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Speed-Controlled Pumps For Vienna Hotel
When the Vienna Hilton, built in the 1970s, was recently renovated, speed-controlled
pumps from ITT Vogel Pumpen were installed. These state-of-the-art pumping
systems are delivering significant cost savings in the operation of the hotel’s
heating, air-conditioning and water supply systems.
The hotel has undergone a total refurbishment that required the building
to be closed for one and a half years. The renewed hotel has 579 modern guest
rooms
and 45 luxury suites. In addition, the Vienna Hilton now offers Austria’s
biggest and newest hotel conference hall. The hall has an area of 830 square
meters and can accommodate an audience of 900 people. The hotel has retained
its 423-square-meter ballroom and it can now offer an additional 11 other meeting
rooms, ranging in size from 60 to 180 square meters. A brand new bar has been
added, the gym expanded and the restaurant has been completely re-designed
along ultra-modern lines. The works of several Austrian artists have been included
in the interior designs.
Transportation between the hotel and airport has been dramatically upgraded
by a new direct airport shuttle service, CAT, which departs from directly beneath
the hotel. The service incorporates flight check-in facilities and the journey
time is 14 minutes.
The total cost of the refurbishment was $61 million (Euro). The renowned
architect Hans Hollein was responsible for the design aspects and the over-all
construction
contractor was Stadtpark Hotelreal AG, a company of Soravia Group. The required
technical engineering, including electrical, heating, air-conditioning, ventilation
and sanitary systems, was provided by VA Tech Elin EBG. ITT Vogel Pumps provided
a total of 52 pumps and related equipment to the project; 34 pumps for heating,
12 for air conditioning and 6 for the hotel’s water supply.
Twelve of the pumps were equipped with ITT Industries’ ‘smart’ speed
control system, Hydrovar. According to ITT, the system provides major energy
savings (50% to 70%) by enabling pumps to run at variable speeds. Hydrovar units
use microprocessor technology to optimize pump performance. The units can be
mounted on the pump itself and provide complete ‘plumb in and switch on’ capability.
With installation costs dramatically reduced and the plunging costs of electronic
components, the pumps pay for their higher capital costs many times over during
their lifetime. Throughout the world, possibly about 80 per cent of pumps are
still constant speed units so the scope for energy saving worldwide is huge.
The heart of the energy-saving principle of variable-speed pumps is the basic
hydrodynamic law that the power consumed by centrifugal pumps decreases 4-times
in relation to impeller speed. If pump speed is reduced by one unit, energy
consumption is reduced by four units. Hydrovar’s intelligent controllers
improve on this already significant saving by minimizing friction losses associated
with
the fluid flow.
At low fluid flow speeds the head lost by friction is proportional to the
velocity. But at higher speeds, the head loss is proportional to the square
of the velocity.
The Hydrovar system maintains a curve that reduces pump speed to reduce fluid
flow wherever possible to below the critical speed where linear losses become
square law losses; this additional function increases energy savings by some
20 per cent. In addition, the units have a patented cutout, which switches
off the pump when the flow is zero.
Manfred Sacher, product manager for the Hydrovar speed control system at
ITT, describes the system by using a car analogy. He suggests that constant
speed
pumps operate very much as if a person was driving a car with one foot constantly
on the accelerator and using the brakes to control the car’s speed and
to stop. “The Hydrovar system,” he says, “is like a car with
an automatic gearbox; and, extending the analogy, even like a car with cruise
control.”
He explains that with a constant speed pump there are basically three flow
control methods. First, flow can be reduced mechanically by throttling the
discharge
or returning excess flow to the suction side of the pump. Secondly, a by-pass
system can reduce the flow to the pump; apart from wasting energy, this system
can induce cavitations in the impeller causing additional wear. Thirdly, hydraulic
accumulators can be used to absorb excess flow and store it under pressure.
When the pump output drops below demand, the accumulator can be used to bring
the
flow up to the desired level. Accumulators are expensive, take up space, have
limited capacity and seldom produce a smooth and constant flow.
The speed of a simple induction motor depends on the frequency of the AC
power supplying it. In most of Europe electricity supply is at 50 Hz (cycles
per
second) and in the United States 60 Hz, so motors connected directly to the
mains turn
at multiples of these figures depending on how the motor is wound. To alter
the frequency of the motor supply and thus regulate pump speed, the Hydrovar
system
rectifies the main supply to DC and then inverts it under command from the
controller to provide the frequency required to match pump demand.
Input to the frequency controller comes from pressure and flow sensors; these
inputs are integrated with the operator’s program to provide a fully
flexible operating regime. The system provides not only economical pumping
but also incorporates
safety features and provides solutions to special requirements.
The key to this level of automation and flexibility is the inclusion of a
microprocessor within the pump system. Pressure and flow sensors are also attached
to the
actual pump. The concept is to have all the equipment necessary for a variable
speed
control system mounted on the pump itself. One of the many advantages to this ‘pump-mounted’ solution
is that air from the motor cooling fan can be used to cool the electronics.
Since the unit is so self-contained, it can be moved from one pump motor to
another
and can also be retrofitted to existing pumps.
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