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I Combination Units Installation Instructions
5. Air Distribution System
Ductwork
NOTE: The total heat lossfrom the structure as expressed in
total Btu/hr(Kw) MUST be calculated by manufacturer's
method or in accordance with "A.S.H.R.A.E. Guide" or
"Manual N - Load Calculations" published by the Air Condi-
tioning Contractors ofAmerica or in Canada H.R.A.I. "Manu-
al N". The total heat loss calculated should be equal to or
less than the unit heating capacity, output based on D.O.E.
test procedures, steady state efficiency times input.
Ductwork, supply registers, and return air grilles MUST be
designed and sized to handle the greater of the units heating
or cooling air volume requirements. If the unit isconnected to
an existing system, the ductwork MUST be checked to make
sure it is adequate. Extra runs or larger duct sizes may have
to be installed. Use only non-combustible type insula-
tion on supply plenum or supply ductwork within 6
feet(2m) of unit,
Maximum recommended velocity in supply trunk ducts is
1000 feet (305m) per minute and 800 feet (244m) per minute
in return trunk ducts. Velocity in branches should not exceed
800 feet (244m) per minute supply and 600 feet (183m) per
minute in the return.
Ductwork installed outdoors should have a minimum of 2"
(50.8mm) of fiberglass insulation and a weatherproof vapor
barrier. It should also be protected against damage. Caulk
and flashing, or other means adequate to provide a perma-
nent weather seal should be used.
Ductwork installed in attics or other areas exposed to out-
side temperatures should be installed with a minimum of 2"
(50.8mm) fiberglass insulation and have an indoor type va-
por barrier.
The use of flexible, non-combustible connectors between
main trunk ducts and supply and return air plenums is rec-
ommended to minimize vibration transmission.
NOTE: Connect supply and return air plenums to unit in a
manner that will allow the top of the unit to be removed with-
out removing plenums. Plenums MUST be individually
sealed to unit casing.
Filters
CAUTION
Do NOT operate the unit without all filters in place.
All air MUST pass through a filter before entering the unit.
Electronic air cleaner, optional filter racks, or other accessi-
ble filter arrangements MUST be installed in the return air
ductwork.
NOTE: Ifthe unit has an economizer or any other type of out-
door air damper, disposable filters MUST be used inthe in-
ternal filter racks.
For replacement filter sizes and instructions, see Air Filters.
Circulating Blower
DeterminingPulleyTurns
1. From the system design, determine the external static
pressure (ESP) for the supply ducts, return ducts and
registers, diffusers, grilles, dampers, heaters and spe-
cial filters (if any).
2. If unit isto be set up in cooling mode, add .08" W.C. (20
Pa) for wet coil operation to the total ESP determined
in Step 1.
3. From the system design, determine the desired airflow
in CFM (L/s).
4. To determine the pulley turns necessary to obtain the
desired CFM (L/s), go to the Circulating Blower Perfor-
mance Data graph for the unit.
513 01 1002 00 [_]
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