Install Instructions

IM-PR 566442 1114 (Design Manual)
40
1.10 Expansion
1.10.1 Selecting an expansion tank
Expansion tanks are required within hydronic
heating systems to allow for the expansion of the
working fluid as the temperature is increased.
For simple, 100% water-based hydronic heating
systems, you may refer to Table 1-9 for expansion
tank sizing. Table 1-9 provides expansion tank
sizing as a function of the system’s maximum
operating water temperature when expansion tanks
have an air side pressurization of ≤ 12 psi and a
pressure relief valve setting of ≥ 30 psi. For other
applications, you may use the following equation
to calculate the minimum expansion tank volume
required. Always round up when selecting an
expansion tank.
V
t
= V
s
(
D
c
D
h
) (
P
rv
+ 9.7
P
rv
- P
a
- 5
)
•
•
-1
where
Vt = minimum tank volume (gal)
Vs = fluid volume in system (gal)
Dc = density of the fluid at its initial start
temperature (lbs/ft
3
), whether water or glycol mix
Dh = density of the fluid at its maximum operating
temperature (lbs/ft
3
), whether water or glycol mix
Pa = air side pressurization on the opposite side of
the bladder, typically set at 12 psi from factory (psi)
Prv = pressure relief valve setting in (psi)
Example:
A radiant heating system with 100% water solution
and a maximum operating temperature of 120°F
has a total volume of 100 gal. The pressure
relief valve setting is 30 psi, and the air side
pressurization of the tank is 12 psi.
From water density tables, find the density of water
at its initial start temperature of 50°F to be 62.4
lbs/ft
3
and the density of water at its maximum
operating temperature of 120°F to be 61.7 lbs/ft
3
.
Plugging the values into the equation gives:
62.4
V
t
= 100
(
61.7
) (
30 + 9.7
30 - 12 - 5
)
•
•
-1
V
t
= 100 • (0.0113) • (3.054)
V
t
= 3.45
NOTE: This value is slightly different than the
corresponding value in Table 1-9 due to differences
in rounding.
Water
Volume
in System
(gal)
Max Operating Temperature (°F)
120 140 200
Expansion Tank Size (Gal)
20 0.7 1.0 2.3
30 1.0 1.5 3.5
40 1.3 2.0 4.6
50 1.7 2.5 5.8
60 2.0 3.0 6.9
70 2.3 3.5 8.1
80 2.7 4.0 9.2
90 3.0 4.5 10.4
100 3.3 5.0 11.5
125 4.2 6.3 14.4
150 5.0 7.6 17.3
175 5.8 8.8 20.2
200 6.6 10.1 23.0
225 7.5 11.3 25.9
250 8.3 12.6 28.8
275 9.1 13.9 31.7
300 10.0 15.1 34.5
Table 1-9. Minimum expansion tank size for 100%
water systems at various maximum operating
temperatures. Assumes 12 psi air side
pressurization and 30 psi pressure relief valve
setting.