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

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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. 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.

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Window with A/C unit

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Report Question How much heat is lost through the window? How much heat is lost through the window? Six scenarios are considered. Six scenarios are considered. 1. A/C unit with blinds and curtains open 2. A/C unit with blinds closed and curtains open 3. A/C unit with blinds and curtains closed 4. No A/C unit with blinds and curtains open 5. No A/C unit with blinds closed and curtains open 6. No A/C unit with blinds and curtains closed

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

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Methods 1. Temperatures were measured using a temperature gun, inside the room, outside, and the at the outer surfaces. 2. Appropriate thermal circuits were constructed for each scenario. 3. Heat transfer rates were calculated using the temperatures measured and the circuits.

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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

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Discussion of Results We expected the first three scenarios to have a much higher heat transfer rate than the last three scenarios. 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: 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 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 Radiation from inside the room is neglected

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

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Recommendations In order to minimize the heat loss through the bedroom window, the following actions should be taken: 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 A/C unit and plexiglass should be removed The window should be closed The window should be closed The blinds should be closed The blinds should be closed The curtains should be closed. The curtains should be closed.

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On average, home heating uses more energy than any other system in a home About 45% of total energy use More than half of homes use natural gas.

On average, home heating uses more energy than any other system in a home About 45% of total energy use More than half of homes use natural gas.

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