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Designing A Passive Solar Home
My new passive solar home, located in the community of Fly Creek in upstate New York, looks just like a traditional-style 4,000-square-foot house and costs about the same to build, but it uses 70 percent less energy to heat than a home of a comparable size. From June 2007 to June 2008, I spent about $900 (or about $2.50 a day) on propane for combined heat and hot water, and only $100 a month, on average, for electricity.
Passive solar design uses the sun’s direct energy to heat a home. As an example of what a powerful heat source the sun can be, consider my home on January 3, 2008. It was sunny all day. At 8 a.m., the temperature outside was negative 10 degrees. Inside, my home was 68.7 degrees, so the auxiliary heat had just cycled off. By 1:30 p.m. it was 7.7 degrees outside and had warmed to 75.7 degrees inside, thanks to the sun’s energy. By 6:00 p.m. it had cooled to negative 0.4 degrees outside and 68.7 degrees inside, when my auxiliary heat finally cycled on again. That means on a sunny single-digit day in January, my 4,000-square-foot house was heated only by the sun for 10 straight hours.
I live in the snow belt, in a rural area east of Syracuse, so sunny days are limited in the winter. But if you were to build a passive solar home with the same square footage as mine, in a comparably cold location with more sunny days, and you kept your ceilings at a regular height instead of my high ceilings, you could easily see energy savings of about 80 percent over a traditionally built home of a comparable size.
I’m a big proponent of passive solar homes. In my opinion, we are not going to be able to earn our way out of this current energy crisis, and as a country we are not going to grow our way out of it. The cost of energy will continue to increasingly outpace the growth of our incomes. In the 21st century, any home design that is not super energy-efficient is a non-starter. And a new home that incorporates passive solar design is one of the best hedges against rising energy costs.
Three Simple Concepts My home is simple to explain and easy to understand. A passive solar home operates on three related concepts: a source to get the energy (heat) into the house, a way to store it and a means to keep it from leaking out.
The primary source for heat is the sun. It comes in through south-facing windows, which is why passive solar homes have so many windows on their south walls. Quality windows are essential. We installed Simonton ProFinish Energy Star qualified low-E (low-emissivity) double-glazed windows.
A one-foot-thick concrete slab, called a solar thermal storage battery, which is located under the house, stores excess heat and then releases it slowly, as needed, to stay in equilibrium with the house. To better understand how it works, think of the simple physics of a cup of coffee. Pour hot coffee in a cold mug and within minutes the mug heats up and the coffee cools down until they are the same temperature. Everything evens out. That principle is how the solar thermal concrete storage battery works.
The slab has air ducts embedded in it. If the air passing through the ducts is warmer than the slab, it absorbs the excess heat. If the air is cooler than the slab, it releases heat. Those ducts deliver the air to registers on all floors of the house.
To keep moisture out of the slab, we used one foot of gravel under the slab and three feet of gravel footings around the perimeter. We installed drainage pipes in the gravel, and laid Tyvek and a high-tech pool liner over the gravel. Finally, we covered the pool liner with two layers of two-inch-thick foil-covered Dow Tuff-R rigid polyurethane insulation before pouring the concrete.
In the attic ceiling, we installed a horizontal air return that runs the length of the house. Warm air rises and enters grilles in the horizontal return, which empties into a vertical shaft that travels down to the concrete slab. At the bottom of the shaft is a large squirrel cage fan, which is left on 24/7, 365 days a year to facilitate air movement throughout the house and ductwork.
Above the fan are filters that remove any dust from the air. Below the fan is a horizontal square single-row coil hot water radiator. When the thermostat calls for auxiliary heat, hot water runs through the coils. The air passes through the radiator and picks up heat as it proceeds down into the concrete slab.
The hot water for auxiliary heat comes from a high-tech propane Baxi boiler. It is linked to Baxi solar hot water panels outside the house, which preheat water for both domestic hot water and closed-loop hot water for heat. We also use a Vermont Castings high-efficiency, non-catalytic-converter Defiant wood stove in the evenings for warmth and ambiance.
Keeping the Heat In To keep the heat in, we created a thermal envelope using two layers of Tuff-R rigid insulation on the outside of the exterior walls. We also installed rigid insulation on the roof. It is like building a soda picnic cooler, except you’re the soda. This insulation performs more than three times better than fiberglass insulation.
This is not some experimental technology — Bruce Brownell, the solar engineer who tailored the passive solar system in the house I designed, has been creating these home systems for more than 30 years. He has worked on homes from 1,000-square-feet to 5,000-square-feet in size.
When a home is this efficient in retaining heat, everything helps heat the home — not just the sun and the supplementary heating plant, but also the lights (regular and energy-efficient bulbs), appliances (including Energy Star qualified appliances) and even the body heat of the occupants.
This heat gain is not negligible because the heat loss from the home is dramatically less than the heat loss in a traditionally built home. Add a state-of-the-art wood stove and the heat gain is spectacular.
We also use less electricity in the home because we have much more natural light most of the time, thanks to the passive solar design. So when we compare the total energy costs of a traditional home (heat, gas, electric) verses our passive solar home, the difference in energy costs becomes dramatic.
Small Footprint Building green and embracing sustainability encompasses many areas besides energy efficiency. One goal is to create a small footprint to impact the environment less and to minimize building materials. My passive solar home is only about 30 by 50 feet with an attached 30-by-34-foot garage. The total square footage includes an attic that is usable heated space.
A solar house, by its nature, should be a simple architectural form (like a long rectangle) to maximize solar gain. These simple architectural building forms minimize building materials and building costs without sacrificing distinctive design.
In addition, we used recycled and renewable materials throughout the home. For instance, the ceramic tiles we used in the bathrooms and for the backsplash in the kitchen are Crossville Ceramic eco-tiles made with recycled content. The bamboo in our Mannington flooring is a renewable resource.
We also used durable, long-lasting materials, which are another aspect of green building. Our CertainTeed Presidential Shake asphalt roofing has a 50-year limited warranty. The James Hardie HardiePlank concrete siding and trim on our home also has a 50-year limited warranty for the siding and a 15-year limited warranty for the pre-finished color coating.
Other green and energy-efficient materials used in the home include Therma-Tru Energy Star exterior doors, Velux Energy Star skylights and Profile Energy Star appliances from GE.
Even the home’s interior layout adds to its efficiency. The open floor plan on the first floor and the unique U-shaped bedroom on the second floor surround a glass-enclosed atrium that is open from the ceiling of the first floor to the attic floor dormer ceiling, creating a dramatic 32-foot-high design statement that is also integral to the home’s solar efficiency. The atrium provides southern exposure lighting to the kitchen/dining/living area and serves as an airshaft to circulate air.
A Time to Build Saving $3,000 to $5,000 annually in energy costs (and more as we go into the future) thanks to passive solar design is serious money, and can go towards financing part of a mortgage. So my first, best advice is counter-intuitive in our present collapsed building market and hard-to-get-qualified mortgage environment: Build a new super-insulated passive solar home now.
Building labor is readily available, making labor costs very reasonable, and probably less expensive than they will be six to 12 months from now. If petroleum costs continue to rise in the next few years at the same rate they have over the past year, we can expect to see escalating costs for building materials and services. Although mortgage rates are reasonable, it’s hard to qualify for a loan in the current market, but that may ease by the time you’re ready to build. Rates float anyway — If they drop two points, you can refinance. My point is this: Now is the most affordable time you may ever see to build a new passive solar home.
Imagine a future 21st century in which you spend 70 percent less to heat your new home. Imagine a future 21st century America where everyone spends 70 percent less to heat their homes. This is the possible 21st century American future I want to be in.
John Kosmer has been the Home Improvement Editor of Victorian Homes magazine for 23 years.