MD 15116 - 2006 Computer Room Air-conditioning Systems

Chapter 5 - Measurements During Commissioning

5.1 General

Standard wall-mounted temperature and humidity sensors are generally inadequate for ensuring adequate cooling of computer rooms. This is because the electronic equipment performs correctly only when required environmental conditions are maintained at the inlet to the equipment. Simply maintaining the room temperature at the required value will not ensure proper cooling, especially in today's high-density computer racks. For example, if the computer manufacturers require 21 deg.C at the inlet to the rack for proper operation, then a supply air temperature of 21 deg.C may lead to equipment failure, due to localized overheating. Localized humidity conditions may also cause problems, even if the wall sensor indicates the correct value. Hence, temperature and humidity measurements at various points in the computer room are required to ensure proper operation. Three types of tests and measurements should be performed:

  1. Facility health and audit tests.
  2. Equipment installation verification tests.
  3. Equipment troubleshooting tests.

The user should perform the appropriate type of test that best fits the application, following the recommended procedures in ASHRAE Thermal Guidelines for Data Processing Environments, latest edition.

5.2 Facility Health and Audit Tests

5.2.1 bjective

These tests are required to proactively determine the health of the facility, to prevent any potential equipment failures. They should be performed on a regular basis.

5.2.2 Measurement locations

Temperature and humidity measurement locations should be established on each aisle that has equipment air inlets, using the following guidelines:

  1. Establish at least one measurement point for every 3-9m of aisle.
  2. Locate measurement points midway along the aisle, centred between equipment rows.
  3. The measurement points should be located at the appropriate height based on the type of electronic equipment, and the manufacturers' recommendations. A typical height may be 1.5 m.
  4. Where hot aisle/cold aisle configuration is used, measurement points are required only in the cold aisle.

5.2.3 HVAC Operation

Record operating status of the HVAC unit (including fan status), fan speed, supply air temperature and humidity, return air temperature and humidity.

5.2.4 Evaluation of Results

Any temperatures and/or humidity levels outside the recommended operating range should be identified, documented, and, investigated. Possible corrective action should be taken including air balancing, or modification of the cooling system.

Temperature and humidity at the HVAC should be within the design range. If the return air temperature is significantly below the ambient temperature, possible short circuiting of the supply air should be investigated, and corrective action taken.

5.3 Equipment Installation Verification Tests

5.3.1 Objective

These tests are required to verify that the equipment is correctly installed, and that the bulk temperature and humidity conditions at the entrance to the equipment rack are within acceptable limits.

5.3.2 Measurement Locations

  1. Locate measurement points at the geometric centres of the air intakes for the top, bottom, and, middle rack servers for each rack assembly, if there are three or more servers.
  2. Locate measurement point at the geometric centre of top and bottom rack servers, if there are only two servers.
  3. Ensure that the measurement points are 50 mm away from the racks.

5.3.3 Evaluation of Results

  1. All temperature and humidity readings should be within the acceptable environmental limits prescribed in Section 2.
  2. If any readings fall outside these limits, take corrective action such as air balancing, and/or changes to the cooling system.
  3. If corrective action is not readily possible, evaluate the risks in consultation with the equipment manufacturer.

5.4 Equipment Trouble-shooting Tests

5.4.1 Objective

These tests are required after equipment failure has occurred, to determine whether the failure could have occurred due to inadequate environmental conditions, such as excessive temperature at the air inlets to the equipment.

5.4.2 Measurement Locations

  1. Locate at least three measurement points across the entire air intake to the equipment, at a distance of 50 mm from the rack server.
  2. Use a larger number of measurement points for larger servers, the objective being to cover the entire air intake.

5.4.3 Evaluation of Results

  1. If all the measurements fall within the acceptable environmental limits, the failure is most likely not the result of inadequate HVAC system and consultations with the equipment manufacturer may be required to determine the cause of failure.
  2. If some readings are outside the acceptable limits, then modifica-tions to the HVAC system may be required.

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