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zeolite
group of aluminosilicates containing very loosely held cations, used in molecular sieves and ion exchangers.
zeotrope
blend comprising multiple components of different volatilities that, when used in refrigeration cycles, change volumetric composition and saturation temperatures as they evaporate (boil) or condense at constant pressure.
zeotropic
refers to blends comprising multiple components of different volatility that, when used in refrigeration cycles, change volumetric composition and saturation temperatures as they evaporate (boil) or condense at constant pressure. The word is derived from the Greek words zein (to boil) and tropos (to change).
zeotropic refrigerant
a zeotropic refrigerant contains two or more components whose equilibrium vapor phase and liquid phase compositions differ. The temperature of a zeotropic refrigerant changes as it evaporates or condenses at constant pressure (Compare to azeotropic refrigerant).
zero energy band
the dead band between control setpoints, such as between heating and cooling, where the lowest amount of mechanical energy is being utilized. Contrast dead band.
zero point energy
residual energy of a system at absolute zero.
zeroth law of thermodynamics
if two systems are both in thermal equilibrium with a third one, they are in mutual thermal equilibrium.
zone
(1) a separately controlled heated or cooled space. (2) one occupied space or several occupied spaces with similar occupancy category, occupant density, zone air distribution effectiveness, and zone primary airflow per unit area. (3) space or group of spaces within a building for which the heating, cooling, or lighting requirements are sufficiently similar that desired conditions can be maintained throughout by a single controlling device.
zone (control zone)
space or group of spaces within a building with heating or cooling requirements sufficiently similar that comfort conditions can be maintained by a single controlling device.
zone valve
valve that modulates water flow to a thermal zone in response to a downstream temperature signal.
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About ASHRAE Terminology

ASHRAE Terminology, a free resource, is a comprehensive online glossary of more than 3700 terms and definitions related to the built environment, with a focus on heating, ventilating, and air conditioning (HVAC), as well as refrigeration, building envelope, electrical, lighting, water and energy use, and measurement terms.

This searchable glossary was designed for use by engineering professionals but is also useful for architects, building owners and operators, educators, public officials, and homeowners.

The terms in ASHRAE Terminology have been assembled and defined and are updated on an ongoing basis by ASHRAE Technical Committee (TC) 1.6, Terminology. TC 1.6 is concerned with terminology, nomenclature, definitions, abbreviations, symbols, and the International System (SI) and Inch-Pound (I-P) units used in the fields of heating, ventilating, air conditioning, water heating, and refrigeration.

To request a free electronic file of the complete list of terms and definitions, email ashraetermseditor@ashrae.org.