Passive Solar Heating
- Passive solar heating is about keeping the summer sun out and letting the winter sun in. It is the least expensive way to heat your home.
- Passive solar heating is the least expensive way to heat your home. It is also:
- Free when designed into a new home or addition.
- Appropriate for all climates where winter heating is required (generally latitudes south of 27.50S).
- Achievable when building or renovating on any site with solar access - often with little effort.
- Achievable when buying a project home, with correct orientation and slight floor plan changes.
- Achievable when choosing an existing house, villa or unit. Look for good orientation and shading.
- The sheet explains how the following key elements of passive solar heating are applied.
- Northerly orientation of window areas.
- Passive shading of glass.
- Thermal mass for storing heat.
Passive solar heating requires careful application of the following passive design principles:
- * Northerly orientation of daytime living areas.
- * Appropriate areas of glass on northern facades.
- * Passive shading of glass.
- * Thermal mass for storing heat.
- * Insulation and draught sealing.
- * Floor plan zoning based on heating needs.
- * Advanced glazing solutions.
This will maximise winter heat gain, minimise winter heat loss and concentrate heating where it is most needed.
Passive solar houses look like other homes but cost less to run and are more comfortable to live in.
HOW PASSIVE SOLAR HEATING WORK
- Solar radiation is trapped by the greenhouse action of correctly oriented (north facing) windows exposed to full sun. Window frames and glazing type have a significant effect on the efficiency of this process
- Trapped heat is absorbed and stored by materials with high thermal mass (usually masonry) inside the house. It is re-released at night when it is needed to offset heat losses to lower outdoor temperatures.
- Passive shading allows maximum winter solar gain and prevents summer overheating. This is most simply achieved with northerly orientation of appropriate areas of glass and well designed eaves overhangs.
- Heat is re-radiated and distributed to where it is needed. Direct re-radiation is the most effective means. Design floor plans to ensure that the most important rooms (usually day-use living areas) face north for the best solar access. Heat is also conducted through building materials and distributed by air movement.
- Heat loss is minimised with appropriate window treatments and well insulated walls, ceilings and exposed floors. Thermal mass must be insulated to be effective (including ground slab edges in cool and cold climates)
- Air infiltration is minimised with airlocks, draught sealing, airtight construction detailing and quality windows and doors.
- Appropriate house shape and room layout is important to minimise heat loss, which occurs mostly through the roof and then through external walls. In cool and cold climates, compact shapes that minimise roof and external wall area are more efficient. As the climate gets warmer more external wall area is appropriate.
PASSIVE SOLAR DESIGN PRINCIPLES
- Passive design relies on greenhouse principles to trap solar radiation.
- Heat is gained when short wave radiation passes through glass, where it is absorbed by building elements and furnishings and re-radiated as longwave radiation. Longwave radiation cannot pass back through glass as easily.
- This diagram shows the percentage of solar heat gain through standard 3mm glazing. For comparison to advanced glazing materials
- Heat is lost through glass by conduction, particularly at night. Conductive loss can be controlled by window insulation treatments such as close fitting heavy drapes with snug pelmets, double glazing and other advanced glazing technology.
ORIENTATION FOR PASSIVE SOLAR HEATING
- For best passive heating performance, daytime living areas should face north. Ideal orientation is true north and can be extended to between 15o west and 20o east of solar north.
- Where solar access is limited, as is often the case in urban areas, energy efficiency can still be achieved with careful design.
- Homes on poorly oriented or narrow blocks with limited solar access can employ alternative passive solutions to increase comfort and reduce heating costs.
- Minimising heat loss with insulation, draught sealing and advanced glazing.
- Floor plan zoning to get heating to where it is most needed and keep it there.
- Passive solar houses can look like any other home but they are more comfortable to live in and cost less to run.
PASSIVE SOLAR SHADING
- Fixed shading devices can maximise solar access to north facing glass throughout the year, without requiring any user effort. Good orientation is essential for effective passive shading.
- Fixed shading above openings excludes high angle summer sun but admits lower angle winter sun.
- Use adjustable shading to regulate solar access on other elevations.
- Correctly designed eaves are the simplest and least expensive shading method for northern elevations.
- Permanently shaded glass at the top of the window is a significant source of heat loss. To avoid this, the distance between the top of glazing and eaves underside should be at least the distance indicated in the diagram.
- Heat loss through glass (and walls) is proportional to the difference between internal and external temperatures. Because the hottest air rises to the ceiling, the greatest temperature difference occurs at the top of the window.
PLANNING AND DESIGN
FLOOR PLANNING
- Plan carefully to ensure passive solar gain to the rooms that most need it.
- In general, group living areas along the north facade and bedrooms along the south or east facade.
- Living areas and the kitchen are usually the most important locations for passive heating as they are used day and evening.
- Bedrooms require less heating. It is easy to get warm and stay warm in bed. Children's bedrooms can be classified as living areas if considerable hours are spent there.
- Utility and service areas such as bathrooms, laundries and garages are used for short periods and generally require less heating. These areas are best located:
- To the west or south west, to act as a buffer to hot afternoon sun and the cold westerly winds common to many regions.
- To the east and south east, except where this is the direction of cooling breezes.
- Detached garages to the east and west can protect north facing courtyards from low angle summer sun and direct cooling breezes into living spaces.
- Compact floor plans minimise external wall and roof area, thereby minimising heat loss. Determine a balance between minimising heat loss and achieving adequate daylighting and ventilation.
- Consider specific regional heating and cooling needs and the site characteristics to determine an ideal building shape.
PASSIVE SOLAR ADDITIONS
- Many opportunities exist for improving or including passive solar design features when renovating an existing home. They include:
- Design extensions to allow passive solar access and to facilitate movement of passive heat gains to other parts of the house.
- Include thermal mass in these areas. (Use slab on ground, reverse brick veneer or other insulated mass walls).
- Use high performance windows and glazing for all new windows and doors. Replace poorly performing windows where possible.
- Seal existing windows and external doors, replace warped or poorly fitted doors.
- Create air locks at entrances.
- Add doors and walls to group areas with similar heating needs into zones.
- Consider a solar conservatory to maximise solar gains in colder climates. Ensure it can be sealed off from the rest of the house at night.
- Install curtains or pelmet boxes where required.
- Improve natural ventilation with roof vents and maximum window opening areas.
- Increase natural daylighting with new appropriately shaded skylights and windows.
- Increase existing insulation levels and insulate previsouly uninsulated ceilings and walls (and floors in cool climates). Access to roof spaces and walls is often easier during an alteration.
- This fact sheet examines ways to design and modify homes to achieve summer comfort through passive cooling.
Four key approaches for achieving thermal comfort in cooling applications are examined:
* Envelope design.
* Natural cooling sources.
* Hybrid cooling systems.
* Adapting lifestyle.