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Rainwater harvesting: Sizing and modeling (view source)
Revision as of 22:51, 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===
*Five percent of the average annual yield can be estimated:
{{plainlist|
o*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>
*Y<sub>0.05</sub> = Five percent of the average annual yield (L)
*Y<sub>0.05</sub> = Five percent of the average annual yield (L)
*C<sub>vol, A</sub> = The annual runoff coefficient for the catchment
*C<sub>vol, A</sub> = The annual runoff coefficient for the catchment
*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}}
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>
{{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}}
Then the following calculations are based upon two criteria:
Then the following calculations are based upon two criteria: