Abstract:
An apparatus for operating a gas valve in a gas-fired heating system includes a solenoid having a pick coil and a hold coil connected to the pick coil and to a thermo-generator. A power supply powers the pick coil to open the gas valve. The thermo-generator powers the hold coil to hold the gas valve open. The apparatus is small and inexpensive compared to systems that use DC-DC converters and/or stepper motors to operate a millivolt valve. A millivolt valve can be operated via power from a heater thermostat, without AC power having to be wired to the heater.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to gas furnaces and, more particularly, to an apparatus for operating a gas valve in a millivolt heating system such as a water heater.  
       BACKGROUND OF THE INVENTION  
       [0002]     Gas-powered furnace systems such as water heaters commonly are millivolt systems in which a thermo-generator or thermopile supplies low-voltage power for operating a gas valve. The thermo-generator typically has wires of dissimilar metals that produce a voltage when heated together in a furnace pilot flame. A millivolt gas valve typically has a solenoid or magnetic coil that can be actuated to open the valve and keep it open for as long as needed. When the coil is actuated, it “pulls in” a valve member from an opening in the valve so as to allow the flow of gas through the valve. When current to the coil is stopped, the valve member returns to its normal position and thus closes the valve.  
         [0003]     A magnetic actuator for a gas valve must be strong enough to open the gas valve to a gas port and also to hold the valve open for the duration of a call for heat. A magnetic actuator typically uses about twice as much power to open a gas valve as it does to keep the valve in an open position. Thus the coil needs to be large enough to be able to utilize enough power from the thermo-generator to open the gas valve, even though only half as much power typically is needed to hold the valve open. Space requirements and costs, however, increase with coil size.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention, in one embodiment, is directed to an apparatus for operating a gas valve that supplies gas to a burner in a gas-fired heating system. The apparatus includes a solenoid having a pick coil and a hold coil connected to the pick coil and to a thermo-generator. The apparatus also includes a power supply connected to the pick coil. The pick coil is powered via the power supply to open the gas valve, and the hold coil is powered by the thermo-generator to hold the gas valve open.  
         [0005]     Embodiments of the above apparatus are small and inexpensive compared to existing systems that make use of costly DC-DC converters and/or stepper motors to open and close a millivolt valve. A millivolt gas valve can be operated, for example, via power from a water heater thermostat, without AC power having to be wired to the heater.  
         [0006]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a perspective view of a water heater according to one embodiment of the present invention, with portions cut away to expose a burner and the interior of a tank; and  
         [0009]      FIG. 2  is a schematic diagram of an apparatus for operating a gas valve according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]     The following description of embodiments of the invention is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Although embodiments of the present invention are described in connection with a gas water heater, the invention is not so limited. The invention can be practiced in connection with other gas-powered systems, including but not limited to gas log fireplaces and room heaters and furnaces.  
         [0011]     A gas water heater according to one embodiment of the present invention is indicated generally by reference number  20  in  FIG. 1 . The heater  20  has a tank  24  into which cold water enters via a cold water pipe  28 . Cold water entering the bottom  32  of the tank is heated by a gas burner  36  beneath the tank. The burner  36  can be lighted using a pilot flame (not shown in  FIG. 1 ). Heated water rises to the top  40  of the tank and leaves the tank via a hot water pipe  44 . Combustion gases leave the heater via a flue  48 .  
         [0012]     A thermostat  52  signals a gas valve  56  to control gas flow to the burner  36  as further described below. The thermostat  52  may be remote from the heater  20 , as shown in  FIG. 1 . Embodiments are contemplated, however, wherein the thermostat is integral to the heater.  
         [0013]     An embodiment of an apparatus for operating a gas valve, for example, in the heater  20 , is indicated generally by reference number  100  in  FIG. 2 . A pilot flame  104  used for lighting the burner  36  also powers a thermo-generator  108 . The thermo-generator  108  converts heat into electrical current which is deliverable to a solenoid  112 . A pilot valve  116 , after having been manually opened by a user of the heater, is kept open by the solenoid  112  to maintain gas flow to the pilot flame. An emergency cut-off (ECO) device  120  preferably is connected in series between a node  124  and the thermo-generator  108 .  
         [0014]     Electrical current is carried from the thermo-generator  108  to the solenoid  112  and to a dual-winding solenoid  128  via the node  124 . As shall be further described below, the solenoid  128  opens and closes a main valve  132  of the gas valve  56  during operation of the heater. The solenoid  128  includes a pull-in or pick coil  136  electrically connected to a hold coil  140  at a tap  144 . As shall also be discussed further below, the solenoid  128  preferably is small and preferably is mounted in an enclosure in which other gas-controlling elements of the heater are mounted. An outer end  148  of the hold coil  140  is electrically connected to the thermo-generator  108  via the node  124 .  
         [0015]     The thermostat  52  includes a microprocessor  152  that receives temperature information from temperature sensors  156  located, for example, in the top  40  and bottom  32  of the water tank  24 . A latching relay  160 , when closed, electrically connects the thermostat  52  and components of the gas valve  56  as further described below. The latching relay  160  has a grounded coil  164  and a magnetic latch  168 . While current flows through the coil  164  in one direction under control of the microprocessor  152 , the latch  168  is pulled toward the coil  164  and closes the relay  160 . When current is reversed to flow through the coil  164  in the opposite direction under control of the microprocessor  152 , the latch  168  is repelled by the coil and opens the relay  160 . The relay is preferably an Arromat (NAIS) TX2-L2 manufactured by Arromat.  
         [0016]     The coil  164  is connected between a pair of transistor switches  170  connected to and controlled by the microprocessor  152 . The microprocessor  152  uses the switches  170  to control the direction of current flow through the latch coil  164 . The transistor is preferably a type 2N3904 manufactured by On Semiconductor. The latch  168 , when closed, electrically connects the tap  144  with a node  172  between the thermo-generator  108  and an end  176  of the pilot solenoid  112 .  
         [0017]     A battery  180  connected across the microprocessor  152  supplies, for example, a voltage of about 3 volts. The battery  180  is connected to the emitter terminal  184  of a pnp transistor  188  controlled by the microprocessor  152 . The transistor is preferably a type 2N3904 manufactured by On Semiconductor. The collector terminal  190  of the transistor  188  is connected to an outer end  192  of the pick coil  136 . Although the battery  180  is internal to the thermostat  52  in the present embodiment, in another embodiment the battery can be remote from the thermostat. In yet another embodiment, another DC source may be used instead of a battery.  
         [0018]     As previously mentioned, the solenoid  128  is preferably small. As a specific example, the pick coil  136  can have about 100 ampere-turns, and the hold coil  140  can have about 40 ampere-turns. Where the battery  180  or other DC voltage source provides about 3 volts, the pick coil  136  can have, for example, about 700 turns of AWG number 35 magnet wire. With approximately a 2-ohm load, the thermo-generator  108  typically provides about 300 milli-volts or 150 milli-amperes. Accordingly, where the hold coil  140  is of magnet wire having about 24 feet per pound, the hold coil  140  can have, for example, 220 turns of AWG number 29 magnet wire.  
         [0019]     When the heater  20  is in operation, input from the sensors  156  may prompt the thermostat  52  to issue a call for heat. In such event, the microprocessor  152  causes current to flow through the latch relay coil  164  in a predetermined direction so as to cause the latching relay  160  to close. When the latch is closed, the battery  180  is electrically connected in a “pull-in” circuit, via which current can flow through the transistor  188  and the pick coil  136  to ground. Current also flows to the hold coil  140 , the solenoid  112 , the ECO  120 , the thermo-generator  108  to ground.  
         [0020]     After the “pull-in” circuit is closed, the microprocessor  152  supplies a pulse from the battery  180  via the transistor  188 , through the pick coil  136 . The voltage pulse through the pick coil  136  causes the solenoid  128  to retract or “pull in” a valve member (not shown) relative to the main valve  132 , so that the main valve  132  is opened to allow the flow of gas to the burner  36 . The duration of the pull-in pulse from the battery  180  is, for example, about 10 milliseconds. When the valve member has been “pulled in” and the pulse has ended, the latch remains closed until opened again as further described below. While the latch  160  is closed, it is part of a “hold-in” circuit, via which current can flow through the thermo-generator  108 , the hold coil  140 , the pilot solenoid  112  and the ECO  120 . The thermo-generator  108  provides sufficient voltage to the hold coil  140  to hold open the main valve  132 . Thus gas continues to flow through the valve  132  to the burner  36  for the duration of a call for heat.  
         [0021]     When the microprocessor  152  determines, for example, from input from temperature sensors  156  that a call for heat is to be ended, it signals the switch transistors  170  to cause a reversal of polarity of the voltage across the latch coil  164 . The latch  168  thus is caused to open and break the electrical connection between the hold coil  140  and the thermo-generator  108 . The open-circuited hold coil  140  allows the valve member to close the main valve  132 , which remains closed until a subsequent call for heat.  
         [0022]     The foregoing apparatus allows a millivolt gas valve to be operated at lower energy and in less space than previously possible. Because a very small solenoid can be used, magnetic actuating device complexity and tolerances are greatly reduced. Thus the device is significantly less expensive than an actuating device that must be powered by the thermo-generator for valve “pull-in”. The gas valve can be operated via power from the thermostat, and under control of a microprocessor in the thermostat. The above gas valve operating apparatus is small, inexpensive and can be used with a gas water heater that is operated mechanically. There is no need to wire AC power to the heater, nor is there any need to install costly DC-DC converters or stepper motors.  
         [0023]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.