TECHNICAL 85 Volume Volume is the amount of space that a matter occupies. In the metric system, it is expressed in cubic metres or litres. 1 cubic metre = 1 000 litres Practical application This can be used to determine the size of a tank or hot water vessel or any other vessel for that matter. • To determine the volume of a rectangular or square vessel: L (length) × W (width) × H (height) = Volume Example 1m wide × 1m high × 3m long = 3 000ℓ (3m 3 ) Or a tank 1m wide × 2m long × 1.5m high = 3 000ℓ (3m 3 ) • To determine the volume of a cylindrical vessel π r2² × H or L Where: π = 3.14 r2²= radius of the vessel (½ the diameter of the vessel multiplied by itself) H = Height; L = Length Example A cylindrical vessel having a diameter of 2.5m and height of 3m: Volume = 3.14 × (1.25 × 1.25) × 3 = 14.718m 3 or 14,718.75ℓ Note: To determine the required volume of cold and hot water storage required for a building, SANS 10252:1 section 4 (Assessment of water demand) Tables 1 to 5 can be referred to. • To determine the volume of a pipe The same formula can be applied as above: π r2² × L Example The volume of a pipe 20m in length and having an internal diameter of 20mm: By formula: 3.14 × (10mm × 10mm) × 20m = 6 280mℓ ÷ 1 000 to bring the answer to 6.28ℓ. This is a useful calculation to determine the volume of a dead leg of hot water piping. SANS 10252:1 section 7 (Hot water piping) states that the maximum dead-leg length of hot water piping shall be such that no more than four litres of water may be wasted before water at full temperature is received at a terminal fitting. Although this is the standard, in our water-strapped environment we should all be concerned with keeping the dead legs of hot water piping to a minimum so that as little water as possible is wasted while waiting for hot water to arrive at a tap and as little energy is wasted to heat that water too. August 2018 Volume 24 I Number 6