Outdoor unit for the production of chilled water, equipped with semi-hermetic screw compressors, R513A refrigerant, axial-fans, condensing coil with copper tubes and aluminum fins, shell and tube evaporator single pass and electronic expansion valve. Base, supporting structure and panels are of galvanized epoxy powder coated steel. The unit is supplied with anti-freeze oil and refrigerant and has been factory tested. These chillers, fitted with free-cooling coils, are used when the cooling load is constant all-year-round or the outdoor air temperature is lower than the temperature of the liquid return line. In free cooling mode, the liquid is cooled by outdoor air, thus lowering the load of the compressors until it is reduced to zero; this occurs already at positive outdoor temperature (T+ versions and SL-T+). The NG configuration complies with applications where it is not allowed or desired the use of ethylene glycol.