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Intelligent Electronically Controlled
Circulator Pumps
by Niels Bidstrup, Grundfos
This new generation of intelligent electronically controlled circulator
pumps can save up to 58% energy compared to non-controlled circulator
pumps and save up to 36% energy compared to existing electronically
controlled circulator pumps on the market. The energy savings are
achieved by using new motor technologies and built in intelligent
functions, which continuously adjusts the pump pressure to the demands
from the heating system.
The use of electronically controlled circulator pumps for water based
heating systems is increasing. Substantial electrical energy savings are
made possible by using electronically controlled circulator pumps
instead of standard non-controlled circulators. A study under the SAVE
II programme have shown that small circulator pumps (P1<250 W) in
household central heating systems in EU consumes approximately 40 TWh/year,
comparable to all washing maschines in EU [Bidstrup et al, 2001]. Apart
from the fact that electronically controlled circulator pumps saves
energy it can also improved the control performance of the heating
systems because it delivers a suitable differential pressure both at
full load as well as at partial load operation [Bidstrup, 1999]. This
paper describes functionalities and energy savings by using the new
generation of circulator pumps, which are entering the market now.
Electronically controlled circulator pumps
Figure 1 shows the trend in the development of electronically
controlled circulator pumps starting from the first wet-runner with
integrated frequency converter, denoted 1st generation, on to the 3rd
generation. With the introduction of pumps with integrated frequency
converter, it became possible to operate the pump at different impeller
speeds, which made it possible to realize other relations between flow
and differential pressure than those given by a fixed speed pump. This
offers the possibility of choosing relations between flow and
differential pressure, which improves the conditions for the control
valves, thus minimizing hydraulic loses and saving electrical energy.
These relations are realized by preprogrammed control curves in the
electronically controlled circulator pump.
Constant pressure control
Constant pressure control is recommended if flow resistance in the
distribution and supply system (pipe, boiler, heat exchanger etc.) is
low. Figure 2 shows the differential pressure across the circulator when
constant pressure control is selected. A1-A3 are different operating
points. The differential pressure across the circulator is constant and
independent of the flow. Due to the low flow resistance in the
distribution system the differential pressure across the control valves
is nearly constant and optimal control performance is obtained both at
full load as well as at partial load operation. Different setting of
constant pressure is possible and selected manually or by an external
signal (e. g. bus or infrared communication).
Proportional pressure control
If flow resistance in the distribution system is not negligible
Proportional pressure control is recommended. Figure 3 shows the
differential pressure across the circulator when Proportional pressure
control is selected. Again A1-A3 are different operating points The
differential pressure across the circulator increases when flow
increases. The proportional pressure control compensates for the flow
resistance in the distribution and supply system with the result that
the differential pressure across the control valves is nearly constant
and a good control performance is obtained both at full load as well as
at partial load operation. Different slopes of the proportional control
curves can be selected to fit the pump to the resistance in the actual
heating system, in which it is installed. Since the introduction of
proportional pressure control it has proven its efficiency and has
become an accepted control method in industry.
Permanent magnet motors
The new generation (3rd generation) of electronically controlled
circulator pumps is based on a permanent magnet motor. This reduces
losses in the motor and thereby results in a significant increase in
efficiency. Figure 4 shows a rotor with permanent magnets. These types
of circulator pumps are wet runners, which means that the rotor is
running in the circulated fluid. The permanent magnets are encapsulated
to protect them against the fluid. For more information on circulators
with permanent magnet motors and how they are controlled see (Rasmussen
et al, 2002).
System adaptation
To obtain further energy saving the new generation circulator pumps have
built in adaptive functions. These adaptive functions select control
curve settings depending on the system and the operating conditions. Two
examples of adaptive functions are automatic set point control and
automatic night setback.
Automatic set point control
The proportional pressure control methods introduced in 2nd generation
electronically controlled pumps can be improved with respect to energy
savings if the pump selects the setting of the control curve after
installation and thereby adapts to the system where it is installed.
This functionality is denoted automatic set point control. The method is
showed in figure 5. The automatic set point control automatically
adjusts the setting of the proportional control curve. The method is
based on an observation of maximum flow. The pump operates on control
curve A (A1-A3). If more flow is required than at point A3 the pump will
follow the maximum curve to operating point B3. From now on the pump
will operate on the proportional control curve B (B1-B3) until a new
maximum flow is observed and an even lower proportional control curve is
selected. Finally the pump has found the lowest possible control curve
for the system, where it is installed, and extra energy savings are
achieved.
Automatic night setback
In heating systems with night setback the thermostatic valves will open
due to the reduced room temperatures. A 2nd generation electronically
controlled pump will misinterpret this as an increased heat demand and
it will speed up to compensate for that. This will result in an
unnecessary increase in power consumption and can also result in flow
noise. The new generation circulator pumps have a built in adaptive
function, which reduce the speed when the heating system is at night set
back. This functionality is called automatic night setback and is shown
in figure 6. Based on measurements of the flow temperature the
circulator pump detects the night set back from the heating controller
and changes the setting to a fixed minimum speed. In figure 6 this
implies that the pump will operate in the operating point B1 instead of
A3. When the heating system returns to day operation the pump returns to
control curve A (A1- A3). If the pump is connected to a building
management system it is also possible to force the pumps in minimum
speed via an external control signal.
Comparison of annual energy consumption
To compare the annual energy consumption of non-controlled, 2nd and 3rd
generation electronically controlled circulator pumps, measurements have
been performed by three independent test centres. The calculation of the
annual energy consumption in the test was based on the following load
file, which is an accepted load profile in industry and is used to label
the pumps according to the German Blue Angel labelling scheme [Blauer
Engel], which came in force primo 2002. The load profile is displayed in
table 1. The load profile shows that the pump only runs at full speed
for a short percentage of the time during a year and runs below 50% flow
most of the time. With such a load profile it is evident that the pump
operation should be optimized at partial load. The results from the
comparative tests are shown in figure 7. The energy savings by changing
from an non-controlled pump to a 3rd generation pump is 2569-1148 =
1421 kWh/year or 58%. This is a substantial saving and the pay back time
for this change is also low. The energy savings by changing from a 2nd
generation pump to a 3rd generation pump is 1783-1148 = 635 kWh/year or
36%. It is estimated that the energy saving potential in EU by changing
pumps in this size alone from non-controlled pumps to 3rd generation
pumps is 3,3 TWh/year comparable to the electricity consumption of
700.000 single family houses.
Conclusions
The energy saving potential by using electronically controlled
circulator pumps is huge. Small circulator pumps in household central
heating systems in EU consume approximately 40 TWh/year. Energy savings
of 10 TWh/year is possible with these small pumps. For the new
generation of electronically controlled circulator pumps the energy
saving potential is even larger. Comparative tests at three independent
test centres have shown energy savings of 58%, with the new generation
of electronically controlled pumps, when compared to non-controlled
circulator pumps. The energy savings in the tests are mainly due to the
high efficiency motors with permanent magnets and built in intelligent
functions. The effect of the new adaptive functions is not incorporated
in these comparative tests, which means that the saving in a specific
system may be larger. <<
REFERENCES:
Bidstrup, N., van Elburg, M. and Lane, K., Promotion of Energy
Efficiency in Circulation Pumps especially in Domestic Heating Systems,
Study under SAVE II programme, June 2001.
Bidstrup, N., Energy savings by using electronically controlled
circulator pumps, in proceedings from District Heating Control, Zlin,
Czech Republic, October 1999.
Rasmussen, K. F., Thorup, N., Permanent Magnet Motors find its way to
circulator pumps, submitted to EEMODS, Treviso, Italy, September 2002
Blauer Engel, http://www.blauer-engel.de
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