Innovative Energy Concepts in the Water Supply Sector - Implementing Environmental and Resource Management - page 24

into account, it can be further assumed that the coverage of water supply via cen-
tral water supply systems will continue to rise during the forthcoming years.
The generalised concept of a central water supply system is as follows: a water
source - such as groundwater or surface water - is captured and treated. After-
wards the water is transported via a main system to storage tanks. From there, it is
conveyed via primary and secondary distribution pipes to the customers. Usually,
the water source is situated at a lower elevation than the end consumer. Therefore,
energy is needed to pump the water from lower to higher situated geographical
points. At the house connection level, a pressure of at least 1.5 bar (15 m water
column) is recommended in Germany (DVGW 2004). Additionally, energy is
needed for the treatment of the water. The energy intensity of the treatment de-
pends mainly on the method used. Within this chapter, only the energy demand of
the water transport will be discussed.

4.3 How Much Energy is Used in the Water Supply Sector

- Some Selected Examples

It is difficult to find literature on the overall energy consumption of water trans-
port in central water supply systems. It seems that this question has been more or
less neglected in scientific literature (Zhou and Tol 2004). In general it can be said
that four factors influence the energy intensity of water distribution systems.
These are (1) the vertical elevation difference between the source and the con-
sumer; (2) the horizontal distance between the source and the consumer in combi-
nation with the physical properties of the system (wall roughness, pipe diameters,
pipe bending, etc.); (3) the quantity that is consumed per capita, and; (4) the effi-
ciency of the transport system (operational strategy, water losses, etc). The in-
stalled power needed by a water supply system can be calculated as follows:

P = η ∗ ρ ∗ g ∗ H

f ∗

Q

(4.1)

Where P

= Power (W) g = Gravity constant (m/s²)

η = Efficiency (-) Q = Discharge (m³/s)

H f

= Density (kg/m³)

ρ Elevation

= (m)

The elevation H f consists of the vertical elevation distance and the frictional head
losses during the transport. In general it can be said that lifting water in the verti-
cal direction is much more energy intense than in the horizontal direction. A verti-
cal lift of 100 m is approximately as energy intense as a horizontal transport of
100 km (Zhou and Tol 2004). The influence of the water quantity is linear.
According to information provided by pump manufacturers, about 30% of the
industrial electricity demand within the European Union is used for pumping sys-
tems (includes all kind of industrial systems) (Broderson 2006). This equals to ap-
proximately 9% of European Union's overall energy consumption. In the United