From heat to cold: rethinking standstill air conditioning

• A revolutionary concept for MAHLE’s parking coolers
• A powerful, engine-independent, and very quiet solution

The transportation of goods by road is one of the main pacesetters of today’s densely interconnected economy. The driver’s rest periods play a key role, because only well-rested drivers are able to fulfill the heavy demands of their job and get their freight to its destination safely and on time. This is particularly important during the warmer months. Overheated driver’s cabins are not conducive to restful sleep. However, interior air conditioning requires a great deal of energy, which is why diesel engines are often used for this purpose. This results in emissions, vibrations, exhaust fumes, and a high noise level during the night. In addition, this particular alternative is regulated by strict legislation (NIAC, no-idle A/C) in the USA, which will soon be introduced in Europe too.

Alternatives: functionally limited

There are currently two technical alternatives for powering the standstill air conditioning without using the combustion engine. One option is a purely electric compressor, and the other is a suitable diesel generator.

At present, neither system adequately fulfills the customers’ requirements. The disadvantages are evident: while an electrical system produces no local emissions or noise, it is restricted in terms of its maximum cooling performance and running time due to the limited capacity of the battery.

Powering the standstill air conditioning using a specially designed diesel generator solves the problems of insufficient running time and cooling performance, but significantly increases pollutant emissions, fuel consumption, and noise levels. Such units also require considerable maintenance.

MAHLE adsorption standstill air conditioning: a new concept

With its adsorption standstill air conditioning, MAHLE presents a completely new functional principle that eliminates the need for a mechanical compressor drive. It could more accurately be described as a thermal compressor, since the cold-generating process is driven by heat. Ideally, this can be provided by the existing fuel cabin heater.

In a sealed cylinder, methane—a natural refrigerant—evaporates and cools a coolant to approximately 5°C, which is then used to provide air conditioning to the cabin. It adsorbs in an activated carbon layer and heats this layer to around 40°C (waste heat). This utilization process continues until all the methanol adsorbs by itself—i.e., without external power. In the subsequent regeneration process, the activated carbon is heated to around 110°C (drive heat) and, as a result, the methanol is desorbed and condenses at around 40°C. The process then starts again from the beginning. During this regeneration, a second cylinder takes over the air conditioning, and the two cylinders alternate.

The advantages

The cycle of evaporation, adsorption, condensation, and desorption does not require a compressor or other moving components and is therefore low-wear and totally noise-free. The actual adsorption system can be housed in an add-on box and only requires an additional heat exchanger—e.g., on the outer wall of the cabin—where the process heat is dissipated until just above ambient temperature. In comparison to an electric, compressor-based solution, the adsorption-based standstill air conditioning offers the following advantages:

• Significantly higher maximum output under extreme conditions (+37 percent at 43°C in strong sunshine)
• Significantly longer running time under extreme conditions (+65 percent)
• Even longer running time under partial-load operation (+180 percent at 30°C with cloudy sky or at night)

However, the advantages are also evident when compared with systems that use a fossil-fueled generator:

• Less fuel consumption: −50 percent
• Considerably quieter
• Much more comfortable (no vibrations)
• Easier maintenance

Conclusion: longer service life, lower emissions

Demand for high-performance, clean NIAC systems with long running times is steadily growing. The adsorption parking cooler presented by MAHLE utilizes the existing onboard fuel cabin heater. The advantages of this innovation include its significantly longer service life, higher maximum output, low emissions, very quiet operation, and robust design.

About MAHLE

MAHLE is a leading international development partner and supplier to the automotive industry as well as a pioneer for the mobility of the future. The MAHLE Group is committed to making transportation more efficient, more environmentally friendly, and more comfortable by continuously optimizing the combustion engine, driving forward the use of alternative fuels, and laying the foundation for the worldwide introduction of e-mobility. The group’s product portfolio addresses all the crucial issues relating to the powertrain and air conditioning technology—both for drives with combustion engines and for e-mobility. MAHLE products are fitted in at least every second vehicle worldwide. Components and systems from MAHLE are also used off the road—in stationary applications, for mobile machinery, rail transport, as well as marine applications.

In 2017, the group generated sales of approximately EUR 12.8 billion with about 78,000 employees and is represented in more than 30 countries with 170 production locations. At 16 major research and development centers in Germany, Great Britain, Luxembourg, Spain, Slovenia, the USA, Brazil, Japan, China, and India, around 6,100 development engineers and technicians are working on innovative solutions for the mobility of the future.  

For further information, contact:

MAHLE GmbH
Christopher Rimmele
Pragstraße 26 – 46
70376 Stuttgart, Deutschland
Phone: +49 711 501-12374
Fax: +49 711 501-13700
E-Mail: christopher.rimmele@mahle.com