Welcome to Twin Pines
Lodge!
By now we are certain
that you have noticed that Twin Pines Lodge incorporates a unique structural
design. The design is referred to as
Passive Solar. Below is discussion
regarding this unique design. We are sure
that you will recognize concepts that are present in this home.
Passive solar design
uses sunshine to heat, cool and light homes and other buildings without
mechanical or electrical devices. It is
usually part of the design of the building itself, using certain materials and
placement of windows or skylights. A
successful passive solar building needs to be very well insulated in order to
make best use of the sun's energy. The
result is a quiet and comfortable space, free of drafts and cold spots. 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. In the winter when heating is required, the
sun is low in the sky, which allows the heat to penetrate into windows on the
south face of a structure. In the
summer, south-facing windows can be shaded by an overhanging roof or awning to
keep out the high hot summer sun. Because much of a building's heat is lost
through its windows, the majority of windows in a passive solar building are
located on the south wall. Depending on
the climate and the design, as much as 100 percent of a building's heating
needs can be provided by the sun. In a
climate such as
THE ADVANTAGES OF PASSIVE SOLAR DESIGN:
H igh energy
performance: lower
energy bills all year round.
I nvestment:
independent from future rises in fuel costs, continues to save money long after
initial cost recovery.
V alue: high owner satisfaction, high
resale value.
A ttractive living
environment: large
windows and views, sunny interiors, open floor plans.
L ow Maintenance: durable, reduced operation and
repair.
U nwavering comfort: quiet (no operating noise), warmer in winter,
cooler in summer (even during a power failure).
E nvironmentally
friendly: clean, renewable energy doesn't contribute to
global warming, acid rain or air pollution.
PASSIVE SOLAR DESIGN: The Tools
SOUTH FACING GLASS
South facing glass, also called glazing, is a key component of any
passive solar system in the northern hemisphere. The system must include enough solar glazing
for good performance in winter, but not so much that cooling performance in
summer will be compromised. When the
solar glazing is tilted, its winter effectiveness as a solar collector
increases. However, tilted glazing can
cause serious overheating in the summer if it is not shaded very
carefully. Ordinary vertical glazing is
easier to shade, less likely to overheat, less susceptible to damage and
leaking, and so is almost always a better year-round solution. Even in the winter, with the sun low in the
sky and reflecting off snow cover, vertical glazing can often offer energy
performance just as effective as tilted.
THERMAL MASS
Almost
all passive solar systems work in conjunction with thermal mass, or materials with a high capacity for absorbing and
storing heat (e.g., brick, concrete masonry, concrete slab, tile, adobe,
water). Thermal mass can be incorporated
into a building design as floors, interior walls, fireplaces, or bancos. The sun does not need to hit these surfaces
directly to store the heat, nor do these surfaces necessarily need to be a dark
color. The thermal storage capabilities
of a given material depend on the material's thermal conductivity, specific
heat and density. Conductivity tends
to increase with increasing density; generally, the higher the density of the
material, the better. Effective
materials for floors include painted, colored or acid-etched concrete, brick,
quarry tile, and dark ceramic tile. When
more mass is required, interior walls or interior masonry fireplaces can be
incorporated into the design. Mass walls
serve the dual functions of serving as structural elements or fire protection
as well as for thermal storage. From an
energy standpoint, it would be difficult to add too much thermal mass in a
house. But thermal mass has a cost, and
so adding too much mass just for thermal storage purposes can be unnecessarily
expensive. As with all aspects of solar
design planning, it is necessary to achieve a workable balance.
ORIENTATION
In order for passive solar systems
to work effectively, care must be taken to ensure that the building is oriented
to take advantage of year-round energy savings.
The ideal orientation for solar glazing is within 5 degrees of true
south. This orientation will provide
maximum performance. Glazing oriented to
within 15 degrees of true south will perform almost as well, and orientations
up to 30 degrees off—although less effective—will still provide a substantial
level of solar contribution. In
SUNTEMPERING
Sun tempering is the most basic of
passive solar techniques, it is simply increasing the number of windows on the
south side, without adding additional thermal mass apart from the framing,
gypsum board, etc, that is normally part of a conventional house. In a conventional house, about 25 percent of
the windows face south which amounts to about 3 percent of the house's total
floor space. In a sun tempered house, the percentage is increased to a maximum of
about 7 percent. Energy savings are
modest with this system, but sun tempering is very low cost.
DIRECT GAIN
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. During the sunlight hours, this
heat can be stored in thermal mass incorporated into floors or interior walls
made of adobe, brick, concrete, stone, or water. The heat held by the thermal mass will
continue to radiate into the space after the sun goes down. Designing a direct gain system includes
calculating how much window area and how much thermal mass are required to
provide the desired quantity of heat for the space. In general, total direct gain glass area
should be at least 7 percent, but not exceed 12 percent of the house's floor
area. Double glazing is recommended for direct gain windows. Night insulation, such as window shades,
quilts or insulating drapes, improves energy
efficiency dramatically.
THERMAL STORAGE WALLS
Trombe Wall
A trombe wall is a technique used to capture solar heat that was
developed by French engineer Felix Trombe (Trombe rhymes with prom).
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A portion of the south wall is
constructed of thermal mass material such as adobe or poured concrete, then
covered and sealed by a pane of glass positioned about two inches from its
surface. Sunlight enters and the heat is
then trapped by the glass, allowing it to be absorbed by the thermal mass
wall. The heat then radiates into the
interior of the room in the evening and nighttime hours. Trombe walls do not require ventilation,
because the idea is not to circulate warm air, but to allow the wall itself to
radiate heat. The masonry thermal
storage wall should be solid, and there should be no openings or vents either
to the outside or to the living space.
Trombe walls perform better in summer (about 84 percent less heat gain)
than a comparable area of direct glazing. Trombe walls can be combined with direct gain
windows in the same wall, and furniture can be placed up against a trombe wall
without changing its effectiveness. Trombe
walls are particularly useful in a design where less window area in a room is
desired, and nighttime comfort is sought, i.e., bedrooms and bathrooms. Double glazing is recommended for thermal
storage walls, and the space between the glazing and the thermal mass should be
1-3 inches. In general, the effectiveness of the thermal storage wall will
increase as the density of the material increases.
Water Walls
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. Containers are shipped from manufacturers
empty and are easily installed. At least
30 pounds (3.5 gallons) of water should be provided for each square foot of
glazing. An indoor hot tub or a pool can
also be used as a heat storing mass.
GREENHOUSES AND SUNSPACES
When built onto the south wall of a
structure, a solar greenhouse or sunspace provides an insulating air
cushion between the outside and inside of the building, lowering heating bills
in the winter. Sunspaces are referred to
as "isolated gain" passive solar systems because the sunlight is
collected in an area which can be closed off from the rest of the house. During the day, the doors or windows between
the sunspace and the house can be opened to circulate collected heat, and then
closed at night, and the temperature in the sunspace allowed to drop. Thermal mass in the greenhouse/sunspace will
also generate heat which can be moved into the building either mechanically or
by designing the structure to encourage a convective air current. Greenhouses
generally have glass or plastic panels in the roof to allow light and heat
for growing plants and early seed-starting. They are difficult to insulate in areas with
very cold winters because often much heat is lost through the roof, but the
tradeoff is an extended growing season. Sunspaces
usually have an insulated roof and full length windows on the south side. They are often more practical than greenhouses
as living spaces, but will still provide an excellent environment for plants,
and a more even temperature level throughout the year. Climate and desired use will dictate how a
greenhouse or sunspace is designed for a particular application. Ventilation, roof glass, and thermal mass are
important design features that make either structure a valuable money-saving
and comfort-enhancing addition to a home or design. A rule of thumb for sunspaces is to
incorporate 3 square feet of 4-inch thick thermal mass for each square foot of
sunspace glazing. A good place for
thermal mass in the sunspace is the flooring.
The lower edge of the south-facing windows should be no more than 6
inches from the floor or the planter bed to make sure the mass in the floor
receives sufficient direct sunlight. If
the thermal mass is instead located in the common wall, it should be solid
masonry approximately 4 to 8 inches thick, or a frame wall with masonry veneer.
Windows on the east and west walls are
useful for cross-ventilation but should be kept small (no more than 10 percent
of the total sunspace area). Double
glazing is recommended for sunspaces.
ENERGY CONSERVATION: Insulation, Infiltration and Non-Solar Glazing
Adding insulation to walls, floors,
ceilings, roof and foundations improves their thermal resistance (R-value), or resistance to heat flowing out of the
house. Ensuring that the insulation is
properly installed is very important to the house's overall energy
performance. Sealing the house carefully
to reduce air infiltration (air
leakage) is also essential. Air will
flow rapidly through cracks and crevices in the wall in the same way that water
flows through the drain in a bathtub, so even a small opening can allow heat to
bypass the insulation and lead to big energy losses. The tightness of a house is generally
measured in the number of air exchanges per hour (ACH). A good, comfortable, energy efficient house
will have approximately 0.35 to 0.50 air exchanges per hour under normal winter
conditions. Increasing the tightness of
the house beyond that may improve energy performance, but it may also create
problems with indoor air quality, moisture build-up, and inadequately vented
fireplaces and furnaces. Some kind of additional mechanical ventilation—for
example, small fans, heat pump heat exchangers, integrated ventilation systems
or air-to-air heat exchangers—is usually necessary to avoid such problems in
houses with less than 0.35 ACH.
Windows that are not south facing
are considered non-solar glazing.
Windows on the north side of a house in almost every climate lose
significant heat energy and gain very little useful sunlight in the
winter. East and west windows are likely
to increase air conditioning needs unless heat gain is minimized with careful
attention to shading. Of course, people
want windows for reasons other than energy gain, so a good design will be a
balance between efficiency and other benefits, such as views and bright living
spaces. Some rules of thumb for
non-solar glazing: triple-glazing (meaning three panes of glass) or low-e
("e" stands for emissivity)
coating will reduce heat loss while allowing for light to enter; north facing
windows should be small and have high insulation or R-value; east windows catch
the morning sun and can cause potential overheating, therefore shading should
be planned with care; west windows also have a high potential for overheating,
tinted glass or low-e glass may be effective; and lastly, as many windows as
possible should be kept operable for easy natural ventilation in summer.
INFILTRATION CHECK LIST:
• tighten
seals around windows and doors, weather-strip around all openings to outdoors;
• caulk
around all windows and doors before hanging drywall, seal plumbing &
electrical conduit openings;
• insulate
behind wall outlets and/or plumbing lines in exterior walls;
• caulk
under headers and sills;
• chink
spaces between rough openings and millwork with insulation or fill with foam;
• seal
larger openings such as ducts into attics or crawlspaces with taped polyethylene
covered with insulation;
• locate
continuous vapor retardants on the warm side of the insulation (building wrap,
etc.);
• install
dampers and/or glass doors on fireplaces; combined with outside combustion air
intake;
• install back
draft dampers on all exhaust fan openings
• caulk and
seal the joint between the basement slab (or the slab on grade) and the
basement wall;
• remove
wood grade stakes from slabs and seal;
• cover and
seal sump cracks;
• close core
voids in top of block foundation walls;
• control
concrete and masonry cracking;
• employ proper
radon mitigation techniques.
BACK UP AND MECHANICAL SYSTEMS
The passive solar features in a
house and the mechanical heating, ventilating and air conditioning systems
(HVAC) will interact all year round so the most effective approach is to design
the system as an integrated whole.
System Sizing
Mechanical systems are often
oversized for the relatively low heating loads in well-insulated passive solar
houses. Oversized systems will cost more
in the first place, and will cycle on and off more often, wasting energy. The back-up systems in passive solar houses
should be sized to provide 100 percent of the heating or cooling load on the
design day, but no larger.
Night Setback
Clock thermostats for automatic
night shutoff are usually very effective, but in passive solar systems with
large amounts of thermal mass releasing heat during the night, night setback of
the thermostat may not save very much energy.
Ducts for Air Heating Furnaces
Both the supply and return ducts
should be located within insulated areas, or be well-insulated if they run in
cold areas of the house, and they should be well sealed at the joints.
INTERIOR SPACE PLANNING
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 houses with passive solar features, the lay out of rooms and interior
zones is particularly important. A
longer East-West axis will allow more rooms to face south. In general, living areas and other
high-activity rooms should be located on the south side to benefit from the
solar heat. The closets, storage areas,
garage and other less-used rooms can act as buffers along the north side, but
entryways should be located away from the wind.
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.
Other ideas include:
• orienting internal mass walls as
north-south partitions that can be "charged" on both sides thus
making maximum use of the mass;
• using an east-west partition wall
for thermal mass, but avoid dividing the interior space into a north zone that
may get too cold and south zone that may get too warm;
• using thermal storage walls;
• collecting the solar energy in one
zone of the house and transporting it to another by fans, natural convection
and/or an open floor plan;
• providing south-facing clerestories to "charge"
north zones.
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, and 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 10 feet of the
south wall of a solar building; fences should be located beyond 10 feet; one
story buildings should be located beyond 17 feet; and two story buildings
should be located beyond 40 feet.
NATURAL COOLING GUIDELINES
"Natural cooling" refers
to techniques which help a house stay cool in the summer but which require
little to no energy. Such techniques
help to reduce air conditioning, not replace it. Shading is particularly important in passive
solar houses, because the same features that collect sunlight in winter will go
right on collecting it in summer unless they are shaded and the house itself is
designed to help cool itself. Thermal
mass performs well year round; masonry materials can be effective in staying
cool as well as storing heat in winter.
If mass surfaces are exposed to cool night time temperatures, they will
help the house stay cooler the next day.
The additional insulation that increases winter performance will also
work to improve summer performance by conserving the conditioned air inside the
house. Some low-e windows and other
glazes with high R-values can help shield against unwanted heat gain in summer.
SHADING: Landscaping, overhangs and
shading devices
Landscaping
Trees and other landscaping features
may be effectively used to shade east and west windows from summer solar
gains. Trees on the south side, 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 accommodate the south-facing glazing while leaving in as many trees
as possible. Other landscaping ideas for
summer shade include: trellises on the east and west covered with vines;
shrubbery or other plantings to shade paved areas; use of ground cover to
prevent glare and heat absorption; trees, fences, or shrubbery planted so as to
"channel" breezes into the house; and deciduous trees on the east and
west sides of the house, to balance solar gains in all seasons.
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Roof Overhangs
Fixed overhangs are an inexpensive
feature and require no operation by the homeowner. They must be carefully designed, however. Otherwise, an overhang that blocks the summer
sun may also block sun in the spring, when solar heating is desired. Likewise, an overhang sized for maximum solar
gain in winter will allow solar gain in the fall on hot days. A combination of carefully sized overhangs on
south windows and shading devices on the other windows usually allows for an
effective solution. The following figure
may be used to determine the optimum overhang size. In
Shading Devices
External devices stop solar gain
before the sun hits the building. These
include awnings, solar screens, roll-down blinds, shutters and vertical
louvers. They are adjustable and perform
well, but require action by the homeowner to operate. Interior shading elements also require
homeowner operation, and also permit the sun to enter the house and be trapped
between the window and the shade.
Reflective interior blinds and curtains are relatively low cost and are
easy to operate. Another option in
shading is a porch or carport, preferably located on the east or west sides.
VENTILATION
When possible, the house should be
positioned on the site to take advantage of prevailing winds. The prevailing winds direction is from the
south during the summer. The free vent
area (unobstructed openings like open windows) should be between 6 to 7.5 percent
of total floor area, half located on the leeward and half on the windward side
of the building. Ceiling fans will
probably save more energy than any other single cooling strategy, since air
movement can make people feel comfortable at higher temperatures. A whole house fan can also assist with
ventilation, but is not very effective at cooling when the temperature is
higher than 76 degrees F.
Using a combination of the above
cooling techniques will substantially reduce the need for air conditioning.
PASSIVE SOLAR DESIGN CHECKLIST:
1). Is the
house oriented to optimize both winter
heating and summer cooling needs?
2). Does
the house effectively incorporate sufficient thermal mass?
3). Does
the house design include thorough insulation
throughout?
4). Does
the house design optimize glazing so
as not to over or under heat?
5). Is the backup heat system appropriately
sized?
6). Does
the interior design maximize solar
heating and cooling benefits?
SUNPATHS:
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SOURCES: This primer was adapted from Passive Solar Design
Strategies: Guidelines for Builders, published by the Passive Solar
Industries Council (PSIC), used by permission.
Additional material was adapted
from Residential Passive Solar Energy Seminars 1993, by Mark Chalom,
Quentin Wilson and Bill Yanda (sponsored
by the NM Energy, Minerals and Natural Resources Department and NM State
University Cooperative Extension), the NM Energy Conservation and Management
Division website, and the National Renewable Energy Lab website. Graphics by Mark Chalom and PSIC used by
permission. Prepared by