I've got a new radio program on KLDK (Tuesdays at 7pm) that will be posted here on the Dallies in blog format to keep the conversation alive. So feel free to leave questions and comments.
This is an overview of a zero energy home. Future shows will include Transportation, food, and the local economy are other areas of consumption.
We want our home to be warm in winter cool in summer, have both hot and cold running water, lights, a cooking zone with cold food storage and other things that are considered normal in a modern home. All these things take energy, which can be provided without spoiling the planet for future generations.
Here in northern New Mexico our climate is usually sunny, except for this past year with a record amount of clouds. The first 2 months this year had only 9 full sun days. Climate change data shows this to continue in the foreseeable future. The average day this winter was partly cloudy. This had a big influence on a solar home this year especially a passive solar home. The amount of heat that a building looses at night is the same weather the sun was shining that day or not. A passive solar house needs at least twice as much window area as an average house to heat it in winter. This means twice as much heat loss through the windows at night. Also the vertical panes of glass collect less heat per square foot than a more efficient and tilted solar collector.
Even with a reduced amount of sun a home can get all of its energy from the sun. This can be done by thinking of the shell of a house as a thermos. Much less heat is required to keep a house warm, if little, leaks through the walls, roof, windows and floor. This brings up the question of fresh air, which can be supplied by a low wattage Energy Recovery Ventilator. These fairly inexpensive units heat the incoming fresh air with the exhaust air. (More on this latter)
The most cost effective way to reduce the energy consumption of a building is to minimize its heat loss, before designing or improving a heating system. The 3 most important things in an energy efficient building are insulation, insulation and insulation. Technology has advanced in recent years to the point where heat loss in buildings can be greatly reduced. Roof insulation of R-75, wall and floor insulation of R-40 is not overkill in most of the United States where freezing temperatures are the norm in winter.
The windows and doors complete the high performance envelope of the house. Windows that let the sun’s energy in also let it out. Modern windows and frames of R-9 or more are now available here in the United States. There is 3-4 times less heat lost through these than standard double pane windows. These highly insulated windows and doors have been used in Europe for a long time and have proven their cost effectiveness. They block much of the heat of the sun from entering the house, but are essential to balance the heat loss of the windows with the other building components.
Air tightness is important, as this amount of insulation would go to waste if cold air were to leak into the building. This level of tightness creates its own challenge as we need fresh air. An Energy Recovery Ventilator becomes necessary to provide this fresh air, while capturing most of the heat and moisture from the outgoing air. It’s important to use an ERV not a HRV (heat recovery ventilator) as the HRV saves the heat but sends moisture out with the exhausted air. This lowers the humidity in the home, and in most cases in NM the air in the home is already plenty dry.
Insulation and air tightness are separate issues so installing a continuous air barrier is a primary concern when building an energy efficient house.
Standard wood frame homes leak a lot of cold air in winter and hot air in summer even if the weather stripping around doors and windows is tight. There are many penetrations through the walls and ceiling; and through the floor, if it’s over a crawl space. These penetrations for plumbing and electrical systems leak a surprising amount of air. A continuous air barrier is essential to create a thermos like shell for the home. These leaks can be sealed more easily in new construction, but many can be accessed in an existing home. Vent pipes are water tight where they go through the roof, but most roofs are vented. The ceiling penetration below the insulation is the place to look for leaks. The plumbing and electrical penetrations in the top plate of the walls is where much of the leaks occur. These can be foamed or caulked in the attic to stop the air flow through roof insulation. Dryer vents, kitchen and bath exhaust fans allow cold air in through the unit itself and around the outside perimeter of the duct. Most exhaust fans come with a damper but unfortunately they don’t seal very well. There are ad-on dampers that mount outside on the end of the duct. They are inexpensive and easy to install. Sealing around the duct where it penetrates the air barrier can be more difficult in an existing house but just sealing at the drywall penetration can be helpful. In some cases caulking an outside faucet can minimize air leakage.
Holding a lit match or lighter near a light switch or electric outlet will show the air movement especially if it’s windy. The pressure difference between the up-wind and down-wind side of the house pushes a surprising amount of air through a building. Gaskets are made for both inside and outside electrical boxes. In new frame construction attention to air barrier can save a lot of energy over the life of the house. There are very few contractors who know how to build a frame house this tight. The Passive house system, used in Germany details the air barrier for a frame house. It can be done but takes a lot of attention to detail.
Other wall systems like adobe or conc. block with a continuous layer of spray foam are air tight as all the penetrations are automatically sealed with the foam. If the roof is also foam the house becomes one continuous layer of foam with little opportunity for air leaks. Structural insulated panels also called sips are another construction system that by design is easy to make air tight. They also use much less wood than conventional framing. Another advantage in these systems is that they have unvented roofs.
On the question of the earth friendliness of building materials. This foam is made from oil and I think it’s better to make it into something that will last for 50 years than to burn it in a car or use it to heat a house. Here’s an example. If we burn more than 300 gallons of propane in a winter we’ve used more oil than is used to spray foam an average house. If an old un-insulated adobe house uses 600 gallons of propane in a winter for heating, is spray foamed using 300 gal. of oil; in one year it will make up the difference and every year following will save 300 gallons of oil.
This is a summary of things to consider when designing the shell of a new house or improving the efficiency of an existing house. It can be tempting to go right for a solar system instead of insulation but dollar for dollar it’s best to get the shell tight first.
The sun is by far our greatest asset to provide useful energy to a home. Active and Passive solar systems reduce or even eliminate the use of fossil fuels in buildings. In the past I considered passive solar the purest way to heat a house. It is better than standard home construction but it’s more expensive and doesn’t perform as well as a tight house with a small active solar system. One of the main advantages of an active system is that there is no heat loss at night through the windows as in a passive solar design. There are only about six hours per day that the sun can effectively heat a building, this gives the active system quite an advantage. Since only one quarter of the time the building is being heated, capturing this heat is critical in maintaining a comfortable temperature.
Storing the solar heat is the other half of the system. In a passive system some of the solar heat is absorbed in the mass of the south side of the house. And the rest tends to make the house to warm during the day. At night the extra heat loss of the south glass combined with less efficient heat storage allow the house to cool off. This night day swing is quite high compared to a house with a well insulated house with an active solar system. Also the active system can be used to heat the hot water.
Next week I’ll focus on solar hot water systems. So call during the show at 7 on Tues. or check out my blog at www. s w solardesign.com to find resources and to continue this conversation.
Quote of the Week
"To be hopeful in bad times is not just foolishly romantic. It is based on the fact that human history is a history not only of cruelty, but also of compassion, sacrifice, courage, kindness. What we choose to emphasize in this complex history will determine our lives. If we see only the worst, it destroys our capacity to do something. If we remember those times and places (and there are so many) where people have behaved magnificently, this gives us the energy to act, and at least the possibility of sending this spinning top of a world in a different direction. And if we do act, in however small a way, we don't have to wait for some grand utopian future. The future is an infinite succession of presents, and to live now as we think human beings should live, in defiance of all that is bad around us, is itself a marvelous victory."
-Howard Zinn