We wanted to home to use as little energy and fossil fuel as possible – tempered with the reality that we enjoy indulgences such as our beloved hot tub, and did not want to surrender comforts if possible. We retained two firms that to assist us – the Davis Energy Group which modeled the entire home and analyzed various design tradeoffs, and the Monterey Energy Group which did the detailed plumbing and heating designs.
Building Shell. Our home is directly on bluff about 80 feet above sea level above the Pacific Ocean. The average temperature is about 55°F most of the year, but stiff breezes and winter storms buffet the home from the ocean side, and fog can approach the home from the mountain side.
- Windows. The greatest loss of energy by far in the shell of the building occurs through the windows. Insulating value is measured as “R” value – the higher the number – the greater the insulation. Most windows are between R-1 and R-3, even the “high performance thermal panel pane windows with heat mirror glass. This compares with walls typically rated at R-10 to R-20. It is easy to understand why a home with R-1.5 windows and R-15 walls looses most heat through the windows – the analogy I like is riding your bike on a cool day with a heavy jacket (the walls) – but the zipper is open (the windows). Very recently, new technology was developed offering a quantum leap in window performance. Serious Materials (www.seriousmaterials.com) offers windows in the R-7 to R-11 range, using a radiant barrier film suspended between two glass panes, and by filling insulation in the normally hollow mullion frame which holds the glass. We specified R-11 in our home. The incremental first cost of these windows is less than 1/3 more than standard windows, but offer very fast payback of less than 5 years compared with the energy saved. In addition to saving energy high performance window systems greatly improve comfort by eliminating the feeling of “chill” that accompanies radiant heat loss. To extend the life of the windows and protect them from the ocean’s corrosive salinity, we will install a clear film on the outer windows for the ocean side. This film can be easily changed once a decade – greatly extending the life of the windows.
- Wall Insulation. We are in a reasonably mild climate in which a tremendous amount of wall insulation would only provide a modest improvement in energy savings. We modeled a variety of construction and insulation alternatives, especially the following:
- 2x4 stud construction – with the cavities filled with high performance insulation. Effective R-value about R-14:
We eliminated this option as insulation was insufficient to meet project goals.
- 2x6 stud construction – with the cavities filled with high performance insulation for effective insulating value of about R-20:
This option has benefit of 50% more insulating material, and simple construction techniques. However – additional floor area is lost on the interior of the building.
- 2x4 stud construction – with the cavities filled with high performance insulation, plus a layer of 1” polystyrene insulation on the exterior of the building, resulting in an effective shell R-value of about R-22:
We selected this option for several reasons. The first is that we believe it provided the best insulation value of the 3 options we considered. While high performance insulation offers about R-5 per inch, one must keep in mind that the wood studs in the walls only provide R-1 per inch, and thus create “porosity” in the wall insulation. Adding a rigid polystyrene board externally covers the weakly insulated stud areas, and also would cover any gaps in construction – critical for performance. This approach also conserved interior area, as the external insulation does not change the setback requirements of the building from the property line. The downside of this approach is that certain construction activities related to attaching siding and fixtures is more difficult.
Proximity to the ocean limits the maximum temperature in our neighborhood such that air conditioning on the relatively few hot days best accomplished by opening the windows and allowing the sea breezes to cool the home. The exception is our music studio in the largely sub terrain level; to the extent required; simple air exchanges with fresh outside air would be used.
- Radiant Floors
We elected to use radiant floor technology for heating. Radiant heat is much more efficient, more comfortable, and healthier (due to eliminating forced air/dust mites) than other forms of heating such as forced hot air. Radiant floors are much lower cost when installed in the construction vs. retrofit phase. Two dominant approaches are used in radiant floors – with, and without thermal mass. We chose a system without thermal mass – a metal surface conducts heat from tubes. This system is very fast in response in comparison to a thermal mass system. Our home will have multiple zones that can be individually adjusted and remain unheated if an area is not in use. The system is tied into a central home energy control system. To enable heating of the water in the “off peak”, a well-insulated storage tank of about 100 gallons is planned. This approach allows valuable daytime solar electricity to be “sold” back to the utility, and low cost electricity used to heat the water in the evening. These approaches improve the efficiency and reduce the environmental impact of the electric utility which otherwise uses least efficient resources to generate peak daytime electricity. Electricity for the Radiant Floors is discussed below under Solar Power.
- Air-Sourced vs. Ground-Sourced Heat Pumps. Initially we planned a ground-sourced approach for the heat pump. The heat pump works in a manner similar to an air-condition operating in reverse – heat is used inside the building, and “cold” is dumped to the outside. A proposed ground sourced system for our home featured 4 wells drilled 250’ feet. Loop of circulating water flow in through the wells, and heat from the adjacent ground is absorbed in the loop. Overtime the adjacent ground can cool down and the efficiency of the system degrades unless the loop design is sufficiently large. A budgetary cost of the $50k was quoted for the wells and installed circulating pipes. This ground source approach offered the advantage of being silent in operation. However, many disadvantages were clear, starting with cost. Maintenance of the installed loops was a concern. Also I didn’t like the idea of penetrating potential aquifers even though suppliers assured us this was OK.
Ultimately we chose an air-sourced heat pump using new technology from Europe. Since our air is relatively constant temperature and similar to the ground temperature, efficiency was similar between the two approaches, though cost of the air-sourced unit was less than 20% of the ground approach. The air-air exchanger is a small free standing unit to be located on the side of the home so maintenance is easy though it does have a fan blower creating some noise on that side of the property. The unit heats water used in the radiant floor loop and generates domestic hot water.
For ambiance and occasional heating we designed a fireplace for the downstairs music room and the great room. We chose natural gas instead of wood due to reduced particulate emissions from gas. While gas is a fossil fuel, we estimate less than a 5% of our heat energy will come from gas.
LED lighting was used wherever possible. This lighting technology is extremely efficient but still rapidly evolving and relatively expensive; with limits on color, packaging, and intensity levels. Where LED doesn’t work, typically halogen lighting was used.
All our appliances feature Energy Star ratings, and many were chosen as best in class from an energy standpoint. Televisions used in the home are based on LED technology which uses a small fraction of the energy consumed by plasma or other LCD designs. Kathleen prefers to use gas for cooking so we used that in the main kitchen range and stove; electric kettles are used for preparing tea in other areas of the home. High efficiency front loading clothing washers were used to minimize energy requirements and water consumption. We used gas for clothes drying.