Abstract:
A single pair of polarity independent wires conveys electrical power and two-way communication between a remote thermostat and a temperature-conditioning unit. The system is functional even if the wires are crossed, so mis-wiring is nearly impossible. The system is selectively operable in three independently distinct modes: a power mode for conveying electrical power from the temperature-conditioning unit to the thermostat, an output mode for transmitting a communication signal from the temperature-conditioning unit to the thermostat, and a feedback mode for conveying a communication signal from the thermostat to the temperature-conditioning unit. When the power mode is inactive during the output mode and feedback mode, the thermostat relies on electrical power that the thermostat stored during a previous power mode. Communication is provided by a current loop circuit that is generally immune to electrical noise and tolerant of wire impedance.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The subject invention generally pertains to a controller for an HVAC system (heating ventilating and air conditioning system) and more specifically to a power and communication link for such a system. 
         [0003]    2. Description of Related Art 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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 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, however, usually require additional wiring for conveying communication signals between the thermostat and the PTAC unit and for conveying electrical power to the thermostat. 
         [0009]    Such wiring, unfortunately, is often mis-wired and can be prone to electrical noise. If the PTAC system requires two-way communication between the PTAC unit and the remote thermostat, additional wiring may be needed. In some cases, wire impedance can be an issue that limits the wire length. Consequently, a need exists for a simple wiring scheme that overcomes the limitations of current systems. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the invention to use a single pair of wires for providing electrical power and two-way communication between a remote thermostat and a PTAC or some other type of temperature-conditioning unit. 
         [0011]    Another object of some embodiments is use a polarity independent pair of wires (i.e., the wires can be crossed) for providing electrical power and two-way communication between a remote thermostat and a PTAC or some other type of temperature-conditioning unit. 
         [0012]    Another object of some embodiments is to selectively operate a PTAC or some other type of temperature conditioning unit in three independent modes: a power mode for conveying electrical power from the PTAC to a remote thermostat, an output mode for transmitting a communication signal from the PTAC to the thermostat, and a feedback mode for receiving a communication signal from the thermostat to the PTAC. 
         [0013]    Another object of some embodiments is to provide a remote thermostat with an electrical power storage circuit that powers the thermostat at times when power from a PTAC or other type of temperature-conditioning unit is temporarily interrupted for communication purposes. 
         [0014]    Another object of some embodiments is to use a current loop circuit for two-way communication between a remote thermostat and a PTAC or other type of temperature-conditioning unit, wherein the current loop is generally immune to electrical noise and tolerant of wire impedance. 
         [0015]    Another object of some embodiments is to avoid conveying substantial electrical power while conveying a communication signal. 
         [0016]    Another object of some embodiments is to allow almost any amount and type of data to be sent between a remote thermostat and a PTAC or other type of temperature-conditioning unit. 
         [0017]    Another object of some embodiments is to provide a remote thermostat that can display various conditions occurring at a PTAC or other type of temperature-conditioning unit. 
         [0018]    One or more of these and/or other objects of the invention are provided by a control system that includes a single pair of polarity independent wires for conveying both electrical power and two-way communication but not at the same time. 
         [0019]    The present invention provides a control system. The control system comprises a first controller that includes a first terminal-A and a first terminal-B, and a second controller that includes a second terminal-A and a second terminal-B. The first controller is operable to provide an output signal and receive a feedback signal. The second controller is operable to provide the feedback signal and receive the output signal. The control system also includes a power storage system connected to the second controller, and; a pair of wires that includes a first wire connected to the first terminal-A and a second wire connected to the first terminal-B. The first wire and the second wire are interchangeably connected to the second terminal-A and the second terminal-B. The control system is selectively operable in a power mode, an output mode, and a feedback mode such that:
       a) in the power mode, the first controller provides electrical power to the second controller via the pair of wires to store at least some of the electrical power on the power storage system;   b) in the output mode, the power mode and the feedback mode are momentarily inactive so that the first controller can provide the output signal to the second controller via the pair of wires; and   c) in the feedback mode, the power mode and the output mode are momentarily inactive so that the second controller can provide the feedback signal to the first controller via the pair of wires.       
 
         [0023]    The present invention also provides a control system. The control system comprises a temperature-conditioning unit; a thermostat disposed at a remote location relative to the temperature-conditioning unit; a first controller connected to the temperature-conditioning unit; a second controller connected to the thermostat; a power storage system connected to the second controller; and a pair of wires that includes a first wire and a second wire. The first controller includes a first terminal-A and a first terminal-B, and is operable to provide an output signal and receive a feedback signal. The second controller includes a second terminal-A and a second terminal-B, and is operable to provide the feedback signal and receive the output signal. The first wire is connected to the first terminal-A and the second terminal-A, and the second wire is connected to the first terminal-B and the second terminal-B. The control system is selectively operable in a power mode, an output mode, and a feedback mode such that:
       a) in the power mode, the first controller provides electrical power to the second controller via the pair of wires to store at least some of the electrical power on the power storage system;   b) in the output mode, the power mode and the feedback mode are momentarily inactive so that the first controller can provide the output signal to the second controller via the pair of wires; and   c) in the feedback mode, the power mode and the output mode are momentarily inactive so that the second controller can provide the feedback signal to the first controller via the pair of wires.       
 
         [0027]    The present invention additionally provides a control system. The control system comprising: a temperature-conditioning unit; a thermostat disposed at a remote location relative to the temperature-conditioning unit; a display disposed on the thermostat, which indicates a condition occurring at the temperature-conditioning unit; a first controller connected to the temperature-conditioning unit; a second controller connected to the thermostat, a power storage system being connected to the second controller and receiving DC electrical power from the first controller; and a pair of wires that includes a first wire and a second wire. The first controller includes a first terminal-A and a first terminal-B, the first controller being operable to provide an output signal and receive a feedback signal, wherein the output signal and the feedback signal are digital. The second controller includes a second terminal-A and a second terminal-B, the second controller being operable to provide the feedback signal and receive the output signal. The first wire is connected to the first terminal-A and the second terminal-A, and the second wire is connected to the first terminal-B and the second terminal-B. The control system is selectively operable in a power mode, an output mode, and a feedback mode such that:
       a) in the power mode, the first controller provides electrical power to the second controller via the pair of wires to store at least some of the electrical power on the power storage system;   b) in the output mode, the power mode and the feedback mode are momentarily inactive so that the first controller can provide the output signal to the second controller via the pair of wires; and   c) in the feedback mode, the power mode and the output mode are momentarily inactive so that the second controller can provide the feedback signal to the first controller via the pair of wires.       
 
         [0031]    The present invention further provides a two wire communications link. The two wire communications link comprises an electrical power source; a first controller operably connected to the electrical power source for receiving electrical power therefrom; a second controller; a first electrical connection connecting the first and second controllers and supplying electrical power from the electrical power source to the second controller; and hardware or software, in the first controller, for controlling the connection of the electrical power source to the first electrical connection to create periods of connection, and periods of disconnection, so that a digital communication signal is transmitted over the first electrical connection. 
         [0032]    The present invention still further provides a method of digitally communicating over a power line. The method comprises the steps of: providing an electrical power source; electrically connecting a first controller to the electrical power source; providing a second controller; electrically connecting the first controller to the second controller so that power is supplied to the second controller from the electrical power source; controllably connecting the electrical power source to the electrical connection in a manner that creates periods of disconnection and periods of connection; and varying the periods of connection and the period of disconnection so that a digital communication signal is transmitted from the first controller to the second controller. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is a perspective view of a system that includes remote thermostat and a temperature-conditioning unit installed in a room. 
           [0034]      FIG. 2  is a wiring schematic of two controllers used in the system of  FIG. 1 . 
           [0035]      FIG. 3  is a chart that explains the operation of the controllers shown in  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]      FIG. 1  shows a temperature-conditioning unit  10  (e.g., a PTAC unit) that includes a blower  12  and a heat exchanger  14  for heating, cooling and/or ventilating a comfort zone  16 , such as a room or other area in a building. A control system  18 , shown in  FIG. 2 , controls the operation of unit  10 . Control system  18  includes a first controller  20  installed in unit  10 , and a second controller  22  installed in a remote thermostat  24 . A pair of wires  30 , comprising a first wire  30   a  and a second wire  30   b , conveys DC electrical power and digital communication signals between controllers  20  and  22 . 
         [0037]    First controller  20  provides one or more control functions that may include, but are not necessarily limited to, energizing blower  12 , energizing a compressor or valves associated with heat exchanger  14 , receiving a feedback signal  26  from thermostat  24 , transmitting an output signal  28  to thermostat  24 , and receiving various input signals  32  from temperature sensors, pressure sensors, manual input switches, etc. that are installed in the general vicinity of unit  10 . Feedback signal  26  received from thermostat  24  via wires  30  may include, but is not limited to, temperature set points, room temperature reading, system parameters, and various other inputs  34 . Output signal  28  transmitted from controller  20  to thermostat  24  via wires  30  may include, but is not limited to, temperature set points, outdoor air temperature reading, temperature reading of supply air  36 , temperature reading of return air  38 , system faults and error messages, and system parameters. 
         [0038]    Second controller  22  provides one or more control functions that may include, but are not necessarily limited to, receiving output signal  28  from first controller  20 , transmitting feedback signal  26  to controller  20 , receiving various input signals  34  from temperature sensors, pressure sensors, manual input switches, etc. that are installed in the general vicinity of thermostat  24 . Second controller  22  can also provide an output signal  40  that can be used for controlling a visual display  42  on thermostat  24 . Display  42  can indicate various conditions occurring at unit  10  and/or thermostat  24 . Examples of such conditions include, but are not limited to, the temperature of return air  38 , the temperature of supply air  36 , a setpoint temperature, a diagnostic message  44  pertaining to unit  10 , the room temperature in the vicinity of thermostat  24 , setup parameters of unit  10 , etc. 
         [0039]    A power supply line  46  of the building can supply electrical power to unit  10  and its controller  20 . Wires  30  convey some of that electrical power to energize thermostat  24  and its controller  22 , thus wires  30  convey both communication and electrical power, but not at the same time. 
         [0040]      FIG. 2  shows wire  30   a  connecting a first terminal-A  48  on first controller  20  to a second terminal-A  50  on second controller  22 . Wire  30   b  is shown connecting a first terminal-B  52  on first controller  20  to a second terminal-B  54  on second controller  22 . Wires  30   a  and  30   b , however, can be crossed without creating a problem for the conveyance of communication signals or electrical power. Wire  30   a , for instance could be installed to connect first terminal-A  48  to second terminal-B  54 , and wire  30   b  could connect first terminal-A  52  to second terminal-A  50 . This feature helps ensure that controllers  20  and  22  are properly connected regardless of how wires  30   a  and  30   b  are installed. 
         [0041]    To ensure reliable communication between controllers  20  and  22 , control system  18  employs a current loop circuit that is inherently noise immune and tolerant of wire impedance. To avoid signal interference, control system  18  selectively operates in three distinct modes: a power mode for conveying electrical power along wires  30 , an output mode for conveying output signal  28 , and a feedback mode for conveying feedback signal  26 . Electrical power, output signal  28  and feedback signal  26  are each conveyed independently of the others. In a currently preferred embodiment, first controller  20  includes a conventional microprocessor  56  that determines which operating mode is in effect, and second controller  22  includes another conventional microprocessor  58  that responds accordingly. 
         [0042]    In addition to microprocessor  56 , first controller  20  includes a current source circuit  60 , a current interrupter  62 , and a signal converter  64 . A conventional voltage regulator provides 12-VDC at a point  66 , and 5-VDC at points  68  and  70 . In this particular example, circuit  60  can deliver about 15 mA of current to first terminal-A  48 . During the power mode, wires  30  convey that current to power second controller  22 . That current is also used for charging an energy storage circuit  72  that powers second controller  22  while the current from circuit  60  is interrupted during the output mode or feedback mode. 
         [0043]    In the output mode, current interrupter  62  responds to an output signal  28 ′ from microprocessor  56  to controllably interrupt the current through wires  30 , whereby wires  30  can transmit data (corresponding to output signal  28 ′) in a standard asynchronous, 19,200-baud method. The “start” and “0” valued bits can be defined as current generally less than 7 mA. The “stop” and “1” valued bits can be defined as current generally greater than 7 mA. Signal converter  64  senses the current level and converts it to standard logic levels. 
         [0044]    Second controller  22  includes microprocessor  58 , energy storage circuit  72 , a current limiter  74 , a current interrupter  76 , and a signal converter  78 . In this example, energy storage circuit  72  includes a conventional voltage regulator  80  operating in conjunction with one or more power storage capacitors  82  and  84  (e.g., 220 uF each). Voltage regulator  80  has a voltage input  86 , a regulated DC voltage output  88  (e.g., 3.3 VDC), ON/OFF switch input  90  and a ground  92 . If desired, additional capacitors (e.g., 0.1 uF) can be added to drain high frequency noise and voltage transients from point  88  to point  92 . As explainer earlier, energy storage circuit  72  is charged during the power mode by at least some of the 15 mA from current source  60 , the stored power can then be used for powering second controller  22  (including microprocessor  58 ) during the output mode and feedback mode. 
         [0045]    As wires  30  convey current from controller  20  to controller  22 , current limiter  74  and Zener diode  94  help regulate that current at about 15 mA. To guard against voltage spikes, transient voltage suppression diodes  96  and  98  can be installed between wires  30   a  and  30   b . Second controller  22  includes a full wave bridge rectifier  100  that allows the communication and power link between controllers  20  and  22  to be insensitive to the wiring polarity of wires  30 . 
         [0046]    In response to feedback signal  26 ′, current interrupter  76  interrupts the current in wires  30  in order to communicate feedback signal  26  to first controller  20 . The “start” and “0” valued bits can be defined as current less than 7 mA. The “stop” and “1” valued bits can be defined as current greater than 7 mA. 
         [0047]    Signal converter  78  detects the presence and absence of current as a serial data stream and converts it to the logic levels required by the remote thermostat&#39;s controller  22 . 
         [0048]    Although the actual circuit of control system  18  may vary, in a currently preferred embodiment, system  18  includes resistors R 1 -R 18 . Resistors R 1  and R 2  are 100-ohms, resistors R 3  and R 4  are 47.5-ohms, and resistors R 5 -R 18  are each 11 kilo-ohms. 
         [0049]      FIG. 3  provides more detail as to what is actually occurring with individual elements of control system  18  selectively operating in the power mode, output mode and feedback mode. With the exception of transistors Q 6  and Q 9 , which are used for limiting the current to 15 mA, the other transistors Q 1 -Q 5 , Q 7 , Q 8 , and Q 10 -Q 12  are used as switching transistors generally operating in a binary ON/OFF state. In the chart of  FIG. 3 , “ON-OFF” indicates a transistor that changes from being on (saturated) to off with every pulse of signal  26 ′ or  28 ′, and “OFF-ON” indicates a transistor that changes from being off to on with every pulse of signal  26 ′ or  28 ′. In that same chart, “HI” and “LO” represent relative high and low voltage, respectively. “HI-LO” indicates a voltage drop with every pulse of signal  26 ′ or  28 ′, and “LO-HI” indicates an increase in voltage with every pulse of signal  26 ′ or  28 ′. 
         [0050]    In the power mode, microprocessor  56  does not provide any pulsed signal at a main transmit point  102 , and microprocessor  58  does not provide any pulsed signal at a remote transmit point  104 , thus a remote receive point  106  and a main receive point  108  remain at a generally constant level of “HI,” whereby generally no communication occurs between controllers  20  and  22 . In the power mode, first terminal-A  48  remains relatively “HI” to charge energy storage circuit  72 . 
         [0051]    In the output mode, output signal  28 ′ is communicated from main transmit point  102  of microprocessor  56  to remote receive point  106  on microprocessor  58 . At point  106 , output signal  28 ′ is read as output signal  28 ″. In the output mode, the chart of  FIG. 3  shows that remote receive point  106  goes from “HI” to “LO” with every “HI-LO” pulse of main transmit point  102 . The pulsed information of output signal  28 ,  28 ′ or  28 ″ can represent temperature set points, outdoor air temperature reading, temperature reading of supply air  36 , temperature reading of return air  38 , system faults and error messages, and system parameters. The pulsed information of output signal  28 ,  28 ′ or  28 ″ can also be a means for providing second microprocessor  58  with permission to transmit feedback signal  26 ′. 
         [0052]    In the feedback mode, feedback signal  26 ′ is communicated from remote transmit point  104  of microprocessor  58  to main receive point  108  on microprocessor  56 . At point  108 , feedback signal  26 ′ is read as feedback signal  26 ″. In the feedback mode, the chart of  FIG. 3  shows that main receive point  108  goes from “HI” to “LO” with every “LO-HI” pulse of remote transmit point  104 . Although pulses  26 ′ and  26 ″ are 180-degrees out of phase, the feedback information is conveyed nonetheless. In some embodiments, the electrical power conveyed by wires  30  has a DC voltage amplitude that is substantially equal to that of communication signals  26  and  28 . 
         [0053]    Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. Control system  18 , for instance, does not necessarily have to be used for controlling a PTAC unit, but could be applied to any type of HVAC equipment. Therefore, the scope of the invention is to be determined by reference to the following claims.