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## Q. 9.2

An existing chiller with a capacity of 800 kW and with an average seasonal COP of 3.5 is to be replaced by a new chiller with the same capacity but with an average seasonal COP of 4.5. Determine the simple payback period of the chiller replacement if the cost of electricity is $0.07/kWh and the cost differential of the new chiller is$15,000. Assume that the number of equivalent full-load hours for the chiller is 1,000 per year both before and after the replacement.

## Verified Solution

In this example, the energy use savings can be calculated using Eq. (9.12) with $SEER_{e} = 3.5, SEER_{r} = 4.5, N_{h,C} = 1,000, Q_{C} = 800 kW, and LF_{C}$ = 1.0 (it is assumed 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)

$ΔE_{c}=800kW*1,000 hrs/yr*1.0*(\frac {1}{3.5}-\frac{1}{4.5})=50,800k Wh/yr$

Therefore, the simple payback period for investing in a high-efficiency chiller rather than a standard chiller can be estimated as follows:

$SPB=\frac {\15,000}{50,800k Wh/yr*\0.07/kWh}=4.2 years$

A life-cycle cost analysis may be required to determine if the investment in a high energyefficient chiller is really warranted.