Turbocor compressor shows its energy-saving potential in chiller-replacement projects

The key to the efficiency of Turbomiser chillers is the Turbocor compressor — as seen here in the replacement chiller for the Hilton Hotel at Stansted Airport.
The huge energy-saving capabilities of replacing aging chillers with new models incorporating the Danfoss Turbocor compressor in two recent projects is described by Ken Sharpe.Almost as soon as the Danfoss Turbocor compressor entered volume production in 2004, a number of perceptive manufacturers were very quick to develop chillers to maximise the capabilities of this oil-free R134a centrifugal compressor with its magnetic bearings and capability to be used with air-cooled condensers. One such manufacturer is Geoclima of Italy, whose Turbomiser chillers are available in the UK through Klima-Therm of Wimbledon and Cool-Therm of Bristol. Ken Strong of Cool-Therm explains that what attracts potential users is the very high COPs that the Turbocor compressor makes possible in chillers that are designed to maximise its capabilities. To which he adds the extremely low noise and vibration that are a consequence of the magnetic bearings that support the main impeller shaft. Klima-Therm’s Ian Mundie also highlights the extremely low weight of Turbocor compressors. A compressor with a cooling capacity of 300 kW weighs just 125 kg, which Ian Mundie says is a mere quarter that of an equivalent screw compressor. On that basis a chiller with two compressors will weigh nearly a tonne less than its screw-compressor equivalent. Other benefits include turndown to 25% of full load, very low starting current of just 5 A and a power factor of 0.95. Those benefits are attracting the attention of specifiers, especially for refurbishment projects where R22 chillers around 20 years old are coming up for replacement. Indeed, two recent projects, one each by Klima-Therm and Cool-Therm, demonstrate the benefits. The larger of the two projects is the replacement of chillers and cooling towers at the Dorchester Hotel in London. The original R22 chillers were in the basement with a condensing water riser to the cooling towers on the roof. They were removed in stages as they were replaced by three Turbomiser chillers on the roof, each with a cooling capacity of 1 MW. The Birmingham office of Cudd Bentley Consulting specified the chillers, which were supplied by Klima-Therm and installed by All Group Services. Even though cooling towers generally deliver more efficient operation than air-cooled con­densers, such is the efficiency of Turbomiser chillers that energy costs have been reduced by £10 000 a month compared with the previous system — even better than the £8000 to £9000 savings originally anticipated. Those savings are expected to achieve a payback in the first year on the additional capital cost compared with a conventional screw chiller. There are also savings in water treatment and chemical costs associated with the cooling towers. Ian Mundie of Klima-Therm tells us that the analysis of the cooling load throughout the year suggested a £90 000 a year saving compared with a screw compressor, a 30% saving. The consultant was cautious, anticipated half that saving — and went ahead with Turbomiser chillers. Two chillers were positioned on the roof of the tenth floor and one of the roof of the third rear floor — freeing up the basement plant room. Two chillers were installed in space previously occupied by cooling towers, and the condensing water riser was converted to carry chilled water. There were strict planning conditions regarding noise, and it is intriguing that the Turbomiser chillers are quieter than the previous cooling towers.
One of three Turbomiser chillers is craned into position at the Dorchester Hotel in London.
The second project is the simple replacement at the Hilton Hotel at Stansted Airport of a 20-year-old air-cooled reciprocating chiller with a cooling capacity of 630 kW and using R22. With compressor problems starting to arise and 24/7 operation required, the decision was taken to replace the chiller. That task was achieved with just a 12 hour interruption to chilled-water services. Cool-Therm’s Ken Strong tells us that the typical base load was around 150 kW, which a reciprocating compressor does not readily turn down to — but which the Turbocor compressor responds to very well. The replacement Turbomiser chiller provides 630 kW of cooling using two compressors and is expected to use 30% less energy than a traditional design based on reciprocating, screw or scroll compressors. Ken Strong says that his latest feedback is savings of £8000 a year, implying a payback of 18 to 24 months on the higher cost of the Turbomiser chiller. Ken Strong explains, ‘The flooded evaporator enables a high evaporating and low condensing temperature. In this application at the typical load point, we find the machine running with 5°C saturated suction and 25°C condensing temperature. ‘This delivers a remarkable COP of around five, including fans. This compares with the previous machine’s part-load COP of around two and takes chiller performance into new territory.’ All Geoclima Turbomiser chillers are individually built, so connections for chilled water, power and footprint can be specified exactly — a considerable benefit for refurbishment projects. Both clients are very enthusiastic about their new chiller plant. Ray Pask, chief engineer at The Dorchester Hotel, says, ‘The installation has delivered everything promised, and more. I am a strong believer in Turbocor technology, having specified it on another high-profile project. It offers major efficiency benefits, and the oiless bearings make start-up from standby mode straightforward.’ Trevor Bennett, facilities manager at the Hilton at Stansted Airport says, ‘The project has been an unqualified success. It combines innovative engineering, outstanding per­formance and serious energy savings — in one compact package. We are delighted with the result. When running at part load, the machine is so quiet you have to check the display to see if is operating.’
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