How Passive Solar Design Works

Understanding how passive solar house design works you will need to understand the way heat moves and how it can be stored.

The basic law of physics states that heat moves from hot to cold.

Therefore if your house has a higher internal temperature than the external temperature then heat will flow out to the outside.

This applies to materials as well so if a wall is hot it will release heat if the surrounding air is cooler.

Passive solar makes use of this to distribute heat in your house.

Heat moving by conduction is really heat travelling from molecule to molecule.

That's how heat moves through a wall or any mass.

A poker is placed in a fire conducts the heat to the end outside the fire making it too hot to touch.

Heat transfer by convection is through the medium of gases and liquids.

Warm air rises and so does liquids. Passive solar uses this method to transfer heat from a south facing wall to the house interiors.

Radiation or radiant heat moves heat through the air from hot to cold.

Passive solar uses two types, solar radiation and infrared radiation.

As radiation strikes an object it will reflected or transmitted or absorbed depending on the object properties.

Black objects absorb more radiation than say white coloured object sand that is why solar products are black in colour.

Within a house heat is radiated from hot to cold areas such as glass,windows and walls.

Glass transmits about 90% of solar radiation and absorbs a small percentage either and reflects an even smaller percentage.

When the solar radiation strikes an object within the home it is absorbed or radiated out words again.

The glass absorbs this infrared radiation and radiates it back to the home.

This way the glass traps the heat as solar gain in the home.

Heat Storage

Heat is stored in materials and the ability to store heat is called thermal capacitance.

Thermal mass stores heat by changing its temperature. The greater the thermal mass the easier to store heat.

Walls of block work concrete are very useful to store heat as well as water.


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