Drain back solar hot water systems are one of the most common types of solar thermal systems used today. In short, they utilize two temperature sensors to control the system. When rising temperatures are detected in the solar collectors, cold water from the storage tank is pumped through, absorbing heat as it’s pushed through. The water then flows back into the drain back tank to maintain a certain temperature.
Drain back solar hot water systems can be designed a few different ways:
Type 1 drain back design, often called a two-tank system, uses a full size solar hot water storage tank, and a separate solar storage tank. This design can be used for large or small systems. When hot water is used in the home, it passes through the heat exchanger into the hot water heater, preheating the water and minimizing the energy used by the regular water heater.
Type 2 drain back design uses a solar hot water heater with a built-in heat exchanger. This one-tank system uses one pump to run the collector loop, and holds the volume for solar storage and for the regular hot water heater. They are used mainly for smaller residential systems.
Type 3 drain back design is used for similar applications, and has a heat exchanger located within a small reservoir tank, making it compatible with gas or electric conventional hot water heaters. A second pump is usually needed to circulate water within the system.
The advantages and disadvantages of each system design vary by application. Depending on your home and the configuration required, one solar hot water system design may offer better results and more energy savings. The experts at Smith Sustainable Design will plan your solar hot water system design using the most appropriate configuration for your home. If you have questions about the drain back options available, please give us a call.