With the introduction of Ducted indoor unit products, some
information on duct selection and design seems appropriate. Considering the
performance and design of these indoor units, selection and proper duct sizing
and installation will be necessary for satisfactory application. The maximum
available static pressure from the low profile ducted indoor unit is 0.2” H2O.
With this in mind, the ductwork design must be taken into consideration to
ensure proper airflow to the space is achieved. The emphasis should still be on
moving refrigerant and not air; not only will this help to work within the
static pressure available but it is also more efficient. Here are some good
practices when ducting the low profile unit.
• When reviewing static pressure duct loss in a system, the longest duct run
from the unit is the maximum static pressure the unit will see.
• flexible ductwork, while making installations simpler, can add
unnecessary static pressure loss if not utilized properly. Most of the static
pressure duct loss comes from allowing the duct work to sag. Allowing even a 30%
sag in the ductwork can increase the static pressure
loss up eight times. Flexible ductwork runs should be kept to less than 15 feet.
Elbows should be kept to a minimum and made as wide as possible.
• Grilles should be selected so that the air velocity is less than 500 ft per
minute, this will help to minimize static pressure loss.