Diagram of the test setup

In the future, the EU Commission plans to measure the energy efficiency of mobile air conditioning systems in vehicles by means of a standardised procedure as part of type approvals and to display the result on an efficiency label similar to the ones on refrigerators.

Together with TNO, LAT, and KTI, our Institute was awarded the tender for the development of this procedure. A draft of this procedure has existed since November 2010. The initial plan is to have industry and measurement laboratories implement it in a pilot phase. Industry was actively involved in the development process. Die Industrie war bereits im Entwicklungsprozess aktiv eingebunden.

In order to create a cost-effective, realistic procedure, it was decided to test the entire vehicle on the chassis dynamometer, once with the MAC off and once with the MAC on. In these tests, the marginal conditions and tolerances are clearly defined (dynamometer temperature, humidity, inside temperature, mass flow).

MAC test cycle for the chassis dynamometer

The additional consumption caused by the MAC is calculated from the difference of the measured values with and without MAC. In order to obtain a good level of repeatability, the preconditioning and all measurements are carried out in just one test cycle.

Since existing test stand controllers can show relatively high deviations in temperature and humidity compared to the reference value, correction functions have been calculated that correct the measured fuel consumption value according to the measured values. The correction functions were determined by means of simulation of the fuel consumption of the MAC and validated through measurements.

Since artificial sunlight at the dynamometer causes high expenses, the effects of solar radiation and of the quality of the glazing are taken into account with the help of simulation and correction factor. The transmission and heat conduction of the glazing are measured according to ISO 13837 and defined by means of the TTS value.

MAC fuel consumption results for a EURO 5 passenger car

With these measurements, the heat transfer into the vehicle can be calculated for average radiation conditions. For easy application in type approvals, a reference table was created with which the correction factor can be determined depending on TTS, installation angle, and glass size. All in all, such an approach appears to be a representative, easily repeatable test.