Passive solar

Before the introduction of boilers and heat distribution systems like radiators or warm air flow, the primary form of controlling the climate inside a building was by means of passive solar architecture. The basic natural processes used in passive solar architecture are the thermal energy flows associated with radiation, conduction, and natural convection. When sunlight shines on a building, the building materials can reflect, transmit, or absorb the solar radiation. Additionally, the heat produced by the sun causes air movement that can be predicted.

These basic responses to solar heat have lead to design elements, material choices and placements that can provide heating and cooling effects in a home. These can often be seen in older buildings and particularly in southern Europe where for example, windows have external shutters which can be used to limit the solar gain during the summer and retain heat in the winter.

Passive architecture has the great advantage in that it requires no external energy source and therefore has neither a running cost nor does it contribute to environmental pollution. Such features can enhance the visual appearance of a building and will help to preserve its fabric. Whilst it is best considered when designing a new building, many of the techniques can be retrofitted to existing buildings. The potential of any building will depend upon the age, orientation and type.

When sunlight falls on a building some of it will be reflected depending upon the colour of the wall –

• white walls will reflect the greatest amount of heat and so traditional buildings in southern Europe generally have white walls to reduce the solar gain in summer
• darker colours reflect less heat but absorb more heat so traditional buildings in northern Europe are often painted red to capture solar radiation.

Heat will flow from the hotter to the colder parts of the building through one of three processes –

• conduction through the external to the internal wall of the building
• convection through the movement of air inside a room from the hotter to colder par of the room or by air movement through open windows or doors
• radiation from walls and roofs when air temperature falls below that of building element

Traditional forms of architecture either enhance or reduce heat flows by altering one or more of these flow processes.

Advantages

• reduction in solar gain in summer so decreasing the need for cooling
• increase in solar gain in winter so decreasing the need for heating
• as only passive elements are used no energy is consumed and no pollution created
• cost effectiveness as passive elements have similar life to the building itself
• enhances appearance of buildings as traditional architectural elements used
• reduced use of fossil fuels
• reduced rate of climate change
• reduced noise levels from air conditioning systems

Disadvantages

• they are best undertaken when a building is being designed
• the building may not be suitably orientated to enhance solar gain in winter
• in some protected areas it may not be possible to change the external appearance of buildings
• for some forms of building construction it may be difficult to attach passive solar elements

Thermal inertia is an important characteristic for the thermal comfort in the home. It is the resistance of a body to a change in temperature when the ambient temperature changes: the greater the mass of a body the greater its thermal inertia. Low inertia buildings are quickly heated by the sun and so quickly cool at night. High inertia buildings keep a more constant temperature as the building acts as a thermal store storing energy in its walls during the day and then gives out this stored heat once the sun goes down and the air cools during the night.

Double wall with cavity for high thermal inertia