there is insufficient drain slope, water standing in the supply header can freeze in the
winter and burst the pipe. If the drain slope is too much, water can be trapped in the
stub end of the return header and cause freezing problems in the winter. The drain
slope should be 1 inch in 20 feet (approximately 1/4° slope) to assure proper draining.
To set the correct drain slope, one end of the collectors is positioned higher up the roof
than the other end as shown in fig. 3.2. The specific distance changes according to the
pitch of the roof. To begin, use a chalk line
to lay out a level line 10 or 20 feet long
starting from the lowest corner of the
collector array. On the opposite end mark
the distance up the roof as shown in fig.
3.3. Another method is to hold a bubble
level perpendicular to the level line and 1/2
or 1 inch above the end of the line. Mark
where the level meets the roof. A new
chalk line from the starting point to the
raised mark will give the proper mounting
line for the collector frame.
On a shingle roof, the collector mounting
feet can be bolted to the roof through
purlins nailed in place between the rafters.
As shown in fig.3.4, it is usually not
possible to have all mounting feet hit
rafters. In most cases it is better to avoid the rafters.
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Solar Installation Manual
7
Figure 3.3 Drain slope table for
different roof slopes.
Figure 3.4. Typical shingle roof layout for mounting collectors.