Bozeman HVAC Terms
For All Your Abbreviation Questions
One of our top priorities at
Premier Air Heating & Cooling is making sure that homeowners are educated about the products and equipment
that will be installed in their homes. You can find more Bozeman-specific
information by checking out our
Tips & Tricks page. We have all the
HVAC-related terms you need to know in order to understand how the system works.
Call our team now at
(406) 333-0177 or
contact us online. We serve Bozeman,
Belgrade, and the surrounding areas in Gallatin Valley.
All the HVAC Terms You Need to Know
HVAC (heating, ventilation, and air conditioning) is a major sub-discipline
of mechanical engineering. The goal of HVAC design is to balance indoor
environmental comfort with other factors such as installation cost, ease
of maintenance, and energy efficiency.
An appliance, system, or mechanism designed to dehumidify and extract heat
from an area. Usually this term is reserved for smaller, self-contained
units such as a residential system.
A central unit consisting of a blower, heating, and cooling elements, filter
racks or chamber, dampers, humidifier, and other central equipment in
direct contact with the airflow. This does not include the ductwork through
the building. Abbreviated AH or AHU.
British Thermal Unit (BTU)
Any of several units of energy (heat) in the HVAC industry, each slightly
more than 1 kJ. One BTU is the energy required to raise one pound of water
one-degree Fahrenheit, but the many different types of BTU are based on
different interpretations. In the United States, the power of HVAC systems
(the rate of cooling and dehumidifying or heating) is sometimes expressed
in BTU/hour instead of watts. Abbreviated BTU or Btu.
Equipment that performs heat transfer to air when mounted inside an air
handling unit or ductwork. It is heated or cooled by electrical means
or by circulating liquid or steam within it.
A component in the basic refrigeration cycle that ejects or removes heat
from the system. The condenser is the hot side of an air conditioner or
heat pump. Condensers are heat exchangers, and can transfer heat to air
or to an intermediate fluid (such as water or an aqueous solution of ethylene
glycol) to carry heat to a distant sink, such as ground (earth sink),
a body of water, or air.
A device that controls the operation of part of a system, or the entire
system. It may simply turn a device on and off, or it may more subtly
modulate the set point of components. Most controllers are automatic but
have user input such as temperature set points, e.g. a thermostat. Controls
may be analog or digital.
A plate or gate placed in a duct to control air flow by increasing friction
in the duct.
Specialized housing for the air flow. Typically made of metal.
A dehumidifier is the equipment that extracts and removes humidity from
the air. It works by cooling air to the point where water turns to liquid
from vapor form and then the liquid is removed.
A diffuser is placed over ductwork and separates air with vanes going in
differing directions. It evenly distributes air flow in the desired directions.
An HVAC component that uses outside air, under suitable climate conditions,
to reduce required mechanical cooling. When the outside air’s enthalpy
is less than the required supply air during a call for cooling, an economizer
allows a building’s mechanical ventilation system to use up to the
maximum amount of outside air.
A component in the basic refrigeration cycle that absorbs or adds heat
to the system. Evaporators can be used to absorb heat from air or from
a liquid. The evaporator is the cold side of an air conditioner or heat pump.
A small terminal unit that is often composed of only a blower and a heating
and/or cooling coil, as is often used in hotels, condominiums, or apartments.
An opening through which outside air is drawn into the building. This may
be to replace air in the building that has been exhausted by the ventilation
system, or to provide fresh air for combustion of fuel. Abbreviated FAI.
A component of an HVAC system that adds heat to air or an intermediate
fluid by burning fuel (natural gas, oil, propane, butane, or other flammable
substances) in a heat exchanger.
Gas Furnace Heat Exchanger
A gas furnace heat exchanger is responsible for the transfer of heat from
inside the furnace into the air outside the furnace. The duct system then
transfers this exchanged air to different rooms in the building or space.
A facing across a duct opening, often rectangular in shape, containing
multiple parallel slots through which air may be delivered or withdrawn
from a ventilated space. The grill directs the air flow in a particular
direction and prevents the passage of large items.
A heating coil is the part of the system that conducts heat. It allows
electricity to act as fire.
A heat exchanger is the part of the system that transfers heat from the
hot parts of the machine or a system to the cold parts of the machine
Terms for the amount of cooling (heat gain) or heating (heat loss) needed
to maintain desired temperatures and humidities in controlled air. Regardless
of how well-insulated and sealed a building is, buildings gain heat from
sunlight, conduction through the walls, and internal heat sources such
as people and electrical equipment. Buildings lose heat through conduction
during cold weather. Engineers use heat load calculations to determine
the HVAC needs of the space being cooled or heated.
A heat pump is a compressor that cycles hot or cold air. It is a device
that is designed to move thermal energy in the opposite direction of heat
flow by absorbing heat from a cold space which is released to a warmer space.
- Components made of multiple smaller blades, sometimes adjustable, placed
in ducts or duct entries to control the volume of air flow. When used
inside of ducts, their function is similar to that of a damper, but they
can be manufactured to fit larger openings than a single-piece damper.
- Blades in a rectangular frame placed in doors or walls to permit the movement of air.
An air handler that conditions 100% outside air. Typically used in industrial
or commercial settings, or in “once-through” (blower sections
that only blow air one-way into the building), “low flow”
(air handling systems that blow air at a low flow rate), or “primary-secondary”
(air handling systems that have an air handler or rooftop unit connected
to an add-on makeup unit or hood) commercial HVAC systems. Abbreviated MAU.
The lowest amount of fresh air flow that can be allowed into a recirculating
system. This limit is sent to ensure that the interior air remains safe
and comfortable to breathe.
An automatic louver or damper that controls the fresh air flow into an
air handler and modulates to the most energy efficient setting.
A measure of the air temperature outside a building. The temperature and
humidity of air inside and outside the building are used in enthalpy calculations
to determine when outside air can be used for free heating or cooling.
Packed Thermal Air Conditioner
An air conditioner and heater combined into a single, electrically powered
unit, typically installed through a wall and often found in hotels. Abbreviated PTAC.
An air-handling unit, defined as either “recirculating” or
“once-through” design, made specifically for outdoor installation.
They most often include, internally, their own heating and cooling devices.
Very common in some regions, particularly in single-story commercial buildings.
Also called a rooftop unit (RTU)
An enclosed space inside a building or other structure, used for airflow.
Often refers to the space between a dropped ceiling and the structural
ceiling, or a raised floor and the hard floor. Distinct from ductwork
as a plenum is part of the structure itself. Cable and piping within a
plenum must be properly rated for its fire and smoke indices. See also:
Usually metal panels suspended under the ceiling, insulated from the building
structure. The primary cooling/heating agent temperature is close to the
A type of radiant heating system where the building floor contains channels
or tubes through which hot fluids such as air or water are circulated.
The whole floor is evenly heated. Thus, the room is heated from the bottom
up. Radiant floor heating eliminates the draft and dust problems associated
with forced air heating systems.
The SEER (Seasonal Energy Efficiency Ratio) rating of a unit is the cooling
output during a typical cooling-season divided by the total electric energy
input during the same period. The higher the unit’s SEER rating
the more energy efficient it is.
A damper or adjustable louver designed to augment the ventilation of a
space during a fire.
A split system is the combination of an outdoor unit and an indoor unit.
This is the most common type of system.
The number of degrees a vapor is above its boiling point at a specific pressure.
The condition where liquid refrigerant is colder than the minimum temperature
required to keep it from boiling, which would change it from a liquid
to a gas phase. Subcooling is the difference between its saturation temperature
and the actual liquid refrigerant temperature.
General term used to refer to the set or a subset of components that perform
a specific HVAC function within a building.
A small component that contains a heating coil, cooling coil, automatic
damper, or some combination of the three. Used to control the temperature
of a single room. Abbreviated TU.
An individual space or group of neighboring indoor spaces that the HVAC
designer expects will have similar thermal loads. Building codes may require
zoning to save energy in commercial buildings. Zones are defined in the
building to reduce the number of HVAC subsystems, and thus initial cost.
For example, for perimeter offices, rather than one zone for each office,
all offices facing west can be combined into one zone. Small residences
typically have only one conditioned thermal zone, plus unconditioned spaces
such as garages, attics, and crawlspaces, and basements.
A thermostat is a system that monitors and regulates a heating or cooling
system. It can be used to set the desired temperature at which it keeps
the environment either heated or cooled.
Two-Stage (Cooling & Heating)
A two-stage air conditioner is designed to operate on high and low settings
during different weather conditions and seasons. The high setting is used
during extreme weather, and the low setting is used during moderate weather.
This type of air conditioner produces a balanced temperature and is in
use for a longer period of time.
Thermostatic Expansion Valve (TXV)
A thermostatic expansion valve is a piece of equipment that meters the
flow of liquid refrigerant into the evaporator while measuring the vapor
refrigerant leaving the evaporator. It thereby controls the superheating
at the outlet of the evaporator.
Underfloor Air Distribution
A method for providing ventilation and space conditioning by using the
air plenum below a raised floor to distribute conditioned air through
diffusers directly to the occupied zone. Abbreviated UFAD.
A unitary controller is a device that controls only one zone in a building.
Variable Air Volume (VAV)
An HVAC system that has a stable supply-air temperature, and varies the
air flow rate to meet the temperature requirements. Compared to constant
air volume systems, these systems conserve energy through lower fan speeds
during times of lower temperature control demand. Most new commercial
buildings have VAV systems. VAVs may be bypass type or pressure dependent.
Pressure dependent type VAVs save energy while both types help in maintaining
temperature of the zone that it feeds. Abbreviated VAV.
A zoning system sections a building or a space into zones which are controlled
independently of each other. This is beneficial when different areas or
rooms of a building have different temperatures as well as when the desired
temperatures in different rooms are different. Temperature is controlled
by different thermostats.
For more information or to schedule an appointment, call our Bozeman HVAC