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