HVAC Glossary

Alternative HVAC Solutions would like to offer the following HVAC Glossary as a helpful tool for you, our customer, to help with the various terms and technical definitions for the heating, cooling and indoor air quality industry.

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Temperature -  Degree of hotness or coldness measured on one of several arbitrary scales based on some observable phenomenon (such as the expansion).
Temperature Differential -  The difference between the entering and leaving temperature for a given fluid. For example, a 10-degree evaporator temperature differential for a chiller would describe an operating condition where the entering water temperature is 54 degrees and the leaving is 44 degrees.
Testing, Adjusting, And Balancing -  (TAB) The diagnostic and corrective procedures for HVAC controls and operating components to ensure provision of specified airflow rates and environmental conditions.
Therm -  Another measurement of heat. One therm equals One hundred thousand (100,000) British thermal units (1 therm = 100,000 Btu).
Thermal (Energy) Storage -  A technology that lowers the amount of electricity needed for comfort conditioning during utility peak load periods. A buildings thermal energy storage system might, for example, use off-peak power to make ice or to chill water at night, later using the ice or chilled water in a power saving process for cooling during the day. See THERMAL MASS.
Thermal Mass -  A material used to store heat, thereby slowing the temperature variation within a space. Typical thermal mass materials include concrete, brick, masonry, tile and mortar, water, and rock or other materials with high heat capacity.
Thermodynamics -  The study of the transformation of energy into other manifested forms and of their practical applications. Commonly encountered forms of the statements of the three principal laws of thermodynamics are: (0) The heat capacity and entropy of every crystalline solid becomes zero at absolute zero (0 degrees Kelvin). (1) The Law of the Conservation of Energy -- energy may be transformed in an isolated system, but its total is constant. (2) Heat from a reservoir at a constant temperature cannot be changed completely into work by a cyclic process.
Thermostat -  A temperature sensitive switch for controlling the operation of a heater or furnace. Typically found on a wall inside the home, that consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system. A device that allows you to control the temperature inside your home by telling the heating or cooling system how much air to produce. An automatic control device designed to be responsive to temperature and typically used to maintain set temperatures by cycling the HVAC system.
Thermostat, Air-Sensing -  Thermostat unit in which sensing element is located in refrigerated space.
Thermostat, Setback -  (Programmable Thermostat) A state-of-the-art electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day. A device, containing a clock mechanism, which can automatically change the inside temperature maintained by the HVAC system according to a preset schedule. The heating or cooling requirements can be reduced when a building is unoccupied or when occupants are asleep.
Threshold -  (IAQ) The contaminant dose or exposure level below which there is no expected significant effect.
Threshold Limit Value -  (TLV) The American Conference of Governmental Industrial Hygienists recommended guideline for exposure limit represented in terms of exposure over a work day (8 hours) or a work week (40 hours).
Threshold Limit Values -  (TLVs) Threshold Limit Values (guidelines recommended by the American Conference of Governmental Industrial Hygenists).
Throw -  (Lt) The maximum distance between the center of the core and a plane which is tangent to a specified envelope and perpendicular to the intended direction of flow The throw is generally referred to as the envelope corresponding to 0.25 m/s for zero supply temperature differential (i.e., under isothermal conditions).
Tight Building Syndrome -  (TBS) A condition in which a building is very tightly insulated against infiltration, its ventilation is reduced for energy conservation, and airborne contaminants are sufficiently elevated to cause health effects in occupants; often used synonymously with sick building syndrome (SBS).
Time Delay -  Usually refers to a device that will not allow the condenser to restart for an average of 5 minutes.
Ton or "Ton of Cooling" -  A cooling unit of measure. Each ton equals the cooling effect of 12,000 Btuh. Heat pumps and air conditioners are generally sized in tons. Typical sizes for single family residences are between two and five tons. It is important to note that actual capacity is not constant and will change based on outdoor or indoor temperatures. The published capacity rating of air conditioners and heat pumps is based on performance at the ARI standard temperature levels of 95 F outside, 80 F inside, and 50% relative humidity. The number of tons a system has is the total BTU capacity of the system. The size of the area to be cooled will determine the correct size of the system in tons. While an air conditioner may be called a three ton unit, it may not produce 36,000 Btu/h in cooling. There is a wide variety of actual capacities that are called "three tons."
Total air flow rate -  (QL) Sum of the primary and secondary air flow rates which are moved in the treated space.
Total Home Comfort System -  The ultimate solution to providing you with consistent, customized home comfort, despite the ever-changing weather.
Total Volatile Organic Compounds -  (TVOCs) A measure representing the sum of all VOCs present in the air to provide an approximate indication of pollutant levels. Indoor air typically contains hundreds of different VOCs in very low concentrations, some of which can have additive effects.
Toxicant -  A substance that can cause tissue damage or otherwise affect organs or systems within the body.
Tracer Gas -  An inert compound that is a rare constituent of indoor air which is released into building air and monitored qualitatively and/or quantitatively to characterize airflow characteristics to detemine air pathways, infiltration, and ventilation efficiency measurements.
Tracer Gases -  Compounds, such as sulfur hexaflouride, which are used to identify suspected pollutant pathways and to quantify ventilation rates. Trace gases may be detected qualitivatively by their odor or quantitatively by air monitoring equipment.
Transformer -  A device, which through electromagnetic induction but without the use of moving parts, transforms alternating electric energy in one circuit into energy of similar type in another circuit, commonly with altered values of voltage and current.
Transmittance -  The time rate of heat flow per unit area under steady conditions from the air (or other fluid) on the warm side of a barrier to the air (or fluid) on the cool side, per unit temperature difference between the two sides.