Passive solar energy system –solar home design issues.
Passive Solar energy system presents the most cost effective means of providing day-lighting, passive heating and cooling of homes by utilizing and controlling the sun’s heat without use of any additional mechanical or electrical devices. In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and minimize the effects of solar radiation in the summer. The buildings are designed in such a way that the solar heat-flow is by natural means, such as radiation, convection, and conduction, and the thermal storage is in the structure itself. Thus, passive solar heating and cooling can save electricity bills significantly.
How does passive solar energy work?
Passive solar energy system refers to the use of the sun’s energy for heating and cooling of living spaces by exposure to the sun. In simple terms, passive solar energy technique captures, stores and transmits or releases the heat energy from sunlight directly during the winter months, and minimizes the overheating effects of solar radiation through shading or generating air flows with convection ventilation during hot summer days. Unlike active solar heating systems, passive systems do not involve use of additional mechanical or electrical devices, such as pumps, fans, or electrical controls for using the solar energy.
Passive solar energy basics
Typically solar home design involves the following basic elements to make the best use of passive solar energy techniques.
1. Collection of sun’s heat energy from sunlight through properly-oriented, large south-facing windows;
2. Absorption and storage of heat energy from sunlight in ‘high thermal mass’ building components (dense materials that retain or store the heat produced by sunlight) such as stone, brick, concrete or ceramic tile forming the walls, floors, or partitions that sit in the direct path of sunlight;
3. Distribution of the stored solar heat energy back to the different living areas of the building during the winter months, through the mechanisms of natural heat transfer modes i.e. conduction, convection and radiation;
4. Controlling the overheating effects of solar radiation through roof overhangs or shading or generating air flows with convection ventilation during hot summer months;
Passive solar energy options
The three major options for utilizing passive solar energy in solar home design are, day-lighting, passive solar heating and passive cooling.
Day-lighting is the controlled admission of natural sunlight and diffuse skylight—into a building to illuminate building’s interior rather than relying solely on electric lighting during the day. Successful day-lighting can provide substantial energy saving, reduce building peak loads, increase visibility, and improve overall lighting quality. Climate and geographical position, as well as building type, use and orientation, are big factors in designing a successfully day-lit building.
A good day-lighting system takes several factors into consideration such as,
- The general orientation and planning of areas to be lit;
- Location, form and dimensions of the apertures and openings through which the daylight will pass;
- Choosing the shape and size of windows and a mix of window types depending on the building’s orientation;
- Choosing the glazing and shading systems;
- Placement and orientation of room surfaces so that reflectance values for room surfaces are kept as high as possible;
- Location of movable or permanent objects which provide protection from excessive light or glare;
Passive solar heating
Passive solar heating, on its most basic level, works like this: Rays from the sun enter a building through properly oriented windows and get the heat energy absorbed by the masonry floors and/or walls that have a high thermal mass. Thermal mass can be defined as a material’s ability to absorb, store and release heat. High thermal mass include materials that are dense, such as stone, brick, concrete or ceramic tile. These materials absorb and store the solar heat during the period of time that the sun shines on them. As the air cools at night, the absorbed heat slowly releases into the building throughout the night-time and maintains a comfortable temperature.
Passive cooling system in solar home design focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort during summer months with almost no energy consumption. Specially, utilizing passive cooling strategies like shading, generating air flows with convection ventilation and air cooling can reduce the demand for mechanical cooling while maintaining thermal comfort. Shading devices, fixed or adjustable, reduce solar radiation. We can shade a building by natural vegetation and by using special glazing in windows. External heat gain can also be minimized by good insulation, reduced window size and by the use of reflective materials in the walls and roof. A well designed overhang also can shade south facing windows from the high summer sun, while still allowing the low winter sun to shine in and provide welcome solar heating. Thermal mass is also used in a passive cooling design to absorb heat and moderate internal temperature rise on hot days. During the night, thermal mass can be cooled using ventilation, allowing it to be ready the next day to absorb heat again.
At their simplest, passive solar cooling systems include overhangs or shades on south facing windows, shade trees, thermal mass and cross ventilation.
Advantages of using passive solar energy
- Passive solar system is Eco-friendly. When homeowners harness the power of the sun, they don’t have to rely too much on fossil fuels. As a result, the passive energy system helps in saving the earth’s non-renewable energy resources and reducing greenhouse gasses in the atmosphere;
- Passive solar energy uses an energy source that occurs naturally and is almost always available free of cost. Passive solar home design may involve initial costs, but the reduction in utility bills will more than offset the cost in the long run;
- Compared to the equipment needed in active solar energy (such as solar panels, inverters, wires, etc.), the materials required in passive solar energy is relatively cheap. This is great advantage for homeowners who don’t have a large budget to create an eco-friendly home;
To sum up, although any good solar home design for best utilization of passive solar energy is region-specific since each building site has its own weather and temperature patterns, as well as a unique topography that affects heating and cooling, but despite regional differences, there are a handful of strategies at the heart of passive solar buildings anywhere. The key design issues and strategies are:
- Building site and its orientation;
- Shape of the building and its thermal envelope (outer walls, roof, foundation, windows and doors) which prevents heat transfer form interior of a house to its exterior in winter and vice versa in summer;
- Size, type, and location of windows;
- Use of high thermal mass (ability of a material to absorb and store heat energy) materials to moderate interior temperature swings;
- Design of roof overhangs that shade windows and doors;