Danfoss compressors are used in the new ETT air conditioning units that maintain a constant temperature in Airbus aircraft while they are under construction or being serviced. This is a positive partnership in many ways, crowning 15 years of partnership between ETT and Danfoss for variable-speed solutions.
Since 2009, ETT has developed air conditioning units fitted with inverter compressors known as the ACU-SRV (air-conditioning unit - variable refrigeration system).
The company, a long-term partner of Danfoss located in Brittany, specializes in climate control equipment. They won a contract for mobile air conditioning units in response to a call for tenders by the aircraft manufacturer Airbus in the late 2000s. This application has been around for a long time, but the criteria for awarding contracts have changed considerably over the past 10 years. Flexibility, energy savings and precise temperature control during the manufacture and maintenance of aircraft are the determining factors - now more than ever before - when selecting equipment.
The internal volumes of the aircraft manufactured by Airbus vary according to the model concerned (A350, A320 etc.). Also, when Airbus tendered out the new air conditioning units in 2009, ETT proposed a system that uses multiple cooling circuits and compressors fitted in tandem. Tandem configurations are a very common way of modulating cooling capacity. The first ACU SRV-units used to modulate the capacity stepwise, depending on the number and type of compressors in parallel (25%-50%-75%-100%). The capacity modulation allowed by the units previously used, with semi-hermetic compressors, was more limited as there were 1 or 2 compressors per system.
The second step in the partnership between Airbus and ETT was to move to units with compressors in tandem with the units that equipped with inverter compressors. "For these units, we selected the Danfoss Maneurop VTZ inverter compressors. They work with the refrigerant required by the aircraft manufacturer, namely R407C, and they are highly reliable. We have been using them for many years in other applications and we have even been among the pioneers for variable speed systems in commercial applications with Danfoss. Thanks to inverter technology, the airflow blown into the cabin is kept at a constant temperature of 8°C. This helps guarantee the reliability of installation, welding, cleaning, control and electronics work as well as the comfort of the installation or maintenance teams. This benefit could only be obtained so accurately and efficiently with variable speed. The system consumes far less energy than fixed-speed compressors because it is constantly adapting to external and internal temperatures," says Christophe Marziou, Special Projects manager at ETT.
The move from fixed-speed to variable-speed compressors was possible thanks to ETT's skills in integrating electrical and electronic features, with technical support from Danfoss. "Only Danfoss provides a pre-qualified ‘compressor-and-drive’ solution. This qualification makes for a huge level of certainty in our development." explains Christophe Marziou. "We can focus on overall optimization of the system."
Operation of the unit:
The solution for Airbus consists of an ACU-SRV unit connected to the plane by means of a flexible duct 40cm in diameter, blowing in air at a constant temperature of 8°C.
This unit has a refrigeration capacity of 40kW.
Several patents have been filed for the ACU-SRV.
Installation and commissioning are easily handled by a qualified installer.