With the improvement of electrical equipment integration degree, the increasing of equipment unit volume power density, also more and more strict control of the indoor temperature, room temperature control equipment, to ensure good indoor environment is becoming more and more important to the equipment room dedicated air cooling conditioning units. Precision air cooling systems have 24"365 full-year refrigeration, can reduce the indoor temperature effectively, and can introduce outdoor air to replace the wind, reduce the refrigeration system on time, according to the setting of indoor temperature and outdoor natural temperature difference between air section.