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Solar water heating facts

Solar Water Heating Systems (SWHS) comprise of the tank, the collector and the Controller. There are two major types of solar water heating systems: Direct and Indirect. These can be installed in two ways, Split system and Closed Couple. In addition one can chose between two types of collectors, Flat Plate and Evacuated Tubes. These terms are defined below.

System type

Indirect systems (closed loop system)
The medium (propylene glycol) with a low specific heat capacity, constantly flows through the collector in a winding close loop copper pipe. Glycol absorbs heat while in the collector and through heat exchangers heats up water in the tank. The Indirect System is suitable for coastal (where there is hard water) and/or frost areas.

Direct System
Water flows past the collector through one long – winding pipe and directly absorbs heat from the sun. The Direct System works without any medium nor heat exchangers and is suitable for generally sunny or non coastal areas.

SWHS collectors

The collectors play the heat (energy taping) role in the SWHS. The collectors are best placed on the north-facing side of the roof. There are many types of collectors but Flat plate and the Evacuated tubes are the most common in South Africa.

Flat Plate Collector
A weather proof insulated box containing black metal absorber sheets covering water (direct system) or glycol (indirect system) in pipes.

Evacuated Tube Collector
The collector is made up of vacuum tubes which heat up by absorbing solar energy. The evacuated tubes can heat up water even when there is no direct sunshine.

Installation types

When installing a SWHS the installer has to consider a number of options:

Remote or Split System
This is also called split system. In this case the collector is on the roof and the storage tank in the roof. This is chosen when there is no space to work on the roof or the roof is not strong enough.

Close Couple System
The tank and the collector are installed close to each other on the roof with the tank slightly above the collector. The roof must be strong enough for this arrangement. In some areas it is not allowed to have things on the roof.

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