Energy Efficient Windows

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Energy Efficient Windows
Presented by Mike Meaders Ashok Tamang
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Objective To find if we can save energy used in
heating and money by using energy efficient
windows

• Process
• Assumptions
• Analysis
• Calculations
• Result

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Our Assumptions

• Assumptions
• Window dimension
• 1 m 1m
• Inside air Ti 72 0F 22.2 0C 295K Tsi
  15 0C
• For air _at_ Tf
• K 0.0259 W/m.k
• v 15.44 10-6
• alpha 21.8 10-6
• Pr 0.708

• Other Assumptions
• Outside Air Winter Salt Lake City
  To average 0 0C 273K (www.weatherchannel.com)
  Tso 7 0C
• For air _at_ Tf
• K 24.1 10-3 W/m.k
• v 13.49 10-6
• alpha 18.9 10-6
• Pr 0.714
• Tsi 15 0C

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Figurative Analysis
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R total 1/ (2/R1) (2/R2-6) (1/R7-9)
Calculations

• Ra Lo,2-6 26.638
• Nu Lo,2-6 (avg) 1.921
• h o,2-6 (avg) 15.43
• Ra Li,2-6 19.206
• Nu Li ,2-6(avg) 1.838
• h I,2-6 (avg) 15.87
• R2-6 10.925 (0.8547/k frame) (0.6838/K
  pane) (0.5128/K spacer)
• Ra Lo,7-9 0.9004 109
• Nu Lo ,7-9(avg) 119.04
• h o,7-9 (avg) 2.958
• Ra Li ,7-9 705.83 106
• Nu Li,7-9 (avg) 110.32
• h i ,7-9(avg) 2.946
• R 7-9 0.7197 (0.0085/K pane) (0.0064/K
  glass)

• Ra Lo1 1704.8
• Nu Lo1 (avg) 3.7898
• h o1 (avg) 7.611
•  Ra Li1 1229.2
• Nu Li1 (avg) 3.559
• h i1 (avg) 7.682
• R1 5.5154 0.4061/K frame

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Derivation of Formula to calculate the heat
transfer through the entire window structure

• q T i(infinity) T o(infinity) /R total
• R total 1/ (2/R1) (2/R2-6) (1/R7-9)

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Results

• Using the derived equation for heat loss, we
  simply need to plug in the thermal conductivity
  of various materials to compare their
  effectiveness.
• There is surprisingly little innovation
  currently being done to the actual glass pane in
  producing windows that insulate better. However
  there is much being done concerning solar
  radiation admittance. But this is beyond the
  scope of this project. Thus in these
  calculations, we will leave the pane material
  constant at soda lime glass (k 1.4 W/mK). We
  will then vary other common materials for the
  three key points of energy efficient window
  construction.

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Results
Cheapest Window causes average heat loss q
34.55 W Window with all the best features causes
average heat loss q 22.19 W The average
difference 12.36 W
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Results

• With some assumptions, we can calculate the
  average heating costs involved with each type of
  window.
• Assumptions Subject House has 25 m² of windows
  throughout the house in 1m x 1m segments with
  frames in between
• Heat loss is only through windows
• Natural Gas costs in Salt Lake City
  1.007/therm
•  
• Energy Balance
•  
• Ein Eout
•  
• Qin 25q(24 hrs.)
• Cost rateQin
• Cost rate25q(86400 s)
•  
• For Cheapest Windows
• Cost (1.007/therm) 25(34.55 W)(86400 s)(
  therm/105,480,400 joules)
•  
• Average Cost .71/ winter day
•