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Heat transfer rates through a bedroom window with and without an A/C unit PowerPoint PPT Presentation


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Heat transfer rates through a bedroom window with and without an A/C unit . Sam Sanderson David Theurer December 2006. Description of Problem.

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Heat transfer rates through a bedroom window with and without an A/C unit

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Heat transfer rates through a bedroom window with and without an A/C unit

Sam Sanderson

David Theurer

December 2006


Description of Problem

  • A bedroom window has been fitted with a window mounted air conditioning unit. The window has been opened and plexiglas cut and fit to cover the remaining opening.


Window with A/C unit


Report Question

  • How much heat is lost through the window?

  • Six scenarios are considered.

    • A/C unit with blinds and curtains open

    • A/C unit with blinds closed and curtains open

    • A/C unit with blinds and curtains closed

    • No A/C unit with blinds and curtains open

    • No A/C unit with blinds closed and curtains open

    • No A/C unit with blinds and curtains closed


Assumptions

  • We will only consider the heat modes of convection and conduction from the room to the window and convection and radiation from the outer surfaces to the outside.

  • We assume that the convection coefficient for the inside is 5 and for the outside is 15. These are both in the range of natural convection.

  • The room temperature is 70 degrees Fahrenheit and the outside temperature is 22 degrees Fahrenheit.


Methods

  • Temperatures were measured using a temperature gun, inside the room, outside, and the at the outer surfaces.

  • Appropriate thermal circuits were constructed for each scenario.

  • Heat transfer rates were calculated using the temperatures measured and the circuits.


Results

ScenarioHeat Transfer (W)

1A/C only 125.5

2A/C w/ blinds 125.2

3A/C w/ blinds & curtains 121.1

4No A/C 124.3

5No A/C w/blinds 121.1

6No A/C w/blinds & curtains 117.3


Discussion of Results

  • We expected the first three scenarios to have a much higher heat transfer rate than the last three scenarios.

  • Reasons why they were so similar could be:

    • The plexiglas allows high rates of heat transfer, but the two windows stacked together allowed much lower rates of heat transfer which lowered the total heat transfer rates

    • Radiation from inside the room is neglected


Discussion of Results

  • We expected the highest heat transfer rate to be scenario 1 and the lowest to be scenario 6. This was true but the numbers were closer than expected.

  • Each time more insulation was added (closing the blinds and the curtains) the heat transfer rate dropped with the curtains making the largest difference.


Recommendations

  • In order to minimize the heat loss through the bedroom window, the following actions should be taken:

    • The A/C unit and plexiglass should be removed

    • The window should be closed

    • The blinds should be closed

    • The curtains should be closed.


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