Hi whyru,
It's great that you are asking this question, because with careful
thermal design a house can be more economical to heat and cool, and
much more pleasant to live in.
In hot climates, the western face is the hardest one to design. By the
time the sun hits this side, the house will already have warmed up
considerably, and as the sun approaches the horizon it shines directly
into the western windows. Unlike the south face (or the north face in
the southern hemisphere) the roof eaves cannot be used to effectively
shade windows on the west face.
The usual advice is to eliminate or minimize west-facing windows in
hot climates. Understandably, you wouldn't want to lose your
attractive view by building a windowless wall. Luckily there are steps
that you can take to alleviate potential overheating.
You have not indicated where you live, and not all of these ideas will
be applicable to your house. Also, some may not be acceptable to the
local authorities if they do not comply with local design codes. You
will need to review them with your architect.
Many of the following ideas are drawn from a delightful book about
designing a house to be comfortable whatever the climate. It's written
for Australian housing, but most of the content is universally
applicable:
"Warm House Cool House" by Nick Hollo
Choice Books, 1995 (ISBN 0-947277-22-6)
http://www.choice.com.au/viewProduct.aspx?sku=WHCH
A light-colored western wall will reflect as much as possible of the
incoming radiant solar heat. A white rendered finish or light
sand-colored bricks are two possibilities. Also avoid dark roof
coverings such as black tiles as these will absorb more heat during
the day.
Naturally, the house should be well-insulated. Many people consider it
desirable for the insulation to include a reflective layer in addition
to bulk insulation such as fiberglass or rockwool.
If possible, the house should be elongated in shape, with the long
sides facing north and south, so that the west face is relatively
small.
Can you arrange to have an extensive roof overhang on the west, such
as a roofed-over balcony or verandah? Although this can't block the
radiant heat around sunset, it can delay the time at which the sun
starts to shine through the western windows. You would need a
substantial roof overhang to provide a significant benefit; perhaps
two metres (around six feet) or more.
If you do create a verandah or balcony on the west, is it enough to be
able to enjoy the view from this outdoor space? In that case, you can
eliminate or greatly reduce the windows on the west.
If you don't like the idea of a verandah, you could consider having a
pergola against the west wall. To provide effective solar screening
you can do one of two things. You can attach slanted, closely spaced
timber slats to the top of the pergola, oriented so that they shade
direct sunshine but allow in plenty of light. Or, you can train a vine
to grow over the pergola, which will then provide useful shade in
summer and admit sunshine in winter (after the leaves have fallen).
Do you wish to admire the view all year round, or would you be content
to have it as a winter view? If so, you can plant deciduous trees to
the west of the house, which will shade the house on summer afternoons
yet allow views and sunshine in winter.
You could combine some of the above ideas by planting deciduous trees
against part of the west wall and having a verandah on the other part.
In summer you gain your view from the verandah (which has little or no
glazing between it and the house), and in winter you gain your view
from the room behind the other part of the west wall, which has larger
windows but is shaded in summer by the trees.
It is also possible to use trees to provide shading whilst preserving
almost all the view, but it takes time. You can plant a row of trees
to the west of the house, then when they have grown you can trim away
the lower branches so that you have just a few trunks at the height of
the view, but retaining dense and extensive canopies above to provide
shading from the sun (and from the hot western sky in general).
Naturally you would want to consider fast-growing species if this is
your plan.
One approach to designing for a hostile climate is to make the "core
house" comfortable all year round, then wrap additional "layers"
around it that work best at certain times of the year and provide
additional delights. For example, you could have a western verandah
with enough glazing between it and the house to admit a superb view,
but you would also build some sliding lattice panels on the verandah.
You could enjoy the view from the verandah and from within the house
for most of the year, except for the hottest few afternoons of summer
when you would slide the lattice panels across to achieve thermal
comfort by shading the house.
Consider your local climate. Do you tend to get an afternoon breeze in
summer? For example, many locations near the coast will experience
summer afternoon sea-breezes. If so, make sure you can capture this
breeze into the western rooms. If the wind is typically from the west,
this is easy. If it is from the north or south, you can capture it
with side windows on the western rooms or with outward-opening west
windows that will deflect the breeze into the room. If the breeze is
from the east, outward-opening side windows on the western rooms can
deflect the breeze into the room. If the breeze is irregular or not so
strong, you could perhaps provide windows on three sides of a large
western room that can be opened and closed to suit changing
conditions.
Consider also the microclimate around the west side of your house. Is
there dry, exposed ground cover? If so, this will reflect considerable
amounts of solar radiation towards your house throughout the
afternoon. You can reduce this by shading this area, planting
water-retaining plants, or installing a pond.
When designing the windows, make them large enough to admit the view,
but no larger. Perhaps they don't need to be floor-to-ceiling windows?
Perhaps they can be fairly high windows, so that you can see the whole
view from head height whilst minimizing the window area. Perhaps the
windows don't need to be very wide: do you need to provide a view to
everyone sitting at a dining table, or is it sufficient to provide a
glorious view as people walk down the corridoor?
There is a quirky but wonderful book propounding "patterns" for the
design of houses (and indeed cities) that are pleasurable to live in:
"A Pettern Language"
Christopher Alexander, Sara Ishikawa and Murray Silverstein
Oxford University Press, 1977 (ISBN 0-19-501919-9)
http://www.amazon.com/exec/obidos/tg/detail/-/0195019199/
In a section entitled "Zen View", Alexander comments on how to make
the most of a view:
"If there is a beautiful view, don't spoil it by building huge windows
that gape incessantly at it. Instead, put the windows which look onto
the view at places of transition ? along paths, in hallways, in entry
ways, on stairs, between rooms. If the view window is correctly
placed, people will see a glimpse of the distant view as they come up
to the window or pass it: but the view is never visible from the
places where people stay."
The idea is that you will never tire of the view, and the passing
glimpses will be a source of never-ending delight. It's called a "Zen
View" by reference to a Buddhist monk who lived in a small stone house
in the mountains. The beautiful ocean view in the distance was not
visible from the house, nor from the approach path. But there was a
courtyard in front of the house, with a slot in its wall, and as a
person walked across the court there was "one spot, where his position
lined up with the slit in the wall, [where] for an instant, he could
see the ocean. And then he was past it once again, and went into the
house." (Page 642).
Alexander continues: "This is the essence of the problem with any
view. It is a beautiful thing. One wants to enjoy it and drink it in
every day. But the more open it is, the more obvious, the more it
shouts, the sooner it will fade. Gradually it will become part of the
building, like the wallpaper; and the intensity of its beauty will no
longer be accessible to the people who live there." (Page 643).
Alexander's viewpoint may or may not appeal to you: if it does, most
of your thermal problems are solved. Alexander gives some specific
recommendations: "Put in windows to complete the indirectness of the
view ... place them to help the tapestry of light and dark ... build a
seat from which a person can enjoy the view ... If the view must be
visible from inside a room, make a special corner of the room which
looks onto the view, so that enjoyment of the view becomes a definite
act in its own right." (Page 643).
In many climates, it will be worthwhile designing considerable thermal
mass into the building. Thermal mass is massive construction within
the thermal envelope of the building. This can be achieved by using
masonry construction for the inner skin of the building, or by adding
masonry features such as internal brickwork (even a fireplace and
chimney if you have cold winters), or by building on a concrete slab
foundation. Thermal mass smoothes out extremes of temperature: in
general the house will be cooler during the day and warmer at night as
the thermal mass "soaks up" heat input during the day and releases it
again at night.
Consider how the rooms are laid out within the house. The rooms on the
west face should be those for which higher temperatures can be
tolerated. For example, most people would prefer to have a lounge or
dining room on the west, and to move the kitchen (a source of heat
during cooking) away from the west face. In most situations, bedrooms
are ideally located on the east side where they will benefit from
cooler nights and morning sunshine.
Are you planning a two-storey house? Or, if you are on sloping land,
will it be two-storey at the western end? If so, you may be able to
provide the larger western windows on the lower floor where the room
is to some extent earth-sheltered on three sides by the sloping
ground. You've probably been in two-storey houses where on a hot
summer's day one can retreat to a lower floor or a basement to enjoy
the "coolth" provided by the mass of cool earth directly around and
underneath. The exact details of this will depend on whether you have
a slab floor, and how the grade of the land slopes around the house.
It may even be possible to "berm up" the earth around the lower part
of the west wall to reduce afternoon solar heating.
Care should be taken to choose appropriate glazing and shading. You
can glaze with glass that is clear, tinted (smoky), reflectorized
(coated with a thin metallic coating) or coated with a low-emissivity
layer (sometimes called "low-E" glass). Low-E glass provides excellent
heat retention in winter (by accentuating the greenhouse effect within
the room) but if used on a sunny room in a hot climate should have
external shading (such as shutters) to keep the heat out on hot days ?
so this option is unlikely to meet your needs. Tinted or reflectorized
glass can help, but you should view samples first to check that you
don't feel they spoil the quality of the view when you look through
them. Shading can be used to reduce incoming heat on extreme days,
even if you keep the window unshaded for most of the year. External
shutters (hinged or roll-up) or canvas blinds are the most effective ?
preferably light-colored. If you use internal shading (curtains,
vertical blinds or venetian blinds) it's even more important that they
show a white or very light side facing outwards as the light and heat
have already penetrated the window and need to be reflected back out
as efficiently as possible.
It's important to consider that the sun does not trace a path from due
east to due west during the day. Its path depends on your latitude and
the season. I'm assuming you're in a warm temperate area, in which
case the sun will set due west in mid-spring and mid-autumn
(mid-fall). In mid-summer, the sun will set somewhat south of west in
the northern hemisphere, or north of west in the southern hemisphere.
Your architect can advise you the exact position of sunset at
different times of the year for your latitude, and you may be able to
use this fact to your advantage. Can you plant trees or shrubs to
screen the position of actual sunset during the hottest part of the
year, whilst retaining a good view directly to the west? You may even
be able to use parallel vertical screening (such as trellises)
oriented east-west to allow the view through whilst screening the hot
sun that is not coming directly from true west. Or, if the main view
is away from the position of hottest sunsets you may be able to angle
the building slightly to provide a cooler view, or to construct an
alcove in the external wall to admit the view whilst screening some of
the sunshine.
After you have considered all of these "passive solar" design issues,
you may wish to look at active cooling. Air conditioning is the
"easiest" option here, but it can be noisy, and expensive to run. More
esoteric options to explore include wet roofs to produce evaporative
cooling and thermal chimneys to ventilate the wall cavities. These and
other ideas are discussed in the following document (mostly in the
context of Texan conditions):
"The Future of Passive Solar Design"
http://www.cmpbs.org/publications/AD2.6-Future_Passive.pdf
If you will be needing to install some kind of heating system for
winter months anyway, you could consider a geothermal heat pump system
which can provide economical summer cooling in addition to effective
winter heating. However, it would be hard to cost-justify such a
system if you do not need winter cooling. An introduction to heat
pumps is here:
Geothermal Heat Pumps
http://www.eere.energy.gov/erec/factsheets/geo_heatpumps.html
In this answer I've touched on a range of issues, not all of which
will be relevant to your own circumstances. You will need to discuss
the ideas with your architect to refine them. Please request
clarification if you have any further questions.
Designing your own house is really exciting. I'm doing the same
myself, and I also have great views to the west. However, I'm in a
cold part of England and am having to employ some very different
strategies to make the house pleasant to live in!
All the best for your project. You are lucky to have such a desirable
site, and once the house is built I'm sure it will give you a lifetime
of pleasure.
Google Search Strategy:
"west wall" summer overheating
://www.google.com/search?q=%22west+wall%22+summer+overheating
(lots of useful results are returned by this search)
"warm house cool house"
://www.google.com/search?q=%22warm+house+cool+house%22
"pattern language" alexander
://www.google.com/search?q=%22pattern+language%22+alexander
"water roof" cooling
://www.google.com/search?q=%22water+roof%22+cooling
geothermal "heat pump" summer cooling
://www.google.com/search?q=geothermal+%22heat+pump%22+summer+cooling
Regards,
eiffel-ga |
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