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Line 1: − + + + + + + + + + + + + − ====Rapid====+ − <p>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>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 − <ul> − <li>Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information. </li> − <li>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.</li> − </ul> − </p> − <p>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>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>n = The number of occupants − </p> − <p>Then the following calculations are based upon two criteria:+ − <ol>+ − <li>A design rainfall depth is to be captured entirely by the RWH system.</li>+ − <li>The average annual demand (D) is greater than the average annual yield (Y) from the catchment. </li>+ − </ol>+ − </p>+ − <p>When Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.33, the storage volume required can be estimated:+ − <br><strong>V<sub>S</sub> = A × C<sub>vol</sub> × R<sub>d</sub> × e</strong>+ − <br>V<sub>S</sub> = Storage volume required (L)+ − <br>A = The catchment area (m<sup>2</sup>)+ − <br>C<sub>vol, E</sub> = The design storm runoff coefficient for the catchment+ − <br>R<sub>d</sub> = The design storm rainfall depth (mm), and+ − <br>e = The efficiency of the pre-storage filter.+ − <ul>+ − <li>Good catchment selection means that the runoff coefficient, for a rainstorm event (C<sub>vol, E</sub>) should be 0.9 or greater.</li>+ − </ul> − </p> − <p>When 0.33 − < Y<sub>0.05</sub>/ D<sub>0.05</sub> − < 0.7, the total storage required can be estimated by adding Y<sub>0.05</sub>: − <br> − <strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong> − </p> − </div>+ − <div class="col-md-4">+ − <panelWarning>+ − <gallery mode="packed" widths=300px heights=300px> − Cistern Size.png| Schematic diagram of the inputs and outputs to a rainwater harvesting cistern − </gallery> − </panelWarning> − </div> − <div class="col-md-12"> − − ====STEP Rainwater Harvesting Tool==== − </div> − <div class="col-md-8"> − <p>The Sustainable Technologies Evaluation Program have produced a rainwater harvesting design and costing tool specific to Ontario. The tool is in a simple to use Excel format and is free to download.</p> − </div> − <div class="col-md-4"> − <panelWarning> − <gallery mode="packed" widths=300px heights=300px> − RWH_tank_capacity_table.jpg| 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. − </gallery> − </panelWarning> − </div> − <div class="col-md-12"> − + − ====STEP Treatment Train Tool====+ − <p> Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system could be integrated into a site plan using STEP's Treatment Train Tool. − <ul>+ − <li>The catchment (roof) would be 100% impervious</li>+ − <li>The rainwater harvesting system would be a 'Storage' Element with the following properties:</li>+ − <ul>+ − <li>Storage type = No removal</li>+ − <li>Lined</li>+ − <li>Underlying soil = <em>doesn't matter, can ignore</em></li>+ − <li>Evaporation factor = 0</li>+ − <li>Suction head (mm) = 0</li>+ − <li>Saturated conductivity (mm/hr) = 0</li>+ − <li>Initial soil moisture deficit (fraction) = 0</li> + − </ul>+ − + − <ol>+ − <li>Bottom elevation (m)</li> − <li>Maximum depth (m)</li> − <li>Initial water depth (m)</li> − <li>The Curves table is set up to accommodate ponds of roughly conical dimensions. A rainwater cistern is usually cuboid or cylindrical in shape, so that the area (m<sup>2</sup>) will remain the same throughout the depth. </li> − </ol> − </ul> − </p>
Rainwater harvesting: Sizing and modeling (view source)
Revision as of 20:54, 11 August 2017
, 6 years agono edit summary
<div class="col-md-8">
<div class="col-md-8">
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[[File:Cistern Size.png|thumb|Schematic diagram of the inputs and outputs to a rainwater harvesting cistern]]
===Simple===
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>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
*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.
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>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>n = The number of occupants
----
----
Then the following calculations are based upon two criteria:
#A design rainfall depth is to be captured entirely by the RWH system.
#The average annual demand (D) is greater than the average annual yield (Y) from the catchment.
When Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.33, the storage volume required can be estimated:
<br><strong>V<sub>S</sub> = A × C<sub>vol</sub> × R<sub>d</sub> × e</strong>
<br>V<sub>S</sub> = Storage volume required (L)
<br>A = The catchment area (m<sup>2</sup>)
<br>C<sub>vol, E</sub> = The design storm runoff coefficient for the catchment
<br>R<sub>d</sub> = The design storm rainfall depth (mm), and
<br>e = The efficiency of the pre-storage filter.
/*Good catchment selection means that the runoff coefficient, for a rainstorm event (C<sub>vol, E</sub>) should be 0.9 or greater.
When 0.33 < Y<sub>0.05</sub>/ D<sub>0.05</sub>< 0.7, the total storage required can be estimated by adding Y<sub>0.05</sub>:
<br>
<strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong>
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----
===STEP Rainwater Harvesting Tool===
[[File:RWH_tank_capacity_table.jpg| 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.]]
The Sustainable Technologies Evaluation Program have produced a rainwater harvesting design and costing tool specific to Ontario. The tool is in a simple to use Excel format and is free to download.
<strong>[http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/rainwater-harvesting-design-and-costing-tool/| Rainwater Harvesting Tool]</strong>
<strong>[http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/rainwater-harvesting-design-and-costing-tool/| Rainwater Harvesting Tool]</strong>
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----
===STEP Treatment Train Tool===
Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system could be integrated into a site plan using STEP's Treatment Train Tool.
In a typical configuration:
In a typical configuration:
*The catchment (roof) would be 100% impervious
*The rainwater harvesting system would be a 'Storage' Element with the following properties:
**Storage type = No removal
**Lined
**Underlying soil = <em>doesn't matter, can ignore</em>
**Evaporation factor = 0
**Suction head (mm) = 0
**Saturated conductivity (mm/hr) = 0
**Initial soil moisture deficit (fraction) = 0
*The dimensions of the rainwater cistern can be placed into the fields:
#Bottom elevation (m)
#Maximum depth (m)
The dimensions of the rainwater cistern can be placed into the fields:
#Initial water depth (m)
#The Curves table is designed to accommodate ponds of roughly conical dimensions. A rainwater cistern is usually cuboid or cylindrical in shape, so that the area (m<sup>2</sup>) will remain the same throughout the depth.
<strong>[http://www.sustainabletechnologies.ca/wp/low-impact-development-treatment-train-tool/|The Treatment Train Tool]</strong>
<strong>[http://www.sustainabletechnologies.ca/wp/low-impact-development-treatment-train-tool/|The Treatment Train Tool]</strong>
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[[category:modeling]]
[[category:modeling]]