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Energy

A primary project goal was to minimize carbon dioxide emissions. This was achieved through passive solar design and, more importantly, by employing renewable energy systems.

Electricity is generated by a 6.4 KW photovoltaic collector system using PV slates as roofing on the three south-facing roof surfaces. The PV system is interconnected to the grid, providing power to the grid during peak times (hot summer days) and buying back off-peak (at night and in winter). On a typical summer day, between 15-20 KWH of power are sold to the grid during the day and 6-10 KWH are purchased at night. Even during the winter months, it is not unusual to sell 4-8 KWH/day. A battery backup system, although reducing the overall efficiency of the design, can provide about 24 hours of power to essential electrical loads. Rechargable batteries are used in all control systems.

Strategies to reduce consumption were implemented as well. Compact and tubed fluorescent lights are used in all locations, with the exception of a dining room halogen fixture and two bedroom reading lights. Gross electrical consumption is 570 KWH/month--62 percent of what an average house typically uses. With 80 percent of the year-round electrical demand produced by solar power, the net electrical consumption from the grid is 124 KWH/month, or roughly 13 percent of the average house.

Monitoring over the past three years shows that the PV system generates more than 80 percent of the year-round electrical load for the house, and over 100 percent from March through October.

Seven 4'x8' hot water solar collectors installed along the driveway provide much of the heat for the radiant-floor heating system. The collectors, in combination with tight construction, triple-glazed windows, and passive solar design features, reduce gas consumption for heating to 4.13 BTU/sq ft/degree day. A high-efficiency woodburning fireplace further reduces the need for gas heating by approximately one therm/day and makes the house particularly comfortable on gloomy days in winter.

Bioclimatic Design

In the upper Midwest, the primary climatic concerns are the extremes of temperature. Average heating degree days in the Chicago area exceed 6,000/year, and cooling degree days average 800/year. With windows comprising a large percentage of the exterior wall in order to take full advantage of the lake views, superior energy performance was a top priority. The triple-glazed, low-E, argon-filled windows and doors selected provide excellent insulation from winter winds and summer heat.

South-facing windows allow sunlight in during winter months, while deciduous trees and overhangs help block heat gain in summer. Some windows on the lake side of the house are oriented 30°SE to provide direct sunlight on the winter solstice; others are oriented 30°NE to admit direct sunlight at dawn on the summer solstice. Thermal shades have been installed on all windows and are closed on sunny summer days to reduce solar gain and at night in winter to reduce heat loss.

Most of the windows can be opened to admit cool lake breezes in summer. In addition, the open central stairwell works with the small third-floor belvedere to provide natural stack ventilation. Airlocks at the front and side doors provide further insulation from temperature extremes.

Energy security

Eight 225 AmpH 12V batteries are charged by the solar array. This would provide one day of full backup power even without any solar recharging. The battery backup system is connected to essential equipment (boiler pumps and ignition, sump pumps, refrigeration) as well as to some lighting and wall outlets.

Data Sources & Reliability

Utility bills
Commonwealth Edison: January 2003-present. Nicor: January 2003 - present.

Reliability
Given the temperatures in the upper Midwest, an important calculation is BTU/sq ft/degree day. The number of degree days for the past 12 months totaled 5817, and thus the total energy consumption was 5.71 BTU/sq ft/dd. Of that, 4.36 BTU/sq ft/dd were carbon producing.

Base load electrical calculations are estimates based on 10th percentile of daily electrical consumption over 3 years. Usage attributed to pumps and fans is estimated by winter vs. summer electrical consumption (pumps and fans being used primarily for radiant heat distribution and ERV operation). Gas for cooking and the clothes dryer is estimated based on gas consumption during July + August (times 6). Given the lack of precision in these calculations, total consumption figures are much more accurate than consumption per category.

Electrical purchases are net of amount purchased from, minus amount sold to, the utility. Actual 12 months (March 2005 - March 2006) purchases/sales were 4479 and 3032 KWH respectively.

Green Strategies

• Wall Insulation
  • Achieve a whole-wall R-value of 15 or greater
  • Use advanced framing techniques
• Photovoltaics
  • Use building-integrated photovoltaics (PV) to generate electricity on-site
  • Arrange for sale of excess electricity into the grid
• Foundation Insulation
  • Use basement wall insulation with an R-value of at least 16
• High-performance Windows and Doors
  • Optimize energy performance of glazing systems
  • Use storm doors
  • Use exterior doors with rated R-values of R-4 or greater
  • Use superwindows with a whole-unit U-factor less than 0.25 (greater than R-4.0)
  • Avoid divided-lite windows to reduce edge losses
• Heating Systems
  • Use active solar heating
• Air Infiltration
  • Keep all mechanical, electrical and plumbing systems within the air and vapor barriers
  • Use air lock entries
  • Seal all penetrations through the building envelope
  • Seal all joints with caulks or gaskets
  • Use windows with infiltration rates no greater than 0.06 cfm/ft
  • Perform blower door testing
• HVAC Distribution Systems
  • Insulate duct work located in unconditioned space
• Other Energy-Efficient Appliances
  • Use high-efficiency clothes washers
  • Use Energy Star dishwashers

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