Your task consists of four parts. The first is to calculate the total heat loss for the bungalow above. In parts two and three you recalculate heat loss, taking into account the effects of using insulating materials, and of rebuilding the bungalow using more energy efficient materials. Part four includes some suggestions for additional work.

In order to calculate the total heat loss, you will first need to calculate the heat lost through each of four areas (walls, roof, floor, windows), using the information in the table below. You will also need to refer to the U values table (above). You should assume the internal temperature is 20° and the external temperature is 5°C.

Now complete the following table and calculate the total heat loss.

The bungalow is very basic and it is possible to reduce heat loss with a minimum of structure alteration. Refer to the U values table and make changes that do not involve rebuilding. Calculate the new heat loss figures for walls, roof, floors and windows and for the house as a whole.

You decide to rebuild your bungalow to the same design and you decide to reduce heat loss to as much as possible by using different materials. Use the U value table to select your materials and calculate the heat loss by filling in the following tables.

1. How much energy would you save if you decided to:

• insulate the roof space with 10 cm of fibreglass?
• cover the floors with carpet and underlay?

2. Calculate the total heat loss in watts if the temperature outside falls to 0°C.

Questions

A heated house loses heat in several ways:

a. Through which material is heat loss greatest?

b. What percentage of heat is lost through the roof?

c. How could you reduce heat loss through the floors?

Heat loss values during the year

With reference to the graph above:

d. What is the meaning of k in kJ?

e. Which period of the year is most costly in terms of heating?

a. In which of the following is convection likely to be the main method of heat transfer?

i. Food being cooled in a microwave oven.

ii. Energy from the sun reaching the Earth.

iii. A room heated by a radiator.

iv. Heating a wire with a soldering iron.

v. Food being cooled under an electric grill.

b. For each of the others state what the main method of heat transfer would be.

During a spell of very cold weather heat loss through different surfaces was as follows:

a. Which surface gives the lowest rate of energy loss?

b. Why is less heat lost heat through interior rather than exterior walls?

c. What is the total heat lost per hour from the room?

d. If one bar of an electric fire supplies 2700kJ/h, how many bars would be needed to maintain the temperature of the room?

a. A tiled roof with no insulation has a U value of 2.2 W/m2°C. Explain what is meant by the phrase underlined.

b. A room in a house has a wall area of 15m2 and a window area of 4m2. The room temperature is 20°C and the outside is 8°C. Use the U-values below to calculate the saving in energy per second when the house owner decides to insulate the cavity walls and install double glazing.

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