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| [[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=== |
| {{plainlist| | | {{textbox|{{plainlist| |
| *Five percent of the average annual yield can be estimated: | | *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> | | *<strong>Y<sub>0.05</sub>= A × C<sub>vol, A</sub> × R<sub>a</sub> × e × 0.05</strong> |
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| *R<sub>a</sub> = The average annual rainfall depth (mm) | | *R<sub>a</sub> = The average annual rainfall depth (mm) |
| *e = The efficiency of the pre-storage filter | | *e = The efficiency of the pre-storage filter |
| }} | | }}}} |
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| 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.<br> | | 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.<br> |
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| {{plainlist| | | {{textbox|{{plainlist| |
| *Five percent of the average annual demand (D<sub>0.05</sub>) can be estimated: | | *Five percent of the average annual demand (D<sub>0.05</sub>) can be estimated: |
| *<strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong> | | *<strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong> |
| *D<sub>0.05</sub> = Five percent of the average annual demand (L) | | *D<sub>0.05</sub> = Five percent of the average annual demand (L) |
| *P<sub>d</sub> = The daily demand per person (L) | | *P<sub>d</sub> = The daily demand per person (L) |
| *n = The number of occupants}} | | *n = The number of occupants}}}} |
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| Then the following calculations are based upon two criteria: | | Then the following calculations are based upon two criteria: |