Lecture Notes - 03 Direct Gain [PDF]

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Building Science 3B



BUILDING SCIENCE 3B Lecture 3: Passive Solar Design



DIRECT SOLAR GAIN Lawrence Ogunsanya [email protected]



Direct gain Design Overview • Sunlight incident on transparent surfaces allows the energy to enter the living space directly and is called Direct Gain. • Direct Gain systems are designed primarily for heating. In a direct gain system, the collection, absorption, and storage of solar energy occur directly within the living space. • The aim of the designer is normally to maximise solar gain within the building in the winter (to reduce space heating demand), and to control it in summer (to minimise cooling requirements). • The system can also be used to even out the fluctuations during the day, and to some extent between days. • During the winter, sunlight enters the living space through the north facing façade/glazing. The solar radiation is in turn absorbed by elements in the interior space. (e.g. floor, walls, ceiling and furnishings)



Direct Gain Design Overview • During the summer, the north facades should be well shaded to prevent excessive solar heat gain. • Shading elements, such as overhangs can be an effective device to achieve this. • Therefore, North facing windows thus form the basis for the simplest type of solar heating system. • With some simple guidelines, this design is the cheapest and best way to incorporate solar into a house. • Surfaces should be generally facing North (to within 20-23 degrees) • Overhangs should prevent unwanted summer gains. (it should be minimum of meter long) • Window area should be 8-12% of the house floor area if no extra thermal mass is added



Direct Gain Passive Solar Design • Excess window area can result in a loss of privacy, too much glare, under heating and overheating • This amount of passive solar gain should provide no more than 40-50% of the yearly heating load



Direct Gain Passive Solar Design



Direct solar is applied through the following: • Collectors • Storage • Control



Direct Gain Collectors • The principal function of a direct gain collector is to admit and trap solar energy so that it can be absorbed and stored by elements within the direct gain space. • There are three basic types of direct gain collectors: solar windows, clerestories, and skylights.



Direct Gain Collectors Solar window • A solar window is simply a standard, off-the-shelf window or patio door Installed on the north facade using conventional construction methods. • The collector frame can be wood or metal and should be well caulked (sealed) and weather stripped. • The solar window can be vertical, or it can be slightly tilted to maximize the amount of incoming solar radiation. • Double glazing is recommended standard for the windows, However high performance glazing with low-e coatings, gas fills (triple pane) are better but expensive.



Direct Gain Collectors



Double Glazing



Triple Glazing



Direct Gain Collectors Clerestories • Clerestories serve the same function as solar windows. They also allow light to penetrate deeper into a space better than solar windows , often enabling direct sunlight to strike the south wall of the space. • As in solar windows, clerestories can be vertical or tilted, using the same type of recommended glazing. • Clerestories can be used together in a sawtooth pattern In order to increase the total amount of solar radiation entering a building



Sawtooth Glazing



Direct Gain Collectors Clerestories • Clerestories can also be used for ventilation purposes and air movement. • Its important that the ceiling adjacent to the clerestory should be light in colour to reflect sunlight into the space.



Direct Gain Collectors Skylights • Skylights serve the same function as the other direct gain collectors and can be placed flat on flat roof or tilted In a south/north facing sloped roof. Skylights are often the least effective collector type. • The collective character can be improved with a reflector.



Skylight with reflector



Direct Gain Storage • In direct gain systems, solar energy can be stored in the floor. walls, ceiling, and/or furnishes of the living space. • These components have sufficient capacity to absorb and store heat and to reradiate the heat to the living space slowly • Most high-mass materials (concrete, wool, brick and water) have the thermal storage capability and can be used effectively in direct gain applications. • Its recommended that storage floors, walls and ceilings in direct sunlight should be dark in colour to increase the absorption of the solar energy. • Recommended thickness of floor and wall finishes should be 5mm to 10mm (or more)



Direct Gain Control • Direct solar gain control systems can be achieved through shading, reflecting and insulating. Shading • To avoid excessive heat gain in the summer, it is recommended that you provide shading for the direct gain collector. • The most thermally effective shading devices are those placed on the exterior of the home, such as simple overhangs (fixed or adjustable), pergolas, vegetation, awnings, and louvers • Interior shading devices include roller shades, blinds, curtains and movable panels. • Interior shading devices provide insulation for the interior space.



Direct Gain Control



Direct Gain Control Reflecting • Reflectors placed strategically above or below a collector can help increase overall system performance. • The provision of reflectors can also improve solar collection by 30% to 40%. • Light coloured landscape elements such as patios or terraces are recommended. It is noted , that these elements are not as effective as reflector panels. However, they do not present glare and they require no additional maintenance.



Direct Gain Control Insulating • Direct gain storage ceiling ,wall and floors that are exposed should be insulated externally and internally to reduce heat loss and absorb excessive heat.



Direct Gain Control



Direct Gain : Advantage and Disadvantages Advantages • Direct gain can be the easiest to build using standard construction materials and methods • The system dose not radically alter the appearance of the home • The system provides effective natural light and reduces energy consumption. • Improves the comfort of the interior space. Disadvantages • Large expanse of north facing glazing can cause glare and privacy problems • Ultraviolet radiation in sunlight can fade and degrade fabrics • Some high performance devices can be costly.



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