  906 . Region  947  illustrates the temperature of the inside space floating. The highest temperature to which the temperature of the inside space is allowed to float is the high switch-point temperature  901 . 
         [0050]    Having thus described the preferred embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. It will be understood that this disclosure is, in many respect, only illustrative. The scope, of course, is defined in the language in which the appended claims are expressed.