Line 3: |
Line 3: |
| [[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=== |
| Five percent of the average annual yield can be estimated: | | <blockquote>Five percent of the average annual yield can be estimated: |
| <br><strong>Y<sub>0.05</sub>= A × C<sub>vol, A</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, A</sub> = The annual 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</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. |
| | | <blockquote>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: | |
| <br><strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong> | | <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>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>P<sub>d</sub> = The daily demand per person (L) |
| <br>n = The number of occupants | | <br>n = The number of occupants </blockquote> |
| ---
| |
| Then the following calculations are based upon two criteria: | | Then the following calculations are based upon two criteria: |
| #A design rainfall depth is to be captured entirely by the RWH system. | | #A design rainfall depth is to be captured entirely by the RWH system. |