There is not a financing issue unless the house does not include mechanical cooling. Lenders feel that the resale value of a home is reduced if mechanical cooling is not present. There is a basic understanding and acceptance in regards to passive heating among a large number of persons who have relocated here from colder regions.
Passive cooling approaches are not well known. It is normally not necessary to exceed that amount in order to achieve significant passive solar energy in Austin. However, this amount can be exceeded if an approved computer analysis shows that more glass will improve the energy use pattern in the building. Solar energy is a radiant heat source that causes natural processes upon which all life depends. Some of the natural processes can be managed through building design in a manner that helps heat and cool the building.
The basic natural processes that are used in passive solar energy are the thermal energy flows associated with radiation, conduction, and natural convection.
When sunlight strikes a building, the building materials can reflect, transmit, or absorb the solar radiation. Additionally, the heat produced by the sun causes air movement that can be predictable in designed spaces. These basic responses to solar heat lead to design elements, material choices and placements that can provide heating and cooling effects in a home. There are three approaches to passive systems — direct gain, indirect gain, and isolated gain. In this system, the actual living space is a solar collector, heat absorber and distribution system.
South facing glass admits solar energy into the house where it strikes directly and indirectly thermal mass materials in the house such as masonry floors and walls.
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Figure 1 Thermal mass in the interior absorbs the sunlight and radiates the heat at night. In a direct gain system, the thermal mass floors and walls are functional parts of the house. It is also possible to use water containers inside the house to store heat. However, it is more difficult to integrate water storage containers in the design of the house. The thermal mass will temper the intensity of the heat during the day by absorbing the heat. At night, the thermal mass radiates heat into the living space.
In an indirect gain system, thermal mass is located between the sun and the living space. The thermal mass absorbs the sunlight that strikes it and transfers it to the living space by conduction. Operable vents at the top and bottom of a thermal storage wall permit heat to convect from between the wall and the glass into the living space. When the vents are closed at night radiant heat from the wall heats the living space.
This system is best for cooling in low humidity climates but can be modified to work in high humidity climates. Effectively provides heat in southern U. Water is usually stored in large plastic or fiberglass containers covered by glazing and the space below is warmed by radiant heat from the warm water above. Thermal wall thickness should be approximately inches for brick, inches for concrete, inches for adobe or other earth material and at least 6 inches for water.
An isolated gain system has its integral parts separate from the main living area of a house. Examples are a sunroom and a convective loop through an air collector to a storage system in the house.
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The ability to isolate the system from the primary living areas is the point of distinction for this type of system. See Figure 3. Solar energy is also retained in the sunroom itself. Sunrooms or solar greenhouses employ a combination of direct gain and indirect gain system features. Sunlight entering the sunroom is retained in the thermal mass and air of the room.
Sunlight is brought into the house by means of conduction through a shared mass wall in the rear of the sunroom, or by vents that permit the air between the sunroom and living space to be exchanged by convection. The use of a south facing air collector to naturally convect air into a storage area is a variation on the active solar system air collector.
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These are passive collectors. Convective air collectors are located lower than the storage area so that the heated air generated in the collector naturally rises into the storage area and is replaced by return air from the lower cooler section of the storage area. Heat can be released from the storage area either by opening vents that access the storage by mechanical means fans , or by conduction if the storage is built into the house.
Passive Solar Design vs Passive House
The sunroom has some advantages as an isolated gain approach in that it can provide additional usable space to the house and plants can be grown in it quite effectively. The convective air collector by comparison becomes more complex in trying to achieve additional functions from the system. This is a drawback in this area where space heating is less of a concern than in colder regions where the system would be used longer. It is best to use a system that provides more than one function if the system is not an integral part of the building. The sunroom approach will be emphasized in this information since it can provide multiple functions.
A sunroom will function adequately without overhead or sloped glazing. Due to long hot summers in this area, it is important to use adequate ventilation to let the heat out. Sloped or overhead glazing is also a maintenance concern. Due to the intensity of weather conditions for glazing facing the full.
A thermal wall on the back of the sunroom against the living space will function like the indirect gain thermal mass wall. With a thermal wall in the sunroom, the extra heat during the day can be brought into the living space via high and low vents like in the indirect gain thermal wall. More elaborate uses of the heated air generated in the sunspace can be designed into this system, such as transferring the hot air into thermal mass located in another part of the house.
The thickness of the thermal wall should be inches for adobe or earth materials, inches for brick, inches for dense concrete. Withdraw excess heat in the sunroom if not used for warm weather plants until the room reaches 45 degrees and put the excess heat into thermal mass materials in other parts of the house.
For a sunroom with a masonry thermal wall, use 0.
If a water wall is used between the sunroom and living space instead of masonry, use 0. If overhead glass is used in a sunroom, use heat reflecting glass and or shading systems in the overhead areas. A primary strategy for cooling buildings without mechanical assistance passive cooling in hot humid climates is to employ natural ventilation.
The Fan and Landscape sections also address ventilation strategies. In the Austin area, prevailing summer breezes are from the south and southeast. This matches nicely with the increased glazing on the south side needed for passive heating, making it possible to achieve helpful solar gain and ventilation with the following strategies:.
Passive solar building design
Wing walls are vertical solid panels placed alongside of windows perpendicular to the wall on the windward side of the house. Wing walls will accelerate the natural wind speed due to pressure differences created by the wing wall. A thermal chimney employs convective currents to draw air out of a building.
By creating a warm or hot zone with an exterior exhaust outlet, air can be drawn into the house ventilating the structure. Sunrooms can be designed to perform this function. The excessive heat generated in a south facing sunroom during the summer can be vented at the top. With the connecting lower vents to the living space open along with windows on the north side, air is drawn through the living space to be exhausted through the sunroom upper vents.
The upper vents from the sunroom to the living space and any side operable windows must be closed and the thermal mass wall in the sunroom must be shaded. Thermal mass indirect gain walls can be made to function similarly except that the mass wall should be insulated on the inside when performing this function. Thermal chimneys can be constructed in a narrow configuration like a chimney with an easily heated black metal absorber on the inside behind a glazed front that can reach high temperatures and be insulated from the house.
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Natural gas is considerably cheaper, but the price bounces up and down. A passive house may rely on some moving parts: windows and vents that need to be opened and closed to regulate temperature on sunny days and insulated drapes, blinds or shutters that can be closed to seal in heat at night.
Passive Solar Energy and Passive Solar Design of Homes
The principles: Build the house with large windows facing the sun. Use insulated glass that lets heat energy pass in and then holds it inside. Use floors and interior walls of masonry or concrete to soak up and store heat during the day and thick, airtight insulation in outer walls to seal in heat overnight. Additional insulating windows on the other three walls, not shown here, provide daylighting. The simple home shown here uses wide eaves to shade the solar-gain windows from summer sun, and windows under the roof peak can be opened to create a chimney effect to vent summer heat.