Roberts Gorden CRV-B-4 - Manual (Page 24)

CRV-S ERIES D ESIGN M ANUAL
18
EXAMPLE 3: B-10 Radiant Tube vs. Tailpipe Length
Table 5: Operating Characteristics; Condensing or Non-Condensing
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.
6.5.1 Rule of Thumb Unshared Calculations
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
See Page 14, Figure 15 for maximum permissible
length of tailpipe for the number of flow units entering
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.
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
Compare the results to Page 17, Table 4 and Page 18,
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
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.
Total tailpipe ' (includes 1 elbow / 50').
Total tailpipe - 10' = Optimum unshared
tailpipe per branch Number of branches
Total system tailpipe
= Tailpipe ft/flow unit
Total flow units