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Passive Solar Design. Passive solar has been used for thousands of years Southwest United States. Adobe solar architecture. Passive Solar Design.
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Passive solar has been used for thousands of yearsSouthwest United States
Passive Solar Design • Passive solar heating is defined as using solar energy striking windows, skylights, greenhouses, clerestories, and mass walls in order to provide heating for a house. • Generally, such solar collection occurs passively, without the extensive use of pumps or fans typically used in active solar collector systems. • Because heating is needed only over the colder part of the year (Sept. to May), passive solar design must also eliminate unwanted solar heat gains during the summer. • The use of techniques to eliminate solar gains and to cool a house with the use of active systems is often referred to as passive cooling
General Rules: 1. Conservation Levels: Higher than normal levels of insulation and airtightness 2. Distribution of Solar Glazing: distributed throughout the building proportional to the heat loss of each zone 3. Orientation: Optimum within 5 degrees of true south 4. Glazing Tilt: Looking for perpendicular to sun angle in winter, although vertical efficient where lots of reflective snow cover 5. Number of glazing layers: 3 to 4 for severe climates, less otherwise 6. Night insulation and Low-E glazing: Greatly improves reduction of night heat losses 7. Mixing passive systems can increase comfort levels.
Types of Passive Systems Direct Gain Trombe Wall or Mass Wall Sunspace or Greenhouse Roof Systems
Direct Gain Systems • Sunlight incident on transparent surfaces allows the energy to enter the living space directly and is called Direct Gain. • South 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 south (to within 20 degrees) Overhangs should prevent unwanted summer gains (2 ft typical at 40 degrees latitude) Window area should be 8-12% of the house floor area if no extra thermal mass is added This amount of passive solar gain should provide no more than 40-50% of the yearly heating load More area may be possible if additional thermal mass is added. PRECAUTIONS Excess window area can result in a loss of privacy, too much glare, underheating and overheating Movable insulation should be designed to be easy to install and use Direct Gain Passive Solar Design
Direct Gain Rules: • Mass Distribution: spread it around evenly; 6 times glazing area (3X minimum) • Mass Thickness: thin and spread out better than thick. More than 4” for masonry or concrete not useful • Colour: Floors dark to absorb more heat, walls and ceilings lighter to reflect light. • Surface Covering: insulative coverings (ie. Rugs) greatly decrease performance of thermal mass • Concrete Block Masonry: If used, a high density with cores filled with grout
Direct Gain Rules, cont'd: • Floor Materials: Concrete or brick preferred. If insulating under, at least 4” thick (100mm). More than 6” (150mm) not useful. • Limits on Direct Gain Glazing Area: South facing glazing limited to prevent large temperature swings. 7% of floor area for low mass buildings, 13% of floor area for high mass buildings. • Glazing orientation: Vertical facing due south preferred. Vertical easiest to build, and easiest to shade in summer. Performance penalty for 15degrees off due south is 10% and for 30 degrees is 20% loss; so within 15 degrees recommended. • Night insulation: Really helpful but can be very costly. • Thermal Insulation: Insulation located OUTSIDE the thermal mass.
Good design is based on combining several elements and ideas Knowledge of seasonal changes in sun path Landscaping in the site plan Overhangs Appropriate use of thermal mass Energy efficient design for the thermal envelope
The Sun’s Seasonal PathThis path is hemisphere and latitude dependent
40 Degree Latitude Sun Chartshowing altitude and azimuth angles for different months of the year and times of the day
Site PlanDon’t shade the south, except for overhangs, but do shade the east and west sides. Decks, porches and carports also may be used to shade.
Thermal Massprovided by normal drywall and furnishings and also by slabs, mass walls, fireplaces, etc.
Clerestory is also direct gain • Excellent for bringing daylighting to northern spaces (deep houses) • Can use north wall masonry heat storage • Overhang over clerestory window shades in summer
Thermal Storage Walls or Trombe Walls • Advantages: • Eliminates glare • Lowers temperature swings in room • Vents allow partition of energy into daytime and nighttime heating • Sun hits entire mass • Precautions: • More expensive and less efficient than direct gain • More difficult to reduce nighttime losses • Best for sunnier climates • Occupies valuable spacein building
Operation of Trombe Wall Sunlight hits the darkened mass wall and absorbed heat moves slowly across the wall The inside surface temperature peaks 6-8 hours after the midday outside surface peak Operational vents allow optional controlled air circulation into the space during the day Overhang reduces wall sun exposure during the warmer months Vent added to outside at the top can drive warm air out in the summer and bring cooler air from a north vent can be used as part of a south-facing greenhouse may be retrofitted to existing houses with brick or stone construction
What is a Sunspace?? Sunspace -- a passive solar heating system type consisting of a glassed-in room like a greenhouse, atrium or conservatory, located on the south side of a building and separated from other building spaces by a common wall. Common Wall -- a wall separating a sunspace from other living spaces. Greenhouse -- a sunspace used primarily for growing plants Projected GlazingArea -- net glazing projected onto a single vertical wall.
Attached Greenhouses or Sunspaces • Advantages: • Lower temperature swings in adjacent living space • Flexible – can be operated in many modes • Provides additional living or growing space • Works well in late winter and spring when standard overhangs block direct gain through windows • Precautions: • Price moderate to high • Thermal performance depends greatly on how it is operated
Sunspace Rules: • Effect of orientation: optimum due south. Penalties about 5% for 30degrees off due south. More summer overheating for off south directions. • Use of Mass: increases space’s livability. Reduces overheating. Optimum thickness for masonry walls between 8 and 12”. • Area of Mass: direct gain rules apply: 3mass to 1glazing. • Do not glaze end walls: for both summer and winter performance. • Summer Venting: needs to be vented during summer especially if not well shaded. • Wall Colour: Direct gain rules apply, except: • a. use darker colours in general as light colours tend to reflect light and heat out of the space • b. if used as a green house, surfaces in corners need to be light to improve plant performance/life.
Sunspace Rules, cont'd: • Sunspace width: 15 to 20 feet works well. • Colour: dark colours work better to absorb heat. • Plants and other lightweight objects: Limit. • Roof: Need to be able to shade it in the summer to avoid overheating. Curtain, awnings or internal shades, OK. • Common Wall: Needs to be able to be closed off from main living space to avoid overheating. Preferably masonry (like trombe wall). • Common wall vents: required as one of the ways heat is transferred to the living space. • a. doorways, 15% of glazing area • b. window openings, 20% of glazing area • c. high and low vent pairs, 10% of glazing area
Solar Greenhouse with thermal mass in the floor and in water barrels
Thermal Storage Roofs • Advantages: • Provides both heating and cooling • Provides low temperature swing in the building • Can provide 100% of heating and cooling in milder climates • Precautions: • Structural support for heavy mass expensive • Most easily used in 1 story buildings • Typically 50% size of floor area • Least acceptable design in earthquake prone areas
Passive Solar Design Style The effectiveness of solar heating does not depend on the style (Cape Cod, Colonial, modern, contemporary) of house that you design. Houses may be small and simple, or spectacular; the solar concept being applied is the same. Of course, the smaller the house, the less resources and cost will be needed to build and maintain it.
