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SOLAR ENERGY SYSTEMS
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR LEAK MINIMIZATION
AIR LEAK SEALING PROCEDURE
AIR SEALING STRATEGIES
BIOGAS PRODUCTION & USE
EVAPORATIVE COOLING SYSTEMS
FLOOR FRAMING & SUBFLOOR for TILE
FLOOR POURED FINISH ON CONCRETE SLABS
FLOOR RADIANT HEAT Mistakes to Avoid
FLOOR TYPES & DEFECTS
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FRAMING METAL STUD PERFORMANCE
FREEZE-PROOF A BUILDING
FROST HEAVES, FOUNDATION, SLAB
GREEN BUILDING CONSTRUCTION CODES GUIDES
GREENHOUSE DESIGN for SOLAR HEATING
GREENHOUSE / SUNSPACE GLARE
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HEAT LOSS RATE CALCULATIONS
HEATING SMALL LOADS
HOUSEWRAP INSTALLATION DETAILS
HUMIDITY LEVEL TARGET
INSULATION IDENTIFICATION GUIDE
INSULATION LOCATION - WHERE TO PUT IT
LEED GREEN BUILDING CERTIFICATION
LEED Building Designation & IAQ
MOISTURE CONTROL in BUILDINGS
NOISE / SOUND DIAGNOSIS & CURE
ODORS GASES SMELLS, DIAGNOSIS & CURE
PLUMBING SYSTEM INSPECT DIAGNOSE REPAIR
RADIANT SLAB FLOORING CHOICES
RADIANT SLAB TUBING & FLUID CHOICES
ROOFING INSPECTION & REPAIR
ROOF VENTILATION SPECIFICATIONS
ROOF ICE DAM LEAKS
SHEATHING, FOIL FACED - VENTS
STRUCTURAL INSPECTIONS & DEFECTS
SUMP PUMPS GUIDE
SWEATING (CONDENSATION) on PIPES, TANKS
Thermal Expansion Cracking of Brick
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
THERMAL IMAGING MOLD SCANS
THERMAL MASS in BUILDINGS
THERMAL TRACKING & HEAT LOSS
VAPOR BARRIERS & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
VENTILATION in BUILDINGS
WATER SOFTENERS & CONDITIONERS
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING
WINDOWS & DOORS
WINTERIZE A BUILDING
WOOD Burning Heaters Fireplaces Stoves
Definition & uses of passive solar gain for heating homes. Our page top photo illustrates a simple method for controlling passive solar gain through South facing windows and sliding glass doors and into a ceramic tile floor on a concrete slab. The movable Japanese-style screens are hung from pegs and can be moved or relocated depending on the amount of solar gain desired. The original design for this home was intended to use exterior solar shading but that feature was omitted during construction in the 1960's.
This article includes adaptations from U.S. DOE publications about passive solar design.
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Direct gain is the simplest passive solar home design technique. Sunlight enters the house through the aperture (collector)—usually south-facing windows with a glazing material made of transparent or translucent glass.
The sunlight then strikes masonry floors and/or walls, which absorb and store the solar heat. The surfaces of these masonry floors and walls are typically a dark color because dark colors usually absorb more heat than light colors. At night, as the room cools, the heat stored in the thermal mass convects and radiates into the room.
[Another example of direct solar gain is at our page top photo.- DF]
Some builders and homeowners have used water-filled containers located inside the living space to absorb and store solar heat. Water stores twice as much heat as masonry materials per cubic foot of volume. Unlike masonry, water doesn't support itself. Water thermal storage, therefore, requires carefully designed structural support. Also, water tanks require some minimal maintenance, including periodic (yearly) water treatment to prevent microbial growth.
The amount of passive solar (sometimes called the passive solar fraction) depends on the area of glazing and the amount of thermal mass. The glazing area determines how much solar heat can be collected. And the amount of thermal mass determines how much of that heat can be stored. It is possible to undersize the thermal mass, which results in the house overheating. There is a diminishing return on over sizing thermal mass, but excess mass will not hurt the performance. The ideal ratio of thermal mass to glazing varies by climate.
[Our photo (left) shows a small area designed by D. Friedman & J. Church for both direct solar gain and a brick on concrete floor providing thermal mass at a home in Poughkeepsie, NY - DF]
Another important thing to remember is that the thermal mass must be insulated from the outside temperature. If the thermal mass is not insulated, the collected solar heat can drain away rapidly. Loss of heat is especially likely when the thermal mass is directly connected to the ground or is in contact with outside air at a lower temperature than the desired temperature of the mass.
Even if you simply have a conventional home with south-facing windows without thermal mass, you probably still have some passive solar heating potential (this is often called solar-tempering). To use it to your best advantage, keep windows clean and install window treatments that enhance passive solar heating, reduce nighttime heat loss, and prevent summer overheating.
An indirect-gain passive solar home has its thermal storage between the south-facing windows and the living spaces.
Illustration of a Trombe wall (left) U.S. DOE.
Using a Trombe wall is the most common indirect-gain approach. The wall consists of an 8–16 inch-thick masonry wall on the south side of a house. A single or double layer of glass is mounted about 1 inch 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.
The Trombe wall distributes or releases heat into the home over a period of several hours.
Solar heat migrates through the wall, reaching its rear surface in the late afternoon or early evening. When the indoor temperature falls below that of the wall's surface, heat begins to radiate and transfer into the room. For example, heat travels through a masonry wall at an average rate of 1 hour per inch. Therefore, the heat absorbed on the outside of an 8-inch-thick concrete wall at noon will enter the interior living space around 8 p.m.
The most common isolated-gain passive solar home design is a sunspace. A sunspace—also known as a solar room or solarium—can be built as part of a new home or as an addition to an existing one.
The simplest and most reliable sunspace design is to install vertical windows with no overhead glazing. Sunspaces may experience high heat gain and high heat loss through their abundance of glazing. The temperature variations caused by the heat losses and gains can be moderated by thermal mass and low-emissivity windows. For more information, see sunspace orientation and glazing angles.
The thermal masses that can be used include a masonry floor, a masonry wall bordering the house, or water containers. The distribution of heat to the house can be accomplished through ceiling and floor level vents, windows, doors, or fans.
Most homeowners and builders also separate the sunspace from the home with doors and/or windows so that home comfort isn't overly affected by the sunspace's temperature variations. For more information, see [at U.S.DOE or below] sunspace heat distribution and control.
Sunspaces may often be called and look a lot like "greenhouses." However, a greenhouse is designed to grow plants while a sunspace is designed to provide heat and aesthetics to a home, as our photographs of a Poughkeepsie New York home illustrate [left & below].
Many elements of a greenhouse design that are optimized for growing plants, such as overhead and sloped glazing, are counterproductive to an efficient sunspace.
Moisture-related mold and mildew, insects, and dust inherent to gardening in a greenhouse are not especially compatible with a comfortable and healthy living space. [See HUMIDITY LEVEL TARGET and see INDOOR AIR QUALITY IMPROVEMENT GUIDE -DF]
Also, it is difficult to shade sloped glass to avoid overheating, while vertical glass can be shaded by a properly sized overhang.
Photo-Example of A Sunspace for a Cold Climate
[Our photos (above and at left) show a sunspace constructed by the website author (D Friedman) & J Church, in Poughkeepsie, New York. This addition includes continuous operable awning-type windows around three sides of the structure (North, East, South). In order to maximize solar gain during winter months in this northern climate (Mid Hudson Valley, New York).
The roof was designed with only a minimal overhang. The West side of the addition is its point of attachment to the original building.
This sunspace was well insulated in its roof and lower walls below the windows, and the space can be opened to share air and heat with the rest of the building (lifting out a sliding glass door).
As this sunspace was built by modifying an existing screened porch, we did not construct a thermal-mass floor: the space was constructed over a crawl area, but the floor has been insulated below using two-inch solid-foam board insulation placed between the floor joists, immediately below the wood flooring. Even with heat turned off into this room, it reaches the high 50's, low 60's in cold winter months. Roof overhang design for passive solar homes is discussed below. -DF]
List of Passive Solar Design Key Reference Books including Online Texts
The first three passive solar design handbook links below are to free, online documents.
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
Readers who have not already done so should start reading at PASSIVE SOLAR DESIGN KEY ELEMENTS. Readers wanting more detail about passive solar design should see SOLAR ENERGY SYSTEMS. Readers concerned with accurate calculation of the "percent solar" and similar energy savings assessments should see PASSIVE SOLAR HEAT PERFORMANCE. Readers should also see SOLAR HOUSE EVALUATION. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
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