MD 15116 - 2006 Computer Room Air-conditioning Systems
Chapter 4 - Computer Room A/C Equipment
4.1 Selection of A/C equipment
The following types of A/C units are acceptable:
- Refrigerant cooled units with either air-or liquid-cooled condensers. The units may be of the up-flow or the down-flow type.
In the up-flow units, the supply air may be discharged directly into the computer room, or discharged into the ceiling space from which it will enter the computer room from ceiling diffusers.
In the down-flow units, the supply air may be discharged into the space below the raised floor from which it will enter the computer room through perforated grilles or diffusers.
- Chilled water/glycol units with remotely located air/liquid cooled chiller units. The units may be of the up-flow or the down-flow type as described above.
See Appendix A Supplementary Material for more details.
4.2 Functional Requirements for Air Distribution
- Air may be returned directly to the A/C unit. Alternatively, the ceiling space may be used as a return air plenum with return grilles or small hoods located immediately over the heat-generating computer equipment.
- Supply air distribution should be carefully designed to eliminate drafts and cold spots in the computer room.
- When using under-floor plenums, adequate clearances should be provided within the raised floor cavity, to achieve uniform air flow.
- If under-floor air distribution is employed, turbulence of supply air discharged into the space below the raised floor should be minimized by the use of turning vanes.
- Floors and floor panels should be properly sealed. The walls under the raised floor should also be sealed properly.
- Ducting serving other areas of the building should not pass through the computer room. If this is absolutely necessary, the ducts shall be completely enclosed in membrane having the same fire rating as the computer room enclosure.
4.3 Functional requirements for A/C units
- The A/C units should be designed for dry coil operation i.e. there should be no condensation at the coil. Whenever condensation occurs, an energy penalty is imposed, due to the change of state of water vapour. See Appendix A for more details.
- The A/C units shall be designed to prevent simultaneous humidifica-tion and dehumidification.
- The A/C system should be designed for highest energy efficiency.
- All cooling systems should incorporate capacity controls so that refrigeration load matches the cooling load.
- Reheat shall be provided only in those cases where de-humidifica-tion is required. If operation is in the "dry coil" mode, then de-humidification would not normally be required.
- The system should be designed for year-round cooling.
- Computer room applications are often mission critical. For example, a computer room may process sensitive data for a number of Government departments, and any interruption, even for a few seconds, could lead to the loss of sensitive data. In such cases, standby air-conditioning systems should be provided. Standby equipment should be used on a regularly scheduled basis, to ensure operational readiness at all times.
- Heat recovery from the computer room A.C. system should be considered, including the following options:
- Free cooling
- Heat recovery from condensers/ dry coolers, used for heating of domestic hot water
- Recovery heat from condensers/dry coolers used for heating outside air
However, the addition of heat recovery systems should not reduce the performance, or reliability, of the A/C equipment.
- Liquid leak detectors should be installed in the space below the raised floor to detect any fluid leakage.
- Hub or funnel drains should be installed adjacent to each A.C. unit complete with deep seal trap, and, trap primer connected to a suitable water source.
- The computer room should be reasonably airtight to minimize the quantity of outside air required to maintain positive pressure within the space. Doors should be tight fitting and gasketted. If necessary, air locks shall be provided.
- The computer room should be enveloped in a good vapor barrier to reduce moisture migration and structural damage. Computer rooms in areas where the winter outside design temperature is 0°C or lower should be located in the interior zone of the building and away from outside walls, roofs and floors. Cables and piping passing through the vapor barrier should be properly sealed and caulked.
- Minimum clear space below raised floors should be 300 mm.
- The A/C system shall be designed such that the airflow patterns match the equipment placement requirements. See ASHRAE Thermal Guidelines for Data Processing Environments, latest edition, for more details.
- Temperature/humidity alarms should be provided within the computer room, and connected to the building automation system.
4.4 Fire Protection
- Single-interlocked preaction fire suppression systems should be used for computer rooms.
- A Fire-protection system using halon should not be used.
- All fire protection systems should be constructed in compliance with applicable Codes and applicable Treasury Board and/or HRSDC guidelines.
Also, refer to Appendix B: Fire Protection, for more details.
4.5 Servicing Requirements
Provisions for servicing of computer room A/C units should be included during the design phase of the project. These provisions should include:
- Selection of equipment with a view to durability, reliability and maintainability.
- Easy access to all components requiring servicing.
- Selection of the most efficient point of operation.
Servicing facilities should include:
- Uninterrupted availability of service during the hours and days of the week specified in the project brief.
- Local servicing facilities stocked with a complete range of computer room A/C unit components.
- Local servicing personnel trained and qualified by the computer room A/C unit manufacturer.
- Security classification clearance requirements that must be satisfied to gain access to the computer room.
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