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O&M for MEP: What Do These Acronyms Mean? | Learning FM

O&M for MEP

What?!?  We have so many acronyms in this business!  Okay – so, MEP refers to services for Mechanical (most commonly referred to as HVAC – Heating, Ventilation, and Air-conditioning), Electrical, and Plumbing.  As a facility manager, you will definitely need to become familiar with these systems and who maintains them.  While much of the O&M (operations and maintenance) is done by qualified specialists, there are some user-level preventative maintenance that should be performed ongoing with operations.  Below is a brief overview of MEP and my approach on these systems as a practicing FM (who is not a licensed specialist in any of them).


Heating, ventilation, and air conditioning (HVAC) systems regulate a space’s temperature, humidity, and air quality.  The basic theory is that there is some form of heat exchange between the system and the air to either remove heat from the air (“cool”) or add heat to it.  There are several different types of HVAC systems and I will cover the most common.

  • Air Handling Unit (AHU) – this is a large metal enclosure that helps condition and circulate air to create a particular kind of atmosphere as part of the HVAC system. It usually contains a blower, heating or cooling elements, filters, dampers, and sound attenuators.  This is then connected to ductwork used to distribute the air to the space (supply duct) and return the air back to the AHU (return duct).
  • Makeup Air Unit (MAU) – a large AHU that conditions 100% outside air (does not recirculate any air). These are typically used in spaces where you cannot recirculate the air.  Examples include hospital surgical rooms, commercial kitchen exhausts, and commercial paint booths.
  • Packaged Unit (PU) – an AHU designed for outdoor use. A PU will contain all of its parts within one unit (heating and cooling).
  • Roof Top Unit (RTU) – a PU designed to sit on the roof.
  • Terminal Unit (TU) – a small system used to control the temperature of a single room. It contains a heating coil, cooling coil, and damper or a combination thereof.  Think of these as those all-in-one wall units you may have seen in a motel room.
  • Split System – a two component system, where the AHU is located inside and the condensing unit is located outside. Refrigerant lines run between the two.  These are used commonly in modern residential construction for central heat and air.

There are many different components of the HVAC systems.  Here are just a few:

  • Boiler – heats water to generate steam for distribution. These are licensed and routinely inspected.
  • Furnace – burns fuel to heat water or air for distribution.
  • Heat Exchanger – transfers heat from one material to another.
  • Chiller – a machine that removes heat from a liquid.
  • Compressor – compresses refrigerant to the right pressure and temperature before passing it through the coil.
  • Cooling tower – a heat exchanger that uses evaporation to reduce the water’s temperature.
  • Geothermal / Ground Source Heat Pump (GSHP) – a heat exchanger that uses the relatively constant temperature of the earth and a series of buried pipes as part of the HVAC system.

Ensure a qualified, licensed technician conducts the O&M activities on mechanical systems (aside from the owner’s level of maintenance such as replacing filters).  In addition to knowing how to service the system, anyone that handles refrigerant must be certified through the Environmental Protection Agency (EPA).  Identify the types of systems in your facility and what maintenance options you have.  From there, you can set your O&M strategy for HVAC.


Plumbing systems do two basic things, distribute liquids and gas and remove waste.  O&M of plumbing systems is vital because the majority of the system is hidden and when a problem occurs, it can potentially cause a lot of damage.  Again, qualified and licensed professionals should maintain these systems.  There are potential safety hazards inherent in plumbing systems and a knowledge of codes and maintenance practices is vital for success.

Examples of distribution components include:

  • Sinks/Fixtures providing potable water (water that is suitable for consumption)
  • Gas lines for fuel
  • Fire suppression systems
  • Water lines for certain HVAC equipment
  • Fire hydrants
  • Irrigation systems
  • Valves and pressure regulators
  • Water heaters
  • Backflow preventers
  • Booster pumps

Examples of waste components include:

  • Sanitary sewer lines (for removal of sanitary or “black” waste)
  • Storm sewer lines (for removal of rain/groundwater or “gray” water)
  • Grease traps (these prevent grease and solids from getting into the sewer system and must be emptied periodically)
  • Sink drains, floor drains, manholes, cleanouts
  • Vents
  • Lift stations

Conduct periodic routine inspections looking for small drips/leaks, signs of corrosion, safe temperatures, cracks, etc. of the distribution system where visible.  Ensure leaks are reported and corrected immediately.  Ensure grease traps are emptied routinely and check for unwanted sewer smells during walk-throughs (could be a sign of an empty p-trap or something more serious like a broken sewer line).


Electrical systems generate and distribute power.  Only qualified, licensed technicians should maintain these systems.  Safety is paramount when working on an electrical system.  As the FM, ensure that anyone working on an electrical system uses a lockout-tagout (LOTO) procedure.  LOTO is a safety procedure that safeguards workers from coming in contact with hazardous electrical energy while working on a piece of equipment or component of an electrical system.  You can find OSHA’s standard for LOTO in 29 CFR 1910.147.

There are many potential components of an electrical distribution system, but here are some of the most common:

  • Switchgears
  • Transformers
  • Meters
  • Wiring, panels, receptacles, switches
  • Protection devices – circuit breakers, GFCIs
  • Lights/Emergency lights
  • Generators

PM is very important for electrical components and PdM (such as IR technology to see if circuits are overheating) can help you detect potential failures before they occur.  Routine inspections should include looking for any moisture intrusion, proper grounding, proper connections, corrosion, clean equipment, overloaded circuits, etc.  I will talk about ways to reduce electric consumption in a later section.

One additional thing you can do to increase safety around electrical equipment is to have an arc flash hazard analysis.  An arc flash is the light and heat produced from an electric arc.  This is a rapid release of energy caused by an arcing fault between a phase bus bar and neutral, ground, or other bus bar.  I mention it because it can cause severe injuries.  The arc flash analysis will label the electrical equipment with potential energy ratings and personal protective equipment required when working on them.  Consult NFPA 70E for more information.

In Summary

That is just a very basic overview of three extremely complex services.  Anytime I need to plan major work with MEP, I contract with licensed MEP engineers to ensure the design and specifications adhere to code and meet all facility requirements that we have.  Thanks so much for reading and please feel free to email me with any questions at