Type storage tank used

A leak in one side would become visible and the other fluid could not become contaminated. Leak detection would involve noting a change in the fluid level in the interim space or a change in color of the interim fluid. When plate-and-frame heat exchangers are used leak detection can be provided by an additional heat exchanger circulating loop filled with a colored fluid for detection fluid between the glycol used in the collector circulating loop and the domestic water system. A check of the current building code should be made to determine the acceptable method of isolation. To help minimize pumping energy, the pressure loss of the heat transfer fluids passing through the heat exchanger should be limited to 1 to 2 psi (6.9 to 14 kPa). Heat exchangers used to heat domestic water are exposed to the potable water pressure and thus should be rated for that pressure, typically above 75 psi (517 kPa).

Domestic hot water storage tanks should be in the building where the hot water is consumed. These tanks would be typically smaller than the system storage tank and should be of a pressurized type. The tank can be piped so its water is warmed by water flowing from the solar heated storage tank and non-solar methods. Here a fossil fuel or electric heater can assure the proper domestic hot water temperature is being maintained.

Storage tanks can be made using steel, fiberglass/plastic, or concrete. Steel tanks make connections with the piping easy, are subject to corrosion; large tanks may require on-site fabrication. Fiberglass/plastic tanks do not corrode, but have a maximum temperature in the range of the temperature that could be expected during stagnation, they cannot be pressurized, and they are more costly. Concrete tanks are low cost, but must be site fabricated, cannot be pressurized, and can make plumbing connections difficult. Steel tanks should be lined with glass, epoxy, or other corrosion resistant material rated for the highest system temperature and working fluid. Alternatively, stainless steel tanks may be provided. Tank life should be at least 15 yrs.

Fiberglass and plastic tanks are corrosion resistant and easily installed, and are available in many shapes and sizes. Although many commonly fabricated tanks will begin to soften at temperatures above the temperature range of 140 to 160 °F (60 to 71 °C). There are more expensive, specially fabricated tanks available that can withstand temperatures up to 250 °F (121 °C). The types of plastics needed to store large quantities of water at high temperatures can be more expensive than steel.

All storage tanks require insulation with a rating at least R-19.It is a good practice to insulate tank supports from the ground if possible. Additional information on tank insulation can be found in the Solar Energy Equipment Chapter of the ASHRAE Handbook – HVAC Systems and Equipment.

All storage tanks for liquids should be located so that if they leak, damage to the building will be prevented. The drain back tank needs a drain line piped to a nearby floor drain. The cost of housing the tank or burying it must be included in the total cost of the solar heating system. Buried tanks must be protected from ground water, and buoyant forces resisted. Underground tanks are not preferred, if other options are available. Tanks must be reasonably accessible for repairs. Tank connections should comply with local codes with regards to backflow preventers, safety relief valves, etc.