PASSIVE SOLAR HEATING PHYS 471 SOLAR ENERGY I

PASSIVE SOLAR HEATING PHYS 471 SOLAR ENERGY I Presented by: Gülten KARAOĞLAN Instructor: Prof. Dr. Ahmet ECEVIT 2004 -1

TABLE OF CONTENT 1. Introduction 1. 1. What Passive Solar Heating is ü Heating ü Cooling 1. 2. History 1. 3. Insulation 1. 4. Heat Movement Physics ü ü ü Conduction Convection Radiant 1. 5. Five Elements of Passive Solar Design ü ü ü Aperture (Collector) Absorber Thermal Mass Distribution Control 1. 6. The Working Conditions

2. Direct Gain 2. 1. 2. 2. 2. 3. What it is Thermal Mass Design 2. 3. 1 Interior Space Planing Main Considerations 2. 3. 1. 1 2. 3. 1. 2 2. 3. 1. 3 2. 3. 1. 4 2. 3. 1. 5 Surface Colour Thermal Conductivity Thermal Capacity Design Requirements Protection From Losses 2. 3. 2 Site Planning for Solar Access 2. 3. 3 Overhangs and Shading 2. 3. 4 Landscaping 2. 4. Direct Gain System Rules

3. Indirect Gain 3. 1. 3. 2. 3. 3. 4. Thermal Storage Wall (Trombe Wall) Roof Pond Systems Indirect Gain System Rules Isolated Gain 4. 1. Sunspaces 4. 2. Main Functions of Sunspaces ü ü ü Auxiliary Heating To Grow Plants Living Area 4. 3. Main Considerations ü ü ü Siting Heat Distribution Glazing

5. Cost 6. The Advantages of Passive Solar Design References

1. Introduction 1. 1. What Passive Solar Heating is ► Passive solar design uses sunshine to heat and light homes and other buildings without mechanical or electrical devices [1]. Heating the building through the use of solar energy involves the absorption and storage of incoming solar radiation, which is then used to meet the heating requirements of the space [2].

► Heating: A successful passive solar building needs to be very well insulated in order to make best use of the sun's energy [1]. ► Cooling: Passive solar design can also achieve summer cooling and ventilating by making use of convective air currents which are created by the natural tendency of hot air to rise [1].

1. 2 History ► The Figure 1. Montezuma's Castle [3]. Sinagua cliff dwelling known as Montezuma's Castle was occupied between AD 1100 -1300 and is located inside a shallow south-facing limestone rock shelter as shown in the Figure 1.

► The O'Odham ki, or round house provides protection from heat, cold, and wind as seen in the Figure 2 [3]. Figure 2. O'Odham ki House [3].

1. 3 Insulation ► Materials that insulate well do so because they are poor conductors of heat. Having a home without insulation is doing just that leaving the house open year round. Ideally, you should insulate every surface between your house and the outside world. There are lots of choices for insulation - from loose fill, batts or rolls of the "pink stuff, " to rigid boards and foam-in-place products [4].

1. 4 Physics of Heat-Movement As a fundamental law, heat moves from warmer materials to cooler ones until there is no longer a temperature difference between the two. Conduction is the way heat moves through materials, traveling from molecule to molecule. Ø Convection is the way heat circulates through liquids and gases. Lighter, warmer fluid rises, and cooler, denser fluid sinks. Ø Radiant heat moves through the air from warmer objects to cooler ones. There are two types of radiation important to passive solar design: solar radiation and infrared radiation. When radiation strikes an object, it is absorbed, reflected, or transmitted, depending on certain properties of that object [5]. Ø

1. 5 Five Elements of Passive Solar Design Aperture (Collector): the large glass (window) area through which sunlight enters the building. ► Absorber: the hard, darkened surface of the storage element. ► Thermal mass: the materials that retain or store the heat produced by sunlight. ► Distribution: the method by which solar heat circulates from the collection and storage points to different areas of the house. ► Control: roof overhangs can be used to shade the aperture area during summer months [6]. The elements can be seen in Figure 3. ► Figure 3. Five Elements of Passive Solar Design [7].

1. 6 The Working Conditions 1. 2. 3. 4. 5. 6. Use passive solar heating strategies only when they are appropriate. Passive solar heating works better in smaller buildings where the envelope design controls the energy demand. Careful attention should be paid to constructing a durable, energyconserving building envelope. Specify windows and glazings that have low thermal transmittance values (U values) while admitting adequate levels of incoming solar radiation. Ensure that the south glass in a passive solar building does not contribute to increased summer cooling. In many areas, shading in summer is just as critical as admitting solar gain in winter. For large buildings with high internal heat gains, passive solar heat gain is a liability, because it increases cooling costs more than the amount saved in space heating. Design for natural ventilation in summer with operable windows designed for cross ventilation. Provide natural light to every room. Some of the most attractive passive solar heated buildings incorporate elements of both direct and indirect gain.

7. 8. 9. 10. 11. 12. If possible, elongate the building along the east-west axis to maximize the south-facing elevation and the number of south-facing windows that can be incorporated. Plan active living or working areas on the south and less frequently used spaces, such as storage and bathrooms, on the north. Improve building performance by employing either highperformance, low-e glazings or night-time, moveable insulation to reduce heat loss from glass at night. Include overhangs or other devices, such as trellises or deciduous trees, for shading in summer. Make sure there is adequate quantity of thermal mass. In passive solar heated buildings with high solar contributions, it can be difficult to provide adequate quantities of effective thermal mass. Design to avoid sun glare. Room and furniture layouts needs to be planned to avoid glare from the sun on equipment such as computers and televisions [8].

► There are three approaches to passive systems - direct gain, indirect gain, and isolated gain as seen in the Figure 4. The goal of all passive solar heating systems is to capture the sun's heat within the building's elements and release that heat during periods when the sun is not shining [9]. Figure 4. Direct Gain, Indirect Gain, and Isolated Gain [10].

2. DIRECT GAIN 2. 1 What it is ► The most common passive solar system is called direct gain. Direct gain refers to the sunlight that enters a building through windows, warming the interior space as seen in the Figure 5. A direct gain system includes south-facing windows and a large mass placed within the space to receive the most direct sunlight in cold weather and the least direct sunlight in hot weather. Direct gain systems are probably the least costly passive system [11].

Figure 5. Direct Gain [11]

2. 2 Thermal Mass ► If solar heat is to be used when the sun is not shining, excess heat must be stored. Thermal mass, or materials used to store heat, is an integral part of most passive solar design. They are the materials with a high capacity for absorbing and storing heat (e. g. , brick, concrete masonry, concrete slab, tile, adobe, water) [13] as shown in the Figure 6.

Figure 6. Thermal Mass [14].

2. 3 Design 2. 3. 1 Interior Space Planing ► Planning room lay out by considering how the rooms will be used in different seasons, and at different times of the day, can save energy and increase comfort. In general, living areas and other high-activity rooms should be located on the south side to benefit from the solar heat. Clustering baths, kitchens and laundry rooms near the water heater will save the heat that would be lost from longer water lines. Another general principle is that an open floor plan will allow the collected solar heat to circulate freely through natural convection [15].

Main Considerations ► ► ► Surface Colour The amount of heat storage depends on the amount of exposed thermal mass within the space, and its colour. Light coloured surfaces will reflect light around within the space, distributing it over a greater number of surfaces. Dark coloured materials will absorb most of the incident energy as soon as it strikes. Thermal Conductivity Highly conducting materials will quickly transfer any heat build away from the surface deeper into the material resulting in less instantaneous reradiation back into the space. In a poorly conductive material, however, the surface will heat up more and will quickly re-radiate most of the heat back into the space. Thermal Capacity For a given amount of incident sunlight, thermally lightweight materials will heat up more than heavyweight materials. Design Requirements The recommended mass surface-to-glass area ratio is 6: 1. In general, comfort and performance increase with increase of thermal mass, and there is no upper limit for the amount of thermal mass. It is important to locate as much thermal mass in direct sunlight (heated by radiation) as possible. Remember that covering the mass with materials such as carpet, cork, wallboard or othermally resistive materials will effectively insulate the mass from the solar energy you're trying to collect. Protection From Losses It is important to note that the same large areas of glazing that let heat in during the day can also readily let heat out at night. Thus, some form of night-time protection should be incorporated to minimise any conduction and convection losses through windows. Thick drawn curtains with a pelmet that forms a good seal at the top can be used as well as insulated internal/external roller shutters [16].

2. 3. 2 Site Planning for Solar Access ► The main objective of site planning for passive solar homes is to allow the south side as much unshaded exposure as possible during the winter months. A good design balances energy performance with other important factors such as, the slope of the site, the individual house plan, the direction of prevailing breezes for summer cooling, the views, the street lay out and so on. Ideally, the glazing on the house should be exposed to sunlight with no obstructions within an arc of 60 degrees on either side of true south, but reasonably good solar access will still be guaranteed if the glazing is unshaded within an arc of 45 degrees. Buildings, trees, or other obstructions should not be located so as to shade the south wall of solar buildings. At this latitude, no structures should be allowed within 330 cm of the south wall of a solar building; fences should be located beyond 330 cm; one story buildings should be located beyond 560 cm; and two story buildings should be located beyond 1320 cm [1].

2. 3. 3 Overhangs and Shading ► Figure 7. Overhangs [17]. Figure 8. Overhang [18]. Overhangs are one of the best (and least costly) shade design elements to include in your home. In the summer, when the sun is high in the sky, the overhangs should shade the room completely. In the winter, when the sun is low, the overhangs should allow the full sun to enter, warming the air, as well as the floor, wall and other features [18] as shown in the Figure 7 and 8.

2. 3. 4 Landscaping ► Trees and other landscaping features may be effectively used to shade east and west windows from summer solar gains. Trees on the southside, however, can all but eliminate passive solar performance, unless they are very close to the house and the lower branches can be removed to allow the winter sun to penetrate under the tree canopy. If a careful study of shading patterns is done before construction, it should be possible to accomodate the south-facing glazing while leaving in as many trees as possible [19].

2. 4 Direct Gain System Rules § § § § § A heat load analysis of the house should be conducted. Do not exceed 15 cm of thickness in thermal mass materials. Do not cover thermal mass floors with wall to wall carpeting; keep as bare as functionally and aesthetically possible. Use a medium dark color for masonry floors; use light colors for other lightweight walls; thermal mass walls can be any color. For every square foot of south glass, use 68 kg of masonry or 18 lt of water for thermal mass. Fill the cavities of any concrete block used as thermal storage with concrete. Use thermal mass at less thickness throughout the living space rather than a concentrated area of thicker mass. The surface area of mass exposed to direct sunlight should be 9 times the area of the glazing. Sun tempering is the use of direct gain without added thermal mass. For most homes, multiply the house square footage by 0. 08 to determine the amount of south facing glass for sun tempering [9].

3. Indirect Gain ► 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. Using a Trombe wall is the most common indirect-gain approach. The wall consists of an 20 to 40 cm-thick masonry wall on the south side of a house. A single or double layer of glass is mounted about 2. 5 cm or less in front of the wall's surface. Solar heat is absorbed by the wall's dark-colored outside surface and stored in the wall's mass, where it radiates into the living space as shown in the Figure 9 and 10. There are two types of indirect gain systems: § Thermal storage wall systems (Trombe Walls) § Roof pond systems [12].

Figure 9. Indirect Gain [20]. Figure 10. Indirect Gain [12].

3. 1 Trombe Wall ►A trombe wall is a technique used to capture solar heat that was developed by French engineer Felix Trombe. ► In water walls, water is held in light, rigid containers. Water provides about twice the heat storage per unit volume as masonry, so a smaller volume of mass can be used [14].

3. 2 Roof pond ► Figure 11. Roof pond [21]. A roof pond uses a store of water above the roof to mediate internal temperatures, usually in hot desert environments as seen in the Figure 11. This system is best for cooling in low humidity climates but can be modified to work in high humidity climates [12].

3. 3 Indirect gain system rules ü The exterior of the mass wall (toward the sun) should be a dark color. ü Use a minimum space of 10 cm between thermal mass wall and the glass. ü Vents used in a thermal mass wall must be closed at night. ü If movable night insulation will be used in thermal wall system, reduce thermal mass wall area by 15%. ü Thermal wall thickness should be approximately 60 -85 cm for brick, 75 -110 cm for concrete, 50 -75 cm for adobe or other earth material and at least 35 cm for water [12].

4. Isolated Gains ► Isolated gain, or sunspace, passive heating collects the sunlight in an area that can be closed off from the rest of the building as shown in the Figure 12. The doors or windows between the sunspace and the building are opened during the day to circulate collected heat, and then closed at night, allowing the temperature in the sunspace to drop [22].

4. 1 Sunspaces Figure 12. Sunspaces [17].

4. 2 Main Functions of Sunspaces üAuxiliary Heating üTo Grow Plants üLiving Area

4. 3 Main Considerations ► Siting: A sunspace must face south. Due solar south is ideal, but 30 degrees east or west of due south is acceptable ► Heat Distribution: Warm air can be blown through ductwork to other living areas. It can also move passively from the sunspace into the house through doors, vents, or open windows between the sunspace and the interior living space. ► Glazing: Sloped or Vertical? Although sloped glazing collects more heat in the winter, many designers prefer vertical glazing or a combination of vertical and sloped glazing. Sloped glazing loses more heat at night and can cause overheating in warmer weather. Vertical glazing allows maximum gain in winter, when the angle of the sun is low, and less heat gain as the sun rises toward its summer zenith [23].

5. Cost ► Passive solar technology may still be new to many designers and builders. So you're sometimes required to pay extra for them to master unfamiliar design and construction details. But if you're lucky enough to be working with an experienced solar designer and builder who are committed to excellence, a passive solar home may cost no more than a conventional one or even less in some situations. Also, properly sized heating equipment, which are typically smaller in passive solar homes, will sometimes offset the cost of the passive solar features [5].

6. The Advantages of Passive Solar Design High energy performance: lower energy bills all year round. ► Investment: independent from future rises in fuel costs, continues to save money long after initial cost recovery. ► Value: high owner satisfaction, high resale value ► Attractive living environment: large windows and views, sunny interiors, open floor plans ► Low Maintenance: durable, reduced operation and repair ► Unwavering comfort: quiet (no operating noise), warmer in winter, cooler in summer (even during a power failure) ► Environmentally friendly: clean, renewable energy doesn't contribute to global warming, acid rain or air pollution [1]. ►

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