Server Room Ventilation: Fresh Air and System Planning

Updated August 31, 2026 — English wording, readability and the equipment inlet temperature guidance reviewed. Original publication date retained.

Server room environmental planning includes temperature, humidity and airborne contamination. This article introduces fresh air ventilation considerations and the questions to discuss with the project designer when planning a server room system.

In the information age, the server room, as the core data center, occupies a pivotal position. High precision server room has very high requirements for the surrounding environment, such as temperature, humidity, power supply, etc. Of course, cleanliness is also one of the very important factors, once the internal dust is too much, it may lead to the problem of electrostatic discharge, which will damage the components and cause incalculable losses.

In order to solve this problem, in addition to the use of special precision air conditioning for the server room to ensure constant temperature and humidity, it is also necessary to supplement the fresh air to maintain the positive pressure difference between the server room and the outdoors, to maintain the cleanliness of the air and thus control the amount of dust in the air. Therefore, many large server rooms are installed with fresh air systems to achieve the purpose of protecting server room equipment.

After the installation of the fresh air ventilation system in the server room, there are two main roles

1, the fresh air ventilation system can be a source of outdoor air filtered and purified to the room, indoor and outdoor ventilation, oxygen rich, clean air, more conducive to the physical and mental health of the staff inside the room.    

2, the room installation of fresh air system, can effectively filter and purify the air outside the room, so that the air delivered to the room is clean and fresh, without any impurities, effectively solving the problem of static electricity caused by impurities inside the room.

To ensure the cleanliness of the server room, temperature and humidity should meet the following requirements:

For air-cooled IT equipment in ASHRAE environmental classes A1–A4, the recommended equipment inlet air temperature range is 18–27°C. Specific temperature and humidity conditions should follow equipment manufacturer requirements and the standards applicable to the project, while avoiding condensation. This is an equipment inlet temperature recommendation, not a universal room temperature requirement or a direct equivalent of the Grade A/B classifications used in older references.

Reference: ASHRAE Handbook — Data Centers and Telecommunication Facilities, Table 1.

Relative humidity 45%-65% (Class A) 40%-70% (Class B)

Grade A server room temperature change rate <5℃/h and no condensation;

The rate of change of temperature in the class B server room <10℃/h and shall not condense;

The concentration of dust in the air in the mainframe room shall be less than 18,000 dust particles per liter of air greater than or equal to 0.5μm when tested under surface conditions.  

Fresh air system solution for the server room:

The form of airflow organization in the server room should be considered in conjunction with the computer system requirements and building conditions. The air duct and air outlet position of the new exhaust system should be reasonably laid out with the air conditioning system and indoor structure, and the air volume should be determined according to the size of the air conditioning air supply and the number of operators in the server room, and the general value of the new air volume per person is: 50m3/h. The new air ventilation system can be installed by ceiling type or cabinet type unit, and the two-way independent circulation of new air and dirty air is carried out through the air duct. Fire system linkage, but in the event of a fire accident, it can automatically cut off the fresh air intake.

The working principle of the fresh air system in the server room:

Working principle: When the indoor air conditioning return air and outdoor fresh air are in a positive cross way by the heat exchanger, due to the difference in temperature and water vapor pressure difference between the airflow on both sides of the flat partition, the heat transfer between the two airflows is generated at the same time, causing a total heat exchange process. When the full heat exchanger installed on the system in summer operation, the new air from the air conditioning return air to obtain cold, so that the temperature is reduced; at the same time by the return air dry, is the new air from the air conditioning return air to obtain heat, so that the temperature rises, while the return air humidification.

Do I need both an air conditioner and a fresh air ventilation system in my server room?

Yes. The purpose of regulating the temperature is to make the equipment inside the room work in the right temperature range. The role of the fresh air ventilation system is to ventilate the room, mainly to maintain the freshness of the air in the room, which has certain benefits for the machine and the people working in and out of it.

What is the standard of air supply for fresh air in the server room? How many cubic meters per person per hour?

The design specification of fresh air volume in the server room requires

(1)The cleanliness of the class A server room is 300,000, and the cleanliness of the class B server room is 200,000.

(2)The fresh air volume per person should be 40～60m³/h.

(3) The standard number of air circulation in the server room should be greater than 2 to 3 times/h.

(4)5% of the total circulating air volume in the room.

(5) The air volume required to maintain positive indoor pressure.

The fresh air system in the server room plays a vital role in the normal operation of the equipment, after all, high-end equipment in the server room is expensive and difficult to maintain, only a certain amount of maintenance in the early stage to maintain constant temperature and humidity and reduce the invasion of dust particles, in order to reduce the occurrence of server room failures, so that a variety of information equipment and servers in the server room play a strong role in creating more value, but also for the server room personnel to create a healthy working environment.