1.5 Heating and Insulating Buildings
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There is a plethora of ways that individuals can do to minimise the amount of heat that is lost from one’s home. Heat in a house will want to escape and into the outside. There is an incentive for households to minimise the amount of heat loss because heating homes is very expensive. There are many methods to reduce the amount of heat that is lost from a home and some are more cost effective than others. The most cost effective methods will give you the biggest annual saving per pound spent. Over time the savings made from reducing heat loss will be so great that they cover the cost of purchasing/ implementing a certain method. This time period is known as the payback time. The formula for the payback time is:
Payback Time (in year) = Initial Outlay / Annual Saving
Some methods of reducing heat loss are:
- Loft insulation – this is a layer of fibreglass wool laid out across the whole floor under the floor boards to reduce conduction and radiation. Loft insulation tends to be fairly cheap and has a fairly short payback time. (The government used to engage in a scheme whereby they would pay half of the cost to individuals who got their lofts insulated).
- Double glazing – replacing windows is very expensive and the savings per year are relatively low with respect to the initial outlay. Therefore, the payback time for double glazing is very long.
- Curtains – windows are in contact with the outside and are considerably colder than the inside of the room. If there were no curtains the windows would cause the room to drop in temperature because of conduction and radiation. Curtains provide an air buffer against the cold glass in the windows, thus reducing the amount of heat loss. Curtains are cheap and provide a significant saving, meaning that the payback time is low.
- Cavity wall insulation – there is a cavity in a home’s exterior walls. You can fill this void with foam, which reduces the heat loss. The outlay for cavity walls tends to be between £400 and £1,000 and the payback period is between 5 and 10 years.
- Draught proofing – this reduces heat loss through convection. Draught proofing is making sure that all draughts are prevented from coming inside the house. You can draught proof your front door.
A few ways to reduce heat loss from homes.
U-Values
We can measure how fast heat can move through a material by using U-values. The higher the U-value is, the more heat is transferred through the material. Metals are good transferers of heat because of their free roaming electrons and have a high U-value. On the contrary, insulators, which are poor transferor’s of heat, have low U-values. Loft insulation is a poor conductor of heat and therefore has a low U-value.
We can measure how fast heat can move through a material by using U-values. The higher the U-value is, the more heat is transferred through the material. Metals are good transferers of heat because of their free roaming electrons and have a high U-value. On the contrary, insulators, which are poor transferor’s of heat, have low U-values. Loft insulation is a poor conductor of heat and therefore has a low U-value.
Specific Heat Capacity
Different substances require different amounts of energy to heat them up by one degree. For example, to heat one kilogram of water by 1 degree it takes 4181 J/kg°C, for oxygen it is 918 J/kg°C and for lead it is 128 J/kg°C. The specific heat capacity formula is:
Different substances require different amounts of energy to heat them up by one degree. For example, to heat one kilogram of water by 1 degree it takes 4181 J/kg°C, for oxygen it is 918 J/kg°C and for lead it is 128 J/kg°C. The specific heat capacity formula is:
E = m x c x θ
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Whereby:
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Let’s work out how much energy is needed to increase the temperature of 4kg of water from 15°C to 30°C. (note: it takes 4181 J to increase one kg of water by 1°C).
E = 4 x 4181 x 15 Energy required = 250,860 J or 250.86 kJ |
Water has a high specific heat capacity, which makes it useful for storing heat energy. Also, it is a liquid, which makes it easy to be transported. That is why water is used for central heating.