Solar Heating and Cooling

Jim Harmon designed his San Diego-area home to fully function via solar heating and cooling.

| May/June 1980


Diagram illustrates how Jim Harmon designed his home to achieve solar heating and cooling through air convection.


In the desert region of Southern California's Imperial Valley — just to the east of the urban sprawl of San Diego — the ambient temperature can seasonally fluctuate from a high of 130° to as low as 27°F, with humidity usually resting at a bone-drying 10%.

Nonetheless, folks do live in the area, and — needless to say — most such desert dwellers consume inordinate amounts of precious energy just keeping their air-conditioned homes comfortable ... especially during the scorching hot summer months. However, one particularly resourceful resident of this arid wilderness — university professor James Harmon — has chosen to abandon the "conventional" methods of climate control and let the desert environment passively temper his abode all year round!

It Pays to Plan Ahead

Achieving a natural climate control system takes a good deal of planning and sound research, even in an area of moderate climate, so in order to make the solar heating and cooling 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 over-hangs in summer — both at ground level and within the roof's skylight "wall".

When Mr. Harmon first moved to his ten acres of desert property more than five years ago, his plans included not only the construction of a practical, inexpensive, 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 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 wherever possible, and — this is quite important to me — leaves an almost indiscernible impression on the landscape."

And It Works Like a Charm...

Exactly how does Jim's home achieve his goals? First, the concrete foundation was poured in an excavation four feet 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 to help warm the structure and, by the same token, assimilate the home's excess interior heat in the summer and transfer that warmth to the earth. 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, too.

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 all year round. A total of eight unperforated, 4"-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 — simply a 2' X 2' concrete block "manifold" extending from ground level to a depth of about four feet — is capped with a reworked kitchen exhaust fan that allows air to be drawn through even when the motor is off. (On rare occasions, 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 perfectly. 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 board 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" 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 immediately heats the air within the ventilation channels. Naturally, this hot air begins to rise, moving upward with the slope of the roof. As the heated air flows out of the house by way of the tower, more air is drawn in from the outside eave vents ... and the process continues, resulting in a steady flow through the roof passageways.

This rapidly moving air, in turn, creates a suction which pulls more air directly from inside the house itself, through the ducts at the top of the tower. And, since a slight vacuum is actually created inside the dwelling, fresh outside air is pulled in from the only source possible: the underground ventilation tubes, which thermally condition the entering atmosphere by virtue of the constant 75-80°F ground temperature.

To help the cooling process during periods of intense summer heat, Jim also had the foresight 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 actually 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 year round to provide humidity and/or heat as required depending on the season.)

...And in the Winter

The same system that cools the air in summer also furnishes a temperate climate during the colder months. Since the sun is lower in the sky in wintertime (and because ol' Sol's effects are less intense then than in the summer), the heat buildup within the roof channels is not as great ... and the airflow is likewise reduced slightly. Fortunately, the home's roof was so designed that wind moving, as it usually does in that locale, from the northwest helps to draw air from inside the house — and thus through the tubes — by virtue of a suction effect as it passes over the peak.

In case the flow is not sufficient to provide proper ventilation, Jim always has the option of activating the electric fan in order to force tempered air through the buried pipe network.

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 necessary summer shade and delicious fruit. Come cold weather, the vines dry up, so sunlight can pass through the arbors when it's most needed.)

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