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A wide variety of energy efficiency technologies are available, and the list seems to grow continually as new technologies and approaches are attempted. The case studies presented here include a broad overview of projects that have incorporated a large number of energy efficiency measures.
Case Studies
Case Study: Side-by-Side Homes Demonstrate Benefits of Energy Efficiency
"PV Residence," Lakeland, Florida
In 1997, the Florida Solar Energy Center set out to demonstrate the benefits of energy efficiency and solar energy by building two houses, one a control house built to typical Florida building standards, and the other an energy-efficient house with solar hot water and photovoltaic electric systems. The energy-efficient house includes wider overhangs to control solar heat gain, concrete block walls with exterior R-10 insulation (versus a reflective foil in the control home that achieve R-4.2), a reflective white concrete tile roof, a low-friction interior-mounted duct system, compact fluorescent lighting, and a two-ton air conditioner with a seasonal energy efficiency ratio (SEER) of 14.4 Btu/W (versus a 4-ton unit with SEER 10 in the control house). Windows for the energy-efficient house are low-E, argon-filled windows with spectrally selective coatings that minimize heat transmission while allowing most visible light to enter; the frames are white vinyl and include thermal breaks. The control house uses single-pane windows in aluminum frames.
To further reduce load, the energy-efficient house included a 4-kW solar electric (PV) system, with 2.7 kW facing south and 1.3 kW facing west, where it could best meet afternoon peak load requirements. The house also used propane to replace many electrical loads, serving as a backup heating source for hot water as well as for the oven and stove, the clothes dryer, and a direct-vented fireplace. As the primary hot water heating source, a 40-square-foot solar collector provides 45,600 Btu per day.
On a hot day (May 17, 1998), with similar interior conditions maintained and both houses unoccupied, the control house's air conditioning load averaged 3.62 kW during the peak hour between 5 and 6 PM EDT while the energy-efficient house had a cooling demand during the same hour of 0.50 kW — a load reduction of 86%. Over the same period, the average PV power production averaged 0.619 kW, thus sending valuable electricity to the grid when most needed by the utility. Total daily electricity consumption for cooling was 5.84 kWh in the energy-efficient house versus 37.5 kWh in the control house — a reduction in daily cooling energy of 84%. Moreover, the PV system produced 17.9 kWh
— three times as much electricity as the cooling system used.
On June 18, 1998, Lakeland recorded the hottest daytime temperatures on record. On that day, the occupied energy-efficient home showed dramatically lower cooling and total electricity requirements than the unoccupied control house. For the entire day, the efficient home only used 28% of the air conditioning power that the control home required. During the utility peak period the control home air conditioner required 2.98 kW on average as opposed to 0.833 kW for the efficient home — a 72% reduction. When the PV electric generation is included during the same peak period, the efficient house's net demand was only 0.199 kW — a 93% reduction in electricity requirements from the 4.5 kW required for the control house. Over the entire month of June, the PV system produced 60% of the power required for all electrical end-uses by the efficient house (837 kWh). In contrast, the control house used 1739 kWh in June solely for air conditioning.
More information:
Case Study: Efficient Small Home Strives for Zero Net Energy Use
Captain Planet Cottage, Atlanta, Georgia
The 1700-square-foot Captain Planet Cottage combines structural insulated panels (SIPs), a sealing system to reduce air infiltration, whole house ventilation, high-performance glazing, daylighting, and a geothermal heat pump system to minimize energy use. Cooling needs are minimized through the use of overhangs, operable windows, and high-efficiency ceiling fans. The cottage's few energy needs are met with two solar hot water panels and a 4-kW photovoltaic system. The cottage is actually a traveling exhibit, although it spends most of its time in Atlanta, Georgia. It was funded in part by DOE's Building America program and by the Captain Planet Foundation.
Case Study: Efficient Large Home Strives for Zero Net Energy Use
Zero-Energy Home, Livermore, California
This 3070-square-foot house features a foam-core insulated foundation, cellulose insulation blown into the walls, high-efficiency windows, energy efficient appliances and water heater, fluorescent lighting, and high-efficiency fans. In addition, the roof has been coated with a substance to reflect the sun's rays, and radiant barriers have been installed in the interior of the roof to further help reduce heat buildup in the attic. Most of the house's energy needs are met with a photovoltaic system and a solar water heating.
For further information, see:
- Article on the Million Solar Roofs Web site
- Article from the California Solar Center.
Case Study: Natural Ventilation and Energy Efficiency Cuts Office Building Energy Use
Philip Merrill Environmental Center, Chesapeake Bay Foundation, Annapolis, Maryland
The 32,000 square-foot headquarters building for the Chesapeake Foundation uses two-thirds less energy than a typical office building of the same size. Natural ventilation boosts energy efficiency by taking advantage of Chesapeake Bay's breezes to cool the building, reducing its reliance on air conditioning. When sensors determine that the outdoor climate is suitable, the mechanical system shuts down, motor-operated windows open, and "open window" signs signal employees to open their windows.
Other energy efficiency features include structural insulating panels, a geothermal heat pump, and a desiccant dehumidification system. A solar electric system produces a portion of the building's electricity, and solar water heating reduces electricity demand.
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