Sterlco 30RA Outdoor Air Cooled Central Chillers 10-60 Tons - Manual (Page 17)

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Table 6 — Maximum Loop Volume Limits
NOTE: Max loop volume is based on typical system of 12 psi and
30 psi of min/max pressures, and 100 F mean temperature. If the
volume in the system is greater than the limits listed, then extra
expansion tank volume must be added to the system.
Pump Modification/Trimming — Since the pumps are
constant speed, the only way to obtain greater flow with a
given pump/impeller is to decrease system head. This will
allow the pump to “ride” its curve to the right, resulting in
increased flow. If greater flow is necessary, look at opening the
balance valve. Also, verify that the strainer is clean, and that no
unnecessary system resistance is present, such as partially
closed isolation valves.
Increasing system resistance by closing the balancing valve
will force the pump to “ride” its curve to the left, resulting in
less flow. Although this does reduce power consumption
slightly, it may not be the desirable method of reducing the
flow, especially if a rather large reduction is needed.
The other method for reducing flow on a constant speed
pump is impeller trimming. The impellers in the pumps provid-
ed in the 30RA hydronic kit are easily removable for this pur-
pose. Refer to the ITT literature packet supplied with the
hydronic package information on Seal Replacement in the
Service Section, and follow its instructions for impeller remov-
al. Trimming should only be done by a qualified machine shop
that has experience in this operation. Contact your local Sterling
representative for a recommended machine shop. After trim-
ming, the impeller MUST be balanced. Failure to balance
trimmed impellers can result in excessive vibration, noise, and
premature bearing failure.
Impeller trimming has the added benefit of maximum BHP
savings. It is very possible for power savings to pay for the
trimming cost very quickly.
Freeze Protection — The 30RA units are provided with a
water strainer and a flow switch to protect against freezing situ-
ations that occur from no water flow. While the flow switch
(paddle-type) is helpful in preventing freezing during no-flow
situations, it does not protect the chiller in case of power fail-
ure, or in other cases where water temperature falls below the
freezing mark. Appropriate concentrations of inhibited ethyl-
ene glycol or other suitable inhibited antifreeze solution should
be considered for chiller protection where ambient tempera-
tures are expected to fall below 32 F. Consult local water treat-
ment specialist on characteristics of the system water and add a
recommended inhibitor to the chilled water.
1. If the pump will be subjected to freezing temperatures,
steps must be taken to prevent freeze damage. If the
pump will not be used during this time, it is recommend-
ed to drain the pump and hydronic package and these
components back-flushed with inhibited glycol. Other-
wise, a glycol-water solution should be considered as the
heat transfer fluid. Drains are located on the balancing
valves for units with hydronic kits. Units without hydron-
ic kits have a drain mounted on the piping leaving the
heat exchanger. Drain knockouts are located on the sheet
metal base of all units.
NOTE: Do not use automobile anti-freeze, or any other fluid
that is not approved for heat exchanger duty. Only use appro-
priately inhibited glycols, concentrated to provide adequate
protection for the temperature considered.
2. Use an electric tape heater for the internal piping (exclud-
ing those within the pump box) if unit will be exposed to
freezing temperature.
3. Ensure that power is available to the chiller at all times,
even during the off-season, so that the pump and cooler
heaters have power. Also make sure that the piping tape
heaters also have power.
4. On units with pump packages, a heater is supplied in the
pump box that will protect this section from freezing in
outdoor-air temperatures down to –20 F, except in case of
a power failure. Sterling warranty does not cover damage
due to freezing.
5. Cooler heaters that will protect down to –20 F can be
installed as a factory option. Again, it should be noted
that these heaters will not protect the cooler from freezing
in the event of a power failure.
Preparation for Winter Shutdown — Do not shut off power
disconnect during off-season shutdown. At the end of the cool-
ing season:
1. Drain water from system.
2. Replace drain plug(s) and add sufficient inhibited ethyl-
ene glycol (or other suitable inhibited antifreeze) to
cooler, pump and piping to prevent freezing of residual
water.
3. At the beginning of the next cooling season, refill cooler
and add recommended inhibitor.
MAX LOOP VOLUME IN GALLONS (LITERS)
% Ethylene Glycol 30RA010-030 30RA032-055
0 (Pure Water) 310 (1173) 725 (2744)
10 180 (681) 425 (1609)
20 175 (662) 410 (1552)
30 155 (587) 370 (1400)
40 150 (568) 350 (1325)
50 145 (549) 340 (1287)
% Propylene Glycol 30RA010-030 30RA032-055
10 175 (662) 410 (1552)
20 150 (568) 350 (1325)
30 128 (484) 300 (1136)
40 118 (447) 275 (1041)
BAD
BAD
GOOD
GOOD
Fig. 17 — Tank Baffling