Thermal Ratings for boilers and chillers should be
Mechanical / HVAC
specified in even nominal MW or kW increments to the
largest degree possible:
Air Flow out of grilles and diffusers should be rounded
(Ex, 500 kW, 0.9 MW, 3.5 MW)
to even increments of 5 or 10 L/s, wherever possible.
Pipe Steel pipe (ASTM A53) and copper tube sizes
Ductwork (Round, Rigid) Most designers are showing
(ASTM B88) will not physically change by switching to
the metric system. They are now classified by new
nominal mm sizes.
Ductwork (Round, Flexible) Many designers are
showing flexible round duct in hard metric sizes, but
ASTM B88M, hard metric copper tube sizes, should not
accepting soft metric during construction.
yet be utilized.
(ex, 200, 250)
Schedule designations remain the same (example:
Ductwork (Rectangular) Use 50 and 100 mm sizes,
Schedule 40, and type K,L,M)
(ex, 500 x 1000, 250 x 350) unless not possible.
The Mechanical Task Group, under leadership of ASME,
Equipment We regularly receive updated catalogs from
recently recommended use of 18 mm for 5/8, instead of
producers that have added metric data to their catalogs or
the 16 stated in the last guide.
literature. Where this did not exist, we have had no
All other designations remain the same.
difficulty receiving modified data on a project, or
obtaining a bond paper supplement.
Metric pipe designations are:
Schedules To think metric, flow rates, pressures, thermal
15 18 20 25 32 40 50 65 80 90 100 125 150 mm
powers, and other criteria on schedules should be
rounded wherever possible.
Over 150, inch x 25 = mm (24 " x 25 = 600 mm)
The 1 % Analysis provides a useful technique.
Units Use units from the ASHRAE SI Guide.
Ex 1, A fan flowrate converts to 8,022 L/s.
1% is +/- 80.22 L/s. This fan could possibly be shown as
minimum 8000 L/s (8 m3/s) and is easier and faster to
Ex 2, A pump flow converts to 75.7 L/s. 1 % of this is
0.757 L/s. 75 L/s could possibly be used.
It is important to note that in some cases codes or design
criteria may not allow this liberty. In other cases
however, 2 or 3 % analysis may be feasible, and could
lead to rounded, easily spoken numbers.
Temperature People will rarely speak in decimal
degrees. (ex, 23.8 degrees C). All mechanical schedule
temperatures, design temperatures, leaving and entering
temperatures, and others shall be stated in even Celcius
(ex, 5, 12, 25, and 40 degrees C) unless not possible.
New construction projects shall use Celcius only.
Renovation projects where new control systems are
being installed, should use Celcius.
HVAC calculations shall be in SI to the fullest extent