Active Systems Active systems involve moving parts that circulate air through a building or move a liquid, most often water. Such systems may be used either in conjunction with passive design or as stand-alone heating or cooling systems. A fan, when combined with a passive system, is a common method to pull hot air to other locations in the building. Warm air is often brought to a low point in the building to create an assisted convective loop, helping to circulate air throughout the building. These systems may also be combined with thermal storage to further increase energy savings and comfort.
Roofs can also support active systems, such as solar water heaters.
Today's water heating technology is far superior to the solar water heaters of the 1970s, and utility incentives for solar water heating are on the increase. The payback period for the heaters depends on the system, on the climatic conditions, and on local utility incentives. Possible future use of the roof for photovoltaics and solar water heaters represents an additional rationale for orienting roofs to the south. Daylighting Daylighting, or the use of natural light in a building, reduces the need for electric lights and improves the visual qualities of a space. It is one of the most rewarding design measures and is consistent with the heating and cooling aspects of passive design.