Estimation and Analysis of Refrigeration Capacity of Air Conditioning System in Data Center

All electronic equipment generates heat, and in order to prevent the temperature of the equipment from rising to an unacceptable level, the heat must be diffused away. Most IT equipment and other equipment in data centers or network rooms are cooled by air. In order to determine the capacity of the refrigeration system, it is necessary to understand the heat generated by the equipment in the enclosed space and the heat generated by other common heat sources.

Determine the calorific value of the entire system

The total calorific value of a system is equal to the sum of the calorific value of all its components. The entire system should include IT equipment and other items, such as UPS, power distribution systems, air conditioning units, lighting facilities and personnel. However, the calorific value of each item can be determined according to simple standard rules.

The heat generation of the UPS and the power distribution system is composed of two parts: one part is a fixed loss value, and the other part is proportional to the load power. For different brands and models of equipment, the heat loss of these two parts can be considered to be the same, so their calorific value can be estimated more accurately. The heat generated by lighting facilities and personnel can also be estimated using standard values. To determine the thermal load of the entire system, only some easily obtained numerical information, such as the floor area (square feet) and the rated power of the power system, etc.

The fan and compressor of the air conditioner will generate considerable heat. However, most of this heat will be released to the outside of the room, and will not bring heat load to the inside of the data center. But it will reduce the efficiency of the air conditioning system, so it is usually necessary to consider when determining the power of the air conditioning system.

You can use the calorific value of each item in the data center for a detailed calorie analysis, but there is a faster method that uses simple rules to estimate, so that the results obtained are not much different from the results of complex analysis. The advantage of this rapid estimation method is that anyone who does not have any professional knowledge or has not received professional training can do the job.

Table 1 is a data table for quick calculation of heat load. Using this data sheet, the total heat load of the data center can be quickly and reliably determined. The method of using this data sheet is shown in the calculation steps after Table 1.

Table 1-Data Sheet for Calculation of Heat Dissipation in Data Center or Network Room

Estimation and Analysis of Refrigeration Capacity of Air Conditioning System in Data Center

calculation steps

First collect the information required in the "Required Data" list. If in doubt, please refer to the data definition below. Then calculate the calorific value and fill the result into the "calorific value classification summary" list. Add up the various summary items to get the total calorific value.

Data definition

IT equipment total load power (W)-the sum of all IT equipment power input power.

Power system rated power—The rated power of the UPS system. If a redundant system is used, do not include the power of the redundant UPS.

Typical system example

The following uses a typical system as an example to explain how to calculate the calorific value. The system is a data center with an area of ​​5,000 square feet (465 square meters) and a rated power of 250kW, with 150 racks and a maximum of 20 people. In this example, the power load of the data center is assumed to be 30% of the rated power by convention. In this way, the total load power of IT equipment in the data center is 30% of 250kW, or 75kW. Under the above conditions, the total heat generation of the data center is 108kW, which is about 1.5 times the load of IT equipment.

Please note that since the system only works at 30% of the maximum power, the estimated proportion of UPS and power distribution system in the total heat output is higher than its actual value. If the system is running at full load, the efficiency of the power system will increase, and its proportion in the total system heat will decrease. If the system is over-planned, it will pay a high price for greatly reduced efficiency.

Other heat sources

The above analysis did not consider the heat sources in the surrounding environment, such as the sunlight shining through the window and the heat conducted from outside the wall. Many small data centers and network rooms are not exposed to outdoor walls or windows, and it is correct to disregard the above heat source. However, for large data centers where walls or roofs are exposed outdoors, additional heat enters the data center, and the air conditioning system must remove the heat.

If the data room is located in an enclosed space with air conditioning equipment, the effects of other heat sources are negligible. If the data center has a large area of ​​walls or roof exposed outdoors, you need to ask an air-conditioning expert to estimate the maximum heat load, and then add this value to the heat generation of the entire system determined in the previous section.

Humidify

In addition to heat exchange, the data center air conditioner should also be able to control the relative humidity of the room. Under ideal circumstances, when the required relative humidity is reached, the system will work in air with a stable moisture content, at which time there is no need for continuous humidification. Unfortunately, in most air-conditioning systems, the air cooling function causes a large amount of water vapor to condense, which makes the relative humidity of the air insufficient. Therefore, compensatory humidification is required to maintain the required humidity.

Compensating humidification will bring additional heat load to the air conditioning system, which actually reduces the cooling capacity of the air conditioning system, which needs to be considered when designing the capacity.

For small data rooms or large wiring closets, the air-conditioning system isolates the supply and return air through pipes, which will not cause condensation, so no need for continuous compensating humidification. In this way, the cooling capacity of the air conditioner can be fully utilized to maximize the cooling efficiency.

For large data centers with a large amount of mixed airflow, the air conditioning system must provide cooler air to counteract the impact of the hot air released by the equipment. This will result in a significant reduction in the relative humidity of the air, which requires compensatory humidification. This greatly affects the performance and cooling capacity of the air conditioning system. Therefore, when determining the cooling capacity of the air conditioning system, it must be increased by 30%.

In short, when estimating the cooling capacity of the computer room air conditioning system, it needs to be increased as appropriate: if it is a small system that isolates the return air through the pipeline, there is no need to increase; if it is a system with a high degree of indoor air mixing, it needs to be increased by 30%.

Determine the cooling capacity of the air conditioning system

After specifying the cooling requirements, the cooling capacity of the air-conditioning system can be determined. As mentioned earlier, the following factors need to be considered during this process:

Thermal load of equipment (including power equipment)

Conducted heat load of building

Consider the additional heat load required for humidification

Additional thermal load required to support redundancy

Additional heat load required in the future

The sum of the heat loads (W) of all these factors is the total heat load.

in conclusion

When determining the cooling requirements of an IT system, a simplified process can be used, and anyone without specialized training can do the job. Using a unified watt unit for power and cooling capacity helps simplify this process. In general, the rated power of the computer room air conditioning system must be 1.3 times the sum of the expected IT rated load and redundant load. For small network rooms with an area of ​​less than 4000 square feet (372 square meters), this method is applicable.

For larger data centers, other factors besides cooling requirements are usually considered when choosing an air conditioning system. Generally speaking, the influence caused by other heat sources such as walls and roofs and the return of air cannot be ignored, and must be considered for specific situations.

The design of ventilation ducts or raised floors has a greater effect on the overall system performance and also significantly affects the temperature uniformity in the data center. The use of simple, standardized, and modular air distribution system structures, as well as the simple heat load estimation method introduced in this article, can greatly reduce the engineering design requirements in the data center design process.

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