Download Problem Statement - University of Colorado Boulder

MCEN 5228
Sustainable Energy
9/14/06
Week 2 Problem, Part A:
All variable values used to calculate the Total Levelized Cost were obtained from Table
5.3 and Table 7.6 of the “Levelized Cost of Coal” handout posted on the website. The
equations to calculate the Total Levelized Cost are on p. 216 of the aforementioned
handout. See attached spreadsheet for calculations. The Total Levelized Cost of the
coal-fired power plant was 6.63 cents/kWh. Note: I used an average coal power plant
thermal efficiency of 35%, as was discussed in class.
Week 2 Problem, Part B:
Assumptions:
1. Average outdoor temperature: The average outdoor temperature in Boulder was
obtained from the provided website, http://www.wrcc.dri.edu/cgibin/cliMONtavt.pl?coboul. This yielded an average temperature of 9.1 C.
2. Number of hours in a year: I obtained an average of 8766 hours per year from
Google.
3. Cost of electricity: My most recent XCEL power bill showed 7.9 cents/kWhr.
4. Power plant efficiency: I assumed that the electric power was generated using a
coal-fired power plant, since this is the primary source of electricity in Boulder. I
assumed an efficiency of 35% for this power plant when calculating the total
reduction in CO2 emissions.
5. Coal heating value: I assumed a coal heating value (kW-hr/kg) of 8, again from
Google.
6. Coal carbon content: I assumed a 40% carbon content for coal, also from Google.
Analysis:
1. Annual reduction in heat loss if double-pane windows are used instead of
single-pane: Using the window schematic provided, I calculated the annual heat
loss (kW-hr) through the single-pane and double-pane glass from inside the
building to the ambient temperature outside. Of course, the annual heat loss
through the double-paned windows was less than that of the single-paned
windows. The difference in heat loss highlighted in yellow and called “yearly
heat loss reduction” on the Excel spreadsheet. Basically, this is the annual heat
that is saved by using double-paned windows. Quantified, this annual heat loss
reduction is 179,814 kW-hr/yr, resulting in an annual power bill reduction of
about $14,000.
2. Estimated payback time for the extra energy used to make double-paned instead
of single-paned windows: Using the material breakdown given in the problem
statement, I first calculated the individual cost associated with the various window
materials (glass, metal, etc), as well as production and installation. Additionally, I
obtained corresponding energy intensity values from table III.4, but for
production and installation I used the energy intensity parameters given in the
problem statement. Next, I calculated the total energy required to produce all the
single and double-paned windows required. The difference of these two values
resulted in the additional energy investment required to manufacture doublepaned windows. This energy investment, divided by the heat loss savings,
resulted in an energy payback time of about 1.5 years.
3. The total reduction in CO2 emissions if double-paned windows are used
(assume electric heating): First, using the coal power plant efficiency, I
calculated the total annual energy savings from using double-paned windows,
which was 513,754 kW-hr. Using the heating value of coal, this resulted in an
annual savings of 64,219 kg of coal. This amount of coal not being combusted to
produce power corresponds to an annual CO2 reduction of 94,188 kg, and a
lifetime reduction of 2,825,649 kg of CO2.
4. The financial payback periods & estimate of he time value of money at an
interest rate of 7% and an inflation rate of 3%: Using the previously calculated
values of the additional material cost investment, and the annual electricity bill
savings, I projected these values into their corresponding future values using the
interest and inflation rates provided. These values were used to calculate a
financial payback period of about 2 years, which is well below the threshold of 5
years discussed in class. Therefore, this is definitely a worthwhile project.
Recommendations:
Switch to double paned windows (at a minimum). Further efficiencies from windows
involve Low-E glass, gas-fill between the 2 panes, or triple-paning. I’m sure there are
several more options that I’m unaware of also.