Information on how the
direction your home faces, particularly the direction the windows
face, radiant barrier, solar hot water, solar pool system, PV
system, can affect your comfort, and heating and cooling costs.
Which way's the right way?
Properly positioning your
house on your site can save you money on your utility bills and make
your house more comfortable year-round. Orientation is a critical
component of energy efficiency and the ability of a building to
properly mediate the summer and winter sun heat loads which
penetrate through a building's skin (the outer shell of the
building), especially in smaller buildings such as houses. This
differs from larger buildings like office buildings which are more
dominated by internal loads like lights, business machines, and
large numbers of people. This fact sheet will cover eight areas:
compass direction, views and other site amenities, building
configuration, radiant barriers, types of windows,solar hot water,
solar pool heating and whole house PV systems.
Compass Direction
Here in Florida, and in any climate where the sun and its heat
play a dominant role in human comfort, the direction your house is
oriented (which side faces which direction) is the most effective
difference you can make in keeping your cooling costs down. This can
prove difficult in pre-plotted subdivisions or tighter urban lots,
where your house's orientation may be inflexible because of a
tradition to face the street. The optimal orientation corresponds to
the cardinal directions of the compass, due north, due south, due
east, and due west.
The north and south exposures are the easiest to deal with here
in Florida . The north side can be considered the cool side as the
sun spends very little time in the northern sky. The south side can
be considered the sunny side, since during the course of the day the
sun spends more time in the southern sky. But, here in Florida,
because of our southern latitude, the sun is almost straight up in
the sky at solar noon in summer which means that a southern wall can
be very well shaded from the sun with a very slight overhang. The
advantage here being that in winter, when the sun is lower in the
sky, these slight overhangs allow sun penetration deep into a house
to provide some passive solar heating. Bear in mind though, that the
sun spends very little time directly in the south, it spends most of
its time climbing up to its peak (in the southeastern sky) and
descending (in the southwestern sky), so although an overhang as
small as 3 inches may shade a southern orientation at solar noon, it
will do little to reduce solar gain throughout the rest of the day.
Here in Florida, on a one story building, overhangs of 2 feet are
the minimum for effective shading.
The east side of a house oriented to the cardinal compass
directions will take a lot of the sun's morning heat. Since the sun
spends much of its morning climbing through the east, east
Southeast, and south southeastern sky, this sunlight penalty can be
very large to you and your checkbook. Minimal window area on the
east side is recommended, even overhangs on this east side will only
work minimally because the sun is so low in the sky during the
morning hours.
The west side of a house oriented in the
cardinal compass direction will bear the brunt of the sun's heat. In
this case, minimize not only the window area but the total wall area
facing west. Here in Florida, the overheated period (the time when
your air conditioner will run the most, and the time to avoid going
outside and doing strenuous activities) occurs between 2pm and 5pm.
If you listen to the weather report you'll notice that the
temperature usually climbs throughout the day and reaches its peak
at the start of the evening rush hour (its usually only 90 at 2pm
and the temperature doesn't get close to the century mark until 4:30
or 5pm). Since the ambient heat of the day has built up (air
temperature), the sun's added heat will compound this. For this
reason, the western exposure of a house should be devoid of all
windows, or if windows are required by the dictates of the site or
design, this exposure should be buffered with porches, trees,
trellises, sunshades, carports, out buildings, or other
means.
Most houses cannot match these cardinal
directions straight on because of site set-back (unbuildable areas
surrounding most any plotted site.) For these conditions, it is best
to determine the worst exposure (that is, which side or sides of the
house get the most west, Southwest, and western exposure) and
minimize windows on these sides. One important question to ask
your builder is whether or not the air conditioner is sized for each
individual house in the subdivision and its particular orientation
or if they just size the worst case scenario and then put that
system in every house. It is far better for your comfort and
your checkbook if they size each house's air conditioning
individually. This will ensure the system will perform optimally for
your house's orientation. It is still best to avoid purchasing a
home with a lot of western exposure, even if the air conditioning
system is sized specifically for it, since this home will consume
more energy to keep cool than one with less western exposure and/or
minimal windows.
Views and Other Site Amenities
You may have your eye on a lot with a beautiful view of a field
or the lake. If this view is to the west or west Southwest you will
have to resign yourself to paying for that view should you decide to
have lots of windows to capture it. Often, lots with good views have
a higher price tag associated with them, and building a house on
that lot will have a higher price tag over the long term because of
its energy consumption. This is not to say that a lot with a view to
the west or west Southwest is a bad lot, you just need to consider
that building to capture this view will cost more unless your
house's exposure can be tempered with existing tall trees which you
view through or a deep porch which will shade that side of the
house. Also consider a viewing porch with a solid house wall behind,
this will allow you to use the view from the porch and without any
compromise of comfort and energy use.
Trees are another site amenity not to be overlooked. Deciduous
trees are a particularly great site asset as they can be used to
shade a house in summer with their leaves and allow winter sun in
when the trees lose their leaves in the fall. Bear in mind though,
that some deciduous trees like Live Oaks and Post Oaks don't lose
their leaves during the fall, the old leaves only fall off when they
are pushed off by new leaves the next spring. A tree or stand of
trees to the west would be optimal here in Florida, to screen the
house from the hot western sun. Your house's design could also be
constricted by trees on the site, but keep in mind that a tall
mature tree in good health is equivalent to 2-3 tons of air
conditioning system capacity because of the shade it will provide
and cooling by evapotranspiration.
House Configuration
Your house can be designed to shield the worst orientation.
Placing the detached or un-conditioned garage on the west or
Southwest side can be a large help. Also a carport or porch can
shield your western side. There are some sites which will prohibit
this, remember that placing a garage or carport means a driveway
must be able to reach it. Often a porch or trellis is easier since
these architectural devices don't have the same access
requirements. Again, avoid a cookie cutter house where the
orientation is ignored. Your house could also be built into the side
of a hill to avoid an unfavorable exposure, or shielded by hill or
outcropping. Indigenous people used this technique, called
earth sheltering, to mediate temperatures in dwellings while
maximizing solar gain. When dealing with these conditions, pay
careful attention to water flow around and away from your house.
Finding a house or
lot with a favorable exposure may take some looking and
question-asking. Bring your old Boy/Girl Scouts compass along to
verify the exact orientation, and draw a sketch if it helps you
remember.
If you are planning a new house, be sure to do an extensive site
planning exercise, decide what's important to you and your site
(views, low energy bills, open space preservation) and use this
exercise to guide your building's design to keep your utility bills
low. On some lots, vehicular access is the factor which may dictate
house placement. If you turn the question around, why would you pay
more in utility bills to park your car where it was easiest for the
builder to put it? Don't let the driveway force the design, let the
proper orientation be the prevailing factor, vehicular access is
secondary to the house itself.
Radiant
barriers or reflective barriers work by reducing heat transfer by thermal radiation. All materials give off, or
emit, energy by thermal radiation as a result of their temperature.
The amount of energy emitted depends on the surface temperature and
a property called the emissivity
(also called the "emittance"). The emissivity is a number
between zero (0) and one (1). The higher the emissivity, the greater
the emitted radiation.
A closely related material property is the reflectivity (also
called the "reflectance"). This is a measure of how much radiant
heat is reflected by a material. The reflectivity is also a number
between 0 and 1 (sometimes, it is given as a percentage, and then it
is between 0 and 100%). For a material that is opaque (that is, it
does not allow radiation to pass directly through it), when the
emissivity and reflectivity are added together, the sum is one (1).
Hence, a material with a high reflectivity has a low emissivity, and
vice versa. Radiant barrier materials must have high reflectivity
(usually 0.9, or 90%, or more) and low emissivity (usually 0.1 or
less), and must face an open air space to perform properly.
On a sunny summer day, solar energy is absorbed by a roof,
heating the roof sheathing and causing the underside of the
sheathing and the roof framing to radiate heat downward toward the
attic floor. When a radiant barrier is placed directly on top of
existing attic insulation, with the reflective side up, much of the
heat radiated from the hot roof is reflected back toward the roof.
This makes the top surface of the insulation cooler than it would
have been without a radiant barrier and thus reduces the amount of
heat that moves through the insulation into the rooms below the
ceiling.
Radiant barrier can now be purchased already applied to the
back of roof sheathing. If you add only one energy saving product to
your new home it should be the roof sheathing with radiant barrier
affixed to it. Let your builder know this is what you want. The
extra cost will be offset by the energy savings in the long run.
The type of
windows you order with your new home don’t have to be double
pained, like a home being built in a northern climate. I can’t
remember when the temperature in Florida got to -5 degrees. I think
during the last ice age10-12 thousand years ago. Pay
close attention to the type of windows your builder is giving
you. The money you save using standard windows could pay for
the radiant barrier.
A Solar Hot Water System can
reduce your electric bill by up to 30-40%. For more information on a
Solar Hot Water System click on the Solar Hot Water System link on
our site.
Our Solar Pool Systems can also cut down on your energy usage
compared to using a heat pump or gas heater. When purchasing a solar
pool system make sure that it is sized right based upon the size of
your pool. Some companies may under size the amount of collectors
needed to heat your pool only to get the job. The undersized system
will work fine during the summer months, but will not adequately
heat your pool during the cooler months of the year, and this is
when you want warm water. Click on the Solar Pool System link for
more information on solar pool heating.
Solar Whole House PV System is the idea way to go to save
energy, but their initial cost can put them out of the reach of the
average consumer. If you can manage to fit one into your building
budget, you should consider splitting the power. That is making the
house both DC and AC power. The DC power can be used
to power all the light fixtures in the house with the AC power for
the appliances. Consult an electrical engineer about designing such
a system. The other Solar product should also be designed into the
house to make it the most energy efficient.
If your are planning on building a new home in Florida and would
like more information on Solar Products that will conserve energy
and save you money on your electric bill feel free to call one of
our energy consultants at:
386-437-2671
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