How many of you sang "Auld Lang Syne," the Scottish poem based on Robert Burns', the National Poet of Scotland, ballad this New Year’s Eve as we entered into 2022? The title, translated literally into English, is "Old Long Since." The words can be interpreted as a farewell or ending to occasions of the past.

In the HVAC industry, see if you know all of these words, expressions, equipment, and systems that have heard their Auld Land Syne sung:

Words and Expressions

  • No. 6, 5, and 4 fuel oil: Used frequently to serve steam boiler plants in hospitals, industries, and schools up to the mid-1970s, before the energy crisis and fuel shortage hit America.
  • Steam tank heater: Used to heat No. 6 fuel oil (Bunker C heavy fossil fuel) to maintain fuel oil at 104°-122°F within the fuel oil tank.
  • Electro-pneumatic (EP) and pressure-electric switches: EP and PE switches were standard controller devices in pneumatic air control systems before electrical controls systems took hold in the 1970s and 80s, the predecessor to today’s building automation systems (BASs).
  • Silicon controlled rectifier (SCR): A solid-state switching device designed to provide infinitely variable proportional control of electric power, often used as the next generation of electrical controls in the late 20th century.
  • Equivalence of direct radiation (EDR): A standardized comparison method for estimating the output of a radiator or convector (which were cast-iron construction at one point of time).


  • Medium- to high-pressure induction units: Often found in high-rise office buildings, a supply air velocity ducted directly into the perimeter induction unit would provide primary air along with induced return air for HVAC equipment in lieu of the perimeter unit having an electrical fan to provide the combination outside and return air.
  • Single-fan, double-duct central air-handling units: These units delivered supply discharge air through two parallel coils within the unit. One coil was hot air to a hot air supply duct main and the second coil was a cold air supply air duct main. These parallel duct mains served multiple double-duct terminal units.
  • Multi-zone central air-handling units: Similar to single-fan, double-duct central air-handling units, these types of units will have multiple hot and cold air discharge but with each zone having its own hot and cold air connection into a common supply air duct with a thermostatically controlled mixing damper at the central air-handling unit discharge, blending supply air to the associated space served by a multi-zone duct.
  • Three-pipe heating-cooling terminal units: A perimeter fan coil unit with a hot water supply pipe to a heating coil and a chilled water supply pipe to a cooling coil. The water returns, one from each coil, connected to a common return water pipe main.
  • Steam and hot water convectors: Once abandoned from the contract specification pages of a construction project, these terminal units have made a stylish, architectural return to the building industry often installed in residential homes and locations where multiple feet of baseboard will not fit on the wall.


  • Steam heating systems: What would have been previously engineered as a low-pressure steam (LPS) system, hot water systems have displaced the majority of LPS systems both to perimeter baseboard radiation, unit heaters, etc. as well as central air-handling units that had steam heating coils within their central air-handling units and their associated supply air ductwork distribution to terminal heating and/or reheat coils.
  • Overhead unit heaters at loading docks system: What would have been previously engineered to have down-blast, fan-powered unit heaters with high heat output are often displaced with gas-fired radiant heat terminals that heat the objects, e.g., occupants/workers rather than heating the entire loading dock space.
  • Variable refrigerant flow (VRF) cooling systems: A direct expansion (DX) single- and multiple-stage cooling unit VRF flow system designed to vary the cooling through terminal fan coil units. VRF systems also offer heat pump HVAC applications, too.

And, so, the choirs chime in with the first verse of "Auld Lang Syne" in honor of these fallen technologies!