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