About Measuring Air Flow - Data Warehouse Appliances

2750 Platform Product and Site Preparation Guide

Data Warehouse Appliances
March 2018
Product Guide
For environmental evaluation, you may need to measure air flow rates of conditioned air entering a computer room through openings that include:
  • Vented floor tiles, including both perforated tiles (typically having an overall opening area of approximately 20%), and grate tiles (typically having an overall opening area greater than 50%)
  • Floor tiles with unblocked openings (such as cable cutouts)
  • Cold air diffusers in overhead cold air delivery systems
Two methods for measuring air flow rate through these openings are:
  • Using an Alnor meter
  • Using an air flow meter and a handmade air capture hood

The Alnor flow rate meter is a specialized instrument that can be used to directly measure air flow rate. It has an air capture hood, and is instrumented to measure air flow rate in m 3/s or ft 3/min. However, the Alnor meter is relatively expensive and lacks portability, even when folded.

A cost-effective and portable method to get reasonably accurate air flow rate measurements is to use a digital air velocity meter and a handmade cardboard air capture hood.

When using an air capture hood of the dimensions specified in Measuring Air Flow Rate Using an Air Flow Meter and Handmade Air Capture Hood, and an air velocity meter set to feet per minute (fpm), the flow rate in cubic feet per minute (CFM) is the velocity reading in feet per minute (fpm). The calculation is straightforward because the top opening area is exactly one square foot (ft 2).

Because any air capture hood restricts air flow to a certain extent, thus introducing air flow impedance and associated measurement errors, an instrument calibration is required to ensure measurement accuracy. The following correction table is the result of calibration with the hood of the preferred dimensions. If a hood of different dimensions is constructed and used, a new calibration will be required.
Air Flow Velocity (ft/min) Flow Rate (ft 3/min or CFM) Correction Factor
< 200 1.10
< 400 and > 200 1.18
< 600 and > 400 1.25

For example, if air flow velocity measured with an air capture hood of the preferred dimensions is 250 ft/min, the actual flow rate is estimated to be 250 x 1.18 = 295 CFM.

If the opening is too small for a hood of the preferred dimensions, flow rates can be estimated by measuring the flow velocity and multiplying it by the open area.

To derive flow rates using units other than CFM, use the following conversion table.
From Unit To Unit Multiply by:
CFM m 3/s 1/2119
CFM m 3/hr 1.69

For detailed information on the recommended flow meter, the dimensions and fabrication of the hood, and the correction factor, contact your local Teradata Regional Technical Specialist (RTS), Teradata Customer Support, or Teradata Engineering.