Indirect, drainback systems separate the fluid in the solar collector from the potable water using a heat exchanger. This variant is suited for larger systems using a larger, atmospheric (unpressurized) storage tank for both thermal storage and drainback duties. An immersed coil heat exchanger carries potable water from the boiler and/or main storage tank heating it as it travels through the solar storage tank. Since the tank is unpressurized it can be made of thermoplastics or insulated sheet metal. Multiple heat exchangers can be placed in the tank for multiple heating duties (DHW, pool heating, space heating, etc.).
- Eliminates the chance of fluid freezing or overheating
- Uses water as the heat transfer fluid
- Large, unpressurized tank provides an affordable alternative
- For use in all climates
- Collector(s) and exposed piping must be sloped to drain automatically