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.

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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.
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

Scenario Heat Transfer (W)

1 A/C only 125.5

2 A/C w/ blinds 125.2

3 A/C w/ blinds & curtains 121.1

4 No A/C 124.3

5 No A/C w/blinds 121.1

6 No 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.