Hopper Design, LLC


Toward Healthy and Sustainable Homes

Energy - Conservation

To conserve energy at your home consider in decreasing priority:

  1. Integrity of the air barrier,
  2. Quality of the insulation,
  3. Orientation of the home in relation to the sun,
  4. Location and quality of the windows and
  5. Thermal energy storage.

With conservation you can save up to 50% of your nonrenewable energy needs compared to a conventional home.1 You save money and help the environment by using fewer nonrenewable resources (i.e., by reducing your carbon footprint).

In order of importance:

1. Provide an Airtight Envelope

The importance of the integrity of a building envelope is pivotal to success in all energy conserving measures. The air barrier should be well-sealed. Typical homes have many air leaks that cannot be seen. The DOE reports that if you add up all the air leaks in an average house, they are equivalent to a hole in the side of the house roughly two feet on a side. In the winter you are paying a lot of money to heat the great outdoors! To "close the hole" a continuous air barrier with taped and sealed joints must be properly installed over the entire surround of the house.

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2. Install Super Insulation

Super insulation is thicker than that used in a conventional home and should be placed as continuously as possible, just like the air barrier discussed above. Your home is always gaining or losing heat energy from the environment. This cannot be stopped. Insulation can only slow the rate of energy exchange, that is, how fast your house loses heat energy in the winter and how fast it gains it in the summer. Insulation types are rated by their R value per inch thickness. R values are additive per inch - the higher the number, the better. (The inverse of the total R value for an assembly is the U value for that assembly, U = 1/R.) Hot air rises, so insulation in the roof should have the highest R value. In New England one should target R values near R-60 for the roof, R-40 for the exterior walls and R-20 for the foundation down to the footing.

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By implementing energy conserving techniques 1 and 2 you can reduce your homes's energy requirements by 30% compared to a conventional home. These techniques can be applied to any home, regardless of orientation.

3. Position House with Appropriate Orientation

By designing and orienting homes intelligently we use sunlight for space heating and save a significant amount of nonrenewable resources as well as offset our largest energy bill here in New England. It is critical to have a large facade with large areas of glass facing south. Deviations from true south are acceptable up to about 15 degrees (the angle the sun appears to sweep in one hour's time). As an example, you may decide to face your south side 15 degrees to the east for early morning solar gain, and this is quite reasonable because homes are usually cooler on winter mornings. You may also choose to face your south side 15 degrees to the west if that works best for capturing a special view. By studying Shade Study you can see that it is possible to collect enough energy with up to 15 degrees deviation from true south.

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4. Install well-insulated windows appropriately

Glass allows solar energy to flow into your home. Windows also act as insulation - a typical good R value for residential glazing is about R-3. It is important to place the largest area of glazing in the wall facing south as described above as this is the key to obtaining seasonally appropriate passive solar gain. Often it is also desirable to have fairly substantial glazing to the east for early morning solar gain and daylighting. Medium to small glazing is appropriate for the west due to the possibility of gaining unwanted solar heating during hot summer afternoons.

Glazing to the north should be minimal but carefully positioned to aid natural ventilation with the stack effect in summer. The stack effect is a passive strategy requiring no energy for air cooling in summer. It relies on the fact that heat rises and simply requires high windows or skylights to be open and low windows to the north to be open. The stack effect pumps cool air in from the north as hot air escapes above.

In winter a desirable addition for windows with R-3 performance is interior mounted movable insulation. Systems are available for the addition of R-5 movable insulation, making the total R value R-8, useful in slowing unwanted energy flow on winter evenings.

To learn more about energy efficient windows see The Efficient Windows Collaborative.

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By adding the techniques of items 3 and 4 to 1 and 2 above you can reduce your energy needs by an additional 20%, to a total of 50%.

5. Thermal energy storage

Thermal energy storage is required to retain the solar energy coming through your windows. This can be achieved by using construction materials with high thermal capacitance, such as concrete for slab construction, gypsum concrete for encapsulation of a radiant floor system and insulated masonry or rammed earth walls. Certain finishes, such as brick, terra cotta, quarry and slate tile for flooring or walls, also have high thermal capacitance. A masonry fireplace and chimney that is mounted inside your house also provides high thermal capacitance.

For a given volume, water will store two times the thermal energy as masonry and so is an excellent choice for thermal energy storage.

To learn more about thermal energy storage see DOE: Thermal Storage (pdf).

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See also: Conduct a Shade Study of your site if you plan to build a solar home and to use solar energy for passive gain or production. It is important to coordinate the correct relationships between passive gain, orientation, movable insulation and interior positioned thermal energy storage. We can help - see Services or email us directly.