MD 15116 - 2006 Computer Room Air-conditioning Systems

Chapter 3 - Design Cooling Loads

3.1 Heat Load due to IT Equipment

Heat gains from computer equipment are highly concentrated and non-uniform within the space.

The heat gains in computer rooms have increased rapidly with time, as computer hardware has become smaller and more powerful, resulting in higher equipment density. Data centres are also being designed for longer life spans of 15 years or more, and allowance has to be made for increases in cooling load of the facility during its life span. A minimum spare capacity of 25% should be provided to allow for future expansion.

Heat gains should not be based on nameplate values, as these are generally misleading and imply higher levels of power consumption and heat dissipation than will actually occur. The purpose of a nameplate rating is primarily to indicate the maximum power draw for safety and regulatory approval. Very often, manufacturers provide excess capacity in the power supplies to allow for future product enhancements and upgrades.

Heat loads should be based on manufacturers' data. We recommend obtaining a "Thermal Report" from the equipment manufacturers, in a standardized format. The report should include at least the following information:

  1. Indication of several equipment configurations, for example a minimum configuration, a full configuration and, a typical configuration.
  2. Description of each configuration.
  3. Dimensions and weight for each configuration.
  4. Steady state heat release, in watts, for each configuration, at an ambient temperature range of 20-25 deg.C.
  5. Maximum airflow for each configuration, in cu.m./h at 35 deg.

An example of a thermal report is given below:

Table Summary

Table showing an example of a thermal report with minimum, maximum and typical configurations. Column headings are titled: dimensions, typical heat release watts, nominal airflow, maximum airflow and weight (kg).

Table 1 Sample Thermal Report
Company Name: ABC Company
Product: XYZ Server
Configuration Description Dimensions Typical Nominal Maximum Weight
    (WxDxH) Heat release Airflow Airflow kg
    mm Watts cu.m/h cu.m/h  
Minimum 1 CPU-A, 1GB, 2I/ 764x1016x1828 1765 680 1020 406
Maximum 8 CPU-B, 16GB, 64 I/ 1549x1016x1828 10740 1275 1913 693
Typical 4 CPU-A, 8GB, 32 I/ 764x1016x1828 5040 943 1415 472
Air flow pattern Front to rear          

The equipment layout design team should decide which configuration shall be used, and determine the equipment heat load based on the thermal report from the manufacturer. In most cases, the "typical" configuration would be appropriate, but some designers may want to use the "maximum" configuration, depending upon the requirements for the project.

3.2 Lighting Loads

Lighting levels will generally be the same as for office spaces, as detailed in PWGSC/PSPC Federal Office Building Standards. The actual lighting loads should be followed for design.

3.3 People Load

People load will be based on the occupancy requirements for the computer room. In general, the occupancy will be much lower than for office spaces. Heat generation per person should be calculated using ASHRAE Fundamentals Handbook.

3.4 Building Envelope Heat Gains

In general, computer rooms should be located in interior spaces, so that there is no heat transfer through the building envelope. However, large data centres may be housed in a separate facility, and heat gains from the building envelope should be considered in the design of the air-conditioning system.

3.5 UPS Systems

Heat gains from the UPS/Battery system should be considered, if it is served by the same air-conditioning system as the computer room. In addition, the ventilation requirements for the UPS/Battery system should be considered.

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