Roberts Gorden CRV-B-2, CRV-B-8, CRV-B-6, CRV-B-4 service manual Flow Loading, Radiant Branch Flow

CRV-SERIES DESIGN MANUAL

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 radi- ant 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 chamber 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 representation of flow units for various types of branches.

The limiting factor for maximum flow in the radiant sec- tion has been determined experimentally in terms of the maximum burner inlet flow units that can be toler- ated without degradation of combustion characteris- tics at the last downstream burner. If more than the maximum number of burners are installed per radiant branch, the vacuum loss across the additional burners will increase appreciably.

This maximum flow in the radiant branch can be expressed for each burner firing rate by either a maxi- mum number of burners per branch or the maximum number of flow units. See Page 12, Table 1.

Table 1: CORAYVAC® Design Parameters

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	2	4	6	8	9	10	12	12
Flow Units per End Vent	6	10	15	20	15	20	20	20
(minimum flow units entering combustion chamber)
Maximum Number of Burners per Branch	6	4	4	4	2	4	3	3
Maximum Number of Flow Units per Branch	18	26	39	52	33	60	56	56
Radiant Tube Length (average distance between burners)
Minimum (ft)	10	12.5	20	20	20	30	35	35
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

* CRV B-9 requires first downstream tube from burner to be aluminized heat-treated.

12