Balancing
Owing to the fall in pressure in the length of the main duct, the air outlets at the initial end will deliver more air, and those at the extreme end less air, than the mean if the system is not balanced.
In a blowing system with round piping designed on the percentage system there are 2 similar lines of ducts each with 14 outlets. No balancing adjustments were provided, and tests were
|
Outlet pop No. |
Line 1 m3/s |
Line 2 cfm |
|
1 |
0.107 {+ 12% on Mean) |
0.093 (+ 19% on Mean) |
|
2 |
0.106 |
0.091 |
|
3 |
0.104 |
0.089 |
|
4 |
0.103 |
0.088 |
|
5 |
0.101 |
0.085 |
|
6 |
0.099 |
0.083 |
|
7 |
0.098 |
0.080 |
|
8 |
0.094 |
0.078 |
|
9 |
0.093 |
0.077 |
|
10 |
0.091 |
0.073 |
|
11 |
0.088 |
0.070 |
|
12 |
0.086 |
0.067 |
|
13 |
0.083 |
0.065 |
|
14 |
(74% of No 1) 0.079 (-17% on Mean) |
(66% of No 1) 0.061 (-22% on Mean) |
|
1.332 |
1.100 |
|
Table 3.9 Variation in flow on a typical unbalanced system |
|
Made for the air volume flowrate discharged. The results are To balance the system, the resistance from A to B must be given in Table 3.9. equal to that from AtoC. the difference is the friction of the main Between B and C and this must be compensated by adding resistance at B. This has been checked by experiments as will be seen later. |
|
Posted in Fans Ventilation A Practical Guide |