Abstract:
A refrigerant PTAC system, such as those commonly found in hotel rooms, can be selectively configured in a hardwire or wireless configuration with respect to its thermostat. The system is controlled in response to the better of two temperature sensors, which is determined based on the PTAC&#39;s configuration and the validity of the readings provided by the sensors. While the PTAC is controlled in response to a preferred temperature sensor, the alternate sensor may be monitored for diagnostics or other reasons. In the event that the preferred sensor fails to provide valid readings, the controller automatically switches to controlling the system in response to the alternate sensor. To minimize manufacturing costs and the variety of stocked parts, the PTAC&#39;s controller preferably includes two substantially identical transceivers.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject invention generally pertains to PTAC refrigerant systems such as those commonly used for hotel rooms. The invention more specifically pertains to a way of selectively configuring the system for local or remote control. 
   2. Description of Related Art 
   Packaged Terminal Air Conditioners/Heat Pumps or PTACs, as they are known in the HVAC industry, are self-contained refrigerant systems often used for cooling and heating hotel rooms; however, they are also used in a variety of other commercial and residential applications such as apartments, hospitals, nursing homes, schools, and government buildings. PTACs are usually installed in an opening of a building&#39;s outer wall, so an exterior-facing refrigerant coil can exchange heat with the outside air. 
   In warmer climates, PTACs might only be used for cooling. In cooler climates, however, the refrigerant side of the system may be a heat pump for heating or cooling. PTACs may also include an electric heater if the refrigerant system lacks a heating mode or if the heat pump is unable to meet the heating demand of particularly cold days. PTAC&#39;s are also available with a hydronic (water/steam) heating option. 
   To control the temperature of a room, PTACs can be controlled in response to a temperature sensor that is usually installed in one of two locations. The temperature sensor can be installed within the PTAC&#39;s housing itself or in a thermostat mounted to a wall or some other remote location in the room. Both locations have their advantages and disadvantages. 
   Installing the sensor within the PTAC&#39;s housing is usually less expensive and simplifies the installation of the system. In such a location, however, the sensor may not necessarily provide the best temperature reading, as the temperature is being sensed at the elevation and vicinity of where the heating or cooling is occurring rather than at the location of the occupants in the room. Moreover, since PTACs are usually mounted along an outside wall and usually beneath a window, the temperature of the outside air and sunshine through the window can affect the sensor. 
   A wall-mounted sensor, on the other hand, can be spaced apart from the window, outside wall, and PTAC housing, and it can be installed closer to the occupants. Thus, a wall-mounted sensor may provide a reading that more accurately represents the room&#39;s overall temperature. In the case of a hotel installation, a temperature sensor installed within a wall-mounted thermostat may resemble thermostats that room guests have in their own homes, which can provide the guests with a more familiar, home-like environment, rather than an impersonal hotel atmosphere. Wall-mounted thermostats, unfortunately, are generally more expensive to install due to behind-the-wall wiring that is normally run between the thermostat and the rest of the PTAC unit. 
   To avoid or minimize the cost of the added wiring, some remotely mounted thermostats communicate via a wireless communication link. Even so-called wireless wall-mounted thermostats, however, still need a power source, which may require behind-the-wall wiring or batteries. Batteries may eliminate the wiring but can be a nuisance to replace. Moreover, since some users still prefer the less expensive PTAC units with a built-in temperature sensor, it can be expensive for a PTAC manufacturer to provide and stock both types of PTAC units, i.e., those with and without remote temperature sensing. 
   Some manufactures provide thermostats that can be selectively mounted locally or remotely. With such systems, the temperature sensor is normally contained within the thermostat&#39;s housing, which may be fine if the thermostat is remotely mounted to a wall. If, on the other hand, the thermostat is installed where the heating or cooling occurs, the best location for the temperature sensor may be directly upstream of the system&#39;s heat exchanger, but that may be impossible if the temperature sensor is still contained and sheltered within the thermostat&#39;s housing. 
   Consequently, there is still a need for a practical and effective PTAC system whose thermostat can be selectively installed locally or remotely without sacrificing its ability to sense the air temperature at the best available location. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a PTAC refrigerant system that can be selectively configured in a hardwire or wireless configuration to communicate with a local or remote temperature sensor. 
   Another object of some embodiments is to enable a PTAC microprocessor controller to selectively respond to the better of two temperature sensors. 
   Another object of some embodiments is to have a controller employ two interchangeable wireless transceivers or two interchangeable hardwire transceivers. 
   Another object of some embodiments is to provide a PTAC controller with two individual microprocessors each communicating with its own temperature sensor, such that the two microprocessors can be readily spaced apart for wireless communication. 
   Another object of some embodiments is to have two temperature sensors such that the most appropriate sensor depends on whether the system is in a wireless or hardwire configuration. 
   Another object of some embodiments is to control a PTAC system in response to a preferred temperature sensor while monitoring an alternate sensor. In the event of a failure associated with the preferred sensor, the PTAC is automatically switched to being controlled in response to the alternate sensor. 
   One or more of these and/or other objects of the invention are provided by a refrigerant PTAC system that can be selectively configured in a hardwire or wireless configuration. The system is controlled in response to the better of two temperature sensors, which is determined based on the PTAC&#39;s configuration and the validity of the readings provided by the sensors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematically illustrated cross-sectional side view of a PTAC refrigerant system according to one embodiment of the invention. 
       FIG. 2  is a front schematic view of  FIG. 1  with the PTAC system in a hardwire configuration. 
       FIG. 3  is a front schematic view of  FIG. 1  with the PTAC system in a remote wireless configuration. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Although PTACs come in various designs,  FIG. 1  illustrates one example of a refrigerant PTAC system  10  installed at an opening  12  of a building&#39;s exterior wall  14 . System  10  has an outer housing  16  that contains a refrigerant circuit  18 , an outdoor fan  20 , a supply air blower  22 , and an optional electric heater  24 . Housing  16  defines an inlet  26  for receiving a current of air  30  from within a room  28  or other area to be conditioned, an outlet  32  for discharging conditioned air  30  back into room  28 , a supply air chamber  34  for conveying air  30  from inlet  26  to outlet  32 , and a controls chamber  36  for housing a primary microprocessor  38  and other electrical components that help control or power the operation of system  10 . 
   Refrigerant circuit  18  of system  10  comprises a compressor  40  for compressing refrigerant, an outdoor refrigerant heat exchanger  42 , an expansion device  44  (e.g., thermal expansion valve, electronic expansion valve, orifice, capillary, etc.), and an indoor refrigerant heat exchanger  46 . In a cooling mode, compressor  40  forces refrigerant sequentially through outdoor heat exchanger  42  functioning as a condenser to cool the refrigerant with outdoor air  48  moved by fan  20 , through expansion device  44  to cool the refrigerant by expansion, and through indoor heat exchanger  46  functioning as an evaporator to absorb heat from indoor air  30  (and/or some outside air) moved by blower  22 . 
   If refrigerant circuit  18  is a heat pump system operating in a heating mode, the refrigerant&#39;s direction of flow through heat exchanger  42 , expansion device  44  and heat exchanger  46  is generally reversed so that indoor heat exchanger  46  functions as a condenser to heat air  30 , and outdoor heat exchanger  42  functions as an evaporator to absorb heat from outdoor air  48 . If additional heat is needed or refrigerant circuit  18  is only operable in a cooling mode, heater  24  can be energized for heating air  30 . 
   In this particular example, blower  22  forces air  30  sequentially through inlet  26 , supply air chamber  34 , and outlet  32 . Upon passing through supply air chamber  34 , air  30  passes sequentially through indoor heat exchanger  46 , heater  24 , and blower  22 . To help prevent high volumes of air  30  from depositing dust on the electrical components in controls chamber  36 , most of air  30  travels through supply air chamber  34  and bypasses controls chamber  36 . While PTACs may include dampers and other well-known means for mixing air  30  with fresh outside air  48  or for altering the air&#39;s flow path, such dampers and other means are not shown in the drawing figures so that the basic elements of the invention can be illustrated and understood more clearly. 
   PTAC system  10  is selectively configurable in a hardwire configuration (one example shown in  FIG. 2 ) or a wireless configuration (one example shown in  FIG. 3 ). The term, “hardwire” and its derivatives refer to communication that does not rely on signals being transmitted through the air over a distance that extends appreciably beyond housing  16 . Examples of hardwire include, but are not limited to, conventional metal wires, semiconductors, plugs and sockets, terminals, switches, optical isolators contained within housing  16 , fiber optics, etc. The term, “wireless” and its derivatives refer to a communication signal that travels through the air between housing  16  and a separate element (e.g., a wall-mounted thermostat) spaced apart from housing  16 . Examples of wireless include, but are not limited to, infrared transmission, radio waves, and other electromagnetic radiation. 
   In the hardwire configuration of  FIG. 2 , a control circuit  50  controls the operation of compressor  40 , blower  22  and perhaps other components associated with refrigerant circuit  18 . Circuit  50  comprises primary microprocessor  38 , a supplementary microprocessor  52 , a high airflow temperature sensor  64 , a low airflow temperature sensor  54 , a first transceiver  56 , a second transceiver  56 ′, an output device  60 , and a user input device  62 . To sense an air temperature that is close to the overall air temperature of the room, high airflow sensor  64  is preferably installed upstream of indoor heat exchanger  46  and heater  24 . 
   Sensors  64  and  54  are respectively referred to as a “high airflow” and “low airflow” temperature sensors simply because sensor  64  is more directly positioned in the main current of air  30  and is thus exposed to higher airflow rates than the more sheltered low airflow temperature sensor  54 . Nonetheless, sensors  54  and  64  both sense the temperature of air  30 . When operating properly, sensor  64  provides primary microprocessor  38  with a high airflow temperature reading  66  that is preferably within a predetermined valid range of values, and sensor  54  provides supplementary microprocessor  62  with a low airflow temperature reading  68  that is also preferably within a predetermined valid range of values. 
   Supplementary microprocessor  52  also receives a desired setpoint temperature and perhaps other information from user input device  62 . Examples of such other information include, but are not limited to, fan speed, cooling/heating mode, ventilation mode, etc. Input device  62  can be in the form of a selector switch, push buttons, touch pad, or any other interface that enables a user to enter information into microprocessor  52 . To provide the user with visual feedback of various settings and operating conditions associated with system  10 , output device  60  is wired to supplementary microprocessor  52 . Output device  60  may assume various forms including, but not limited to, an alphanumeric liquid crystal display, LED display, indicator lights, etc. 
   To communicate the desired setpoint temperature, low airflow temperature reading  68 , and perhaps other information between microprocessors  38  and  62 , the two microprocessors are in hardwire communication with each other via transceivers  56  and  56 ′. 
   Since the hardwire configuration of  FIG. 2  places low airflow temperature sensor  54  in relatively stagnant air that is rather close to where air  30  is being heated or cooled, high airflow temperature sensor  64  is the preferred sensor for controlling compressor  40  and blower  22  in the hardwire configuration. Thus, if primary microprocessor  38  determines that high airflow temperature reading  66  is valid, primary microprocessor  38  will use high airflow temperature sensor  64  in controlling compressor  40  and blower  22  and will just monitor low airflow reading  68  for diagnostics, data logging, or other reasons. If, however, primary microprocessor  38  determines that high airflow temperature reading  66  is abnormal or beyond a predetermined valid range of values, primary microprocessor  38  will switch over to controlling compressor  40  and blower  22  in response to low airflow temperature sensor  54  instead. 
   In the wireless configuration of  FIG. 3 , low airflow temperature sensor  54 , supplementary microprocessor  52 , user input device  62  and output device  60  are removed from within controls chamber  36  and installed in the room at a remote location within a wall-mountable thermostat housing  70 , which is spaced apart from housing  16 . A cover plate  72  can be used to cover the void left in controls chamber  36 . To communicate the desired setpoint temperature, low airflow temperature reading  68 , and perhaps other information between microprocessors  38  and  52 , two transceivers  58  and  58 ′ couple the two microprocessors  38  and  52  in wireless communication with each other via a wireless communication link  74 . 
   Since wireless configuration of  FIG. 3  places the low airflow temperature sensor in a more desirable location, low airflow temperature sensor  54  is the preferred sensor for controlling compressor  40  and blower  22  in the wireless configuration. Thus, if microprocessor  38  or  52  determines that low airflow temperature reading  68  is valid, primary microprocessor  38  will use low airflow temperature sensor  54  in controlling compressor  40  and blower  22  and will just monitor high airflow reading  66  for diagnostics, data logging, or other reasons. If, however, microprocessor  38  or  52  determines that low airflow temperature reading  68  is abnormal or beyond a predetermined valid range of values, primary microprocessor  38  will switch over to controlling compressor  40  and blower  22  in response to high airflow temperature sensor  64  instead. 
   Although the actual component of microprocessors  38  and  52 , and transceivers  56  and  58  may vary, in a currently preferred embodiment, primary microprocessor  38  is an HD39014 (e.g., HD64F39014-GFXV) provided by Renesas Technology Corp. of Tokyo, Japan; supplementary microprocessor  52  is an HD64F38102 also provided by Renesas Technology Corp; wireless transceiver  58  is a CC1100 (ZigBee protocol) provided by Chipcon of Oslo, Norway (acquired by Texas Instruments of Dallas, Tex.); and hardwire transceiver  56  is an ADM4850 provided by Analog Devices of Norwood, Mass. 
   To minimize the variety of parts a manufacture needs to stock, in some embodiments certain parts are substantially identical (i.e., interchangeable), such as transceivers  56  and  56 ′, transceivers  58  and  58 ′, or temperature sensors  54  and  64 . 
   Switching from the hardwire configuration of  FIG. 2  to the wireless configuration of  FIG. 3  may require minor changes to the electrical circuit. In some embodiments, for instance, a temperature signal wire  76  connecting high airflow temperature sensor  64  to primary microprocessor  38  may need to be rerouted from a first input terminal  80  on microprocessor  38  to a second terminal  78 . This can be done in various ways including, but not limited to, physically reconnecting wire  76  or by using dip-switches, jumpers, etc. 
   Microprocessors  52  and  64  can be programmed with software-based algorithms that perform one or more of the following functions: directing primary microprocessor  38  to communicate with supplementary microprocessor  52  via a hardwired communication link  82  in the hardwire configuration ( FIG. 2 ); directing primary microprocessor  38  to control supply air blower  22  and compressor  40  in response to high airflow temperature sensor  64  in the hardwire configuration ( FIG. 2 ); determining whether a valid high airflow temperature reading  66  from high airflow temperature sensor  64  fails to be communicated to primary microprocessor  38  while in the hardwire configuration ( FIG. 2 ), and in the event of such failure, redirecting primary microprocessor  38  to control supply air blower  22  and compressor  40  in response to low airflow temperature sensor  54  during the hardwire configuration ( FIG. 2 ); directing primary microprocessor  38  to communicate with supplementary microprocessor  52  via wireless communication link  74  in the wireless configuration ( FIG. 3 ); directing primary microprocessor  38  to control supply air blower  22  and compressor  40  in response to low airflow temperature sensor  54  in the wireless configuration ( FIG. 3 ); determining in the wireless configuration ( FIG. 3 ) whether a valid low airflow temperature reading  68  fails to be communicated to microprocessor  38  and  52 , and in the event of such failure, redirecting primary microprocessor  38  to control supply air blower  22  and compressor  40  in response to high airflow temperature sensor  64  during the wireless configuration ( FIG. 3 ); monitoring low airflow temperature sensor  54  while in the hardwire configuration ( FIG. 2 ) even though primary microprocessor  38  is controlling supply air blower  22  and compressor  40  in response to high airflow temperature sensor  64 ; and/or monitoring high airflow temperature sensor  64  while in the wireless configuration ( FIG. 3 ) even though primary microprocessor  38  is controlling supply air blower  22  and compressor  40  in response to low airflow temperature sensor  54 . The actual software code for performing the aforementioned functions as well as control algorithms for controlling the operation of a refrigerant compressor and supply air blower in response to a sensed room temperature and desired setpoint temperature can be readily written by those of ordinary skill in the art. 
   In  FIG. 2 , arrow  84  schematically illustrates the step of installing supplementary microprocessor  52  within controls chamber  36 , and arrow  86  schematically illustrates the step of installing low airflow temperature sensor  54  within controls chamber  36  along with primary microprocessor  38  and supplementary microprocessor  52 .  FIG. 3  schematically illustrates the steps of positioning supplementary microprocessor  52  at a location that is spaced apart from PTAC housing  16  and positioning low airflow temperature sensor  54  at a position that is spaced apart from PTAC housing  16 . Line  88  of  FIG. 3  illustrates the step of hardwiring transceiver  58  to primary microprocessor  38  when the PTAC system is in the wireless configuration, line  90  illustrates the step of hardwiring transceiver  58 ′ to supplementary microprocessor  52  when the PTAC system is in the wireless configuration, and link  74  represents the step of placing first transceivers  58  and  58 ′ in communication with each other via wireless communication link  74 . Line  92  of  FIG. 2  illustrates the step of hardwiring transceiver  56  to primary microprocessor  38  when the PTAC system is in the hardwired configuration, line  94  illustrates the step of hardwiring transceiver  56 ′ to supplementary microprocessor  52  when the PTAC system is in the hardwired configuration and line  82  illustrates the step of hardwiring transceiver  56  to transceiver  56 ′ to enable communication between primary microprocessor  38  and supplementary microprocessor  52 . 
   Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. Therefore, the scope of the invention is to be determined by reference to the following claims.