Abstract:
A thermostat method and apparatus has one or more demand circuits, an energy storage device; a DC regulator connected to the energy storage device, and a thermostat control connected to the DC regulator and to the energy storage device. Current is drawn from the one or more demand circuits when demand associated with the demand circuits is not active and the energy storage device is charged with the current drawn from the one or more demand circuits. If energy stored in the energy storage device is below the first predetermined threshold, activity in the thermostat is reduced and if energy stored in the energy storage device is above the second predetermined threshold, activity in the thermostat is allowed to increase.

Description:
BACKGROUND 
       [0001]    Digital thermostats need power. Operating power is typically provided from battery or from the thermostat wiring. A typical HVAC system runs on low voltage 24 VAC system and has a 110/220 VAC to 24 VAC transformer. The two sides of the transformer are typically marked as R (Return) and C (Common). Newer house wirings routes both taps of the transformer to the thermostat and thus the thermostat has direct access to this 24 VAC system and can derive its required internal supply voltages from the 24 VAC directly. 
         [0002]    However, older houses do not typically have the C wire routed to the thermostat. Instead the C side of the terminal is routed through various demand controls, such as Fan, Heat, Cool, etc. The thermostat activates a relay and shorts these connections to the R, thus signaling a demand. When the contacts of the relays are open, the full 24 VAC is available between the various demand lines and the R. When the contacts are closed, the voltage drops to 0 VAC and the current flows from the C terminal of the 24 VAC transformer via the demand wires back to the R terminal of the transformer. 
         [0003]    There have been on the market various power stealing methods that allow stealing power from these demand wires when the relay is open (voltage driven) and even when the relay is closed. The problem with these solutions is that they only allow a ‘small’ amount of power to be harvested, because if the current increases above approximately 10 mA or so in the demand line, the HVAC controller might detect a false demand on the control line. Most digital thermostats are very low power and may survive on this small amount of power harvested from one or more control lines. They may also be supported with battery backup and power stealing may be used just extend the battery life. There is also a solution that steals power from systems with a single demand line when the demand is not active, storing some of the energy in a rechargeable battery or super capacitor, and then powers the thermostat from this battery when the demand is active. 
         [0004]    Newer thermostats are now getting network attached. Some network attached thermostats use a wireless interface and nowadays Wi-Fi is popular. The problem with a Wi-Fi attached thermostat is that it needs more power than can be stolen from an HVAC system without the C terminal. Thus this thermostat either requires the presence of the C wire or requires an external wall mount power supply. 
         [0005]    What is needed is a system and method for powering a digital thermostat in the absence of an external power source such as a C wire or an external power supply. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
           [0007]      FIG. 1  illustrates an example heating, ventilation and cooling (HVAC) system; 
           [0008]      FIG. 2  illustrates an example thermostat system that can be used in the HVAC system of  FIG. 1 ; 
           [0009]      FIG. 3  illustrates another example of a thermostat system; 
           [0010]      FIG. 4  illustrates a method of controlling a thermostat system; 
           [0011]      FIG. 5  illustrates an example wireless thermostat system; and 
           [0012]      FIG. 6  illustrates another method of controlling a thermostat system. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the following detailed description of example embodiments of the invention, reference is made to specific examples by way of drawings and illustrations. These examples are described in sufficient detail to enable those skilled in the art to practice the invention, and serve to illustrate how the invention may be applied to various purposes or embodiments. Other embodiments of the invention exist and are within the scope of the invention, and logical, mechanical, electrical, and other changes may be made without departing from the subject or scope of the present invention. Features or limitations of various embodiments of the invention described herein, however essential to the example embodiments in which they are incorporated, do not limit the invention as a whole, and any reference to the invention, its elements, operation, and application do not limit the invention as a whole but serve only to define these example embodiments. The following detailed description does not, therefore, limit the scope of the invention, which is defined only by the appended claims. 
         [0014]    An example heating, ventilation and cooling (HVAC) system is shown in  FIG. 1 . In the example shown in  FIG. 1 , system  10  includes a heating unit  12 , a cooling unit  14  and a ventilation unit  16  connected to the ventilation system  18  used to control a building&#39;s climate. In the example shown in  FIG. 1 , system  10  includes a thermostat system  100  that controls each of heating unit  12 , cooling unit  14  and ventilation unit  16 . 
         [0015]    An example thermostat system  100  is shown in  FIG. 2 . In the example shown in  FIG. 2 , thermostat system  100  includes a first demand circuit  102  and a second demand circuit  112  connected to a first limited current source  104  and a second limited current source  114 , respectively. In the example shown, limited current sources  104  and  114  include a bridge rectifier  106  connected to a current limiter  108 . In the example shown, first demand circuit  102  includes a switch connected between wires RH and W; in the example shown, first demand circuit  102  serves to power a HVAC unit such as a heating unit off and on. Similarly, demand circuit  112  is connected between wires RC and Y; in the example shown in  FIG. 2 , second demand circuit  112  serves to power a HVAC unit such as a condenser or other cooling unit off and on. In one example embodiment, wires RH and RC provide 24 VAC to their respective HVAC units via their corresponding demand circuits  102  and  112 . 
         [0016]    In one embodiment, demand circuits  102  and  112  include relays. In another embodiment, semiconductor devices such as triacs are used in demand circuits  102  and  112  to provide power to the HVAC units. 
         [0017]    In the example thermostat system  100  of  FIG. 2 , current sources  104  and  114  store energy into energy storage  116 . In one such embodiment, current flows from limited current sources  104  and  114  only when the corresponding demand of the HVAC unit is turned off. 
         [0018]    In the example embodiment shown in  FIG. 2 , when energy stored in energy storage  116  passes a particular threshold, thermostat control  120  wakes from a low power sleeping state. Typically, the threshold is selected to be a sufficient number of volts over the output of DC regulator  118  to ensure that DC regulator  118  is capable of driving sufficient current for a predetermined minimum time at the desired voltage to drive thermostat control  120 . For a 5V power supply, the number might be 2 volts above the desired voltage, or 7 volts DC. 
         [0019]    In one embodiment, thermostat control  120  is placed into a reduced power mode (sleep mode) if the voltage across energy storage  116  falls below a predetermined threshold. 
         [0020]    In one embodiment, energy storage  116  is a rechargeable battery. In another embodiment, energy storage  116  is a capacitor. 
         [0021]    In the embodiment shown in  FIG. 2 , thermostat control  120  includes a charge monitor  122 , sleep/wakeup logic  124  and thermostat processing engine  126 . 
         [0022]    As noted above, previous attempts to power thermostats from power stolen from the demand lines required very low powered thermostat controls. It is difficult to extend such a mechanism so that it can include higher powered features such as Wi-Fi, Zigbee or other wireless devices. Thermostat system  100  solves this problem by providing at least two sources of the power needed to store energy into energy storage  116 . It is unlikely that an HVAC system that supports both heating and cooling would be doing both simultaneously. The assumption is that both of these demands will rarely be activated simultaneously, thus at least one of the relays are always open providing 24 VAC to power current source  104  or  114 . 
         [0023]    In one embodiment, additional demand lines (such as second stage cooling or heating) can be used in similar configurations to provide additional power sources. 
         [0024]    In addition, as shown in  FIG. 2 , in one embodiment thermostat control  120  includes sleep/wakeup logic  124  used to power down thermostat  100  when the energy stored in energy storage  116  drops below a particular threshold and wake up when it rises above a particular threshold. Such an approach allows a network attached wireless digital thermostat to work without battery, C wire or external power supply. This approach also is capable of employing a low power requirement RF network, such as a Zigbee network that can sleep most of the time and wake-up periodically, resume the network connection quickly, transfer the required data and then go back to deep sleep. The power profile of such system is for low power consumption for an extended period followed by a burst power demand for a short period in time, followed by another low power period, etc. 
         [0025]    This burst demand for power can be harvested via power stealing over a longer period of time. By carefully selecting the ratio of the deep sleep and the active burst power, an improved power stealing system can harvest enough energy from the HVAC system without a C wire or external power supply to maintain a wireless RF Digital Thermostat operation. 
         [0026]    In one embodiment, the system employs a constant current limiting network via current limiter  108  (adjustable, but typically less than 10 mA) to make sure that no false demand would be presented. This constant current source than would charge a rechargeable battery or a storage cap. The output of energy source  116  is then fed into a high-efficiency, wide input range, DC/DC controller  118  providing required operating voltages. 
         [0027]    Another example embodiment of a thermostat system is shown in  FIG. 3 . In the example shown in  FIG. 3 , thermostat system  200  includes a first relay  202  as a first demand circuit and a second relay  212  as a second demand circuit. First relay  202  and second relay  212  are connected to a first current source  104  and a second current source  114 , respectively. In the example shown, current sources  104  and  114  include a bridge rectifier  106  connected to a current limiter  108 . In the example shown, first relay  202  is connected between wires RH and W, and serves to power a HVAC unit such as a heating unit off and on. Similarly, relay  212  is connected between wires RC and Y, and serves to power a HVAC unit such as a condenser or other cooling unit off and on. In one example embodiment, wires RH and RC provide 24 VAC to their respective HVAC units via their corresponding relays  202  and  212 . Additional current sources may be implemented by duplicating circuit  104  for additional demand lines, such as second stage cooling or heating, if available. 
         [0028]    In the example thermostat system  200  of  FIG. 3 , current sources  104  and  114  store energy into charge capacitor  216 . In one such embodiment, current flows from current sources  104  and  114  only when the corresponding demand of the HVAC unit is turned off. 
         [0029]    In the example embodiment shown in  FIG. 3 , when energy stored in energy storage  216  rises above a particular threshold, thermostat control  120  wakes from a sleeping state. Typically, the threshold is selected to be a sufficient number of volts over the output of DC regulator  118  to ensure that DC regulator  118  is capable of driving sufficient current at the desired voltage for a predetermined minimum cycle time to drive thermostat control  120 . For a 5V power supply, the number might be 2 volts above the desired voltage, or 7 volts DC. 
         [0030]    In one embodiment, system  200  provides an active monitoring of the energy stored in the charge capacitor  216  and forces the system to go to sleep when the energy stored in the charge capacitor  216  drops below a predetermined critical level. In one such embodiment, system  200  includes a feature that wakes the system up when the energy stored in the cap reaches a preset level. This feature may not be required in all applications, because selecting the proper duty cycle might be sufficient. Such an approach can, however, be helpful during periods when more power is needed, such as during, for instance, a code download or a Flash update. 
         [0031]    An example of such an active monitoring approach is shown in  FIG. 4 . In  FIG. 4 , at  300 , a controller detects the voltage across energy storage  116  (or charge capacitor  216  in  FIG. 2 ) and, at  302 , determines if the voltage is above a first threshold T 1 . If so, the controller moves to  304 , the thermostat processing engine  126  is awakened and control moves to  306 . 
         [0032]    If the voltage at  302  is not above a first threshold T 1 , the controller waits at  302  until the voltage is above the first threshold T 1 . 
         [0033]    At  306 , a check is made to determine if the voltage across energy storage  116  is below a second threshold T 2 . If the voltage is below that threshold, control moves to  308  and the thermostat processing engine  126  is placed in a low power state, or is put to sleep. Control them moves to  300 . 
         [0034]    If the voltage at  302  is not below the second threshold T 2 , the controller waits at  306  until the voltage is below the second threshold T 2 . 
         [0035]    In one embodiment, as is shown in  FIG. 5 , thermostat  400  includes a wireless interface  402 . In one such example, the wireless interface is a Wi-Fi interface. In one such embodiment, thermostat  400  establishes the thermostat as a wireless node. In one embodiment, the wireless interface is a Zigbee interface. 
         [0036]    In the example shown in  FIG. 5 , thermostat  400  includes a first relay  202  and a second relay  212  connected to a first current source  104  and a second current source  114 , respectively. In the example shown, current sources  104  and  114  include a bridge rectifier  106  connected to a current limiter  108 . Additional current sources may be implemented if additional demand lines are available. In the example shown, first relay  202  is connected between wires RH and W, and serves to power a HVAC unit such as a heating unit off and on. Similarly, relay  212  is connected between wires RC and Y, and serves to power a HVAC unit such as a condenser or other cooling unit off and on. In one example embodiment, wires RH and RC provide 24 VAC to their respective HVAC units via their corresponding relays  202  and  212 . 
         [0037]    In the example thermostat system  400  of  FIG. 5 , current sources  104  and  114  store energy into energy storage  116 . In one such embodiment, current flows from current sources  104  and  114  only when the corresponding demand of the HVAC unit is turned off. 
         [0038]    In the example embodiment shown in  FIG. 5 , when energy stored in energy storage  216  rises above a particular threshold, thermostat control  120  wakes from a sleeping state. Typically, the threshold is selected to be a sufficient number of volts over the output of DC regulator  118  to ensure that DC regulator  118  is capable of driving sufficient current at the desired voltage to drive thermostat control  120 . For a 5V power supply, the number might be 2 volts above the desired voltage, or 7 volts DC. Since wireless interface  402  interface typically requires a significant amount of power, in one embodiment wireless interface  402  is only enabled when the voltage across energy storage  116  is above a second, higher, threshold. 
         [0039]    In one embodiment, thermostat  400  provides an active monitoring of the energy stored in the energy storage  116  and forces the system to go to sleep when the energy stored in the energy storage  116  drops below a first predetermined critical level. In one such embodiment, thermostat  400  includes a feature that wakes the system up when the energy stored in energy storage  116  reaches a first preset level and that enables wireless interface  402  to operate when the energy stored in energy storage  116  reaches a second higher preset level. In one such embodiment, shut down is stepped as well. If the energy stored in energy storage  116  drops below a preset level, the wireless interface is powered down. In one such embodiment, if the energy stored in energy storage  116  drops further, the thermostat is put into a sleep mode. 
         [0040]    An example of such an active monitoring approach is shown in  FIG. 6 . In  FIG. 6 , at  500 , a controller detects the voltage across energy storage  116  and, at  502 , determines if the voltage is above a first threshold T 1 . If so, the controller moves to  504 , the thermostat processing engine  126  is awakened and control moves to  506 . 
         [0041]    If the voltage at  502  is not above a first threshold T 1 , the controller waits at  502  until the voltage is above the first threshold T 1 . 
         [0042]    At  506 , a check is made to determine if the voltage across energy storage  116  is above a second threshold T 2  or below a threshold T 4 . If the voltage is above the threshold T 2 , control moves to  508  and wireless interface  402  is enabled. Control them moves to  510 . 
         [0043]    If the voltage at  506  is below threshold T 4 , the controller moves to  516  and the thermostat is put to sleep. Control then moves to  500 . 
         [0044]    If the voltage at  506  is not above the second threshold T 2  and not below threshold T 4 , the controller waits at  506  until the voltage is above threshold T 2  or below threshold T 4 . 
         [0045]    At  510 , a check is made to determine if the voltage across energy storage  116  is below a threshold T 3 . If the voltage is below that threshold, wireless interface  402  is turned off at  512  to conserve power. Control then moves to control moves to  514 . 
         [0046]    If the voltage at  510  is not below the threshold T 3 , the controller waits at  510  until the voltage is below the threshold T 3 . 
         [0047]    At  514 , a check is made to determine if the voltage across energy storage  116  is above threshold T 2  or below threshold T 4 . If the voltage is above the threshold T 2 , control moves to  508  and wireless interface  402  is enabled. Control them moves to  510 . 
         [0048]    If the voltage at  514  is below threshold T 4 , control moves to  516  and the thermostat processing engine  126  is placed in a low power state, or is put to sleep. Control them moves to  500 . 
         [0049]    If the voltage at  514  is not above threshold T 2  and not below the threshold T 4 , the controller waits at  514  until the voltage is above threshold T 2  or below threshold T 4 . 
         [0050]    As noted above, other thermostat systems typically have fairly constant power requirements. For low power they can survive on a traditional power stealing. For higher power they require the C wire or an external power supply. The solutions described above rely on the bursty power profile of an RF system and the harvesting of the required energy over time for the burst operation, thus eliminating the need for the C wire or external power supply. The system also monitors the energy stored in the storage cap and can wake the system up or forces it to go to sleep based on the level. 
         [0051]    In addition, the above described thermostat system and method makes installation easier, faster, more bulletproof, thus lower cost. It also eliminates the need for external power supply when the C wire is not available. 
         [0052]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. The invention may be implemented in various modules and in hardware, software, and various combinations thereof, and any combination of the features described in the examples presented herein is explicitly contemplated as an additional example embodiment. This application is intended to cover any adaptations or variations of the example embodiments of the invention described herein. It is intended that this invention be limited only by the claims, and the full scope of equivalents thereof.