Patent Application
20050269420
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.
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.
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.
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.
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.
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.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
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.
A gas water heater according to one embodiment of the present invention is indicated generally by reference number 20 in
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
An embodiment of an apparatus for operating a gas valve, for example, in the heater 20, is indicated generally by reference number 100 in
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
