Roberts Gorden CRV-B-2 Manual Do Utilizador

15

The main purpose of the tailpipe and the radiant tube 
is to provide sufficient tube surface to transfer the heat 
from the flue gases to the tube wall where it radiates 
from the tube. Radiant tube is defined as the tubing 
between burners firing in a radiant branch, plus the 
radiant tubing immediately following the last down-
stream burner. Tailpipe is defined as all tubing 
between the radiant tube and the pump.

Most of the radiant heat supplied by each burner is 
released from the radiant tube; the balance is released 
by the tailpipe. The placement of radiant tube to corre-
spond to areas of major heat loss is the key to provid-
ing uniform comfort levels. The use of adequate 
tailpipe is the key to high combustion efficiency and 
proper operation of the pump.

The considerations in the selection of the length of 
radiant tube include the following:

Provides for the highest level of intensity per length of 
radiant tube and good radiant heat uniformity between 
burners. More tailpipe length is required to maintain 
operating efficiency and pump capacity.

Provides the lowest level of intensity per length of radi-
ant tube, and consequently the largest span between 
burners. The radiant intensity will be reduced slightly 
for the last 5'-10' (2-3 m) of radiant tube before the 
next burner.

The length of radiant tube required varies according to 
the burner input. Consideration has been given to the 
use of a standard 10' (3 m) length of tube or lengths 
that can be cut from same without waste. See Page 
12, Table 1.

When positioning radiant tube to give the required 
radiant distribution, it is important to consider:

• Clearances to combustible materials.

• Lighting equipment and other suspended objects.

Tailpipe provides a low level of radiant intensity per 
length. The length of tailpipe for systems can be varied 
according to the flow units in the system and the 
designed radiant length. Longer lengths of tailpipe will 
attain higher operating efficiencies and therefore con-
densation will occur.

Page 16, Figure 16 relates the effect on system ther-
mal efficiency of variations in radiant and tailpipe 
lengths. The chart was created based on test data 
obtained in accordance with methodology developed 
by the National Bureau of Standards (NBSIR 80-2110) 
and recommendations on flue loss calculation con-
tained in ANSI Z83.20/CSA 2.34 (latest edition). 
Actual installation variables (gas BTU content, air tem-
perature and operation cycle, etc.) may effect efficien-
cies (positively or negatively). Page 16, Figure 16 is 
presented as a guide to the designer for information 
only.

NOTE: When accounting for the required tailpipe 
lengths during the design process, it is important to 
verify that the tailpipe for each branch is at least equal 
to the specified minimum.