Heat transfer rates through Heat transfer rates through a bedroom window with and a bedroom window with and

without an A/C unit without an A/C unit

Sam SandersonSam SandersonDavid TheurerDavid Theurer

December 2006December 2006

Description of ProblemDescription of Problem

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

Window with A/C unitWindow with A/C unit

Report QuestionReport 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.1.1. A/C unit with blinds and curtains openA/C unit with blinds and curtains open2.2. A/C unit with blinds closed and curtains openA/C unit with blinds closed and curtains open3.3. A/C unit with blinds and curtains closedA/C unit with blinds and curtains closed4.4. No A/C unit with blinds and curtains openNo A/C unit with blinds and curtains open5.5. No A/C unit with blinds closed and curtains openNo A/C unit with blinds closed and curtains open6.6. No A/C unit with blinds and curtains closedNo A/C unit with blinds and curtains closed

AssumptionsAssumptions

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

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

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

MethodsMethods

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

2.2. Appropriate thermal circuits were Appropriate thermal circuits were constructed for each scenario.constructed for each scenario.

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

ResultsResults

ScenarioScenario Heat Transfer (W)Heat Transfer (W)

11 A/C onlyA/C only 125.5125.5

22 A/C w/ blindsA/C w/ blinds 125.2125.2

33 A/C w/ blinds & curtainsA/C w/ blinds & curtains 121.1121.1

44 No A/CNo A/C 124.3124.3

55 No A/C w/blindsNo A/C w/blinds 121.1121.1

66 No A/C w/blinds & curtains No A/C w/blinds & curtains 117.3117.3

Discussion of ResultsDiscussion of Results

We expected the first three scenarios to have a We expected the first three scenarios to have a much higher heat transfer rate than the last much higher heat transfer rate than the last three scenarios. 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 plexiglas allows high rates of heat transfer, but

the two windows stacked together allowed much the two windows stacked together allowed much lower rates of heat transfer which lowered the total lower rates of heat transfer which lowered the total heat transfer ratesheat transfer rates

Radiation from inside the room is neglectedRadiation from inside the room is neglected

Discussion of ResultsDiscussion of Results

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

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

RecommendationsRecommendations

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