HVAC Abbreviation List | Acronyms | Terminology

There are a lot of abbreviations, acronyms, terminologies, definitions and short forms used in HVAC. Beginners often struggle to understand the terms used in HVAC. So, I compile a list of the common abbreviations used in HVAC with a short explanation.

AHU

AHU stands for Air Handling Unit. AHU is a large-capacity, customizable air conditioner that made of an air filter, a cooling coil and a blower fan. It typically runs chilled water through its cooling coil to provide cooling. Learn the basics of AHU here.

ACCU

ACCU stands for Air Cooled Condensing Unit. ACCU is the outdoor unit of a split air conditioning system. It usually paired with ACSU which stands for Air Cooled Split Unit. In drawing, you should find ACCU connected to ACSU by a pair of refrigerant pipe.

AHRI

AHRI stands for Air Conditioning, Heating, and Refrigeration Institute. AHRI is a North American trade association of manufacturers of air conditioning, heating, and commercial refrigeration equipment. They published many guidelines known as AHRI Standard which many of us working in the HVAC industry follow and comply.

ACH

ACH stands for Air Change per Hour. ACH is the number of air volume replaced in one hour. It is calculated by dividing the airflow per hour by the volume of the room. For example, a 10×10 ft (3.05×3.05 m) room has a ceiling height of 10 ft (3.05 m). So, 10x10x10 ft (3x3x3 m) results in 1000 ft³ (28 m³) of volume. Given the airflow is 50 ft³/min (85 m³/hr), converting the airflow to per hour will give us 50×60 = 3000 ft³/hr (85 m³/hr is already per hour). Therefore, 3000 ft³/hr ÷ 1000 ft³ = 3 ACH (85 m³/hr ÷ 28 m³ = 3 ACH).

ACU

ACU stands for Air Conditioning Unit. ACU is a generic term used to indicate an air conditioning unit, regardless of the type. The air conditioning unit can be AHU, FCU or any other type of air conditioners that provides airflow and air conditioning to a room.

ATC

ATC stands for Automated Temperature Control. ATC is used to indicate the temperature and humidity in certain sections/zones of a building is automatically controlled by the air conditioning system.

ARI

ARI stands for Air Conditioning, Heating, and Refrigeration Institute. ARI is a North American trade association of manufacturers of air conditioning, heating, and commercial refrigeration equipment. They published many guidelines known as ARI Standard which many of us working in the HVAC industry follow and comply.

AC

AC stands for Air Conditioner. AC is a generic term used to indicate an air conditioner, regardless of the type. The air conditioner can be AHU, FCU or any other type that provides airflow and air conditioning to a room.

ACMV

ACMV stands for Air Conditioning and Mechanical Ventilation. In regions where heating is not required, ACMV is used instead of HVAC. It excludes equipment such as heat pumps, furnaces, boilers, radiators and electric resistive heaters.

BMS

BMS stands for Building Management System. BMS is the central control system for the mechanical and electrical system in a building. It monitors and controls the start/stop, the schedule, the faulty/alert of the building’s air conditioners and ventilation fans. Learn how HVAC system integrates with BMS here.

BAS

BAS stands for Building Automation System. BAS is the central control system of the mechanical and electrical system in a building that focuses more on automation. It controls the start/stop, the schedule, the faulty/alert of the building’s air conditioners and ventilation fans.

BTU

BTU stands for British Thermal Unit. BTU is the most common unit of measurement for air conditioner cooling and heating capacity. It measures the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Other measurement units for air conditioner capacity include Ton, kW and HP.

BCU

BCU stands for Blower Coil Unit. BCU is a compact type of floor-standing air handler that use either chilled water or refrigerant to provide air conditioning. BCU itself usually doesn’t have compressor and condenser.

BC

BC stands for Branch Circuit. BC or BC controller is referring to the controller used in the piping branch unit in a VRF system. It controls the amount of refrigerant flowing to each circuit based on the cooling demand.

BS

BS stands for British Standard. BS is a non-profit distributing organization and offers global services in the linked fields of standardization, systems assessment, product certification, training and advisory services. Certain HVAC components adopt the British Standard as a guideline. For example, chilled water pipes are manufactured based on BS 1387 standard. Cables/wires shall comply to BS 6004 standard.

BDD

BDD stands for Backdraft Damper. BDD is used to ensure air flows in one direction. It prohibit air from flowing in the reverse direction by using a mechanism to automatically close the damper when the air is flowing in the wrong direction.

CFM

CFM stands for Cubic Feet per Minute. CFM is the Imperial unit for airflow. In mathematic, CFM is expressed as ft³/min. It is the most common unit of measurement for airflow in HVAC.

COP

COP stands for Coefficient of Performance. COP is the universal measurement unit for the energy efficiency of air conditioners. COP is calculated by dividing the cooling output in kW by the power input in kW. For example, an air conditioner has a cooling capacity of 2.5 kW with a power input of 700 W. So, the COP of the air conditioner is 2.5 ÷ 0.7 = 3.57. In other words, COP tells us how many times is the cooling output for every kW of power input. For the example, 3.57 COP means for every kW of power input, the air conditioner produces 3.57 times of the cooling output. The higher the COP, the greater the efficiency.

CAV

CAV stands for Constant Air Volume. CAV is the counterpart of VAV which stands for Variable Air Volume. Before variable air becomes mainstream, the term CAV was not necessary because most air conditioning systems are constant air volume. With VAV becoming more and more common, it is necessary to use a different term to describe constant air systems.

CFC

CFC stands for Chlorofluorocarbons. CFC are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine, better known as refrigerant. A popular example is R-12 refrigerant which is a type of refrigerant used in old air conditioners (prior to 2000).

CRAC

CRAC stands for Computer Room Air Conditioning. CRAC units are air conditioners specifically designed for computer room applications. They have higher sensible cooling capacity and spot/target cooling to focus on cooling only the necessary places such as the server, processor and computer chips/cards.

CRU

CRU stands for Condensate Recovery Unit. CRU is a tank or a system that recovers the condensate water produced by the air conditioners in a building. It is an energy conservation system that reuse the condensate water for other purposes such as plant watering and drainage cleaning.

CUH

CUH stands for Cabinet Unit Heater. CUH is an electric heater to defrost or prevent condensation in a cabinet air conditioning unit. A heater is necessary to prevent condensate water from forming internally when an air conditioner or a control panel is located in cold places such as places with winter weather and mountains.

CHWS

CHWS stands for Chilled Water Supply. CHWS is commonly found in the chilled water system layout and schematic drawings. It is also common to have the CHWS word physically painted on the chilled water pipe to indicate the chilled water flow direction from the chiller to the air handling unit.

CHWR

CHWR stands for Chilled Water Return. CHWR is commonly found in the chilled water system layout and schematic drawings. It is also common to have the CHWR word physically painted on the chilled water pipe to indicate the chilled water flow direction from the air handling unit to the chiller.

CWS

CWS stands for Condenser Water Supply. CWS is commonly found in the chilled water system layout and schematic drawings. It is also common to have the CWS word physically painted on the condenser water pipe to indicate the condenser water flow direction from the cooling tower to the chiller.

CWR

CWR stands for Condenser Water Return. CWR is commonly found in the chilled water system layout and schematic drawings. It is also common to have the CWR word physically painted on the condenser water pipe to indicate the condenser water flow direction from the chiller to the cooling tower.

CP

CP stands for Control Panel. CP is commonly found in layout and panel drawings. AHUs and FCUs usually have a CP nearby or within the same room. CP is also very common in fan rooms. Sometimes, DB which stands for distribution box is used instead of CP.

DOAS

DOAS stands for Dedicated Outdoor Air System. DOAS is a stand-alone outdoor air system that brings in outdoor air independent of the operation of the air conditioning system. Normally, air conditioners can bring in outdoor air by attached a duct to the exterior of the building. However, the amount of outdoor air coming into the building is depending on a certain percentage of the air conditioning airflow. If the air conditioning airflow decreases, the outdoor airflow decreases. DOAS is necessary to improve indoor air quality and occupant health in certain applications where outdoor airflow is critical.

DDC

DDC stands for Direct Digital Control. DDC can take in data from multiple sensors and output as one. An example of DDC application is the basement ventilation system. In a basement carpark, multiple CO₂ sensors are installed to measure the CO₂ level. However, only one fan serves that area. A DDC controller connects multiple CO₂ sensors, analyse them and produce one signal to the fan to control the start/stop.

DX

DX stands for Direct Expansion. DX refers to air conditioners that use refrigerant as the medium of heat transfer to cool the air. Examples of DX systems include split air conditioners, multi-split air conditioners, and VRF/VRV systems. Contrarily, non-DX or indirect expansion refers to equipment like chillers which use chilled water as the medium of heat transfer instead of refrigerant.

DHU

DHU stands for Dehumidified Air Handling Unit. DHU is designed to remove water vapor or dehumidify much more effectively than conventional AHU. It can deploy components such as desiccant to improve the dehumidification capability of the system.

ERV

ERV stands for Energy Recovery Ventilator. ERV is an energy recovery devices that often transfer the heat from the incoming outdoor air to the outgoing exhaust air. In other words, it uses the exhaust air that has been air conditioned to cool the outdoor air that’s going to enter the building. A certain amount of air must be exhausted out and a certain amount of outdoor air must be brought in for ventilation purposes. Instead of exhausting out the cold air, a portion of its energy is transferred to the outdoor air, reducing the air conditioning load and saving energy.

EDH

EDH stands for Electric Duct Heater. EDH is used to reheat the air after the air leaves the cooling coil of an air handling unit. It increases the temperature of the air so that the air can absorb more moisture and better control the humidity level in the room. Additionally, EDH can also be used to prevent condensation from forming inside the duct.

EMS

EMS stands for Energy Management System. EMS monitor, control and optimize the air conditioning and ventilation system in a building. Unlike BMS or BAS, EMS focuses more on saving energy and reducing the operating cost of the mechanical system for the owner of the building.

ERU

ERU stands for Energy Recovery Unit. ERU is a generic term used to indicate equipment that recovers energy. Examples of ERU include ERV, heat wheel and heat pipe. Generally, ERU recovers the energy from the exhaust air or unwanted air to the outdoor air that’s being introduced into the system. It saves energy and improve the efficiency of the air conditioning system.

ECM

ECM stands for Electronically Commutated Motor. ECM is also known as DC brushless motor. It is a high-efficient motor that commonly found in FCU, ceiling ducted unit and other small-capacity air conditioners. ECM has a motor efficiency class rating of at least IE3 and above.

EAC

EAC stands for Electronic Air Cleaner. EAC is the secondary filter of large-capacity air conditioning units such as AHUs. It uses a small amount of electricity to catch/trap fine dust and particles which a conventional mesh filter unable to block.

EER

EER stands for Energy Efficiency Ratio. EER is another universal measurement for the energy efficiency of air conditioners. EER is calculated by dividing the capacity in BTU by the power input in W. For example, an air conditioner has a cooling capacity of 9000 BTU with a power input of 700 W. So, the EER of the air conditioner is 9000 ÷ 700 = 12.86. The higher the EER, the greater the efficiency.

EPA

EPA stands for Environmental Protection Agency. EPA is an independent agency of the United States government tasked with environmental protection matters. Certain aspects of HVAC must comply with the EPA requirement such as the energy efficiency rating and the type of refrigerant used.

ESP

ESP stands for External Static Pressure. ESP is the static pressure of a fan for air resistances outside the fan. Contrarily, internal static pressure is the air resistance within the fan itself. The ESP of a fan must be greater than the total resistances due to duct friction loss, fitting dynamic loss and equipment pressure drop. Learn how to calculate ESP here.

EAD

EAD stands for Exhaust Air Duct. EAD is commonly found in duct layout drawings, especially for the ventilation system. A duct size may be written right next to EAD to indicate the exhaust air duct size. It is also common to have the EAD word physically painted on the exhaust duct.

EA

EA stands for Exhaust Air. EA is commonly found in duct layout drawings, especially for the ventilation system. EA is commonly written next to the exhaust air grille, vent or register. It is usually accompanied by an arrow pointing away from the exhaust air grille indicating the airflow direction.

EAL

EAL stands for External Air Louver. EAL is commonly found in duct layout drawings, especially for the ventilation system. EAL is commonly written near the external wall. It is often used to emphasize the weatherproof requirement. Instead, it could be written as WPEAL which stands for weatherproof external air louver.

FCU

FCU stands for Fan Coil Unit. FCU is a small-capacity air conditioner that often uses duct for air distribution. Sometimes, wall-mounted and ceiling cassette type of air conditioning unit can also be referred to as FCU. It is comprised of a cooling coil, a filter and a blower fan. FCU is much smaller than AHU.

FLA

FLA stands for Full Load Amp. FLA is the amount of electrical current used when a motor is running at 100% capacity. It can be found on the nameplate of compressor, pump, fan and basically any equipment with a motor. When sizing cable, FLA should be used to ensure the cable has enough capacity to within the amperage during full load conditions.

FPB

FPB stands for Fan Powered Box. FPB is a variant of VAV box that has an additional fan and a heat source (electric heater or hot water coil). It uses the additional fan to ensure the temperature of the room doesn’t fall below a certain setpoint by utilizing the heat source to warm the air, preventing overcool.

FC

FC stands for Flexible Connector. FC indicates the connection between two components (eg: duct and diffuser, pump and pipe) requires a flexible connector. The flexible connector can be a flexible duct from the rigid duct to the supply air diffuser or a flexible joint from the pipe to the pump.

FPT

FPT stands for Fan Powered Terminal. FPT is a variant of VAV box that has an additional fan and a heat source (electric heater or hot water coil). It uses the additional fan to ensure the temperature of the room doesn’t fall below a certain setpoint by utilizing the heat source to warm the air, preventing overcool.

FFH

FFH stands for Fuel Fired Heater. FFH is a heater powered by fuel. It burns fuel to generate heat for air conditioning. A gas furnace is a type of FFH. It burns fossil fuel to provide heating.

FAU

FAU stands for Fresh Air Unit. FAU is a dedicated outdoor unit or fresh air that designed to cool and dehumidify outdoor air. It can supply fresh air to other AHUs or directly into the room. FAU are usually built with a good air filtration system to ensure the outside air is thoroughly filtered and cleaned before introducing it into the building.

FA

FA stands for Fresh Air. FA is commonly found in duct layout drawings, especially for the ventilation system. FA is commonly written next to the fresh air grille, vent or register. It is usually accompanied by an arrow pointing toward the fresh air grille indicating the airflow direction.

FAD

FAD stands for Fresh Air Duct. FAD is commonly found in duct layout drawings, especially for the ventilation system. A duct size may be written right next to FAD to indicate the fresh air duct size. It is also common to have the FAD word physically painted on the fresh air duct.

GRD

GRD stands for Grille, Register and Diffuser. GRD indicates a component is either a grille, a register or a diffuser. It is a generic term used to describe anything that’s supply/return and exhaust/intake air.

GWP

GWP stands for Global Warming Potential. GWP refers to the harmfulness of various types of refrigerant. For example, R410A has a GWP of 2090, R32 has a GWP of 675. Therefore, in terms of causing global warming, R32 is less harmful than R410A.

GUH

GUH stands for Gas Unit Heater. GUH is a heater powered by gas. It burns gas to generate heat for air conditioning. A gas furnace is a type of FFH. It burns natural gas to provide heating.

GPM

GPM stands for Gallon per Minute. GPM is the Imperial unit for water flow rate. It measure how many gallons of water flow for every minute. It is the most common measurement unit for water flow rate in HVAC.

HRV

HRV stands for Heat Recover Ventilator. HRV is a heat recovery devices that often transfer the heat from the incoming outdoor air to the outgoing exhaust air. In other words, it uses the exhaust air that has been air conditioned to cool the outdoor air that’s going to enter the building. A certain amount of air must be exhausted out and a certain amount of outdoor air must be brought in for ventilation purposes. Instead of exhausting out the cold air, a portion of its energy is transferred to the outdoor air, reducing the air conditioning load and saving energy.

HVAC

HVAC stands for Heating, Ventilation and Air Conditioning. HVAC is about controlling and maintaining the temperature, humidity and air quality in an enclosed space using various technologies including air conditioners, heat pumps, furnaces, boilers and ventilation fans.

IDM

IDM stands for Induced Draft Motor. IDM is the motor of the draft fan that’s located inside the heat exchanger coil of a furnace. It draws air and flame across the heat exchanger as well as discharge them out of the furnace. Meanwhile, the furnace blower fan blows air across the heat exchanger to produce heat.

IDU

IDU stands for Indoor Unit. IDU is used to describe air conditioning units that are located inside the building. On the other hand, ODU which stands for Outdoor Unit, is the counterpart. IDU and ODU often connected by a pair of refrigerant pipes.

ISO

ISO stands for International Standard Organization. ISO is a worldwide federation of national standards bodies. Many HVAC work involve complying various ISO standards. For example, ISO 7547 outlines the procedures to design an HVAC system for marine ships.

IU

IU stands for Induction Unit. IU is a secondary air conditioning unit that is often located near the target cooling/heating space. It takes in air conditioned by the primary air conditioning unit such as an AHU, and further cool/heat the air to the target space temperature.

IFM

IFM stands for Indoor Fan Motor. IFM can be found on the internal schematic diagram of various types of air conditioners. It is an acronym used to describe indoor fan motor.

IFR

IFR stands for Indoor Fan Relay. IFR is used to control the operation of the indoor fan motor. Upon energized, it will physically lid and close the circuit thereby allowing electricity to pass through and start the indoor fan motor.

KED

KED stands for Kitchen Exhaust Duct. KED is used to indicate the function of a duct. It describes the purpose of the duct is for exhausting the oil and smoke that the kitchen produce when cooking. KED is often made of carbon steel duct and low leakage is required to prevent smell from spreading into other areas.

KSF

KSF stands for Kitchen Supply Fan. KSF is a fresh air fan that supply outdoor air into the kitchen. The outdoor air acts as the makeup air as the kitchen has a powerful exhaust air system. Without the makeup air, the exhaust performance will be poor as the kitchen becomes a vacuum space.

LRA

LRA stands for Locked Rotor Amperage. LRA is known as the starting current of a motor. It measures the amount of electric current needed to turn a motor from a stationary position. LRA is an important value to account for when designing a power surge protection system.

LPC

LPC stands for Low Pressure Control. LPC is commonly found in compressor and refrigeration system. When the cooling demand is too low, the refrigerant doesn’t absorb enough heat. This cause the refrigerant pressure entering the compressor to be too low. If this persist, the compressor may freeze. Thus, the LPC will shut off the system to protect the compressor.

LPS

LPS stands for Low Pressure Switch. LPS is commonly found in compressor and refrigeration system. When the cooling demand is too low, the refrigerant doesn’t absorb enough heat. This cause the refrigerant pressure entering the compressor to be too low. If this persist, the compressor may freeze. Thus, the LPS will shut off the system to protect the compressor.

LSAT

LSAT stands for Liquid Saturation Temperature. LSAT refer to the saturation temperature of refrigerant in liquid form. It can be found in the PT chart of refrigerant. For example, the saturation temperature of liquid R410A refrigerant at 130 psi of pressure is 45°F (7°C).

LPF

LPF stands for Low Pass Filter. LPF is used to block unwanted high frequency signals by allowing only certain low frequency signals to pass through. It is basically a filter for electrical signals. LPF improves the electronics and control systems of various air conditioning units.

MUA

MUA stands for Make Up Air. MUA is necessary for any exhaust system to perform well. When the air in a room is being exhausted out, the room becomes negatively pressurized. If the negative pressure is significant, the exhaust system won’t work anymore. Therefore, MUA is needed to ensure the room won’t be turned into a vacuum space and the exhaust system can continuously perform.

MAU

MAU stands for Makeup Air Unit. MUA typically brings in outside air to replenish the air in the room as it being exhausted out. Without makeup air, the exhaust performance will be poor as the room becomes a vacuum space.

MCA

MCA stands for Minimum Circuit Ampacity. MCA is provided by the equipment manufacturer for installer to size the cable/wire. For example, if the MCA of an air conditioner is 10A, then 14 AWG (2.5 mm²) cable is needed.

MBH

MBH stands for Mille British Thermal Unit per Hour. MBH is equivalent to one thousand British Thermal Unit per hour or btu/hr. Multiple 1000 by btu/hr to get MBH. It is used for very large capacity air conditioners where the btu/hr has a lot of zero. For example, 200000 btu/hr is rewritten as 200 MBH. MBH usually found in catalogs and manuals.

MFD

MFD stands for Motorized Fire Damper. MFD is a type of damper that is both motorized and resistant to fire. It uses an actuator to automatically/remotely open and close. Its fire resistance is usually two hours. MFD is needed when a duct penetrates through a fire compartment wall.

MERV

MERV stands for Minimum Efficiency Reporting Value. MERV is used to indicate the filtration grade of air filters. The higher the MERV, the better the filtration grade. For example, MERV-16 can filter >95% of 0.1-1.0 microns of dust particles while MERV-11 can only filter >20% of the same dust particle size.

MV

MV stands for Motorized Valve. MV is used to indicate a valve is automatically operated. An automatically operated valve has an actuator which is a small motor that turns upon receiving the signal. MV is often found in chilled water system where water is involved.

MAHU

MAHU stands for Modular Air Handling Unit. MAHU is a type of air handling unit that can be joined/connected to form a large system. The term modular means it can be attached or detached depending on how big of a capacity is needed. The benefit of MAHU is flexibility as more units can be added in the future to increase the capacity.

MEP

MEP stands for Mechanical, Electrical and Plumbing. MEP includes air conditioning, mechanical ventilation, fire protection, plumbing, electrical, CCTV, security door, automated door and other systems that involve mechanical, electrical and plumbing field. HVAC is part of MEP.

NO

NO stands for Normally Open. NO refers to the position of a valve or an actuator during normal operation. It means that a particular valve or damper should be in open position by default. In special occasions such as a mode change (eg: from normal mode to fire mode), the valve or damper should close from an open position.

NRD

NRD stands for Non Return Damper. NRD is a type of damper that allows air to move in one direction only. It utilize the force of gravity and material weight to close. When air is moving in the correct direction, the mechanism of NRD allows it to open thereby letting the air to flow through. But, if the air moves in the wrong direction, the NRD blades will fall due to gravity, effectively prevent the air from passing through.

NPS

NPS stands for Nominal Pipe Size. NPS is a North American set of standard sizes for pipes expressed in inch. It refers to the internal diameter of a pipe. For example, an NPS 2 pipe is equivalent to a 50 mm pipe and an NPS 10 pipe is equivalent to a 250 mm pipe.

N+1

N+1 stands for Number of Duty plus 1. N+1 refers to an equipment or a system having a redundancy. N is the number of equipment in operation, often referred to as duty. 1 is the number of redundancy, often referred to as standby. For example, a chiller system with N+1 design means it could have 4 chillers on duty and 1 chiller as backup. Hence, 4+1.

OAHU

OAHU stands for Outdoor Air Handling Unit. OAHU is a type of air handling unit that process 100% outdoor air. It has an additional layer of air filter, a bigger cooling coil and other extra components needed to bring in outdoor air, process it (cooling, heating, humidifying or dehumidifying) and supply it to other air conditioning units or directly into the building.

OFM

OFM stands for Outdoor Fan Motor. OFM can be found on the internal schematic diagram of various types of air conditioners. It is an acronym used to describe outdoor fan motor.

OT

OT stands for Operating Theatre. OT is where doctors and surgeons perform surgical operation to patients in a hospital. It is a special room that requires extensive care in the design of the air conditioning system. OT rooms often require the humidity level to be less than 50% to allow sweat to quickly dry out. Also, OT rooms need to have 15-20 ACH and laminar flow to ensure the air quality stays good all the time.

ODU

ODU stands for Outdoor Unit. ODU is used to describe air conditioning units that are located outside the building. On the other hand, IDU which stands for Indoor Unit, is the counterpart. ODU and IDU often connected by a pair of refrigerant pipes.

O/A

O/A stands for Outdoor Air. O/A refers to air from outside the building. It is also known as fresh air (FA) or outside air (OA). Introducing a proper amount of O/A into the building through an HVAC system is important for the well being of occupants.

ODDB

ODDB stands for Outdoor Dry Bulb. ODDB is the dry bulb temperature of the outdoor air. It refers to the temperature that most thermometers and temperature sensors are capable of showing. Its counterpart, wet bulb temperature is another metric used to determine the moisture content in the outdoor air.

ODT

ODT stands for Outdoor Thermostat. ODT is a thermostat located outside the building used to control a secondary heating system when the outside temperature drop below the setpoint. It can be found on two-stage heat pumps or any systems that has a backup heater such as an auxiliary electric heater. ODT ensures the power-hunger backup heater only activates when the outside temperature is too cold.

OAD

OAD stands for Outdoor Air Duct. OAD is commonly found in duct layout drawings, especially for the ventilation system. A duct size may be written right next to OAD to indicate the outdoor air duct size. It is also common to have the OAD word physically painted on the outdoor air duct.

OA

OA stands for Outdoor Air. OA is commonly found in duct layout drawings, especially for the ventilation system. OA is commonly written next to the outdoor air grille, vent or register. It is usually accompanied by an arrow pointing toward the outdoor air grille indicating the airflow direction.

PID

PID stands for Proportional, Integral and Derivative. PID refers to a controller that can change the operation of HVAC systems based on data from various sensors. For example, if a flow meter senses the water flow rate exceeds the setpoint, it’ll feedback the data to the PID controller where the PID controller will call the respective valve to close.

PACU

PACU stands for Precision Air Conditioning Unit. PACU is a type of air conditioning unit dedicated for computer and server rooms. It comprised of multiple small-capacity air conditioners that cools the server racks instead of the entire room. PACU is capable of precisely control the temperature of the server racks.

PAC

PAC stands for Precision Air Conditioning. PAC is a type of air conditioning system dedicated for computer and server rooms. It comprised of multiple small-capacity air conditioners that cools the server racks instead of the entire room. PAC is capable of precisely control the temperature of the server racks.

PAU

PAU stands for Primary Air Handling Unit. PAU is a type of air handling unit that processed the outdoor air. It has an additional layer of air filter, a bigger cooling coil and other extra components needed to bring in outdoor air, process it (cooling, heating, humidifying or dehumidifying) and supply it to other secondary air handing units in the building.

PIU

PIU stands for Power Induction Unit. PIU is a secondary air conditioning unit that is often located near the target cooling/heating space. It takes in air conditioned by the primary air conditioning unit such as an AHU, and further cool/heat the air to the target space temperature.

PTAC

PTAC stands for Packaged Terminal Air Conditioner. PTAC is a compact type of air conditioners that combines the compressor, condenser, evaporator and expansion valve in one single unit. It is often found mounted on the wall below a window in hotels. PTAC is similar to the through-the-wall type of window air conditioner.

PAHU

PAHU stands for Pre-Cooled Air Handling Unit. PHAU is a type of air handling unit that processed the outdoor air. It has an additional layer of air filter, a bigger cooling coil and other extra components needed to bring in outdoor air, process it (cooling, heating, humidifying or dehumidifying) and supply it to other secondary air handing units in the building.

PSIG

PSIG stands for Pound per Square Inch Gauge. PSIG is the Imperial unit for pressure measured by a pressure gauge. It is often found in refrigerant pressure and chilled water pressure. For example, the low side pressure of a split air conditioner is 130 PSIG. The minimum pressure of a chilled water system is 25 PSIG. PSIG is often used interchangeably with PSI.

RTU

RTU stands for Roof Top Unit. RTU is a type of packaged air conditioner that located on the roof. It sits on the roof, supply air through the bottom by penetrating through the roof and dissipate heat through the top where its condenser coil is located at.

RLA

RLA stands for Rated Load Amp. RLA is the electric current drawn by a motor or compressor when operating under the rated conditions. For example, if the compressor of an air conditioner has a RLA of 10A, it means the electric current drawn by the compressor is 10 amps when the outdoor temperature is 95°FDB / 75°FWB. The outdoor temperature of 95°FDB / 75°FWB is where the air conditioner is tested or rated on.

RAF

RAF stands for Return Air Filter. RAF refers to the filter inside a return duct or on a return grille. It is an air filter used to prevent dust from accumulating inside the return duct. In cases where the air filter of the air conditioner is not available (missing or not accessible), having RAF ensures dust does not enter the air conditioning system and block critical component such as the cooling coil.

RPM

RPM stands for Revolution per Minute. RPM refers to the rotational speed of fans and pumps. For example, a pump has a flow rate of 200 GPM at 1450 RPM. If the RPM increases, the flow rate increases. According to the pump affinity law, RPM is directly proportional to flow rate.

RHC

RHC stands for Radiant Heating and Cooling. RHC is a type of heating and cooling system that rely on radiant heat transfer for heating and cooling. It is often more efficient than other heating and cooling systems because it doesn’t have duct losses. Besides, RHC usually use water as the medium for heat transfer and water has 4 times more specific heat than air, making the heat transfer process much more efficient.

RAD

RAD stands for Return Air Duct. RAD is commonly found in duct layout drawings. RAD is usually located at the center of the duct on a drawing. Often, the duct size can be found right after RAD to indicate the return air duct size. It is also common to have the RAD word physically painted on the return duct.

SEER

SEER stands for Seasonal Energy Efficiency Ratio. SEER indicates the energy efficiency of an air conditioner in cooling. It requires the air conditioner to be tested under an environment that resemble the cooling season. The higher the SEER number, the greater the efficiency.

SF

SF stands for Service Factor. SF is the percentage of overloading a motor can handle without failure. For example, if a motor has a full load amp of 10A, 1.5 SF means the maximum overload current the motor can handle is 15A. If a motor continuously run above 1.0 SF, its lifespan, efficiency and performance will reduce.

SFA

SFA stands for Service Factor Amp. SFA is the amount of electric current a motor can handle above its full load amp without failure. For example, if a motor has a full load amp of 10A, having 1.5 SF means the motor SFA is 15A. If a motor continuously run above 1.0 SF, its lifespan, efficiency and performance will reduce.

SAV

SAV stands for Staged Air Volume. SAV refers to design that changes the indoor fan motor speed for better comfort and energy efficiency. It utilize a variable speed drive and sensors to control the fan speed of the indoor unit based on the cooling demand.

SAD

SAD stands for Supply Air Duct. SAD is commonly found in duct layout drawings. SAD is usually located at the center of the duct on a drawing. Often, the duct size can be found right after SAD to indicate the supply air duct size. It is also common to have the SAD word physically painted on the supply duct.

TXV

TXV stands for Thermal Expansion Valve. TXV is used to expand and control the amount of refrigerant going into the evaporator of an air conditioner. It is a small device filled with a specific type of substance that expands at a specific temperature. If the temperature of the refrigerant leaving the evaporator is high, it’ll cause the substance inside the TXV to expand which result in the closing of the TXV. Therefore, reducing the amount of refrigerant going into the evaporator.

TEF

TEF stands for Toilet Exhaust Fan. TEF refers to the fan that exhaust air out of the toilet. The fan can be any type but usually either ceiling-mounted propeller fan, cabinet fan or mixed-flow fan. TEF can discharge individually at every toilet or combined and centralized at one discharge outlet.

TA

TA stands for Temperature of Air. TA indicates the temperature of the air at a given room/space/point. For example, if a room has a design temperature of 75°F (24°C), the indication in drawings may be TA 75°F or TA 24°C.

TF

TF stands for Toilet Fan. TF refers to the fan that exhaust air out of the toilet. The fan can be any type but usually either ceiling-mounted propeller fan, cabinet fan or mixed-flow fan. TF can discharge individually at every toilet or combined and centralized at one discharge outlet.

TC

TC stands for Thermocouple. TC is a type of temperature sensor consisting of two wires of different metals joined at each end. It is normally used in gas furnaces and hot water tanks for valve and operation controls.

VRF

VRF stands for Variable Refrigerant Flow. VRF is a type of air conditioning system that distribute refrigerant from one outdoor unit to multiple indoor units. It distinct itself from multi-split air conditioning systems by having only a pair of refrigerant pipes. The refrigerant pipes are connected by y-joints.

VAV

VAV stands for Variable Air Volume. VAV is a type of air distribution system that capable of controlling the amount of air supplied to each zone based on a local thermostat. When the room temperature reaches the setpoint, the thermostat sends a signal to close the damper in the VAV box which triggers the differential pressure sensor in the duct to slow down the AHU fan speed.

VRV

VRV stands for Variable Refrigerant Volume. The VRV is patented by Daikin which refers to a type of air conditioning system that distribute refrigerant from one outdoor unit to multiple indoor units. It distinct itself from multi-split air conditioning systems by having only a pair of refrigerant pipes. The refrigerant pipes are connected by y-joints

VFD

VFD stands for Variable Frequency Drive. VFD is used to control the motor speed of AHU and pump. It allows the system to manipulate the frequency of the electricity supplied to the motor thereby allowing the motor to change its rotational speed.

VVT

VVT stands for Variable Volume and Temperature. VVT is used in VRF/VRV system to describe the ability to change the refrigerant volume and the refrigerant temperature. By default, VRF/VRV systems are capable of changing the refrigerant volume. However, some VRF/VRV systems have the capability to change the refrigerant temperature for better comfort and energy efficiency.

VSAT

VSAT stands for Vapor Saturation Temperature. VSAT is the point where liquid refrigerant start turning into vapor/gas. It is also known as the refrigerant evaporating temperature. VSAT can be used to determine if an evaporator is working well.

VAC

VAC stands for Volt Alternating Current. VAC is the electrical voltage in alternating current. On the other hand, VDC which stands for Volt Direct Current is the electrical voltage in direct current. Some HVAC relays required 24VDC of power supply. Meaning it needs 24V of direct current power. If the incoming power supply is 240VAC (240V alternating current), then a 240VAC to 24VDC transformer is needed for the power conversion.

VVR

VVR stands for Variable Volume Ratio. VVR is a technology by Daikin. It enables the chiller’s compressor to adjust the compression ratio automatically when it senses the amount of lift needed in any given moment. It optimize the performance of the chiller and saves energy.

VSD

VSD stands for Variable Speed Drive. VSD is used to control the motor speed of AHU and pump. It allows the system to manipulate the frequency of the electricity supplied to the motor thereby allowing the motor to change its rotational speed.

WSHP

WSHP stands for Water Source Heat Pump. WSHP is a type of heat pump that uses water as the source of heat. For example, WSHP can harvest heat from chilled water, condenser water and even ground water and river water. The heat can then be used for water heating.

WG

WG stands for Water Gauge. WG is part of the measurement unit for the pressure of fan and pump. IN.WG which stands for inch water gauge is the Imperial unit for pressure. For example, ducts are normally designed with 0.1 in.wg of pressure loss per 100 ft of duct length.

HX

HX stands for Heat Exchanger. HX refers to the evaporator, condenser or the cooling coil of an air conditioner or a chiller. It can be any type including finned-tube heat exchanger which is commonly found in residential split air conditioners or shell-and-tube heat exchanger which is more commonly found in water-cooled chiller.

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