Download Energy Cost Savings Using Insulative Plastic Film

Energy Cost Savings Using
Insulative Plastic Film
ME 340 Project – Nolan Crook
How can I reduce my home energy costs?
• Plastic film is a very cheap and simple option for adding window
insulation, but how well does it work?
• Objective: Determine cost savings per year when using plastic film
insulation
Problem Setup and Procedure
• Determine the temperatures of:
Tinf_outside
Tsurface_outside
Tsurface_inside_window
Tsurface_plastic_film
Tinf_outside
Plastic film
Tinf_inside
Tsurface_outside
2-pane window
•
•
•
•
•
Tsurface_inside_window
Tsurface_plastic_film
Tinf_inside
• Use this info to find heat transfer coefficient “h” using free convection with
vertical plate
• Describe the window with and without film as a single resistor
• Use this resistance value to find insulation efficiency throughout the year
Case 1 – No film (double paned window)
• Resistor Network:
Routside
Tinf_outside
Rwindow
Tsurface_outside
Rinside
Tsurface_inside_window
Tinf_inside
Case 2 – Plastic film included
• Resistor Network:
Routside
Tinf_outside
Rwindow
Tsurface_outside
Rfilm+enclosed_air
Tsurface_inside_window
Tplastic
Rinside
Tinf_inside
Actual Measured Air Temperatures (from my
room window)
Convection for vertical Plate
• Find Grashof Number
• Find Rayleigh Number using Grashof
• Find Nusselt Number using Rayleigh (Nusselt for vertical plate free
convection)
• Find convection coefficient for both cases from Nuzzelt Number
• Find q (W/m^2) for both cases using convection coefficient
• Find Rfilm and Rno_film using q and Tinf_out as well as Tinf_in
• (See attached calculation sheet for more details)
Energy analysis
• Define q as a function of Tinf_out so that the outside temperature can be varied
over the course of the year while holding a constant Tinf_in
• The area of the windows was calculated using parameters for my apartment (6
windows, 12.26m^2 total)
Energy Analysis Continued
• Define Energy (kW*hr) as a function of q(Tinf_out)
Taken from weather.com for Provo, UT
•
In the above equations, 12 hours was used
instead of 24 to evaluate at both average high
and low temperatures for Provo.
• Also, the absolute values of the above equations
were taken to account for heating or cooling
(energy leaving or entering through window)
Results over course of year
Results/Discussion
•
•
•
As can be seen from previous slide, energy transfer through the window is much less
using plastic film, especially during the winter
Total energy transfer values over year:
•
•
No film: 18,804 kW*hr
Plastic film: 3,012 kW*hr (six times less!)
Total energy costs (assuming 1 kW*hr electricity = $0.08, and all heating cooling done
with electricity at 100% efficiency)
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•
•
•
No film: $1504
Plastic film: $241
Savings: $1263
Cost of plastic film: $12.95
Conclusions
•
•
•
There is a large energy cost savings for using an extra insulative layer on
inside of windows, at only a cost of $12.95 from amazon.com
This is accomplished by reducing the temperature difference between most
inner surface temperature and Tinf_inner ,thereby reducing free convection
The savings of $1200/year seems very large; this may be due to the following
inaccuracies:
•
•
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The thermal resistance of the window is held constant across changing temperatures,
but in reality the convection coefficient of the free convection will change at different
temperatures
Average low and high temperatures are assumed to be at 12 hour durations each, which
is not accurate at Provo’s latitude
All heating and cooling is assumed to be electric (no natural gas), with 100% efficiencies