AHRI K2WT, Installation, Operating And Service Instructions

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B. Near Boiler Piping Design
Proper operation of this boiler requires that the water flow rate through it remain within the limits shown in Table 9.1
any time the boiler is firing. At flow rates below the minimum shown, the boiler’s flow switch and/or temperature rise limit
function may prevent the boiler from firing. Flow rates through the boiler in excess of the maximum shown in Table 9.1 can
result in excessive noise or erosion damage to piping
There are two basic methods that can be used to pipe this boiler into the system. Method #1 (primary-secondary piping)
is always preferred. Additional information on hydronic system design can be found in the
I=B=R
Guide RHH published by
the Air-Conditioning, Heating and Refrigeration Institute (AHRI).
Model
Flow (GPM)
Minimum Maximum
K2WT-080 5.0 13.3
K2WT-100 5.1 13.3
K2WT-120 6.2 13.3
K2WT-150 7.7 13.3
K2WT-180 9.3 13.3
Method 1: Primary/Secondary Piping (Strongly Recommended)
This method can be used in heat-only applications as shown in Figures 9.2 and 9.2a or with an indirect water heater as shown
in Figure 9.3a or 9.3b. In this system, the flow rate through the boiler (“secondary loop”) is completely independent of the
flow rate through the system (“primary loop”). Use the following guidelines to ensure that the boiler will have the required
flow shown in Table 9.1 regardless of the flow in the heating system.
1) System Loop Piping - Size the system circulator and piping to obtain the design flow rate through the heating system
as you would on any other heating system. All piping between the expansion tank and secondary connection tees must
be at least 1”. In order to keep the flow rates in the system and boiler loops independent of each other, provide at least
8 diameters of straight pipe upstream of the first tee and 4 diameters downstream of the second tee. Keep the distance
between the expansion tank and the first secondary tee as short as practical.
2) Boiler Loop Piping – All boilers are supplied with a built in circulator which will deliver the flow required by Table 9.1
provided both of the following conditions are met:
• All piping in the boiler loop has a nominal size of at least 1”
• The equivalent length of all piping in the boiler loop is 60 ft or less.
To verify that the 60 ft, equivalent length is not exceeded, do the following:
a) Count all fittings in the planned boiler loop (the shaded piping in Figure 9.6). In doing so, do not count the
secondary connection tees, unions, or the fittings supplied with the boiler (these have already been accounted for).
b) Using Table 9.4, find the equivalent lengths of all fittings in the secondary loop. Total these equivalent lengths and
add them to the total length of planned straight pipe in the secondary loop.
c) The result is the total equivalent length of the planned boiler loop. If the equivalent length calculated in (b) is
under the limit shown in Table 9.5, the boiler pump will achieve a flow rate and temperature rise approximately
equal to that shown in this table. Otherwise, the equivalent length must be reduced.
IX. System Piping
(continued)
Table 9.1: Flow Limitations