Engineering Glossary

The terms MEPF & solar projects run on

60 working definitions written by practising engineers — each with the governing Indian codes, a specification table, the mistakes we actually see on sites, and the calculator that turns the concept into your number.

Fire

Fire Damper — An automatic closure device inside ductwork that shuts where a duct crosses a fire-rated wall or floor, restoring the barrier's rating and stopping fire/smoke spread through the HVAC system.
Fire Extinguisher Rating — The classification of a portable extinguisher by the fire classes it fights (A/B/C/D/F) and its tested extinguishing capacity — selection and placement per IS 2190.
Fire Hydrant System — A pressurised piped network of landing valves and yard hydrants, fed by fire pumps from the static tank, giving firefighters water at every floor and around the perimeter.
Fire NOC — The No Objection Certificate from the State Fire Service confirming a building's fire-safety provisions meet NBC/state rules — required at plan stage (provisional) and before occupation (final), then renewed periodically.
Fire Pump Room — The dedicated room housing the fire pumps (main, standby, jockey), controllers and headers that pressurise the hydrant and sprinkler systems — sized and located per NBC 2016.
Fire Water Tank Capacity — The statutory volume of stored water (underground static + terrace tank) a building must reserve exclusively for firefighting under NBC 2016.
Hydrant Pressure Test — The live verification that the hydrant network delivers the code-required residual pressure at the hydraulically remotest outlet with pumps running — the test that decides Fire NOC inspections.
Jockey Pump — A small pressure-maintenance pump that keeps the fire mains topped up against minor seepage, so the main fire pump only starts for genuine demand.
Refuge Area — Protected floor area mandated in high-rise buildings where occupants can safely wait during a fire — with minimum area, height intervals and access rules set by NBC 2016 Part 4.
Sprinkler K-Factor — The discharge coefficient of a sprinkler head relating flow to pressure (Q = K√P) — the number hydraulic design is built on and head selection must match.
Sprinkler System — An automatic suppression network of heat-activated sprinkler heads on charged piping — each head opens individually over the fire, designed in India to IS 15105 and NBC 2016.
Wet Riser — A vertical fire main kept permanently charged with pressurised water, with a landing valve at every floor — the standard arrangement for buildings above the low-rise threshold.

HVAC

AHU (Air Handling Unit) — The packaged unit that conditions and moves air — filters, cooling/heating coils and blower in one casing — feeding conditioned air to a zone through ducting.
Air Change Rate (ACPH) — Air changes per hour — how many times a room's full air volume is replaced hourly; the governing number for ventilation of basements, kitchens, plant rooms and cleanrooms.
Cleanroom Classification (ISO 14644) — The ISO 14644-1 class system (ISO 5–9 in common industry) grading cleanrooms by permitted airborne particle counts — the spec that drives filtration, air changes and pressure cascades.
Cooling Load — The calculated rate of heat a space gains — from sun, people, equipment, lights and fresh air — that the HVAC system must remove; the foundation of every equipment selection.
Dehumidification — Removing moisture from air — by cooling below dew point or desiccant systems — the half of air conditioning that Indian monsoons test hardest.
Duct Static Pressure — The resistance pressure a fan must overcome to push design airflow through ducts, filters, coils and grilles — the number that sizes fan power and decides whether far rooms get air.
HVAC Commissioning — The measured proving that an installed HVAC system delivers its design intent — air/water balancing, controls verification and performance runs, documented before handover.
Precision Cooling — Close-control air conditioning for heat-dense, sensitive spaces — server rooms, labs, MRI suites — holding tight temperature/humidity bands 24×7 with high sensible capacity.
Ton of Refrigeration (TR) — The standard unit of cooling capacity: 1 TR = 3,024 kcal/h ≈ 3.517 kW — the number every chiller, VRF and AC selection in India is quoted in.
VAV (Variable Air Volume) — An air-side control strategy where zone boxes modulate airflow to match load, letting the central fan slow down — comfort per zone with fan energy that tracks demand.
VFD (Variable Frequency Drive) — Power electronics that vary a motor's supply frequency to control its speed — on fans and pumps, where power falls with the cube of speed, the single biggest retrofit energy lever.
VRF vs Chiller — The central air-conditioning architecture decision: refrigerant-based VRF (modular outdoor units, indoor cassettes) versus chilled-water plant (chillers, pumps, AHUs) — driven by size, load profile and operations.

Electrical

APFC Panel — An Automatic Power Factor Correction panel — capacitor steps switched in and out by a controller reading the live PF — keeping correction matched to a moving load.
Arc Flash Study — An engineering analysis of the incident energy released by an arcing fault at each switchboard — defining safe working boundaries, PPE categories and labelling for live work.
Cable Derating — The reduction of a cable's usable current capacity below catalogue rating due to grouping, ambient temperature, and installation method — the factor undersized feeders forgot.
CEIG Approval — Clearance from the Chief Electrical Inspector to Government (Electrical Inspectorate) for HT installations, substations, DG sets and specified works — mandatory before energisation.
Changeover Panel (AMF) — The switching assembly that transfers load between grid and DG — from manual changeovers to AMF panels that start the set and transfer automatically, with interlocks that make backfeed impossible.
DG Set Sizing — Selecting standby generator kVA from the essential-load list, starting kVA of big motors, and healthy loading bands — not from the incomer rating.
Earthing / Grounding (IS 3043) — The engineered connection of an installation to earth — electrodes, conductors and bonding per IS 3043 — that makes protection operate and touch voltages safe, proven by measured resistance.
Harmonic Distortion (THD) — The pollution of the supply waveform by multiples of 50 Hz — injected by drives, UPS, LED drivers and inverters — measured as THD and responsible for hot neutrals, nuisance trips and capacitor failures.
LT vs HT Distribution — The supply-voltage divide: LT (low tension, 415 V class) taken directly usable, versus HT (high tension, typically 11 kV) with your own transformer — decided by load size, tariff and DISCOM rules.
Power Factor Correction — Raising a facility's power factor toward unity — usually with capacitor banks — to cut kVA demand, avoid DISCOM penalties/earn incentives, and free electrical capacity.
Sanctioned Load vs Connected Load — Sanctioned load is what the DISCOM has approved you to draw; connected load is everything actually wired in your premises. The gap between them is billing risk and compliance exposure.
Transformer Sizing (kVA) — Selecting distribution-transformer capacity from connected load, diversity and growth — the decision that sets your facility's power ceiling and its CEIG file.

Plumbing / PHE

Drainage Stack Sizing — Sizing the vertical soil/waste stacks and their venting from fixture-unit loads so drainage flows by gravity without siphoning traps or breathing sewer gas into rooms.
ETP (Effluent Treatment Plant) — The treatment system for industrial process effluent — chemistry-specific, unlike an STP — designed from the effluent characterisation and bound to SPCB discharge norms.
Hydro-Pneumatic System — A pressurised water-supply system — VFD pump set plus pressure vessel — that delivers steady pressure on demand without overhead tanks driving every floor.
Pump Head — The total pressure a pump must generate — static lift plus friction losses plus residual pressure at the outlet — expressed in metres; with flow, it defines every pump selection.
Rainwater Harvesting — Capturing roof and surface runoff for storage/reuse or aquifer recharge — mandated by most building bye-laws above plot thresholds and tied to CGWA compliance for groundwater users.
STP Capacity — The design throughput of a sewage treatment plant in KLD — sized from occupancy-based water demand and sewage generation, and locked into pollution-control consents.
Water Demand (NBC) — The per-capita daily water requirement by occupancy class (the NBC Part 9 / IS 1172 basis) from which tanks, pumps, mains and STP capacity are all sized.

Solar

ALMM — MNRE's Approved List of Models and Manufacturers — the gate deciding which solar modules may be used in most grid-connected Indian projects, now extending to cells (List-II).
CAPEX vs OPEX Solar — The two ways to buy rooftop solar: own the plant outright (CAPEX) or buy its output from a developer who owns it on your roof (OPEX/RESCO PPA) — an ownership, balance-sheet and TCO decision.
DCR Modules — Domestic Content Requirement modules — cells and modules made in India — mandatory in specified government-linked schemes, distinct from (and pricier than) general ALMM-listed modules.
Gross Metering — The regime where all solar generation is exported and paid at a feed-in tariff, while all consumption is billed at retail — generation and usage settled as separate streams.
Module Mounting Structure — The engineered steel/aluminium framework fixing solar modules to roof or ground — designed for IS 875 wind loads, the component that decides whether the plant survives storms and the roof survives the plant.
Net Metering — The settlement regime where solar exports offset grid imports through a bidirectional meter — exported units credited against consumed units under your state's regulations.
Open Access (Solar) — Buying solar power from an off-site plant wheeled over the grid — open to consumers from 100 kW contracted demand under the Green Energy Open Access Rules, with state-set charges deciding the landed price.
PM Surya Ghar Subsidy — The central subsidy for residential rooftop solar under PM Surya Ghar: Muft Bijli Yojana — ₹30,000/kW up to 2 kW and ₹18,000 for the third kW, capped at ₹78,000; residential connections only.
PPA (Power Purchase Agreement) — The long-term contract to buy power from a generator at agreed rates and terms — the commercial backbone of OPEX rooftop deals and open-access supply.
Shadow-Free Area — The portion of a roof that stays unshaded through the solar day year-round — the honest constraint on plant capacity, mapped by shadow analysis before any sizing promise.
Solar Payback Period — The years for cumulative solar savings to repay plant cost — the first-filter metric, computed honestly from tariff, yield and offset share before IRR/NPV refine it.
String Inverter vs Central Inverter — The plant-architecture choice between many modular string inverters and one large central unit — deciding failure blast-radius, monitoring granularity and the year-12 replacement pattern.

Contracting

AMC / O&M SLA — The maintenance contract (Annual Maintenance Contract / Operations & Maintenance) whose Service Level Agreement fixes preventive schedules, response times and compliance duties in measurable terms.
BOQ (Bill of Quantities) — The itemised schedule of measured quantities and rates that prices a works contract — the commercial spine of tendering, billing and variation control.
DLP (Defect Liability Period) — The post-completion window — commonly 12 months for building services — during which the contractor must rectify defects at own cost, secured by retention or bank guarantee.
EPC — Engineering, Procurement and Construction — the contract model where one party designs, buys and builds against a defined performance outcome, owning the integration risk.
MEPF — Mechanical, Electrical, Plumbing and Fire protection — the four building-services disciplines that make a structure operable, increasingly contracted as one integrated scope.