Solar Heating and Cooling With the Sun

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The "tower of power" divides the bank of clerestory windows and accommodates the unique sun-powered air powered air exchange system.
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Much of the home's aesthetic warmth comes from the broad use of wood in the interior . . . And a small, but open, floor arrangement.
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Diagram of the solar heating and cooling system adapted from Middle Eastern home design.

Reprinted from MOTHER EARTH NEWS NO. 63. 

Though designed for the California desert, Jim Harmon’s
attractive and innovative home incorporates features that
would prove a blessing in any climate.

Solar Heating and Cooling With the Sun

In the desert region of Southern California’s Imperial
Valley–just east of San Diego’s urban
sprawl–the ambient temperature can seasonally
fluctuate from a high of 130 degrees Fahrenheit to as low as the
mid-20s, with humidity usually resting at a bone-drying
10%.

Nonetheless, folks do live in the area, and it’s no secret
that most such desert dwellers consume inordinate
amounts of precious energy just keeping their
air-conditioned homes comfortable . . . especially during
the scorching hot summer months.

But one particularly resourceful resident of this arid
wilderness–university professor James
Harmon–has chosen to abandon the conventional methods
of climate control using natural solar heating and cooling and let the desert environment
passively temper his home all year-round!

Planning Paid Off

Achieving a natural climate control system using solar heating and cooling demands a good
deal of planning and sound research, even in an area of
moderate climate, so in order to make his concept
a working reality in the often-uncompromising desert, Jim
really had to do his homework. The house he eventually
designed [1] rests on a concrete slab foundation that’s set
about four feet below the desert floor to take advantage of
the temperature-stabilizing effect of the earth, [2]
incorporates a naturally convected ventilation system that
serves to heat the home in winter and cool it in summer,
[3] uses insulation to the utmost on both interior and
exterior walls, and [4] takes advantage of desirable
wintertime sunlight through the use of south-facing glass
(much of which is shaded by roof overhangs in summer) both
at ground level and within the clerestory wall.

When Mr. Harmon first moved to his ten acres of desert
property more than a decade ago, his plans included not
only the construction of a practical, inexpensive, and
energy-efficient dwelling, but–on a more
comprehensive level–the creation of a nearly (or
fully) self-sufficient homestead. And, except for his
modest needs for outside electrical power, Jim has pretty
much accomplished his goal of independence.

The house itself is only part of a master layout . . .
which includes organic vegetable gardens and orchards (all
of which are irrigated with underground watering systems),
food drying bins, a workshop, a compost pile, a grape
arbor, a greenhouse, and even a solar-heated outdoor hot
tub!

Since construction of a dwelling was Jim’s primary project
(and because he scrounged much of his building material
over a long period of time), the resourceful professor
began to plan his structure long before he drove the first
nail. “When you build a house like this, you go through a
long period of information gathering and gestation before
drawing even the first few simple plans. You’ve got to
have some kind of idea about just what you want to
accomplish and how your system should work.

“The design I used incorporates a bit of commonsense
technology, some ancient architectural methods of the
Middle East, and a smattering of Southwestern American
Indian building techniques. The result is a structure
that’s almost wholly passive, uses native building
materials where possible, and–this is quite important
to me–leaves an almost indiscernible impression on
the landscape.”

It Works Superbly

Exactly how does Jim’s home achieve his goals? First, the
concrete foundation was poured in an excavation 4′ deep,
and surrounded with a low block wall that rises up to
ground level. The slab doesn’t utilize a bed layer of
insulation, because–being a thermal sink–it
must be given the chance to absorb ground heat in the
winter and, by the same token, to assimilate the home’s
excess interior heat in the summer. Other factors were
considered, too: The effect of occasional strong winds is
minimized by the protective natural earth berming and the
low profile of the dwelling. And, as an aesthetic plus, the
line of sight to a nearby tarmac highway is conveniently
interrupted.

But that’s only part of the story . . . a natural
ventilation system (adapted from Middle Eastern home
design) is the major means of maintaining an
acceptable comfort level in the house year-round. A total
of eight unperforated, 4 inch-diameter, corrugated ABS plastic
drainage pipes are connected–using vent holes
previously formed in the structure’s foundation–to
the sides of the octagonally shaped dwelling. From these
openings underneath the house, the tubes curve around, then
come together (a slight distance is maintained between them
to assure proper thermal conductivity) within a broad
underground channel, and run to a point about 100 feet away.
Jim figures the depth of this ditch–40 inches–to be
something of a compromise . . . between a shallower trench
(which wouldn’t afford proper air tempering) and a much
deeper chasm (which would be excessively labor-intensive
for a relatively slight gain in efficiency).

The terminal point for the tubes–just a 2 foot by 2 foot
concrete-block well extending from ground level to a depth
of about 4 feet–is capped with a reworked kitchen exhaust
fan that allows air to be drawn through even when the motor
is off. Occasionally, use of the fan is required to force
air through the system and into the house.

Normally, though, the intensity of the sun (and, in part,
the direction of the prevailing winds) is great enough to
cause the ventilation cycle to operate admirably. In
addition to the underground tubes, Professor Harmon’s
design incorporates, in effect, two useful layers
of roof on its windward side: the standard exterior
surface, covered with tar and gravel, and an
interior roof which is nothing more than pine
tongue-and-groove finish sheathing fastened to the lower
face of the roof joists. The upper surface of the inner
roof is lined with builder’s foil to form air passageways
within the home’s “cap.” Jim provided inlets and outlets
for the built-in ventilation channels by drilling a
quantity of 1/2 inch holes (in circular groups) through the
soffits outside the house, and likewise by opening the
ducts to the atmosphere at the apex of the roof, where he’s
built what he calls the “tower of power” . . . which is
also ventilated, through the use of small ducts, to the air
within the home itself.

In the Summer . . .

Hence, during the hot season, as the sun beats down on the
structure’s roof with a vengeance, it initiates a
natural convection and suction (see sidebar) that
provides the home with fresh, comparatively cool air. To
help the cooling process during periods of intense summer
heat, Jim also had the fore sight to install
exterior venetian blinds on the south-facing,
leeward side of the house . . . which he closes to prevent
the sun from beating in through the windows. Since these
“light shutters” are external (not to mention
white in color), heat never has a chance to find its way
into the house.

Another trick up Jim Harmon’s thermal sleeve is the very
convenient cooling effect of evaporation. During the
hottest part of the year (when J. H.’s gardens need the
most moisture anyway), the professor supplies the
liquid by activating his buried sprinkling system. The
sprinklers soak the ground, and as the water evaporates
from the sandy soil, the temperature of the earth decreases
considerably . . . which, in turn, helps to further cool
the incoming air in the underground vent tubes!

Mr. Harmon can achieve still more indoor air conditioning
by activating his “swamp cooler”: a broad belt of thin foam
pad, revolving in a shallow tub of water, through which
forced air is passed. (Jim also has plans for an indoor hot
tub . . . which could function all year to provide humidity
or heat as required, depending on the season.)

And in the Winter

The same system that cools the interior air in summer also
furnishes a temperate climate during the colder months. And
even though the convective action is not as pronounced in
the wintertime, the design and orientation of the
structure’s roof–backed up with the option of
activating the electric fan–assures that comfortable
ventilation is always available.

In addition, a considerable amount of winter heat is
derived from direct insolation. Because the sun is low in
the sky, its light can stream unhindered through the main
south-facing windows and the vertical clerestory glazing at
the peak of the roof. Jim has installed freestanding
redwood grape arbors above all the southern-exposed
windows, to provide summer shade and delicious fruit. Come
cold weather, the vines dry up, so sunlight can pass
through the arbors.

An Airtight Thermos Bottle

Of course, the home’s unique ventilation system operates
properly only if the doors and windows are closed and the
walls are relatively airtight. But varying levels
of comfort can be attained at any time of the year by
opening the windows as desired.

Another factor which contributes to the success of the
Harmon desert home design is the fact that J. H. has gone
to great lengths to properly insulate the structure. The
lower portion of the dwelling is, of course, earth-sheltered
. . . and the upper part, framed with 2 by 6 studs, is also
just about impervious to nearly any temperature fluctuation
that may occur. Behind the tongue-and-groove interior
sheathing are two batts of fiberglass insulation, then a
layer of 3/8 inch plywood. This surface is covered with 1 inch
polystyrene, which, in turn, is veneered with builder’s
foil.

The final covering is an exterior facade of
ladrillos , or Mexican brick (similar in its
thermal mass effects to the materials used in Native
American earthen shelters), which is set slightly away from
the backing wall’s foil-covered surface . . . to provide an
air space through which excess heat-absorbed by the brick
and reflected from the builder’s foil–can escape into
the roof channels. In addition to practicing careful wall
construction, the professor has fully insulated each thick
exterior door to create a thermal barrier and a work of art
in one unit.

“It’s a lot more economical,” Jim observes, “to pay for
good thermal protection today –especially
before a structure is completed–than to continue
shelling out money over the next 10 or 20 or 30 years to
cover the rising cost of heating. And if, after a period of
time, you should decide to add insulation, the cost will
always be greater . . . because of inflation and the extra
work involved in tearing a finished house apart to do the
job.

“Profit and loss considerations aside, however,” Harmon
points out, “the design of my home is based not so much on
the painful fact that energy costs are rising as on my
conviction that energy consumption is an ethical rather
than an economic issue. Energy waste, whether it proceeds
from senselessness or selfishness, seems to me downright
immoral . . . because it will adversely affect the lives of
future generations.”

Sound Construction and Low Cost

Even though his chief emphasis was not on economy, as close
as Jim Harmon can figure his partially earth-sheltered,
1,000-square-foot octagonal desert home cost him about
$22,000 to construct . . . an easy to swallow $22 per square
foot. Of course, Jim is quick to point out that the price
would be difficult to duplicate today, partly because he
purchased much of his wood before the noted lumber price
increase of the mid-70s, and also because he and some of
his good friends did much of the work themselves.

But even with the sharp increase in lumber costs, Mr.
Harmon still believes that wood construction is a sound
choice. “Framing a house with lumber remains a good way to
go . . . mainly because if you use some of the synthetics
available on the market nowadays, you’ll find they often
are just as expensive yet provide less quality and
longevity. I’d rather spend my money now and get it over
with, and have the satisfaction of a well-done job.”

Another reason Jim chose to go with wood (in conjunction
with concrete and some of the materials native to his area)
was that he wanted his dwelling impervious to all but the
very worst earthquakes . . . phenomena which are often
problems in the Imperial Valley area. In order to assure
his home’s integrity, he designed the structure like a
wagon wheel, with a central hub plate in the
roof–acting as a pivot–from which the “spokes”
(in this case surplus railroad trestle beams) radiate and
fasten to the eight corners formed by the walls of the
house. In theory, this arrangement distributes both
horizontal and vertical shocks evenly throughout the
structure with little or no damage to the framework. In
practice, Jim’s design passed the acid test when a severe
quake hit the area and did considerable damage to several
local communities . . . while merely causing the Harmon
home to creak ominously.

At Home in the Desert

Now that Jim’s had a chance to live in the house through
quite a few seasons, he’s truly pleased with the
structure’s performance. Since the dwelling’s systems are
almost entirely passive, including its gravity-fed solar
domestic water heater, Jim’s normal power requirements are
merely for lighting, refrigeration, and pumping water into
a storage tank from his 330 foot well. The happy result is that
the desert dweller’s utility bill averages only a
quarter of what his neighbors are accustomed to
paying! (The Harmon household does use some bottled gas for
cooking, but Jim hopes to construct a small
methane-from-compost plant, which should help take care of
kitchen needs.)

Otherwise, Jim’s ten-acre microcommunity is relatively
self-sufficient . . . with the help of the sun. And since,
in addition to growing much of his food, the Golden Stater
raises cacti for sale to nurseries and the like, the desert
itself provides him with an extra source of income
for a minimum of effort . . . and that’s a hard-to-beat
combination in any territory.


How It Works

Simply put, the Harmon house works on the principle of
pressure differential caused by rapidly moving air. In the
summer, as the sun beats down on the surface of the roof,
the air within the ceiling channel absorbs heat. Because
the heated air has a much lower specific gravity than the
ambient atmosphere, it tends to rise, flow upward along the
channel between the inner and outer roof, and exhaust out
the louvers in the “tower of power.”

Naturally, with all this air escaping, a new supply must be
brought in . . . and it enters by way of the groups of 1/2 inch
holes drilled through the soffits under the outside eaves.
So, what results is a constant–sometimes downright
furious–flow from the outdoors, through the roof
channels, and outside again.

In order to take advantage of the air current, Jim Harmon
has cut several small openings into the tower, at its
highest point inside the house. As the heated air
rushes past these holes, it actually entrains–or
pulls–the air within the building right through the
vents . . . in much the same way that an automobile’s
carburetor draws fuel out of its float reservoir.

Of course, since air is then being drawn from the living
area of the house itself, it must be replaced . .
. and the only available sources of supply–as long as
the home’s doors and windows remain closed–are the
eight ventilation tubes buried 40 inch beneath the surface of
the earth . . . where temperature is maintained at about
75 degrees to 80 degrees Fahrenheit year-round.

During the winter–when the path of the sun and its
intensity result in lower temperatures within the roof
channels–the system still functions, though not quite
as efficiently. Fortunately, prevailing winds from the
northwest, flowing over and around the outside of the
“tower of power,” tend to pull air out of the roof also.
And, if this breeze effect is not sufficient to draw warmed
air through the underground pipe network, the blower fan
can always be activated.