1. single cycle system with hydrocarbons

pros:
* no ODP and no GWP
* high efficiency
* introduction into the market nearly at once possible
* low costs for the change of production lines
* refrigerant easy to refill
* no oil problems
* no trouble by penetrating water vapour
* no toxic potential
* no increased selling-price

cons:
* flammability
* subjective prejudices in spite of very low additional risk
* low chance for selling on the American market

solutions:
* two cycle system (see 3. and 4.)
* more information and objective testing
* introduction into the market for open minded customers
* installation of a safety evaporator with a little loss of efficiency

2. single cycle system with carbon dioxide

pros:
* no ODP and no GWP
* moderate efficiency
* natural refrigerant
* no flammability, no toxic potential

cons:
* high requirements for materials caused by high pressures
* operation in transcritical range => no use of evaporation enthalpy
* sightly greater space demand
* market introduction in 8-10 years at the earliest => no solution for the current environmental problems
* higher costs for the change of production lines
* refilling of refrigerant more complicated
* increased selling-price

solutions:
* considerable speeding of development

3. two cycle system with HCs and glycol/water

pros:
* no ODP and no GWP
* moderate efficiency
* no components containing flammable refrigerant in the passenger compartment
* nearly at once available
* only slightly more space as for 1. necessary

cons:
* cooling effect starts later as in single cycle systems
* lower efficiency as for 1.

solutions:
* change over to 4.

4. two cycle system HCs and carbon dioxide

pros:
* no ODP and no GWP
* good efficiency (better as 3.)
* no components containing flammable refrigerant in the passenger compartment
* cooling effect starts earlier as in concept 3.
* no movable parts in the second cycle
* in short time available

cons:
* greater space demand as in concept 3.
* slightly higher selling-price

5. cold air system with expander

pros:
* no ODP and no GWP
* easy handling of refrigerant
* considerably improved efficiency by use of the expander
* no closed unit under high pressure
* only one phase change

cons:
* research and development necessary
* real efficiency unknown (amount of friction losses ?)
* greater space demand for heat exchanger

solutions:
* development of smaller expanders with good efficiency
* efficiency testing necessary