TankSizeCalculator.xls_1

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www.RainWaterHarvesting.co.uk Client and details

Insert your building's data in the yellow boxes.

From the roof area off your property, you assess the amount of water available, and equate it to the amount you will use.

1 Main Building area

Building width (metres) 10

Building depth(metres) 15Rain Collection Area 1 (square metres) 150

2 First extension/conservatory/porch/garage/shed etcwidth (metres) 10Depth (metres) 15Rain Collection Area 2 (square metres) 150

3 Second extension/conservatory/porch/garage/shed etcwidth (metres)Depth (metres)Rain Collection Area 3 (square metres) 0

4 Third extension/conservatory/porch/garage/shed etcwidth (metres)Depth (metres)Rain Collection Area 4 (square metres) 0

5 Calculate the area of any remaining useful roofs as a figurein square metres and enter directly in the yellow box to the right

6 TOTAL of collectable roof areas (square metres) 300

7 66

8 Collectable rainwater per annum (in litres - discounted by 20% to account for water loss) (YIELD) 158,400

9 Use of water in the buildingWashing machine and toilet flushing are the main usage for rain water in domestic systems. Add an allowance for daily garden use.Number of people in the house 5 people

Number of clothes washing cycles per day (50 litres each) 1.25 63

Number of toilet flushes per day (4.42 flushes per person, average 5 litres each) 22 111

or adjust till F46 = F35 more or less 25

10 Amount of water you require every day 198Amount of water you require every year (DEMAND) 72,270

11 40

12 Capacity of water storage in litres required for drought protection 7,920

The lesser of YIELD (8) or DEMAND (10) per annum 72,270Therefore, volume of rainwater storage required 7,920

13 Is there sufficient roof water available (CONCLUSION): YES

14 Use a twin 6500 Carat kit [13,000 litres]Use multiple Platin tanks

Use multiple Rondus tanksUse a 10000 litre Balmoral tank

15 Cross check with the British Standard BS 8515:2009

5% of annual rainwater yield (in litres) 7,920

5% of annual non-potable water demand in the home (in litres) 3,614

To be conform to BS8515, tank must hold at least (in litres) 3,614

Check stock and prices at www.rainwaterharvesting .co.uk or by email at [email protected]

TANK SIZE CALCULATOR 2009 2011 RainWaterHarvesting.co.uk

Rainfall per year in your area (cms). Use rainfall chart on sheet 2, a figure between 60 and 170.

Outdoor use per day ( minimum 5 litres per person per day)

How many days drought protection do you need? Enter a number in the box to the right, typically 21

Tank size required - either, in the bestselling Carat range,

or, in the shallow-dig Platin range,

or, in the Rondus range,or, if your tank is going to be above ground, in the Balmoral range...

Based on British Standard BS 8515, the rainwater tank must be big enough to hold 5% of the annual rainwater yield, or 5% of the annual non-potable water demand, whichever is the lesser. The figures below serve as a check against the tank size recommended above.


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MB file Tank_Size_Calculator Rev7f 30Mar2011.xls


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UK Rainfall (source Met Office) Historical data for comparison

Annual rainfall in centimetres 2010 2006 2008 2009 2010

UK 94 118 130 121 94

England 72 85 98 88 72

Wales 112 142 166 149 112

Scotland 123 165 172 169 123N Ireland 105 116 127 126 105

England & Wales 78 93 108 96 78

England N 82 102 117 101 82

England S 67 76 88 81 67

Scotland N 126 182 185 177 126

Scotland E 108 117 131 131 108

Scotland W 135 194 198 199 135

England E & NE 73 79 95 80 73

England NW & Wales N 102 140 155 136 102

Midlands 64 80 94 78 64

East Anglia 58 63 68 60 58

England SW & Wales S 135 113 169 162 135

England SE & central S 68 79 85 82 68


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V% 06-10

80%

85%

79%

74%91%

2006 2008 2009 20100

20

40

60

80

100

120

140

160

180

200

Rainfall in centimetres per year: UK trend by regions

EnglandWalesScotlandN Ireland


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www.RainWaterHarvesting.co.ukTANK SIZE CALCULATOR 2009 2011 RainWaterHarvesting.co.uk

1) Lines 8 to 52 replicate the calculations of the UK Communities and Local Government paper"The Water Efficiency Calculator for new Dwellings" May 2009 available on the internet at

This is the official version of the same calculator required by the Code for Sustainable Homesas issued by BREEAM and by the Building Regulations Part G

2) Our tank size calculator is simplified in only one respect, that is the amount of water used bytypical toilets. The official calculator provides space s for you to define single flush or dual flushtoilets and their capacity or flow rate, whereas ours simplifies this to an average flush of 5 litres(at best, cistern of 6 litres and low flush of 2 litres, but often larger flush volumes). We retain theCode's 4.42 flushes per day ("Use Factor") times this 5 litres average volume per flush. If in doubtor if required by the authorities you should run the complete calculation which you can find at

Our washing machine usage is based on a wash for everyone in the home every 4 days.

3) The official calculator requires a minimum outdoor water of 5 litres per person per day. If youinsert a larger figure in cell F42, as we suggest, and if the rainwater Yield of your roof is greaterthan the Demand, then the calculator will recommend a suitably larger tank. A small garden needs200 litres a day and half an acre more like 400 litres a day (in spring and summer).

4) Paragraph 12 provides you the volume of rainwater storage required according to the "Code"calculation as referred to in 1 and 2 above. Our tank size recommendations are based on this.5) We add in the light green box at the bottom the recommendations of the British StandardBS 8515-2009. This will typically give a smaller tank size because the drought protection is about18 days not 21 days. Use it as a check, or select this volume, as you choose. Our calculator

uses the BS 8515 "intermediate approach".

5) Paragraph 8 use a roof and filter coefficient of 80% (cell F35) which is 10% loss of water off the roof (mostly evaporation) and 10% filter loss (water going to drain with debris and leaves).Roof loss is much greater is you have a cedum or other organic roof.

Please address comments and questions to [email protected]

UPDATES to this calculator (for office use only)

Oct08 MB. Rev 5 Jun09 MB (BSI check added). Rev 6 Nov09 Text tab changed. Rev 7 Feb11 Other tank ranges, redundant lines deleted

Rev 7b Feb11 Other tank ranges, redundant lines deleted, toilet volumes adjusted, notes addedRev 7e Mar11 Rainfall figures updated and trend graph added

Rev 7f Mar11 Flush reinstated to 5 litres average from 3 as unrealistic

http://www.planningportal.gov.uk/uploads/br/water_efficiency_calculator.pdf

http://www.wrcplc.co.uk/PartGCalculator/Calculator.aspx
http://www.planningportal.gov.uk/uploads/br/water_efficiency_calculator.pdfhttp://www.wrcplc.co.uk/PartGCalculator/Calculator.aspxhttp://www.wrcplc.co.uk/PartGCalculator/Calculator.aspxhttp://www.planningportal.gov.uk/uploads/br/water_efficiency_calculator.pdf


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a roof area of square metresannual rainfall in your area of centimetresand, therefore, total annual collectable rain (Yield) of litres

The number of people in the building is taken as people A washing machine cycle needs 50 litres and we assume washing machine cycles per dayFor toilets, we assume an average flush of 3 litres and flushes per day per personWe assume some water needed outdoors of litres per dayThis makes a total daily use of litres per dayor a total annual use (Demand) of litres across a whole year

3) The drought protection provided by this rainwater system is: daysThe capacity of rainwater storage for drought protection is litresThe lesser of Yield and Demand litresTherefore optimal volume of rainwater storage is litres

4) Cross check with the British Standard BS 8515:2009

5% of annual rainwater yield (in litres) litres5% of annual non-potable water demand in the home (in litres) litresTo be conform to BS8515, tank must hold at least (in litres) litres

1) We attach the Tank Size calculator completed with yourfigures showing

2) We have then calculated your typical daily usage of rain waterindoors and in the garden.

You can see that if the total amount of rain collectable, above, ismore than or about the same as this figure,you have a coherentrain water "budget". Do you?

Tank size required - if in the bestselling Carat range

Based on British Standard BS8515, the rainwater tank must be big enough to hold 5% of the annual rainwater yield, or 5% of the annual non-potable waterdemand, whichever is the lesser. The figures below serve as a check against the tank size recommended above.


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TankSizeCalculator.xls_1

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