BTE Solar: Principle and Components of a Solar Water Heating System

Principle and Components of a Solar Water Heating System

Utilization of Solar Energy:

A solar water heater is a heating device that converts sunlight into thermal energy, heating water from low temperatures to high temperatures to meet people's hot water needs for daily life and production. Solar water heaters are categorized by their structural type into vacuum tube solar water heaters and flat plate solar water heaters.

Working Principle:

Sunlight passes through the first layer of glass in the heat-absorbing tube and hits the black heat-absorbing layer of the second layer, which absorbs the solar energy. Because the vacuum insulation between the two layers of glass significantly reduces heat transfer (radiative heat transfer still occurs, but heat conduction and convection are eliminated). Most of the heat is transferred to the water inside the glass tube, heating it. The heated water becomes lighter and flows upward along the heated surface of the glass tube into the insulated water storage tank. The relatively cooler water in the tank flows along the backlit surface of the glass tube to replenish the water. This cycle continues, continuously heating the water in the insulated water storage tank, thus achieving hot water.

Components of a Solar Water Heating System

1. Flat Plate Solar Collector

This is the heat-collecting element in the system. Its function is similar to the heating element in an electric water heater. Unlike electric and gas water heaters, solar collectors utilize solar radiant heat, so heating time is limited to when solar radiation reaches a certain level.

Currently, the most common type of solar collector in the Chinese market is the all-glass vacuum tube. It consists of an outer tube and an inner tube, with the inner tube coated with a selectively absorbing coating. Flat-plate solar collectors use a heat-absorbing film such as black chrome on the collector panel, and the metal tube is welded to the collector panel. Flat-plate solar collectors are slightly more expensive than vacuum tube collectors, but their cost has been rising in recent years, particularly for balcony-mounted solar water heaters in high-rise residential buildings. All-glass vacuum tubes are generally made of high-borosilicate 3.3-meter ultra-hard glass, and the selectively absorbing coating is applied using a vacuum sputtering selective coating process.

2. Insulated Water Tank

A container for storing hot water. Hot water collected by the collector tubes must be stored in an insulated water tank to prevent heat loss. The insulated water tank of a solar water heater consists of an inner tank, an insulation layer, and a water tank shell. The water tank's inner liner is a crucial component for storing hot water, and its material strength and corrosion resistance are crucial. Available materials include stainless steel and enamel. The quality of the insulation material directly impacts thermal insulation effectiveness, which is particularly important in cold weather. Polyurethane integral foaming is a preferred insulation method. The outer shell is typically constructed of color-coated steel, galvanized steel, or stainless steel. An insulated water tank requires excellent insulation, corrosion resistance, and clean water quality.

3. Bracket

This bracket supports the collector and insulated water tank. It must be sturdy, stable, and resistant to wind, snow, aging, and rust. It is typically made of stainless steel, aluminum alloy, or steel with a plastic-spray finish.

4. Connecting Pipes

A solar water heater first draws cold water into the hot water tank, where it then transfers heat through the collector to the insulated water tank. The hot water tank is connected to the indoor cold and hot water lines, forming a closed loop for the entire system. Properly designed and properly connected solar piping is crucial for optimal solar system operation. Solar pipes must be insulated. In cold northern regions, heating cables should be installed on the outer walls of the pipes to ensure users can enjoy solar hot water even in the cold winter.

5. Control Components

Temperature-Differential Controlled Heat Collection Circulation: A solar hot water floor heating system includes a collector temperature sensor and a water temperature sensor. After the collector absorbs solar radiation, the temperature of the collector pipes rises. When the temperature difference between the collector and the water tank exceeds the set value, the detection system initiates a command, initiating a circulation pump to pump cold water from the central water heater into the collector. The heated water then returns to the water tank, bringing the water in the tank to the set temperature.