Carrier 30GB060 - Manual (Page 6)

Time clock shutdown (or other controlled shutdown
not associated with leaving chilled water temperature)
requires use of accessory demand limit control module.
Second step of the demand limit control (0-50% of
capacity) is set for 0 (zero) capacity. This allows unit to
go through a normal pumpout cycle at shutdown.
Part-wind start
Not generally required on 30GB chillers due to use of
multiple compressors allowing smaller electrical load
increments, but is available if required. Maximum
instantaneous current flow (see ICF in Electrical Data)
should be used in determining need.
Application data (cont)
Vibration isolation
Compressors are spring isolated,
isolation is not generally required.
External vibration
Hot gas bypass usage (units with TXV only)
Hot gas bi^pass usage, while frequently specified, is not
normally recommended because it results in equipment
being applied below its normal application range. Before
applying hot gas bypass, it is recommended that use of 2
machines be considered, including one that can be run at
the system minimum load without addition of hot gas
bypass. In those instances where there is no alternative,
it is recommended that the appropriate hot gas bypass
package can be used with the factory option TXV unit.
Medium temperature brine application — Application
of 30GB outdoor chillers for brine duty within the 39.9 F
to 34 F (4.4 C to 1°C) range is possible with proper field
change of control configuration. Application in the
range 34 F to 15 F (1°C to -9.4 C) requires 30GB unit
with factory modification.
Selection procedure
I Determine unit size and operating conditions
required to provide specified capacity at given
conditions:
Capacity required............................................. 60 tons
Leaving chilled water temperature ....................... 45 F
Chilled water temperature rise ............................. 14 F
Condenser entering air temperature (CEAT) .. 95 F
Loop volume ............................................. 230 gallons
Ratings are based on 10 F rise and are suitable for rise
from 5 F to 15 F without adjustment. In this case,
however, greater accuracy is desired.
II Correct LCWT for 14 F cooler water tempera­
ture rise.
Enter correction curve at 14 F and read a correction
of 0.3 F. Corrected LCWT is, therefore, 45 + 0.3 = 45.3 F.
III Determine capacity, unit size and power input.
Enter rating table at given CEAT and LCWT —
respectively 95 F and 45 F.
Read down capacity column until the capacity nearest
to but higher than specified required capacity is
reached. In this case, 60.9 tons is delivered by a
30GB060. Interpolate between 45 F and 46 F to find
determined capacity and power input at corrected
LCWT (45.3 F). Values are:
Capacity......................................................... 61.3 tons
Power input .....................................................71.1 kW
IV Calculate corrected cooler water flow.
Water _ 24 x corr capacity in tons
flow temperature rise F
24 X 61.3
U.S. gpm
14
105.1 U.S. gpm
V Calculate the cooler pressure drop.
Enter cooler pressure drop curve at the corrected
flow rate (105.1 U.S. gpm) and read, for the 30GB060,
a pressure drop of 9 ft of water.
VI Check loop volume and cooler water flow rate.
Minimum loop volume, from application data, is
180 gallons for 30GB060. Therefore, given volume of
230 gallons is satisfactory. Minimum water flow rate,
from application data, is 67 gpm for 30GB060. Flow rate
of 105.1 gpm is well above minimum required.