6.4.1 INFLUENCE OF DESIGN PARAMETERS ON THE SYSTEM PERFORMANCE

The size of the gas chamber is a predominant parameter that influences how much water can be pushed out of a tank. To evaluate the influences of chamber surface area and chamber volume on performance, two groups of

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FIGURE 7: Gas temperature variation in a design day.

the gas chambers were analysed. In the first group, the chambers have the same surface area of 2.5 m2 but with different volumes of 1.5, 1.25, 1 and

0. 75 m3, respectively. The second group has a fixed volume of 1.25 m3 but with the different surface areas of 3, 2.5, 2 and 1.5 m2, respectively. In this system, water is pushed up through a 0.9-m-high vertical pipe (Figure 4).

The results show that, for the same chamber volume, the gas tempera­ture in the chamber slightly increases with the surface area. But the in­crease is within 1oC. This could be a result of the heat gain from the larger surface area being offset by the heat losses from the same larger surface area. Figure 6 presents accumulated water volume pushed due to gas ex­pansion. It can be seen that the amount of water pumped increases with the gas chamber volume. It increases from 123 l/day with a 0.75-m3 chamber to 200 l/day with a 1.5-m3 gas chamber. The amount pumped increasing with the chamber volume is due to the assumption of uniform air tempera­ture in the chamber. The volume expands more with the air mass increases in the chamber. However, this phenomenon should become less significant when the air temperature profile in the chamber is treated as non-uniform. Without any control, the gas chamber can pump the maximum amount of water to the PV panel at 7 am, and the amount gradually decreases to zero around 1 pm. It was estimated approximately that 165 l/day of rainwater is available for the climate under the consideration. To pump this amount of water, a 1-m3 gas chamber is needed.