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

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

2. 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.

3. Window with A/C unit

4. 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

5. 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.

6. 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.

7. 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

8. 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

9. 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.

10. 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.