GPS-X Technical Reference

Other Models 328
PUMP MODEL
Pump Energy Model using Characteristics Curve
The energy consumed in a pumping system depends on the pumped flow rate, pump head
and pump efficiency. For a give pumped flow rate, the energy consumption will depend
on pump head and pump efficiency. The required pump head for a piping system has to
overcome the static head and dynamic head loss in the pipes, valves and fittings. While
static head is independent of the pumped flow rate, the dynamic pump head is a function
of pumped flow rate and piping system. The pump efficiency is also a function of the
pump flow rate and normally available from the pump characteristic curve. The simple
pump energy models applied to variable flow conditions typically use a constant head
and constant efficiency, leading to inaccurate estimation of pumping requirement. These
models also cannot be used to compare energy performance of pumps having different
pump characteristics curves. Therefore, in situations where large variation in the
pumped flow rates are expected, better energy consumption estimates can be made giving
adequate attention to pump characteristics curve.
With the above objectives in mind, an advanced pump energy model is implemented in
GPS-X to dynamically estimate the pump head and pump efficiency under variable pump
flow conditions. Two pump models are implemented 1) Fixed speed pump model and 2)
Variable speed pump model. The essential parts of the models are as described below.
Fixed Speed Pump Model
System Curve Characteristics
The pump model requires that a system curve is defined for the pumping system. In the
GPS-X model following equation is used to define the system curve.
Where:
h static = static system head, m
h dynamic = static dynamic head, m
h sys = h static + h dynamic
h dynamic = K. Q 2
K = dynamic head-loss coefficient, -
Q = flow rate in the system, -
In GPS-X model, the head-loss coefficient (K) is estimated using one set of value for
h dynamic and Q. In addition to this, the model requires an input value for h static . The
GPS-X input screen for system curve characteristics is as shown below in Figure 11-21
and Figure 11-22:
GPS-X Technical Reference