Maryland homeowners Phil and Lisa Malone describe themselves as fairly average, well-traveled and pretty independent people. They're also quite savvy when it comes to energy efficiency. When the couple decided to leave city life behind and relocate to Deep Creek Lake in the rural hills of western Maryland, they built a home that is "a unique fusion of energy-efficient techniques and environmental sanity," as they put it.

By using Sun, earth and water to heat and cool the home, they drastically reduced energy costs and created a comfortable living environment. The Malones' single-story, triangular home integrates several innovative building techniques, including an earth-sheltered passive-solar design, geothermal heating and cooling, and a fresh-air system using an energy recovery ventilator (ERV).

"My original plan was to reduce the total amount of energy we needed [to live comfortably]," Phil Malone says. "To me, this was the most effective way to have a positive impact on the environment - my ultimate goal." The experiment in greenbuilding began in September 1998. Malone, an

Australian-born software designer, had just returned to his Annapolis home after three weeks at sea with an RMS Titanic Expedition, for which he provided software and electrical support for one of the expedition's deep-sea vehicles.

One day, after converting his walk-out basement into an office for his consulting firm, Malone had an epiphany. He realized the basement office stayed cool and comfortable all year round, even on the hottest days, which made him wonder if this concept could be applied on a grander scale. "My daydreaming and research led me through the apparently independent areas of earth-sheltering, passive-solar design, ground-source heat pumps and energy recovery systems," Malone says. "As a systems integrator by nature, the challenge for me was to integrate these concepts into a single design. The earth aspect ended up playing a big part."

Earth Sheltering In the course of his research, Malone happened upon a book by Malcolm Wells (a self-proclaimed "underground architect"), The Earth-Sheltered House: An Architect's Sketchbook. This and James Kachadorian's The Passive Solar House, inspired Malone's initial designs. "Wells' book is full of inspirational thoughts designed to expand your horizons," Malone explains. "It graphically illustrates a wide range of design ideas without dwelling on the technical side of things. On the other hand, Kachadorian's book is a wealth of technical information and practical data, designed to separate fact from fiction." (The Solar House: Passive Heating and Cooling, by Daniel Chiras, is another good source.)

Malone recalls that, as a child, he visited the opal-mining town of Coober Pedy in south central Australia. Many locals built their homes below ground in abandoned mines to ensure temperatures of around 68°, sheltering them from the scorching heat on the surface. This memory - and an experience with an underground house in the Virginia mountains in the late 1980s - also helped to spark his interest in earth sheltering. The basic idea is quite simple. If the temperature outside is 85°, then the 60° earth will help cool your home, Malone explains.

Conversely, if it is 10° outside, the 55° earth will help warm the home. "The only time earth sheltering isn't better than a traditional house is when the outside air temperature is in the 60- to 75-degree range. Then you just open the windows!" Malone says. The Malones' home is built into a wedge carved out of a hill and surrounded by earth on two sides. The third side faces south, so the Malones can reap the full benefits of the Sun during the winter. A few factors must be accounted for when designing an earth-sheltered home, Malone notes. The east/west orientation of the home's major axis is one of them, as it can determine how much heat your home rejects during the summer and retains during the winter. One also must consider earth expansion caused by freezing, and waterproofing the roof system. Historically, earth-sheltered designs have had a number of drawbacks.

For instance, light from a single direction can cause objects and people to appear flat and can cause glare, making lighting design difficult. There's also no natural cross-ventilation, and with no windows, the earth-sheltered area of the home can be dark and gloomy. To address these issues, Malone designed the house with a "high space" - a small second-story tower, or observatory, accessed by a spiral staircase. Part of the 250-square-foot area is open to the lower level. Windows provide natural light and ventilation, while blinds help prevent overheating in the summer. Passive Solar, Radiant Heat Homeowners not familiar with earth sheltering might assume that since the home is surrounded by earth, much like a basement, it gets uncomfortably cool in the winter months. But as Malone explains, "Earth-sheltered homes really aren't basements, just like penthouses really aren't attics."

One reason for the distinction is insulation. The Malones' home has 2 inches of foam insulation under its concrete slab floor, as well as insulated below-grade walls. The concrete slab is an integration of both passive solar and geothermal design. It acts as thermal mass, soaking up the sunlight from the south-facing windows, retaining the heat and gradually releasing it. The Malones also embedded radiant hydronic coils in the slab floor, which helps them control the indoor temperature. Water heated through geothermal exchange flows through the coils, providing radiant heat throughout the house.

Malone loves the radiant floor. He works from home, spending most of the day in socks or barefoot. But the radiant heating system is more an essential than a luxury, as Deep Creek Lake can get upwards of 80 inches of snow annually. Geothermal Exchange Climate plays an important role when deciding what kind of HVAC system is right for a home, Malone says, adding that his home is a perfect example. "In my climate, winter temperatures are pretty much always below 45 degrees. So it's either use a fuel that is less than 100 percent efficient, or use a GSHP (ground source heat pump) that is 300 to 400 percent efficient." For Malone, the choice was easy. "No matter how you cut it, energy costs money, so the less efficient your heating system is, the more it will cost. Heat pumps can be more than 100 percent efficient because they don't generate heat - they pump it." Several devices, including air conditioners and refrigerators, use heat pumps to move heat from one place to another.

But if the differential between the inside and outside temperatures is too great, these pumps fail. For example, Malone explains that if it's 95° outside, a heat pump can cool your home to 65° fairly easily, but it can't heat your home to 65° if the outside air temperature is below zero. GSHPs work so well because they do not move heat between your home and the air, but rather between your home and the Earth. "[Ten to 12] feet beneath the surface, the Earth's temperature remains fairly constant year round, ranging from 45 degrees or so in northern latitudes to about 70 degrees in the deep South," explains Wael El-Sharif, executive director of the Geothermal Heat Pump Consortium (http://www.geoexchange.org). "Geo-exchange takes advantage of this constant temperature to provide extremely efficient heating and cooling." (To determine the exact constant temperature for your area, call a local well driller and ask for the groundwater temperature.) The Malones use a GSHP to provide hot water for the radiant slab as well as domestic hot water, which is stored in a conventional 75-gallon water heater.

The water that heats the slab, which is at a lower temperature than the water for domestic use, bypasses the water heater and heats the slab directly. By reversing the GSHP, the Malones can cool the slab if required. The system is so efficient that they estimate 60 percent savings on heating costs, compared with a traditional HVAC system. A key component of a geothermal exchange system is the ground loop, which basically is a series of long tubes buried in the ground either horizontally or vertically. In winter, a water solution contained in the tubes absorbs heat and delivers it from the Earth to the home via the GSHP and the radiant coils in the flooring. In summer, the process reverses, as heat inside the home is drawn away by the water solution and delivered to the Earth, where it is cooled before it returns to the home. As Malone notes, installing a ground loop can be expensive, depending on the configuration.

"If you have a large lot, you could dig a trench [to install horizontal pipes] about 6 feet deep around the [house] perimeter to keep costs low," he says, "but going vertical comes with the added expense of hiring a drilling company to install the loop." Malone continues, "My installation was a vertical loop, and is more elaborate than most. I'd estimate that [the geothermal system] cost an additional $10,000 to buy and install over a traditional boiler system." Going Green, Saving Green? Many homeowners might be dissuaded by the added cost of going green. But once the energy savings are factored in, these systems can save more money than they cost. Homeowners with geothermal systems enjoy utility bills 25 to 50 percent lower than those with conventional systems, according to the Geothermal Heat Pump Consortium.

Operating costs can run as low as $1 per day for a typical 2,000-square-foot home, El-Sharif says. Lisa Malone definitely has noticed the energy savings in her home. "Our utility bills are quite a bit less than for our previous house, which was a three-level duplex in a milder climate," she says. "Phil did a great job convincing me that passive solar and geothermal were great energy-saving ideas, so I was all for it. But I really didn't know what to expect. I get it now!" What is perhaps most interesting about this experiment in greenbuilding - apart from the seamless integration of energy-efficient systems - is that the entire design and building process has been documented by the Malones on their own website, which you can visit at http://www.ourcoolhouse.com. "I started the website before I had a design for the home," Phil Malone says. "I was determined to document my design process from start to finish.

I wanted to share the insights, the stumbles and the results, be they good or bad. I got lots of great ideas from my forum, and others have, too." The website provides a wealth of information documenting the design and building processes, including detailed explanations of earth sheltering, passive solar design, and geothermal heating and cooling. The site also includes a timeline, room guide, 3-D model and both the preliminary and final designs of the home. But what really sets the site apart is interactivity. You can monitor data from the Malones' HVAC system live over the Internet. If you have an experiment in greenbuilding you'd like to share, you can post it on the site's Designer Showcase, which Phil Malone set up "so other green-home designers can post their own sagas for all to see." In building their earth-sheltered home, Phil and Lisa Malone have broken new ground.

Not only did they set out to design and build a home that was energy efficient, environmentally friendly and specified to their needs, but they also managed to document the process in a fun and interesting way. The end result is a home that maximizes comfort and truly is down to earth. "This project was a real learning experience for me," Phil Malone says. "I enjoyed the process a lot, so much so that I'm thinking of doing it again. We already have the land. Everyone should have a hobby, right?" Trevor McNally is based in Austin, Texas.