Patent ID: 6860114

Claim:
Transportable cooling unit for maintaining a transport volume at a defined temperature, comprising: a closed cooling circuit serially including a multi-stage compressor, a condensor, an expansion device and an evaporator arranged in said transport volume, a speed controlled electric motor driving said compressor, and a controller sensing a temperature present within said transport volume and controlling said electric motor so as to provide heating or cooling power demanded at said evaporator for maintaining said defined temperature and minimizing energy consumption, said controller operating said closed cooling circuit between a maximum possible heating power and a maximum possible cooling power in a sequence of different operational stages comprising a lowest operational stage and a sequence of at least two upper operational cooling stages, said controller operating said closed cooling circuit in each one of said upper operational cooling stages at a compressor speed related cooling capacity different from said compressor speed related cooling capacity in said other upper operational cooling stages, within said respective upper operational cooling stages said controller operating said electric motor in an uninterrupted mode and adjusting said cooling power provided by said closed cooling circuit by an essentially stepless speed control of said electric motor, said heating power is obtained in addition to cooling power by providing an inoperable mode of said condenser in addition to an operable mode of said condenser, and said controller operates said compressor in said lowest operational stage in an uninterrupted mode at low speed and operates said closed cooling circuit by changing between the operable and inoperable mode of said condenser according to respective mode intervals and adjusts said cooling or heating power by adjusting at least one of the parameters comprising speed of said compressor and duration of said mode intervals.