ASHRAE Terminology

recirculate absorbent solution over the absorber tube bundle to ensure adequate wetting of the absorber surfaces. These pumps are not found in all equipment designs.

a component or system able to meet specified design parameters under actual load.

an entity identified by the owner who leads, plans, schedules, and coordinates the activities needed to implement the building acceptance testing activities. The acceptance representative may be a qualified employee or consultant of the owner. The individual serving as the acceptance representative shall be independent of the project design and construction management, though this individual may be an employee of a firm providing those services.

a model that relates indoor design temperatures or acceptable temperature ranges to outdoor meteorological or climatological parameters.

ASHRAE Advanced Energy Design Guide

(1) controlled stream of air moving across the height and width of an opening with sufficient velocity and volume to reduce the infiltration or transfer of air from one side of the opening to the other and to inhibit insects, dust, and debris from passing through. (2) In a refrigerated display cabinet, air flow designed to go from the air discharge toward the air return, thereby limiting both heat and mass transfers between the cabinet's net volume and the surrounding environment.

any diffuser system designed to, both, convey air within a room, space, or area and diffuse air into that space while operating under positive pressure. Systems are commonly constructed of, but not limited to, fabric or plastic film.

interior and exterior air surface film coefficients for winter and summer design conditions.

ratio of the rate of useful, sensible heat removal from the conditioned space to the energy input to the supply and return fan motor(s), expressed in consistent units and within designated operating conditions.

modular air-terminal device designed to diffuse air to the treated space from a pressurized plenum through holes or slots in the ceiling surface or the supporting framework. Also see air terminal device.

construction in which the building envelope is designed with a continuous air barrier.

the ratio of path pressure drop, including fully open control damper pressure drop, to the pressure drop across the fully open damper at design flow.

product of the volts and amperes of a circuit. This product generally is divided by 1000 and designated in kilovolt-amperes (kVA). It comprises both real and reactive power.

part-load value based on operation at actual design conditions. Typically used in system design and specification.

thermostat designed for use in water.

designation reserved, usually by law, for a person professionally qualified and duly licensed to perform architectural services, including, but not necessarily limited to, analysis of project requirements, creation and development of project design, preparation of drawings, specifications and bidding requirements, and general administration of the construction contract.

International, diverse organization representing building system design and industrial processes professionals around the world. (Formally known as American Society of Heating, Refrigerating and Air-Conditioning Engineers.)

International, diverse organization representing building system design and industrial processes professionals around the world. (For the US Internal Revenue Service (IRS), known as the American Society of Heating, Refrigerating and Air-Conditioning Engineers.)

This is a genus that includes several hundred species of mold. Some species can cause paranasal sinus infections or Aspergillosis. Aspergillus is of particular concern in health care facilities because many patients already have compromised immune systems. If HVAC systems are not properly maintained or designed, mold growth may be likely.

(1) implementation of process by automatic means. (2) investigation, design, development, and application of methods of rendering processes automatic, self moving, or self controlling. (3) theory, art, or technique of making a process more automatic.

device designed to prevent reverse flow in a water system. Note: term normally used where back-pressure-type backflow is implied.

program, ordinance, or code designed to prevent backflow into a potable water system and to discover, eliminate, and prevent all uncontrolled cross connections, existing or potential.

fluid flows where the design supply flow volumetric rate equals the design return/exhaust volumetric rate. Also called balanced ventilation or balanced system.

the methodical proportioning of air and hydronic flows through the system mains, branches, and terminal devices using acceptable procedures to achieve the specified airflow or hydronic flow within testing, design, and installation limitations.

a computer representation of a hypothetical design based on the proposed building project. This representation is used as the basis for calculating the baseline building performance for rating above standard design.

the annual energy cost for a building design intended for use as a baseline for rating above standard design.

the measurements and facts describing facility operations and design during the baseline period. This will include energy use or demand and parameters of facility operation that govern energy use or demand.

a document that records the concepts, calculations, decisions, and product selections used to meet the Owner’s Project Requirements and to satisfy applicable regulatory requirements, standards, and guidelines. The document includes both narrative descriptions and lists of individual items that support the design process.

boiler designed especially for gas and oil and sold integrally with the burner.

design maximum rate of heat output.

carryover of boiler water with the steam due to insufficient steam space, faulty boiler design, or operating conditions. Compare to foaming.

design maximum rating of a steam or water boiler expressed as the total heat transferred by the heating surfaces in Btu/h (kW). Sometimes expressed in horsepower or pounds (torque, kilograms) of steam per hour. Compare to boiler capacity.

a computer representation of a hypothetical design based on the actual proposed building design. This representation is used as the basis for calculating the energy cost budget.

the officer or other designated representative authorized to act on behalf of the authority having jurisdiction.

parts design and manufacturing method utilizing a computer database where drawings are not needed. Synonymous with computer integrated manufacturing.

(1) measure of the maximum amount of energy or material that may be stored in a given system. See also nameplate rating, air-conditioner capacity. (2) the rate of heat removal by the refrigerant used in the compressor or condensing unit in a refrigerating system. This rate equals the product of the refrigerant mass flow rate and the difference in the specific enthalpies of the refrigerant vapor at its thermodynamic state entering the compressor or condensing unit and refrigerant liquid at the thermodynamic state entering the mass flow control device. (3) the rate that heat is removed or added to a system. (4) maximum load for which a machine, apparatus, device, or system is designed or constructed.

fan in which the air enters the impeller axially and leaves it substantially in a radial direction. Fan rotor or wheel within a scroll-type casing (shroud) that includes supports for either belt drive or direct connection. Centrifugal-fan-types are as follows: forward curve, backwardly inclined (backward curved), airfoil, or radial blade design. Fans can be provided as single width, single inlet (SWSI) or double width, double inlet (DWDI) configurations and are limited to 16 predefined arrangement types based on discharge location and rotation.

outdoor temperature the designer selects as the point of changeover from cooling to heating by the HVAC system.

(1) direct-expansion chillers are complete refrigerating systems consisting of a compressor, condenser, and evaporator with all operating and safety controls. Compressor types include the following: reciprocating, centrifugal, or screw design. Compare to absorption chiller. (2) refrigerating machine used to transfer heat between fluids. Chillers are either direct expansion with a compressor or absorption type.

a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically at a predetermined overcurrent without damage to itself (when properly applied within its rating).

free flow propeller fan designed to circulate the air in a room without any air duct.

a device that is designed for use in pumping water with a maximum nonabsorbent free solid content of 0.016 lb/ft3 (0.26 kg/m3) and a maximum dissolved solid content of 3.1 lb/ft3 (50 kg/m3), provided that the total gas content of the water does not exceed the saturation volume, and disregarding any additives necessary to prevent the water from freezing at a minimum of 14°F (–10°C).

(1) ratio of the rate of net heat output to the total energy input expressed in consistent units and under designated rating conditions. (2) ratio of the refrigerating capacity to the work absorbed by the compressor per unit time.

the ratio of the rate of heat delivered to the rate of energy input, in consistent units, for a complete heat pump system, including the compressor and, if applicable, auxiliary heat, under designated operating conditions.

cold room designed to receive and store produce sometimes already cooled down to approximately the desired storage temperature.

a unit that is designed to provide space heating and potable water heating from a single, primary energy source.

a complete ceiling panel that is designed and can be independently installed and operated for both sensible cooling and sensible heating of an indoor space through heat transfer between the thermally effective panel surfaces and the occupants and/or the indoor space by thermal radiation and natural convection.

a quality-focused process for enhancing the delivery of a project. The process focuses on verifying and documenting that the facility and all of its systems and assemblies are planned, designated, installed, tested, operated, and maintained to meet the Owner’s Project Requirements (OPR).

a quality-focused process for enhancing the delivery of a project. The process focuses upon verifying and documenting that the facility and all of its systems and assemblies are planned, designed, installed, tested, operated, and maintained to meet the Owner’s Project Requirements. (See Owner’s Project Requirements).

(1) design maximum rate of heat removal by the refrigerant assigned to the compressor in a refrigerating system. This is equal to the product of the mass rate of refrigerant flow produced by the compressor and the difference in specific enthalpies of the refrigerant vapor at its thermodynamic state entering the compressor and the refrigerant liquid at saturation temperature corresponding to the pressure of the vapor leaving the compressor. (2) device, such as a clearance pocket, movable cylinder head, or suction bypass, by which compressor capacity can be adjusted without otherwise changing the operating conditions.

a refrigerating component, designed to compress a specific refrigerant vapor, consisting of compressor, prime mover, and regularly furnished accessories.

equivalent to conventional drafting, only performed on a computer. Points, lines, and symbols are used to convey design intent or detail construction means and methods. Most often plotted onto paper media and published in that form for drawings and specifications and delivered to the owner, contractor, and reviewing authorities and agencies for approval and actual construction.

(1) an apparatus for processing low-pressure refrigerant vapor back into high-pressure liquid refrigerant to be used for cooling a refrigerator. (2) machine designed to condense refrigerant vapor to a liquid by compressing the vapor in a positive displacement compressor and rejecting heat to a cooling medium. A condensing unit usually consists of one or more positive displacement compressors and motors, condensing coils, liquid receivers, and other devices mounted on a common base.

(1) the methods and means of governing the performance of any apparatus, machine, or system. (2) system governing the starting, stopping, direction of motion, acceleration, speed, and retardation of the moving member. (3) designation of how the equipment is governed (i.e., by an attendant, by automatic means, or partially by automatic means and partially by an attendant). (4) one or more of the components in a mechanism responsible for interpreting and carrying out manually initiated directions.

surface designed to transfer its heat to a surrounding fluid largely or wholly by forced and/or natural convection.

(also known as total cooling capacity), design maximum rate at which equipment removes heat from a fluid under specified conditions of operation.

the outdoor dry-bulb temperature equal to the temperature that is exceeded by 1% of the number of hours during a typical weather year.

the outdoor wet-bulb temperature equal to the temperature that exceeds a stated number of hours during a typical weather year. The value is normally stated as a percent. This value is applicable to cooling systems where the main purpose is dehumidification and the prevention of mold and mildew.

directional pattern of the heat transfer fluids used in energy-exchange equipment where the warmest fluid “A” indirectly contacts the warmest fluid “B” at the entering side of the equipment and the coldest fluid “A” indirectly contacts the coldest fluid “B” at the leaving side of the equipment. Most energy exchange equipment is designed to use this method of heat transfer as it creates the highest log mean temperature difference (LMTD). When an energy exchange equipment is designed for counterflow heat transfer, and it is correctly connected in the field, the results would be loss in heat transfer capacity.

device designed for producing an ultrahigh vacuum by condensation or adsorption of a gas at a very low temperature, usually below –320°F (–196°C, 77 K).

the combined power in kilowatts of all the ITE loads for which the ITE system was designed. The data center ITE power shall not include any additional loads, such as cabinet fans or other devices, that are not inherent parts of the ITE, even if the loads are part of the UPS operational design load.

designated individual responsible for risk management of a given facility.

equipment and controls designed to remove frost (ice) from cooling coils of a refrigerating system.

air temperature which an HVAC system or apparatus is designed to maintain (indoor design air temperature) or to operate against (outdoor design air temperature).

required airflow when the system is operating under assumed maximum conditions of design, including diversity.

output capacity of a system or piece of equipment at design conditions.

specified environmental conditions, such as temperature and light intensity, required to be produced and maintained by a system and under which the system must operate.

the design electrical loss component for the data center or data center addition shall be the combined losses (or the losses calculated from efficiencies) of three segments of the electrical chain: incoming electrical service segment, UPS segment, and ITE distribution segment. The design ELC shall be calculated using the worst-case parts of each segment of the power chain in order to demonstrate a minimum level of electrically efficient design. The design ELC does not, and is not intended to, integrate all electrical losses in the facility.

the annual energy cost calculated for a proposed design.

an initial version of the operating manual developed in the conceptual design stage. It contains a description of the building functions for which the design is intended, lists the design parameters of systems to perform these functions, and provides a brief description of the operating routines that are to be followed to comply with the functional requirements of the building.

a detailed, written document evolving throughout the commissioning process, clearly defining items and criteria of the design intent.

peak instantaneous load that a system is expected to meet.

the maximum allowable working pressure that a system, a part of a system, or an apparatus is designed to and/or can withstand.

individual responsible for the design and preparation of architectural or engineering contract documents. An architect or engineer licensed to practice in accordance with applicable state licensing laws.

(1) the temperature at which a system or zone is meant to maintain. (2) the temperature, or range of temperatures, at which a piece of equipment is selected to perform.

specific voltage for which a line or piece of equipment is designed. A reference level of voltage for identification and not necessarily the precise level at which it operates.

in the United States, the maximum working pressure for which an apparatus has been designed. See design pressure. In some countries, the design pressure is greater than the maximum working pressure. Compare to operating pressure.

piece of equipment or a mechanism designed to serve a special purpose or to perform a special function.

flue designed to effect the dilution of flue gases with air before discharge from an appliance.

filters that are designed to operate through a specified performance range and then be discarded and replaced. An example is the cartridge filter.

a backflow prevention device designed to protect water supplies from contamination. It consists of two check valves assembled in series, usually with a ball valve or gate valve installed at each end for isolation and testing. Often, test cocks (very small ball valves) are in place to attach test equipment for evaluating whether the double-check assembly is still functional. The double-check valve assembly is suitable for prevention of back pressure and back siphonage but is not suitable for high-hazard applications. It is commonly used on lawn irrigation, fire sprinkler, and combi-boiler systems. May also be referred to as double-check assembly (DCA).

device designed to serve also as a detector check on fire-protection systems where pollutants are involved. Note: DDC includes a line size, approved double-check valve backflow preventer with a metered bypass, into which has been incorporated a three-quarter inch, approved, double-check valve backflow preventer.

one designed with airflow essentially in a vertical path, discharging air at or near the bottom of the furnace.

a device that is not an integral part of the furnace or boiler and is connected to the furnace or boiler by a short length of flue pipe. It is designed to (a) provide for the exhaust of the products of combustion in the event of no draft, back draft, or stoppage beyond the draft hood, (b) prevent a back draft from entering the furnace, and (c) neutralize the effect of stack action of the chimney or gas vent upon the operation of the furnace.

graphic and pictorial document showing the design, location, and dimensions of the elements of a project.

(1) pneumatic thermostat designed to maintain one temperature during the day and a lower temperature during the night. (2) changes thermostat output from direct acting (DA) to reverse acting (RA) for seasonal changeover. (3) two temperature controls in one enclosure.

burner designed to burn either gas or oil (but not both simultaneously).

a listed, packaged system incorporating a hood, a fan, and air-treatment devices designed to remove most grease and particulate matter from the airstream before reintroducing the treated air into the occupied space.

(1) capability of a building, assembly, component, product, or construction to maintain serviceability for which it was designed over at least a specified time, based on assumed levels of use and maintenance. Compare to serviceability. (2) the average expected service life of a system or facility. Individual manufacturers quantify durability as design life, which is the average number of hours of operation before failure, extrapolated from accelerated life tests and from stressing critical components to economic destruction.

for devices whose renewal mechanism is designed to restore the performance characteristics of the device to starting conditions, dust -holding capacity per cycle is determined by feeding dust until a steady-state condition is achieved. The dust-holding capacity per cycle is averaged over at least four cycles. The result is expressed in g/cycle to the nearest gram.

thermometer designed to indicate temperature by closing in succession a series of electrical contacts.

(1) comparison of electricity use to electric demand for a given time period, calculated by dividing electricity usage in kilowatt hours (kWh) by the product of electric demand in kilowatts (kW) times the hours in the period. (2) ratio of average load in kilowatts supplied during a designated period to the peak or maximum load in kilowatts occurring in that period.

case enclosing electrical equipment and wiring that is designed expressly to prevent (1) a person from accidentally contacting uninsulated energized parts, (2) burning or molten materials from contacting adjacent combustible materials or falling onto combustible materials, (3) conductive or combustible materials from dropping on uninsulated energized parts, and (4) mechanical abuse of electrical equipment not designed or approved to withstand the intended normal use without such additional enclosure.

semiconductor device designed to operate without mechanical contacts (e.g., SCR).

two-dimensional graphic representation of the design, location, and dimensions of a project, or parts thereof, seen in a vertical plane viewed from a given direction.

the annual energy cost for the budget building design.

(1) ratio of net cooling capacity in Btu/h to total rate of electric input in watts under designated operating conditions. (2) ratio of the net total cooling capacity to the effective power input at any given set of rating conditions, in watts per watt.

heat exchanger assembly for transferring heat between two isolated fluid sources. The recovery system may be of air-to-air design or a closed loop hydronic system design. The system will include all necessary equipment such as fans and pumps, associated ducts or piping and all controls (operating and safety), and other custom-designed features.

an organization that designs, procures, installs, and possibly maintains one or more energy conservation measures (ECMs) at an owner’s facility or facilities.

energy use value to which a building is designed.

the discipline, art, and profession of acquiring and applying technical, scientific, and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or invention.

all of the elements over which a designer has no control and that affect a system and its input or output.

(also known as climatic chamber), enclosed space designed to create a particular environment.

building or portion of a building serving one of the following functions: \na) hospitals and other health care facilities having surgery or emergency treatment facilities\nb) fire, rescue, and police stations and emergency vehicle garages\nc) designated earthquake, hurricane, or other emergency shelters\nd) designated emergency preparedness, communication, and operation centers and other facilities required for emergency response\ne) power-generating stations and other public utility facilities required as emergency backup facilities for other essential facilities\nf) structures containing highly toxic materials where the quantity of the material exceeds the maximum allowable quantities\ng) aviation control towers, air traffic control centers, and emergency aircraft hangars, or \nh) buildings and other structures having critical national defense functions

the outdoor wet-bulb temperature used in conjunction with the mean coincident dry-bulb temperature, often used for the sizing of evaporative systems such as cooling towers.

device or switch designed to disconnect load from a power source or distribution center under an overload or short-circuit condition.

(1) a machine used to create flow within a fluid, typically a gas, such as air. (2) any device with two or more blades or vanes attached to a rotating shaft used to produce an airflow for the purpose of comfort, ventilation, exhaust, heating, cooling, or any other gaseous transport. The opening(s) may or may not have an element or elements for connection to ductwork. (3) fan consists of a rotating arrangement of vanes or blades that act on the air (impeller). Usually it is contained within some form of housing or case. This housing or case may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors and internal combustion engines. Fans produce airflows with high volume and low pressure, as opposed to compressors, which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan. (4) see also impeller.

the sum of the nominal power demand (nameplate horsepower) of motors of all fans that are required to operate at design conditions to supply air from the heating or cooling source to the conditioned space(s) and return it to the source or exhaust it to the outdoors.

an alphanumeric designation assigned to each symbol for ease in referencing.

firefighter's smoke control station (FSCS) includes monitoring and overriding capability over smoke-control systems and equipment provided at designated location(s) within the building for use by the fire department.

(1) a perforated plate installed downstream of a fan in an air-handling unit designed to diffuse airflow equally across a downstream coil. Also called a diffuser plate. (2) in a multiple cooling tower installation, a pipe installed below and interconnecting the cold basin of multiple cooling towers to equalize the basin water levels and prevent the sump suction in one tower from drawing air or creating a vortex. (3) in refrigeration, a line or lines installed between compressors to equalize oil levels. (4) the bypass pipe in a primary/secondary flow system that hydronically decouples the primary from the secondary pumping system. See cross connection.

that portion of an appliance designed for attachment to a chimney, vent connector, or a draft hood.

an electrical or mechanical device in the flue outlet or in the inlet of or upstream of the draft control device of an individual, automatically operated, fossil-fuel-fired appliance that is designed to automatically open the flue outlet during appliance operation and to automatically close the flue outlet when the appliance is in a standby condition.

chamber designed to capture the products of combustion and accompanying excess air.

an electric, gas, or oil-burning appliance designed to supply heat through a system of ducts with air as the heating medium. Forced-air furnaces circulate the heated air by means of a fan or blower, whereas gravity furnaces depend primarily on natural convection.

(1) the process of determining the ability of the HVAC system to deliver heating, ventilating, and air-conditioning services in accordance with the final design intent. (2) that full range of checks and tests carried out to determine if all components, subsystems, systems, and interfaces between systems function in accordance with the contract documents. In this context, function includes all modes and sequences of control operation, all interlocks and conditional control responses, and all specified responses to emergency conditions.

a containment system for the transportation of air and grease vapor. The system is designed and installed to reduce the possibility of the accumulation of combustible condensation, thus reducing the possibility of damage if a fire occurs within the ventilation system.

a listed device (such as, but not limited to, baffle filters, removable extractors, and stationary extractors) designed and installed to remove grease vapor and/or particles from the airstream, .

load (uncorrected) that a machine, apparatus, device, or system is designed to deliver.

the outdoor dry-bulb temperature equal to the temperature that is exceeded at least 99.6% of the number of hours during a typical weather year.

switch designed to stop the compressor or machinery when the discharge pressure reaches a predetermined high value.

describes a building or space that has been specifically designated as historically significant by the adopting authority or is listed in The National Register of Historic Places or has been determined to be eligible for such listing by the U.S. Secretary of the Interior.

a device designed to capture cooking and/or ware washing effluent. See Type I hood and Type II hood.

units using inches, pounds, and other designations. Examples are: foot, Btu, horsepower, gallon. As compared to SI unit system.

thermometer designed for the visual display of temperature.

a perceived indoor experience of the building indoor environment that includes aspects of design, analysis, and operation of energy efficient, healthy, and comfortable buildings. Fields of specialization include architecture, HVAC design, thermal comfort, indoor air quality (IAQ), lighting, acoustics, and control systems. See indoor air quality (IAQ).

person(s) designated by governing codes to inspect installed systems for compliance with regulations.

a device that is an integral part of a furnace or boiler and is designed to (a) provide for the exhaust of the products of combustion in the event of no draft, back draft, or stoppage beyond the draft diverter, (b) prevent a back draft from entering the furnace, and (c) neutralize the effect of stack action of the chimney or gas vent upon the operation of the furnace.

(1) more than one building system, such as lights and air distribution, combined into a common design. (2) system in which many subsystems of a building are combined into a single package (e.g., fire, security, clock, and HVAC).

small back-pressure- and back-siphonage-type backflow prevention device designed to operate under continuous pressure, for use where certain quasi contaminants are involved.

facility acceptable to the local, national, or international recognized authority having jurisdiction and which provides uniform testing and examination procedures and standards for meeting design, manufacturing, and factory testing requirements.

any operation designed to reveal a leak in a system.

controller designed to provide limit control.

(1) a factory-made assembly of elements in which the heat is transferred from the liquid to the refrigerant, causing the refrigerant to evaporate and the liquid to be cooled. (2) heat exchanger designed to cool liquids.

summary of thermal or other energy loads in a system over a period of time. Note: for example, a common load profile on a peak design day for thermal storage designs would show hourly system load requirements for 24 hours.

electric, gas, or oil-burning appliance designed to supply low-pressure steam or hot water for space-heating application. A low-pressure steam boiler operates at or below 15 psig [103 kPa (gage)] steam pressure, a hot-water boiler operates at or below 160 psig [1100 kPa (gage)] water pressure and 250°F (120°C) water temperature.

(also known as suction pressure safety cut-out), switch designed to stop the compressor motor when the suction pressure reaches a predetermined low value.

air terminal device that is designed for thermally controlled ventilation (e.g., displacement flow applications). Also see air terminal device.

a complete lighting unit consisting of a lamp or lamps together with the housing designed to distribute the light, position and protect the lamps, and connect the lamps to the power supply.

a space that is designed to safely house compressors and pressure vessels.

the period of time within which charging of the thermal storage device must be completed. This period is typically determined by the utility rate structure, the building operating schedule, and the design operating strategy.

see design pressure.

scaled rating of the effectiveness of air filters. The scale is designed to represent the worst-case performance of a filter when dealing with particles in the range of 0.3 to 10 micrometers. The MERV rating is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass, with a MERV rating of 16 filter capturing more than 95% of particles over the full range.

an encased, factory-made assembly or assemblies designed to be used as permanently installed equipment to provide conditioned air to an enclosed space(s). It normally includes multiple evaporators, compressor(s), and condenser(s). Such equipment may be provided in more than one assembly, the separated assemblies of which are intended to be used together.

specific activities, technologies, or equipment designed or deployed to capture or control substances upon loss of containment to minimize exposure of the public or the environment. Passive mitigation means equipment, devices, or technologies that function without human, mechanical, or other energy input. Active mitigation means equipment, devices, or technologies that need human, mechanical, or other energy input to function.

in a system undergoing vibration, a mode of vibration designates the characteristic pattern of displacement assumed by the system vibrating at one of its resonance frequencies.

boiler designed and constructed to include increments of capacity.

full-load, continuous rating of a generator, prime mover, or other equipment under specified conditions, as designated by the manufacturer and usually indicated on an attached plate. Compare to capacity.

reference dimension used for designation, calculation, and application of duct and fitting.

devices that are designed to operate through a specified performance range and then be manually cleaned or reconditioned by equipment not included in the air cleaner itself. An example is the washable expanded metal filter.

designer specializing in the operations and maintenance aspects of the project.

(1) collection of data in a control system in order to produce the best possible output, usually in accordance with what is most economical. (2) procedure used in the design of a system to maximize or minimize some performance index. May entail the selection of a component, a principle of operation, or a technique. (3) refinement of a system to reduce its energy requirements.

charge achieving maximum possible refrigerant effect within design limitations.

a control system that is designed to automatically adjust the start time of an HVAC system each day with the intention of bringing the space to desired occupied temperature levels immediately before scheduled occupancy.

ratio of the useful energy at the point of use to the thermal energy input over a designated time period.

pressure in excess of the designed normal operating range.

used in most lithium bromide equipment to achieve design performance. The typical additive is one of the octyl alcohols.

a calculation procedure that generates an index of merit for the performance of building designs that substantially exceed the energy efficiency levels required.

radiometer designed for measuring luminous intensity, luminous flux, or illumination.

two dimensional graphic representation of the design, location, and dimensions of a project, or parts thereof, seen in a horizontal plane viewed from above.

(also called plenum box and plenum chamber) (1) a compartment or chamber, to which one or more ducts are connected, that forms a part of the air-distribution system and that is not used for occupancy or storage. A plenum often is formed in part or in total by portions of the building. (2) an air compartment that is attached to, or is an integral part of, a forced-air furnace which is designed to either distribute the heated air after it leaves the heat exchanger in the case of a supply plenum or to collect air that enters the return inlet in the case of a return plenum. (3) component forming an interface between a ductwork and one or more air terminal devices, by virtue of its design or by the inclusion of accessories, it can also be used to equalize the pressure/velocity across the air terminal device.

fan assembly consisting of a single inlet impeller mounted perpendicular to airflow that pressurizes a plenum chamber in an air-distribution system. The impeller is typically an airfoil or backward-inclined design.

the design that permits the continued operation of the combustion blower in a power vented unit, power burner unit, or forced draft unit for a period of time after the main burner is shut off for the purpose of venting of residual flue gas in the heat exchanger and the venting system.

(also referred to as an up blast fan). A fan designed for curb mounting on a roof or, within size and design constraints, for wall mounting. Air enters the fan in a typical axial arrangement but discharges radially from the centrifugal impeller and turns 90 degrees to exit through the top of the fan. It may be listed under UL Standard 705, Standard for Power Ventilators, in accordance with UL Subject 762, “Outline of Investigation for Power Roof Ventilators for Restaurant Exhaust Applications.”

a fan consisting of a centrifugal or axial impeller with an integral driver in a weather-resistant housing and with a base designed to fit, usually by means of a curb, over a wall or roof opening.

fan consisting of a centrifugal- or axial-type impeller with integral driver in a weather-resistant housing with base designed to fit (usually by means of a curb) over a wall or roof opening.

an elaboration of the design intent that includes operating information developed during the construction documents design stage.

for energy compliance alternatives , a prescriptive design includes specified assumptions concerning shape, orientation, HVAC, and other system design features. The prescriptive design is compared with the proposed design using the annual energy cost method.

(1) a pressure-actuated (not temperature-actuated) valve or rupture member designed to automatically relieve excessive pressure. (2) means for relieving internal pressure and preventing explosive shattering of the housing. (3) valve or rupture member designed to relieve excessive pressure automatically.

a pressure-responsive electronic or mechanical control designed to automatically stop the operation of the pressure-imposing element at a predetermined pressure.

valve providing maintenance of designated pressure level within a system.

an air cooler designed for use with external elements that impose air resistance.

the annual energy cost calculated for a proposed design.

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

designated spaces freely accessible to the public. These include parking areas, secured entrances and areas, entrance lobbies, reception and waiting areas, public toilets, snack bars, cafeterias, vending areas, gift shops and other retail locations, health education libraries and meeting rooms, chapels, and gardens.

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.

(1) device designed to intercept radiated heat. (2) in a furnace, a sheet of metal or other material supported between the heat exchanger and the casing to protect the casing from heat, not to be considered as a heat transfer surface.

such as frequency, input motor power, conditions, and voltage indicates the condition as specified by the manufacturer or the conditions of design.

a vessel in the refrigerating system designed to ensure the availability of adequate liquid refrigerant for proper functioning of the system and to store the liquid refrigerant when the system is pumped down.

a domestic or service hot-water distribution system that includes a closed-circulation circuit designed to maintain usage temperatures in hot-water pipes near terminal devices (e.g., lavatory faucets, shower heads) in order to reduce the time required to obtain hot water when the terminal device valve is opened. The motive force for circulation is either natural (due to water density variations with temperature) or mechanical (recirculation pump).

(1) a condition pertaining to air-cooled condensers in which a portion of the discharge air enters along with the fresh air, the amount of recirculation is determined by equipment design, placement in regard to adjoining objects, and atmospheric conditions. The effect is generally evaluated on the basis of the decrease in unit capacity. (2) condition pertaining to cooling towers and evaporative condensers in which a portion of the discharge air enters along with the fresh air, the amount of recirculation is determined by equipment design, placement in regard to adjoining objects, and atmospheric conditions. The effect is generally evaluated on the basis of the increase in entering wet-bulb temperature compared to the ambient.

back-pressure and back-siphonage-type device designed to serve as a detector check on fire protection systems where contaminants are involved. Note: RPDC includes a line-size approved, reduced pressure zone backflow preventer with a metered bypass into which has been incorporated a three-quarter inch, approved, reduced pressure zone backflow preventer.

back-pressure and back-siphonage-type device designed to operate under continuous pressure where contaminants are involved.

vessel in a refrigerating system designed to ensure the availability of adequate liquid refrigerant for proper functioning of the system and to store the liquid refrigerant when the system is pumped down.

technique of design, manufacture, application, and operation of refrigerating machinery and its primary equipment.

refrigerating systems are classified according to the degree of probability, low or high, that leaked refrigerant from a failed connection, seal, or component could enter an occupied area. The distinction is based on the basic design or location of the components.

plate, wall, or partition that is designed to perform one or more of the following functions: (1) prevent contact of food with refrigerated surfaces, (2) prevent dripping of condensate on food, (3) regulate and/or direct circulation of refrigerated air.

appropriately qualified and licensed professional engineer. See also design professional.

estimate of the current or future cost to replace existing facilities either as currently structured or as redesigned to embrace new technology with facilities that will perform the same functions.

the commissioning process applied to an existing facility that was not previously commissioned. The same process for retrocommissioning needs to be followed from predesign through occupancy and operations to optimize the benefits of implementing the commissioning process philosophy and practice.

relay designed to reverse the direction of current flow or of function, on actuation.

a dimensionless number, designated Re, that indicates whether the fluid flow is laminar or turbulent. For flow in a pipe, transition generally occurs between Reynolds’ numbers of 2300 and 4000.

(also known as pressure relief device or pressure limiting device), valve or rupture member designed to relieve pressure at a predetermined setting by mechanical failure of the disc. A rupture disc is a single-use device and must be replaced after the incident (as opposed to a relief valve, which may be manually or automatically reset).

a tubular windscreen to be attached to a standard microphone and designed to minimize its sensitivity to airflow noise.

drawing illustrating the relationship of project components and/or the fundamental outline of a functional system.

piston ring of special section, designed to prevent oil from the crankcase entering the cylinder head.

a panel designed for sensible cooling of an indoor space through heat transfer to the thermally effective panel surfaces from the occupants and/or indoor space by thermal radiation and natural convection.

a complete panel that is designed and can be independently installed and operated for sensible heating of an indoor space through heat transfer from the thermally effective panel surfaces to the occupants and/or indoor space by thermal radiation and natural convection.

device or instrument designed to detect and measure a variable.

mechanism that automatically actuates a system according to the variation of input. The device is designed so that a small input power controls a much larger output power.

the international agreement on the metric system of units using meters, grams, and other designations, as opposed to I-P units in the Inch-Pound system.

an approved opening protection device designed to resist the passage of air or smoke that meets the requirements of UL Standard 555S-1983, Leakage Rated Dampers for Use in Smoke Control Systems. A combination fire and smoke damper should also meet the requirements of UL Standard 555-1990, Fire Dampers.

a device designed to absorb incident solar radiation and to transfer the energy to a fluid passing through it.

pipe or tube containing a series of holes designed to equalize the distribution of one fluid stream into another.

(1) movement of air into and out of buildings, chimneys, flue gas stacks, or other containers and is driven by buoyancy. Buoyancy occurs due to a difference in indoor to outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect is also referred to as the chimney effect, and it helps drive natural ventilation and infiltration. (2) movement of air or other gas in a vertical enclosure (e.g., duct, chimney, building), induced by the density difference between the air or other gas in the enclosure and the ambient atmosphere. Note: stack effect is a significant concern in heating-system design for tall buildings in cold climates. Sometimes referred to as chimney effect. (3) pressure difference caused by the difference in density between indoor and outdoor air due to an indoor/outdoor temperature difference. (4) the vertical airflow within buildings caused by temperature differences between the building's interior and exterior.

(1) a device equipped with overload trip mechanisms for its protection. (2) starting a device with a load connected that will require the device to operate outside its designed operating range.

an incremental change in a variable, either by design or as the result of an interval between measurement, typically, an incremental change in a control setpoint.

(1) device for use where a cable passes into a junction box or other piece of apparatus designed to render the joint watertight. (2) packing gland surrounding a shaft, stem, or rod to prevent leakage.

(1) air-conditioning unit designed primarily for cooling and dehumidifying air by passing the air over cooling coils that are below the dew point of the air. (2) dehumidifier with a surface at a temperature below the dew point.

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.

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.

the designated person, company, or agent who specifies the test requirements.

the maximum amount that a designated measured quantity shall vary (i.e., maximum–minimum) during the entire or a specified interval of a test.

pressure, usually higher than the design working pressure, to which a piece of equipment is subjected for testing according to specified procedures.

heat loss characteristics of a physical condition or structure that are not in accordance with intended design or calculated characteristics.

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.

(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.

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.

(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.

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.

(1) single temperature controller designed to control temperature at two distinct setpoints. (2) thermostat that handles two separate circuits in sequence.

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.

a hood designed to capture heat, odors, products of combustion, and/or moisture where smoke or grease laden vapor is not present. A Type II hood may or may not have filters or baffles and does not have a fire suppression system.

pump for exhausting a system, pump designed to produce a vacuum in a closed system or vessel.

burner designed to utilize the temperature of the heated combustion chamber to vaporize the liquid fuel fed into such chamber.

a device intended for installation in the venting system of an individual, automatically operated, fossil-fuel-fired appliance in the outlet or downstream of the appliance draft control device, which is designed to automatically open the venting system when the appliance is in operation and to automatically close off the venting system when the appliance is in a standby or shutdown condition.

(1) designation that water is the fluid in a manometer. (2) gage glass with attached fittings which indicates water level within a vessel. (3) unit of pressure (I-P units). See water column (wc).

those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions. This definition incorporates all areas that would meet the definition of “wetlands” under applicable federal or state guidance—regardless of whether they are officially designated, delineated, or mapped—including manmade areas that are designed, constructed, or restored to include the ecological functions of natural wetlands.

room air conditioner designed for mounting in window.