Transcript Passive Heating and Cooling

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)