A working glossary of commercial VRF, heat pump, HVAC, and NYC compliance terms. Compiled from 35-plus years of NYC commercial HVAC service work. Written for building owners, property managers, facility directors, and engineers who deal with these systems but did not train in them.
Terms are listed alphabetically. Where Mountain Mechanical has a dedicated page on a topic, we link to it.
Jump to: A · B · C · D · E · F · G · H · I · L · M · N · O · P · R · S · T · U · V
A
A2L Refrigerant
A class of mildly flammable refrigerants, including R-32 and R-454B, being introduced to replace higher-GWP refrigerants like R-410A. A2L refrigerants require different leak detection, ventilation, and safety-handling protocols. Many newer commercial heat pump platforms are transitioning to A2L formulations.
AE-200
Mitsubishi Electric’s centralized controller for City Multi VRF systems. Handles zone scheduling, setpoint control, BMS integration via BACnet or Modbus, and diagnostic data pulls. Servicing a City Multi system properly requires AE-200 access.
AIM Act
The American Innovation and Manufacturing Act of 2020. Sets a phased US reduction schedule for high-GWP hydrofluorocarbon refrigerants including R-410A. Drives the long-term transition to A2L refrigerants across commercial heat pump equipment.
ASHRAE
The American Society of Heating, Refrigerating and Air-Conditioning Engineers. Publishes the technical standards most commercial HVAC design and service work relies on, including ASHRAE 62.1 (ventilation), 90.1 (energy efficiency), and 15 (refrigeration safety).
B
BACnet
An open building automation protocol used for communication between HVAC equipment and building management systems. Most commercial VRF brands offer BACnet gateways for BMS integration, though implementation quality varies.
BC Controller (Branch Controller)
A Mitsubishi City Multi component that distributes refrigerant to individual indoor units in a heat recovery system. Houses valves, sensors, and the switching logic that allows simultaneous heating and cooling. BC controller failures affect multiple zones at once. See our BC Controller failure page.
Benchmarking (NYC)
The required annual reporting of building energy and water use to the NYC Department of Buildings under Local Law 84. Covers most buildings 25,000 square feet and larger. Data feeds into Energy Star scoring and public visibility on building performance.
BMS (Building Management System)
The centralized control system that manages HVAC, lighting, access control, and other building systems. VRF systems typically integrate with BMS through BACnet, Modbus, or proprietary gateways. See our VRF BMS integration page.
BSK (Branch Selector Kit)
LG’s equivalent of Mitsubishi’s BC controller. Distributes refrigerant to indoor units in Multi V heat recovery systems. BSK junction points are a known leak development site in aging LG Multi V systems. See our BSK leaks page.
C
City Multi
Mitsubishi Electric’s commercial VRF brand. The dominant VRF platform in Manhattan luxury residential and high-end mixed-use buildings. Uses M-NET communication and the AE-200 controller. See our City Multi service page.
CLCPA (Climate Leadership and Community Protection Act)
New York State’s 2019 climate law. Sets statewide emissions targets of 40 percent reduction by 2030 and 85 percent by 2050 from 1990 levels. Drives state-level funding programs (NYSERDA Clean Heat) that complement NYC Local Law 97.
Clean Heat Rebate
NYSERDA-administered commercial incentive for heat pump installation, including VRF and air-source heat pump projects. Rebates are tied to equipment tonnage and efficiency. See our Clean Heat rebates page.
Commissioning
The formal process of verifying that a newly installed HVAC system meets design intent. Covers refrigerant charge verification, controller programming, airflow balancing, sequence-of-operation testing, and BMS integration. Poor commissioning is one of the most common root causes of long-term VRF problems.
Compressor (Scroll / Inverter)
The heart of any VRF system. Most commercial VRF systems use inverter-driven scroll compressors, which modulate speed continuously rather than cycling on and off. Inverter-scroll compressors are more efficient but have a finite service life and are typically the most expensive single component in a VRF system.
Condensate Drain
The line that carries water drained from indoor unit evaporator coils. Clogs in condensate drains cause water damage and can shut down VRF indoor units via float-switch protection. Drain inspection is part of any proper preventive maintenance visit.
Con Edison C&I Program
Con Edison’s Commercial and Industrial energy-efficiency program. Offers cash incentives for energy-saving equipment including commercial heat pump upgrades. See our Con Edison incentives page.
COP (Coefficient of Performance)
The ratio of useful heat output to energy input for a heat pump system. Commercial heat pump COPs typically range from 2.5 to 4.0 depending on outdoor temperature. Higher COP means more heat delivered per unit of electricity consumed.
D
Daikin Service Checker
Daikin’s proprietary diagnostic software for VRV systems. Connects to the outdoor unit to read operating data, historical faults, and refrigerant charge information. A factory-certified Daikin contractor will have Service Checker access.
DefinedTerm / DefinedTermSet
A Schema.org structured data type used to mark up glossaries for search engines and AI systems. This page uses DefinedTerm markup so that AI search tools can cite individual terms cleanly.
DMS2 (Data Management Server 2)
Samsung’s central controller for DVM VRF systems. Handles BMS integration, zone scheduling, and diagnostic data collection. Servicing a DVM system at the system level requires DMS2 access.
DVM (Digital Variable Multi)
Samsung’s branding for their commercial VRF platform. Underlying technology is identical to other VRF systems. See our Samsung DVM service page.
E
EEV (Electronic Expansion Valve)
A valve that precisely meters refrigerant flow, driven by a stepper motor and modulated in real time based on system demand. Every indoor unit in a VRF system has an EEV, and the outdoor unit has one or more as well. EEV failures cause zone-level comfort issues that are often misdiagnosed.
Electrification
The replacement of fossil-fuel-based heating equipment (gas boilers, fuel oil, PTAC systems) with electric heating technology, most commonly commercial heat pumps and VRF. Local Law 97 is the primary driver of commercial electrification in NYC. See our VRF electrification page.
Energy Star Score
A 1-to-100 scale comparing a building’s energy performance to similar buildings nationally. A score of 75 or higher qualifies for Energy Star certification. NYC benchmarking data (from LL84) generates Energy Star scores for most commercial buildings.
EPA 608 Certification
A federal certification required for any technician who handles refrigerant. Universal-level 608 certification is necessary for commercial HVAC work. A contractor who cannot produce 608 certifications for their technicians is operating illegally.
Error Code
A diagnostic output from a VRF system controller indicating a specific fault condition. Each brand uses its own error code system. See our VRF error codes guide and the error code lookup tool.
F
Factory Certified
A contractor whose technicians have completed manufacturer-specific training on a VRF brand and maintain ongoing training requirements. Each brand runs its own certification program (Daikin factory-certified, Mitsubishi Diamond Contractor, LG-certified, Fujitsu-certified, Samsung DVM-certified). Not all “VRF contractors” are factory-certified on the brand in your building.
Fault Isolation
The diagnostic process of narrowing down which component or subsystem is causing a reported fault. VRF fault isolation often requires systematic bus testing, pressure readings at multiple points, and component-level verification. See our VRF diagnostics page.
G
GWP (Global Warming Potential)
A measure of a refrigerant’s heat-trapping effect relative to CO2 over a 100-year horizon. R-410A has a GWP of 2088; R-32 is around 675; R-454B is around 466. Long-term regulatory direction is toward lower-GWP refrigerants.
H
Head Pressure
The refrigerant pressure measured at the compressor discharge. High head pressure is one of the most common VRF fault triggers, caused by dirty condenser coils, overcharged systems, restricted airflow, or failing components. Sustained high head pressure damages compressors.
Heat Pump (Commercial)
A refrigerant-based system that can both heat and cool a building by reversing the direction of refrigerant flow. Commercial heat pumps include VRF, air-source heat pumps, and water-source heat pumps. See our commercial heat pumps hub.
Heat Recovery
A VRF configuration that can simultaneously heat some zones while cooling others, transferring heat between zones rather than rejecting it to outdoors. More expensive than heat pump VRF but far more efficient in buildings with diverse zone loads. See our heat recovery page.
I
IEER (Integrated Energy Efficiency Ratio)
A part-load efficiency rating for commercial air conditioning and heat pump equipment. Reflects real-world performance across a range of loads better than the older EER metric. Higher IEER correlates with lower operating cost.
Intelligent Touch Manager
Daikin’s commercial controller for VRV systems. Handles scheduling, BMS integration, and zone-level control. Analogous to Mitsubishi’s AE-200 and Samsung’s DMS2.
Inverter Board
The power electronics assembly that drives the compressor at variable speed. One of the most expensive components in a VRF system and a common failure point on systems past 8 to 10 years of service. Power quality issues (sags, surges, harmonics) accelerate inverter board degradation.
L
LGMV
LG Multi V diagnostic software. Connects to Multi V systems to read operating data, fault history, and commissioning parameters. Required for competent service on LG VRF systems.
Local Law 84 (LL84)
NYC’s benchmarking law. Requires annual energy and water use reporting for buildings 25,000 square feet and larger. Generates the data that feeds Energy Star scores and informs Local Law 97 emissions baselines.
Local Law 87 (LL87)
NYC’s energy auditing and retro-commissioning law. Requires periodic comprehensive audits and retro-commissioning for buildings 50,000 square feet and larger. Findings often drive HVAC upgrade decisions.
Local Law 88 (LL88)
NYC’s lighting upgrade and sub-metering law. Affects HVAC indirectly by changing electrical load profiles and BMS integration requirements in upgraded buildings.
Local Law 97 (LL97)
NYC’s carbon emissions law. Sets escalating building-level emissions caps starting with the 2024-2029 period and tightening in 2030-2034 and beyond. Non-compliance carries a penalty of $268 per tCO2e over the cap. Drives the commercial heat pump and VRF retrofit market in NYC. See our LL97 compliance page.
Local Law 152 (LL152)
NYC’s gas piping inspection law. Requires periodic inspection of building gas piping. Relevant to HVAC when buildings are considering gas-to-electric conversion decisions.
M
M-NET
Mitsubishi Electric’s proprietary communication protocol for City Multi VRF systems. Connects outdoor units, indoor units, BC controllers, and controllers on a single bus. Bus faults (P6 and P9 errors) are a common City Multi service call.
Modbus
An open industrial communication protocol commonly used for BMS integration with HVAC equipment. Most VRF brands offer Modbus gateways, usually alongside BACnet.
Multi V
LG’s commercial VRF brand. Includes Multi V 5, Multi V Water IV, and Multi V Heat Recovery variants. See our LG Multi V service page.
N
NYSERDA
The New York State Energy Research and Development Authority. Administers state-level incentive programs for commercial heat pump installation, including Clean Heat rebates and other efficiency-focused funding.
O
Oil Return
The process of circulating lubricating oil back to the compressor through the refrigerant system. Proper oil return depends on refrigerant velocity, piping design, and system commissioning. Oil return problems on long-run VRF systems cause compressor wear and capacity loss.
Outdoor Unit
The condenser-side equipment of a VRF system, typically located on the roof in NYC commercial installations. Houses the compressor, inverter board, fan, and main heat exchanger. Outdoor units are the most exposed and weather-beaten part of a VRF system.
P
Piping Run (Refrigerant)
The refrigerant distribution network that connects the outdoor unit to all indoor units. Each brand publishes maximum piping lengths, height differences, and branching rules. Improper piping design or installation causes performance, oil return, and reliability issues that are difficult to correct after the fact.
Preventive Maintenance (PM)
Scheduled service visits designed to catch problems before they cause failures. Proper commercial VRF PM includes coil cleaning, refrigerant charge verification, electrical inspection, EEV function testing, controller firmware review, and written documentation. See our commercial heat pump maintenance page.
R
R-32
A single-component A2L refrigerant with a GWP of around 675, roughly one-third that of R-410A. Becoming more common in new commercial VRF equipment as the A2L transition progresses.
R-410A
A two-component refrigerant that has been the industry standard for commercial VRF systems for the past two decades. GWP of 2088. Being phased down under the AIM Act in favor of lower-GWP A2L refrigerants. Still serviceable for existing installations but increasingly expensive.
R-454B
An A2L refrigerant blend with a GWP of around 466. Used in some newer commercial heat pump platforms as an R-410A alternative.
Recuperation (System)
The process of bringing a neglected or poorly installed VRF system back into proper operation. Includes diagnostic data pull, refrigerant verification and correction, controller recommissioning, and remediation of installation errors. Distinct from repair in that recuperation addresses systemic issues, not a single fault.
REFNET Joint
Daikin’s branded refrigerant piping branch fitting for VRV systems. Correct REFNET sizing and orientation is specified in Daikin design manuals and is required for warranty coverage and proper oil return.
Refrigerant Charge
The total amount of refrigerant circulating in a system, measured in pounds or kilograms. Proper charge is critical for efficiency and reliability. Overcharge and undercharge both cause faults and component wear. VRF charge is calculated based on pipe lengths and verified through subcooling and superheat measurement.
S
Samsung S-NET
Samsung’s proprietary communication protocol for DVM VRF systems. Connects indoor and outdoor units. Bus faults show up as E201 and E202 error codes.
Service Contract
A formal ongoing service agreement between a building and a service contractor. Defines PM cadence, scope of included work, emergency response commitments, and pricing. Real commercial VRF service contracts include semi-annual minimum visits, coil cleaning, refrigerant verification, electrical checks, controller review, and written reporting. See our VRF service contracts page.
Subcooling
The temperature difference between the refrigerant leaving the condenser and its saturation temperature. Subcooling measurement is one of the primary methods for verifying proper VRF refrigerant charge, especially on Daikin and Mitsubishi platforms.
Superheat
The temperature difference between refrigerant vapor leaving the evaporator and its saturation temperature. Superheat measurement verifies proper EEV operation and refrigerant charge. Improper superheat damages compressors over time.
T
Takeover Service
The process of one service contractor assuming responsibility for a VRF system previously serviced by another contractor. Involves system inventory, diagnostic data pull, documentation review, and remediation of any deferred issues. See our replace your VRF contractor page.
Tonnage
A unit of HVAC capacity. One ton equals 12,000 BTU per hour. Commercial VRF outdoor units are typically specified from 6 to 36 tons, with multiple outdoor units combined for larger buildings.
U
U4 Error (Daikin)
A Daikin VRV communication error between outdoor and indoor units. The most common Daikin fault code in aging Manhattan installations. Causes range from wiring faults to address conflicts to failed communication PCBs. See our Daikin U4 error page.
V
VRF (Variable Refrigerant Flow)
The underlying technology for commercial multi-zone heat pump systems. Uses a single outdoor unit to serve many indoor units, with refrigerant flow modulated zone by zone. Dominant commercial heat pump technology for NYC multi-zone applications. See our VRF systems hub.
VRV (Variable Refrigerant Volume)
Daikin’s branded name for VRF. Functionally identical technology. Using “VRV” in conversation signals Daikin-specific context. See our Daikin VRV service page.
Looking for a Term That Isn’t Here?
If there is a VRF, commercial heat pump, or NYC HVAC compliance term you want defined and it is not on this list, let us know. We add terms based on what building managers and property owners actually ask.
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