Acentrifugal chiller with a capacity of 500 kW and with an average seasonal COP of 4.0 operates with a leaving chilled temperature of 4.5°C. Determine the cost savings incurred by installing an automatic controller that allows the leaving water temperature to be set 2.5°C higher on average. Assume that the number of equivalent full-load hours for the chiller is 1,500 per year and that the electricity cost is $0.07/kWh.
Chapter 9
Q. 9.3
Step-by-Step
Verified Solution
Using Figure 9.13, the increase in the COP for a centrifugal chiller due to increasing the leaving chilled water temperature from 4.5°C to 7.0°C is about 8 percent. The energy use savings can be calculated using Eq. (9.12) with SEER_{e} = 4.0; SEER_{r} = 4.0 * 1.08 = 4.32; N_{h,C} = 1,500, Q_{C} = 500 kW, and LF_{C} = 1.0 (assume that the chiller is sized correctly):
ΔE_{c}=\dot{Q}_{C}.N_{h,C}.LF_{C}.(\frac {1}{SEER_{e}}-\frac{1}{SEER_{r}}) (9.12)
ΔE_{c}=500kW*1500 hrs/yr*1.0*(\frac {1}{4.0}-\frac{1}{4.32})=13,890k Wh/yr
Therefore, the energy cost savings is $970.
