Glossary — VoltAire Cooling

4

1 term

48VDC

Electrical

48-volt direct-current power, the standard for telecom central-office and outside-plant (OSP) equipment powered by battery plants, and increasingly used in edge data centers (Open Compute Project), oil & gas SCADA, utility substations, and federal field sites. DC-powered enclosure cooling eliminates inverter losses and continues running through AC utility outages on the site's −48VDC battery backup. The de facto power standard for outdoor electronic equipment that needs to comply with GR-487 environmental requirements.

A

13 terms

A2L Refrigerant

Refrigerants

ASHRAE Standard 34 safety classification for refrigerants with low toxicity (A) and low flammability (2L) — including R-32, R-454B, R-1234yf, and R-1234ze. A2L refrigerants are mildly flammable but require relatively high concentration and ignition energy. UL 60335-2-40 governs charge limits in equipment.

Adiabatic Cooling

Cooling Concepts

A cooling process that uses water evaporation to pre-cool incoming air before it crosses a condenser coil or heat exchanger. Adiabatic systems can extend the useful range of free-cooling and reduce compressor runtime in dry climates, but require water supply and periodic maintenance to prevent scale and biological growth.

Related: Free Cooling • Evaporator Coil

AHRI

Standards

The Air-Conditioning, Heating, and Refrigeration Institute — North American trade association that publishes and certifies HVAC equipment performance ratings. AHRI 210/240 (residential), 340/360 (commercial unitary), 590 (chillers) define the rating points that EER and IEER are measured at.

AIM Act

Refrigerants

American Innovation and Manufacturing Act of 2020, granting EPA authority to phase down HFC production and consumption by 85% over 15 years. Drives the industry-wide transition from R-410A to lower-GWP A2L refrigerants like R-454B and R-32.

Air-to-Air Heat Exchanger

Heat Exchangers

A closed-loop cooling device that transfers heat from sealed enclosure air to ambient air through a separating wall (tubes or plates) without mixing the two streams. Useful when ambient temperature is consistently 10°F or more below the target internal temperature, since a heat exchanger cannot cool below ambient.

Ambient Temperature

HVAC General

The dry-bulb air temperature surrounding an enclosure or condenser. Maximum rated ambient is a key spec on every enclosure air conditioner — exceeding it causes high-pressure trips, capacity loss, and shortened compressor life. VoltAire AT and AN air conditioners are rated to 131°F (55°C) ambient; HIX and HTC heat exchangers are rated to 158°F (70°C).

AN Series

Applications

VoltAire's narrow-profile outdoor air conditioner family designed to fit cabinets too shallow for standard units. Capacities range from 1,000 BTU/hr (AN01) to 8,000 BTU/hr (AN08). Common in OSP telecom and remote terminal cabinets where depth is constrained.

Related: AT Series • OSP / Outside Plant

ANSI

Standards

The American National Standards Institute, a private non-profit that coordinates the U.S. voluntary standards system and accredits other standards developers (UL, ASTM, NEMA, etc.). ANSI itself rarely publishes standards directly but its accreditation is what makes a UL or NEMA standard authoritative.

Related: UL 484 • NEMA

ASHRAE

Standards

The American Society of Heating, Refrigerating and Air-Conditioning Engineers. Publishes the data center thermal-environment standards (TC 9.9) that define the A1–A4 allowable ranges used to size cooling for IT and edge equipment, plus refrigerant safety classifications referenced by UL and ASHRAE 34.

Related: Data Center • Refrigerant

ASHRAE 90.1

Standards

The energy-efficiency standard for buildings other than low-rise residential. Sets minimum EER and IEER values that mechanical equipment must meet to be specified on commercial projects, and underpins most state energy codes.

ASTM A653

Standards

The specification for steel sheet, zinc-coated (galvanized) by the hot-dip process. G90 designation (0.90 oz/ft² zinc coating) is the most common substrate for industrial enclosure walls before powder coat is applied, providing baseline corrosion protection.

Related: Enclosure • ASTM B117

ASTM B117

Standards

The standard salt-spray (fog) test used to evaluate corrosion resistance of metallic coatings. GR-487-CORE specifies 720 hours of B117 exposure for outside-plant telecom equipment (referenced in section 3.34.1). Some industry specs call for 1,000+ hours. VoltAire enclosure units pass the GR-487 720-hour requirement.

Related: NEMA 4X • OSP / Outside Plant • GR-487 • Telecom Shelter

AT Series

Applications

VoltAire's standard-profile outdoor air conditioner family, ranging from 4,000 BTU/hr (AT04) to 19,000 BTU/hr (AT19). AT units are bolt-for-bolt replacements for nVent McLean, Hoffman, and Pentair Spectracool models in the same BTU class.

Related: AN Series • NEMA 4X

B

5 terms

BABA / Build America Buy America

Standards

Federal procurement requirement passed as part of the Infrastructure Investment and Jobs Act (Nov 2021), with the BABA preference effective May 14, 2022. Mandates that federally-funded infrastructure projects use iron, steel, manufactured products, and construction materials produced in the United States. Manufactured products must be assembled in the U.S. with at least 55% U.S.-sourced component costs. Most BEAD and federal telecom programs require BABA-compliant outside-plant equipment.

Related: BEAD Program • Made in USA • OSP / Outside Plant

BEAD Program

Applications

The Broadband Equity, Access, and Deployment program — a $42.45 billion federal grant program administered by NTIA to fund rural broadband expansion. BEAD-funded builds must use BABA-compliant cabinets and cooling equipment.

BMS / Building Management System

Applications

A centralized control platform that monitors and operates HVAC, lighting, power, and security across a facility. Integration with enclosure cooling typically uses Modbus RTU/TCP, BACnet, or simple dry-contact alarm outputs for remote temperature and fault visibility.

Related: Modbus • SCADA

Bolt-for-Bolt Replacement

Operations

A replacement unit that reuses the existing mounting cutout, hole pattern, and electrical connections of the equipment it replaces — no field modification required. Eliminates the labor and risk of cutting new openings in NEMA-rated enclosures. Many VoltAire AT and AN units are bolt-for-bolt replacements for their corresponding nVent McLean and Pentair Spectracool models; others use an adapter plate or a minor cutout trim — each replacement page states the exact fit.

BTU / British Thermal Unit

Cooling Concepts

The energy required to raise one pound of water by one degree Fahrenheit. Cooling capacity is rated in BTU per hour (BTU/hr): 1 BTU/hr ≈ 0.293 watts, and 12,000 BTU/hr = 1 ton of refrigeration. Used as the universal sizing currency for HVAC and enclosure cooling.

Related: Ton of Refrigeration • Sensible Heat • Watt

C

16 terms

Capacitor (Run / Start)

Components

A passive component that stores and releases electrical energy. Run capacitors stay in the circuit continuously to improve PSC motor efficiency and torque. Start capacitors briefly boost starting torque and drop out via a relay or PTC. Failed capacitors are the most common single-component failure in enclosure air conditioners.

Capillary Tube

Components

A precisely-sized, very small bore copper tube that meters refrigerant from the high-pressure liquid line into the evaporator. Cheaper and more reliable than a thermostatic expansion valve, but optimized for a single operating condition. Common in self-contained enclosure ACs because they run at near-constant load.

CFC / Chlorofluorocarbon

Refrigerants

A class of refrigerants (R-11, R-12) phased out under the 1987 Montreal Protocol due to high ozone-depletion potential. No longer manufactured for new equipment in the U.S. since 1996. Legacy units may still contain reclaimed CFC charges that must be recovered when servicing.

CFM / Cubic Feet per Minute

HVAC General

The volumetric airflow unit used for fans, blowers, and ductwork. Enclosure fans are typically rated in free-air CFM, but the delivered CFM drops sharply as static pressure rises across filters or restricted enclosures. Always size from delivered, not free-air, CFM.

Related: Static Pressure • Fan Motor

Class I Division 2

Enclosures

NEC area classification for locations where flammable gases or vapors may be present only under abnormal conditions (leaks, ruptures). Equipment installed in C1D2 must be certified non-incendive — typical in oil & gas, chemical, and pharmaceutical facilities. Standard enclosure ACs are NOT C1D2 rated; specialized purged or explosion-proof variants are required.

Related: Hazardous Location

Closed-Loop Cooling

Cooling Concepts

A cooling architecture in which the conditioned (internal) air never mixes with ambient (outdoor) air. The enclosure stays sealed and pressurized, protecting electronics from dust, moisture, and corrosive vapors. All compressorized enclosure ACs and air-to-air heat exchangers are closed-loop systems.

CO / Central Office

Telecom

A telephone-company facility housing switching equipment that serves subscribers in a service area. Typically air-conditioned to A1 ASHRAE conditions. CO-grade equipment must meet GR-63 (NEBS Level 3) physical and environmental criteria.

Compressor

Components

The component that raises refrigerant vapor pressure and circulates it through the system. The single largest power consumer and the most expensive part of a vapor-compression circuit. Common types in enclosure ACs are reciprocating, rotary, and scroll.

Condensate

Components

Liquid water that forms on the evaporator coil when warm enclosure air is cooled below its dew point. Must be drained continuously. Field failures from blocked condensate lines are common — a clogged drain causes water to back up into the enclosure and damage electronics.

Related: Condensate Pump • Evaporator Coil • Latent Heat

Condensate Pump

Components

A small float-actuated pump used to lift condensate from the AC drip pan to a higher drain point. Required when gravity drainage is impossible (basement installs, rooftop units with no nearby drain). Typically replaced every 5-7 years; failures cause overflow alarms or water damage.

Related: Condensate • Evaporator Coil

Condenser Coil

Components

The outdoor heat exchanger that rejects heat absorbed from inside the enclosure. Hot, high-pressure refrigerant vapor enters the coil and condenses to liquid as ambient-air-driven fans pull air across the fins. A dirty condenser coil is the #1 cause of high-pressure trips and short cycling.

Related: Evaporator Coil • Fan Motor • Short Cycling

Contactor

Electrical

An electromechanical switch designed to repeatedly make and break load circuits at currents above what a relay can handle. Compressors and large fan motors are switched by contactors rather than relays. Contact erosion is a common end-of-life failure mode and is visible as pitting on the silver tips.

Related: Relay • Compressor

Control Panel

Applications

An enclosure housing the electrical controls for a machine, process, or system — typically PLCs, HMIs, drives, contactors, and terminal blocks. Control panels above ~500W internal dissipation usually require active cooling rather than passive ventilation.

Related: Enclosure • MCC / Motor Control Center • NEMA 12

COP / Coefficient of Performance

Cooling Concepts

A dimensionless ratio of useful cooling output (or heating output) to electrical work input, both expressed in the same units. A COP of 3.0 means the system moves 3 watts of heat per 1 watt of electrical input. Used internationally and for heat pumps; the U.S. HVAC industry typically uses EER instead for cooling-only performance.

Counter-Flow Heat Exchanger

Heat Exchangers

A heat-exchanger arrangement in which the two fluid streams flow in opposite directions along the heat-transfer surface. Achieves the highest possible effectiveness for a given surface area because the temperature differential remains nearly constant along the length, but it is harder to package than cross-flow.

Cross-Flow Heat Exchanger

Heat Exchangers

A heat-exchanger arrangement in which the two fluid streams flow perpendicular to each other. Less efficient than counter-flow but mechanically simpler and easier to package — the most common arrangement in air-to-air enclosure heat exchangers.

D

6 terms

Data Center

Applications

A facility housing networked computer servers and storage. Cooling is typically provided by precision CRAC/CRAH units sized to ASHRAE TC 9.9 envelopes. Edge data centers and micro-data-center cabinets often use enclosure-level cooling instead of facility-wide cooling.

Related: Edge Computing • ASHRAE

Delta-T (ΔT)

Cooling Concepts

The temperature difference between two points in a system — most often between target enclosure interior temperature and ambient. ΔT determines whether free cooling, heat exchangers, or active refrigeration is needed: a heat exchanger needs ~10°F minimum ΔT to be useful, while compressorized AC works against any ΔT including negative.

Dew Point

HVAC General

The temperature at which water vapor in air will condense to liquid. When evaporator coil surface temperature drops below the dew point of returning enclosure air, condensate forms. In sealed closed-loop enclosures the internal dew point is stable and predictable; in poorly-sealed cabinets, infiltration drives unpredictable condensation.

Related: Condensate • Latent Heat • RH / Relative Humidity

DOE Energy Conservation Standards

Standards

U.S. Department of Energy minimum efficiency rules that apply to most consumer and commercial HVAC equipment. Self-contained enclosure air conditioners are generally classified as commercial/industrial equipment and are exempt from residential standards but may fall under separate commercial rulemakings.

Drip Loop

Components

A downward U-shape formed in a cable, hose, or condensate line near its entry to an enclosure, allowing water to drip off the bottom of the loop instead of running into the cabinet. A simple but critical detail in any outdoor cable or condensate routing.

Related: Condensate • Enclosure

Duty Cycle

Operations

The fraction of time an AC unit is actively cooling vs. idle, expressed as a percentage. Healthy enclosure ACs typically run at 30-70% duty cycle in normal conditions; a unit running at 100% duty has no spare capacity for hot-day spikes and indicates the system is undersized.

Related: Short Cycling • Heat Load

E

7 terms

ECM Motor

Components

Electronically Commutated Motor — a brushless DC motor with onboard electronics for variable-speed operation. 30-50% more efficient than equivalent PSC motors, with stable performance over a wide load range. Increasingly common in premium enclosure cooling but adds cost and electronic complexity.

Edge Computing

Applications

A distributed computing model that places compute and storage close to the data source rather than in centralized data centers. Edge sites are typically small enclosures or micro-data-center cabinets at cell towers, retail locations, or industrial floors — and rely on enclosure-level cooling rather than building HVAC.

EER / Energy Efficiency Ratio

Cooling Concepts

The ratio of cooling capacity (BTU/hr) to electrical input (watts) at the AHRI rating point of 95°F outdoor and 80°F indoor. EER = BTU/hr ÷ watts. Higher is better. Self-contained enclosure ACs typically rate between 7 and 11 EER depending on capacity and refrigerant choice.

EMI / Electromagnetic Interference

Electrical

Unwanted electrical noise that couples between equipment via radiated or conducted paths. Enclosure cooling units must comply with FCC Part 15 limits and may carry CISPR 22/32 markings. VFD-driven fans are a common EMI source and may require shielded cable and line filtering.

Enclosure

Enclosures

A protective housing for electrical or electronic equipment. Industrial enclosures are rated by NEMA in North America and IP in IEC countries to indicate environmental protection. Common materials are powder-coated mild steel, stainless steel (304 or 316L), aluminum, and fiberglass.

Related: NEMA • IP Rating (IEC 60529)

Evaporator Coil

Components

The indoor heat-exchange coil where liquid refrigerant absorbs heat from enclosure return air and boils to vapor. Cold surface temperature drives both sensible cooling and condensation of moisture (latent cooling). Frost on the evaporator indicates low charge, low airflow, or operation below the design return-air temperature.

Related: Condenser Coil • Capillary Tube • Condensate

Expansion Valve (TXV)

Components

A thermostatic metering device that regulates refrigerant flow into the evaporator based on superheat at the outlet. More precise and tolerant of varying load than a capillary tube. Used in larger enclosure ACs and any unit that must operate over a wide temperature range.

Related: Capillary Tube • Evaporator Coil • Superheat

F

6 terms

Fan Motor

Components

The electric motor that drives a condenser or evaporator fan. Common types are PSC (permanent split capacitor), shaded-pole, and ECM (electronically commutated). ECM motors offer 30-50% better efficiency and variable speed but cost more; most enclosure ACs use PSC for the cost/reliability balance.

FCC Part 15

Standards

The FCC rule covering unintentional radiators of radio-frequency energy. Class A is the limit for industrial/commercial environments; Class B is the stricter residential limit. Enclosure cooling products with electronic controls typically declare Class A compliance.

Filter Drier

Components

A canister installed in the liquid line containing molecular sieve and filter screen. Removes residual moisture and particulate from the refrigerant circuit. Standard practice is to replace the filter drier any time the refrigerant circuit is opened for service.

Related: Liquid Line • Refrigerant

FLA / Full Load Amps

Electrical

The rated current draw of a motor at its nameplate horsepower and voltage under continuous full-load operation. Used to size branch-circuit conductors and overcurrent protection per NEC. Distinguished from LRA (locked-rotor amps) which is the brief inrush at startup.

Free Cooling

Cooling Concepts

Any cooling mode that does not run the compressor — typically a damper or economizer that admits cool ambient air, or a heat exchanger that operates without active refrigeration. Substantial energy savings in cool climates. Many modern enclosure ACs include a free-cooling mode that shifts to compressor only when ambient rises above a setpoint.

Free-Air CFM

HVAC General

A fan rating measured with no static pressure resistance — the maximum theoretical airflow. Real installed CFM is always lower because filters, coils, and ductwork add static pressure. Specify based on installed CFM at the operating point, not free-air CFM.

G

4 terms

GR-1089 / NEBS EMC

Telecom

Telcordia spec for electromagnetic compatibility, electrical safety, and bonding/grounding of telecom equipment. Covers radiated and conducted emissions, electrostatic discharge, and lightning surge survivability. Required alongside GR-63 for NEBS compliance.

GR-487

Telecom

Telcordia Generic Requirements for outside-plant electronic equipment cabinets — the single most-cited spec for OSP telecom cooling. Defines environmental (temperature, humidity, salt fog, ingress), mechanical (vibration, seismic, wind), and acoustic requirements. EMC requirements live in the companion document GR-1089. Current edition is GR-487-CORE Issue 5 (2016). Compliance is demanded by all major U.S. telcos for streetside equipment.

GR-63 / NEBS Physical Protection

Telecom

Telcordia spec covering physical protection requirements for network telecommunications equipment — temperature, humidity, fire resistance, earthquake, transportation, and acoustic noise. Together with GR-1089 forms the NEBS Level 3 baseline for central-office equipment.

GWP / Global Warming Potential

Refrigerants

A measure of how much heat a greenhouse gas traps in the atmosphere relative to CO₂ over 100 years. R-134A has GWP of 1,430; R-410A is 2,088; the newer A2L blend R-454B is 466. The AIM Act requires a 40% U.S. HFC reduction by 2024 and 85% by 2036, driving the shift to lower-GWP refrigerants.

Related: HFC / Hydrofluorocarbon • R-134A • AIM Act

H

8 terms

Hazardous Location

Enclosures

An area where fire or explosion hazards may exist due to flammable gases, dust, or fibers. Classified by the NEC into Classes (I, II, III), Divisions (1, 2), and Groups. Equipment for these areas must be specifically certified — standard enclosure cooling products are NOT hazardous-location rated.

Related: Class I Division 2

HCFC

Refrigerants

Hydrochlorofluorocarbons — transitional refrigerants (R-22, R-123) with lower ozone-depletion potential than CFCs but still ozone-depleting. R-22 production for new equipment ended in 2010 and complete phase-out occurred in 2020. Existing equipment can still use reclaimed R-22.

Heat Load

Cooling Concepts

The total rate of heat that must be removed from an enclosure to maintain target interior temperature, expressed in BTU/hr or watts. Three components: internal load (component dissipation), solar gain (outdoor enclosures), and ambient transfer (U-value × surface × ΔT). Always size cooling capacity to the calculated load with a safety margin.

Hermetic Compressor

Components

A compressor in which the motor and pumping mechanism are sealed inside a welded steel shell with refrigerant. Cannot be opened or rebuilt — when it fails, the entire compressor is replaced. All small enclosure-AC compressors are hermetic; semi-hermetic units appear only at larger commercial tonnages.

HFC / Hydrofluorocarbon

Refrigerants

A class of refrigerants containing only hydrogen, fluorine, and carbon — no chlorine, so zero ozone-depletion potential. R-134A, R-410A, and R-407C are common HFCs. The AIM Act of 2020 mandates progressive U.S. HFC production cuts because of their high global-warming potential.

Related: HCFC • GWP / Global Warming Potential • AIM Act • R-134A

High-Ambient Operation

Cooling Concepts

Operation of an air-cooled refrigeration system at outdoor temperatures above 95°F. Standard units lose capacity sharply above 110°F and may trip on high pressure above 125°F. High-ambient-rated units use larger condensers, R-410A or R-454B, and sometimes adiabatic pre-cooling.

Related: Ambient Temperature • Short Cycling

Hoffman

Applications

One of the largest North American enclosure brands, founded in 1944 in Anoka, Minnesota and now part of nVent (acquired by Pentair in 2008, spun off into nVent in 2018). Hoffman enclosures and accessories (cooling, lighting, terminal blocks) are the de-facto standard in industrial control panel construction. VoltAire cooling cross-references match Hoffman product numbers directly.

Hut

Telecom

A small prefabricated outdoor building (often 8' × 12' to 12' × 30') used to house telecom or utility electronics. Larger than a cabinet but smaller than a shelter, huts typically use one or two wall-mount enclosure ACs rather than building-style HVAC.

Related: Shelter • OSP / Outside Plant • Telecom Shelter

I

4 terms

IEER / Integrated Energy Efficiency Ratio

Cooling Concepts

A weighted-average part-load efficiency rating defined by AHRI 340/360 for unitary commercial AC. Captures performance at 100%, 75%, 50%, and 25% load — closer to real-world energy use than EER alone. Required by ASHRAE 90.1 for most commercial unitary equipment ≥ 65,000 BTU/hr.

IP Rating (IEC 60529)

Standards

The Ingress Protection code defined by IEC 60529. The first digit (0–6) rates solids ingress; the second (0–9) rates liquids ingress. Common ratings: IP54 (dust-protected, splash water), IP66 (dust-tight, powerful jets), IP67 (dust-tight, temporary immersion). Roughly maps to NEMA but is not a one-to-one equivalent.

Related: NEMA • IP66 • IP67

IP66

Standards

Dust-tight enclosure (IP6X) that withstands powerful water jets (IPX6 test: 12.5 mm nozzle, 100 L/min, ~100 kPa at the nozzle, 2.5-3 m distance, minimum 1 minute per square meter of enclosure surface) per IEC 60529. Roughly equivalent to NEMA 4 but tested via different methodology. Standard rating for outdoor industrial enclosures.

Related: IP Rating (IEC 60529) • IP67 • NEMA 4

IP67

Standards

Dust-tight enclosure that withstands temporary immersion in 1 meter of water for 30 minutes. Stricter than IP66 for liquid ingress but does not address corrosion. Specified for flood-prone outdoor applications.

Related: IP Rating (IEC 60529) • IP66 • NEMA 6 / 6P

L

3 terms

Latent Heat

Cooling Concepts

The heat absorbed or released during a phase change without a temperature change — for HVAC, the energy required to condense or evaporate water vapor. In sealed closed-loop enclosures, latent load is small and stable; in leaky cabinets, infiltration of humid ambient air drives most of the cooling demand.

Related: Sensible Heat • Condensate • Dew Point

Liquid Line

Components

The refrigerant tubing between the condenser outlet and the metering device, carrying high-pressure subcooled liquid. Smaller diameter than the suction line. Bubbles in the liquid-line sight glass indicate undercharge or non-condensable gases.

Related: Suction Line • Subcooling • Expansion Valve (TXV)

LRA / Locked-Rotor Amps

Electrical

The current a motor draws at the instant of starting before it begins to rotate. Typically 5-7× the FLA. Used to specify contactor and circuit-breaker withstand ratings and to evaluate generator and UPS sizing for compressor loads.

M

8 terms

Made in USA

Standards

A claim regulated by the FTC under the "all or virtually all" standard — the product must contain only de minimis foreign content. Distinct from Buy American Act (federal procurement) and BABA (federal infrastructure). VoltAire AT and AN units are assembled in the USA from primarily domestic content.

MCA / Minimum Circuit Ampacity

Electrical

The minimum branch-circuit conductor ampacity required to feed a piece of equipment, calculated per NEC 440 as 1.25× the largest motor FLA plus the sum of all other loads. Always printed on the equipment nameplate. Wire sizing must equal or exceed MCA.

MCC / Motor Control Center

Applications

A factory-assembled lineup of enclosed motor starters, drives, and control devices in a common power-distribution structure. Large MCCs generate substantial heat and frequently use enclosure cooling on individual sections rather than ambient room cooling.

McLean / nVent McLean

Applications

A long-established brand of industrial enclosure cooling products, now owned by nVent. McLean T-series models (T15, T20, T29, T43, T50, T53) and N-series models set the de-facto bolt-pattern standard that most replacement units — including VoltAire — follow. Common in legacy installations dating from the 1990s through 2010s.

Related: nVent • Hoffman • Pentair Spectracool

MOCP / Maximum Overcurrent Protection

Electrical

The largest fuse or circuit-breaker size that may be installed to protect the equipment branch circuit, per NEC 440. Always printed on the equipment nameplate. Using a breaker larger than MOCP can void warranty and create a fire hazard.

Modbus

Electrical

A serial communications protocol (RTU over RS-485, TCP over Ethernet) widely used in industrial automation. Many modern enclosure ACs offer Modbus interfaces for setpoint adjustment, alarm reporting, and integration with PLCs or BMS systems.

MTBF / Mean Time Between Failures

Operations

The statistical average operating time between component failures, usually measured in hours. Useful for comparing reliability across product designs. Closed-loop enclosure ACs commonly publish MTBF figures of 50,000 to 100,000+ hours for the compressor.

MTTR / Mean Time To Repair

Operations

The statistical average time required to restore a failed system to operation. For enclosure ACs, MTTR is heavily influenced by parts availability — bolt-for-bolt replacements minimize MTTR by eliminating field fabrication and stocking standardized spares.

N

11 terms

NEBS / Network Equipment-Building System

Telecom

The Telcordia-defined performance and physical-protection standards for telecom equipment installed in carrier facilities. Three levels: Level 1 (basic operability), Level 2 (operability under common environmental stresses), Level 3 (full CO-grade including fire, earthquake, EMC). Composed primarily of GR-63 and GR-1089.

NEMA

Standards

The National Electrical Manufacturers Association — publishes the NEMA 250 standard that defines enclosure type designations (1, 2, 3, 3R, 4, 4X, 12, etc.). NEMA ratings are widely cited in the U.S. and roughly map to IEC IP ratings, but include corrosion and ice-accumulation criteria that IP does not.

Related: NEMA 1 • NEMA 3R • NEMA 4 • NEMA 4X • NEMA 12 • IP Rating (IEC 60529)

NEMA 1

Standards

General-purpose indoor enclosure protecting against accidental contact with enclosed equipment and against limited falling dirt. Not rated against water. The minimum useful rating for indoor electrical equipment.

Related: NEMA • NEMA 12

NEMA 12

Standards

Indoor enclosure protecting against falling dirt, circulating dust, lint, fibers, and dripping non-corrosive liquids. The most common rating for indoor industrial control panels. Does NOT protect against hose-directed water — use NEMA 4 for washdown.

Related: NEMA 1 • NEMA 4 • Control Panel

NEMA 2

Standards

Indoor enclosure providing NEMA 1 protection plus a degree of protection against limited dripping water. Rare in modern specifications — most users default to NEMA 12 for indoor drip protection.

Related: NEMA 1 • NEMA 12

NEMA 3

Standards

Outdoor enclosure protecting against windblown dust, rain, sleet, and external ice formation. Less common in current usage; NEMA 3R (drip-proof) and NEMA 4 (hose-down) cover most outdoor applications.

Related: NEMA 3R • NEMA 4

NEMA 3R

Standards

Outdoor enclosure protecting against falling rain, sleet, and external ice formation. Common rating for utility meter sockets and outdoor disconnects. Does NOT protect against windblown dust or hose-directed water.

Related: NEMA 3 • NEMA 4

NEMA 4

Standards

Indoor or outdoor enclosure protecting against windblown dust and rain, splashing water, and hose-directed water (65 GPM from a 1-inch nozzle at 10-12 ft (3-3.5 m) for 5 minutes). The standard rating for outdoor industrial equipment in non-corrosive environments.

Related: NEMA 4X • NEMA 3R • IP66

NEMA 4X

Standards

Same protection as NEMA 4 plus corrosion resistance — typically achieved with stainless steel, fiberglass, or polycarbonate construction. Required for coastal, food/beverage, chemical, and washdown environments. VoltAire AT and AN units carry a UL Type 4 (NEMA 4) enclosure rating as standard; a Type 4X rating is available as an option via stainless steel exterior construction (stainless enclosure on AT series, stainless external cover and fasteners on AN series).

Related: NEMA 4 • ASTM B117

NEMA 6 / 6P

Standards

Indoor or outdoor enclosure protecting against occasional temporary submersion (NEMA 6) or prolonged submersion (NEMA 6P) at limited depth. Used in flood-prone applications. Roughly equivalent to IP67/IP68.

Related: NEMA 4 • IP67

nVent

Applications

A global electrical-products company that owns the Hoffman, McLean, and Schroff enclosure brands following its 2018 spin-off from Pentair. nVent is the dominant North American supplier of industrial enclosures and enclosure cooling. VoltAire products are direct cross-references for nVent legacy and current models.

O

3 terms

ODP / Ozone Depletion Potential

Refrigerants

A relative measure of a chemical's ability to destroy stratospheric ozone, with R-11 = 1.0. CFCs have ODPs of 0.6-1.0; HCFCs are lower (R-22 = 0.05); HFCs and HFOs are zero. The Montreal Protocol drove the transition away from ODP-bearing refrigerants; current AIM Act activity targets GWP instead.

Open-Loop Cooling

Cooling Concepts

Cooling architecture in which outside air is drawn through the enclosure, typically by filtered fans. Cheap and simple but exposes electronics to dust, humidity, and corrosive vapors — incompatible with NEMA 4, 4X, or 12 ratings. Useful only in clean indoor environments.

Related: Closed-Loop Cooling • Fan Motor

OSP / Outside Plant

Telecom

Telecom equipment installed outdoors — at street pedestals, on poles, or in remote terminals — between the central office and the customer premises. OSP cabinets must meet GR-487 environmental, mechanical, and security requirements.

Related: GR-487 • CO / Central Office • Telecom Shelter • AN Series

P

10 terms

Parallel-Flow Heat Exchanger

Heat Exchangers

A heat-exchanger arrangement in which both fluid streams flow in the same direction. Lower effectiveness than counter-flow because the temperature differential collapses along the length, but provides a uniform wall temperature — useful for protecting temperature-sensitive surfaces.

Pentair Spectracool

Applications

SpectraCool is the Hoffman-branded line of enclosure air conditioners. Hoffman became part of Pentair in 2008, then nVent spun off from Pentair in 2018, so older units are often labeled "Pentair SpectraCool" while current units are sold under "nVent Hoffman SpectraCool." The N-series (narrow) and standard SpectraCool families are the most commonly cross-referenced product lines in the industry.

Related: nVent • Hoffman • McLean / nVent McLean

Phase (Single / Three)

Electrical

Electrical service configuration. Single-phase (1Ø) provides one alternating voltage between two conductors and is standard for 115V and 230V North American service. Three-phase (3Ø) provides three voltages at 120° offsets, used for 208V, 230V, 460V, and 575V industrial service. Three-phase compressors start more smoothly and run more efficiently.

Plate-Fin Heat Exchanger

Heat Exchangers

A heat-exchanger geometry using stacked corrugated metal plates with fins between them, separating two fluid streams. High surface area in a compact volume and well-suited to air-to-air enclosure HX applications. Aluminum is the most common material.

Plenum

HVAC General

An air-distribution chamber at the inlet or outlet of an HVAC system. In ducted enclosure cooling, supply and return plenums distribute conditioned air across rack-mounted equipment. Plenum-rated cabling has fire-resistant jacketing required for use in air-handling spaces under NEC 800.

PoP / Point of Presence

Telecom

A demarcation point where a long-haul telecom carrier connects to a local network. Often housed in a small building, hut, or outdoor cabinet requiring environmental cooling. PoPs are concentrated in metropolitan areas and along fiber routes.

Related: CO / Central Office • OSP / Outside Plant • Hut

Powder Coat

Enclosures

A finishing process applying dry pigmented polymer powder electrostatically and then curing in an oven. Tougher and more chip-resistant than wet paint, with no VOC emissions. Standard exterior finish on industrial enclosures and most enclosure-AC condenser cabinets.

Related: Enclosure • ASTM B117

Pressurization

Enclosures

Maintaining slight positive pressure inside an enclosure (typically 0.05-0.10 in. w.c.) to prevent infiltration of contaminants. A purge-and-pressurize system uses clean instrument air and is the most common way to certify enclosures for Class I Division 2 hazardous locations.

Preventive Maintenance (PM)

Operations

Scheduled service performed before failure to extend equipment life and avoid unplanned downtime. For enclosure ACs, the typical PM checklist is: clean condenser coil annually, verify condensate drainage every 6 months, inspect fan operation, verify thermostat setpoint, and check refrigerant superheat/subcooling annually.

PSC Motor / Permanent Split Capacitor

Components

An induction motor with a run capacitor permanently in series with the start winding. Simpler and cheaper than capacitor-start motors but produces less starting torque. The dominant fan-motor type in enclosure cooling because of low cost, good reliability, and adequate torque for fan loads.

Related: Fan Motor • Capacitor (Run / Start) • ECM Motor

R

14 terms

R-134A

Refrigerants

Tetrafluoroethane — an HFC refrigerant with zero ODP and GWP of 1,430. The dominant refrigerant in self-contained enclosure ACs because of low working pressure (compatible with smaller-gauge tubing), ASHRAE A1 safety classification (non-flammable), and broad parts availability. Used in all VoltAire AT and AN units.

R-22

Refrigerants

Chlorodifluoromethane — an HCFC refrigerant universally used in commercial AC until the 2010s. New equipment containing R-22 was banned for production in 2010 and complete production phase-out occurred in 2020. Existing R-22 equipment can still be serviced with reclaimed refrigerant but supply is dwindling and expensive.

Related: HCFC • R-134A • R-410A • ODP / Ozone Depletion Potential

R-410A

Refrigerants

A near-azeotropic blend of R-32 and R-125, used in residential and light-commercial AC since the early 2000s. Operates at roughly 60% higher pressure than R-22, requiring different service equipment. GWP of 2,088 — being phased down by AIM Act and replaced by R-454B and R-32.

R-454B

Refrigerants

A blend of R-32 and R-1234yf with GWP of 466 — roughly one-fifth of R-410A. ASHRAE A2L mildly-flammable classification requires updated service practices. The leading R-410A replacement in new commercial unitary AC manufactured after January 2025.

REACH

Standards

EU regulation 1907/2006 on Registration, Evaluation, Authorization, and Restriction of Chemicals. Manufacturers must declare Substances of Very High Concern (SVHCs) above 0.1% by weight. Often paired with RoHS in supplier compliance documentation.

Related: RoHS

Reciprocating Compressor

Components

A positive-displacement compressor using pistons in cylinders. Robust, well-understood, and widely available, but generates more vibration and is less efficient than scroll. Common in older enclosure ACs and in capacities below ~1 ton.

Related: Compressor • Scroll Compressor • Rotary Compressor

Refrigerant

Refrigerants

A working fluid that absorbs heat by evaporating at low pressure and rejects heat by condensing at high pressure. Selected based on operating temperature, ODP, GWP, flammability (ASHRAE 34 class), and material compatibility with system components.

Relay

Electrical

An electromechanical or solid-state switch used to control low-current circuits — fan motors, controls, and signaling. Distinguished from contactors by lower current rating (typically <30A) and shorter mechanical life.

Related: Contactor • Capacitor (Run / Start)

Return Air

HVAC General

The warm air drawn back into the AC unit from the conditioned space. Return-air temperature is the AHRI rating reference for evaporator-side performance. In enclosures, return air is what the thermostat senses to determine when to cycle the compressor.

RH / Relative Humidity

HVAC General

The ratio of partial water-vapor pressure to saturation vapor pressure at a given temperature, expressed as a percentage. ASHRAE TC 9.9 recommends maintaining IT spaces at 8-80% RH; closed-loop enclosure cooling stabilizes RH at low levels because no ambient moisture infiltrates.

Related: Dew Point • Latent Heat

RMA / Return Material Authorization

Operations

A formal authorization issued by the manufacturer to return failed equipment for warranty repair, replacement, or refund. RMA workflows track serial numbers, failure modes, and repair history. To request a VoltAire RMA, contact Super Cool Company support with the serial number and a description of the issue.

RoHS

Standards

Restriction of Hazardous Substances Directive — EU regulation 2011/65/EU restricting lead, mercury, cadmium, hexavalent chromium, PBB, PBDE, and four phthalates in electrical and electronic equipment. RoHS compliance is required for products sold into the EU and is voluntarily adopted in many U.S. industries.

Related: REACH

Rotary Compressor

Components

A positive-displacement compressor using a roller and vane geometry inside a cylinder. Smaller, quieter, and lower-vibration than reciprocating compressors of the same capacity. Common in compact enclosure ACs and small commercial unitary equipment.

RTU / Remote Terminal Unit

Telecom

In telecom, a remote-electronics enclosure containing line cards or DSLAM/OLT equipment serving subscribers from a curbside cabinet. In SCADA contexts, an RTU is a microprocessor-based device that gathers field data and reports to a central station. Both meanings drive demand for closed-loop enclosure cooling.

Related: OSP / Outside Plant • SCADA

S

15 terms

SCADA

Applications

Supervisory Control and Data Acquisition — a control-system architecture for monitoring and controlling distributed industrial processes. SCADA enclosures in water/wastewater, pipeline, and electrical-utility applications routinely require closed-loop cooling.

Scroll Compressor

Components

A positive-displacement compressor using two interleaved spiral scrolls — one fixed, one orbiting. Fewer moving parts than reciprocating, with better efficiency, lower noise, and lower vibration. Dominant in modern commercial AC and in larger enclosure-AC capacities (≥ 1 ton).

SEER / Seasonal Energy Efficiency Ratio

Cooling Concepts

A weighted-average efficiency rating for residential split AC across a defined cooling season, per AHRI 210/240. SEER does NOT typically apply to industrial self-contained enclosure ACs — EER and IEER are the relevant metrics. SEER 14 minimum applies to most residential central AC since 2023.

Sensible Cooling

Cooling Concepts

The portion of cooling capacity that lowers air temperature without changing its moisture content. Closed-loop enclosure cooling is almost entirely sensible because the sealed cabinet has no moisture source. Heat exchangers provide 100% sensible cooling.

Related: Sensible Heat • Latent Heat • Closed-Loop Cooling

Sensible Heat

Cooling Concepts

Heat that causes a temperature change in a substance without changing its phase. Most heat dissipated by electronics inside an enclosure is sensible heat. Contrast with latent heat, which is absorbed or released during phase changes (e.g., water condensation).

Shelter

Telecom

A walk-in prefabricated outdoor structure (typically 12' × 30' to 12' × 50') housing telecom or utility electronics — larger than a hut. Shelters use building-style HVAC plus secondary enclosure cooling for high-density racks.

Short Cycling

Operations

A failure mode in which the compressor turns on and off rapidly without completing meaningful cooling cycles. Causes accelerated wear, high energy use, and poor temperature control. Common root causes: dirty condenser coil, low refrigerant charge, oversized unit, or too-narrow thermostat differential.

Sight Glass

Components

A small viewing window installed in the liquid line, allowing visual inspection of refrigerant flow. Bubbles or foaming indicate undercharge or non-condensable gases. Many sight glasses include a moisture indicator that changes color when the system is wet.

Related: Liquid Line • Subcooling

Soft Start

Electrical

A power-electronic device that limits inrush current during compressor or motor startup, typically reducing LRA by 50-75%. Used to protect generators, UPS systems, and weak utility services from voltage sag during compressor starts.

Solar Gain

Cooling Concepts

Heat absorbed by an enclosure from direct and diffuse solar radiation. For dark outdoor enclosures, solar gain can equal or exceed component dissipation — typically 500-1,500 BTU/hr depending on surface area, color, and latitude. Light-colored or shaded enclosures reduce solar load substantially.

Related: Heat Load • U-Value

Static Pressure

HVAC General

The resistance to airflow through a duct, filter, or coil, measured in inches of water column (in. w.c.). As static pressure rises, fan-delivered CFM falls. Total external static pressure is a critical sizing parameter for ducted enclosures.

Subcooling

Components

The number of degrees a liquid refrigerant is cooled below its saturation temperature at a given pressure. Measured at the condenser outlet. Healthy systems typically run 5-15°F subcooling; low subcooling indicates undercharge, high subcooling indicates overcharge or restriction.

Related: Superheat • Condenser Coil • Liquid Line

Suction Line

Components

The refrigerant tubing between the evaporator outlet and the compressor inlet, carrying low-pressure superheated vapor. Larger diameter than the liquid line. Insulated to prevent sweating and to maintain superheat all the way to the compressor.

Related: Liquid Line • Superheat • Compressor

Superheat

Components

The number of degrees a refrigerant vapor is heated above its saturation temperature at a given pressure. Measured at the evaporator outlet. Proper superheat (typically 8-15°F for capillary systems, 5-12°F for TXV systems) ensures all liquid has boiled off before reaching the compressor.

Supply Air

HVAC General

The conditioned air delivered from the AC unit into the enclosure or room. Supply-to-return ΔT (typically 18-22°F for sensible cooling) is a useful field check for AC performance.

Related: Return Air • Sensible Cooling

T

4 terms

Telecom Shelter

Telecom

Catch-all category covering wireline and wireless telecom equipment housing — central offices, huts, shelters, OSP cabinets, and small-cell enclosures. The largest single application segment for industrial enclosure cooling because telecom equipment runs continuously, generates substantial heat, and is often deployed outdoors.

Related: CO / Central Office • Hut • Shelter • OSP / Outside Plant • GR-487

Thermostat

Components

A temperature-actuated control switch. Mechanical bimetal thermostats are still used in basic enclosure ACs; electronic thermostats with digital setpoint and alarm contacts are standard on modern units. Differential is the temperature swing between cut-in and cut-out — typically 4-8°F to prevent short cycling.

Ton of Refrigeration

Cooling Concepts

A unit of cooling capacity equal to 12,000 BTU/hr (the heat absorbed by melting one short ton of ice in 24 hours). Used for sizing chillers and large unitary AC. A 1-ton unit removes 12,000 BTU/hr; a 0.5-ton unit removes 6,000 BTU/hr.

Tube-Fin Heat Exchanger

Heat Exchangers

A heat-exchanger geometry using parallel tubes (often copper) with mechanically-bonded plate fins (often aluminum). The dominant geometry for refrigerant evaporator and condenser coils. Compact, manufacturable, and tolerant of high pressures.

U

3 terms

U-Value

Cooling Concepts

The overall thermal transmittance of an enclosure wall, in BTU/hr·ft²·°F. Lower is better for insulation. U-value × surface area × ΔT gives ambient heat-transfer load. Steel enclosures have U-values around 0.5-1.0; insulated outdoor cabinets can reach 0.1 or lower.

Related: Heat Load • Delta-T (ΔT) • Solar Gain

UL 1995

Standards

Standard for Heating and Cooling Equipment — covers HVAC equipment outside the scope of UL 484, including larger commercial unitary AC. Being progressively replaced by the harmonized standard UL 60335-2-40.

Related: UL 484

UL 484

Standards

Standard for Safety of Room Air Conditioners — covers self-contained packaged AC equipment of less than 3 tons. Most enclosure ACs in the AT and AN size class are UL 484 Recognized. Defines electrical, mechanical, refrigeration, and marking requirements.

Related: UL 1995 • ANSI

V

2 terms

VFD / Variable Frequency Drive

Electrical

A power-electronic device that varies AC motor speed by changing the frequency and voltage of the supplied power. Drives generate substantial heat (typically 3% of motor power) and are themselves heat-load sources inside the enclosures they control. VFDs also generate harmonic and EMI noise that may require filtering.

Voltage (115 / 230 / 460 VAC)

Electrical

Common North American electrical service voltages. 115VAC single-phase: standard wall outlets. 230VAC single-phase: larger residential and small commercial. 460VAC three-phase (sometimes labeled 480V nominal): industrial. VoltAire AN units are available in 115V and 230V versions; AT units are available in 115V, 230V, and 48VDC versions, with 460V variants coming Q3 2026. Today, 460V three-phase input is available on the PU1600 pressurization unit.

W

3 terms

W/°F

Heat Exchangers

The standard performance metric for air-to-air heat exchangers, expressing the wattage transferred per degree Fahrenheit of temperature differential between internal and ambient air. A 50 W/°F heat exchanger removes 1,000 W (~3,400 BTU/hr) at a 20°F ΔT.

Washdown Environment

Enclosures

An installation environment where equipment is regularly cleaned by direct hose or pressure-washer spray, typical of food, beverage, dairy, and pharmaceutical processing. Requires NEMA 4X (corrosion-resistant) ratings on all enclosures and cooling units, plus stainless hardware and sealed cable entries.

Related: NEMA 4X

Watt

Cooling Concepts

The SI unit of power, equal to one joule per second. Conversion to BTU/hr: 1 watt = 3.412 BTU/hr. Component dissipation is usually published in watts; cooling capacity is usually published in BTU/hr — multiply watts by 3.412 to compare directly.

Industrial Enclosure Cooling Glossary

4

48VDC

A

A2L Refrigerant

Adiabatic Cooling

AHRI

AIM Act

Air-to-Air Heat Exchanger

Ambient Temperature

AN Series

ANSI

ASHRAE

ASHRAE 90.1

ASTM A653

ASTM B117

AT Series

B

BABA / Build America Buy America

BEAD Program

BMS / Building Management System

Bolt-for-Bolt Replacement

BTU / British Thermal Unit

C

Capacitor (Run / Start)

Capillary Tube

CFC / Chlorofluorocarbon

CFM / Cubic Feet per Minute

Class I Division 2

Closed-Loop Cooling

CO / Central Office

Compressor

Condensate

Condensate Pump

Condenser Coil

Contactor

Control Panel

COP / Coefficient of Performance

Counter-Flow Heat Exchanger

Cross-Flow Heat Exchanger

D

Data Center

Delta-T (ΔT)

Dew Point

DOE Energy Conservation Standards

Drip Loop

Duty Cycle

E

ECM Motor

Edge Computing

EER / Energy Efficiency Ratio

EMI / Electromagnetic Interference

Enclosure

Evaporator Coil

Expansion Valve (TXV)

F

Fan Motor

FCC Part 15

Filter Drier

FLA / Full Load Amps

Free Cooling

Free-Air CFM

G

GR-1089 / NEBS EMC

GR-487

GR-63 / NEBS Physical Protection

GWP / Global Warming Potential

H

Hazardous Location

HCFC

Heat Load

Hermetic Compressor

HFC / Hydrofluorocarbon

High-Ambient Operation

Hoffman

Hut

I

IEER / Integrated Energy Efficiency Ratio

IP Rating (IEC 60529)

IP66