Precise air supply lays the foundation for energy saving in the computer room

For a long time, the ambient temperature of the computer room has determined the working condition of the equipment. Whether the ambient temperature of the computer room is qualified reflects the construction and maintenance level of a computer room, but whether the ambient temperature of the computer room can be adjusted in the precise air supply mode has caused controversy in the industry.

The basis for setting the ambient temperature of the equipment room

Traditional computer room air conditioning air supply mode

Traditional network cabinets adopt the design principles of traditional communication equipment cabinets, which are based on two prerequisites: first, the power of the equipment in the cabinet is not large, generally below 1kW; second, it must be compatible with both top and bottom airflow organizations, as shown in Figure 1(a). Therefore, this type of cabinet has the following characteristics:

1. The upper and lower openings ensure that the airflow organization can be formed when the machine room adopts downward air supply;

2. A large number of mesh holes are opened on the front and rear panels to ensure that the airflow organization can be formed when the upper air supply is adopted in the computer room;

3. The server inside the cabinet can be ventilated up and down all around, which helps air flow.

As for the upper air supply method, see Figure 1(b) for details. It is actually a mixed air supply and return method. The air outlet of the ceiling duct on the aisle delivers cold air to the cabinet, and the hot air discharged by the equipment must also be returned to the air conditioning equipment from the cabinet top space or the pedestrian aisle. In the cabinet aisle or the cabinet top space, cold and hot air are mixed, and each point may be a cold and hot air neutralization area, resulting in a high overall ambient temperature in the computer room.

For the downflow air supply method, see Figure 1(c) for details. Although the cold air comes out from the bottom of the cabinet, since the cabinet is not sealed at all, a considerable amount of cold air still leaks from the cabinet to the aisle or the top space and flows back to the air conditioning equipment. Since the downflow air outlet does not have the ability to adjust the air volume, the cold air flowing out of the low-power cabinet also directly returns to the air conditioning equipment, which is essentially a waste.

Indicators and measurement methods of ambient temperature in traditional communication rooms

The latest revised computer room standard: Class A communication room: 10℃～26℃; but IDC room: 20℃～25℃ (cited from YD/T1821-2008 "Environmental Condition Requirements for Communication Center Computer Rooms").

Foreign communication room environment standards:

Optimal temperature conditions: 21℃～23℃; usable temperature conditions: 10℃～32℃.

Indicators and measurement methods of ambient temperature in traditional communication rooms

The computer room environment is a broad concept. In a large computer room filled with cabinets, the air temperature at each point is different. Therefore, what temperature does the ambient temperature refer to? This is also a question that must be clarified. According to relevant communication standards, the ambient temperature can be measured according to the following regulations.

1. Test equipment: mercury thermometer/ electronic thermometer, etc.;

2. The distribution of test points is shown in Figure 2

Note: Measuring point positions 2, 3, 4, and 5 should all be selected near the center points of A~1, B~1, C~1, and D~1.

3. The temperature of the equipment room should be tested 1 hour after the equipment has been operating normally;

4. The measuring point should be selected at a height of 2m from the ground, 0.4m away from the equipment, and away from the air outlet and return outlet;

5. The data at each measuring point is the actual measured temperature of the room, and each point should meet the specified requirements.

Temperature formation mechanism of measuring points in traditional equipment rooms

Taking the traditional upward air supply room with uniform cabinet orientation as an example, the cold air blown downward from the cold air outlet 2.5 to 2.8 meters above the aisle forms a hemispherical surface. As the air delivery distance increases, the spherical surface gradually increases. As can be seen from Figure 3, according to the usual temperature of 35°C for the hot air discharged from the back of the cabinet and 15°C for the cold air delivered by the duct, and assuming that the amount of hot and cold air in the aisle is basically equal, the air temperature in the cabinet aisle after the cold and hot air are neutralized is 25°C, which is a typical site with a relatively qualified ambient temperature in the computer room.

Precise air supply mode for IDC equipment room

The use of traditional air supply mode in large IDC computer rooms not only fails to solve the equipment cooling problem, but also results in huge energy waste. The industry now proposes a precise air supply mode.

Basic principles of precise air delivery

Since the equipment in each cabinet in the IDC room generates a lot of heat, the equipment cooling problem cannot be solved without sufficient cold air entering the cabinet. In order to solve this problem, China Telecom's "Technical Specifications for Data Network Cabinets" defines the principle of precise air supply:

1. Transport cold air into the cabinet: because the equipment inside the cabinet needs cold air.

2. Transport cold air to the front of the cabinet: because cold air can only enter the server chassis from the front of the server to play a cooling role.

3. Accurately adjust the air intake of each cabinet: Because the heat generated by the equipment in the cabinet is different, the required cooling capacity is also different.

4. Prevent the cold air in the cabinet from losing freely: Because only the cold air that enters the server can truly play a cooling role, the cold air should be gathered in the front space of the server.

Structural and functional requirements for cabinet types with different airflow organizations

Precision air supply can be divided into bottom air intake and top air intake. The structure, function and airflow organization layout of bottom air intake cabinet and top air intake cabinet are shown in Figure 4. The bottom air intake means opening an air inlet with adjustable air volume at the bottom of the cabinet to transport the cold air under the raised floor to the special cold air channel in front of the cabinet without loss; the top air intake is basically the same as the bottom air intake in terms of airflow organization principle, the only difference is that the air inlet is set on the top of the cabinet.

The advantage of the precise air supply method is that it can deliver cold air at a fixed point and in a fixed quantity, as shown in Figure 5, which greatly reduces the waste of cold air. More importantly, the precise air supply method can completely separate the cold and hot air flow channels, which to some extent subverts the concept of the traditional room ambient temperature.

Feasibility of adjusting the ambient temperature of the computer room under the precise air supply mode

Under precise air supply conditions, cold and hot air flow separation channels are established, and the cold air channel is directly related to the operation of the cabinet equipment.

In a computer room that uses precise air supply, when cabinets are arranged face to face or back to back, the face-to-face aisle is a cold aisle with a relatively low temperature, while the back-to-back aisle is a hot aisle with a higher temperature. There will be a large temperature difference between the hot and cold aisles, and it is necessary to deal with the hot air return and hot and cold balance in the cabinet environment. A more feasible measure is to install a return air duct or a return relay fan above the hot aisle to increase the air return speed of the hot aisle; add some ventilation holes on the elevated floor of the hot aisle to allow part of the cold air to flow out and neutralize the hot air in the aisle, thereby improving human comfort.

The application of precise air supply has changed the formation mechanism of the traditional computer room ambient temperature, which can not only improve the heat dissipation and cooling effect of the equipment in the computer room, but also create favorable conditions for air conditioning energy saving. However, there is a lot of related work to be done to improve the ambient temperature index of the computer room, especially the impact of human comfort and the problem that batteries cannot tolerate high temperatures must be properly solved. Otherwise, blindly increasing the ambient temperature of the computer room may not necessarily achieve the desired ideal results.