Rainwater Tank Selection and Design

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Design and selection factors for rainwater harvesting tanks

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Rainwater Tank Selection and Design

  1. 1. Sizing – Types - Innovations
  2. 2.      Rainfall Collection Area Water Demand – Use or Purpose Available Space Budget
  3. 3.     Consider intended uses & quantity needed A typical family may use as much as 260 kL/year Perform a water audit to determine demand Example: Newtown Small 2BR House Demand (Litres/day)      Loo flushes Showers Washing Total Aim 6 per day x 4.5L = 27 L/day 2 per day x 9L/min x 10min = 180 L/day 5 washes / week x 80 L/Wash = 57 L/day 264 L/day 250 L/day with mains backup.
  4. 4.  Bureau of Meteorology Rainfall Map  http://www.bom.gov.au/jsp/ncc/climate_averages/rainfall/index.jsp
  5. 5.  Alternative Rainfall Maps  Benson D. Howell J. 1990, Taken for Granted
  6. 6. One millimetre of rainfall on one square metre of roof area results in 1 litre of water collected     Thus 1000mm rain on 1m2 roof area = 1000 litres (=1kL or 1m3) In other words 1000mm rain produces 1000 litres/m2 Allow for losses of 10-15% (Factor of 85-90%) Potential Annual Water Collection = Annual Rainfall x Roof Area x Loss Factor
  7. 7.     Annual Collection = Annual Rainfall x Roof Area x Loss Factor Example Newtown: Annual Rainfall 1000mm (ie: 1000 L/m2) Shed Roof Area 5m x 5m = 25m2 Potential Annual Collection = 1000 (L/m2) x 25 (m2) x 0.85 = 21,250 L = 21.3kL House Roof Area = 8m x 20m = 160m2 Potential Annual Collection = 1000 (L/m2) x 160 (m2) x 0.85 =136,000 L = 136kL
  8. 8.       Elect to use house roof which could collect 136 kL/year Does that mean we need huge 136 kL water tank? Of course not. It is unlikely all the annual rain falls all at once. Rain falls throughout the year Water is used throughout the year Use a Tank Sizing Graph to calculate tank size based on demand and desired reliability of supply.
  9. 9.   Different manufacturers have different graphs Gives tank size based on desired reliability of water supply
  10. 10.   Calculate based on daily demand and best reliability Continuing our Newtown example Roof Area (m2) Demand (L/Day /100m2) Desired Reliability % House Roof 160 m2 House Roof 160 m2 With Shed 185 m2 With Shed 185 m2  Demand (L/Day) Tank Size (kL) 80 Tank Size as % of Roof Area % 20 250 156 250 156 75 10 16 250 135 80 15 27 250 135 75 8 14.8 Aim to collect 15kL with mains backup 32
  11. 11.  As the rain tank won’t supply all our water needs, we can install a mains backup using an interconnect device.
  12. 12.    Must prevent backflow of tank water into mains water. Must be before interconnect device or integrated into interconnect device
  13. 13.  To prevent flow from tank to mains
  14. 14.  http://www.youtube.com/v/hJ7Zvy6SJKs
  15. 15.      Life >40 years 100 % Recyclable Water approved Silicon liner Hygienic clean Not recommended for in ground
  16. 16.  Suitable for in ground
  17. 17.  Variety of shapes sizes and colours

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