Service manual

CRV-SERIES DESIGN MANUAL
12
SECTION 5: FLOW LOADING
The patented CRV-Series burner system allows a
number of burners to be installed in-series, in the
same radiant tube, resulting in a long, continuous
radiant emitting surface to give even heat distribution
within the building.
To enable the burners to be correctly located within
the system, to maintain system operating vacuum
and obtain design flue gas temperatures at the
pump, the design layout is based on a simplified flow
principle using a “flow unit.”
The flow unit is defined as the amount of fuel/air mix-
ture for a heat input of 10,000 (Btu/h). This corre-
sponds to a flow rate of 1.83 cfm at 65-70°F.
For the purpose of design, flow units enter the CRV-
Series system in one of two ways:
• Through the burner.
• Through the end vent plate.
Flow units exit the system as spent products of com-
bustion via the pump.
The purpose of the end vent air is to dilute the hot
combustion gases at the burner, thereby promoting
uniform heating of the tube while avoiding excessive
heating of the combustion chamber.
For the end burner, the burner inlet flow consists of
the end vent air and combustion air. For all other
burners, the burner inlet flow consists the of the total
of the end vent air plus the combustion gases from
all upstream burners.
The requirement for minimum burner inlet flow is met
if the total flow units entering the combustion cham-
ber meets or exceeds the minimum as shown on
Page 12, Table 1.
5.1 Radiant Branch Flow
The flow in a radiant branch consists of the end vent
flow units plus the flow units of combustion air from
all burners. Page 13, Figure 14 shows a representa-
tion of flow units for various types of branches.
The limiting factor for maximum flow in the radiant
section has been determined experimentally in terms
of the maximum burner inlet flow units that can be
tolerated without degradation of combustion charac-
teristics at the last downstream burner. If more than
the maximum number of burners are installed per
radiant branch, the vacuum loss across the addi-
tional burners will increase appreciably.
This maximum flow in the radiant branch can be
expressed for each burner firing rate by either a max-
imum number of burners per branch or the maximum
number of flow units. See Page 12, Table 1.
Table 1: CORAYVAC
®
Design Parameters
* CRV B-9 requires first downstream tube from burner to be aluminized heat-treated.
Burner Model B-2 B-4 B-6 B-8 B-9* B-10 B-12A B-12
Input (Btu/h) x (1000) 20 40 60 80 90 100 110 120
Flow Units per Burner 24689101212
Flow Units per End Vent
(minimum flow units entering combustion chamber)
6 10152015202020
Maximum Number of Burners per Branch 64442433
Maximum Number of Flow Units per Branch 18 26 39 52 33 60 56 56
Radiant Tube Length (average distance between burners)
Minimum (ft) 1012.5202020303535
Recommended (ft) 15 20 25 30 30 40 50 50
Maximum (ft) 20 25 35 45 50 60 70 70
Minimum Distance from Burner to Downstream Elbow (ft) 5 5 10 10 10 15 15 15
Suggested Minimum mounting Height (ft) 8 8 8 10 10 15 15 15