Roberts Gorden CRV-B-8 EXAMPLE 3 B-10Radiant Tube vs. Tailpipe Length, Tailpipe Design Method

CRV-SERIES DESIGN MANUAL

EXAMPLE 3: B-10 Radiant Tube vs. Tailpipe Length

For a B-10 burner system of 200 flow units and an average of 40' radiant tube length per burner, See Page 17, Table 4 for the tailpipe lengths per flow unit that can be used and the corresponding operating characteristic.

From Table 4, we can use between 1.2' per flow unit and 2.5' per flow unit when the average radiant length per B-10 burner is 40'. By multiplying the number of flow units in the system (200 flow units) by the mini- mum tailpipe length from the chart (1.2' per flow unit), we see that we will need a minimum of 240' of tailpipe for this system. Likewise, by multiplying the number of flow units in the system (200 flow units) by the maxi- mum tailpipe length from the chart (2.5' per flow unit), we see that maximum system, tailpipe length is 500'.

Tailpipe length range for a B-10 burner system with 200 flow units and an average radiant tube length of 40’ is 240'-500'. The length of the tailpipe will determine whether the system is condensing or non-condensing. Given a certain radiant tube length and tailpipe length, the operating characteristic can be determined using Table 5.

Table 5: Operating Characteristics; Condensing or Non-Condensing

		Tailpipe Length per Flow Unit
	Minimum		Recommended	1.7 ft/flow unit	Maximum
Radiant Tube Length (average distance between burners)
Minimum	N/A		NC	Borderline	C
Recommended	NC		Borderline	C	C
Maximum	Borderline		C	C	C

N/A=Not Allowed NC=Non Condensing C=Condensing

6.5 Tailpipe Design Method

Given the overall length of tailpipe for the system, the following section provides the method for ensuring the design will function correctly.

Total tailpipe ' (includes 1 elbow / 50').

6.5.1 Rule of Thumb Unshared Calculations

Total tailpipe - 10'	= Optimum unshared
	tailpipe per branch
Number of branches

the section of tailpipe.

If flow units entering a shared tailpipe system exceed 90% of pump capacity, the length of 4" diameter tailpipe must not exceed 20'.

System with EP-300 Series Pump

For shared tailpipe up to 115 flow units, 4" diameter tailpipe can be used. See Page 14, Figure 15 for max- imum permissible length of tailpipe for the number of flow units entering the section of tailpipe.

Select a pump discharge location and plan the route of the tailpipe. For example system layouts See Page 21, Figure 18 through Page 25, Figure 26 for different pump and system efficiency requirements. If these lay- outs are not suitable, it is necessary to customize the layout for the CRV-Series system to the individual building requirements.

For multiple branch systems, always plan to connect the unshared tailpipe together as close to the pump as possible for better system efficiency.

6.5.2 Shared Tailpipe Calculation

System with EP-100 or EP-200 Series Pump

Shared tailpipe greater than 115 flow units use 6" diameter tube. Note that all tailpipe lengths for the pur- poses of calculation are expressed in terms of 4" diameter tube.

Effective length: 10' (3 m) of 6" (15 cm) diameter tube = 13' (4 m) of 4" diameter tube.

6.5.3 To Calculate the Total System Tailpipe

Total unshared tailpipe + shared 4" branch tailpipe + effective length of shared 6".

6.5.4 To Check Performance Criteria

Total system tailpipe	= Tailpipe ft/flow unit
Total flow units

See Page 14, Figure 15 for maximum permissible

length of tailpipe for the number of flow units entering Compare the results to Page 17, Table 4 and Page 18,

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