Velocity Mega-Stor II, Installation And Operation Instructions Manual, Page: 11 / 24

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The maximum equivalent length shown in Table 5.2 is that for the indirect water heater loop (IWH loop). The IWH loop piping is
shaded in Figure 5.1. To calculate the equivalent length of this loop:
1) Count all fittings in the planned boiler loop.
2) Using Table 5.3, find the equivalent length of each fittings in the IWH loop. In doing this, keep the following in mind:
a. In many cases, there will be more than one pipe size in the IWH loop. As long as all piping in the loop exceeds
the size shown in Table 5.2, conservative results can be obtained by treating all piping in the loop as though it
were of the smallest size.
b. The equivalent length of most cast iron boilers can be safely treated as zero. This is often not the case,
however, with condensing and water tube boilers. In such cases either use primary-secondary piping (Figure
5.4) or use an alternate method to size the pump and piping.
3) After the equivalent length for all fittings has been identified, total them and add the result to the total length of straight
pipe in the loop. This sum is the total equivalent length for the IWH loop and must be less than that shown in Table 5.2
in order to use the circulators shown.
4) If primary-secondary piping is used as shown in Figure 5.4, calculation of equivalent length is exactly the same as
shown above, except that IWH loop is the shaded piping in Figure 5.4 (i.e. the IWH loop does not pass through the
boiler).
Example: A 40 gallon IWH is to be installed in the IWH loop piping shown in Figure 5.1 (shaded). The cast iron boiler has a
negligible pressure drop. The loop consists of the following pipe and fittings:
Qty Size Description
3 1-1/4” 90 Elbow
1 1-1/4” Turn in Tee
1 1-1/4” Run of Tee
1 1-1/4” Air scoop
1 1” Swing check
5 1” Elbows
5ft 1-1/4” Straight pipe
15ft 1” Straight pipe.
Solution: For simplicity, treat all pipe as though it were 1”. Equivalent length is then calculated as follows:
Qty Description Equiv. Length/fitting Total Equiv. Length
8 90 Elbow 2.8ft 22.4ft
1 Air scoop 3ft 3.0ft
1 Turn in tee 5.5ft 5.5ft
1 Swing Check 7.0ft 7.0ft
1 Run of Tee 1.8ft 1.8ft
20ft Straight Pipe 1.0ft 20.0ft
Grand Total Equivalent Length: 59.7 ft
Since 59.7 is less than the 90ft maximum equivalent length shown in Table 5.2, the planned system will deliver the required flow
using either a Taco 007 or Grundfos 15-42F.
Model Pipe Size Max Equiv.
Length (ft)
Circulator Model
Taco Grundfos
MS2-030 1” 90 007 15-42F
MS2-040 1” 90 007 15-42F
MS2-050 1” 90 007 15-42F
MS2-075 1” 60 007 15-42F
MS2-075 1” 130 009 26-64F
MS2-119 1-1/4” 30 007
MS2-119 1-1/4” 90 0010
MS2-119 1-1/4” 190 0012 26-64F
TABLE 5.2: SELECT ACCEPTABLE INDIRECT WATER HEATER LOOP CONFIGURATIONS