Glossary of energy terms pertaining to home construction
ACH (Air Changes per Hour): A measurement of air changes per hour at a blower-door induced pressure of 50 Pascals (ACH50.
AFUE (Annual Fuel Utilization Efficiency): The measure of seasonal or annual efficiency of a furnace or boiler. It takes into account the cyclic on/off operation and associated energy losses of the heating unit as it responds to changes in the load, which in turn is affected by changes in weather and occupant controls.
EER (Energy Efficiency Ratio): A measure of the efficiency of central and room air conditioners. It measures instantaneous efficiency and is the cooling capacity in Btu/hr divided by the watts of power consumed for a specific outdoor temperature (usually 95 degrees Fahrenheit). In hotter climates, SEER and EER are more important than HSPF.
HERS (Home Energy Rating System): A standardized system for rating the energy-efficiency of residential buildings. Home Energy Rating Systems are currently governed by three national industry standards: 1) the National Association of State Energy Officials Technical Guidelines (the methods and procedures for rating a home); 2) the Mortgage Industry HERS Accreditation Procedures (the methods and procedures for the certification of Home Energy Rating System by individual state governments and the national home mortgage industry); and 3) the RESNET Training and Certifying Standards (prescriptive minimum competencies for trainers and certified raters).
HSPF (Heating Season Performance Factor): Laboratory test attempts to take into account the reductions in efficiency caused by defrosting, temperature fluctuations, supplemental heat, fans and on/off cycling. The higher the HSPF, the more efficient the heat pump.
IECC (International Energy Conservation Code): Building codes addressing energy efficiency specifically in residential structures as developed by the International Code Council (ICC). The ICC consists of three statutory members: Building Officials & Code Administrators International Inc., International Conference of Building Officials and Southern Building Code Congress International. A new edition of these codes is produced every three years. Most metro-Phoenix area cities have adopted a version (2000 or 2003 of these codes).
IRC (International Residential Code): See previous entry.
Low-E: Most often used in reference to a coating for high-performance windows which incorporates a thin metallic oxide coating increasing the U-factor of the window by reducing heat flow from a warm(er) air space to a cold(er) glazing surface.
R-value: Quantitative measure of resistance to heat flow or conductivity, the reciprocal of U-factor. While many in the building community consider R-value to be the primary indicator of energy efficiency, it only deals with conduction, one of three modes of heat flow, (the other two being convection and radiation). As an example of the context in to which R-value should be placed, 25% to 40% of a typical home's energy use can be attributed to air infiltration due to convection..
RESNET (Residential Energy Services Network): A network of mortgage lenders and other housing and residential energy efficiency professionals. RESNET's mission is to qualify more families for home ownership and improve the energy efficiency of the nation's housing stock through expanding the availability of mortgage finance options and home energy ratings.
SEER (Seasonal Energy Efficiency Ratio): It is the most commonly used measure of the efficiency of consumer central air conditioning systems.
SHGC (Solar Heat Gain Coefficient): The fraction of incident solar radiation entering a home through the windows. The lower the number, the better the window is at blocking heat gain.
U-factor: Quantitative measure of heat flow or conductivity, the reciprocal of R-value. While building scientists will use R-values for measures of the resistance to heat flow for individual building materials, U-factor is always used as a summary measure for the conductive energy measure of building envelopes.
