Selecting Circulators Guide
TD10 – 3
STEP 4: ESTABLISH THE HEAD LOSS OF THE PIPING SYSTEM AT THE TARGET FLOW
RATE
In a system with multiple zones, the head loss needs to be calculated for each parallel loop. The loop with the highest
head loss will be used in figuring the total equivalent length in Example 4.
The formula for estimating the head loss for piping circuits constructed of smooth tubing such as copper, PEX, or PEX-
AL-PEX is:
H
L
= k x c x L x (f
1.75
)
Where:
H
L
= the head of the piping system (feet of head)
k = a number based on tubing type/size (found in Table 3)
c= correction factor for fluid type and temperature (found in Table 4)
L = total equivalent length of piping circuit (feet) (from Step 3)
f
1.75
= flow rate through piping (gpm) raised to 1.75 power (selected values found in Table 5)
Example 4: Find the head loss of the piping system having a total equivalent length of 239 feet of 1-inch type M copper
and operating with water at an average temperature of 140 ºF and at the target flow rate of 10 gpm.
Answer: The k value for 1-inch copper tubing (from Table 3) is k=0.000845.The value of the correction factor (from Table 4)
is 1.000.The value of the flow rate to the 1.75 power (from Table 5) is 56.234.The total equivalent length is L=239 feet
(from Step 3). Multiplying these values together yields:
H
L
= k x c x L x (f
1.75
) = 0.000845 x 1.00 x 239 x 56.234 = 11.36 feet
The target operating condition of our piping system is now defined as 10 gpm with a corresponding head loss of 11.36
feet.This flow / head loss condition is called the target operating point for this system.
TABLE 3
TUBING
SIZE/TYPE
VALUE OF k
(WATER IN
SYSTEM)
3
⁄
8
" copper
0.0484
1
⁄
2
" copper
0.0159
3
⁄
4
" copper
0.00295
1" copper 0.000845
1.25" copper 0.000324
1.5" copper 0.000146
2" copper 0.0000397
2.5" copper 0.0000142
3" copper 0.0000061
3
⁄
8
" PEX
0.140
1
⁄
2
" PEX
0.0374
5
⁄
8
" PEX
0.0140
3
⁄
4
" PEX
0.00731
1" PEX 0.00223
1.25" PEX 0.000794
1.5" PEX 0.00036
2" PEX 0.0001
3
⁄
8
" PEX-AL-PEX
0.16
1
⁄
2
" PEX-AL-PEX
0.0394
5
⁄
8
" PEX-AL-PEX
0.0098
3
⁄
4
" PEX-AL-PEX
0.0034
1" PEX-AL-PEX 0.0012
TABLE 4
Water c = 1.095 c = 1.000 c = 0.933
30% Propylene Glycol c = 1.353 c = 1.187 c = 1.088
50% Propylene Glycol c = 1.582 c = 1.349 c = 1.225
AVERAGE FLUID TEMPERATURE 100°F 140°F 180°F
TABLE 5
FLOW RATE
(gpm)
FLOW RATE
RAISED TO 1.75 POWER
0.5 0.297
1 1.000
1.5 2.033
2 3.364
2.5 4.970
3 6.839
3.5 8.956
4 11.314
4.5 13.903
5 16.719
6 23.002
7 30.125
8 38.055
9 46.765
10 56.234
12 77.369
14 101.327
16 128.000
18 157.229
20 189.148
25 279.508
30 384.558