generated from the UPS of rated capacity 40 kVA. The following parameters were noticed
while performing the assessment of the total system.
UPS Parameters:
Rating Input Power (kW) Output Power (kW)
40 kVA
On Load (16 hrs) 11.94 8.61
No Load (8 hrs) 1.16 0.00
Air conditioner parameters:
Installed capacity of Air conditioner 7.5 TR
Outdoor unit (condenser) air velocity 6.1 m/s
Radius of the fan opening at the point of velocity measurement
in outdoor unit
0.30 m
Air Density 1.174 kg/m3
Ambient temperature 305 0K
Temperature of hot air (condenser outlet) 313.5 0K
Specific heat of air 1.009 kJ/kg K
Power drawn by the compressor 5.40 kW
Efficiency of the compressor motor 90 %
Calculate
a) Present delivery capacity of air conditioner (TR) (3 Marks)
b) Power drawn per TR of refrigeration (3 Marks)
c) Calculate the annual energy savings for 7200 hrs, if the UPS is relocated to a non
air-conditioned ventilated area. Assume energy cost Rs.8/kWh.
ANSWER:
Capacity Installed 7.5 TR
Outdoor unit air velocity 6.1 m/s
Radius of the opening 0.30 m
Area of cross section (3.14x0.3^2) 0.283 m2
Total Air flow (0.283x6.1) 1.72 m3/s
Density of the air 1.174 kg/m3
Mass of air, m (1.72x1.174) 2.02 kg/s
Ambient temperature, T1 305 oK
Air temperature, T2 313.5 oK
Difference in Temperature (T2-T1), (dT) 8.5 oK
Specific Heat at Constant pressure, cp 1.009 kJ/kgK
Heat Transfer (mxCpx(T2-T1)) 17.32 kJ/s
Heat transfer per hour 62352 kJ/hr
14917 kcal/Hr
Heat input from the compressor (5.4x0.9x860) 4180 kcal/Hr
Evaporator heat load (14949-4180) 10737 kcal/Hr
1 Tonne of refrigeration 3024 kCal/Hr
Effective TR 3.55 TR
Power drawn by the compressor 5.40 kW
power taken per TR of refrigeration 1.52 kW/ TR
Heat Load generated by UPS in Conditioned Space
Rating/ Location
Input
Power
(kW)
Output
Power
(kW)
Heat Load
(kW) kCal/Sec kCal/Hr TR/hr
Total
TR/day
40 kVA
On
Load
(16hrs)
11.94 8.61 3.33 0.80 2880 0.95 15.2
No Load
(8hrs)
1.16 0 1.16 0.28 1008 0.33 2.64
Total 17.84
The savings that can be achieved by providing clean, cool and dust free environment for UPS
operation is given below.
AC Load generated by UPS/ day = 17.84 TR
Power taken by AC to generate 17.82 TR at 1.52 kW/ TR = 27.12 kW
Annual energy savings at 300 days of operation = 8136 kWh
Cost of power = Rs.8/ kWh
Annual Cost Savings = Rs.65,088/-
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