Introduction
Passive solar heating of buildings is a great idea to heat, cool and lighten the living rooms by proper design structure of buildings. Ancient civilizations gave importance to the orientation of the building and layout of the cities according to the sun's direction. As the knowledge and technology evolve about solar energy, the building professionals started to incorporate energy-conserving techniques into their projects. There are majorly two types of solar heating of building available. First is active systems and the second is passive systems.
The active solar heating consists of separate solar collectors, storage device and the distribution system. Generally, in an active solar system, sunlight heats flat plate collector through which water flows and the heated water used directly for the buildings hot water needs, or it can be used to heat the house. The water and air are circulated by pumps or fans and are used to distribute the heat to the space of building interiors.
In passive solar building, when the sunlight hit the building structure, the building materials can reflect, absorb or transmit the solar radiation. In this type, solar radiation is collected by some element of the structure itself. The windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This can be achieved by passive solar design elements such as shading, implementing large south-facing windows, and building materials that absorb and slowly release the sun’s heat. The term "passive" implies that energy-consuming mechanical components like HVAC, pumps, fans, etc., are not used in this type of system. Passive heating systems are simple, have few moving parts, and require minimal maintenance. Let us discuss briefly passive solar heating in this article.
Things to be Considered While Designing Passive Solar Heating System for a Building:
- Orientation is very important. The correct orientation of the building allows the yield of solar radiation. In summer the south facade is shined less than the east and west face, but in winter the south face is shined more than east and west face. Therefore, the south face is much more suitable for the use of solar energy.
- The building should be oriented to face the equator.
- The building should be located on an east-west axis to utilize more solar radiation.
- The south face of the building should absorb more sunlight during the mid-day time between the hours of 9:00 A.M. and 3:00 P.M. So we have to orient the building accordingly.
- Windows should have adequate size to face the mid-day sun during winter and use shading to prevent summer sun entering the interior. Sun angles can help us to figure out the overhang calculations.
- The interior spaces of the building that need more light, heating, and cooling should be located along the south face of the building. Less used spaces should be located in the north.
The Five Elements of Passive Solar Buildings
- Aperture or Collector
- Absorber
- Thermal mass
- Distribution
- Control
Aperture or Collector
It is the large glass area through which sunlight enters the building. The apertures should face within 30 degrees of true south and should not be shaded by other buildings or trees during mid-day time (9 A.M. to 3P.M.) to utilize the solar radiation effectively.
Absorber
It is the hard, darkened surface of the storage element. The surface of the absorber could be a masonry wall, floor, or water container, that is located in the direct path of sunlight. Sunlight hitting the surface is absorbed as heat.
Thermal Mass
Thermal mass has the ability to absorb and store heat energy. Generally, more heat is required to change the temperature of high-density materials like concrete, stone, brick or ceramic tile. Therefore, those materials have a high thermal mass. So, it is used to retain or store the heat produced by sunlight. The thermal mass is placed below the surface of the absorber.
Distribution
It is a method by which solar heat circulates from the collector and storage points to different areas of the house. Generally, a passive design will use the three natural heat transfer modes conduction, convection, and radiation. In some cases, fans, ducts, and blowers may be used to distribute the heat through the house.
Control
Roof overhangs can be used to shade the aperture area during the summer months. It has electronic sensing devices such as a differential thermostat that signals a fan to turn on accordingly, operable vents and dampers that allow or restrict heat flow, low-emissivity blinds, and awnings.
Three Methods of Passive Solar Heating:
- Direct gain
- Indirect gain
- Isolated gain
Direct Gain
The direct gain method is the simplest method where the space of the building is directly heated by sunlight. In this type, the living space work as a solar energy collector, heat absorber and distribution system. The system usually has south-facing windows. The south-facing glass allows solar energy into the house where it strikes masonry floors and walls, which absorb and store the solar heat in the thermal mass, which is then radiated back into the room during night time. These thermal mass materials are typically dark in color in order to absorb more heat.
Indirect Gain (Trombe Wall)
In indirect gain, the thermal mass is located between the sun and the living space. The thermal mass absorbs the sunlight and transfers it to the living space by conduction. The sunlight is often received by a south-facing wall. When air moves to internal space, the heat moves through the living room. The indirect gain system utilizes 30 to 45% of the sun’s energy by striking the glass adjoining the thermal mass.
The most common indirect gain systems is a Trombe wall. In Trombe wall, the thermal mass of about 6-18 inch thickness of masonry wall is located behind a single or double layer of south-facing glass. When sunlight hit the wall, the solar heat is absorbed by the wall’s dark-colored outside surface and stored in the wall’s thermal mass, where it radiates into the living space. The solar heat migrates through the wall and reaches its rear surface in the late afternoon or early evening. When the indoor temperature falls below the temperature of the wall’s surface, heat is radiated into the room. That is how indirect gain happens in solar buildings.
The most common indirect gain systems is a Trombe wall. In Trombe wall, the thermal mass of about 6-18 inch thickness of masonry wall is located behind a single or double layer of south-facing glass. When sunlight hit the wall, the solar heat is absorbed by the wall’s dark-colored outside surface and stored in the wall’s thermal mass, where it radiates into the living space. The solar heat migrates through the wall and reaches its rear surface in the late afternoon or early evening. When the indoor temperature falls below the temperature of the wall’s surface, heat is radiated into the room. That is how indirect gain happens in solar buildings.
Isolated Gain
The isolated gain method contains solar energy collection and thermal storage that is separated from actual living space. The isolated gain system has a glazed interior space or room attached to the building. It functions as a solar greenhouse and makes use of a combination of both direct and indirect gain system characteristics. Generally, a solar greenhouse is used to grow plants. But, in this case, it is just a sunspace which is designed to provide heat and aesthetics to a building. Also, this type of sunspaces can also be used to grow plants.
In this system, solar radiation is absorbed by a collector to heat air or water. The warm air or water rises and passes through the storage, to transfer the heat. The cooler air falls to the absorber to get heated up again. The collector is located and oriented properly in the building to attain maximum solar gain. The angular tilt of the collector is generally equal to the latitude of the place. The area of the collector may range from 20% to 40% of the floor area of the living space to be heated. Please read the article about the flat plate collector to know about its working.
The method of distribution of heat from the storage is either by radiation or convection. If the working fluid is water, the hot water will be passed through the pipes installed in the floor slab, where heat is stored and radiated into the living space.
In this system, solar radiation is absorbed by a collector to heat air or water. The warm air or water rises and passes through the storage, to transfer the heat. The cooler air falls to the absorber to get heated up again. The collector is located and oriented properly in the building to attain maximum solar gain. The angular tilt of the collector is generally equal to the latitude of the place. The area of the collector may range from 20% to 40% of the floor area of the living space to be heated. Please read the article about the flat plate collector to know about its working.
The method of distribution of heat from the storage is either by radiation or convection. If the working fluid is water, the hot water will be passed through the pipes installed in the floor slab, where heat is stored and radiated into the living space.
Advantages of Passive Solar Heating
- Provides good natural lighting to the interiors
- Cooler and comfortable in summer
- Warmer in winter
- Reduces greenhouse gas emissions
- Blocks the ultraviolet radiation
- Eco-friendly
- Requires low maintenance
Disadvantages of Passive Solar Heating
- Careful construction is required
- Improperly designed may not work well as expected
- Sunlight not available all-day
- Sometimes it may produce extra heat
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