Document B8kEnRwox54Xrvv5KX0dMLMOX
452
CHAPTER 22
1949 Guide
Fio. 3. Equivalent Length of Fittings (Concluded) GROUP 7. REGISTERS (INCLUDING LOSSES IN STACKHEAO AND VELOCITY PRESSURE).
"TAT 25 EQ. FT.
I,I |
fl.REC.& BOX ONLY
Table 4A. Equivalent Length fob Registers
Deflection Angle A
j o9
Baseboard, High or Low Sidewall Eq. Ft.
Registers
jj
Floor Registers with Box only
J 25
IS' J 22'
40 45
1
SO* 60
by a? sStd^^3fi?S'-Slet^.VertiCal "d tori"ntaI deftetion "*
45 115 and multiply
5 for buildings having a heat loss between 120,000 and 350,000 Btu per hr or Table 6
for buildings having a heat loss greater than 350,000 Btu per hr. Select shortest actual
length and read downward in nearest column in Tables 5 or 6 until lower heavy diago-
nal *fne 13 reached, but do not cross line. Run horizontally to left td obtain value of
maximum bonnet temperature in firat column.,. .Also select longest actual length and
read downward in nearest column in Tables 5 or 6, until upper heavy diagonal line is
just crossed. Run horizontally to left to obtain value for minimum bonnet'tempera
ture in hrst column. Select as the design bonnet temperature any value between
maximum and minimum.
5. Determination of air volume to be delivered through each register and the
respective register air temperatures.
> & .7
. Using Tables 5 or 6 and the design bonnet temperature selected, find the values of crm per 1000 Btu for each duct length.
6. Selection of register sizes and pressure losses to produce necessary throw for
the air volumes handled.
.
3'
Use Tables 7 or 8 to obtain required free area and pressure loss of register. 7. Design of duct system.
A. Warm air branches.
a. Use Table 9 to select maximum bonnet pressure usually required for the
trunk carrying the.maximum volume of air (cfm). If the maximum '
bonnet pressure is not high enough to accomodate the pressure loss through the registers, use a higher bonnet pressure. If the register pres sure is critically large, it may be necessary to reduce it by either using . . two registers m place of one, or using smaller deflection angles.. .
- sb: Obtain actual duct loss by subtracting register pressure loss from maximum bonnet pressure.
c. Obtain the pressure drop in each duct per 100 ft by use of Table 10. '
d. By means of Table 10 (Friction chart) determine duct size, cfmTand pres
sure drop per 100 ft of duct.
.
B.-Return air branches.
a. Select a low value of actual duct loss obtained from step b under item A for the suction loss of return duct system. '
b. Proceed in sizing return air branches by the same method described for the warm air branches.
C. Trunk ducts for warm air and return air sides of system.
a. Add air volumes of branches to be handled by each trunk duct.
b. The friction loss per 100 ft of. trunk duct is determined by taking the
smaller of the two values for friction loss for the!two ducts meeting at
the junction.
.....................
.... c. Determine trunk duct size by using Friction Chart" volume (cfin)i and
.
pressure drop per 100 ft;'of trunk duct. '
. v \ ,. "
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