Carrier 30GB060 - Manual (Page 5)

Correct unit capacity — On glycol performance
capacity correction curve, read 0.95.
Corrected capacity = 0.95 x determined capacity
- 0.95 X 61.3
= 58.2 tons
Correct chilled water flow — On the gpm correction
factor curve, read 1.15.
Chilled water flow (at corrected capacity)
24 X corrected capacity
Application data (cont)
temperature rise
24 X 58.2 tons
= U.S. gpm
14 F
99.8 U.S. gpm
Chilled water flow (40% solution) = 1.15x99.8
= 114.7 U.S. gpm
Correct cooler pressure drop — On cooler pressure
drop correction curve, read 1.33.
On cooler pressure drop curve, for 114.7 gpm, read
PD = 10 ft water gage. The pressure drop for 40% solution =
1.33 X 10.0 = 13.3 ft water.
Correct compressor power input (kW) — On power
correction curve, read 0.97 correction factor at 40%
EG concentration.
Power input from Selection Procedure example
= 71.1 kW.
Corrected power input = 0.97 x 71.1 = 68.9 kW.
ETHYLENE GLYCOL PERFORMANCE
CORRECTION FACTORS AND SOLUTION
CRYSTALLIZATION POINTS
10 20 30 40
% CONCENTRATION (BY WEIGHT)
ETHYLENE GLYCOL
50
(F) -40
-20
-10
0
+20
40
(C) r-40
c -30
-20
-10
0
Oversizing chillers
Oversizing chillers by more than 15% at design conditions
must be avoided as the system operating efficiency would
be affected adversely (resulting in greater/excessive
electrical demand). When future expansion of equipment
is anticipated, it is strongly recommended that a single
chiller be installed to meet present load requirements
and a second chiller added 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.
Multiple chillers
Where chiller capacities greater than 200 tons (703 kW)
are required, or where stand-by capability is desired,
chillers may be installed in parallel. Units should be of
equal size to ensure balanced water flows. Where a large
temperature drop (>25F [13.9 C]) is desired, chillers
may be installed in series. Water temperature sensors
need not be moved for multiple chiller operation. A 10-ft
(3-m) separation is required between units for airflow,
and a 6-ft (1.8-m) distance is required from units to
obstructions. See figure. See Physical Data for service
clearances.
(3m) (I.Sm)
10 FT
6
FT
* MINIMUM MINIMUM
/ / / / / / / /
MULTIPLE UNIT SEPARATION
Electrical/utility interests
Energy management — See 30GB Controls and Trouble­
shooting manual and accessory installation instructions
for details.
Demand limiting (also called load shedding) — When
utilities demand for electricity exceeds a certain level,
loads are shed to keep electricity demand below a pre­
scribed maximum level. Typically, this happens on hot
days when air conditioning is most needed.
Load shedding must be done intelligently. Demand
may be limited on Model 30GB by resetting water tem­
perature, or by using a demand limit accessory that
unloads the chiller to a given predetermined percent of
the load. Both features require signal from an intelligent
central control. Do not cycle demand limiter for less than
10 minutes on and 5 minutes off.
Duty cycling cycles electrical loads at regular intervals
regardless of need. This reduces electrical operating
costs of a building by “fooling” demand indicating
devices. Duty cycling of compressors or fans is not
recommended since motor winding and bearing life
suffer from constant cycling.