general remarks

Mobile air conditioning systems have a considerable share in the manmade influence on the climate due to their number and the amount of refrigerant. It is calculated that the number of cars with mobile air conditioning systems is increasing and will further increase rapidly. Especially in Europe the share of new cars with air conditioning now at 20-30% of all new passenger cars will increase to more than 90% like the actual amount in Japan and USA. In our opinion in Central Europe air conditioning systems in passenger cars should only be used in health depending cases. In other climate zones such as South America or Australia the situation is different. At any rate we should in our very own interest use the system with the least additional energy demand and with the least dangerous potential for the environment. That a halving of fuel demand for passenger cars is possible Greenpeace has shown. This must be required too of all passenger cars with mobile air conditioning. If an air conditioning system is necessary it has to be the most energy efficient and environmentally friendly unit. Nowadays that is not the case. So it is logical to change this state. The alternatives listed in this paper by Greenpeace shall help to gain this aim as soon as possible.
[return]

1. mobile air conditioning system consisting of one cycle with hydrocarbons

The one cycle systems with hydrocarbons are without official announcement in use in many countries as drop-in-systems. The main obstacle for change of the production lines to hydrocarbon systems is the flammability of the hydrocarbons and subjective prejudices. All other characteristics predestine this system - if it is really necessary - for use in passenger cars. Objective survey and the inconspicuous behaviour of the used drop-in-systems show that the additional risk caused by the flammability of the hydrocarbons is very small when used in passenger cars. The greatest risk potential would arise if refrigerant penetrates into the passenger compartment. Therefore the evaporator in the eyes of the experts of the German technical testing association should meet tighter testing conditions (proposed testing procedure: 1. vacuum, 2. testing at 40 bar, 3. vacuum). Permanent tightness of all parts of the plant, which are installed in the passenger compartment, is an additional requirement for acknowledgement by the safety experts. This applies to competent soldered and welded connections of the evaporator, the only refrigerant containing part in the passenger compartment. Furthermore the requirements of the national safety regulations (in Germany VBG 20 and VBG 61) must be met. The installation of magnetic valves on either side of the evaporator, which would detach him in case of a leakage, are not absolutely necessary but possible. Another safety device represents the so called safety evaporator with tube in tube technique. He has the side-effect to reduce the efficiency.

To test the real effectiveness and necessity of the mentioned safeguarding measures would require the mutual examination of a representative prototype by safety experts and producer. A strategy for fast introduction into the market would be to rearrange the production line of an European facility. Here one can expect the greatest acceptance of the customer and a great rate of increase. To wait out the amortisation time for the change of the production lines to R134a or considerations for business relations can not be justified. They can not be an obstacle to this new offer for responsible customers.
[return]

2. mobile air conditioning system consisting of one cycle with carbon dioxide

Caused by the low critical temperature of carbon dioxide it can only be used in transcritical processes in mobile air conditioning systems. After compression the gas can not as usual condense. On the high pressure side of the system very high pressures are reached. The problem to find reliable sealing is not jet solved. The available sealings are not suitable for long time use. The necessary system components differ from the parts commonly in use. For many a new design is necessary. Measurements to find the optimal cooling oil are due. If the refrigerant losses in operation can not considerably be reduced frequent maintenance intervals are inevitable. Moreover it is not definitively clear that under all circumstances the risk of suffocation can be excluded. There is still a considerable demand for research and development, which will according to the industry, need a time period of eight to ten years. It is questionable weather greater financial input can lead to a substantial reduction and weather all problems can be solved. As a means to limit the urgent effects of the increasing number of mobile air conditioning systems on the environment this carbon dioxide system will possibly not be in time.
[return]

3. mobile air conditioning system consisting of two cycles with hydrocarbons and glycol/water respectively [GIF, 29k]

A second cycle with liquid refrigerant enables the use of the advantages of an effective vapour compression air conditioning system with hydrocarbons without having a hydrocarbon containing part in the passenger compartment. The second cycle is connected by a heat exchanger with the first one and the liquid refrigerant is transported by a centrifugal pump. This two cycle system is like the one cycle system with hydrocarbons nearly at once available. The additional components must be inserted into the available space. The energy demand will be slightly higher than in the one cycle system and nearly the same as in the carbon dioxide unit. Caused by the additional heat transfer and the necessary higher mass transport the cooling effect in the passenger compartment will start later as in the single cycle system.
[return]

4. mobile air conditioning system consisting of two cycles with hydrocarbons and carbon dioxide respectively [GIF, 75k]

This unit combines the advantages of the system concept No. 1 and No. 3 (high efficiency, no hydrocarbon containing part in the passenger compartment, soon available and others). The first circulation has a heat exchanger instead of the common evaporator. He is located directly below the bonnet. By way of the refrigerant of the first cycle, the hydrocarbons, the carbon dioxide in the second cycle will condense and is falling down into the evaporator on the bottom of the passenger compartment. In the tube system of the evaporator it becomes gaseous again, rises and reaches again the heat exchanger in the engine compartment. In the second cycle there are no movable parts and no sealing is necessary. the principle of operation is the same as in a heat pipe. After the first filling no maintenance is necessary for the second cycle. Due to the low viscosity and the phase change even of the second refrigerant the cycle is very effective and is fast lowering the temperature in the passenger compartment. The second cycle can be designed in a way so that a part of the carbon dioxide is stored in a collector and can cool the passenger compartment during a temporary standstill (e.g. in the sun).
[return]

5. cold air system with expander [GIF, 17k]

The principle of cooling with expanded air is well known. The most attractive characteristic is ist harmless behaviour towards men and environment and easy handling. In the interesting temperature range no phase change is possible and therefore the efficiency will be lower than with conventional vapour compression units. On the other hand we have an open cycle system with less phase changes and the opportunity of simultaneous cooling and air filtering.

Usually a cold air system consists of compressor, heat exchanger and expansion valve which lets the gas escape directly into the cooling compartment. If an expander with or better without a nozzle is used instead of the expansion valve the efficiency can be considerably increased. Thus part of the input energy necessary for compression is returned and the air is further cooled running through the expander. As expander among others there are possible roots blower, piston engines and turbines. Generally these engines are too large for the use in passenger cars. But there are some promising concepts which should be further developed. The practicability especially with regard to space and energy demand must still be tested. Concentrated work presupposed the period of development will be considerably less than eight to ten years.
[return]