Gas-electric hybrid water heater

Abstract

A system for heating water includes an interior region, a first heat source including a gas burner configured to generate combustion gases; a second heat source including an electric heating element; a temperature or flow or pressure sensor positioned to directly or indirectly sense a temperature or a flow or a pressure of water contained in the interior region; and a mechanical and/or electrical controller coupled to the temperature or flow or pressure sensor, the first heat source, and the second heat source. The controller actuates the first heat source by firing the gas burner in response to a first signal from the temperature or flow or pressure sensor, and/or actuates the second heat source by actuating the electric heating element in response to a second signal from the temperature or flow or pressure sensor.

What is claimed: 
     
         1 . A system for heating water comprising:
 an interior region configured to contain water to be heated;   a first heat source configured to generate heat for transfer to water contained in or entering or exiting the interior region, the first heat source including a gas burner configured to generate combustion gases;   a second heat source configured to generate heat for transfer to the water contained in or entering or exiting the interior region, the second heat source including an electric heating element;   a sensor positioned to directly or indirectly detect a temperature or a flow or a pressure of the water contained in or entering or exiting the interior region; and   a controller coupled to the sensor, the first heat source, and the second heat source, the controller being configured to:   actuate the first heat source in response to a signal from the sensor, and/or   actuate the second heat source in response to a signal from the sensor.   
     
     
         2 . The system of  claim 1 , the controller being further configured to:
 actuate the first heat source in response to a signal from the sensor when hot water demand is above a first threshold, and/or   actuate the second heat source in response to a signal from the sensor when hot water demand is below a second threshold, thereby mitigating short cycling and cyclic losses of the first heat source.   
     
     
         3 . The system of  claim 1 , the controller being further configured to:
 detect when there is no or low hot water demand; and   actuate the second heat source to recover a set point temperature or flow of the system.   
     
     
         4 . The system of  claim 1  comprising a water storage tank at least partially defining the interior region, the water storage tank being configured to contain the water to be heated; and a heat exchanger extending within the interior region defined by the water storage tank; wherein the gas burner is positioned to deliver the combustion gases such that they can enter the heat exchanger for the transfer of heat from the combustion gases to the water contained in the interior region. 
     
     
         5 . The system of  claim 1 , the controller being configured to actuate the first heat source and the second heat source simultaneously. 
     
     
         6 . The system of  claim 1 , the sensor including a thermistor. 
     
     
         7 . The system of  claim 1 , the first heat source having a first recovery efficiency, the second heat source having a second recovery efficiency, and the system having a system recovery efficiency between or greater than the first recovery efficiency and/or the second recovery efficiency. 
     
     
         8 . The system of  claim 7 , the first recovery efficiency, the second recovery efficiency, and the system recovery efficiency each being a first hour rating. 
     
     
         9 . The system of  claim 1 , the system being tankless. 
     
     
         10 . A method for heating water comprising:
 actuating a first heat source to generate heat for transfer to water contained in an interior region of a water heater, wherein actuating the first heat source includes firing a gas burner in response to a signal from a sensor; and   actuating a second heat source to generate heat for transfer to the water contained in the interior region of the water heater, wherein actuating the second heat source includes actuating an electric heating element in response to a signal from the sensor.   
     
     
         11 . The method of  claim 10 , wherein the firing of the gas burner is in response to a call for heat when a temperature or a flow or a pressure sensed by the sensor is below a setpoint or prescribed temperature or flow or pressure. 
     
     
         12 . The method of  claim 10 , wherein actuating the first heat source is performed before actuating the second heat source. 
     
     
         13 . The method of  claim 10 , wherein actuating the first heat source is performed after actuating the second heat source. 
     
     
         14 . A system for heating water comprising:
 an interior region configured to contain water to be heated;   a primary heat source configured to generate heat for transfer to water contained in the interior region, the primary heat source including a gas burner configured to generate combustion gases;   a secondary heat source configured to generate heat for transfer to the water contained in the interior region, the secondary heat source including an electric heating element;   a sensor positioned to directly or indirectly sense a temperature or a flow of the water contained in the interior region or entering or exiting the interior region; and   a controller coupled to the sensor, the first heat source, and the second heat source, the controller being configured to:   actuate the primary heat source in response to a first signal from the sensor when hot water demand is above a primary threshold, and   actuate the secondary heat source in response to a second signal from the sensor when hot water demand is below a secondary threshold, thereby mitigating short cycling and cyclic losses of the primary heat source.   
     
     
         15 . The system of  claim 14 , the controller further configured to:
 detect when there is no or low hot water demand; and   actuate the secondary heat source to recover a set point temperature or flow of the system.   
     
     
         16 . The method of  claim 10 , further comprising:
 mitigating short cycling and cyclic losses of the first heat source by actuating the second heat source.   
     
     
         17 . The method of  claim 16 , further comprising actuating the first heat source when hot water demand is above a first threshold. 
     
     
         18 . The method of  claim 16 , further comprising actuating the second heat source when hot water demand is below a second threshold. 
     
     
         19 . The method of  claim 16 , further comprising:
 detecting when there is no or low hot water demand; and   actuating the secondary heat source by actuating the electric heating element to recover a set point temperature of the system.   
     
     
         20 . The system of  claim 4 , wherein the gas burner of the first heat source is configured to direct the combustion gases downwardly into the heat exchanger for the transfer of heat from the combustion gases to water contained in an upper portion of the water storage tank, the electric heating element of the second heat source is positioned in a lower portion of the water storage tank to transfer heat to water contained in the lower portion of the water storage tank, the sensor is positioned to detect the temperature of water contained in the lower portion of the water storage tank, and the controller is further configured to actuate the electric heating element of the second heat source in response to a signal received from the sensor. 
     
     
         21 . The system of  claim 20 , the controller being configured to actuate the electric heating element of the second heat source in response to the temperature detected by the sensor when the sensor detects a demand for heated water in excess of a pre-determined demand. 
     
     
         22 . The system of  claim 20 , the controller being operable in a plurality of modes, the controller being configured to actuate the electric heating element of the second heat source in response to the temperature detected by the sensor when the controller is in one of the modes, and the controller being configured to not actuate the electric heating element of the second heat source in response to the temperature detected by the sensor when the controller is in another one of the modes. 
     
     
         23 . The system of  claim 1 , the sensor comprising an upper sensor and a lower sensor, and the controller is further configured to:
 actuate the first heat source in response to a signal from the upper sensor when the upper sensor triggers a call for heat; and   actuate the second heat source in response to a signal from the lower sensor when the lower sensor triggers a call for heat.   
     
     
         24 . The system of  claim 23 , the controller being configured to actuate the second heat source in response to the signal from the lower sensor when the controller is set to operate in a selected mode.