Solar Heating and Cooling With the Sun

Jim Harmon achieved an almost self-sufficient homestead constructed of inexpensive materials and a solar heating and cooling system adapted from a natural ventilation system from Middle Eastern home design.
By the MOTHER EARTH NEWS Editors
July/August 1986
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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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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.


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