When your home is producing as much, or more, energy than it is consuming you have a zero energy home. The transition from an old leaky home to a zero-energy home requires three inter-linked strategies: Conservation, efficiency, and renewable energy. These strategies are applied to the energy use sectors of the home: heating/cooling, hot water, refrigeration, lighting, appliances, and electronics. Energy demand is reduced by conservation and efficiency.
CONSERVATION
Conservation means reducing or eliminating the need for energy to run your home. For example, if you plant a shade tree on the west side of your home you keep the sun from overheating your west rooms. This reduces your air-conditioning load and monthly electricity bill. Insulation and a sealed attic would also reduce cooling load.
EFFICIENCY
Efficiency means doing more with less. For example, a high efficiency air conditioner squeezes more cooling per kilowatt hour of electricity than an old clunker. As 11-watt LED light shines as bright as a 100-watt incandescent light bulb. A front-loading clothes washer uses about half the hot water and two-thirds the electricity of an old top loading machine.
RENEWABLE ENERGY
Wind and sun energy are underutilized in most homes. Wind power can be used to ventilate your home or generate electricity. Sunlight may be used to light your rooms, heat your hot water, warm your home, and generate electricity.
Meeting the Zero Energy Home goal minimizes our need for imported energy: electricity, natural gas, propane, oil, coal. This has many positive effects: It reduces carbon dioxide emissions and global warming. It minimizes the impacts of resource extraction, e.g., strip mining coal to be burnt in electrical power plants. Also, it improves our balance of trade.
The United States Department of Energy (DOE) advocates a whole-house systems approach to achieve an energy efficient home.
This approach to weatherization considers the interaction between you, your building site, your climate, and these other elements or components of your home:
• Insulation and air sealing
• Lighting and daylighting
• Space heating and cooling
• Water heating Windows, doors, and skylights
• Solar energy production
• Appliances and home electronics
The design of a new home or renovation of an older home for to be energy efficient requires a recognition that one component in the house can greatly affect other components, which ultimately affects the overall energy efficiency of the house.
Home climate control is a many splendid thing, requiring the greater part of a typical home’s energy budget. It includes sealing the building from wind and rain, regulating entry of sunlight, and controlling internal temperature, humidity, air quality and light.
The following is a listing of typical home climate control measures:
• Air Sealing
• Insulation
• Moisture Control
• Ventilation
• Sunlight Management
• Heating and Cooling Equipment Improvements
Air Sealing
• Sealing bypasses (cracks, gaps, holes), especially around doors, windows, pipes that penetrate the attic ceiling, and other areas with high potential for heat loss, using caulk, foam sealant, weather-stripping, window film, door sweeps, and electrical receptacle gaskets
• Seal heating/cooling air ducts
• Installing storm doors and storm windows.
• Replacing old drafty doors with tightly sealing, foam-core doors.
• Replacing older windows with energy efficient, double-glazed windows.
• Seal attic from outside air.
Insulation
• Installing insulation in attic, walls, floors, and ceilings, around ducts and pipes, around water heaters, and near the foundation and sill.
• Window insulating curtains.
• Protecting pipes from freezing and corrosion.
Moisture Control
• Installing roofing, building wrap, siding, flashing
• Installing footing drains, foundation waterproofing membranes, interior perimeter drains, sump pump, gutters, downspout extensions, downward-sloping grading, French drains, swales, and other techniques to protect a building from both surface water and ground water.
• Installation of vapor barriers to prevent warm, moist interior air from migrating into cool walls and causing condensation and mold problems.
• Providing proper ventilation to unconditioned spaces to protect a building from the effects of condensation.
Ventilation
• Uncontrolled: Ventilation: air movement into a home through cracks, small holes, and vents, such as windows and doors. Not recommended for tightly sealed homes which require fans to keep air fresh,
• Whole-house Ventilation: Controlled air movement using one or more fans and duct systems.
• Spot Ventilation: Controlled air movement using localized exhaust fans to quickly remove pollutants and moisture at their source, e.g., in kitchen and bathroom
Sunlight Management
• Installing and maintaining skylights or solar tubes
• Installing or maintaining sun control devices such as overhands, awnings or sunshades
• Installing efficient low-e windows
• Install solar collectors for heating hot water or generating electricity.
Efficient Heating and Cooling Equipment Improvements
• Seal heating and cooling ducts
• Installation of modern, energy-saving heating and cooling equipment
• Repair of old, inefficient equipment (furnaces, boilers, water heaters, programmable thermostats, air conditioners, and so on).
HOW IS HOME CLIMATE CONTROL USEFUL?
A comprehensive approach to home climate control has many benefits:
• Savings on energy costs for heating, cooling and lighting
• Comfortable even temperatures
• Better air quality with low levels of air pollutants and mold.
• Protection of building structure and savings on maintenance costs.
• Reduced noise.
The climate control measures of air sealing, insulation, moisture control, ventilation, sunlight control, and efficient heating and cooling equipment work together to make a house energy-efficient and livable.
For example air sealing and insulation of walls work together like a nylon windbreaker and a sweater. Air sealing of interior and exterior walls results in an interior wall cavity protected from winds. Wind protection allows insulation to do its job effectively. Insulation assists in air sealing by retarding convection; this is especially true of foam insulation. Insulation also prevents conduction of heat through walls, floors, ceilings and roofs.
Moisture control keeps the insulation from becoming wet and ineffective; this is especially true of loose insulation such as fiberglass and cellulose. Moisture control also prevents damage to the building and maintains healthy indoor air by preventing the growth of mold. Ventilation moist air from bathrooms and kitchen contributes to moisture control. Ventilation of hot air from the home keeps homes cooler in hot weather.
Using skylights or windows to bring in sunlight can make the house more comfortable and reduce heating and lighting costs. Sun shading devices can keep the home cooler and free of glare. Solar collectors for heating water and producing electricity can reduce utility costs.
All of the above measures ease the burden on the home’s heating and cooling equipment e.g., furnace and air conditioner, thus reducing utility bills. Repair or upgrade of furnace and/or air conditioner can further reduce the utility bills. Sealing of leaky air ducts, carrying warm or cool air from the furnace and air conditioner, also improves heating and cooling efficiency.
The tightness of a house, how much air it leaks, can be measured by a blower door. A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure then flows in through all unsealed cracks and openings. The auditors may use a smoke pencil to detect air leaks. These tests determine the air infiltration rate of a building.
Blower doors consist of a frame and flexible panel that fit in a doorway, a variable-speed fan, a pressure gauge to measure the pressure differences inside and outside the home, and an airflow manometer and hoses for measuring airflow.
A blower door is used to both find and measure air leakage. The number of air changes per hour (the complete replacement of the indoor air volume of the house in an hour) at a standard pressure differential (pressure inside the house minus pressure outside the house, measured in Pascals) indicates how the house is performing, and where problems are.
The blower door test places a home under a known pressure and then measures how much airflow is required to maintain the pressure difference between indoors and outdoors. The tighter the house, the less air the blower door must move to maintain a given pressure. Besides measuring the air-tightness of the house, it also helps to pinpoint specific air leaks.
Five air changes per hour at 50 Pascals differential pressure (5 ACH50) is a common performance standard. Older homes commonly have 10 to 15 ACH50; newer homes may have 5 to 10 ACH50; homes built for low air leakage range from 1 to 3 ACH50. By comparison, the Swedish standard for new single-family homes is 0.5 ACH50. The Canadian program for energy-efficient new residential construction has a maximum leakage standard of 1.5 ACH50.
A thermal imaging camera is another device for measuring home weatherization performance. The camera displays the temperature of building surfaces such as windows, walls, ceilings and roofs. It does this by detecting the wavelengths of the infra-red radiation streaming from the building surfaces.
The camera can spot air leaks and areas where insulation is lacking. It can also spot cool areas where moisture is collecting. This information is useful to guide home repairs and upgrades. It is also useful when determining if new houses have been insulated and air-sealed properly.
A home energy rating involves an analysis of a home’s construction plans and onsite inspections. Based on the home’s plans, the Home Energy Rater uses an energy efficiency software package to perform an energy analysis of the home’s design. This analysis yields a projected, pre-construction HERS Index. Upon completion of the plan review, the rater will work with the builder to identify the energy efficiency improvements needed to ensure the house will meet ENERGY STAR performance guidelines. The rater then conducts onsite inspections, typically including a blower door test (to test the leakiness of the house) and a duct test (to test the leakiness of the ducts). Results of these tests, along with inputs derived from the plan review, are used to generate the HERS Index score for the home.
The HERS Index is a scoring system established by the Residential Energy Services Network (RESNET) in which a home built to the specifications of the HERS Reference Home (based on the 2006 International Energy Conservation Code) scores a HERS Index of 100, while a net zero energy home scores a HERS Index of 0. The lower a home’s HERS Index, the more energy efficient it is in comparison to the HERS Reference Home.
Each 1-point decrease in the HERS Index corresponds to a 1% reduction in energy consumption compared to the HERS Reference Home. Thus a home with a HERS Index of 85 is 15% more energy efficient than the HERS Reference Home and a home with a HERS Index of 80 is 20% more energy efficient.
Comparing the New HERS Index with the Old HERS Score
For homes rated before July 1, 2006, the rating score is known as a “HERS Score.” The HERS Score is a system in which a home built to the specifications of the HERS Reference Home (based on the 1993 Model Energy Code) has a HERS Score of 80. Unlike the HERS Index, each 1-point increase in a HERS Score is equivalent to a 5% increase in energy efficiency. Please see the table below for a comparison of the HERS Score and the HERS
Click to enlarge
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