| Solar Storage Tanks |
 |
 |
|
A solar storage tank is an insulated water tank. Cold water from your regular water heater enters, and solar-heated water exits. In closed-loop systems the water is heated by contact with a coil of pipe containing water or antifreeze that circulates through the collectors. In open-loop systems the water is directly circulated through the collectors. The solar preheated water is then plumbed back to the cold side of the water heater, which now functions as a backup heater. When a hot-water tap is opened, preheated water is moved from the solar tank to the backup heater. Water Pump The water within a system has to move by some means, either by a natural method (convection, gravity, natural pressure) or by mechanical pump (or circulator). An AC (plug-in) or DC (photovoltaic) pump can be used to move water or antifreeze between the collector and the storage tank. The size of the pump depends on the distance and elevation difference between the collector and the tank. Mechanical pumps are not used in passive systems (batch and thermosiphon systems). Heat Exchanger This is a device used in closed-loop systems to transfer heat from one fluid to another without mixing the fluids. In storage tanks, some heat exchangers are placed inside the tank (internal), and are often just a coil of metal tubing or pipe in the bottom of the tank. Or the exchanger may be wrapped around the outside of the tank (external) underneath the insulation and cover. External exchangers are often pipes within pipes, with solar fluid in one and water in the other, flowing in opposite directions. The flow is produced by pump or by thermosiphoning (convection), or a combination of both. Expansion Tanks An expansion tank stores air in a bladder or diaphragm. A certain operating pressure for the system is set by the owner. The pipes and system are filled with solar fluid that occupies a specific volume within a certain temperature range. As the fluid gets hotter and expands, the tank compensates by allowing the fluid to compress the air in the bladder or diaphragm, thus keeping the fluid pressure within a safe level. Even with temperatures near boiling, the system doesn't explode, and it remains a beautiful day in the neighborhood. The size of the tank depends on the amount of fluid the system carries (the number and size of the collectors and the length and diameter of the pipes in the solar loop). It's normally about 3 to 6 gallons for a typical home. Usually a 2-gallon tank (#15) is sufficient for home use (a #30 tank has twice the capacity). Expansion tanks are required by closed-loop systems. |
Discuss this item on the forums. (0 posts)