M&V Solar Water Heating Guideline - Eskom
M&V Solar Water Heating Guideline - Eskom
M&V Solar Water Heating Guideline - Eskom
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Measurement and Verification Standard <strong>Guideline</strong> for Low Pressure <strong>Solar</strong> <strong>Water</strong> <strong>Heating</strong> Systems v1r1<br />
strategy of encouraging and assisting all sectors of South African society to reduce electricity<br />
use and to relieve pressure on the electricity network. [1]<br />
3 OVERVIEW OF RESIDENTIAL SOLAR WATER HEATING<br />
TECHNOLOGIES<br />
3.1 General<br />
A conventional <strong>Solar</strong> <strong>Water</strong> <strong>Heating</strong> System operation is based on the physical<br />
phenomenon known as natural convection or thermo siphon effect. This effect manifests in<br />
circulating the water (or other designated heath transfer fluid) through the solar collector<br />
and hot water storage tank. It is essential that the hot water storage tank is positioned<br />
above the solar collector to use the natural flow of the water being heated. As water in the<br />
collector heats, it becomes lighter and naturally rises into the tank above, thus creating a<br />
circulation flow between collector and hot water storage tank.<br />
To eliminate the dependence of the position of the storage tank and to increase the rate of<br />
circulation /heat transfer a forced circulation may be employed, thus allowing the hot water<br />
storage tank to be placed in a convenient place at the house.<br />
3.2 <strong>Solar</strong> Collectors<br />
3.2.1 Main Types of Collectors Used in South Africa<br />
To obtain maximum utilisation of the solar irradiation various collectors are in use. The<br />
collector performance characteristics are shown in Figure 1. and illustrate the efficiencies<br />
of the main three types solar collectors use presently in South Africa, namely:<br />
standard non selective-coated flat-plate collectors<br />
selective coated flat-plate collectors<br />
evacuated glass tube collectors.<br />
From the graphs shown in Figure 1, it is evident that the different collectors should be used<br />
for different purposes, namely:<br />
The tested non-selective coated flat-plate glazed collectors perform poorly at high<br />
operating temperatures. Their normal operational temperatures are in the limits of<br />
30 – 80 o C, heat loss coefficient is above 5 W/m 2 .K, and optical efficiency of 0.8; thus<br />
the applications for these collectors are limited for domestic hot water.<br />
The tested selective coated flat-plate glazed collectors perform well at high<br />
operating temperatures. Their normal operational temperatures are in the limits of<br />
40 – 90 o C, heat loss coefficient is above 3 W/m 2 .K, and optical efficiency of 0.80.<br />
Thus the applications of this collectors is extended for domestic and commercial hot<br />
water large systems. The higher operational temperatures allow reducing the size<br />
of the collector when compared with non-selective coated collectors.<br />
8