Heat exchangers for solar water heaters

Liquid-to-liquid

The heat exchanger uses a Wärmeübertragung Fluid, which circulates throughout the solar collector, absorbs heat and then passes through a heat exchanger to transfer heat to water in a reservoir. In cold weather, heat carrier fluids such as antifreeze prevent the solar collector from freezing. Between the heat carrier and the domestic water supply, liquid-to-liquid heat exchangers are equipped with one or two barriers (einwandig or double-walled). Provide a tube or tube of liquid with a single-heat exchanger. Through the hose or the liquid around the pipe can either be a fluid, while drinking water is a heat-transport fluid. A double-wall heat exchanger has two walls between the two fluids. Often two walls are used when the Wärmeübertragung Fluid is toxic, such as ethylene glycol (antifreeze).

In the event of a leak, double walls serve as a security measure, and help to prevent the antifreeze from mixing with the water supply. The wrap around heat exchanger, which has a tube wrapped around and with the outside of a hot water tank, is an example of a double-walled, liquid-to-liquid heat exchanger. To reduce heat loss, the pipe should be isolated enough.

Air-to-liquid

In solar systems with heating, there cannot be a heat exchanger between the collector and the air collector distribution. Systems with heating collectors heat air through liquid heat exchangers, which are similar to fluid air heat exchangers.

Coil-in-tank

In the storage tank, the heat exchanger is a pipe snake. It can be a single tube (single-tube heat exchanger) or the thickness of two piping (double-walled heat exchanger). A less effective alternative is to cover the coil with insulation on the outside of the bulk container.

Shell-and-tube

Heat exchangers are separate from (external to) storage tanks. A heat exchanger has two separate fluid loops. Through the heat exchanger, fluids flow in opposite directions, maximising heat transfer. During one loop, the fluid to be heated (such as potable water) circulates through the inner tubes. After the second loop, A heat-transfer fluid circulates between the shell and the tubes of water. The tubes and shell should be made of the same material. When the collector or heat-transfer fluid is toxic, double-wall tubes are used, and a non-toxic intermediary transfer fluid is placed between the outer and inner walls of the tubes.

Sizing

A heat-transfer fluid circulates correctly to be effective. There are many factors to consider for proper sizing, including the following:

• Heat exchanger type
• Heat-transfer fluid characteristics (specific heat, viscosity, and density)
• Flow rate
• Inlet and outlet temperatures for each fluid.

Manufacturers usually provide heat transfer ratings for their heat exchangers (in Btu/hour) for various fluid temperatures and flow rates. A heat exchanger’s surface area also affects its speed and efficiency: a large surface area transfers heat faster and more efficiently.