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Rainwater harvesting: Sizing and modeling (view source)
Revision as of 20:30, 26 June 2017
, 6 years ago→Rapid
===Rapid===
===Rapid===
<p>Five percent of the average annual yield (Y<sub>0.05</sub>, in L) is calculated as the product of:
<ul><li>The catchment area (A, in m<sup>2</sup>)</li>
<li>The runoff coefficient for the catchment (C<sub>vol</sub>)</li>
<li>The average annual rainfall depth (R, in mm)</li>
<li> the efficiency of the pre-storage filter (η), and </li>
<li> 0.05 </li></ul></p>
<p>Five percent of the average annual demand (D<sub>N</sub>) is calculated as the product of:
<ul><li> The daily demand per person (P<sub>d</sub>, in L)</li>
<li> The number of occupants (n), and </li>
<li> 0.05 </li></ul></p>
<p>The following calculation is based upon two criteria:
<ol><li>A design rainfall depth is to be captured entirely by the RWH system.</li>
<li>The average annual demand (D<sub>N</sub>) is greater than the average annual yield (Y<sub>R</sub>) coming from the catchment. </li></ol></p>
<p>When Y<sub>R</sub>/ D<sub>N</sub> <0.33 <br>
The total storage volume required (V<sub>S</sub>, in L) is calculated as the product of:
<ul>
<li>The catchment area (A, in m<sup>2</sup>)</li>
<li>The design storm rainfall depth (R<sub>d</sub>, in mm)</li>
<li>The design storm runoff coefficient for the catchment (C<sub>vol</sub>), and </li>
<li> the efficiency of the pre-storage filter (η). </li><ul>
Good catchment selection means that the runoff coefficient (β) should work out to be 0.9 or greater.
Filter efficiency can be reasonably estimated as 0.9 pending manufacturer’s information.
</p>
<p>When 0.33 < Y<sub>R</sub>/ D<sub>N</sub> <0.7 <br>
The total storage required is the sum of V<sub>S</sub> and Y<sub>R</sub>.
<p>Total cistern volume can be estimated by multiplying the depth of design storm the catchment area. <br>One millimeter of rain landing on 1 m<sup>2</sup> results in 1 L of runoff. <br>
<p>Total cistern volume can be estimated by multiplying the depth of design storm the catchment area. <br>One millimeter of rain landing on 1 m<sup>2</sup> results in 1 L of runoff. <br>
For example, the 90th percentile event in Barrie is 26 mm, so every 1 m<sup>2</sup> of rooftop will generate 26 L during this storm event.<br> A 2000 m<sup>2</sup> building would generate approximately 54,000 L. <br>
For example, the 90th percentile event in Barrie is 26 mm, so every 1 m<sup>2</sup> of rooftop will generate 26 L during this storm event.<br> A 2000 m<sup>2</sup> building would generate approximately 54,000 L. <br>