External Gas Controller For Tankless Water Heater

Abstract

This invention is directed to maintaining the output water temperature of a tankless water heater to a constant temperature regardless of changes in water flow rate and/or changes in the temperature of the cold water feed. The water heater has a cold water feed pipe, a fuel line and a hot water output pipe. A temperature monitor attached to the water output pipe generates a signal which varies in direct proportion to the changes in water temperature of the heated water. This signal commands the control motor which operates a fuel valve. The valve then in turn controls the amount of fuel to the water heater. In operation, as the temperature of the hot water changes, the control motor operates the fuel valve to feed more or less fuel to the water heater, maintaining a more constant water temperature regardless of the water flow rate or the incoming water temperature.

What is claimed is: 
     
         1 . Apparatus for maintaining a constant output water temperature of a tankless water heater where output water temperature changes can occur due to changes in incoming water temperature or changes in water flow rate comprising:
 a control valve coupled to a fuel line source to control the fuel flow to the water heater;   an electromechanical device used to control the position of the fuel control valve; and   a temperature sensor that produces an electrical signal which relates to the temperature of water to command the electromechanical device;   wherein the control valve, the electromechanical device and the temperature sensor are coupled th external components of the tankless water heater.   
     
     
         2 . The apparatus of  claim 1  wherein the control valve is a modulated fuel valve. 
     
     
         3 . The apparatus of  claim 2  wherein the fuel valve is located to control the flow of fuel before the fuel reaches the water heater. 
     
     
         4 . The apparatus of  claim 1  wherein the temperature sensor is coupled to monitor the temperature of the water as it leaves the tankless water heater. 
     
     
         5 . The apparatus of  claim 4  wherein the temperature sensor is a thermistor, a thermo coupler, an infrared detector, a solid state temperature sensitive transistor, or a solid state IC. 
     
     
         6 . The apparatus of  claim 1  wherein the electromechanical device is coupled to control the control valve. 
     
     
         7 . The apparatus of  claim 6  wherein the electromechanical device is a stepper motor, a servo motor, a geared motor, a solenoid, or a muscle wire that is coupled to control the fuel valve. 
     
     
         8 . The apparatus of  claim 1  wherein the fuel in the fuel line is natural gas, or propane, or any other liquid or gas fuel source. 
     
     
         9 . The apparatus of  claim 1  wherein the temperature monitor, the control motor and the fuel control valve are adapted to be coupled external to the tankless water heater of the type without a built in feedback control loop. 
     
     
         10 . The Apparatus of  claim 1  wherein a logic device is coupled to the water temperature sensor and the gas valve to prevent oscillations in water temperature. 
     
     
         11 . The apparatus of  claim 10  wherein the logic device is a microcontroller, a microprocessor, a CPLD, a FPGA, or other device with capabilities to translate sensory inputs into signals and send the signals to electromechanical devices for controlling the fuel entering the tankless water heater.