# Energy Management

**Topics:**Imperial units, Conversion of units, Energy

**Pages:**2 (307 words)

**Published:**January 22, 2013

1. A hospital is considering the purchase of a large commercial laundry dryer, and is attempting to decide between an electric and natural gas powered system. If electricity costs $0.06/kWh and is used with an efficiency of 90%, what is the equivalent price of natural gas per therm if it can be burned with an efficiency of 80%?

Dimensional Analysis

|$.06 |29.3 KWh |.8 efficiency | |.90 efficiency |1 therm | |

= 1.5626 = $1.56/ therm

2. A new lighting system will save $25,000 per year for 8 years. How much would a company pay for this device if the interest rate (discount rate) is 15%?

Using[pic], and then solve for P, A =200km r= 15%, t = 8, n=1

P= $65,380.35

3. Which is the simplest method of calculating the economic benefit of an energy saving investment? When is/isn’t this method not recommended?

Simple Payback Period just like the name implies this is best for 1 or 2 year investments. If investment period goes over then should consider another method.

4. A 250,000 sq ft manufacturing facility has annual energy usage of 2.5 million kWh of electricity and 10 million cu ft of natural gas usage in one year. The cost of electricity is $0.10/kWh and the total natural gas bill is $180,000/yr.

a. Calculate the Energy Use Index.

b. Calculate the Energy Cost Index.

A) EUI = 10 million, 1ft3 = 1000 Btu = 10 X 103 MMBtu

2.5 million KWh, = 1kWh= 3,412 Btu = 8.53 X 103 MMBtu

= (10+8.53) X 103 MMBtu/ 250k sq feet = 74,210 Btu/ft2/yr

B) ECI= 2.5 million KWh X .10 KWh = 250k

Total Natural gas bill = 180k

= (250+180)K/ 250K sq feet = 1.72/sq ft/yr

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