A comprehensive online glossary of terms and definitions related to built environment, heating, ventilating, and air conditioning (HVAC), as well as refrigeration, building envelope, electrical, lighting, water and energy use, solar power, concentrating solar power (CSP), and measurement terms.
HVAC and Solar energy engineering Terminology
There are currently 244 terms in this directory beginning with the letter T.
a heat exchanger for indirect heating of water, typically for domestic use, which is designed to be used without a water storage tank. See [[instantaneous heater]].
manually operated device on the end of a pipe in a fluid supply system to enable drawing off quantities of the fluid.
Loss caused by a charge controller. One minus tare loss, expressed as a percentage, is equal to the controller efficiency.
task/ambient conditioning (TAC) system
any space-conditioning system that allows occupants to individually control the thermal environment in the localized zone of their workspace while still maintaining acceptable environmental conditions in the surrounding ambient spaces.
measurement of warmth or coldness with respect to an arbitrary zero or to the absolute zero. Temperatures are indicated on defined scales, such as Kelvin and Rankine for absolute temperatures, and Celsius and Fahrenheit for ordinary temperatures.
A circuit that adjusts the charge controller activation points depending on battery temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from ambient temperature.
device that responds directly or indirectly to deviation from a desired temperature by actuating a control or initiating a control sequence.
difference between the temperatures of two substances, surfaces, or environments involving transfer of heat.
temperature difference method
procedure used in design and system analysis to calculate flow (of air, water, or steam) from load or to determine load when flow and temperature differential are known.
temperature differential (∆t)
the difference between the average test zone temperature (tac) and the average supply air temperature (tdc).
temperature differential sensor
a sensor system composed of two temperature sensors that is capable of providing a signal that is related to the temperature differential of the two sensors.
temperature differential within the occupied zone
largest value of the difference between the measured air temperatures within the occupied zone.
It is common for three elements in photovoltaic system sizing to have distinct temperature corrections: a factor used to decrease battery capacity at cold temperatures; a factor used to decrease PV module voltage at high temperatures; and a factor used to decrease the current carrying capability of wire at high temperatures.
temperature gradient risk
percentage of people predicted to be dissatisfied due to a difference in air temperature between ankle and head.
temperature index coefficient of thermal performance
ratio of the difference in temperature between the inside surface and the exterior ambient to the difference in temperature between the inside ambient and the exterior ambient across a component of the building envelope. The coefficient can be used to estimate the apparent thermal resistance of the component.
temperature of flowing fluids
the mixed mean-stream temperature at a station perpendicular to the flow direction.
graph representing the distribution of temperatures in a plane section of a body or a space, or over a period of time.
a sensor located in the fluid that is capable of producing a signal (output) that is related to the temperature.
interior surfaces whose temperature is controlled or monitored for heating and cooling purposes.
the part of the expansion valve that senses the temperature at the superheat control point, normally located at the outlet of the evaporator. This element may be remote or integral to the expansion valve body.
an environment in which the characteristics, quantity, and location of smoke are limited or otherwise restricted to allow for ready evacuation through the space. Maintenance of a tenable environment in the smoke zone is not within the capability of zoned smoke control.
a device by which energy from a system is finally delivered, e.g., registers, diffusers, lighting fixtures, faucets, etc.
terminal casing leakage
amount of air in ft²/min (L/s at standard conditions) escaping from the terminal at a given inlet pressure with only the outlet(s) blocked and with the damper/valve fully opened.
terminal damper leakage
amount of air in ft²/min (L/s at standard conditions) passing through a fully closed damper/valve at a given inlet pressure.
a device that regulates the volumetric flow rate and/or the temperature of the controlled medium.
terminal-unit casing leakage
air in cubic feet per minute (liters per second) leaking from a terminal unit at a given inlet pressure with the outlets and inlets blocked and with the damper/valve fully opened.
terminal-unit damper leakage
air in cubic feet per minute (liters per second) leaking through a fully closed damper/valve of a supply/exhaust terminal unit at a given inlet/discharge pressure.
(1) the recorded group of readings of required test data taken while equilibrium is maintained and used in the computation of results; those observed or recorded during a sufficient period to indicate that equilibrium was attained prior to the actual test. (2) the recorded group of readings of required test data taken while equilibrium is maintained and used in the computation of results; those recorded during the period of the test. (3) a series of determinations for various points of operation.
the air that flows through the device being tested. During the test, test air should be at the temperature, humidity, pressure, and atmospheric dust concentration prevailing at the time of the test. Test air for arrestance and dust-holding capacity measurement may be indoor ambient air.
test condition tolerance
the maximum permissible variation between the average of a measured quantity and the desired test condition specified in the standard.
definitive procedure that produces a test result. Note: appropriate functions of a test method are identification, measurement, or evaluation of one or more qualities, characteristics, or properties of a material, product, system, or service.
test operating tolerance
the maximum amount that a designated measured quantity shall vary (i.e., maximum–minimum) during the entire or a specified interval of a test.
any sensible heating or cooling panel that is used in testing for performance and/or rating purposes.
the time over which quasi-steady-state conditions are maintained for each measured point.
pressure, usually higher than the design working pressure, to which a piece of equipment is subjected for testing according to specified procedures.
test pressure loss
differential in total pressure between the inlet and the outlet sections of a test duct or across a test fitting. For test fittings, the fitting is assumed to have zero length. For multiflow fittings, the total pressure loss shall be determined for each stream separately.
the two environmental chambers where all components of the combined appliance are installed and tested; one chamber is used to maintain specified indoor ambient conditions, while the second chamber is used to maintain specified outdoor ambient conditions.
the use of specialized and calibrated instruments to measure conditions such as temperatures, pressures, rotational speeds, electrical characteristics, velocities, fluid flows, etc., used in HVAC&R.
standard that sets forth methods of measuring capacity, or other aspects of operation, of a specific unit or system of a given class of equipment, together with a specification of instrumentation, procedure, and calculations. See [[MOT]].
testing, adjusting, and balancing
a systematic process or service applied to heating, ventilating, and air-conditioning (HVAC) systems and other environmental systems to achieve and document air and hydronic flow rates. The adjustment of fluid flow rates through distribution systems by manually adjusting the position of dampers, valves, etc., or by using automatic control devices to control the position of dampers, actuators, valves, etc.
changing the solid phase of water, or frozen moisture within a substance, to the liquid phase by the application of heat.
theoretical storage capacity
the sum of the products of masses and heat capacities of all components (including the transfer fluid) contained within the insulating envelope of the thermal storage device.
device that relies on the cooling effect of the airflow to change the temperature of a heated body in proportion to the air speed. Types include hot-wire anemometer, heated-bulb thermometer, heated-thermocouple anemometer, and heated-thermistor anemometer.
heat loss characteristics of a physical condition or structure that are not in accordance with intended design or calculated characteristics.
thermal boundary resistance
(also known as thermal contact resistance), ratio of temperature difference to heat flux across the boundary between two distinct media (solid/solid or solid/fluid).
nonconducting physical structure, such as a frame around a door or window acting to retard heat flow.
the condition of mind which expresses satisfaction with the surrounding thermal environment and is assessed by subjective evaluation. Thermal comfort is affected by heat conduction, convection, radiation, evaporative heat loss, and relative air motion.
(C-factor), thermal conductivity is the heat flux through a flat body induced by a unit temperature difference between the surfaces of that body. Units are Btu/h·ft2·°F (W/[m2·K]).
(k-factor), time rate of steady-state heat flow through unit thickness of unit area of a homogeneous material, induced by a unit temperature gradient in a direction perpendicular to the isothermal planes of that unit. Units of k are in Btu·in/(h·ft2·°F), Btu·ft/(h·ft2·°F), or W/(m·K). Thermal conductivity must be evaluated for a specific mean temperature, thickness, age, and moisture content. See also [[thermal conductance]].
transfer of heat by a fluid moving by natural variations in density (in the absence of conduction and radiation).
time period between the energization of a heat-producing device and the measurable effect of the heat produced until equilibrium conditions are reached.
phenomenon in which a temperature gradient in a mixture of fluids gives rise to a flow of one constituent relative to the whole mixture.
physical quantity that determines the rate of heat propagation in transient state processes. Thermal conductivity divided by the product of density and specific heat. Units are ft2/s or m2/s.
radiation property of a material, evaluated with its surface optically smooth and clean, and of sufficient thickness to be opaque.
a surface property of a material governing the emission of thermal radiation relative to that emitted by a perfect emitter, or black body, at the same surface temperature.
energy possessed by a system caused by the motion of the molecules and/or intermolecular forces; i.e., heat.
thermal energy storage
(1) thermal energy storage may refer to a number of technologies that stores energy in a thermal reservoir for later reuse. They can be employed to balance energy demand between day time and night time. The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment. The principal application today is the production of ice, chilled water, or eutectic solution at night, which is then used to cool environments during the day. (2) thermal energy storage technologies store heat, usually from active solar collectors in an insulated repository for later use in space heating, domestic or process hot water, or to generate electricity. Most practical active solar heating systems have storage for a few hours to a day's worth of heat collected. There are also a small but growing number of seasonal thermal stores used to store summer heat for space heating during winter.
elements of a structure that enclose conditioned spaces and that control transmission of heat, air, and water vapor between the conditioned spaces and the exterior. See also [[building thermal envelope]].
the surrounding atmosphere characterized by parameters such as air temperature, wet-bulb temperature, dew-point temperature, water vapor pressure, total atmospheric pressure, relative humidity, and specific humidity.
increase in one or more of the dimensions of a solid body or a liquid volume, caused by a temperature rise.
thermal frequency response
response of a thermal system to a periodic thermal excitation expressed as a function of frequency. Note: thermal frequency response usually is displayed by polar plot of amplitude attenuation and time lag versus frequency.
ability of a material, depending on its density and specific heat, to store heat and to resist temperature change.
material or assembly of materials used to provide resistance to heat flow. Also see [[blanket thermal insulation]].
thermal insulation fill
insulation in granular, nodular, fibrous, powdery, or similar form designed for installation by pouring, blowing, or hand placement. Examples are mineral or glass fiber, cellulosic fiber, diatomaceous silica, perlite, silica aerogel, and vermiculite.
delay in action of the sensing element of a control device due to the time required for the sensing element to reach equilibrium with the property being controlled or measured.
the indoor thermal index value corresponding with a mean vote of neutral on the thermal sensation scale.
airflow created by a convective heat source that rises due to natural thermal buoyancy. Plume formation and growth are dependent on the intensity of the heat source and on the degree of stratification of the ambient air.
rate of radiant emission through unit solid angle over unit projected area of a source in a stated angular direction from the surface (usually the normal). Units are watts per square metre.
thermal radiant flux density
rate of radiant energy emitted from unit area of a surface in all radial directions of the overspreading hemisphere. See also [[radiant flux density]].
transmission of energy by means of electromagnetic waves emitted due to temperature. Radiant energy of any wavelength when absorbed may become thermal energy that increases the temperature of the absorbing body. See also [[heat transfer radiation coefficient]].
fraction of the incident radiation on a surface that is reflected from that surface. Note: for an opaque surface, the sum of reflectance, transmittance, and absorptance is unity at any wavelength of radiation.
the fraction of distribution system losses (gains for cooling) that are returned to the conditioned space.
(1) relay activated by change in temperature. (2) relay in which the displacement of the moving contact member is produced by heating of a part of the relay under the action of electric currents.
(R-value), the reciprocal of the time rate of heat flow through a unit area induced by a unit temperature difference between two defined surfaces of material or construction under steady-state conditions. Units of thermal resistance are h·ft2·°F/Btu (m2·°K/W). Thermal resistance is the reciprocal of the thermal conductance.
a conscious feeling commonly graded into the categories cold, cool, slightly cool, neutral, slightly warm, warm, and hot; it requires subjective evaluation.
(1) accumulation of energy in a body or system in the form of sensible heat (temperature rise) or latent heat (change of phase). (2) full storage: thermal storage system having capacity to meet all on-peak cooling or heating requirements by being charged off peak, and without energy added on peak. (3) fully charged condition: the state of a thermal storage device at which, according to the design, no more heat is to be removed from the thermal storage device. This state is generally reached when the control system stops the charge cycle as part of its normal control sequence. (4) fully discharged condition: the state of a thermal storage device at which no more usable cooling energy can be recovered from the storage device. (5) normally interchangeable term with cool storage or ice storage when addressing air-conditioning thermal storage systems. (6) technology or systems of accumulating cooling or heating capacity for subsequent use. (7) temporary storage of high or low-temperature energy for later use.
thermal storage efficiency
(also known as cycle figure of merit), ratio of the integrated discharge capacity to the hypothetical maximum available capacity for a single cycle of operation.
thermal storage load leveling
charging a thermal storage system at a constant rate during a complete cycle.
insulation of very high thermal resistance. Usually refers to that used in cryoengineering.
thermal time lag
(1) phase difference in hours between the exterior and interior surface temperatures when the exterior surface is subjected to a sine wave temperature change having a 24 h period. (2) time interval by which the peak thermal response falls behind (lags) the peak thermal excitation in a thermal system.
(also known as U-factor), heat transmission in unit time through unit area of a material or construction and the boundary air films, induced by unit temperature difference between the environments on each side. Note: this heat transmission rate is also called the overall coefficient of heat transfer. U, in Btu/h·ft2·°F (W/[m2·K]). Thermal transmittance is sometimes called the overall coefficient of heat transfer or U-factor. Thermal transmittance includes surface film conductance.
thermoelectrical element in which the electrical resistance falls appreciably with a rise in temperature; often used as a temperature sensor.
junction of two wires of dissimilar materials, not necessarily metal, with the property of generating an emf related to the temperature of their junction. Compare to [[thermopile]].
equilibrium in a system when the physical variables have uniform values that do not change in time. Furthermore, if the system is not an isolated one, these variables should have the same values for both the system and its surroundings.
those data needed to calculate the equilibrium relations among pressure, volume, and temperature along with the enthalpy and entropy of the fluid in the liquid and vapor states.
implosive impact in liquid, caused by sudden condensation of vapor into its subcooled liquid. This phenomenon can occur when the liquid is about 60°F to 85°F (33°C to 47°C) cooler than the saturation temperature of the contact vapor. It creates a loud sound and can cause severe local pressure stresses in the container or piping system.
in thermodynamics, a region in space or a quantity of matter bounded by a closed surface in which thermal actions occur. The surroundings include everything external to the system, and the system is separated from the surroundings by the system boundaries. These boundaries can be either movable or fixed, either real or imaginary.
steam (disk) trap constructed with a cap containing a steel disc, which fits against a flat seat. Condensate, discharging at close to saturation temperature, increases in velocity and draws the disc down toward the seat, due to the lower pressure caused by the increased velocity (Bernoulli effect). Condensate discharging from high to low pressure flashes off and creates the closing pressure above the disc within the cap. As this flash steam condenses, pressure is dissipated, and the cycle repeats. The trap has limited air venting capabilities.
mechanism that transfers energy from one system to another without accompanying transfer of entropy. Units of thermodynamic work are Btu (W·h).
Thermodynamics First law
law of conservation of energy, which can be expressed as follows: heat and work are mutually convertible; or because energy can neither be created nor destroyed, the total energy associated with an energy conversion remains constant.
photograph or two dimensional record of an image that maps the apparent temperature of a scene as sensed by an infrared imaging system.
process of generating a thermogram by using an infrared imaging system, usually with some means of temperature calibration.
thermometer electric resistance
a temperature measuring and display instrument in which an electric resistance varies as a function of temperature.
thermophotovoltaic cell (TPV)
A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation.
those data needed to calculate heat transfer and fluid flow characteristics of the fluid. Thermophysical properties include both thermodynamic (equilibrium) and transport properties.
a number of thermocouples wired consistently in series or parallel to measure small or average temperature differences.
circulation by the forces induced by the differences in densities of cooler and warmer fluids.
a tube, or coils with interconnecting piping, placed in supply and exhaust airstreams and filled with a refrigerant heat transfer fluid.
an automatic control device used to maintain temperature at a fixed or adjustable setpoint.
in a gas charged thermostat, a device that compensates for fluctuations caused by temperatures, in certain parts of the power system; different from the temperature of the bulb.
thermostatic balanced pressure steam trap
trap installed on the discharge side of a heating unit and designed to pass air freely on start-up and condensate at a subcooled temperature, but to prevent steam vapor passing into the return. It can have a bellows or encapsulated metallic diaphragm containing a small quantity of volatile liquid. At the bottom of the diaphragm or bellows is attached a hardened, self centering valve head operating on the pressure side of the valve seat. At ordinary temperatures and atmospheric pressure, the valve is fully open to permit free passage of air and cold condensate. The trap discharges at a fixed temperature below that of steam saturation temperature and closely follows the steam pressure/temperature curve.
thermostatic bimetallic steam trap
trap installed where low-temperature discharge is required. It incorporates a bimetallic element that, when heated, deflects and causes a downstream valve head to be drawn up, closing the orifice. It discharges air and cold condensate freely on start-up.
an automatic control device or system used to maintain temperature at a fixed or adjustable setpoint.
thermostatic expansion valve
a device for controlling superheat by regulating the mass flow of refrigerant to a refrigeration load, actuated by changes in equalizer pressure and temperature sensing element temperature.
device within an electric controller for completing or interrupting an electrical circuit in response to a temperature change.
Semiconductor material, typically measuring from 200-400 microns thick, that is cut from ingots or ribbons.
A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make photovoltaic cells.
thin film photovoltaic module
A photovoltaic module constructed with sequential layers of thin film semiconductor materials. See also amorphous silicon.
third octave (1/3) band sound pressure level
the sound pressure level at all frequencies contained within a 1/3 octave band filter.
three piece split system
any air conditioner or heat pump that has three major assemblies separated from each other. The compressor would be in a first assembly, with one refrigerant heat exchanger in a second assembly, and the second refrigerant heat exchanger in a third assembly.
three-phase electrical service
(1) electrical service of a three-phase power form. (2) electrical service supplied to the user by the utility company.
three-pipe air-conditioning system
multipiping arrangement in which each unit is fitted with two supply pipes (hot and chilled water) and a single return pipe common to the central heater and refrigerating system.
valve having either a single inlet and two outlets (diverting) or two inlets and a single outlet (mixing), in which either one or the other is open. Can also be a service valve for dual-mounted safety relief valves. See also diverting valve; [[mixing valve]].
threshold limit value®—time weighted average (TLV®—TWA)
(1) the time-weighted average concentration for a normal 8 hworkday and a 40 h workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. (2) the refrigerant concentration in air for a normal 8 h workday and a 40 h workweek to which repeated exposure, day after day, will not cause an adverse effect in most persons.
threshold limit values®
refers to airborne concentrations of substances and represents conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effects. Because of the wide variation in individual susceptibility, however, a small percentage of workers may experience discomfort from some substances at concentrations at or below the threshold limit; a smaller percentage may be affected more seriously by aggravation of a preexisting condition or by development of an occupational illness. Smoking of tobacco is harmful for several reasons. Smoking may act to enhance the biological effects of chemicals encountered in the workplace and may reduce the body’s defense mechanisms against toxic substances. Individuals may also be hypersusceptible or otherwise unusually responsive to some industrial chemicals because of genetic factors, age, personal habits (smoking, use of alcohol or other drugs), medication, or previous exposure. Such workers may not be adequately protected from adverse health effects from certain chemicals at concentrations at or below the threshold limits. An occupational physician should evaluate the extent to which such workers require additional protection. Threshold limit values® (TLVs®) are based on the best available information from industrial experience, from experimental human and animal studies, and, when possible, from a combination of the three. The basis on which the values are established may differ from substance to substance; protection against impairment of health may be a guiding factor for some, whereas reasonable freedom from irritation, narcosis, nuisance, or other forms of stress may form the basis for others. (This definition reprinted by permission of the American Conference of Governmental Industrial Hygienists [ACGIH].)
expansion (via flow restriction) across any orifice during which no mechanical work is transferred by the fluid to the surroundings.
change in controlled variable required to move the actuator or valve from one of its extreme limits of travel to the other.
the distance, in ft (m), from the center of the air device outlet to a point in the mixed airstream where the highest sustained velocity of the mixed airstream has been reduced to a specified level.
defrosting process automatically and intermittently operated for a predetermined period.
(1) time interval between the manifestation of a signal at one point and the manifestation or detection of the same signal at another point. Note: generally, the term “time delay” is used to describe a process whereby an output signal has the same form as the input signal causing it, but is delayed in time; that is, the amplification of all frequency components of the output are related by a single constant to those of corresponding input frequency components, but each output component lags behind the corresponding input component by a phase angle proportional to the frequency of the component. (2) time interval between when a command is given and when it is executed.
A wide band-gap semiconductor similar to indium oxide; used in heterojunction solar cells or to make a transparent conductive film, called NESA glass when deposited on glass.
(as applied to fenestration) bronze, green, blue, or gray coloring that is integral with the glazing material. Tinting does not include surface applied films such as reflective coatings, applied either in the field or during the manufacturing process.
the chemical TiCl4 that generates white visible fumes used in preliminary testing in laboratory fume hoods. (Caution: Titanium tetrachloride is corrosive and irritating; skin contact or inhalation should be avoided.)
ton day of refrigeration
heat removed by a ton of refrigeration operating for a day, 288,000 Btu (approximately 84.3 kWh).
ton of refrigeration
time rate of cooling equal to 12,000 Btu/h (approximately 3517 W). It is a quantity approximately equal to the latent heat of fusion or melting of 1 ton (2000 lb) of ice, from and at 32°F (0°C).
as applied to a fan, a type of excitation in which the external force is applied through the hub in the form of torque pulsations.
total AC load demand
The sum of the alternating current loads. This value is important when selecting an inverter.
total cooling effect
(1) amount of sensible and latent heat removed from the conditioned space. (2) difference between the total enthalpy of the dry air and the water-vapor mixture entering and leaving the cooler.
total harmonic distortion
The measure of closeness in shape between a waveform and it's fundamental component.
total internal reflection
The trapping of light by refraction and reflection at critical angles inside a semiconductor device so that it cannot escape the device and must be eventually absorbed by the semiconductor.
the pressure which exists by virtue of the degree of compression and the rate of motion. It is the algebraic sum of the velocity pressure and the static pressure at a point. Thus, if the fluid is at rest, the total pressure will equal the static pressure.
total pump head pressure
total pump head pressure is composed of four primary components: lift, column friction, surface requirements, and injection head.
total refrigerant heat rejection effect
total useful capacity of a refrigerant condenser for removing heat from the refrigerant circulated through it.
total refrigerating effect
(water or brine cooler), product of the mass rate of refrigerant flow and the difference in enthalpy of the entering and leaving refrigerant fluid, expressed in heat units per unit of time.
total refrigeration capacity
the product of the mass flow rate of refrigerant and the difference in enthalpy between the leaving and entering refrigerant, expressed in energy units per unit of time.
total suspended particulates
mass of particulates suspended in a unit volume of air as collected by an air sampler.
total thermal emittance
emittance that is an integrated average for all wavelengths of radiant energy emitted.
total heat load expressed in tons of cooling; the sum of the sensible tons (dry tons) and the latent tons (wet tons).
in a turbocompressor, the ratio of the variation of enthalpy of an isentropically compressed vapor to the work to be effectively supplied to the compressor (the enthalpy relating to the total pressure of the fluid at inlet and the static pressure at outlet).
(also known as stagnation efficiency), in a turbocompressor, the ratio of the variation of enthalpy of the vapor isentropically compressed from the total pressure at inlet to the total pressure at outlet to the work effectively supplied to the compressor.
vertical vessel filled with plates or suitable packing, through which scrubbing fluid flows upward through the liquid, separating entrained liquids or solids from the gas.
the ability of a substance to be harmful or lethal due to acute or chronic exposure by contact, inhalation, or ingestion. The effects of concern include, but are not limited to, those of carcinogens, poisons, reproductive toxins, irritants, corrosives, sensitizers, hepatoxins, nephrotoxins, neurotoxins, agents that act on the hematopoietic system, and agents that damage the lungs, skin, eyes, or mucous membranes.
toxicity of a refrigerant
the ability of a refrigerant to be harmful or lethal due to acute or chronic exposure by contact, inhalation, or ingestion. The effects of concern include, but are not limited to, those of carcinogens, poisons, reproductive toxins, irritants, corrosives, sensitizers, hepatoxins, nephrotoxins, neurotoxins, agents that act on the hematopoietic system, and agents that damage the lungs, skin, eyes, or mucous membranes.
A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.
a written document that details the expectations, schedule, budget, and deliverables of commissioning process activities related to training of project operating and maintenance personnel, users, and occupants.
(1) a device designed to receive energy from one system and supply energy, of either the same or of a different kind, to another system in such a manner that the desired characteristics of the input energy appear at the output. (2) a device that changes one form of physical quantity into another. In the measurement field, transducers are generally used to sense a variety of measurands, such as line voltage, current, power, pressure, and temperature, and to convert these to a common output signal for use with a controlling or recording instrument.
air transferred from one room to another through openings in the room envelope, whether it is transferred intentionally or not. The driving force for transfer air is generally a small pressure differential between the rooms, although one or more fans may be used.
a piece of electrical equipment used to convert electric power from one voltage to another voltage.
pulse or other temporary phenomenon occurring in a system that is not in a steady-state condition.
the state in which the system undergoes a normal change in operation, such as thermostat cycling or actuation of a defrost control.
at a stated pressure, the temperature (or at a stated temperature, the pressure) at which two phases exist in equilibrium; that is, an allotropic transformation temperature (or pressure).
transport of substances, energy, or indicated values from one place to another with or without impedances.
reduction in magnitude of some characteristic of a power or a signal between two stated points in a system.
portion of thermal radiation incident on a physical surface that is transmitted through that surface. Compare to [[thermal transmittance]]. Note: thermal transmittance usually is used for heat flow through walls, but transmittance (or transmissivity) is more often referred to as a radiation property.
transparent conducting oxide (TCO)
A doped metal oxide used to coat and improve the performance of optoelectronic devices such as photovoltaics and flat panel displays. Most TCO films are fabricated with polycrystalline or amorphous microstructures and are deposited on glass. The current industry-standard TCO is indium tin oxide. Indium is relatively rare and expensive, so research is ongoing to develop improved TCOs based on alternative materials.
transport property data
properties that describe the capability of a fluid to transfer heat and momentum, typically thermal conductivity and dynamic or kinematic viscosity.
device for preventing passage of one type of fluid, often while allowing other fluids to proceed. Compare to [[steam trap]].
trend log (trend record)
record of events taken on a regular schedule or equal time intervals or by change of state or value.
particular temperature and pressure at which three different phases of one substance can coexist in equilibrium. Water is an example of a substance that has a well known triple point.
(also known as luminaire), electric lighting fixture that may be equipped with a means to provide for air supply, air return, and/or heat extraction.
wall that is sun facing and built from material that can act as a thermal mass (such as stone, metal, concrete, adobe, or water tanks). A highmass wall that stores heat from solar gain during the day and slowly radiates the heat.
true solar time
local standard time adjusted by the equation of time (determined from an astronomical almanac) and the longitude correction (four times the difference between the standard longitude of the observer’s time zone and the observer’s actual longitude). A time reference used to compute the apparent position of the sun.
tubular conduit for transport of fluids or finely divided solids; also, a hollow structural member; a hollow product of round or other cross section. A tube may be helical welded, lap welded, spiral welded, butt welded, or seamless. A tube is designated by its exact outside diameter and its exact wall thickness, which may be described in gage numbers or other units. As an example, copper tube is commonly used in the piping and plumbing industry and the normal wall thickness is 0.125 in. (3.2 cm). When describing the outside diameter, it is referred to as copper tube. When describing the nominal pipe size, it is referring to the inside diameter. Tube or tubing identifies the outside diameter. Pipe or piping identifies the inside diameter.
(plate evaporator), evaporator constructed from a pair of plates assembled to form a shallow compartment containing a coil through which refrigerant flows, with the fluid to be cooled circulating in the compartment.
condenser consisting of a tube inserted in a second tube in a helical coil, serpentine coil, or parallel tubes.
(plate coil), type of extended surface evaporator consisting of one or several metal sheets with a coil through which refrigerant flows, brazed to one face.
(1) axial fan whose blades revolve in a cylindrical casing. The term “ducted fan” is used when the casing is of substantial length. (2) propeller or disc-type wheel within a cylinder, and including driving-mechanism supports for either belt drive or direct connection.
formation over a surface of scattered, knob-like mounds of localized corrosion products.
tubular centrifugal fan
(also referred to as an in-line fan) a centrifugal impeller located within a cylindrical or rectangular housing, discharging in an axial direction. Its performance is similar to that of a centrifugal blower except its capacity and pressure are lower due to the less efficient fan arrangement.
chilled, elongated space for cooling foodstuffs on a movable transport system by rapid circulation of cold air.
elongated enclosure provided with rapid cold air circulation for the freezing of foodstuffs. Also called a freezing tunnel or blast freeze tunnel.
Quantum mechanical concept whereby an electron is found on the opposite side of an insulating barrier without having passed through or around the barrier.
fluid-energized acceleration machine for generating rotary mechanical power from the energy in a fluid stream.
phenomenon of instability that may occur in centrifugal or axial flow compressors, characterized by aerodynamic blockage or the breakaway of the flow from certain sections of the passage between the blades.
turboexpander (expansion turbine)
in cold air or gas refrigeration cycles, a turbine in which the compressed gas expands and produces mechanical energy.
fluid flow in which the velocity varies in magnitude and direction in an irregular manner throughout the mass. Turbulent flow exists when the Reynolds Number exceeds a value of 2000 to 4000.
a series of single thickness or airfoil radius sheet metal guides placed within a rectangular duct elbow to reduce turbulence and associated pressure drop within the elbow and to direct air around the bend.
two piece split system, indoor/indoor
any air conditioner or heat pump that has two major assemblies separated from each other with both assemblies being indoor. The compressor and one refrigerant heat exchanger would be in one assembly, with the other refrigerant heat exchanger in a second assembly.
A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).
piping system in which the fluid withdrawn from the supply passes through a heating or cooling unit to a separate return main.
a modulating control that both cycles a controlling device between two preset conditions, could be between OPEN and CLOSED, or between ON and OFF, or between two stages or levels of capacity control.
(1) single temperature controller designed to control temperature at two distinct setpoints. (2) thermostat that handles two separate circuits in sequence.
valve having a single inlet and single outlet. Uses of two way valves could be for throttling, isolation, or shutoff.
Type I hood
a hood designed to capture smoke and/or grease-laden vapor produced by a cooking process, incorporating listed grease removal devices and fire suppression equipment. Type I hoods fall into two categories: listed and nonlisted. Listed hoods have been tested in accordance with UL Standard 710.1. Conventional, or nonlisted hoods are hoods that meet the design, construction, and performance criteria of the applicable national and local codes.