The MEP Acronym & Terms Glossary: Plain English Definitions for Everyone Else
There's a particular moment, familiar to anyone who has ever joined a project meeting slightly out of their depth, where three people around the table start discussing whether the AHU can be tied into the BMS without affecting the SBEM, and you realise that everyone else in the room is entirely comfortable and you are not. Building services has an acronym for almost everything, which is efficient once you're fluent and quietly excluding until you are.
So this is the glossary we'd have liked when we started: important terms written out in full and explained in a sentence or two, without assuming you already know what the other acronyms in the definition mean. It's aimed at the people who work alongside MEP rather than in it: developers, project managers, architects, procurement teams, marketers, anyone who needs to follow the conversation rather than lead it.
The Foundations
MEP - Mechanical, Electrical and Public Health. The three disciplines that make a building actually function once the structure is up. Mechanical covers heating, cooling and ventilation, electrical covers power and lighting, and public health covers water, drainage and sanitation. You'll also see the P expanded as "Plumbing", particularly in American usage, whereas in the UK "Public Health" is the more common reading. Occasionally you'll encounter MEPF, where the F is Fire.
HVAC - Heating, Ventilation and Air Conditioning. The mechanical part of MEP, essentially. Anything concerned with keeping a building at a comfortable temperature with air that's fit to breathe.
M&E - Mechanical and Electrical. An older and still widely used term, broadly interchangeable with MEP in casual conversation, though it doesn't formally include the public health side.
Building Services - Not an acronym, but worth including, as it's the umbrella term the industry uses for the whole lot. If someone describes themselves as a building services engineer, they work in MEP.
Equipment You'll See on a Drawing
AHU - Air Handling Unit. A large box, usually on a roof or in a plant room, that conditions air and pushes it around the building through ductwork. Inside it you'll typically find fans, filters, and heating or cooling coils. It's the workhorse of a commercial ventilation system.
FCU - Fan Coil Unit. A smaller, more local version of the same idea. Rather than conditioning air centrally and distributing it, an FCU sits in or near the room it serves and treats the air there. They come in various forms depending on where they're mounted: highwall, cassette (recessed into a ceiling), or ducted (concealed above one).
VRF - Variable Refrigerant Flow. An air conditioning system where a single outdoor unit serves multiple indoor units, varying the flow of refrigerant to each according to what that particular room needs. The appeal is that different spaces can be heated and cooled independently, which suits buildings where the south-facing offices are baking while the north-facing ones are cold. You'll also see VRV, which means much the same thing but is a Daikin trademark.
DX - Direct Expansion. A cooling system where the refrigerant cools the air directly, rather than cooling water which is then used to cool the air. DX and VRF are frequently mentioned in the same breath because VRF systems are a type of DX system.
MVHR - Mechanical Ventilation with Heat Recovery. A ventilation system that extracts stale air from a building and brings in fresh air, but passes one past the other through a heat exchanger so that most of the warmth in the outgoing air is transferred to the incoming air. You get the ventilation without throwing all your heating out of the window, which is why MVHR turns up constantly in airtight modern buildings.
Chiller - Again not an acronym, but a term worth knowing. A chiller cools water, which is then pumped around the building to FCUs or AHUs that use it to cool air. Common in larger commercial buildings.
ASHP / GSHP - Air Source and Ground Source Heat Pump. Heat pumps move heat rather than generating it, extracting warmth from the outside air (ASHP) or from the ground (GSHP) and concentrating it to heat a building. They're central to UK decarbonisation policy, which is why you'll see them referenced everywhere at the moment.
BESS - Battery Energy Storage System. A battery installation that stores electricity, whether generated on site by solar panels or drawn from the grid at cheaper times, for use later.
PV - Photovoltaic. Solar panels. PV panels convert daylight into electricity.
EV - Electric Vehicle. Mostly encountered in MEP as EV charging, which increasingly needs designing into a building's electrical capacity from the outset rather than bolted on afterwards.
Controls and Systems
BMS - Building Management System. The computerised system that monitors and controls a building's services centrally: heating, ventilation, lighting, metering, and often more besides. If a facilities manager can see the temperature in every zone on a screen, that's the BMS.
BEMS - Building Energy Management System. The same idea with the emphasis on energy monitoring and efficiency. The two terms are often used interchangeably.
LV / HV - Low Voltage and High Voltage. Broad classifications of electrical distribution. An LV switchboard is the panel that takes incoming power and distributes it safely to the building's circuits and equipment.
Zoning - Dividing a building into areas that can be heated or cooled independently. Relevant because it's the thing VRF systems and good controls are largely there to achieve.
Compliance, Assessment and Paperwork
This is the section where the acronyms multiply fastest, largely because each one corresponds to a document somebody has to produce before a building can be signed off.
EPC - Energy Performance Certificate. The familiar A-to-G rating, required whenever a building is constructed, sold or let in the UK.
SAP - Standard Assessment Procedure. The UK government's methodology for assessing the energy performance of dwellings. New homes need a SAP calculation to demonstrate compliance with building regulations, and the EPC for a home is produced from it.
SBEM - Simplified Building Energy Model. The equivalent methodology for non-domestic buildings. Offices, schools, retail units and so on need an SBEM calculation rather than SAP. The easy way to remember the distinction: SAP for homes, SBEM for everything else.
Part L / Part F / Part O - Sections of the Building Regulations for England. Part L covers conservation of fuel and power, Part F covers ventilation, and Part O covers overheating in new residential buildings. Scotland, Wales and Northern Ireland have their own equivalents, which is worth remembering if you work across borders.
TM59 / TM52 - CIBSE technical memoranda setting out how to assess the risk of a building overheating, TM59 for homes and TM52 for other buildings. If someone mentions an overheating assessment, this is usually the methodology behind it.
CIBSE - Chartered Institution of Building Services Engineers. The professional body for building services in the UK, and the source of a great deal of the technical guidance the industry works to.
WLCA - Whole Life Carbon Assessment. An assessment of the carbon emissions associated with a building across its entire life: the materials and construction, the operation, and eventually the demolition. Increasingly requested by planning authorities.
Thermal Modelling - Simulating how a building will behave thermally before it's built, so that problems like overheating can be designed out rather than discovered by the occupants in July.
On Site and In Delivery
O&M Manuals - Operation and Maintenance Manuals. The documentation handed over at the end of a project explaining how everything works and how it should be looked after. Frequently assembled in a hurry at the end, frequently regretted later.
Commissioning - The process of testing and adjusting systems once installed so that they perform as designed. Commissioning management is overseeing that process, while commissioning witnessing is independently verifying it was done properly.
Snagging - Identifying the defects and unfinished bits at the end of a project so they can be put right before handover.
Plant / Plant Room - "Plant" means the major equipment (boilers, chillers, pumps, AHUs) and the plant room is where it lives.
Lead Time - The gap between placing an order and the equipment arriving. Rarely as simple as a single number, since it may or may not include manufacture, shipping, and delivery to site, which is exactly why it's worth asking precisely what's being quoted.
RAMS - Risk Assessment and Method Statement. The safety documentation setting out the hazards of a task and how it will be carried out. No RAMS, no work.
BIM - Building Information Modelling. A digital model of a building containing not just its geometry but data about its components, used so that the various disciplines can coordinate and spot clashes before anyone is on site with a drill.
A Note on Using Any of This
Knowing the vocabulary isn't the same as knowing the engineering, and this glossary won't make anyone competent to specify a system. What it should do is let you follow a conversation, read a drawing schedule without reaching for a search engine every third line, and ask better questions of the people who do this for a living.
And if there's a term you keep running into that isn't here, do let us know, as this is the sort of thing that only improves by being added to!
The MEP Shop supplies HVAC, heat pump, ventilation and energy equipment across the UK, alongside sustainability assessments, MEP surveys and product training. If there's a project you'd like to talk through, get in touch.