Decode the drawings

A

AHU Air Handling Unit HVAC

Central plant that filters, heats, cools and moves air, then distributes it through ductwork. Sized on air volume (l/s) and cooling duty (kW).

As-built drawing General

A drawing revised at the end of a project to show what was actually installed rather than what was designed. The basis of every future maintenance decision.

AVSU Area Valve Service Unit Specialist

A lockable valve box that isolates the medical gas supply to a clinical area, with an emergency access panel. Required by HTM 02-01.

B

Balance tank Specialist

A tank in a deck-level pool system that absorbs surge from bathers, holds backwash volume and takes the make-up water. Without it, the pool floods or the pumps run dry.

BIM Building Information Modelling BIM

Designing the building as a coordinated 3D data model rather than as separate 2D drawings, so clashes and quantities can be checked before construction.

BMS Building Management System Controls

The control and monitoring system that sequences plant, holds set points, logs performance and raises alarms.

Break tank Water

A storage tank fed through an air gap so that stored water can never be drawn back into the mains. The standard backflow protection for a boosted system.

C

Ceiling void BIM

The space between the structural soffit and the finished ceiling, where ductwork, pipework, containment and lighting all have to fit. Zoned by discipline in coordination.

CFD Computational Fluid Dynamics HVAC

Simulation of air or water movement and temperature within a space, used to validate a design before equipment is bought.

Clash detection BIM

Automated checking of one discipline's model against another to find physical conflicts — a duct through a beam, a pipe through a light — before they reach site.

Commissioning General

Setting a completed installation to work and proving it meets the design — balancing flows, verifying controls, recording results. Not the same as switching it on.

D

Diversity General

The allowance made for the fact that not every outlet, unit or load runs at once. Ignoring diversity oversizes plant; overstating it starves the building.

DRV Double-Regulating Valve HVAC

A valve used to set and lock a design flow rate through a branch during commissioning, with test points either side.

F

Fall Drainage

The gradient of a drainage run, written as a ratio such as 1:60. Too flat and solids settle; too steep and the water outruns the solids.

FCU Fan Coil Unit HVAC

A local terminal unit with a fan and a chilled or heating water coil, serving a room or zone from a central water system.

Fire damper Fire

A damper in ductwork that closes automatically at a fire compartment line to stop fire and smoke passing through the duct.

Fire-stopping Fire

A tested system of collars, sleeves and sealants that restores the fire rating of a wall or floor where a service passes through it.

H

Hose reel Fire

A fixed firefighting hose on a drum, typically 30 m of Ø19 mm hose with a 6 m effective jet. Coverage is proven geometrically, not assumed.

I

Index run General

The hydraulically most demanding circuit in a system. Pumps and pressures are set from it — if the index run works, everything else does.

Invert level Drainage

The level of the inside bottom of a drain or manhole. Every below-ground drainage decision is made in invert levels, not depths.

L

Landing valve Fire

The outlet valve on a wet or dry riser at each floor, where the fire service connects its hose. Must hold a minimum running pressure with several open.

Loading unit Water

A weighting given to each sanitary fitting so that a probable simultaneous demand can be calculated and pipework sized from it, rather than guessed.

LOD Level of Development BIM

How much real detail a BIM element carries. LOD 350 means modelled accurately enough to coordinate fabrication, including supports and connections.

Low-loss header HVAC

A hydraulic device that decouples the primary and secondary circuits of a chilled or heating water system so their flow rates can differ safely.

M

Manhole Drainage

An access chamber on a below-ground drain, placed at every change of direction, gradient or pipe size so the run can be rodded and inspected.

MEP Mechanical, Electrical & Plumbing General

The building services disciplines collectively — everything that makes the structure habitable and usable.

N

NRV Non-Return Valve Water

A valve permitting flow in one direction only, used on pump discharges and wherever backflow would be unsafe or wasteful.

P

Permeate Water

The purified water that passes through a reverse-osmosis membrane. What does not pass through is the concentrate, or reject.

PRV Pressure-Reducing Valve Water

A valve that limits downstream pressure to a set value, used to protect lower floors of a tall building from excessive static head.

R

Refnet joint HVAC

A proprietary branch fitting in VRF refrigerant pipework. Must be installed level or vertical — sloping joints cause oil return problems.

Riser General

A vertical service route through a building, and the shaft that contains it. Compartmented and fire-stopped at every floor.

S

Single-line diagram Electrical

A one-page representation of an electrical distribution system showing supplies, protective devices, busbars and outgoing ways — not a wiring diagram.

Snagging General

Systematic inspection at the end of installation to list every defect and incomplete item, then chase each to closure before handover.

SVP Soil & Vent Pipe Drainage

The vertical stack carrying foul drainage down and venting the system to atmosphere above roof level to protect trap seals.

T

Terminal unit Specialist

In medical gas, the gas-specific outlet at a bed head or pendant that a device plugs into. Non-interchangeable by design.

Turnover Specialist

The time taken to circulate a pool's entire volume through the filtration plant once. Four hours is typical for a general-purpose pool.

V

VAV Variable Air Volume HVAC

A ventilation system that varies supply air volume to each zone in response to demand, rather than varying its temperature.

Volt drop Electrical

The loss of voltage along a cable under load. Limited to about 3 % for lighting and 5 % for power so equipment sees usable voltage.

VRF Variable Refrigerant Flow HVAC

An air conditioning system where one outdoor unit serves many indoor units through refrigerant pipework, varying flow to match load.

VSD Variable Speed Drive Controls

An inverter that varies motor speed so a pump or fan matches demand instead of running flat out against a throttle. The single largest energy saving in most plant rooms.

W

Wet riser Fire

A permanently charged vertical fire main with landing valves at each floor, kept pressurised by fire pumps.