Retrofitting For Passive Solar

[jpak]

http://permaculturetokyo.blogspot.com/2007/01/retrofitting-for-passive-solar.html

The following is a write up of a seminar given at Noah’s Café in Tokyo. The focus of the seminar was suggesting potential retrofits to the café to reduce the heating costs. More will be written on passive solar design in the future, but for the purposes of this article, we will just look at enough to understand how to retrofit existing buildings.

In cold climates, 20% of the economy can be dedicated in one way or another to keeping warm. For areas below the Arctic Circle, this need not be the case. On a sunny winter’s day at 45°N (or south) latitude, there is around 957 Wh/m2 available to us for heating… if we use it. This is almost equivalent to the energy used by running a 1000W hairdryer for one hour falling on every square metre of ground.

There are 3 types of heating available to us: convective heating (heating using hot air), conductive heating (an object coming into contact with a hotter object), and radiant heating (heat radiating off a hot object such as the sun). While conductive heating is the most efficient, it is not practical for heating living spaces. Convective heating is the most common, but is also the least efficient. Radiant heating is the most efficient means of heating that is available to us. Luckily, we can get the sun to help us to use radiant heat.

To capture the sun’s heat, we use a technique called passive solar heating. We allow visible sunlight to enter a building through a window. When the sunlight hits objects in a room, some of that light is transformed into longer wave infrared light or heat. The windows then prevent most of the infrared light from escaping the building. Massive structures (concrete, brick or even water tanks) called thermal mass are used to store the heat generated and slowly re-radiate it into the building.

<more with lots o' graphics

[jobycom]

1. Thanks. Good information. nt