Drainback Solar Water Heater

Abstract

A solar water heater includes a drainback unit with a drainback reservoir and an anti-airlock conduit for assuring that working fluid in the solar collectors is consistently drained from the solar collectors into a drainback reservoir once circulation the working fluid in the solar collectors has stopped. The drainback unit also provides rapid startup by positioning the heat exchanger outside of the drainback reservoir and by positioning the inlet and outlet of drainback reservoir in close proximity to each other.

1 . Solar water heater comprising:
 a. a water storage tank heat exchanger circuit comprising:
 i. a water storage tank; 
 ii. a cold water siphon conduit; 
 iii. a hot water return conduit; 
 iv. a storage tank heat exchanger coil in a heat exchanger; and 
 v. storage tank water pump, 
   
       wherein the water storage tank is connected to the storage tank heat exchanger coil by means of the cold water siphon conduit and the hot water return conduit and wherein the storage tank water pump circulates water through the water storage tank and through the storage tank heat exchanger coil;
 b. a solar heat exchanger circuit comprising:
 i. a solar collector; 
 ii. a solar heat exchanger coil in the heat exchanger; 
 iii. a cold fluid conduit; 
 iv. a hot fluid conduit having a cross-sectional area; 
 v. a solar fluid pump; and 
 vi. a drainback unit including
 (a) a drainback reservoir; and 
 (b) an anti-airlock conduit having a cross-sectional area for supplying air to the solar collector during a drainback operation, 
 
 
 
       wherein the solar collector is connected to the solar heat exchanger coil by means of the solar hot fluid conduit, the solar cold fluid conduit, and the drainback reservoir and wherein the solar fluid pump circulates working fluid through the solar collector, the solar heat exchanger coil, and the drainback reservoir;
 c. a control module for turning on and shutting off the storage tank water pump and the solar fluid pump, 
 
       wherein the control module turns on the storage tank water pump and the solar fluid pump during a heating operation and shuts off the storage tank water pump and the solar fluid pump during a drain back operation. 
     
     
         2 . The solar water heater of  claim 1 , wherein the anti-airlock conduit is connected adjacent the top of the drainback reservoir and the solar hot fluid conduit. 
     
     
         3 . The solar water heater of  claim 2 , wherein the cross-sectional area of the anti-airlock conduit is less than half of the cross-sectional area of the hot fluid conduit. 
     
     
         4 . The solar water heater of  claim 3 , wherein a ratio between the cross-sectional area of the anti-airlock conduit and the cross-sectional area of the hot fluid conduit is approximately 1:36. 
     
     
         5 . The solar water heater of  claim 1 , wherein solar water heater includes a storage tank temperature sensor for sensing the temperature of the water in the water storage tank and a hot fluid temperature sensor for sensing the temperature of the working fluid exiting the solar collector. 
     
     
         6 . The solar water heater of  claim 5 , wherein the control module turns on the storage tank water pump and the solar fluid pump, to initiate a heating operation, when the temperature sensed by the hot fluid temperature sensor exceeds the temperature sensed by the storage tank temperature sensor by a first predetermined value. 
     
     
         7 . The solar water heater of  claim 5 , wherein the control module shuts off the storage tank water pump and the solar fluid pump, to initiate a drain back operation, when the temperature sensed by the hot fluid temperature sensor exceeds the temperature sensed by the storage tank temperature sensor by a second predetermined value. 
     
     
         8 . The solar water heater of  claim 4 , wherein the control module shuts off the storage tank water pump and the solar fluid pump when the temperature sensed by the storage tank temperature sensor reaches a third predetermined maximum value. 
     
     
         9 . The solar water heater of  claim 1 , wherein the heat exchanger is positioned outside of drainback reservoir. 
     
     
         10 . The solar water heater of  claim 9 , wherein the drainback reservoir includes a drainback reservoir inlet conduit for receiving working fluid from the solar heat exchanger coil and a drainback reservoir outlet conduit for supplying working fluid to the solar cold fluid conduit and wherein the drainback reservoir inlet conduit and the drainback reservoir outlet conduit are connected to the drainback reservoir in close proximity to each other. 
     
     
         11 . Solar water heater comprising:
 a. a water storage tank heat exchanger circuit comprising:
 i. a water storage tank; 
 ii. a cold water siphon conduit; 
 iii. a hot water return conduit; 
 iv. a storage tank heat exchanger coil in a heat exchanger; and 
 v. storage tank water pump, 
   
       wherein the water storage tank is connected to the storage tank heat exchanger coil by means of the cold water siphon conduit and the hot water return conduit and wherein the storage tank water pump circulates water through the water storage tank and through the storage tank heat exchanger coil;
 b. a solar heat exchanger circuit comprising:
 i. a solar collector; 
 ii. a solar heat exchanger coil in the heat exchanger; 
 iii. a cold fluid conduit; 
 iv. a hot fluid conduit; 
 v. a solar fluid pump; and
 (a) a drainback unit including a drainback reservoir, 
 
 
 
       wherein the solar collector is connected to the solar heat exchanger coil by means of the solar hot fluid conduit, the solar cold fluid conduit, and the drainback reservoir, wherein the heat exchanger is positioned outside of the drainback reservoir, and wherein the solar fluid pump circulates working fluid through the solar collector, the solar heat exchanger coil, and the drainback reservoir;
 c. a control module for turning on and shutting off the storage tank water pump and the solar fluid pump, 
 
       wherein the control module turns on the storage tank water pump and the solar fluid pump during a heating operation and shuts off the storage tank water pump and the solar fluid pump during a drain back operation. 
     
     
         12 . The solar water heater of  claim 11 , wherein the drainback reservoir includes a drainback reservoir inlet conduit for receiving working fluid from the solar heat exchanger coil and a drainback reservoir outlet conduit for supplying working fluid to the solar cold fluid conduit and wherein the drainback reservoir inlet conduit and the drainback reservoir outlet conduit are connected to the drainback reservoir in close proximity to each other.