Roberts Gorden CRV-B-4 - Manual (Page 34)

CRV-S ERIES D ESIGN M ANUAL
28
SECTION 9: AIR SUPPLY SYSTEM
An air supply free of dust and corrosive contaminants
is essential for proper operation and best life expect-
ancy with any heating system. With CRV-Series, there
are two alternatives available to the designer for pro-
viding the air supply. These are:
• Room air, a filter is standard for each burner.
• Outside air system to duct air from an uncontami-
nated source. The outside air system can be
designed as a pressurized or non-pressurized
system.
The first alternative above is usable when the dust
load is not excessive and there is no usage of corro-
sive contaminants such as solvents or vapors inside
the building.
The outside air system must be used in all applica-
tions where corrosive contaminants may be present in
the air even in trace amounts (few parts per million).
It is important for designers and owners of heating
systems to note that the presence of contaminants in
the combustion air supply will greatly accelerate the
rate of corrosion on tube surfaces and will shorten the
useful life of the heating system. This is true regard-
less of whether the heating system is CRV-Series,
other infrared systems or conventional gas or oil-fired
equipment such as unit heaters, central boiler plant,
etc.
With the unique vacuum powered burners, the fuel/air
mix remains constant, even if combustion air filters are
dirty. It can be expected that the use of an outside air
system will reduce but not eliminate the potential for
corrosion due to contamination.
In a way similar to the CRV-Series pump system, the
design of the air supply system also involves consider-
ations of total flow units and acceptable combinations
of duct lengths (and diameters) versus flow units car-
ried. In certain circumstances, it may be desirable to
introduce an outside air blower to pressurize the sys-
tem. A small positive pressure is desirable and neces-
sary to prevent the system from drawing in
contaminated air.
9.1 Pressurized
For pressurized outside air supplies, the outside air
blower motor has a pressure switch that must be used.
Wire this switch in-series with the pump pressure
switch. When using an outside air blower with a ROB-
ERTS GORDON
® System Control, ROBERTS GOR-
DON ® ULTRAVAC ™ or relay transformer, a separate
load relay package is required. Wire the control for the
relay in parallel with the pump. The outside air blower
must have a separate 20 A, 120 V power supply.
9.2 Non-Pressurized
For a non-pressurized outside air supply, a 4" O.D. sin-
gle wall pipe duct may be attached to the burner and
end vent. For length and duct sizing requirements See
Section 9.3. To prevent condensation, insulate the
outside air duct.
9.3 Outside Air System Design Requirements
9.3.1 Non Pressurized
• 6" diameter duct must not exceed 90' (27 m)
• 4" diameter duct must not exceed 90' (27 m)
• Elbows are equivalent to 10' (3 m) of duct length.
• See the CRV-Series Installation, Operation, and
Service Manual (P/N 127102NA) for ducting
installation details.
9.3.2 Pressurized Systems
• 6" diameter duct must not exceed 120' (36 m) total
per system.
• 4" diameter duct must not exceed 120' (36 m) per
radiant branch.
• See the CRV-Series Installation, Operation, and
Service Manual (P/N 127102NA) for ducting
installation details.
FIGURE 27: Air Supply System Capacity by Duct
Length and Diameter
140
120
100
80
60
40
20
0
0 50 100 150 200 250
Flow Units
Straight Duct Length (feet)
4"
5"
6"
7"
NOTE: For capacity requirements larger than shown, use 8" duct.
Duct Diameter