Glossary of Energy Terms

ACRONYMS AND DEFINITIONS

AHAM:
ARI:
ASHRAE:
Btu:
Capacity (Cooling):
Cooling degree hours:
Coefficient of performance (COP):
Economizer System:
Energy-Efficiency Ratio (EER):
Gray water system:
Heating degree days:
Heating Seasonal Performance Factor (HSPF):
Natural air changes per hour (nach):
Phase:
Seasonal Energy-Efficiency Ratio (SEER):
Shading coefficient (SC):
Single-Package System: An air conditioner or heat pump with all major components housed in a single casing. The shading coefficient of a window is the ratio of total solar transmittance to the transmittance through 1/8-inch clear glass. SC, which is being phased out as a glazing metric, is approximately equal to 1.15 times the solar heat gain coefficient. The ratio of the total cooling capacity in Btu during a normal annual usage period to the total electric input in watt-hours to the air conditioner or heat pump during the same period. Phase of electrical service—single-phase or three-phase. Three-phase electrical service is routine in industrial settings and large horsepower motors are routinely wired for three-phase service. Buildings have openings in their conditioned envelopes which cause the exchange of exterior air with inside air. The rate at which this exchange occurs is a function of many variables, including the magnitude, shape, and locus of the openings, the temperature difference between inside and outside of the envelope, the height of the building, and other factors which cause pressure differences. Instantaneous air exchange rates are difficult to measure, as are averages over a heating or cooling season, but a good estimate of nach is critical in estimating convective energy flows. The total heating output of a central air conditioning heat pump, in Btu, during its normal usage period for heating, divided by the total electric energy input in watt-hours during the same period. A term useful in expressing the severity of the weather in a region during the heating season. The heating degree days in a season are derived by summing the difference between the average outdoor temperatures above a base (e.g., 65 degrees F) each 24 hours and the base temperature. Heating degree hours (equal to heating degree days x 24) are used in computing seasonal energy flows in a building due to both conduction and convection. Device and associated fixtures through which energy associated with the heat from warm water that goes down drains can be recovered using water-to-water or water-to-air heat exchangers. The ratio of the cooling capacity in Btus to the electric input to the air conditioner or heat pump in watt-hours. During the cooling season, whenever outside air temperatures go below inside set point temperatures, it is usually appropriate to terminate the use of compressor-based cooling and open HVAC system dampers to supply 100% outside air. This economizer strategy is frequently cost effective in southwestern climates where the absence of clouds during the cooling season allows outside temperatures to drop quite substantially in the evening. Economizers must be maintained and controlled with care to ensure that dampers are fully opened when needed—and fully shut when not. The ratio of energy delivered by an air conditioner or a heat pump to the input energy, where both forms of energy are measured in the same units (typically Btus). A term useful in expressing the severity of the weather in a region during the cooling season. The cooling degree hours in a season are derived by summing the difference between the average outdoor temperatures above a base (e.g., 74 degrees F) each hour and the base temperature. Statistics gathered over recent years suggest a growing number of cooling degree hours in many regions, perhaps owing to the greenhouse effect. Cooling degree hours are used in computing seasonal energy flows in a building due to both conduction and convection. The quantity of heat in Btu which an air conditioner or heat pump is capable of removing from an enclosed space in one hour, expressed as thousands of Btu/hr, millions of Btu/hour (MBtu/hr), or tons. A unit rated at one ton can remove 12,000 Btu/hr of heat. British Thermal Unit American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. Air-Conditioning and Refrigeration Institute Association of Home Appliance Manufacturers