Atlantis Tank disposable formwork

16 The determination of the tank volume is based on the water need and on the rainfall in the area. In particular, the quantity of rainwater that can be collected in a year is calculated with the following formula: Q=S*h*η*φ Where: S (m2) = horizontal projection of all surfaces exposed to the rain. h (mm) = height of the rainfall in a year. It varies for each location; the data can be obtained from the almanacs of the Hydrographic Service of the Ministry of the Environment. η (%) = effectiveness of the fi lter that is provided by the manufacturer and concerns the fraction of the water fl ow that is effectively usable downstream of the fi lter. φ (%) = surface outfl ow coeffi cient. This considers the quantity of water that effectively fl ows towards the accumulation system, depending on the nature of the surface, the orientation and the slope. Determination of the accumulation tank volume Subsequently, the water requirements are evaluated, taking into account the number of people, water use and the irrigated surfaces. The following table shows a calculation example. For large sized systems, the following must be considered, for example: school = 1000 l/person offi ce = 1500 l/person The water need is therefore compared with the quantity of water that can be collected and the smaller of the two obtained values is used for determining the usable quantity. The tank capacity calculation takes the average dry period into account, that is the number of days that it does not rain. This number can be found from the Hydrographic Service publications, but for simplicity a constant equal to 6% of the usable water volume is utilised, which guarantees the water need for three weeks. In conclusion, the tank volume is calculated using the following formula: V = (the lower between Q and Fi) * 0.06 Total Fi (litres) Type of surface Outfl ow coeffi cient (diameter) Sloping roof 80-90 Flat, non gravelly roof 80 Flat gravelly roof 60 Intensive green roof 30 Extensive green roof 50 Stone paved surface 80 Asphalting 90 Use Average yearly use (litres)/person Number of people Specifi c water use (Fis) Wc 9000 x ______________ person + Washing machine 5000 x ______________ person + House cleaning 1000 x ______________ person + Gardening 450 litres/m2 x ______________ person + www.baygar.com