Unit installation

7
GUIDELINES FOR SUPPLY AIR DUCTING
Minimum free area inside the supply duct is 48 square inches.
Ducting with more free area than 48 square inches will
improve system performance and vehicle cool down time.
To decrease restriction and increase air flow, the ducting
should make as few bends and turns as possible. When
corners or turns are required, it is recommended that these
turns be radiused and as gradual as possible.
The supply duct, unless made of an insulating material, must
be insulated to prevent condensation from collecting on its
exterior. Moisture condensation within the ceiling or wall
cavity can damage insulation, stain vehicle interiors or create
odors. 1/8", 3 pound density fiberglass or closed cell foam
insulation has proven effective for this purpose.
Any ducting exposed to heat sources must be further insulated
to prevent significant performance degradation due to heat
gain. An example of an area capable of creating significant
heat gain is the roof area which can sometimes experience
temperatures of 160 degrees or more when exposed to direct
sunlight. For ducting in or near the ceiling, it is impossible to
provide “too much” thermal insulation.
GUIDELINES FOR SUPPLY REGISTERS
Total free area provided by the supply air registers must equal
a minimum of 72 square inches.
Free area is the size of the opening(s) that remain in a grille or
louvered panel after restrictions (the louvers) are
subtracted. Most metal and plastic grilles average 30% to 60%
open. That is the actual “free area” for the grille will be 30%
to 60% of the total opening area.
GUIDELINES FOR RETURN AIR
DUCTING AND FILTERS
All return air must be filtered. A 1-inch thick disposable
fiberglass filter is recommended. A washable filter is
acceptable if supported by a mesh or grille to prevent collapse.
Should the return air filter and filter retainer be located in the
floor, a traffic duty grille will be required. The return air filter
should be located in an area where:
1) drapes or bed sheets cannot block the
opening;
2) the consumer can gain easy access for
servicing.
This system is designed to operate without return air ducting.
However, the fabrication and use of return air ducting is
permissible.
When a return air duct is utilized, it is recommended that:
1) the length of the duct be kept to an absolute
minimum;
2) the inner perimeter of the duct be kept as
large as possible.
Return air ducting will contribute to the overall pressure and
air flow loss of the system. Should the addition of return air
ducting reduce air flow below acceptable levels, then either:
1) the supply air duct inner perimeter will need
to be enlarged;
2) the supply air registers will need to be
added;
3) the return air duct inner perimeter will need
to be enlarged;
4) the return air duct will need to be shortened;
5) all of the above.