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REFRIGERATION UNITS

28th January 1999
Page 43
Page 43, 28th January 1999 — REFRIGERATION UNITS
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IN Developments in refrigeration units include the introduction of scroll compressors from Frigoblock and Thermo King, and the first European refrigeration units from Mitsubishi.

Noise is a perennial problem for operators of temperature-controlled vehicles, a fact recognised by the equipment manufacturers who have moved from noise-suppression techniques to new designs that are inherently quieter in operation, Compared with traditional reciprocating compressors, for example, scroll compressors are said to be quieter and smoother with lower energy consumption. Temperature pull-down is claimed to be faster, so they are ideally suited to multi-drop operations.

A scroll compressor comprises an orbiting spiral and a stationary spiral. Gas is sucked into an opening on the outer edge of the spiral. As the spiral orbits the gas is compressed into a smaller pocket. By the time it arrives at the centre, discharge pressure has been reached.

Frigoblock's ZF range of scroll compressors features welded motor housings to prevent oil leaks and brazed refrigeration lines.

Noise on the Thermo King XDS SR scroll compressor is further cut by a new two-belt drive system that produces a higher torque transfer to reduce belt squeal.

Refrigeration capacities are higher on newer units, partly to help reduce running costs. For example, the latest versions of Carrier's long-established over-cab Supra units are said to have 10% more capacity than previous models, partly through a redesign of their heat exchangers. Carrier has also replaced the old three-blade fan with a six-blade fan to improve evaporator air flow and reduce temperature pull-down times.

Mitsubishi, which claims to be one of the word's largest manufacturers of refrigeration equipment, is now moving into the European market. In the UK it is represented by JR Billows. Initially Mitsubishi is concentrating on lighter vehicles with direct-drive units for 3.5 and 7.5-tanners. These units feature a multifunction valve which is claimed to improve the peformance of the now widely-used R404a refrigerant. The valve helps maximise the capacity of the refrigerant and its ability to cope with fluctuations in temperature by sensing the discharge pressure in the compressor and adjusting the suction pressure accordingly.

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