Solar Thermal Design: How It Works

Every child knows that the sun is hot.  This very fundamental concept is what is behind solar thermal design.  Solar thermal house design uses the sun’s energy and warmth to keep a home at a comfortable living temperature day and night without any need for using other forms of heat energy, such as electric fires or log burners.  Solar thermal house design goes by several other names:

• Passive solar heating
• Passive heating
• Passive cooling
• Passive solar cooling.

Solar Thermal Design For Heating and Cooling

It may seem strange at first glance that solar thermal design can be used to either heat or to cool a building.  But it can.  The principles of solar thermal design that are used to keep a house warm can be used in reverse to cool a house.  The best method to use really depends on the area the house is being built in.  If you live in Tasmania or New Zealand, then solar heating is the ideal.  Conversely, if you live in the Red Centre, passive solar cooling is more what you need.

Solar thermal design makes use of a number of properties of the material world.  The thermal mass of certain building materials is one, the ability of certain colours to absorb heat, and the principles of convection and insulation.

Considerations for Solar Thermal Heating Designs

In a house with solar thermal design intended to heat the house, several things will need to be accomplished:

• Sunlight must be allowed in to as much of the house as possible.
• The heat must be caught and stored.
• The heat must be released at some stage.
• The house cannot get unbearably hot inside.

To maximise the amount of sunshine inside a house, solar thermal design dictates that the house must have as many windows into main rooms facing the sun at its highest point – north in the Southern Hemisphere.  This means that the house will be spread along the east-west axis.  All the main living rooms will be on the north side of the house and will have large windows to let in plenty of light and heat.  Rooms that don’t need as much heating – lavatories, laundries, bathrooms and storage areas – are located on the shady side.

Materials To Use in Solar Thermal Houses

Building materials are an important part of solar thermal design.  Stone, earthbrick and rammed earth all have the property of being able to absorb heat from the sun during the day, then release it at night when the air cools.  Have you ever noticed how more cold blooded creatures (snakes and lizards) like to crawl onto roads at night?  This is because they are making the most of how the road surface releases the heat it has absorbed during the day. This property of stone and rammed earth is known as its thermal mass.  Solar thermal design uses a lot of stone or rammed earth, as this has a high thermal mass.  This means that it absorbs heat during the day, which means that the ambient temperature of the rooms doesn’t get unbearable, but the rooms stay comfortable at night as the stone slowly disperses its heat energy to the cooler air.  

Solar thermal design also makes use of good ventilation, much like a glasshouse.  These windows in the sunny rooms are kept open during the day to allow air to circulate, but are closed at nightfall (this is, of course, done manually) to trap the heat in.