Direct solar gain, or heat from thermal storage, can be distributed throughout a building by either natural convection currents or mechanical ventilation. Hot air naturally rises and cold air sinks. Depending upon climate, design and the existence of backup heating, it may be necessary or advantageous to distribute passive solar energy by mechanical means such as fans and duct-work. Passive Solar Cooling Solar cooling may sound like an oxymoron, but there are a variety of ways in which the sun's energy, albeit indirectly, can be used to cool the interior of buildings. Painting buildings a light colour to reflect sunlight and keep them cool is also often considered to be a passive solar construction technique.
Trees also reduce local air temperatures by several degrees through evapo-transpiration.
Ivy and vines growing on the walls of a building serve the same purpose, but to a lesser degree. In the summer, cities are often several degrees hotter than the surrounding countryside because of sunlight hitting all the roofs and paved areas. An added bonus of deciduous trees is that they lose their leaves in the winter thus allowing passive solar heating, while still providing a wind-block which reduces heating requirements. Careful attention to the placement of windows which open and interior partitions can greatly increase the natural flow of air through a building, by capturing the prevailing winds. In climates with hot days and cool nights, night-time ventilation can be used to cool the thermal mass of a building.