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Required information Sometimes equations can be developed and practical problems solved by knowing nothing more than the dimensions of the key parameters. For example, consider the heat loss through a window in a building. Window efficiency is rated in terms of R value, which has the unit of ft2-hr-F/Btu. A certain manufacturer offers a double-pane window with R=2.5 and also a triple-pane window with R=3.4. Both windows are 3.5 ft by 5 ft. On a given winter day, the temperature difference between the inside and outside is 45°F. Assume that a homeowner buys 20 such triple-pane windows for the house. A typical winter equals about 120 heating days at AT= 45°F. Each triple-pane window costs $85 more than a double-pane window. Ignoring interest and inflation, how many years will it take the homeowner to make up the additional cost of the triple-pane windows from heating bill savings? 9.5 years

Required information Sometimes equations can be developed and practical problems solved by knowing nothing more than the dimensions of the key parameters. For example, consider the heat loss through a window in a building. Window efficiency is rated in terms of R value, which has the unit of ft2-hr-F/Btu. A certain manufacturer offers a double-pane window with R=2.5 and also a triple-pane window with R=3.4. Both windows are 3.5 ft by 5 ft. On a given winter day, the temperature difference between the inside and outside is 45°F. Assume that a homeowner buys 20 such triple-pane windows for the house. A typical winter equals about 120 heating days at AT= 45°F. Each triple-pane window costs $85 more than a double-pane window. Ignoring interest and inflation, how many years will it take the homeowner to make up the additional cost of the triple-pane windows from heating bill savings? 9.5 years

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter5: Analysis Of Convection Heat Transfer
Section: Chapter Questions
Problem 5.18P: The drag on an airplane wing in flight is known to be a function of the density of air (), the...
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### Heat Loss Through Windows: An Example Problem **Required Information** Sometimes equations can be developed and practical problems solved by knowing nothing more than the dimensions of the key parameters. For example, consider the heat loss through a window in a building. Window efficiency is rated in terms of \( R \) value, which has the unit of \( \text{ft}^2 \cdot \text{hr} \cdot ^\circ\text{F} / \text{Btu} \). A certain manufacturer offers a double-pane window with \( R = 2.5 \) and also a triple-pane window with \( R = 3.4 \). Both windows are 3.5 ft by 5 ft. On a given winter day, the temperature difference between the inside and outside is 45°F. **Scenario** Assume that a homeowner buys 20 such triple-pane windows for their house. A typical winter equals about 120 heating days at \( \Delta T = 45^\circ \text{F} \). Each triple-pane window costs $85 more than a double-pane window. Ignoring interest and inflation, how many years will it take the homeowner to make up the additional cost of the triple-pane windows from heating bill savings? **Solution** To solve this problem, the first step is to calculate the heat loss through both types of windows and determine the savings from the more efficient triple-pane option. Given that the need is to cover the additional costs through savings, the number of years required to recover these costs will be computed. **Result** The calculated time to cover the additional cost of installing the triple-pane windows is shown to be: - **9.5 years** **Navigation** - **Previous:** Problem 4 - **Next:** Problem 6 (Note: The solution to the problem necessitates mathematical computations which are to be done separately for educational purposes.)
Transcribed Image Text:### Heat Loss Through Windows: An Example Problem **Required Information** Sometimes equations can be developed and practical problems solved by knowing nothing more than the dimensions of the key parameters. For example, consider the heat loss through a window in a building. Window efficiency is rated in terms of \( R \) value, which has the unit of \( \text{ft}^2 \cdot \text{hr} \cdot ^\circ\text{F} / \text{Btu} \). A certain manufacturer offers a double-pane window with \( R = 2.5 \) and also a triple-pane window with \( R = 3.4 \). Both windows are 3.5 ft by 5 ft. On a given winter day, the temperature difference between the inside and outside is 45°F. **Scenario** Assume that a homeowner buys 20 such triple-pane windows for their house. A typical winter equals about 120 heating days at \( \Delta T = 45^\circ \text{F} \). Each triple-pane window costs $85 more than a double-pane window. Ignoring interest and inflation, how many years will it take the homeowner to make up the additional cost of the triple-pane windows from heating bill savings? **Solution** To solve this problem, the first step is to calculate the heat loss through both types of windows and determine the savings from the more efficient triple-pane option. Given that the need is to cover the additional costs through savings, the number of years required to recover these costs will be computed. **Result** The calculated time to cover the additional cost of installing the triple-pane windows is shown to be: - **9.5 years** **Navigation** - **Previous:** Problem 4 - **Next:** Problem 6 (Note: The solution to the problem necessitates mathematical computations which are to be done separately for educational purposes.)
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