By using air-conditioning the fuel consumption of any vehicle increases by 10 to 15 percent. The additional consumption depends on various factors: length of the trip, vehicle age, ambient temperature, solar radiation, motorisation and preferred inside temperature.

The systems engineering is particularly important: being equipped with a simple, non-regulated air-conditioner the vehicle consumes up to 2.5 times of the fuel amount a vehicle with a modern, electronically controlled system consumes.

No information for car users so far

Currently, there is no consistent measurement method that provides information on the additional fuel consumption caused by air-conditioning systems. The official consumption data provided by manufacturers is determined by the so-called New European Driving Cycle (NEDC). However, additional sets such as air-conditioning system or heater are not considered in this standardised consumption test. Thus, car buyers so far do not have any indication to the actual efficiency of the air-conditioning system in the car.

In the context of a research project the German Federal Environment Agency determined the additional consumption of a VW Touran at different ambient temperatures based on the NEDC. The chart clearly shows that the additional consumption of air-conditioners at higher ambient temperatures increases disproportionately to more than 1.5 liters. The mobile air-conditioning (MAC) system with the natural refrigerant CO2 (R744) particularly in the typical temperature range for Europe works much more efficient than the system with the previously used R134a.

On behalf of AUTO BILD the German Motor Vehicle Inspection Association DEKRA investigated the additional fuel consumption of four different vehicles through the operation of air conditioning. The cars were tested on a dynamometer. The interior of each car had to be cooled down to a temperature of 20 ° degrees at different outside temperatures (20°, 28° und 33°). The measurements were made at a constant speed of 50 and 100 km/h, with and without air conditioning. The best result obtained the Mercedes, with an additional fuel consumption of 12.1 percent at 50 km/h and 3.6 percent at 100 km/h. The Opel Zafira had the highest additional fuel consumption with almost 26 percent more at 50 km/h. Beneath very simple air conditioning technique the reason also is the bigger internal space of this car. Generally, it´s evident that fuel consumption increases more at lower speeds.

The TÜV Nord, on behalf of the Federal Highway Research Institute (BASt), determined the factors that influence fuel consumption. Comparing the consumption-relevant auxiliaries, heating and air-conditioning stand out in particular (see chart). The TÜV Nord concluded that a review of the energy consumption of air-conditioning systems in an additional cycle is advisable and that through the assessment of the air-conditioning the development and sale of energy efficient facilities could be encouraged (TÜV Nord / BASt FE 84.0501 / 2010, p 65).

The Swiss Federal Laboratories for Materials Testing and Research (EMPA) calculated the share of air-conditioning consumption of the total consumption based on numerous tests with cars of different classes. On average, the air-conditioning system contributes more than 5 percent to the total consumption of the vehicle. Many air-conditioning systems are unnecessarily switched on automatically, even at low temperatures. The EMPA pleads for technical changes, so that MAC systems only switch on at a temperature of 18 degrees Celsius (or when windows are steamed up). This could significantly reduce the additional consumption caused by the air-conditioning.

• According to the DAT (German Automobile Trust), the average mileage of a car in 2012 was almost 14,000 km.
• Pursuant to the German Federal Environment Agency an average car currently consumes about 7.5 liters.
• This results in a total fuel consumption of: 14,000/100 x 7.5 liters = 1,050 liters
• The additional consumption caused by air-conditioning has a share of 5.4 % (EMPA, see above): With the amount of fuel spent for this, one could cover the distance between Hamburg and Paris.
• During a vehicle lifetime of 12 years, the current fuel costs for an inefficient air-conditioning can increase by up to 800 euros compared to an efficient system.