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Rainwater harvesting: Sizing and modeling (view source)
Revision as of 19:31, 11 July 2017
, 7 years ago→Rapid
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<p>Five percent of the average annual demand (D<sub>0.05</sub>) can be estimated:<br>
<strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong>
<br>D<sub>0.05</sub> = Five percent of the average annual demand (L)
<br>P<sub>d</sub> = The daily demand per person (L)
<br>n = The number of occupants
<br>Good catchment selection means that the runoff coefficient (C<sub>vol</sub>) should be 0.9 or greater. Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information.</p>
===Rapid===
===Rapid===
<p>Five percent of the average annual yield can be estimated:<br>
<p>Five percent of the average annual yield can be estimated:
<strong>Y<sub>0.05</sub>= A × C<sub>vol</sub> × R<sub>a</sub> × e × 0.05</strong>
<br><strong>Y<sub>0.05</sub>= A × C<sub>vol, A</sub> × R<sub>a</sub> × e × 0.05</strong>
<br>Y<sub>0.05</sub> = Five percent of the average annual yield (L)
<br>Y<sub>0.05</sub> = Five percent of the average annual yield (L)
<br>A = The catchment area ( m<sup>2</sup>)
<br>A = The catchment area ( m<sup>2</sup>)
<br>C<sub>vol</sub> = The runoff coefficient for the catchment
<br>C<sub>vol, A</sub> = The annual runoff coefficient for the catchment
<br>R<sub>a</sub> = The average annual rainfall depth (mm)
<br>R<sub>a</sub> = The average annual rainfall depth (mm)
<br>e = The efficiency of the pre-storage filter
<br>e = The efficiency of the pre-storage filter
<ul>
<li>Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information. </li>
<li>In a study of three sites in Ontario, STEP found the annual C<sub>vol, A</sub> of the rooftops to be around 0.8 [http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. This figure includes losses to evaporation, snow being blown off the roof, and number of overflow events.</li>
</ul>
</p>
<p>Five percent of the average annual demand (D<sub>0.05</sub>) can be estimated:
<br><strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong>
<br>D<sub>0.05</sub> = Five percent of the average annual demand (L)
<br>P<sub>d</sub> = The daily demand per person (L)
<br>n = The number of occupants
</p>
</p>
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<p>Then the following calculations are based upon two criteria:
<p>Then the following calculations are based upon two criteria:
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</ol>
</ol>
</p>
</p>
<p>When Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.33, the storage volume required (V<sub>S</sub>, in L) can be estimated:<br>
<p>When Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.33, the storage volume required can be estimated:
<strong>V<sub>S</sub> = A × C<sub>vol</sub> × R<sub>d</sub> × e</strong><br>
<br><strong>V<sub>S</sub> = A × C<sub>vol</sub> × R<sub>d</sub> × e</strong>
<br>V<sub>S</sub> = Storage volume required (L)
<br>V<sub>S</sub> = Storage volume required (L)
<br>A = The catchment area (m<sup>2</sup>)
<br>A = The catchment area (m<sup>2</sup>)
<br>C<sub>vol</sub> = The design storm runoff coefficient for the catchment
<br>C<sub>vol, E</sub> = The design storm runoff coefficient for the catchment
<br>R<sub>d</sub> = The design storm rainfall depth (mm), and
<br>R<sub>d</sub> = The design storm rainfall depth (mm), and
<br>e = The efficiency of the pre-storage filter.
<br>e = The efficiency of the pre-storage filter.
<ul>
<li>Good catchment selection means that the runoff coefficient, for a rainstorm event (C<sub>vol, E</sub>) should be 0.9 or greater.</li>
</ul>
</p>
</p>
<p>When 0.33 < Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.7, the total storage required can be estimated by adding Y<sub>0.05</sub>: <br>
<p>When 0.33
<strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong>
< Y<sub>0.05</sub>/ D<sub>0.05</sub>
< 0.7, the total storage required can be estimated by adding Y<sub>0.05</sub>:
<br>
<strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong>
</p>
</p>
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<panelInfo>
<panelInfo>
<gallery mode="packed" widths=300px heights=300px>
<gallery mode="packed" widths=300px heights=300px>
Cistern Size.png| Schematic diagram of the inputs and outputs to a rainwater harvesting cistern
Cistern Size.png| Schematic diagram of the inputs and outputs to a rainwater harvesting cistern
</gallery>
</gallery>
</panelInfo>
</panelInfo>
</div>
</div>
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<div class="col-md-12">