Assessments - 2, GPA: 4.5 ( )

Fabricante : Roberts Gorden Arquivo Tamanho: 2.16 mb Arquivo Nome : Língua de Ensino:

See Section 5.3.1 • More than maximum number of burners or flow units per radiant branch. See Page 14, Table 2. • Excessive number of elbow or tee fittings which increases vacuum loss. 5.3 Tailpipe Flow Excessive flow loading in a single section of tailpipe can cause low vacuum and lower effective pump capacity. For the pump to develop the proper vacuum, the length of tailpipe must not be excessive for the Pump Series Exhaust Tube Length Exhaust Tube Diameter EP-100 Up to 25' (7.6 m) 4" 3 Elbows EP-100 Up to 50' (15 m) 5" 3 Elbows EP-200 Up to 10' (3 m) 4" 0 Elbows EP-200 Up to 25' (7.6 m) 5" 3 Elbows EP-200 Up to 50' (15 m) 6" 3 Elbows EP-300 Up to 10' (3 m) 6" 1 Elbows EP-300 Up to 25' (7.6 m) 7" 3 Elbows EP-300 Up to 50' (15 m) 8" 3 Elbows SECTION 6: RADIANT TUBE AND TAILPIPE SECTION 6: RADIANT TUBE AND TAILPIPE 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 downstream 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 correspond to areas of major heat loss is the key to providing uniform comfort levels. The use of adequate tailpipe is the key to high combustion efficiency and proper operation of the pump. 6.1 Radiant Tube Length The considerations in the selection of the length of radiant tube include the following: 6.1.1 Minimum Radiant Tube Length 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. 6.1.2 Maximum Radiant Tube Length Provides the lowest level of intensity per length of radiant 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. 6.2 Tailpipe 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 condensation will occur. Page 16, Figure 16 relates the effect on system thermal 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 contained in ANSI Z83.20/CSA 2.34 (latest edition). Actual installation variables (gas BTU content, air temperature and operation cycle, etc.) may effect efficiencies (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. CRV-SERIES DESIGN MANUAL FIGURE 16: Tube Length vs. Efficiency * "+#,, , .+ . 5, . , , . 5 51 $12 4'. 43. 47. 41. 48. 44. 4$. $%. ' 3' #" ++- -3.4/ NOTE: Thermal efficiency values shown do not include the contribution due to condensing conditions when operating in cyclic fashion. To estimate cyclic efficiencies, add 2-3% to the values obtained from the graph. 6.3 Design Parameters When designing branches of 4 B-8 or larger burners in-series, the following limitation to the pump capacity applies: Pump Model Series Maximum Loading EP-100:Not Allowed EP-200:1 Branch of 4 burners EP-300:2 Branches of 4 burners For systems that are designed above 90% pump capacity, the following limitations of shared tailpipe apply: • 4" (10 cm) tailpipe: limited to maximum of 2 combined branches and length limited to maximum of 20' (6 m). See Page 14, Figure 15 for all other tailpipe considerations. • 6" (15 cm) tailpipe limited to maximum of 4 combined branches and length limited to maximum of 100' (30 m). • When calculating required tailpipe length 1' (.3 m) of 6" manifold tube is equivalent to 1.3' (.4 m) of 4" tailpipe. Failure to comply with the above parameters will result in insufficient vacuum to burners. 6.4 CRV-Series Design Methods 1. Layout the system to suit the BTU in...

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