Oversizing chillers
Oversizing chillers by more than 15% at design conditions
must be avoided as the system operating efficiency would
be adversely affected (resulting in greater and/or excessive
electrical demand and cycling of compressors). When future
expansion of equipment is anticipated, install a single chiller
to meet present load requirements, and install a second chiller
to meet the additional load demand.
It is also recommended that the installation of 2 smaller
chillers be considered where operation at minimum load is
critical. The operation of a smaller chiller loaded to a greater
percent of minimum is preferred to operating a single chiller
at or near its minimum recommended value.
Hot gas bypass should not be used as a means to allow
oversizing chillers. Hot gas bypass should be given consid-
eration where substantial operating time is anticipated be-
low the minimum unloading step.
Multiple chillers
Where chiller capacities required are greater than can be
furnished by a 30H chiller, or where standby capability is
desired, chillers may be installed in
parallel.
Units of equal
size help to ensure balanced fluid flows. Where a large tem-
perature drop (
.
25° F [13.9° C]) is desired, chillers may
be installed in
series.
Fluid temperature sensors need not
be moved for multiple chiller operation.
Part-wind start
Part-wind start is not generally required on 30H chillers due
to use of multiple small compressors allowing smaller elec-
trical load increments, but it is available if required. Maxi-
mum instantaneous current flow (see ICF in Electrical Data
table on page 29) should be used in determining need.
Vibration isolation
Compressors are spring isolated. External vibration isola-
tion is not generally required.
Strainers
For 30HR units, a strainer with a minimum of 20 mesh
should be installed in both the cooler and condenser fluid
inlet lines just ahead of the cooler and condenser, and as
close to the cooler and condenser as possible. For 30HS
units, this recommendation applies only to the cooler.
Capacity correction (antifreeze)
If unit or fluid lines connected to the unit are in an area
where ambient temperature falls below 32 F (0° C), it is
strongly recommended that antifreeze (or other suitable brine)
be used in the chilled fluid circuit. Unit performance data
must be corrected as shown in the following example (us-
ing inhibited ethylene glycol solution):
EXAMPLE — ENGLISH
I Determine concentration of inhibited ethylene
glycol (EG) solution required to protect the sys-
tem to 0° F (at zero flow).
From Solution Crystallization Point correction curve on
page 16: 35% EG concentration is required for solu-
tion crystallization at 0° F.
Consider the 30HR080 unit selected in the Selection
Procedure section on page 17.
II Correct unit capacity.
On Capacity Correction curve on page 16, read 0.965
correction factor at 35% concentration.
Corrected Capacity = 0.965 x Rated Capacity
= 0.965 x 77.2
= 74.5 Tons
III Correct cooler water flow rate (Gpm).
On Cooler Flow Correction curve on page 16, read
1.112 correction factor at 35% concentration.
Cooler Water Flow
(at corrected capacity)
=
=
Tons x 24
74.5 x 24
D
T
10
= 178.8 Gpm
Cooler Water Flow
(35% EG)
= 1.112 x 178.8 = 198.8 Gpm
IV Correct cooler pressure drop.
On Cooler Pressure Drop Correction curve on
page 18, read 1.28 correction factor at 35%
concentration.
On Cooler Pressure Drop curve, (page 19) for
198.8 gpm of water, Pressure Drop = 12.1 ft of
water.
For 35% EG solution,
Pressure Drop
= 1.28 x 12.1
= 15.5 ft of water
V Correct compressor power input (kW).
On Power Correction curve on page 16, read 0.988
correction factor at 35% concentration.
Corrected Power Input = 0.988 x 68.6
= 67.8 kW
15