alk about energy-efficient lighting these days, and there are two technologies that are sure to dominate the discussion: fluorescents (usually compact fluorescents) and light-emitting diodes, or LEDs. As a lighting designer in California—where energy regulations are the strictest in the nation—I have a lot of these conversations. And I can tell you that rather than get­ting turned on by these newer, watt-saving technologies, most people are immediately turned off.

Why? Because most people have already had a lifetime of bad experiences with flick­ering, buzzing fluorescents and know little about LEDs, except that they’ve become ubiquitous as strings of the latest must-have holiday lights.

It’s not that these new light sources aren’t as good—or better—than the incandescent bulbs they’re designed to replace. But here is a classic example of trying to fit a square peg in a round hole (or in lighting terms, a pin
connector into a screw-in socket). We keep expecting these new lighting technologies to act (and cost) the same as the old ones. The problem is that they don’t.

A prime example is the typical screw-in compact fluorescent lamps ("lamp" is the industry term for "bulb") offered at big-box stores. Technology-wise, they are the worst examples of what’s currently available. But marketers wanted to provide a CFL at rough­ly the same price as an incandescent lamp. What you end up with is a cheaply made bulb that can buzz, produce an off-color light, and is not dimmable. So what hap­pens? CFLs in particular, and energy – efficient lighting in general, gets a bum rap. The fact is that many manufacturers (see "Bulb Sources," p. 154) are making efficient lamps that perform well. Yes, they do cost more up front, but in the long run, they offer greater energy savings and let you be earth friendly and design savvy at the same time.

Evocative and efficient. In the

Designauthor’s living room, a collection of photo­graphs is uplit with LED festoon lamps from phantom™ light­ing. Ambient light is provided by recessed fixtures from lucifer® lighting that are outfit­ted with Led MR16s from Focus lighting®.

It’s my job to practice what I preach.

My house is filled to the brim with energy – efficient light sources. In fact, the only two incandescent lamps I own are in my refrig­erator and oven. Other than that, it is all high-efficacy all the time. Is it warm and in­viting? Absolutely. You don’t have to change every lamp in your house, as I did. Start slowly. Maybe put A-lamp shaped CCFLs (cold-cathode compact fluorescent lights) in your exterior lanterns and CFLs in the basement and the attic. Try using daylight – colored CFLs in your closets for better color matching for articles of clothing. Every little bit helps—but it helps the most when each of these different light sources is used to its best advantage.

Contractors Sell Large Systems because They Fear Complaints

In defense of the people selling and install­ing large air-conditioning systems, they do so for a reason. Profit plays a part, sure: If you install a bigger system, you make more money. More important, though, contrac­tors fear complaints about their systems’ inability to maintain set temperatures in extremely hot conditions. Using a rule-of-

thumb measurement or some other method, the contractor sizes the system larger. If 3 tons is good, 4 is better, right? Besides, "Maybe Manual J sizing isn’t quite big enough," a contractor might say, or "Here, it gets hotter than that."

A recent study, however, puts these fears to rest. Proctor Engineering Group (PEG), Electric Power Research Institute, Nevada Power, and Arizona Public Service tested a typical house with outdoor temperatures of up to 116°F (3°F above the mean extreme). The actual cooling required was less than Manual J predicted in all but three of the 1,316 hours that the house was monitored.

It’s not necessary to oversize beyond Manual J, which has a built-in oversizing margin. On the first page of the introduc­tion, Manual J states that "slightly under­sized cooling equipment—by a margin of 10% or less—may actually provide more comfort at a lower cost."

Most Air-Conditioning Systems Are Installed Improperly

Another major reason for poorly performing air-conditioning systems is faulty installation: incorrect refrigerant levels, low airflow, and poorly designed and installed duct systems.

In one study of 55,000 air-conditioning sys­tems by PEG, refrigerant levels were wrong 62% of the time; in another study, the figure was 68%.

Condenser units arrive from the factory with the proper amount of refrigerant for a given length of piping—usually 15 ft. or 25 ft.—to connect the indoor and outdoor units. Refrigerant levels often are wrong because line length in the field can vary, and technicians frequently don’t make adjust­ments according to the manufacturer’s recommendations.

What difference does it make if refriger­ant levels are wrong? According to Armin Rudd of Building Science Corporation, if

Подпись: How Do You Find a Good Installer?Подпись: Because 70% of all central air-conditioning systems are installed improperly (according to a California new-home construction study), you could be paying anywhere from 25% to 50% too much in air-conditioning bills. Choose your airconditioning installer carefully, or pay the difference in higher energy and maintenance costs. One measure of a technician's expertise is whether he or she has completed a training program. All the major manufacturers offer training on installing their systems. In addition, several national certification programs are available through NATE (National Association of Training Excellence®; www.natex .org) and CheckMe! (through Proctor Engineering Group; www. CheckMe! is available in California, much of the Northeast (in some places under the Cool Smart name), and several other states. Technicians who complete their program perform diagnostic tests on each system and call in their results to a CheckMe! staff person to receive immediate feedback on the health of the system. Afterward, PEG sends a certificate of completion to the homeowner. Local electric utilities are another source for installer- certification programs similar to NATE or CheckMe! Rebates or incentives might be available for high-efficiency equipment. In addition to asking about certified training, here are some other questions to ask installers: • Do they use Manual J for sizing air-conditioning systems? • Are they using proper design temperatures for your area? • Will they verify that the indoor unit's evaporator coil and the outdoor unit's con- Contractors Sell Large Systems because They Fear ComplaintsПодпись: denser coil match and that the system has the proper amount of refrigerant? • Do they seal the ducts and test the system for leaks to a level of 10% or less? • Do they test airflow at the evaporator coil? • Can they provide references?

they are a little low, up to 20%, there’s some loss of cooling. More than that, and there’s an unacceptable loss of cooling along with frosting of the evaporator coil and, eventu­ally, complete loss of cooling. If refrigerant levels are too high, the story is similar: loss of cooling with possible damage to the compressor.

The speed and the volume of air mov­ing through air-conditioning systems were incorrect (usually too low) in about 72% of units tested in the PEG study. This was due partly to mismatched indoor and outdoor units, which occurs more often on retrofits than on new installations because only the exterior compressor/condenser unit typically is replaced. Also, airflow at the evaporator coil often is low because it usually isn’t tested, so no one actually knows what it is.

Fan speeds at the evaporator coil should be around 400 cfm (cu. ft. per minute) per ton of cooling capacity. Slightly lower fan speeds improve dehumidification. In dry cli­mates, fan speed should be increased.

Tied to airflow and directly affecting it are duct design and installation. Ducts are the least expensive part of the system and fre­quently are given short shrift. A properly de­signed duct system begins with determining the cooling load for each room (not based on the square footage), which can vary greatly. Duct runs need to be as short as pos­sible; they need to be insulated; and when possible, they should be installed within conditioned space. Ducts also should be sealed. Leaky ducts waste energy and in the right conditions might draw dust, spores, or combustion gas from a gas appliance back into the house.

Adequate return air also is important to minimize air-pressure imbalances that can affect cooling. The placement of registers in the room and the quality of the grilles greatly affect the duct system’s ability to throw air across the room and to mix the air properly.

Chris Green is a carpenter and cabinetmaker in New Milford, Conn.

Подпись: 10

Oversize Units Dehumidify Poorly and Waste Money

Approximately two-thirds of all residential air conditioners are too large. According to Bruce Harley, an HVAC consultant with Conservation Services Group in Westbor- ough, Mass., these oversize units "will cool your house, but they’re not necessarily
designed to run efficiently." The first prob­lem is that they dehumidify poorly. Oversize units satisfy the temperature at the thermo­stat so quickly that only a little moisture has time to condense on the evaporator coil. This phenomenon is known as short cycling, and it’s more of a problem in humid climates. If cycles are very short, moisture on the coil can evaporate back into the house before it drains away.

Second, air-conditioning units are least efficient when they start up. It can take 15 minutes to reach operating efficiency, so oversize units run more short cycles, and more of their time is spent running in the least efficient part of the cycle. As a result, they use more energy, and costs to operate them run 20% to 30% higher than for prop­erly sized systems. Finally, at an installed

Reducing Your Cooling Needs

Oversize Units Dehumidify Poorly and Waste MoneyAir conditioners consume about two-thirds of electricity use during peak summer periods. Save money by making energy-efficient improvements before installing a new air-conditioning system.

• A tight, well-insulated building reduces cooling needs by keeping warm, humid air

• Buy high-performance, low-e, argon-filled windows to reduce solar gain, which accounts for up to 70% of the cooling load on air-conditioning systems.

• Wide overhangs, trees, or vegetation is helpful. East-west glass is more of a problem than south-facing glass in summer.

• Use radiant barriers on the underside of uninsulated roof rafters if the HVAC equipment is in the attic; otherwise, just insulate the attic. In addition, insulate the ductwork.

• Install smart thermostats that turn off the air-conditioning when it’s not needed and then bring the house to the right temperature before you arrive home.

cost of around $1,000 per ton, oversize sys­tems cost more. Why pay for 5 tons if 21/2 will do the job?

How Much Cooling Do You Need?

Smaller systems use less energy and re­move more moisture because they run long enough to reach peak efficiency. So what’s the right size for an air-conditioning system? It depends.

The standard method for calculating the proper size for a residential central air­conditioning system is found in ACCA’s (Air Conditioning Contractors of America) Man­ual J—Residential Load Calculation by Hank Rutkowski, P. E. It’s a methodical approach to arrive at room-by-room cooling loads for sizing ducts and whole-house systems. The room-by-room totals are important because you can’t design a duct system properly without this calculation.

Manual J takes into account and averages solar-heat gains, which don’t peak in all rooms at the same time. It also includes the house’s orientation to the sun and shading, which greatly affect the cooling load as well
as the insulation values of walls, ceilings, and floors. Window types, locations, and specifications as well as internal-heat gains (people, lighting, and appliances) also are figured in.

The right-size system is not a rule-of – thumb amount derived from the square footage of a house. In her book Air­Conditioning America (Johns Hopkins University Press, 1998), Gail Cooper writes that air-conditioning engineers 100 years ago called sizing by the rule-of-thumb method "futile and foolish." According to the folks that I’ve talked to, that remains true today.

Air – Conditioning: Bigger Isn’t Better



itting in a green-and-white woven lawn chair, fanning away the sweat, my grandmother said, "It’s not the heat, it’s the humidity." With seven Virginia summers behind me, I suspected that the heat did have something to do with it, but I kept this thought to myself.

It turns out that each of us had it partly right. It was the combination of high heat and humidity that raised us to our exalted level of discomfort on that oppressive summer day.

Seven years later, my parents finally built a house that included central air­conditioning. Although it was better than being without, the air-conditioning system wasn’t ideal. The house had cold and hot spots, and my basement bedroom always felt cold and damp.

Unfortunately, these problems weren’t limited to my parents’ house nor to the 1970s. Problematic air-conditioning systems
abound nationwide. According to a recent study, 95% of new air-conditioning instal­lations fail in regard to operating efficiency, with more than 70% of systems improperly sized or installed.

The top three reasons for poor air – conditioner performance are improper sizing (1.5 to 2 times too large is common); improper installation (incorrect refrigerant levels and airflow); and poorly designed and installed duct systems. Because air­conditioning systems integrate refrigeration, air distribution, and electronics, there are lots of opportunities for mistakes.

Air Conditioners Move Heat Outside

Heat naturally moves from a higher energy level (warm) to a lower energy level (cool). You could say that heat, like water, flows

Air - Conditioning: Bigger Isn't BetterWhether it’s new

or a replacements properly sized and installed system affords

downhill. Without help, heat that accu­mulates within a home will not leave on its own unless the heat sources (the sun, people, appliances, etc.) are removed. Help comes in the form of air-conditioning, which uses refrigeration combined with ven­tilation essentially to push heat uphill, or move it outside, where it’s even warmer.

Residential air-conditioning systems are made up of an indoor and an outdoor unit connected by a pair of pipes that circu­
late refrigerant in a loop. By manipulating pressure and temperature, the indoor unit absorbs heat by blowing warm indoor air over a cold coil. The heat is released to the outdoor unit, which houses a compressor (which compresses refrigerant and itself generates heat) and a condenser coil and fan (which dissipates the heat to the outside).

In addition to cooling, air conditioners serve another important function: They dehumidify the air. In the same way that

I How It Works

Residential air conditioners are split systems—an indoor and an outdoor unit—that remove heat from the house and release it outdoors. A pair of pipes, which circulate refrigerant, form a loop and connect the units. Cold air is produced when compressed refrigerant is forced through a tiny valve or metering device (1) and expands into the evaporator coil (2), similar to the cold spray an aerosol can produces as the compressed liquid passes through the valve. This causes the refrigerant’s pressure and temperature to drop quickly, cooling the coil.

Air - Conditioning: Bigger Isn't Better

As warm air passes over the evaporator, it is cooled and dehumidified. Moisture condenses on the evaporator’s fins and drains away. After absorbing heat from the home’s interior, the refrigerant is pumped to the outdoor unit, where it passes through the compressor (3)

moisture condenses on the side of a cold soda can sitting outside on a hot day, air conditioners wring moisture from warm, humid air as it is forced across the indoor unit’s cold evaporator coil. Once past the evaporator, cool dehumidified air is deliv­ered to the rest of the house—unless there’s a problem.

Choose Energy-Efficient Mechanical Help

While I’m a firm advocate for passive cooling, I also believe there is a place for mechanical systems. Used in conjunction with passive-cooling techniques, the effec­tiveness of both can be enhanced, leading to lower energy use without any compromise in comfort.

Choose Energy-Efficient Mechanical HelpПодпись: Start small. Strategically placed mechanical devices, such as the fan at the top of the hallway, can enhance passive design.That said, if you are going to use both passive and mechanical systems, it’s im­portant they work together. When hiring a heating and cooling contractor, choose someone who can size a mechanical system with your passive-cooling elements in mind and who will recommend energy-efficient equipment.



Seeking Solar Professionals

When considering passive design, you should seek the services of a qualified pro familiar with the right strategies for your home and climate. professionals accredited by the U. S. Green Building council’s LEED (Leadership in Energy and Environmental Design) program are a good place to start. Make sure anyone you hire to size or install mechanical sys­tems understands the effect your home’s passive elements will have on the sys­tem. The following resources can help in your search:

•U. S. Green Building Council: www. usgbc. org

•American Solar Energy Society: www. ases. org

•North Carolina Solar Center: www. ncsc. ncsu. edu

•Energy Star program: www. energystar. gov

•Southface Energy institute: www. southface. org

Choose Energy-Efficient Mechanical Help

Mechanical assist. This fan, at the top of the sloped ceiling, can also enhance passive design.

If your climate demands it, one mechani­cal component you might consider is a de­humidifier. When you rely on natural ven­tilation to cool your house, you need to be aware that letting in the breeze also means letting in moisture. When the air leaves, the moisture may remain. In these cases, mechanical systems can help to dehumidify the air, preventing mold and damage to your home.

The best way to introduce mechanical cooling to a passive house is to start small. Ceiling fans are a simple way to enhance natural ventilation. If you’ve installed radiant-floor heating tubes in the floor slab, you can boost its cooling effect by pumping cool water through the pipes in summer­time. Although this strategy must be care­fully monitored to avoid condensation, it can have the added benefit of preheating your domestic hot water.

Control Heat with Mass

With the correct orientation and south­facing windows, your house can have great light and heat in winter—but it also can have the potential for overheating if you don’t balance the amount of windows in the house with the amount of mass. Thermal mass comes from materials that absorb heat, such as concrete, tile, brick and concrete

Control Heat with MassFloor mass. The floor is the easiest place to add thermal mass, which regulates tem­peratures all year long. This colored concrete floor is covered with a soy-based sealer and runs throughout the first level of the house. During the day, it absorbs excess heat from the south-facing windows, releasing it at night.

block, and water. However, water requires diligence to prevent algae and mold, and it is harder to incorporate into the structure of a house. The easiest mass to build into a house is some form of masonry.

Generally, the more south-facing win­dows there are, the more mass a house needs to balance the heat gain indoors and keep it cool. When sun shines through the windows, it strikes interior surfaces. Sun­light can either radiate into the air, heating the house, or be absorbed by the material it strikes. If it is absorbed, you get light in the house but not heat. Because heat moves from hot to cold, the mass material will continue to absorb heat as long as it remains colder than the surrounding air.

The right amount of thermal mass draws heat out of the air during the day, and radi­ates the heat to warm the home in the eve­ning when the air temperature drops, mak­ing mechanical heating less necessary. In the morning, when the atmosphere heats up

once more, the cooled mass material starts to absorb the day’s heat all over again.

The easiest way to add mass to a house is on the floor. A significant amount is needed: In a typical passive-solar home, the concrete, tile, or brick floor should be 4 in. thick. Tile installed on cementboard on a subfloor is not enough.

Trombe walls are another design option. They are interior masonry walls behind south-facing windows with a narrow air­space between them. When the sun comes in, the heat is trapped in the airspace and then is absorbed by the wall. It acts as a heat sink for the house and can radiate the heat inside.

If you’re planning a new house, you also can build mass into the walls. Precast concrete panels or AAC blocks introduce a significant amount of mass. These walls can be finished in a variety of ways; stucco is the simplest and most low-maintenance op­tion, but you can attach siding if you prefer.

On the inside, concrete panels are typically painted, while the AAC can be finished with stucco or drywall. Finished this way, the in­teriors look like any other house, except for the added aesthetic of deep windowsills.

Thermal mass has an added benefit: Not only does it absorb heat, but it’s also cool to the touch, which cools you. You can keep the air temperature of your home several de­grees higher in the summer if you’re walking on a cool floor. One way heat is transferred is through conduction—the movement of heat from one object to another through direct contact. You touch the floor, and because you are warmer than the floor, the heat in you (the warmer object) moves to the floor (the cooler object). You feel cooler, no mechanical means required.

Massing is the hardest strategy to add to an existing home. If the house was not designed to accommodate a 4-in.-thick masonry or concrete floor, it’s not easy to add one. If you are adding to the south side of your house, however, you can consider a slab floor, a masonry wall, or a masonry fireplace.

Tighten Up and Insulate the House

As I mentioned in section 2, passive cooling involves being able to control the airflow and heat moving through a house. This means stopping unwanted air infiltration by creating a tight building envelope. You can tighten up the house with good insulation, caulking all penetrations and sealing around windows and doors. Weatherstripping ex­terior doors and installing double-paned, argon-filled windows with low-e coatings can help as well. Put a tight-fitting damper in the chimney and a properly insulated cover over any attic access. Making your home’s envelope tight enables you to let air

Tighten Up and Insulate the House

in and out when you choose and to close up the house when you want.

If you can, use more insulation than local codes require, and add the sealing package that many insulators offer. Spray-foam in­sulation provides a high R-value in a small amount of space and can double as an air seal. That’s particularly important here in the Southeast, where moisture in the air can lead to mold, poor indoor-air quality, and even structural damage.

If you’re building a new house, look into building systems that offer insulation values that are at least double what standard stick – built structures offer. In addition to precast concrete panels and AAC (aerated auto­claved concrete) block, you might consider agriboard panels. Made of compressed wheat straw sandwiched between oriented strand board (OSB), these 8-in.-thick panels offer an R-value of 25.4 versus the R-13 or R-15 of a standard 2×4 fiberglass-filled wall.

Let the House Breathe a Bit

When mechanical systems are sized for a home, they’re often designed with the mind-set that the house is never open to the elements. I find this is rarely true; in fact, most of my clients very much want to connect their home’s indoor and outdoor spaces. Doesn’t it make more sense, then, to

I Overhangs

design houses to work in partnership with their environment rather than to function with no regard for it?

To understand best what ventilation can do for your home, you need to remember two simple principles: One is that heat al­ways moves from hot areas to cold areas, and the other is that warm air rises.

If you are designing a new house, spend some time on the site, learn where the breezes come from, and use that informa­tion when locating the windows on your house. Use casements that swing open to help catch breezes. Having different units open in different directions allows you to take advantage of winds coming from mul­tiple directions.

A studied approach.

Designing this second – floor library as an open balcony permits warm air to rise unimpeded up and out the second- floor windows. ceiling fans assist the natural airflow.


Let the House Breathe a Bit

Подпись: Chimney EffectПодпись: Hot air exits; cross ventilation accelerates air movement.Подпись: Cooler air Let the House Breathe a BitThe simplest form of smart ventilation is cross ventilation. When you open a window in your home, you can let in a slight breeze, but when you then open a window on the opposite side of the room, the strength of that through-breeze increases significantly. If the entry window is small and the window through which the breeze exits is large, it increases in speed. A cool breeze in the eve­ning when the sun is going down absorbs the heat in your house (heat moving from hot to cold); as the air heats up, it rises. So the best way to let hot air out of your house

is to have a large opening up high. The greater the distance between the intake and the output, the better.

This air movement is called the chimney effect (see the drawing on the facing page). I use it in my three-story home. When a cool breeze comes at the end of the day, I open the windows downstairs and the French doors on the third floor and wash out the entire house in minutes. The effect is height­ened by an open plan, a small footprint, and a staircase in the middle that makes the whole house very much like a chimney.

Vaulted ceilings and high windows in a clerestory or cupola also promote the chim­ney effect. The sloped ceiling encourages air to move to the top of the cupola, and operable windows on both sides allow cross ventilation.

If you live in a dry climate, you can boost your home’s ventilation cooling with water cooling. Dry air moving over water absorbs moisture and subsequently drops in tem­perature. (This is how evaporative coolers work.) Placing windows near a pond or an­other water feature lets you capture the cool air as it comes off the water and into the house. You get free air-conditioning along with the soothing bonus of a water view.

Face the Sun, and Shade the Glass

The first step to passively cooling your home is to stop the heat before it ever comes in. This is where siting and shading come into play. When designing a new house, you have a great opportunity to take advantage of orientation, but it’s also important (and often ignored) when adding to or altering an existing house.

Here in the Northern Hemisphere, a house that faces south is optimal because that is where the sun comes from. Southern orientation makes it easier to control the amount of sunlight that enters the house. Even in the South, designing a house with a long east-west axis (minimal exposure to the east and west, maximum exposure on the north and south) allows you to take the best advantage of the sun. This strategy is associated with passive heating, but passive cooling also benefits from the same type of siting.

When the house faces south, simple over­hangs can shade it for the hottest part of the day, generally from 10 a. m. to 2 p. m. The

Подпись: solar gain in the winter as possible. This porch runs along the entire west side of the house, adding living space and providing cross breezes to the living room and master bedroom through two French doors.

Face the Sun, and Shade the Glass
Face the Sun, and Shade the Glass

overhangs need to be sized correctly so that they not only block the sun at its hottest, but also allow light and warmth inside when the sun’s angle changes in the winter, and in the mornings and evenings. Because this fac­tor is based on the latitude where you live, the proper size of the overhang varies from region to region. The latitude where I live in North Carolina is 35 degrees north. That means the sun rises to 78 degrees above the horizon in summer and 30 degrees in winter. Here, a 2-ft. overhang is optimal because it blocks the hottest summer sun but lets the low winter sun shine inside (see the drawing on the facing page). To determine the opti­mal overhang where you live, see the chart on p. 131.

In the early morning and at sunset, when the summer sun is much lower in the sky, it’s harder to keep heat out of the house, even with overhangs. You can minimize this morning and evening heat gain by minimiz­ing the number of windows on the east and west sides of the house.

Another strategy is to locate shading de­vices, such as a screened porch, on the east
or west sides of the house to provide protec­tion from the low sun. By keeping the porch away from the south side, you’re not com­promising the daylighting and heat benefits available from the south. Other options for shading include pergolas, screens, and plant­ings. Pergolas, in particular, are a great op­tion; they not only shade the house but also create an outdoor space to enjoy. Growing vines on pergolas can increase the structure’s shading ability. Be sure to select deciduous varieties; they’ll provide maximum shade when fully leafed out in summer, but won’t block sunlight in winter.

Landscaping complements your house visually and also can help to keep it cool. Plant larger plants and trees to the east and west for shade. Plants absorb heat, lowering the temperature of air moving over them, so air that enters your house after traveling over the garden is actually cooler than the surrounding air. Low bushes and plantings also help by minimizing hard surfaces that absorb heat and radiate it back toward the house. These "heat islands"—driveways, walkways, and patios—work against any passive-cooling measures you might have taken, particularly if your house has win­dows that are low to the ground and capture the hot air that radiates off these surfaces. Lower roofs on porches or bump-outs, espe­cially those covered with asphalt shingles, radiate heat that can enter the house

Подпись: Based on the sun angle where I live in North Carolina, a 2-ft. overhang is optimal.Подпись: Summer sunПодпись: Winter sunFace the Sun, and Shade the Glassthrough windows open above them. In these situations, casement windows are the most effective at guiding cool breezes into the house, and they allow less of the heat radiat­ing off the roof to gain access inside. Avoid awning windows, which channel rising hot air into the house.

Enhancing passive cooling through orien­tation and siting is easiest when designing a new home. But installation of window over­hangs and the use of plantings and attached structures can boost the cooling power of existing homes as well.


People often use internal shading, such as blinds, to keep the heat out of their homes. While it’s certainly better than letting sun­light stream in unimpeded, it’s really not a good strategy if you look at the science. When sunlight shines through the glass in windows, its wavelength lengthens. These longer wavelengths cannot travel back out through the glass, so the heat gets trapped inside. (This is how greenhouses maintain their warm environments.)

When you put up blinds, you block light from getting into the room. However, the heat from the sun’s rays has already entered through the glass. Because heat always moves from hot to cold areas, the heated air trapped between the window glass and the blind moves into the cooler areas of the house. Blinds may help a bit, but it’s better to invest in exterior shading devices to stop the sun from ever entering the house rather than trying to control it once it’s there.

Cool Design for a Comfortable Home


Cool Design for a Comfortable HomeПодпись: Passive in practice. The author's house demonstrates passivecooling strategies that include east-west orientation, overhangs formed both by eaves and a second-floor balcony, and a vertical design that promotes good ventilation.

I live in North Carolina, and I love the look on people’s faces when I tell them that I haven’t turned on my first-floor air­conditioning in 10 years. There’s always a pause, and then they lift their jaw off the floor and ask me, "Really? How?"

As an architect who designs new homes, renovations, and additions, I encourage my clients to explore options for passive heat­ing and cooling and energy-smart design before we ever look at mechanically assisted options. To make your house truly energy – efficient, you must design it with the goal of using as little energy as possible. It’s great when people get excited about adding solar hot-water panels and photovoltaic systems, but before exploring any of that, you should first look at how you can design your new home or alter your existing home to reduce its energy needs. When your house natu­rally needs less energy, you can use smaller mechanical systems to support it. This saves money both up front and in the long run.

Passive Solar vs. Passive Cooling

When we talk about passive-solar design, we often focus on how it can help to heat your home. Passive-cooling design is really the opposite side of the same coin, using the properties of the sun to promote cooling rather than heating.

Passive-solar design can cut heating bills, but in the South and in many areas of the country, keeping your house cool in the summer is a bigger concern. Here, passive­cooling strategies become more important, and more economical. These simple design elements can save you hundreds of dollars every year in energy bills and also make your house more comfortable to live in.

Passive cooling refers to nonmechani­cal ways of cooling your home. It focuses on orientation and shading, air movement, thermal mass, and a tight building envelope. All these strategies can be complemented by mechanical means—from air-conditioning to ceiling fans—but these passive elements can also work successfully on their own.

While the potential for saving energy with any design-focused strategy is greatest when you’re planning a new house, several of the techniques I describe can be used when renovating or adding to an existing home. You may not be able to pick up your house and face it in another direction, but you can add shade structures and window overhangs, relocate window openings, and mitigate nearby "heat islands" (such as a driveway baking in the midday sun), all of which enhance your home’s ability to main­tain a comfortable temperature with less mechanical intervention.

So let’s take a look at how your house can work with the environment. By designing your home to work with nature instead of against it, you can benefit from lower energy bills, better daylighting, and greater indoor comfort.