Are you planning to install a solar water heater in your home or building? First, you must learn about the different types of solar water heaters.
Active Solar Water Heaters
Active solar water heaters are advanced systems that use water pumps and controls to circulate water or heat-transfer fluid through the system. The active (forced) circulation design ensures consistent water temperature and supply.
Active solar water heaters are preferred in applications where the cold-water source is not high enough for water to naturally flow into the water heating system. You should also use this type of heater in large-scale applications as it ensures sufficient water pressure and a dependable hot water supply regardless of the circumstances or conditions.
Active water solar heater types come in two variants:
- Direct-Circulation Systems
Direct-circulation systems directly circulate water through the system. The water is pumped through the collectors before they’re transported and distributed into showers, taps, and other hot-water outlets. Direct-circulation systems are suitable in tropical countries and other places that do not experience freezing temperatures.
- Indirect-Circulation Systems
Indirect-circulation systems do not circulate and directly heat cold water. Instead, a pump forces a non-freezing fluid through the collector. The hot fluid then flows through the heat exchange mechanism to transfer the heat to the water, which is then transported and distributed into the home.
Indirect-circulation systems—i.e., active solar water heaters with heat exchangers—can come in various designs, including the following:
- Coil-in-Tank Heat Exchanger: A coil-in-tank heat exchanger comes with a coiled tube submerged inside the hot water storage tank. The heat-exchanging coil can be single-walled or double-walled, the latter a definite requirement for toxic heat-transfer fluids. Some coil-in-tank exchangers put the coil outside the tank instead of inside it, probably to safeguard the water in the tank against heat-transfer fluid contamination, but they’re less efficient than coil-in-tank options.
- Shell-and-Tube Heat Exchanger: The shell-and-tube heat exchanger is configured so the heat exchange does not occur inside the water storage tank but in a shell-and-tube component. A series of small tubes, i.e., the tube, are enclosed inside a large-pressure vessel, i.e., the shell. After passing through the collector, the hot heat-transfer fluid flows through the tubes. As they do that, they transfer their heat to the water flowing inside the shell,
- Tube-in-Tube Heat Exchanger: Tube-in-tube heat exchangers are highly efficient systems. A small tube is encased inside a bigger tube. The heat-transfer fluid flows inside the small tube, while the water to be heated flows inside the encasing tube. This type of assembly can be coiled to save space. Similar to shell-and-tube designs, it features two loops with the fluids (i.e., the heat-transfer fluid and the water) moving in opposite directions to optimize heat transfer.
- Compact Heat Exchanger: A compact heat exchanger refers to any type that uses tightly packed (typically) steel plates that create an extensive surface area for heat transfer. This design allows the efficient transfer of heat in a relatively small space.
Active solar water heating systems work great with smart home solutions.
You can install smart thermostats to monitor water temperature and automatically adjust your water heater settings to keep water temperature at your desired level. You can also use smart meters to track energy usage, schedule water heating or heated-water circulation, and even integrate with smart assistants to manage your solar water heating system via voice commands.
Passive Solar Water Heaters
Passive solar water heaters differ from active solar water heaters because they don’t force water (or heat-transfer fluid) through the system. In other words, they don’t use additional energy to initiate water heating or heat transfer.
Passive solar water heaters are not as efficient in providing hot water as active water heaters, but they can last longer than active systems.
The following are the primary types of passive solar water heaters:
- Integral Collector-Storage Passive Systems
Integral collector-storage passive systems have a hot water storage tank with a clear or transparent cover through which sunlight can penetrate to heat the water inside. Gravity ensures the heated water in the storage tank can flow directly into the house’s plumbing system.
Integral collector-storage passive systems are most effective in mild climates where freezing is rare and sunny days are the norm.
- Thermosyphon Systems
Thermosyphon systems rely on pressure variations from variable densities caused by temperature differences. As sunlight heats the water in the solar collector, the water temperature increases. The higher temperature makes the water less dense than cold water.
The lower density induces it to rise into a waiting storage tank positioned above the collector. The movement of the hot water leads to a pressure difference that induces circulation, which leads to the cold and denser water in the storage tank to flow into the collector to replace the heated water.
Designed correctly, a thermosyphon system creates a natural water heating and water-circulation loop.
Integral collector-storage and thermosyphon passive solar water heaters are typically installed on the roof or a raised platform. This placement allows maximum exposure to sunlight plus ensures gravity can induce flow from hot water storage tanks to plumbing systems without the aid of pumps.
Choose What’s Best for You
There are two main categories of solar water heating systems: active and passive. Active solar water heaters can be direct- or indirect-circulation types, while passive systems can be integral collector-storage or thermosyphon.
When selecting a system, it’s essential to consider not just your climate and hot water needs but also the necessary piping accessories required for proper installation and long-term efficiency. High-quality piping accessories help ensure the durability and performance of your solar water heater.
Consider your climate and requirements to choose which is best for your home or building. Also, seek the advice of your solar water heater system provider.
