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Download Passive Heating and Cooling - Hatboro
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Passive Heating and Cooling Passive Design • Uses ambient energy sources instead of purchased energy – Daylighting – Natural ventilation – Solar energy Active Design • Uses purchased energy to keep the building comfortable – HVAC – Heat pumps – Radiant panels – Chilled beams – Electrical lights Hybrid Systems • Use some mechanical energy to enhance ambient energy – Heat recovery ventilation – Economizer ventilation – Solar thermal systems – Radiant facades – Ground source heat pumps • Optimize design for passive strategies first – Downsizes the active systems you’ll need Building Massing • Massing is the overall shape and size of the building • Can be one of the most important factors in thermal comfort and daylighting Massing • Take advantage of site conditions – Rainwater harvesting – Avoid shading wild lands • Massing for visual comfort – Some general strategies for using massing to maximize daylight energy and comfort • Difficult to get consistent daylight and control glare from east and west windows – Side of the building facing the sun’s path can generally be easily shaded Massing • Generally buildings longer on their east west axis are better for daylighting and visual comfort Massing • Using skylights can improve the daylighting in single story buildings regardless – Single stories aren’t the best for land use • Larger and taller buildings should have thinner profiles to help maximize daylighting from windows • Can also improve daylighting by having a central courtyard or atria or other cutouts • Increase the height of each story Massing for Thermal Comfort • Often helped by extending the east-west axis to take advantage of the consistent sun on northern/southern exposures – But thinner buildings may not be better Thin/Tall Buildings • Increase the surface area to volume ratio • Makes utilizing natural ventilation for passive cooling easy • Tall buildings increase effective ventilation because wind speeds are faster at greater height – Increases cross ventilation and stack effect ventilation Thin/Tall Buildings • Rules of thumb from 2 scenarios with windows facing the direction of the prevailing wind – For spaces with windows on only one side, natural ventilation will not reach farther than 2x the floor space to the ceiling height into the building – For spaces with windows on opposite sides, the natural ventilation effectiveness limit will be less than 5x the floor to ceiling height into the building • When planning urban centers, specifically in the heating dominated climates, having buildings gradually increase in height will minimize high speed winds at the pedestrian level Solar Radiation & Heat Transfer • Thin and tall buildings also increase the exposed area for heat transfer through the envelope • In cold climates, massing that minimizes the ratio of surface area to volume can avoid unwanted heat loss – The sun’s heat is advantageous and the surface area facing it helps passively heat the building – Side of the building exposed to the sun can be increased while reducing the exposed areas of the other sides • In hot climates thin buildings with their biggest face exposed to the sun – Cause unwanted solar gain, use shading devices and good windows – Taller buildings can reduce unwanted gains • Suns heat strikes stronger on the roof than the walls in warm latitudes • Sun’s heat and light do not come from all directions equally – Windows facing away from the sun’s path get diffuse light, but without heat gain (have heat loss too) – Windows facing east are warmed in the morning when the – Windows facing west are warmed in the afternoon when spaces are generally warm Building Program • Sparsely populated buildings with little activity or equipment have little heat from internal loads • In cold climates you can benefit from a compact floor plan – Minimizes ratio of surface area to volume • Roofs can be angled for optimal solar heating • Reveals and overhangs can shade parts of a building with other parts of the same building • Aerodynamic curves can reduce heat loss from infiltration • Interior buffer zones can be replaced in a building’s west side to protect living and working areas from hot afternoon sun (stairs, restrooms, entry corridors)
