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| ===Simple=== | | ===Simple=== |
| Five percent of the average annual yield can be estimated: | | Five percent of the average annual yield can be estimated: |
| $$Y_{0.05} = A \times C_{vol,A}\times R_{a} \times e \times 0.05$$
| | <math>Y_{0.05} = A_{c} \times C_{vol,A}\times R_{a} \times e \times 0.05</math> |
| where:
| | {{plainlist|Where: |
| {{plainlist| | | *''Y<sub>0.05</sub>'' is five percent of the average annual yield (L) |
| *''Y<sub>0.05</sub>'' = Five percent of the average annual yield (L) | | *''A<sub>c</sub>'' is the catchment area (m<sup>2</sup>) |
| *''A'' = The catchment area (m<sup>2</sup>) | | *''C<sub>vol, A</sub>'' is the annual runoff coefficient for the catchment |
| *''C<sub>vol, A</sub>'' = The annual runoff coefficient for the catchment | | *''R<sub>a</sub>'' is the average annual rainfall depth (mm) |
| *''R<sub>a</sub>'' = The average annual rainfall depth (mm) | | *''e'' is the efficiency of the pre-storage filter}} |
| *''e'' = The efficiency of the pre-storage filter}} | |
| *Filter efficiency (''e'') can be reasonably estimated as 0.9 pending manufacturer’s information.<br> | | *Filter efficiency (''e'') can be reasonably estimated as 0.9 pending manufacturer’s information.<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 a 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 a number of overflow events. |
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| Five percent of the average annual demand can be estimated: | | Five percent of the average annual demand can be estimated: |
| $$D_{0.05} = P_{d} \times n\times 18.25$$
| | <math>D_{0.05} = P_{d} \times #\times 18.25</math> |
| Where:
| | {{plainlist|Where: |
| {{plainlist| | | *''D<sub>0.05</sub>'' is 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>'' is the daily demand per person (L) |
| *''P<sub>d</sub>'' = The daily demand per person (L) | | *''#'' is 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: |
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| When \(Y_{0.05}/D_{0.05}<0.33\), the storage volume required can be estimated: | | When \(Y_{0.05}/D_{0.05}<0.33\), the storage volume required can be estimated: |
| <math>V_{S} = A \times C_{vol,E}\times R_{d} \times e</math> | | <math>V_{S} = A \times C_{vol,E}\times R_{d} \times e</math> |
| Where:
| | {{plainlist|Where: |
| {{plainlist| | |
| *''V<sub>S</sub>'' = Storage volume required (L) | | *''V<sub>S</sub>'' = Storage volume required (L) |
| *''A'' = The catchment area (m<sup>2</sup>) | | *''A'' = The catchment area (m<sup>2</sup>) |