HVAC Engineering

HVAC banner 3HVAC stands for Heating, Ventilation, and Air Conditioning.  It refers to the technology, systems, and equipment used to control and regulate indoor environmental conditions, such as temperature, humidity, air quality, and air flow.  HVAC systems are commonly used in residential, commercial, and industrial buildings to provide thermal comfort and acceptable indoor air quality.


Science Branches

Applied Science
Mechanical Engineering

HVAC Index

Heating systems, a component of HVAC, are used to maintain a comfortable indoor temperature by generating heat using various methods, such as boilers, furnaces, or heat pumps.  Air conditioning systems, on the other hand, are used to cool indoor spaces by removing heat and humidity from the air.  They use refrigeration technology to transfer heat from indoor air to the outside environment.  Ventilation systems are used to maintain indoor air quality by exchanging fresh outdoor air with indoor air, removing pollutants, and regulating humidity levels.  Proper ventilation is essential for occupant health and comfort, as well as for preventing the buildup of harmful gases, such as carbon monoxide.

HVAC systems typically consist of equipment such as air handlers, heat pumps, ducts, fans, filters, and controls.  They may be controlled by thermostats or other automated systems that adjust heating and cooling based on indoor and outdoor temperatures and other environmental factors.  Efficient and effective HVAC systems are important for reducing energy consumption, improving indoor air quality, and ensuring occupant comfort.  Regular maintenance and cleaning are essential for keeping HVAC systems operating at peak efficiency and preventing potential problems.


HVAC Types

  • Duct-free Mini-split System  -  This system has two main components, an outdoor compressor/condenser and an indoor air-handling unit, evaporator.  They are easy to install usually requiring only hole through a wall for the conduit, which houses the power and communication cables, copper tubing, and a condensation drain line, linking the outdoor and indoor units.
  • Ductless HVAC System  -  Involves the installation of two main pieces of equipment, an outdoor compressor/condenser unit that cools and heats air and an indoor air handler that distributes the air.  These components are connected by conduit that contains power and refrigerant lines through your home’s exterior wall, eliminating the need for ducts.
  • Heat Pump System  -  When a heat pump operates, it pumps refrigerant through the lines that absorb the heat within your home.  That refrigerant then circulates from the indoor air handler to the outdoor unit to release that heat. When you want to heat up your home, you simply switch the setting to heat to reverse the process and bring heat into your home.
  • Hybrid Split System  -  A hybrid heating system is the combination of an electric heat pump and a gas furnace.  The combination provides the advantages of both systems while eliminating the drawbacks of each.  The heat pump portion works throughout the summer and much of the winter.  When the temperature gets low enough, the gas furnace takes over.
  • Hydronic Heating System  -  A hydronic system uses water or steam, heated by a boiler, to heat your home. Water enters the boiler’s combustion chamber through a circulator; once heated, the water is distributed through pipes to heat baseboards or radiators throughout your home. The water is eventually recycled back to the boiler to be reheated and used again.
  • Packaged Heating and Cooling System  -  An all-in-one heating and cooling system for spaces that don’t have enough indoor room to house a furnace or an air handler.  A packaged system contains all of its components in a single outdoor unit, which sits on the side of your property or on the roof.
  • Portable Spot Cooler  -  This is an alternative when you cannot install a traditional air conditioning system.  Just roll a unit into place, plug in the power, attach some flexible duct to vent the hot air.
  • Split System  -  The system consists of an outdoor unit and an indoor unit.  The outdoor unit is installed on or near the exterior wall of the room that you wish to cool.
  • Zoned System  -  The system is designed to provide varying temperature conditions in a house or building.  The system helps to customize the cooling and heating effects for different rooms or locations in a building.


HVAC System Requirements

  • Primary Equipment
    • Heating Equipment
    • Cooling Equipment
    • Air Delivery Equipment
  • Space Requirement
    • Equipment Room
    • HVAC Facilitie
    • Fan Room
    • Vertical Shaft
    • Equipment Access
  • Air Distribution
    • Terminal Unit
    • Ductwork
  • Piping
    • System Piping
    • Delivery Piping


Central HVAC System

  • All Air System
    • Single Zone
    • Multizone
    • Terminal Reheat
    • Dual Duct
    • Variable Air Volume
  • Air Water System
    • Fan Coil Unit
    • Induction Unit
  • All Water System
    • Fan Coil Unit
  • Water Source Heat Pump
  • Heating and Cooling Panel


Local HVAC System

  • Local Heating System
  • Local Cooling Sysyem
  • Local Ventilation System
  • Local Air Conditioning System
    • Window Air Conditioner
    • Unitary Air Conditioner
    • Packaged Rooftop Air Conditioner
  • Split System


Basic Parts of a HVAC System

  • Main Unit
  • Heat Exchanger
  • Thermostat
  • Combustion Chamber
  • Blower Motor
  • Condenser Coil
  • Evaporator Coil


HVAC Abbreviations

  • British Thermal Unit (BTU)
  • Chilled Water (CHW)
  • Chilled Water Pump (CHWP)
  • Chilled Water Return (CHWR)
  • Chilled Water Return Temperature (CHWRT)
  • Chilled Water Supply (CWS)
  • Chilled Water Supply Temperature (CWST)
  • Cooling Load Factor (CLF)
  • Cooling Load Temperature Difference (CLTD)
  • Cooling Tower (CT)
  • Demand Controlled Ventilation (DCV)
  • Dew Point (DP)
  • Digital Input (DI)
  • Digital Output (DO)
  • Direct Current (DC)
  • Direct Digital Control (DDC)
  • Discharge Air (DA)
  • Dry Bulb (DB)
  • Duct Heater (DH)
  • Electric Heater (EH)
  • Electric Unit Heater (EUH)
  • Energy Efficiency Ratio (EER)
  • Energy Management System (EMS)
  • Entering Air Temperature (EAT)
  • Entering Water Temperature (EWT)
  • Exhaust Fan (EF)
  • Facility Management System (FMS)
  • Fan Coil Unit (FCU)
  • Feed Water (FW)
  • Heat Exchanger (HX)
  • Heat Recovery (HR)
  • Heat Recovery Unit (HRU)
  • Heat Recovery Ventilator (HRV)
  • Heating Seasonal Performance Factor (HSPF)
  • Heating Ventilation and Air Conditioning (HVAC)
  • High Pressure Steam (HPS)
  • Hot Water Pump (HWP)
  • Hot Water Return (HWR)
  • Hot Water Supply (HWS)
  • Leaving Air Temperature (LAT)
  • Leaving Water Temperature (LWT)
  • Local Operating Network (LON)
  • Low Pressure (LP)
  • Low Pressure Steam (LPS)
  • Mixed Air (MA)
  • Mixed Air Temperature (MAT)
  • Temperature (T)
  • Thermostat (TSTAT)
  • Thermostatic Expansion Valve (TEV)
  • Wet Bulb (WB)


Tags: Abbreviations Nomenclature and Symbols

HVAC Engineering Glossary


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Air Change  -  The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air.
  • Air Changes per Hour  -  The number of times that air in a building is completely replaced with outdoor air in one hour.
  • Air Cleaner  -  A device that removes allergents, pollutants.
  • Air Conditioner  -  A device that changes humidity levels, temperature or air quality.
  • Air Diffuser  -  A device that distributes the air and balances the air flow in the system.
  • Air Flow  -  The distribution or movement of air.
  • Air Flow Rate through Piping  -  Is measured in \(\;ft^3\; /\; min\).
  • Air Handler  -  Fan/blower, filter and housing parts of a system.
  • Air Handling Unit  -  A central unit consisting of fan(s), heating and cooling elements, filter racks or chamber, dampers, humidifier, and other central equipment required to provide suitable ventilation and extract.
  • Air Infiltration  -  Leakage of air into rooms through cracks, windows doors and other openings.
  • Air Return  -  The part of your system that marks the starting point of the ventilation cycle.  This return sucks in air, draws it through a filter, and then passes it into the main system.
  • Air Sensor  -  A device that registers changes in air conditions such as pressure, velocity, temperature, or moisture content.
  • Air Vent  -  A fitting used to vent air manually or automatically from a system.
  • Airflow  -  The volume of air moving through a blower or duct.
  • Alternating Current  -  An electric current that reverses its direction over and over.
  • Ambient Temperature  -  When outdoors the ambient temperature is the current surrounding environment air temperature.  This temperature has nothing to do with high or low forcasts.
  • Amp  -  Amp is a unit of current.
  • Annual Fuel Utilization Efficiency  -  The efficiency of a gas furnace or boiler will operate over an entire heating season.
  • Anometer  -  An instrument used to measure air velocities.
  • Atmospheric Pressure  -  The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth.
  • Azeotropic Point  -  The temperature where a liquid mixture boils and produces a vapour with exactly the same composition as the liquid.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Barometer  -  An instrument for measuring atmospheric pressure.
  • Bioaerosols  -  Microscopic living organisms suspended in the air that grow and multiply in warm, humid places.
  • Blend  -  A refrigerant mixture of two or more refrigerants blended in a specific ratio which can be separated by distillation.
  • Blower  -  The blower draws in warm air through the main section of the unit.  Pushes air through the system.
  • Bubble point  -  The pressure at which a refrigerant liquid starts to vaporise.
  • Burner  -  A device that promotes the combustion of air and gas.
  • Butterfly Flat Disk Damper  -  Uses a blade on a hinge that completely fills the duct and is more efficient and requires less maintenance.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Capacity  -  The ability of a heating or cooling system to heat or cool a given amount of space.
  • Capillary Tube  -  A metering device consisting of a small diameter tube designed to restrict flow. This is best used in constant ambient conditions.
  • Carbon Monoxide  -  A colorless, odorless, and poisonous gas that occures as a byproduct of burning fuel.
  • Cascade System  -  A system with two or more refrigerant circuits working in series to provide the designated level of cooling.
  • Cassette Unit  -  Cassette air conditioning units are designed for commercial and residential applications. Ideal for large open plan areas or irregular shaped rooms they fit conveniently and discreetly into any area with a false or suspended ceiling.
  • Central Air  -  Central air-conditioning offers comfort for your whole home. Air is cooled at a central location and distributed throughout your home via a fan and ductwork, as opposed to a window unit, which focuses on a certain room.
  • Centrifugal Fan  -  A device that draws air in axially and discharges it radially.
  • Charging a System  -  Adding coolant or refrigerant to an HVAC system.
  • Chilled Water System  -  A system using water (or glycol solutions) as a secondary cooling medium.  The primary cooling medium (refrigerant) is contained in a chiller, which is located remotely.  The chiller cools the water, which is then piped to the air conditioner to cool the space.
  • Chiller  -  A machine that removes heat from a secondary cooling medium (water, glycol solution, etc.) via a vapour-compression or absorption refrigeration cycle.  The secondary cooling medium can then be circulated through a heat exchanger to cool air or equipment as required.
  • Circuit Breaker  -  A device that opens an electric circuit when an overload occurs.
  • Clean room  -  A clean room is an environment, typically used in manufacturing or scientific research, with a low level of environmental pollutants such as dust, airborne microbes, aerosol particles, and chemical vapours.
  • Coil  -  Usually another part of the outdoor unit, coils cool the air as it passes through with a little help from the refrigerant.
  • Cold  -  Is when the temperature is less than normal or the lack of heat.  The faster atoms and molecules move the more heat they create, so the opposite also holds true, the slower they move the colder it becomes.
  • Comfort Air Conditioning  -  Comfort air conditioning systems are designed for the comfort of people, livestock, etc. and not for the protection of computer-based electrical systems or other process operations requiring close control of the environment.
  • Commercial Air Conditioning  -  Air conditioning for large buildings such as hotels, hospitals and other commercial buildings, providing suitable ventilation and space conditioning.
  • Composite Fan Blades  -  Used in select outdoor air conditioner or heat pump units, blades are manufactured with rugged materials and an exclusive angled design that improve operation and durability, even in the harshest environments.
  • Compressor  -  As a part of the outdoor unit, the compressor is responsible for converting refrigerant from a gas to liquid and sends it to the coils.
  • Condensate  -  Vapor that is turned into a liquid as its temperature is lowered.
  • Condensate Coil  -  A device remove heat from the refrigerant.
  • Condensate Fan  -  A fan that passes air over the condensate coils to remove heat from the refrigerant.
  • Condenser  -  An outdoor part of the AC or heat pump that releases or collects heat.
  • Cooling Load  -  The rate at which heat must be exchanged from a space in order to maintain the desired temperature within the space.
  • Cooling Load Temperature Differential  -  An equivalent temperature difference used for calculating the instantaneous external cooling load across a wall or roof.
  • Cooling Tower  -  A water conservation device used to supply water for cooling condensers.
  • Current  -  The rate of flow of electricity in a circuit, measured in amperes.
  • Cycling  -  The heating and cooling system cycles when it turns on and off.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Damper  -  A device that regulates and redirects the flow of air.  Also called duct damper and volume balancing dampener.
  • Dehumidifier  -  A device used to draw moisture out of indoor air.
  • Dehumidification  -  The process of removing moisture from the air within a conditioned space to maintain the required humidity level.
  • Direct Gas-fired Heater  -  The burner fires directly in the air stream being heated, rather than through a heat exchanger.
  • Duct  -  A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.
  • Duct Leakage  -  Air leakage out of or into ductwork can have much greater impact than the duct heat gain or loss.
  • Ductwork  -  A series of ducts that makeup the entire coolung/heating system.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Economiser  -  An economiser is a mechanical device used to reduce energy consumption. Economisers recycle energy produced within a system or optimise environmental temperature differences to achieve efficiency improvements.
  • Electronic Air Cleaner  -  An electronic device that filters out large particles and bioaerosols in indoor air.
  • Energy Efficiency Rating  -  Measure the efficiency with which a product uses energy to function.
  • Enthalpy  -  Measures the sum of internal energy changes in heat under constant pressure of the system.
  • Evaporative Cooler  -  Also called swamp cooler, is cooling by exchanging of latent heat from the water spray or wetted material.
  • Evaporator Coil  -  Is usually located indoors as part of a split unit or within an air handler or duct system.  Inside the coil, refrigerant evaporates as it absorbs heat from the air that passes over it.
  • Exhaust Outlet  -  Another part of your system is the exhaust outlets where the exhaust created by the heating system is expelled.
  • Expansion Valve  -  A device that regulates the amount of refrigerant flowing from the liquid line into the evaporator.  Can be a thermostatically operated valve, a capillary tube or a fixed orifice device.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Fan  -  A device that has a motor and wheel with blades that creates air flow.
  • Fan Coil Unit (FCU)  -  Normally a chilled water device consisting of a heating and/or cooling coil, fan, valve/s and local controller.  It forms part of a larger HVAC system found in residential, commercial, and industrial buildings.
  • Filter  -  Your filter is the second part of the air return in which the air is drawn through.
  • Flash Tank  -  In a processing operation, a flash tank is a vessel used to separate the gas created from liquid when it is flashed from a high pressure to a low pressure.
  • Free Cooling  -  This may apply to a system using fresh air for cooling the space or a water cooled or glycol cooled system with an additional coil that provides chilled water cooling when the outdoor ambient is cold, thereby reducing or eliminating compressor operation.
  • Freon  -  A cooling agent used in most air conditioning systems.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Glycol-Cooled System  -  A system using a water/glycol solution as a condensing medium. Typically, the glycol-cooled condenser is located inside the air conditioner with the rest of the refrigeration components.  Water/glycol is piped to the unit from a drycooler or other suitable source. The glycol keeps the solution from freezing during winter operation.
  • Guillotine Damper  -  It will completely block the duct.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Heat  -  A form of energy that causes physical change in what is being heated.  The lack of heat is cold.
  • Heat Capacity  -  The ratio of heat transferred to raise the temperature of an object.
  • Heat Exchanger  -  A device used to transer heat from one medium to another at different temperatures.  The heat transfer can be air or a liquid such as water or oil.
  • Heat Flow Rate  -  The rate at which heat moves from an area of higher temperature to an area of lower temperature.  Heat flow is generally used to quantify the rate of total heat gain or heat loss of a system.
  • Heat Loss or Heat Gain  -  The measure of the total heat transfer through your body, clorhing, building walls, etc.
  • Heat Pump  -  An outdoor unit that can both heat and cool indoor air.
  • Heat Transfer  -  The exertion of power that is created by heat, or the increase in temperature.  It is the transfer of heat from one system to another.
  • Heat Transfer by Convection  -  Convection is the energy transfer of heat by air, water, or any other fluid to and object. It includes energy transferred by random molecular motion as well as energy transferred by the bulk motion of the fluid.
  • Hemi-anechoic Chamber  -  A room designed to completely absorb reflections of either sound or electromagnetic waves.  Hemi-anechoic chambers have a solid floor that acts as a work surface for supporting heavy items such as large air conditioning units for testing sound levels.
  • Horizontal Flow  -  When an air handler or furnace is positioned on its side and circulates air in one end and out the other. Ideal for attic or crawl space installations.
  • Humidifier  -  A device that adds moisture to warm air being circulated or directed into a space.
  • Humidistat  -  A humidistat is a part of your heating and cooling system that senses the moisture level in the air and automatically adjusts it to maintain a set humidity level.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Internal Energy  -  The total of all energies associated with the motion of the molecules in the system.
  • Inverter Compressor  -  This compressor uses an inverter drive to control the compressor motor speed to modulate capacity as demand varies.




  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Latent Heat  -  The energy absorbed or released by a substance during a constant temperature or phase change from a solid to liquid, liquid to gas or vise versa.
  • Latent Heat Gain  - The energy added to the space when moisture is added to the space by means of vapo emitted by the occupants, generated by a process or through air infiltration from outside or adjacent areas.
  • Latent Heat Loads  -  Latent heat gain occurs when moisture is added to the space either from internal sources, vapor emitted by occupants and equipment, or from outdoor air as a result of infiltration or ventilation to maintain proper indoor air quality.
  • Led  -  Light emitting diode used to display the status of the system.
  • Load  - The amount of cooling or heating a building requires.
  • Louver Damper  -  Uses flat blades on hinges and used for quick responce time.
  • Low Boy  -  A type of furnace configuration in which the furnace is lower in height and occupies more floor space.
  • Low Pressure Stage  -  The part of a single stage refrigerant system from the outlet of the expansion device to the compressor suction inlet.  On a multi-stage system it is the part where the lowest temperature is achieved.
  • Low Pressure Steam  -  Is when the pressure is less than or equal to that of the atmosphere.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Matched System  -  A heating and cooling system comprised of products certified to perform at promised comfort and efficiency levels when used together according to design and engineering specifications.
  • Multipoise  -  A multi-direction configuration that allows for both upflow and downflow installations.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Nanometer  -  An instrument used for measuring the pressure of liquids and gases.
  • Non-condensable Gas  -  A gas system that does not condense at the temperature and partial pressure that exists in the condenser, therefore leading to a higher head pressure.  This is often the case if air has leaked into a system, and lowers system efficiency and leads to longer term reliability issues.
  • Normally Closed  -  The circuit is closed when the switch is not open.
  • Normally Open  -  The circuit is open when the switch is not operated.



  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Package System or Unit  -  All HVAC components are located in one cabinet outside.
  • Power  -  The rate of doing work or the rate of using energy per unit time.
  • Pressure Balancing  -  The process of neutralizing pressure differences within a system.
  • Programmable Thermostat  -  A type of thermostat that can be programmed to be run only when needed.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Outdoor Unit  -  The outdoor unit houses the fan which provides air flow.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • R-22  -  A cooling agent commonly known as freon.
  • R-value  -  A measure of a material's thermal resistance.
  • Radiant Heat Gain  -  The rate at which heat absorbed is by the surfaces enclosing the space and the objects within the space.
  • Refrigerant  -  A chemical that produces a cooling effect while expanding or vaporizing. Most residential air conditioning units contain the standard R-22 refrigerant, or Freon.
  • Refrigerant Lines  -  Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.
  • Relative Humidity  -  A measure of the amount of moisture in the air with respect to the temperature.
  • Return Air  -  Air that is returned to the evaporator coil from outside the building.
  • Return Duct  -  The duct through which warm air is drawn into the cooling system, cooled, then returned to the cooling system.
  • Room  -  An enclosure or partitioned apace that is usually treated as a single load.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Seasonal Energy Efficiency Rating (SEER)  -  Measures the efficiency a residental central cooling will operate over an entire cooling season.
  • Sensible Heat  -  The heat added to a substance which increases its temperature but not the phase.
  • Sensible Heat Gain  -  The energy added to the space by conduction, convection and/or radiation.
  • Sensor  -  A device that reacts to any change in conditions.
  • Single Package  -  A heating and cooling system contained in one outdoor unit.
  • Single-speed  -  A motor that runs a full speed until it reaches the set temperature then shuts off.
  • Space  -  A site without a partititioned space or a partitioned room or group of rooms.
  • Space Cooling Load  -  The rate at which energy must be removed from a space to maintain a constant space air temperature.
  • Space Heat Extraction Rate  -  The rate at which heat is removed from the conditioned space and is equal to the space cooling load if the room temperature remains constant.
  • Space Heat Gain  -  The rate at which heat enters into and/or is generated within the conditioned space during a given time interval.
  • Space Heater  -  A self-contained appliance used to heat enclosed spaces.
  • Split System  -  Refers to an air conditioner or heat pump that has components in two locations. Usually, one part of the system is located inside (evaporator coil) and the other is located outside your home (condenser coil).
  • Static Pressure  -  The difference in air pressure between the suction side and pressure side of a blower.  The higher the static pressure or resistance, the more energy it takes to move air through the object.
    Supply Air  -  Air delivered to the conditioned space by heating and cooling equipment.
  • Swamp Cooler  -  Also called evaporative cooler, is cooling by exchanging of latent heat from the water spray or wetted material.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Temperature  -  Normally described as the amount of heat or cold, but it is neither heat or cold.  Temperature is expressed as a number that is related to energy and porportional to a type of energy, but it is not energy.
  • Temperature Differential  -  The difference between two specific temperature points of a volume at a given time in a system.
  • Temperature Zones  -  Areas of a building or rooms where the temperature can be controlled seperately.
  • Thermal Energy  -  The exertion of power that is created by heat, or the increase in temperature.
  • Thermal Resistance  -  The temperature difference by which an object or material resists a heat flow.
  • Thermostat  -  A temperature sensitive switch for controlling the operation of cooling and heating.
  • Thermodynamics  -   A branch of physics and an engineering science that deals with large scale reactions of a system that can be observed and measures and the relationship between properties such as energy, heat, pressure, temperature, work, etc. on a system.
  • Thermostat  -  A wall mounted device uesd to monitor and control the HVAC system output.
  • Tonnage  -  A unit of measurement in air conditioning to describe the cooling capacity of the system.
  • Two-Stage Operation  -  Provides two levels of heating or cooling output for greater temperature control, energy efficiency and improved indoor air quality.



  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Vacuum  -  A contained space having little or no matter or a volume having a pressure lower than the outside atmospheric pressure.
  • Vacuum Test  -  Check to see if the refigerant lines are sealed before changing with refrigerant. 
  • Varactor Diode  -  The capacitance varies according to the applied input voltage.
  • Variable Capacitor  -  Used in tuning the circuit to a required frequency.
  • Variable Indicator  -  Allows the value of the inductance to be changed.
  • Variable-speed  -  A motor that has variable speeds to be choosen.
  • Variable Speed Motor  -  A motor that automatically adjusts the flow of warm or cool air for ultimate comfort.
  • Ventilation  -  A natural or mechanical process of moving air into or out of interior spaces.
  • Ventilation Air  -  The total air brought from the outdoors and the air re-circulated inside the building.
  • Ventilation Rate  -  The rate at which air enters or leaves a building.
  • Ventilator  -  A system that exchanges stale, recirculated indoor air with fresh, filtered outside air.
  • Vent Pipe  -  A pipe or tube used to vent combustable gasses to the outside air.
  • Volt  -  A unit of electrical pressure.
  • Voltage  -  The amount of pressure that will cause one ampere of current in one ohm of resistance.


  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Water-Cooled System  -  A type of refrigerant based air conditioning system that uses water as a condensing medium.  Typically, the water-cooled condenser is located inside the air conditioner with the rest of the refrigeration components.  Water is piped to the unit from a cooling tower or other suitable source.
  • Weather-stripping  -  A material used to seal gaps around exterior doors and windows.
  • Weatherization  -  Process of modifying a building/home to protect it from the outside elements.
  • Weatherstrip  -  Narrow, thin pieces of metal or other material installed around windows and doors to prevent the air and moisture from coming in.
  • Weep Hole  -  A small hole in storm windows frames that allow moisture to escape.
  • Wet Bulb Thermometer  -  Measures the relative humidity in the air.




  • A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
  • Zone  -  A space in a building under the control of a thermostat.
  • Zoning  -  Allows control of the heating and cooling system delivered to different parts of the system.


Piping Designer Logo 1




Display #
Air Change
Air Changes Per Hour
Air Conditioning
Air Diffuser
Air Infiltration

Tags: Mechanical Heat Air HVAC Heat Exchanger Engineering Glossary