ETL 1110-1-181
12 Jan 98
c. First Cost Difference. The difference in first cost values of 2
different chillers is the first cost difference. In Table C3 for
example, the first cost difference of the 0.65 kW/ton chiller verses the
0.70 chiller is equal to ,000 (,400 - ,400).
d. Annual Energy Usage. The chiller capacity times the chiller
efficiency times the EFLH is the annual energy usage. In Table C3 for
example, the annual energy usage of a 200 ton chiller with an efficiency
of 0.70 kW/ton and an EFLH of 1,000 is equal to 140,000 kWh/year (200 x
0.70 x 1,000).
e. Demand Charges. Demand charges are additional charges or fees
that utility companies require most installations to pay in addition to
the energy usage charges. The structure of demand charges in comparison
around the country vary significantly most specifically in price and
length of occurrence. Demand charges can range in price from per kW
up to per kW and can be incurred over an entire year or just certain
months. Demand charges also often include additional rachet clauses
which are typically used to determine an installation's minimum demand
charges. In example 1, no demand charges were included into the
calculations. In example 2 on page C-10, a monthly demand charge of
per kW is used and are shown to occur 12 months out of the year. On
page C-11, the annual demand charge is calculated to be the monthly
demand charge times the number of months times the chiller capacity
times the chiller efficiency. In Table C9 for example, the annual
demand charge incurred by a 200 ton chiller with an efficiency of 0.70
kW/ton which incurs a monthly demand charge of per kW over a 12 month
period is equal to ,400 (8 x 12 x 200 x 0.70).
f. Annual Energy Costs. A chiller's annual energy usage times the
energy cost plus any applicable demand charges is the annual energy
costs. In Table C4 for example, a 200 ton chiller with an efficiency of
0.70 kW/ton operating under energy costs of 0.02 $/kWh has an annual
energy cost of ,800 (140,000 x 0.02).
g. Incremental Savings. The difference in the annual energy costs
between 2 different chillers is the incremental savings. In Table C4
for example, the incremental savings for the chiller with an efficiency
of 0.65 kW/ton verses the chiller with an efficiency of 0.70 kW/ton
(both operate with an energy cost of 0.02 $/kWh) is equal to 0
(,800 - ,600).
h. Discounted Savings. The incremental savings times the
appropriate discount factor is the discounted savings. Discounted
savings can be thought of as a number which represents what the
projected savings of selecting one chiller verses another will be over a
certain length of time. The discount factor (or uniform present worth
factor) used in the calculations was taken from NISTIR 85-3273-10.
NISTIR 85-3273-10 includes energy price indices and discount factors for
performing life-cycle cost analysis of energy conservation projects.
The discount factor was determined based upon the United States average
for commercial applications over a 20 year economic life. In Table C4
for example, the discounted savings for the chiller with an efficiency
of 0.65 kW/ton verses the chiller with an efficiency of 0.70 kW/ton
(both operate with an energy cost of 0.02 $/kWh) is equal to ,618
C-2
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