METRIC DESIGN GUIDE
Pressure. While the English system has pounds per square inch (psi), pounds per square
foot (psf), tons per square foot (tons/SF), inches of water (inHO), inches of mercury
2
(inHg), and kips/SF, the SI metric system has only one pressure unit, the pascal (Pa). If
more than 1 000 Pa are present, the kilopascal (kPa) is used. If more than 1 000 000 Pa, the
Megapascal (MPa).
tons, boiler hp, and other units. SI uses only W, kilowatts (kW), or milliwatts (mW),
depending on the size of the number. An example of metric simplicity:
If an additional light fixture produces 600 W of heat, how many additional Btu's of
cooling are needed to prevent a room temperature rise? Exactly how much will this
add to system requirements? This must be calculated when using English units.
In SI, all thermal power units are measured in W.
The fixture produces 600 W, so the net system capacity must increase by 600W.
Standards
See Standard for Metric Practice (ASTM E380), SI Guide for HVAC & R (ASHRAE), and
Handbook of Fundamentals (ASHRAE) for accepted units and conversion tables.
Summary
The American construction community is able to meet the metric conversion challenge in
Federal construction, and it is in our long-term strategic interest to do so. There will be
some initial effort involved, but close cooperation between the public and private sector
will allow the goals to be successfully met.
PBS-PQ260
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