Unit installation

7
8. DUCT AND REGISTER
SPECIFICATIONS
GENERAL INFORMATION
All supply air ducts, registers, return air ducts, return air filters
and filter retainers must be supplied by the installer or vehicle
manufacturer.
Any ducting (supply or return) exposed to a heat source or
outdoor environment must be sealed and insulated to prevent
heat gain and decreased system performance.
Supplied with these instructions is a blower performance table,
See Chart 1. The blower performance table is provided so that
the installer has a method for testing and determining duct
efficiency. The blower performance table shows the resulting
evaporator blower air delivery and amperage draw when
operating against various external static pressures.
By measuring the air distribution system operating pressure,
the installer can determine the amount of air that the system is
delivering. The design rated air flow on high fan speed in
600 SCFM (standard cubic feet per minute), with approximately
.5 inches of static pressure in the ducting. Increased system
performance and quicker vehicle cool down can be achieved
by reducing the duct system static pressure. An increase in
duct static pressure reduces air flow, system performance and
vehicle cool down time.
RV Products strongly recommends that all air distribution
systems be tested by the vehicle manufacturer in a floor mock-
up prior to installation in the vehicle. In doing so, the vehicle
manufacturer can insure that air volume, distribution and noise
levels are optimized.
GUIDELINES FOR SUPPLY AIR DUCTING
Total free area inside the supply duct can be no less than
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 AIR 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, 10" x 20"
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. The unit must have at least 200 square inches of
filtered return air register or registers if ducting is used.
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;