The following is a compilation of building energy-code related terms and acronyms used on the Building Energy Codes website and throughout the building construction industry.

Select a letter to navigate through the glossary:


A (25) B (22) C (41) D (27) E (27) F (15) G (12) H (21) I (20) K (5) L (11) M (16) N (15) O (11) P (21) R (22) S (37) T (14) U (12) V (11) W (10) Z (1)
Packaged Terminal Air Conditioner (PTAC)

A factory-selected wall sleeve and separate unencased combination of heating and cooling components, assemblies, or sections. It may include heating capability by hot water, steam, or electricity and is intended for mounting through the wall to serve a single room or zone.

Packaged Terminal Heat Pump (PTHP)

A PTAC capable of using the refrigerating system in a reverse cycle or heat pump mode to provide heat.

Party Wall

A fire wall on an interior lot line used or adapted for joint service between two buildings.

Performance Approach

A performance approach (also known as a systems performance approach) compares a proposed design with a baseline or reference design, and demonstrates that the proposed design is at least as efficient as the baseline in terms of annual energy use. This approach allows the greatest flexibility but may require considerably more effort. A performance approach is often necessary to obtain credit for special features such as a passive solar design, photovoltaic cells, thermal energy storage, fuel cells, and other nontraditional building components. This approach requires an annual energy use value. There are several commercially available software tools that perform this analysis.

Perm Rating

The amount of water vapor that passes through an area in a certain period of time.

Permanantly Wired Luminaires

Light fixtures physically attached to a surface (e.g., ceiling or wall) using a permanent mounting system and wired directly to a power source. Examples include fluorescent fixtures located in a ceiling grid and wall sconces.

Permanently Installed

Equipment that is fixed in place and is not portable or movable.

Photo Cell

A light-sensing device used to control luminaires and dimmers in response to detected light levels.


An enclosure that is part of the air-handling system and is distinguished by having a very low air velocity. A plenum often is formed in part or in total by portions of the building.


Any structure, basin, or tank containing an artificial body of water for swimming, diving, or recreational bathing. The term includes, but is not limited to, swimming pool, whirlpool, spa, and hot tub.

Positive Cooling Supply

Mechanical cooling deliberately supplied to a space, such as through a supply register. Also, mechanical cooling indirectly supplied to a space through uninsulated surfaces of space-cooling components, such as evaporator coil cases and cooling distribution systems that continually maintain air temperatures within the space of 85°F (29°C) or lower during normal operation.

Positive Heat Supply

Heat deliberately supplied to a space by design, such as a supply register, radiator, or heating element. Also, heat indirectly supplied to a space through uninsulated surfaces of service water heaters and space-heating components, such as furnaces, boilers, and heating and cooling distribution systems that continually maintain air temperature within the space of 50°F (10°C) or higher during normal operation.

Power Factor

The ratio of total real power in watts to the apparent power (root-mean-square volt amperes).

Prescriptive Approach

A prescriptive approach lists the minimum R-value or maximum U-factor requirements for each building component such as windows, walls, and roofs. For lighting systems in commercial buildings, a prescriptive approach would simply list the allowable watts per square foot for various building types. For mechanical systems and equipment, a prescriptive approach would list the minimum required equipment efficiencies.

Primary Air System

The central, air-moving, heating, and cooling equipment that serves multiple zones through mixing boxes, VAV boxes, or reheat coils.

Process Energy

Energy consumed in support of a manufacturing, industrial, or commercial process other than conditioning spaces and maintaining comfort and amenities for the occupants of a building.

Process Load

The load on a building resulting from the consumption or release of process energy.

Projection Factor (PF)

The ratio of the distance the overhang projects from the window surface to its height above the sill of the window it shades.

Proposed Design

A computer representation of the actual proposed building design or portion thereof used as the basis for calculating the design energy cost.

psi (g)

Pounds per square inch gauge.

Pump System Energy Demand (Pump System Power)

The sum of the nominal power demand (nameplate horsepower) of motors of all pumps that are required to operate at design conditions to supply fluid from the heating or cooling source to all heat transfer devices (e.g., coils, heat exchanger) and return it to the source.