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Chapter 10

Q. 10.3

A centrifugal chiller (having a capacity of 500 kW and an average seasonal COP of 4.0) operates with a leaving chilled water temperature of 4.5°C. Determine the cost savings incurred by installing an automatic controller that allows the leaving chilled 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.

Step-by-Step

Verified Solution

Using Figure 9.13 (refer to Chapter 9), 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;  and  Q_{C} = 500 kW; 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 annual energy cost savings are $970/yr.