SWH GilSerem

This is a passive system that works on the principle of density difference to transport heat energy. Potable heat transfer fluid (i.e., water) is heated by a solar collector and the natural convection drives the water from the solar collector unit to the hot water storage tank unit. Water becomes less dense due to solar heating and expands according to the temperature rise. Hot water is circulated to the storage tank, and the relatively cooler water from the bottom of the tank is circulated to the solar collector device. This flow is dependent on the duration of sunshine, since it aids density variation which in turn affects the flow of water. To reduce pipe friction, a larger pipe diameter is recommended rather than the normal size (2–3 in. diameter). Usually, connecting lines are kept at an angle to prevent the development of larger air bubbles that would resist the flow of water. Also, the solar collector–inlet is connected to the bottom of the storage tank to avoid reverse flow. In situations, where the collector working pressure is less than the direct supply of city water, suitable pressure reduction valves are used. Usually an auxiliary heater is included to augment the heating process of a SWH, in particularly when used in solar adverse regions (Raisul et al., 2012). Thermo-syphon systems account for almost 75% of installed capacity and are mainly used in warm climates, such as in Southern China, Africa, South America, Southern Europe and the Middle East and Africa (MENA) region. They are less suitable for cooler climates because of the high heat loss from external hot water stores and the danger of freezing during winter time (IRENA, 2015). 17 Figure 2.2- Thermosyphon system(passive)(Source: Solar domestic hot water heating systems, Christopher,2009.) 2.2.4 Integrated collector storage (ICS) systems (passive) Unlike the conventional SWH system in which a collector acts as an absorber of sunlight, the ICS system utilizes both the collector as well as the storage tank as an absorber to collect solar radiation. In most cases, the entire exterior part of the reservoir acts as an absorber. However, these systems are subjected to heavy heat losses, especially during non-sunshine hours. Several measures, such as selective absorber surface coatings, insulating materials, and a single or double glazing glass covers have been used to reduce the heat losses. A few other techniques were also attempted to culminate the heat loses: movable protection cover, insulated baffle plate, and utilizing phase change material (PCM) inside the storage tank. Researchers have also attempted to use transparent insulating materials for the appropriate 18 exposed parts. Further, to reduce the heat losses, the storage tank was operated on thermal stratification modes, by drawing the hot water from the top of the storage tank and cold water inlet to the bottom of the tank. Figure 2.3- Intergrated collector system(Passive)(Source: Florida solar energy centre, 2006) 2.2.5 Batch system The simplest of all solar water heating systems is a batch system. It is simply one or several storage tanks coated with a black, solar-absorbing material in an enclosure with glazing across the top and insulation around the other sides. It is the simplest solar system to make and is quite popular with do-it-yourselfers. When exposed to direct sun during the day, the tank transfers the heat it absorbs to the water it holds. The heated water can be drawn for service directly from the tank or it can replace hot water that is drawn from an interior tank inside the residence.