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Line 3: <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>A = The catchment area (m<sup>2</sup>)<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>e = The efficiency of the pre-storage filter</blockquote> Line 33:
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Rainwater harvesting: Sizing and modeling (view source)
Revision as of 21:03, 11 August 2017
, 7 years ago→Simple
[[File:Cistern Size.png|thumb|Schematic diagram of the inputs and outputs to a rainwater harvesting cistern]]
[[File:Cistern Size.png|thumb|Schematic diagram of the inputs and outputs to a rainwater harvesting cistern]]
===Simple===
===Simple===
<blockquote>Five percent of the average annual yield can be estimated:
<blockquote>
*Five percent of the average annual yield can be estimated:
*<strong>Y<sub>0.05</sub>= A × C<sub>vol, A</sub> × R<sub>a</sub> × e × 0.05</strong>
*Y<sub>0.05</sub> = Five percent of the average annual yield (L)
*A = The catchment area (m<sup>2</sup>)
*C<sub>vol, A</sub> = The annual runoff coefficient for the catchment
*R<sub>a</sub> = The average annual rainfall depth (mm)
*e = The efficiency of the pre-storage filter</blockquote>
Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information.
Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information.
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.
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.
<strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong>
<strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong>
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===STEP Rainwater Harvesting Tool===
===STEP Rainwater Harvesting Tool===
[[File:RWH_tank_capacity_table.jpg|thumb|Quick reference table generated using STEP RWH tool, (data for the City of Toronto (median annual rainfall 678 mm). Optimal cistern size is that providing at least a 2.5% improvement in water savings following an increase of 1,000 Litres in storage capacity.]]
[[File:RWH_tank_capacity_table.jpg|thumb|Quick reference table generated using STEP RWH tool, (data for the City of Toronto (median annual rainfall 678 mm). Optimal cistern size is that providing at least a 2.5% improvement in water savings following an increase of 1,000 Litres in storage capacity.]]