Solar heating system with back-up electric heating

Abstract

A system for heating water including a water heater and a solar collector is provided. The water heater includes a water storage tank, a heating element positioned within the bottom end of the water tank and a lower thermostat configured to selectively activate the heating element as a function of the water temperature sensed by the temperature sensor of the thermostat. A tank heat exchanger is also positioned within the bottom end portion of the water storage tank. The tank heat exchanger is configured to contain a fluid medium for heat exchange with water in the bottom end portion of the water storage tank. The solar collector is fluidly coupled to the tank heat exchanger of the water heater for circulating the fluid medium through the tank heat exchanger.

1 . A system for heating water comprising:
 a water heater including
 a water storage tank; 
 a lower heating element positioned within a bottom end portion of the water storage tank for heating water within the bottom end portion of the water storage tank; 
 a thermostat including a temperature sensor positioned at an elevation above the lower heating element for sensing a temperature of water within the water storage tank, said thermostat being configured to selectively activate the lower heating element as a function of the water temperature sensed by the temperature sensor of the thermostat; 
 a tank heat exchanger positioned within the bottom end portion of the water storage tank, said tank heat exchanger being configured to contain a fluid medium for heat exchange with water in the bottom end portion of the water storage tank; and 
   a solar collector fluidly coupled to the tank heat exchanger of the water heater for circulating the fluid medium through the tank heat exchanger.   
     
     
         2 . The system of  claim 1  further comprising a pump for circulating the fluid medium through the tank heat exchanger and the solar collector. 
     
     
         3 . The system of  claim 1  further comprising a tank temperature sensor positioned at the bottom end of the water storage tank for sensing a temperature of water within the bottom end of the water storage tank. 
     
     
         4 . The system of  claim 3 , wherein the tank temperature sensor is positioned at an elevation at or above a bottom end of the tank heat exchanger. 
     
     
         5 . The system of  claim 3  further comprising:
 a solar temperature sensor positioned on a surface of the solar heat exchanger for sensing a temperature of the fluid medium within the solar heat exchanger; and 
 a control system for comparing the temperatures sensed by the tank temperature sensor and the solar temperature sensor. 
 
     
     
         6 . The system of  claim 5 , wherein the control system is configured to circulate the fluid medium through the solar heat exchanger and the tank heat exchanger when a difference between the temperatures sensed by the tank temperature sensor and the solar temperature sensor meets or exceeds a pre-determined level. 
     
     
         7 . The system of  claim 1 , said water heater further comprising an upper heating element positioned within a top end portion of the water storage tank for heating water within the top end portion of the water storage tank. 
     
     
         8 . The system of  claim 7 , wherein a top surface of the tank heat exchanger is positioned at an elevation below the upper heating element. 
     
     
         9 . The system of  claim 1 , said water heater further comprising:
 an inlet port positioned on the water storage tank for receiving cold water delivered from a cold water supply line;   an outlet port positioned on the water storage tank for distributing hot water from the water storage tank toward a hot water supply line; and   a water tempering device coupled to both the inlet port and to the outlet port for diverting a portion of the cold water from the cold water supply line to the hot water supply line, wherein the water tempering device is configured to selectively mix the cold water with the hot water for delivery of the mixed water into the hot water supply line.