# Physics - Heating and Insulating Buildings (AQA Syllabus A)

The transfer of heat (thermal) energy is studied in GCSE Science. This is one of eight quizzes on that topic and it looks specifically at some ways of heating and insulating buildings in order to save both energy and money.

Keeping the warmth inside a home is an important consideration for many people. The architect who designs buildings needs to know how good different materials are at insulating them, so they can work out what sort of heating system will work the best. For whoever pays the bills, knowing where the most heat is being lost, and how to slow down that heat loss, will help them to save money on their heating bills. For anyone keen on environmental issues and keeping their carbon footprint as low as possible, knowing which environmentally friendly materials are the best insulators is essential.

This is the point that U-values step in! These are a measure of how fast heat can pass through a material. Building materials have been tested and their U-values worked out. A lower U-value indicates that heat only passes through the material slowly, therefore the material is better at insulating than one with a high U-value, and vice-versa. You don't need to know any specific U-values or how they are calculated.

Heating well insulated buildings requires less energy overall and so saves money on the heating costs. It also helps to reduce the emissions of carbon dioxide. Unless the building is heated by a non-polluting supply of electricity or by geothermal energy, somewhere down the line carbon dioxide will be released into the air. Let's take for example using electric storage heaters. These transfer electrical energy into heat, taking their electricity from the National Grid. Most National Grid electricity is produced in conventional power stations which release large quantities of carbon dioxide into the air. Using gas or oil fired central heating systems puts carbon dioxide into the air directly.

Using wood fired heating is more environmentally friendly as the carbon dioxide released is called current carbon. In other words, it is carbon from the present time rather than being from millions of years in the past, as happens when burning fossil fuels. For hot water, solar panels on the roof of a building use the Sun's heat instead of burning fuels.

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1. Which of the following is not a good reason for having solar hot water panels fitted?
On cloudy days the temperature of the water would need boosting using some other method of heating. There are other disadvantages too, for example the savings you make on your energy bills are quite small and, even on a small house, you need quite a large area of panels on a south facing roof to get sufficient hot water
2. If it costs £2,000 to insulate the walls and roof of a house, how long will the payback time be if it saves £250 per year?
There are other considerations to take into account when insulating a building, such as improved comfort. It's not just about the money
3. What are U-values?
No material is a perfect insulator - U-values tell you the rate at which heat energy can get through
4. A homeowner has part of the outside brick wall of her house demolished and fits double-glazed glass doors in the gap. The U-value of the wall was 0.4 and the U-value of glass doors is 1.8. What does this mean?
The higher U-value means that the new doors are less insulating than the original wall, so she will need to use more energy to keep the room as warm as it was before
5. To heat the water in a domestic hot water storage tank from 42°C to 50°C, an immersion heater transfers 4,536 kJ of energy to the water. How much water is in the tank? The specific heat capacity of water is 4,200 J/kgoC
You need to rearrange the specific heat equation to isolate the mass on the left hand side and remember to convert kJ to J
6. How do solar hot water panels work?
Heat reaches the Earth from the Sun in the form of infrared radiation. The water heating tubes are coloured black as that is the best colour for absorbing infrared
7. During the day, the Sun transfers energy to an outdoor swimming pool. The mass of water in the pool is 5,000 kg. The specific heat capacity of water is 4,200 J/kg °C. How much energy needs to be supplied to increase the water temperature by 5oC?
The correct equation for this calculation is Energy = Mass x Specific heat capacity x Temperature change. In the exam you should have a data sheet with a list of equations but it is still a good idea to memorise as many of the equations as you can
8. The best insulators have what sort of U-value?
The U-value is a measure of how many watts can pass through one square metre of the material if there is a 1oC temperature difference from one side to the other, so the best insulators have low U-values. A lower U-value means that fewer watts are getting through in any given period of time than would in a material with a higher U-value
9. What is meant by payback time in the context of insulating a building?
Payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£). It works for any energy saving situation, for example swapping conventional lightbulbs with low energy bulbs or LED lighting. The shorter the payback time, the more cost-effective it will be
10. At night, a storage heater transfers electrical energy into thermal energy which is stored. During the day, the heat is released to warm the room. Which of the following would store the most thermal energy per kg?
Of these materials only oil is actually used - this question is testing your understanding of specific heat capacity. In reality, storage heaters have a core of specially designed high density thermal blocks. These are heated by electric elements using cheap rate electricity during the night. These blocks are preferred instead of water or oil, even though they have a lower specific heat capacity. They are much more dense and can store more thermal energy without the risk of a leak. Oil storage heaters do not work as effectively as those fitted with the thermal blocks