Wednesday, 11 August 2010

Dew Quantity Variations

We’ve yet to connect the guttering on the solar-panel shed to one of our new tanks. Consequently each morning when dew has formed on the roof the resultant water runs out of the guttering onto the ground. I decided to measure the quantity of water generated by the dew process over 3 nights by placing a 200 litre drum under one of the gutters.

The shed dimensions are 12.2 metres width and 17 metres in length giving a total roof area of 207.4 square metres. The roof is peaked in the middle with gutters along both of the long edges. This means that the roof area feeding into a single gutter is half of 207.4 square metres = 103.7 square metres. The quantity of water captured from ‘normal’ overnight dew was 3 litres; on a ‘light frost’ night 8.5 litres water was measured and on a ‘heavy frost’ night 22 litres resulted.

22 litres from 103.7 square metres equates to receiving 0.21 litres (210 millilitres) of water per square metre of roof area … or the same as receiving 0.21 mm of rain. This is just less than a cup of water (250 millilitres) per square metre … quite a bit of water in the scheme of things.

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