Roberts Gorden CRV-B-2, CRV-B-8 AIR Supply System, Non-Pressurized, Pressurized Systems

CRV-SERIES DESIGN MANUAL

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.

9.3Outside 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

NOTE: For capacity requirements larger than shown, use 8" duct.

	140
Units	120
	100
								7"
	80
									Diameter
Flow
	60
								6"
	40
								5"	Duct
	20
								4"
	0
		0	50	100	150	200	250

Straight Duct Length (feet)

28