19
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.
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:
Output 612,000
Required Flow =
________
=
_________
= 61.2 GPM
D
T
x 500
20 x 500
d. The boiler pressure drop for various flow rates
can be determined using Figure 4.3,
P
ure
F
ire
®
Circulator Sizing Graph below.
WATER PIPING & CONTROLS
Figure 4.3:
Series PFC
TM
C
irculator Sizing Graph (General Pump – Primary/Secondary)
0
5
10
15
20
0
100
200
300
400
500
600
700
800
0
5
10
15
20
25
0
20
40
60
80
100
Flow Rate [m
3
/hr]
Pr
essur
e
Dr
op
[mb
ar
]
Pr
essur
e
Dr
op
[F
ee
t o
f Wate
r]
Flow Rate [GPM]
PFC-625
PFC-750
Figure 4.2: Relief Valve and Pressure/Temperature
Gauge Installation
SYSTEM
SUPPLY
SYSTEM
RETURN
PRESSURE/
TEMERATURE
GAUGE
SAFETY RELIEF VALVE
(PIPE TO WITHIN
12 INCHES
OF THE FLOOR TO
PREVENT INJURY)
Table 4.5: Boiler Input and Output
P
ure
F
ire
®
Model
Boiler Input
Boiler Output
Btu/hr
kW
Btu/hr
kW
PFC-625
625,000
183.2
612,000
179.4
PFC-750
750,000
219.8
735,000
215.4
