ETL 1110-1-181

12 Jan 98

Appendix C

Sample Economic Comparisons

C-1. OBJECTIVE. The objective of this Appendix is to perform a sample

economical analysis to determine the optimum efficiency to specify for a

specific chiller capacity. The type and size of chiller to be evaluated

is an electrically-driven, water-cooled 200 ton centrifugal type unit.

First cost and efficiency values used in the calculations and presented

in Table C1 below are approximations. This data should not be used in

any other economic comparisons.

Table C1. Typical Data for a 200 Ton

Centrifugal Type Chiller

IPLV (kW/ton)

First Costs

0.70

,400

0.65

,400

0.62

,700

0.60

,000

0.58

,000

C-2. CALCULATIONS. Two example efficiency comparison calculations are

provided in this Appendix. Example 1 calculations, as presented on

pages C-4 through C-9, are based on energy costs without any demand

charge factors. Example 2 calculations, as presented on pages C-10

through C-15, are based on energy costs which include demand charge

factors. The terms and definitions used in the calculations are

explained in the following paragraph. The calculations provide the most

economical solutions for variable energy costs and variable chiller

energy usage.

C-3. DEFINITIONS. The following is a list of terms and definitions

used throughout the calculations.

a. Energy Costs. Optimum chiller efficiencies were determined using

energy costs equal to 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08 and 0.09

$/kWh. These energy costs are typical values for what can be

encountered across the country.

b. Equivalent Full-Load Hours (EFLH). Over a year's period a

chiller will operate at partial load the majority of the time. Full-

load conditions are experienced only a small percentage of the time.

For this exercise, the only way to estimate a chiller's annual energy

usage is to estimate the chiller's annual full-load run hours or EFLH.

For most typical chiller applications the EFLH can be approximated to be

equal to 50% of a chiller's estimated run hours over a year's period

(e.g., a chiller that is estimated to run approximately 8000 hours/year

will have an EFLH of 4000). Optimum chiller efficiencies were

determined in the attached calculations using EFLH equal to 1000, 2000,

3000, and 4000. Note: Instead of using the EFLH method to determine

chiller energy usage, the ideal way to determine actual energy usage

would be to model the installation using an annual energy load

calculation program such as BLAST or Trane's Trace 600.

C-1

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