Transcript PASSIVE SOLAR HEATING

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
 Heating
 Cooling
1.2. History
1.3. Insulation
1.4. Heat Movement Physics



Conduction
Convection
Radiant
1.5. Five Elements of Passive Solar Design





Aperture (Collector)
Absorber
Thermal Mass
Distribution
Control
1.6. The Working Conditions
2. Direct Gain
2.1. What it is
2.2. Thermal Mass
2.3. 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. Thermal Storage Wall (Trombe Wall)
3.2. Roof Pond Systems
3.3. Indirect Gain System Rules
4.
Isolated Gain
4.1. Sunspaces
4.2. Main Functions of Sunspaces



Auxiliary Heating
To Grow Plants
Living Area
4.3. Main Considerations



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.
 Convection is the way heat circulates through liquids
and gases. Lighter, warmer fluid rises, and cooler,
denser fluid sinks.
 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].

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 other thermally 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
 The exterior of the mass wall (toward the sun) should
be a dark color.
 Use a minimum space of 10 cm between the thermal
mass wall and the glass.
 Vents used in a thermal mass wall must be closed at
night.
 If movable night insulation will be used in the thermal
wall system, reduce the thermal mass wall area by
15%.
 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
Auxiliary
Heating
To Grow Plants
Living 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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Thank you for listening
