A

A2L refrigerant

A lower-GWP refrigerant class (e.g. R-32, R-454B) with mild flammability. Requires A2L-rated equipment, updated safety practices, and trained technicians.

Acceptance testing

Functional tests required by California's energy code (Title 24) to verify that installed mechanical systems operate as designed, performed by a certified technician and documented for the building department.

AHJ (authority having jurisdiction)

The government body that issues permits and enforces codes for a project, usually the local building department.

AIM Act

The American Innovation and Manufacturing Act, a federal law that phases down HFC production and use and supports emissions-reduction and reclamation requirements.

Air handling unit (AHU)

A central unit that conditions and circulates air through ductwork, containing fans, coils, filters, and dampers.

Air-cooled condenser

A condenser that rejects heat to outdoor air using fans, as opposed to water. Standard on rooftop units and most walk-in condensing units.

Anode rod

A sacrificial metal rod in a storage water heater that corrodes in place of the tank. When it is consumed, the tank begins to corrode.

ASHRAE 188

A standard that sets requirements for Legionellosis risk management in building water systems, including cooling towers and hot water.

ASHRAE 90.1

A national energy standard for commercial buildings, used by many states instead of or alongside local energy codes.

B

Balancing (TAB)

Testing, adjusting, and balancing: measuring and adjusting airflow or water flow so each space receives its design quantity.

BAS / BMS

Building automation system or building management system. A networked control system that schedules, monitors, and alarms HVAC and other building equipment.

Bid bond

A guarantee from a surety that the bidder will sign the contract and provide required bonds if awarded the project.

Blowdown

Water intentionally discharged from a boiler or cooling tower to control the concentration of dissolved solids.

C

Capacitor (run / start)

An electrical component that helps start or run motors and compressors. Weak capacitors are among the most common causes of no-cool calls.

Certified payroll

A payroll report, signed under penalty of perjury, showing each worker, classification, hours, and wages paid on a prevailing-wage project.

Chilled water system

A system in which a chiller cools water that is circulated to air handlers or fan coils instead of using refrigerant in distribution piping.

Chiller

A machine that removes heat from water using a refrigeration cycle. Air-cooled or water-cooled.

Commissioning (Cx)

A quality-assurance process that verifies a building's systems are installed and operate according to the design intent.

Compressor

The component that pressurizes refrigerant and circulates it through the system. Scroll, screw, reciprocating, and centrifugal types are common in commercial work.

Condensate drain

The pipe that removes water produced by cooling coils. A clogged drain is a leading cause of ceiling leaks.

Condenser

The coil where refrigerant rejects heat and turns from vapor to liquid.

Condensing boiler

A high-efficiency boiler that extracts heat from flue gases by condensing water vapor, requiring a condensate drain and low return-water temperatures.

Condensing unit

An outdoor assembly containing the compressor and condenser, used with walk-ins and split systems.

Contactor

An electrical switch that starts and stops compressors and fan motors. Contacts wear and pit over time.

Curb adapter

A fabricated adapter that lets a new rooftop unit fit an existing roof curb of a different size.

D

DAS / DSA

In California schools, the Division of the State Architect, which reviews and oversees K-12 and community college construction.

Davis-Bacon Act

A federal law requiring prevailing wages on covered federal construction contracts.

Defrost cycle

A scheduled process that melts frost from evaporator coils using electric heaters, hot refrigerant gas, or warm air.

Delta-T (ΔT)

The temperature difference across a coil, chiller, or heat exchanger. A key diagnostic measurement.

Demand-control ventilation (DCV)

A strategy that adjusts outdoor-air intake based on measured occupancy, typically using CO2 sensors.

DIR registration

Registration with California's Department of Industrial Relations, required for contractors and subcontractors on public works projects.

Discharge pressure / head pressure

The pressure on the high side of a refrigeration system, after the compressor. High head pressure often indicates a dirty condenser or failed fan.

E

ECM motor

An electronically commutated motor. Efficient, variable-speed motors increasingly used in evaporator and condenser fans.

Economizer

A set of dampers and controls that brings in cool outdoor air for free cooling when conditions allow.

EER / SEER / IEER

Efficiency ratings for cooling equipment. IEER (integrated energy efficiency ratio) is used for commercial equipment and reflects part-load operation.

Evaporator

The coil where refrigerant absorbs heat and evaporates, cooling the air or water passing over it.

Expansion valve (TXV / EEV)

A metering device that controls refrigerant flow into the evaporator. Thermostatic (TXV) and electronic (EEV) types.

F

Fault detection and diagnostics (FDD)

Built-in controls that identify equipment faults such as economizer failures or refrigerant problems.

G

GWP (global warming potential)

A measure of how much a refrigerant contributes to warming compared with carbon dioxide over a set period. Lower is better.

H

Heat exchanger

A surface that transfers heat between two media. In gas furnaces, a cracked heat exchanger is a safety hazard.

HFC

Hydrofluorocarbon refrigerants (e.g. R-410A, R-404A) that do not harm the ozone layer but have high GWP and are being phased down.

J

Job order contract (JOC)

A public contracting method using a unit-price book to issue repeated task orders.

L

Latent load

Cooling load associated with removing moisture from air, as opposed to sensible load which changes temperature.

Legionella

Bacteria that grow in warm water systems, including cooling towers and hot water systems, and can cause Legionnaires' disease.

Line set

The pair of refrigerant pipes connecting an outdoor unit to an indoor coil or evaporator.

M

MERV

Minimum efficiency reporting value, a rating of air filter effectiveness from 1 to 16.

Miller Act

A federal law requiring payment and performance bonds on federal construction contracts above a threshold.

N

NAICS 238220

North American Industry Classification code for plumbing, heating, and air-conditioning contractors, used in federal contracting.

NOx

Nitrogen oxides, air pollutants regulated by the South Coast AQMD for gas-fired water heaters and boilers.

P

PLA (project labor agreement)

A pre-hire collective bargaining agreement for a specific construction project that sets labor terms for all contractors on the job.

PM (preventive maintenance)

Scheduled inspection and service intended to prevent failures and extend equipment life.

Prevailing wage

The minimum hourly wage and benefits rate for a craft in a locality, required on covered public works.

R

Reach-in

A self-contained commercial refrigerator or freezer with doors the user reaches into, as opposed to walk-ins.

Reclaim

Processing used refrigerant to meet purity standards of new product, performed by an EPA-certified reclaimer.

Recovery

Removing refrigerant from equipment and storing it in an approved container, as required before repairs or disposal.

Retention

A percentage of each progress payment held back by the owner until project completion.

RFI

Request for information, a formal question from the contractor to the designer during a project.

Rooftop unit (RTU)

A self-contained packaged HVAC unit installed on a roof, containing cooling, heating, fans, and controls.

S

Scroll compressor

A compressor with two interleaved spiral elements, common in commercial rooftop units and refrigeration.

Section 608

The section of the Clean Air Act governing refrigerant handling, technician certification, recovery, and leak repair.

Sensible load

Cooling load associated with changing air temperature, as opposed to removing moisture.

Static pressure

The pressure in a duct system that resists airflow, measured in inches of water column. A diagnostic indicator of duct and filter conditions.

Subcooling

Cooling of liquid refrigerant below its condensing temperature. Used to evaluate refrigerant charge.

Submittal

Documentation of proposed equipment or materials submitted to the engineer for approval before purchase or installation.

Suction pressure

The pressure on the low side of a refrigeration system before the compressor.

Superheat

The temperature of refrigerant vapor above its boiling point at a given pressure. Used to evaluate evaporator feeding and charge.

T

Title 20

California appliance efficiency regulations applying to certain equipment sold in the state.

Title 24

California's Building Energy Efficiency Standards (Title 24, Part 6), which set efficiency and compliance requirements for new buildings and alterations.

Tonnage

A unit of cooling capacity. One ton equals 12,000 BTU per hour.

U

UA Local 250

A local union of the United Association of Plumbers, Pipefitters, Steamfitters, and Service Techs in Southern California.

V

VAV (variable air volume)

A system that varies the amount of conditioned air delivered to each zone to match load.

VFD (variable frequency drive)

An electronic controller that varies motor speed to match demand, saving energy on fans and pumps.

W

Walk-in

An insulated, room-size cooler or freezer served by a refrigeration system, typically with a remote or roof-mounted condensing unit.