CHAPTER 21 I PASSIVE DESIGN


The design of low-energy housing is based on the concept of solar gain – capturing radiant energy from the sun to provide space heating, water heating and lighting.


Solar principles


When designing homes that capture the sun’s energy, it is essential to understand the movement of the sun in the sky and how this changes with the seasons.


Earth’s orbit


  the change in radiation, length of day, and climate between summer and winter. If there were no tilt, there would be uniform climatic conditions throughout the year (i.e. no seasons). The intensity of radiation from the sun also varies with the season of the year. The angle at which radiation from the sun falls on a surface changes as the relative tilt and orbit of the earth around the sun changes.


Arctic Circle


Tropic of Cancer (23.5°N) Equator


Tropic of Capricorn (23.5°S) Equinox


21–22 March sun vertical at Equator


23.5°


sun


Solstice


21–22 June sun vertical at latitude 23.5°N


Equinox


22–23 September sun vertical at Equator


orbit


Solstice


21–22 December sun vertical at latitude 23.5°S


21.01 The earth’s orbit: the earth rotates about the sun once per year; it rotates on its axis (towards the east, 


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