Handbook of air conditioning and refrigeration / Shan K

Refrigeration load, tons Electric demand, MW
9
8
7
6
5
3600
3200
2800
2400
2000
Part-Load Operation
Off-peak On-peak
Charging
AIR CONDITIONING SYSTEMS: THERMAL STORAGE SYSTEMS 31.27
Drop in electric
demand in on-peak
hours
Refrigeration
load
Discharging
Off-peak
Charging
Direct cooling Direct cooling
0 2 4 6 8 10 12 14 16 18 20 22 24
Midnight
Noon Midnight
FIGURE 31.11 Electric demand curves and the storage cycle of the stratified chilled water storage system for an
electronic manufacturing facility in Dallas, Texas.
Electric
demand with
storage
Electric
demand without
storage
Estimated
refrigeration
load curve
temperature T rc � 56°F (13.3°C) is then forced through solenoid valve SV-7 and control valve CV-1
and introduced to the stratified tank through the top diffusers.
Temperature T rc is maintained by changing the chilled water temperature supplied to the air-handling
units from 45 to 52°F (7.2 to 11.1°C) instead of 41°F (5°C). As soon as temperature sensor T2
senses a return chilled water temperature T rc drop below 56°F (13.3°C), the DDC controller closes
the control valve CV-z slightly. Less stored chilled water is extracted by the building pumps. The
required amount of return chilled water at 56°F (13.3°C) bypasses the crossover and mixes with the
41°F (5°C) stored chilled water, which results in a higher supply temperature to the cooling coils.
During on-peak hours, the discharging process requires a refrigeration load from 2500 to 2800
tons (8790 to 9845 kW), with a total of 21,250 ton� h (74,715 kWh) for the 8-h on-peak period.
This electronic manufacturing facility includes clean rooms, computer rooms, compressed air aftercoolers,
and manufacturing equipment, all of which need 24-h continuous cooling. Its daytime
refrigeration load averages about 1240 tons (4360 kW).