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Heat loss in buildings
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Heat loss in buildings

SDG Ensure access to affordable, reliable, sustainable and modern energy for all

The level of comfort inside a building depends upon the season, time of day and whether the room is being heated or cooled; it also depends upon the level of activity such as working during the day or sleeping at night. In the home the largest amount of energy is used for space heating and it is important to understand the ways in which heat can flow in order to reduce our energy consumption and use energy more efficiently.

Heat flow

Heat is a form of energy which flows from a hotter to a colder source. Solar radiance is the most important factor in determining heat flow; in summer heat is likely to flow into a building whilst during the winter the flow is reversed. Northern Europe has long winters and short summers whereas the length of the seasons is reversed in southern Europe.

The level of comfort inside a building depends upon the season, time of day and whether the room is being heated or cooled; it also depends upon the level of activity such as working during the day or sleeping at night. In the home the largest amount of energy is used for space heating and it is important to understand the ways in which heat can flow in order to reduce our energy consumption and use energy more efficiently.

Heat transfer

Heat energy can be transferred from a hot to a colder object in three ways -

  • Conduction where the heat is physically transferred across a like a wall or window
  • Convection in which the heat is circulated away from the heat source by moving air
  • Radiation in which heat is transferred by heat waves, the sun being the ultimate radiation source

These heat transfer processes are all dependent upon the difference in temperature between the hot and cold source; the greater the temperature difference the faster the heat transfer


Adding insulation

The average life time of a dwelling in the EU is now more than 100 years. Over the years the building standards have increased in all countries so that the older the dwelling, the poorer is the insulation standard. Increasing the level of insulation to that closer to today’s standards will improve the fabric of the dwelling, extend its life and reduce any condensation that might be present. In this way, savings can be made in terms of energy, money and the environment. A grant may be available to insulate your home so it is worth checking with your local energy advice centre or utility.

As heating our homes in winter is the biggest consumer of energy in middle and northern Europe, it is essential to insulate our buildings in order to reduce the heat loss and thereby the energy demand.


Walls are the largest source heat loss because they represent the largest area in contact with the cold air outside. If the wall has a cavity between the outer and inner wall then it can be insulated at any time. If there is no cavity then the walls can be insulated internally or externally. External insulation is not easy as it also requires weather proofing and will generally require installation by a technical specialist.

Special reflection foils made of aluminium can be stuck to the wall behind the radiators so that they are not visible. Heat will be reflected from the radiator back into the room minimising the heat to be lost through the walls.

The heat loss is greatest for a detached dwelling which has the largest number of outside walls and least for an apartment in a multi-family dwelling.

Windows are responsible for up to a quarter of the total energy loss either through the glass pane directly or by ventilation through any gap between the window frame and the wall. To reduce heat loss it is possible to replace a single glass pane with two (or even three) glass panes within the same window frame. To prevent convection of heat between the panes, the space between is either partially evacuated or filled with an inert gas like argon. Whether it is necessary to replace the window frame will depend upon the type and condition of the frame and how well it is sealed into the opening in the wall.

Typical heat loss in a building


windows

Single panes of glass can also contribute to condensation during the winter as moisture condenses on the inside of the window.

High levels of condensation can contribute to health problems as these can create conditions in which house mites can flourish which can lead to bronchial illnesses such as asthma or allergies. So reducing heat transfer rates through windows has more than one benefit.

Roof and floors

May be responsible for up to 25% of the total energy losses The exact value will depend on the type of building and its level of existing insulation – the loss will be smallest in apartment buildings where t apartments have neighbours with heated flats above and below and highest in individual homes.

A variety of insulating materials exist for both roofs and floors. If there is access to the loft space between the ceiling and the roof, it is generally possible to add additional insulation at relatively low cost for which a grant or subsidy might well be available. If there is no loft, then insulation can only be added beneath the ceiling if height allows or on the roof if it is flat.

It is generally not possible to check whether there is any insulation under the floor unless the house has wooden sprung floors. Only new houses are likely to have insulation under the floor. Floor carpets do provide some level of insulation.


Doors leading to the outside or onto a balcony are fewer than windows and so contribute less to heat loss.

Green roofs
Green roofs will provide insulation of the roof with plants growing on soil above a waterproof membrane.

Passive architecture
Passive architecture is common in older buildings and well-designed modern buildings to retain heat in winter and keep out solar gain from sunshine in summer. Shutters for example can admit light and solar gain during the day in winter and can be closed at night to keep the heat in. Conversely they can be close during the day on summer to keep out solar gain and opened at night to allow the building to cool.

Energy labelling of buildings
Energy efficiency and the environmental impact of buildings have now also been labelled and these labels are illustrated below and need to be displayed or shown for all buildings when rented or sold.

energy label

Energy efficiency and environmental impact labels for buildings

These labels are accompanied by a description of the current insulation level and what is possible and cost effective to reduce the heat loss and heating bill

Thermostats
One of the easiest ways of saving energy is to regulate the temperature! This can be done by installing thermostatic valves on radiators so it is possible to vary the temperatures in each room. With a programmable thermostatic regulator, the temperature can be reduced when the family is out of the home, at work, school or on holiday. Setting the temperature down by 1 degree saves about 6% of heat energy! A room which is not used for longer times may be heated only to 16C rather than 20C for normal occupancy.

Descaler and inhibitors in central heating systems

Radiators in houses are sized to meet their heat loss. If however the water in the central heating system is not maintained at its neutral level (pH 7.0) then a chemical reaction will occur between the water and the steel pipework and radiators resulting in the build up of corrosion products. These products comprise gases which congregate in the top of radiators so limiting the heat transfer area and the build up of inorganic salts on the internal walls of radiators so limiting their ability to transfer heat.


Sachet containing 250cc inhibitor/descaler to reduce corrosion and scale inside radiators


Possible energy saving measures include -

  • Installing thermostatic valves on each radiator so that the appropriate temperature can be set in each room
  • Placing reflecting panels behind radiators to ensure that heat is reflected into the room
  • Descaling radiators by adding inhibitor/descaler to central heating water system
  • Increasing thermal insulation
  • installing passive solar measures
KITH # Activity Age range
4.3 Heat loss detective
  Science
  11 – 16  
 

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