| Active Solar Water Heater Systems | | | | collector by opening a valve when a |
| | | | thermostat indicates that the water is near |
| Solar water heater systems are designed to be | | | | freezing. If electricity is down, then the |
| active, with pumps or fans to promote the | | | | collector empties all water. |
| gathering of heat, or passive, with no | | | | |
| mechanical parts added to the system. Solar | | | | The drain-back system |
| water heaters have been around since the late | | | | |
| 1800's. Standard natural gas water heaters | | | | This system uses a heat exchanger to store |
| took their place in the early 1900's. For | | | | drained water from the collector when it |
| the last four decades, newer technologies | | | | nears freezing. The heat exchanger |
| have fixed many problems with solar water | | | | coordinated with a storage tank, pushes the |
| heaters. Problems like excessive oxidation | | | | water through to the water heater and then |
| and just plain not having enough hot water | | | | the rest of the house. The drain-back system |
| are not problems now. | | | | has an electrical pump that works most of the |
| | | | time. If the pump is not working, the heat |
| The difference between the different kinds of | | | | exchanger stores warm water from the |
| active solar water heaters is the way the | | | | collector and uses this water itself as the |
| heat collector protects itself against cold | | | | heating fluid to heat the water. The heat |
| conditions. These systems are called: | | | | exchanger can lose up to 10% of its heating |
| Recirculate, drain-down, drain-back, and heat | | | | efficiency. |
| exchange. | | | | |
| | | | The heat exchange system |
| The recirculate system | | | | |
| | | | This system is the only system which does not |
| This system uses an electrical pump to move | | | | drain out any water from the collector when |
| water through the collector to prevent it | | | | it nears freezing. The heat exchanger uses |
| from freezing. Moving water will not freeze, | | | | an oily fluid that prevents freezing to |
| but some heat is sacrificed to do this. | | | | travel to the collector and keep the water |
| | | | warm. Some of these systems use compressed |
| The drain-down system | | | | air to heat the water instead of an oily |
| | | | fluid. |
| This system simply takes the water out of the | | | | |