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Passive Solar Energy Design

 

Passive solar design uses the heat of the sun to regulate a building's temperature, without using other energy sources. In comparison, active solar design uses other [mechanical] means are used to supplement or supply heating.

Passive solar technologies convert sunlight into usable heat to:

  • Heating - for current heating needs and to store heat for future use. Heat is absorbed into the building and slowly released back into the house as it cools.
  • Ventilation - by generating air-movement for passive cooling - part of passive solar technology.

Passive solar construction has a number of design benefits:

  1. Saves energy
  2. Reduces dampness and condensation
  3. Improves sound insulation
  4. Increases the durability of building materials
  5. Makes the home healthier

Solar heating can be the sole source of warmth or can be supplemented by other sources. Consequently passive solar design has the potential to reduce New Zealand’s greenhouse gas emissions.

Most houses do not use energy efficiently. Space and water heating savings from employing passive solar design and technology can be significant

Hot summers and cold winters provide design challenges for solar buildings. Passive solar design elements aims to:

  1. Use correct window design to admit as much solar heat as possible
  2. Use the right materials to store as much heat as possible
  3. Install plenty of insulation to conserve heat.
  4. Correct placement of shading, ventilation and insulation to keep a house cool in summer without the need for air-conditioning, and warm in winter.

Basic passive solar design principles can produce year-round comfort in your home for little cost and can be retrofitted to existing homes as well as new homes. Any additional cost is quickly paid in savings on energy costs.

 

Levels of Passive Solar Design

There are 3 levels of passive solar design employed by architects:

  1. Direct - use of windows and shutters and other design features designed to capture a 'short cycle' of solar energy
  2. Indirect - uses building structures such as walls, water tanks and earthen roofs to make greater use of solar energy by acting as both as insulation and as a mechanism for the slow-release of heat capability
  3. Isolated - techniques and purpose built structures, such as solar stoves and chimneys, that capture solar energy and release it slowly through the building.

 

Integrating Passive Solar Design Into Your Building Plan

The integration of passive solar design into building design can be complicated; demanding creativity and flexibility to capture energy most effectively.

Key design components are:

Location - a common mistake is using too many large windows facing the sun, making houses uncomfortably hot during the day. Consideration must also be given to adjacent buildings and trees to provide shade for all or part of the day.

Locally Available Materials - to construct passive solar structural features of the building, as well as ancillary technologies

Joinery - careful consideration must be given to the type and size of windows, as well as their location.

Shape of Building - taking advantage of local terrain and established trees and adjacent structures to insulate against both heat, noise and pollution.

Heating, cooling and ventilation (HVAC) systems - to provide thermal comfort, acceptable indoor air quality, and reasonable installation, operation, and maintenance costs. Conventional HVAC systems account for 25 - 35% of a countries total energy use.

Materials

The success of passive solar design also depends upon the best use of materials.

Heavy materials are used to store the heat, acting as a thermal mass, known as a heat tank. Such materials include:

  • Concrete
  • Terracotta or ceramic tiles
  • Brick
  • Stone

These are used internally to absorb the sun's rediant heat, and then release it slowly into the house during the evening and night. Additional heating may be required in cooler regions during winter.

In deciding the proportion and placement of thermal mass materials a designer considers:

  • Climate
  • Daylighting
  • Shading conditions

Heating Systems

An energy efficient home is one where temperatures are constant, throughout the day and throughout the house. The home will be warm in winter, and cool in the summer. Pollution through excessive energy consumption is reduced, and a healthier home results.

A correctly sized heating system is assessed in consideration of passive solar heating and the additional heating and cooling required during the peaks of winter and summer. Combined with improved airtight construction and design, the overall heating system reduces the amount of energy consumed by the house, significantly reducing long term costs.

Active solar technologies are those that use significant amounts of conventional energy to power pumps or fans. In contrast, some passive systems use minimal conventional energy to control dampers, shutters, night insulation, and other devices that enhance solar energy collection, storage, use, and reduce undesirable heat transfer.

Passive solar technologies include:

  • Direct and indirect solar gain - space heating
  • Solar water heating systems - based on the thermosiphon
  • Thermal mass and phase-change materials - to even out indoor air temperature fluctuations. Proximal deciduous trees provide natural shade during the summer and allow light and solar warming into the building during the winter. The water content of trees alsos help moderate local temperatures.
  • Solar cookers
  • Solar chimney - enhances natural ventilation. Composed of a hollow thermal mass venting the interior to outside the building. As the chimney warms, air inside the chimney structre is heated and rises, generating an updraft, pulling air through the building.
  • Earth sheltering
  • Trombe wall - a passive solar heating and ventilation system consisting of an air channel sandwiched between a window and a sun-facing thermal mass. The thermal mass stores heat from the sun, warming the air channel, causing circulation through vents at the top and bottom of the wall.
  • Solar roof ponds - a solar heating and cooling technology consisting of a roof mounted water bladder with a movable insulating cover. The systemcontrols heat exchange between the interior and exterior environments by covering and uncovering the bladder between night and day.
    • To Heat - the bladder is uncovered to heat the water during the day to store heat for evening use.
    • To Cool - the bladder is covered during the day to draw heat from the building's interior and uncovered at night to allow the heat to escape to the cooler exterior atmosphere.
  • Smart windows and shading methods - to provide cooling.

Hybrid Passive Solar Technology

Hybrid passive solar technologies such as solar furnaces and solar forges, require external energy for aligning their concentrating mirrors or receivers. Such technologies have not proven to be either practical or cost effective for wide-spread use.

Materials Used in Passive Solar Technology

Typcially, materials and techniques used by producers of passive solar technology incorporate properties of::

  • low emission double-glazing - allows the solar energy in, and prevents it from escaping.
  • thermal breaking - identifying poorer insulating materials used in construction, and using an additional insulating material to reduce heat loss.

Construction

A key component in passive solar management, that complements materials, is air tight construction. This includes robust joinery, employing the right insulating material in the right places, and aiming for higher overall insulation values. This results in a home with greater energy efficiency, and improved comfort.

Next: Solar Hot Water Heating Systems

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