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SAFETY RELIEF VALVE
(PIPE TO WITHIN
12 INCHES
OF THE FLOOR TO
PREVENT INJURY)
PRESSURE/
TEMERATURE
GAUGE
Figure 4.2: Relief Valve and Pressure/Temperature
Gauge Installation
0
25
20
15
10
5
0
0
Figure 4.3: Series PFC
TM
SYSTEM
RETURN
SYSTEM
SUPPLY
5
10
20
40
Circulator Sizing Graph (General Pump – Primary/Secondary)
9. Circulator: The boiler circulator is to be sized to
overcome the pressure drop of the system while
providing the flow required by the boiler.
a. If the boiler is piped in a secondary loop of a
primary/secondary heating system, the circulator
will need only to overcome the resistance of the
boiler and any fittings in that loop.
b. The circulator should be sized based on gross
output of the boiler. Table 4.4 shows the Boiler
Output as reported to the Hydronics Institute
Section of AHRI.
Table 4.5: Boiler Input and Output
P
F
®
ure
ire
Model
PFC-625
625,000
PFC-750
750,000
c. The required flow is calculated based on the design
temperature difference from the return to the
supply of the boiler. For a PFC-625 with a design
temperature difference of 20°F the calculation is as
follows:
Required Flow = ________ = _________ = 61.2 GPM
d. The boiler pressure drop for various flow rates
can be determined using Figure 4.3, P
Circulator Sizing Graph below.
Flow Rate [m
/hr]
3
15
60
Flow Rate [GPM]
WATER PIPING & CONTROLS
Boiler Input
Boiler Output
Btu/hr
kW
Btu/hr
183.2
612,000
219.8
735,000
Output
612,000
DT x 500
20 x 500
20
PFC-625
PFC-750
80
100
kW
179.4
215.4
F
®
ure
ire
800
700
600
500
400
300
200
100
0
19
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