The air-conditioning of telecommunication centers is generally characterized by an all year high cooling load and by low outside air requirements. Therefore a chance would exist for the inexpensive so-called "free cooling" by use of colder outside air during most of the operating time throughout the year, if the expenditure for the then necessary humidification would not soon exceed the saved-up expenditure for cooling. This paper describes a new technical and operational concept to overcome this disadvantage of "free cooling", which allows savings of operating costs for air-conditioning up to 75%.