Differences between Passive Heating and Passive Cooling

June 5, 2015

Passive components / devices store or hold energy and do not require an external source for their operation. Conversely, active components produce energy through current or voltage.

Passive Design

Passive design depends upon greenhouse rules and passive methods used to trap solar radiation, and to cool and circulate air. The intent is to achieve a comfortable building temperature environment by maximizing naturally-obtained heat and cooling sources and air circulation.

Passive indoor climates are not achieved by electrical or mechanical means. Passive heating and cooling are based on controlling heat gain and dissipation. They are essentially accomplished

1. Through the natural removal of heat by thermal mass, dispersing heat gain through heat transfer, or

2. By preventing accumulated internal / external heat.

Passive heating and cooling design objectives are similar. However, the emphasis on which passive design to focus on, depends on the particular region’s climate.

Passive Heating

Passive solar heating design allows winter sun in and keeps it in, while keeping the summer sun out and letting the heat build-up escape. Solar heating is the least expensive method of home-heating. This passive design also depends on opening and closing windows and isolating zone spaces.

Effective passive solar heating design includes:

  • a northern exposure for daytime living areas,
  • designed zoning spaces,
  • selection of appropriate passive window glazing,
  • thermal mass (for storing heat), and
  • insulation and sealing.

Direct solar gain heating is passive short-wave sun radiation that comes through window glazing to heat the interior space. Indirect solar gain heating is long-wave infrared radiated passive heating achieved from re-radiating the heat already within the building’s fabric. Indirect solar gain heating is sometimes referred to as the greenhouse effect. Variations in results can occur during differences during daylight hours or time of year.

Solar gains can be maximized through a combination of active and passive thermal mass insulation and systems that absorb, store, and release heat.

Passive Cooling

Passive cooling is the least expensive means of home cooling. Effective passive cooling design that reduce thermal gains includes:

  • natural ventilation,
  • evaporative cooling,
  • shading and insulation, and
  • green roofs and reflective surfaces.

Cooling the building envelope to minimize heat gain can be maximized using:

  • direct shading systems for windows, walls, and roofs from direct solar gain,
  • lighter-colored roofs to reflect heat,
  • insulation and zoning, and
  • Limited thermal mass systems (avoiding daytime heat gain storage).

There is a wider variety of passive cooling sources than passive heating that only comes from solar radiation. Passive cooling is supplemented in particularly hot, humid climates and extreme conditions by mechanical / electrical means. However, heat loss can naturally be maximized using:

  • air movement,
  • natural air flow (cool breezes),
  • evaporation,
  • earth coupling, and
  • reflection / reflective surfaces.

Air movement is the most important passive cooling element since it cools people by increasing evaporation and buildings by removing warm air out of the building and replacing it with cool external air. Well-designed openings, including windows, doors, and vents, and breeze paths are important for unobstructed air movement. Air movement is less effective in high humidity. Increased air speeds increase evaporation, but not necessarily cooling at lower relative humidity.

Moisture evaporation from the building surface is accomplished through evaporative cooling. Passive cooling fountains, ponds, and other water aid in evaporative cooling. Essentially, large amounts of heat from the air is removed as water evaporates. Evaporation is most effective when relative humidity is low. Evaporation increases relative to air movement.

Connor Pincus Group. Consulting Engineers.

Address: 1196 Toorak Road, CAMBERWELL, VIC 3124

Phone: (03) 9835 5000
Fax: (03) 9835 5050

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