Key Project Terms : Mechanical (Building Systems Installation & Modifications)

The following is a list of useful terms to use when researching additional plumbing information on each of the topics discussed:

Air Handlers

An air handling unit (AHU) is the fan equipment unit which is used to regulate the quantity of air, and circulate the air of a heating, ventilation, and air conditioning system.

Air Outlets – Diffusers, Grilles, Louvers

Air outlets are either the entry or exit points for air. For example, an outside air louver is the entry point for the outside air for a building. A diffuser is the exit point for the supply air into a room.

Certificate of Compliance

Per MC 107.2.4, a Certificate of Compliance is issued upon completion of the special inspection and sign-off for the following service equipment:

  • Air conditioning and ventilation systems,
  • Fuel-burning and fuel-oil storage equipment, including generators,
  • Refrigeration systems
  • Heating systems, and
  • Boilers

Chillers, Chilled Water

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment.

Chilled water is used to cool a building's air and equipment, for example in situations where many individual rooms of a hotel must be controlled separately, chilled water could be provided to coils of terminal units serving such rooms.


Refers to quality assurance testing process that verifies, and documents that the selected building systems have been designed, installed, and function according to the owner’s project requirements and construction documents, and to minimum code requirements.  Mandatory when the total permitted equipment is greater than or equal to a total heating input capacity of 600,000 BTU/h and/or a total cooling capacity of 480,000 BTU/h.

Condensers, Compressors, Evaporators

A Condenser and a Compressor can be combined into a single piece of equipment that is part of an air-conditioning system, used to condense refrigerant from a gaseous state to its liquid state, while discharging heat in the process.

An Evaporator is a device used in an air-conditioning system to allow a compressed refrigerant to evaporate from liquid to gas while absorbing heat in the process.

Cooling Towers

A cooling tower is a heat rejection device which rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers are often used with chillers as part of the building’s chilled water process.

Ductwork/Duct System

Ducts or Ductwork, are pathways utilized for conveying air, such as fabricated & formed sheet metal, conduits, or tubes originating from air moving equipment, such as a fan, and typically terminating in the room being served.

The Duct System is a continuous passageway for the transmission of air that, in addition to ducts, includes duct fittings, volume control dampers, fire dampers, fans and accessory air-handling equipment and appliances.


Exhaust air is mechanically discharged from rooms and the building without recirculation. For example toilet rooms or kitchens with hoods over stoves may need to be exhausted.

Fan Coil Units

A Fan Coil Unit (FCU) is a device consisting of a heating coil and/or a cooling coil and fan, sometimes using ductwork, which controls the temperature of the space in which it is installed.

Fresh Air/Outside Air

Fresh air is that portion of a building’s air supply that is taken from outside the building.

Heating and Cooling Coils

A device used at a central air handler, or at a terminal fan unit such as a fan coil unit or similar, composed of tubes carrying refrigerant, hot or chilled water, and air fins. A heating or cooling coil acts as a heat exchanger, which allows the air flowing across such coil, to be either heated or cooled.

Heat Pump

Heat pumps move thermal energy opposite to the direction of spontaneous heat flow (natural heat transfer) by absorbing heat from a cold space and releasing it to a warmer one.  As an example, a heat pump may have a reversible refrigeration cycle, thereby providing either warm or cool air to a space depending on the outside conditions.

Mechanical (System) Work

Installation, additions, alterations, modifications, replacement to heating, ventilation, air conditioning, refrigeration systems and their components.

PTAC (Packaged Terminal Air Conditioner)

A packaged terminal air conditioner (PTAC) is a type of self-contained heating and/or air conditioning unit commonly designed to go through a wall, and serving a limited area of a building.


A refrigerant is the substance or mixture, usually a fluid, used in a refrigeration cycle, of a heat pump or other type of air conditioning unit. In most refrigeration cycles, the refrigerant undergoes phase transitions from a liquid to a gas and back again to provide cooled air for a space.

Return Air

Return air is that portion of a building’s air supply, of a sufficient quality, for recirculation.

Rooftop Package Units

A rooftop packaged unit (RTU) is a single piece of equipment that sits on a building’s roof and typically rests on a curb or curb adaptor and which has all of the necessary equipment components to provide heating, ventilation and/or air-conditioning for all or part of a building.

Split-System AC

Split-system air conditioners provide cooled air to a space using an inside refrigerant evaporator coil and fan, which is connected through refrigerant piping, to an outside compressor/condenser.

Supply Air

Supply air is mechanically introduced into building rooms, as required by outside air requirements, exhaust air requirements, and to maintain the thermal comfort of such rooms.


Air movement mechanically controlled by fans and the air is transported through ductwork. The ventilation of a room is determined by airflow that is calculated from the fresh air, return air, and exhaust air.

Key Points & Project Terms Categories

  1. Alterations

  2. Building Systems Installation & Modifications

  3. Construction Equipment

  4. Demolition COMING SOON!

  5. New Buildings COMING SOON!

  6. Renovations

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