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Chapter 9

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.

Step-by-Step

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.