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The compression tank pressure must be set BEFORE the system is
filled. Expansion tanks are factory supplied. The tanks are pre-
charged at the factory to 40 psig (276 kPa). If the 30RC unit with
expansion tank is the high point in the system, tank pre-charge
pressure of 40 psig (276 kPa) will be adequate. If the 30RC unit
with expansion tank is NOT at the high point in the system, then
the minimum pre-charge pressure for the water system must be
determined using Table 11 and the method below:
Tank Pressure =
4 + (height from tank to top of
system in feet/"X")
[27.6 + (height in m x 22.6/"X")]
For example, assuming a system containing a 20% concentration
of ethylene glycol and 50 ft (15.2 m) in height from the top of the
system to the expansion tank, the minimum tank pre-charge pres-
sure would be:
Tank Pressure
= 4 + (50 / 2.38) = 25.0 psig
= 27.6 + (15.2 x 22.6 / 2.38) = 171.9 kPa
Table 11 — "X" Factor for Setting Tank Pressure
ETHYLENE
% GLYCOL
0 (pure water)
10
20
30
40
50
NOTE: If expansion tanks are placed elsewhere in the system this method cannot
be used since extra pressure drop between the tank and the pump must be
accounted for.
NOTE: If the system requires a pre-charge greater than 40 psig
(276 kPa), increase pressure as described below.
Expansion Tank Pre-Charge
To pre-charge the expansion tank, do the following steps:
1.
Check the tank air pressure at the pre-charge connection with
an accurate pressure gage. Adjust as needed.
2.
If additional pressure is required, charge the tank with oil-free
compressed air or nitrogen gas. Occasionally check the pres-
sure as when filling a tire.
3.
Check the air valve for leakage. If it leaks, relieve the pres-
sure and replace the core with a Schrader-type tire core. DO
NOT depend on the valve cap to seal the leak.
Once the system is pressurized, the pressure at the connection
point of the expansion tank to water piping will not change unless
the water loop volume changes (either due to addition/subtraction
of water or temperature expansion/contraction). The pressure at
this point remains the same regardless of whether or not the pump
is running.
Since the expansion tank acts as a reference point for the pump,
there cannot be two reference points (two expansion tanks) in a
system (unless manifolded together). If system volume or other
design considerations warrant the placement of another expansion
tank somewhere in the system, the expansion tank in the 30RC hy-
dronic package MUST be disconnected from its hose and the end
of the hose securely plugged.
PROPYLENE
GLYCOL
GLYCOL
2.31
2.31
2.36
2.33
2.38
2.36
2.40
2.38
2.43
2.38
2.47
2.40
This is also true for applications where two or more 30RC chillers
are placed in parallel. There should not be more than one expan-
sion tank in the system (as seen in Fig. 17) unless manifolded to-
gether. When multiple 30RC chillers are applied in parallel, the
expansion tanks must be disconnected from the 30RC hydronic
package. It is permissible to install the expansion tank(s) in a por-
tion of the return water line that is common to all pumps, provid-
ing that the tank is properly sized for combined system volume.
If the application involves two or more chillers in a primary/sec-
ondary system, a common place for mounting the expansion tank
is in the chilled water return line, just before the decoupler. Refer
to Fig. 18 for placement of expansion tank in primary/secondary
systems.
The expansion tank included in the 30RC hydronic package is a
diaphragm tank, meaning that a flexible diaphragm physically
separates the water/air interface. With this type of expansion tank,
it is undesirable to have any air in the water loop. See the section
on air separation below for instructions on providing air separation
equipment.
AIR SEPARATION
For proper system operation, it is essential that water loops be in-
stalled with proper means to manage air in the system. Free air in
the system can cause noise, reduce terminal output, stop flow, or
even cause pump failure due to pump cavitation. For closed sys-
tems, equipment should be provided to eliminate all air from the
system.
The amount of air that water can hold in solution depends on the
pressure and temperature of the water/air mixture. Air is less solu-
ble at higher temperatures and at lower pressures. Therefore, sepa-
ration can best be done at the point of highest water temperature
and lowest pressure. Typically, this point would be on the suction
side of the pump as the water is returning from the system or ter-
minals. Generally speaking, this is the best place to install an air
separator, if possible.
1.
Install automatic air vents at all high points in the system. (If
the 30RC unit is located at the high point of the system, a vent
can be installed on the piping entering the heat exchanger on
the 1/4-in. NPT female port.)
2.
Install an air separator in the water loop, at the place where
the water is at higher temperatures and lower pressures —
usually in the chilled water return piping. On a primary-sec-
ondary system, the highest temperature water is normally in
the secondary loop, close to the decoupler. Preference should
be given to that point on the system (see Fig. 18). In-line or
centrifugal air separators are readily available in the field.
It may not be possible to install air separators at the place of lowest
pressure and highest temperature. In such cases, preference should
be given to the points of highest temperature. It is important that
pipe be sized correctly so that free air can be moved to the point of
separation. Generally, a water velocity of at least 2 ft (610 mm)
per second will keep free air entrained and prevent it from forming
air pockets.
Automatic vents should be installed at all physically elevated
points in the system so that air can be eliminated during system
operation. Provision should also be made for manual venting
during the water loop fill. It is important that the automatic vents
be located in accessible locations for maintenance purposes, and
that they be located where they can be prevented from freezing.
28
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