Passive Solar Design
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Have you ever wondered how your house stays warm in the winter and cool in the summer? Have you ever noticed that sometimes when it is cold outside, it is nice and warm in a sunny spot next to a window inside? Well, the sun is full of energy. We can use the sun's energy (solar energy) to help us heat our homes.
There are two ways civil engineers use solar energy to keep comfortable building temperatures: active solar heating and passive solar heating. Active solar heating systems use mechanical and electrical components to control the movement of warmed air or water. Passive solar systems use only the structure (floors, walls, windows) to collect, store and distribute heat from the sun in the winter and keep heat from the sun out in the summer. Passive solar heating systems can also be used to provide daylighting (natural lighting from the sun) to light up the inside of your house. People from different cultures and regions throughout history have used various types of passive solar design. Active solar systems require a lot more design, installation and maintenance than passive systems. Engineers also think carefully about the type of materials used in building design. Some materials are good for thermal mass, or solar heat storage (see Figures 1 and 2), and some materials make good insulators to keep heat ( thermal energy) from leaving or entering the building. Materials that are slow to heat up and cool down provide thermal mass because they store more energy as temperature increases. Insulation stops heat from passing through. Insulating materials are important to include in passive solar design because they slow the amount of heat transfer in and out of buildings through the walls, floors and roof. There are three necessary elements in passive solar design: a collector, thermal mass and some sort of control system. Thermal mass is a body of material with a significant density, such as a concrete floor, brick wall or barrel of water. Sunlight strikes the thermal mass after entering through the collector — a window. The efficiency of a passive solar system is greater if the thermal mass has a dark surface so it absorbs more sunlight. A simple control system might be a window overhang or awning, blinds or curtains. In direct gain systems, sunlight enters through a window and directly strikes the building's thermal mass. A direct gain system with a winter sun angle is shown in Figure 3.The solar energy is absorbed by a masonry floor and/or interior walls in the building, thus increasing their temperature, which stores the energy. At night, the energy stored in the thermal mass is released because of the temperature difference between the thermal mass and the surroundings, warming the building interior. If ventilation and overhangs or other shading devices are used, this thermal mass can cool the building in summer. Ventilating a building at night exposes the thermal mass to cooler air and the thermal mass loses energy to the air. This cools the thermal mass. During the day, the thermal mass absorbs energy from the surroundings, cooling the building. In indirect gain systems, such as the Trombe wall shown in Figure 4, sunlight strikes a dark wall that is placed between sun-facing (south in the northern hemisphere) windows and the building interior. The wall absorbs solar energy through radiation, stores it, and then releases it into the building when the indoor temperature falls below that of the wall's surface. These systems cannot be used for cooling. Trombe walls must be shaded in summer to avoid overheating the building. In insulated gain systems (sunspaces), a separate room with a thermal mass floor or inside walls is designed to store thermal energy. Heat is distributed throughout the building through ceiling vents, floor vents, windows and doors. Sunspaces cannot be used in summer for cooling, except for improving ventilation. It is best to minimize or eliminate ceiling glazing in sunspaces because it causes overheating in summer. |
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Vocabulary
Active solar system: Solar systems that use electrical or mechanical components, such as fans, pumps and electrical controls in circulating fluids; these systems can be used for heating water or heating/cooling buildings.
Daylighting: A passive lighting system that maximizes natural lighting from the sun for interior illumination.
Insulation: A material used to prevent the passage of heat, electricity or sound; a non-conducting material.
Passive solar system: Solar systems that do not require electrical or mechanical components. These systems directly heat water or buildings, or reduce solar heat gain (for example, with window awnings to keep buildings cool).
Thermal energy: Heat energy produced when the molecules of a substance vibrate. The more heat a substance has, the more rapid the vibration of its molecules. Heat energy flows from places of higher temperature to places of lower temperature.
Thermal mass: Material used to store thermal energy (heat). Stone, concrete, adobe, brick and water work best. Thermal mass is used in a building to absorb or emit heat, and reduce interior temperature swings.
Trombe wall: A wall in a building that absorbs solar energy through radiation, stores it, and then releases it into the building when the indoor temperature falls below that of the wall's surface. Names after French inventor Felix Trombe in the late 1950s. See an example at NREL: http://www.nrel.gov/buildings/highperformance/zion_ee_features.html
Ventilation: To admit fresh air into a space, to replace existing air.
From: Teach Engineering http://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_energy2/cub_energy2_lesson09_activity1.xml#intro
Contributors
Xochitl Zamora-Thompson, Sabre Duren, Jeff Lyng, Malinda Schaefer Zarske, Denise Carlson
Copyright
© 2005 by the University of Colorado.
Supporting Program
Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Last Modified: July 16, 2012
Contributors
Xochitl Zamora-Thompson, Sabre Duren, Jeff Lyng, Malinda Schaefer Zarske, Denise Carlson
Copyright
© 2005 by the University of Colorado.
Supporting Program
Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Last Modified: July 16, 2012