Systems

Saving costs with 'smart' pumps

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, says Steve Minett, PhD .

The Hilton hotel in Vienna has under gone a total refurbishment, requiring the building to be closed for one and a half years. The renewed hotel now has 579 modern guest rooms and 45 luxury suites. In addition, the Vienna Hilton can now also offer Austria's biggest and newest hotel conference hall. This 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.

State-of-the-art pumping

The total cost of the refurbishment was Euro 61 million. The renowned architect Hans Hollein was responsible for the design aspects and the overall 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 delivered by VA Tech Elin EBG. ITT Vogel Pumpen delivered 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 supplied by ITT Vogel to the Vienna Hilton were equipped with ITT Industries' 'smart' speed control system, Hydrovar. This provides major energy savings (50 per cent to 70 cent) by enabling pumps to run at variable speeds. Hydrovar units use microprocessor technology to optimise 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, Hydrovar 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.

Basic principle

The heart of the energy-saving principle of variable-speed pumps is the basic hydrodynamic law that the power consumed by centrifugal pumps varies as the cube of impeller speed. So 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 minimising 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 plant curve which 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 cut-out which switches off the pump when the flow is zero.

An analogy

Manfred Sacher, who is the product manager for the Hydrovar speed control system at ITT Vogel Pumpen, just outside Vienna, likes to use 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 an automatic car with cruise control."

He explains that with a constant speed pump there are basically three flow control methods. Firstly, the flow can be reduced mechanically by throttling the discharge or returning excess flow to the suction side of the pump. Secondly, a bypass system can reduce the flow to the pump; apart from wasting energy, this system can induce cavitation 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.

Frequency conversion

The speed of a simple induction motor depends on the frequency of the AC power supplying it. In most of Europe mains 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 mains 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 programme 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.

Packaged system

The key to this level of automation and flexibility in the Hydrovar, Manfred explains, is the inclusion of a micro processor actually in the Hydrovar unit. Pressure and flow sensors are also attached to the actual pump. The Hydrovar concept therefore 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. Exceptionally, for pumps operating in hostile environments, the control gear is available as a wall mounted unit. Since the Hydrovar unit is so self-contained, it can be moved from one pump motor to another and can also be retrofitted to existing pumps.

Manfred comments that several competitors offer frequency inverters but without micro processors which must be supplied separately. This means that they have to be connected to remote control units, thus introducing additional installation costs. They also have to be programmed before the variable speed system can be used. Many inverters are limited to a maximum rating of 7.5 Kw whereas the Hydrovar is rated up to 22 Kw.

Multi-pump systems

Another unique feature of the Hydrovar is its application in multi-pump systems. With the plumb in and pump principle, the only extra installation work is for each pump in the system to be connected with an interface cable to its neighbour, and for the pumps to be named so that the micro processors can identify each pump. Hydrovar can be retrofitted to existing multi-pump systems and it can include the friction loss compensation system.

The multi-pump system is available for a maximum of four units and it ensures a step-less transition between each pump coming to maximum speed and the next one starting. Uniquely to Hydrovar, built-in redundancy ensures that if any component on any one pump fails, for example sensors, inverter or micro processor, the other three can maintain system pressure and avoid breakdown.

Advanced features

Another feature of the Hydrovar is what Manfred calls the inverse function. He explains that, "normally speed control systems depend on signals from sensors located on the discharge side of the pump. Hydrovar can also be programmed to respond to signals from a pick-up on the inlet side of the pump." An example of where the inverse function might be used is in cooling water systems where the temperature of the incoming water would be a factor in the control of pump speed. This would enable flow through the heat exchanger to be increased to augment the cooling effect.

Hydrovar can be programmed with two different pressure levels to accommodate different operating regimes, for example, daytime and night time, with a timer to switch over to each pre-determined setting. The system can also use different variables, for example pressure, fluid level or fluid flow. The pump could be programmed to operate at a constant pressure up to a point determined by flow or water level and then its speed would be determined by the second variable.

Manfred emphasises that Hydrovar is not simply a pump speed control system. He likes to call it the independent brain on a pump. It can enable operators to get optimal pump performance without having to acquire a quantity of additional equipment.

The Hilton Vienna experience

Ing. Erich Geyer, Project Engineer for VA Tech Elin EBG, points out that, "The Hilton was built in the 1970s, so the pumping equipment for heating, cooling and water suppy was not really up-to-date and economic from today's standpoint. They were all conventional, fixed speed pumps." When asked why they selected ITT Vogel equipment including the Hydrovar units, Erich Geyer responds, "We had to choose an economic solution and also consider the full, lifecycle cost of the equipment we were going to install. Vogel offered very competitive prices and we've had very positive experiences with them from former projects." Specifically in relation to the Hydrovar units, Geyer adds, "Selecting these speed-control units for the pumps in the circulation and the booster systems represented‚ state-of-the-art, amongst the technology choices available to us." So, how is the new system working? "It's operating in a really economic way - making significant energy savings especially in partial load conditions", concludes Geyer.