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Rainwater harvesting: Sizing and modeling (view source)
Revision as of 20:52, 20 February 2018
, 6 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===
The following approximations
Five percent of the average annual yield can be estimated:
Five percent of the average annual yield can be estimated:
<math>Y_{0.05} = A_{c} \times C_{vol,A}\times R_{a} \times e \times 0.05</math>
<math>Y_{0.05} = A_{c} \times C_{vol,A}\times R_{a} \times e \times 0.05</math>
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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.
#The average annual demand (''D'') is greater than the average annual yield (''Y'') from the catchment.
# The average annual demand (''D'') is greater than the average annual yield (''Y'') from the catchment.
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_{c} \times C_{vol,E}\times R_{d} \times e</math>
<math>V_{S} = A_{c} \times C_{vol,E}\times R_{d} \times e</math>
<math>TotalStorage = V_{S} + Y_{0.05}</math>
<math>TotalStorage = V_{S} + Y_{0.05}</math>
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===Example calculation===
==STEP Rainwater Harvesting Tool==
==STEP Rainwater Harvesting Tool==
[[File:RWH_tank_capacity_table.jpg|thumb|500 px|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.]]
[[File:RWH_tank_capacity_table.jpg|thumb|500 px|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.]]