MEP Design for a Cleanroom: Air Changes, Pressure Cascade, Utilities and Qualification

MEP design for a cleanroom starts from the required class, not the room size. The class sets particle limits, the limits set filtration and airflow, the airflow sets AHU, chiller and power size, and room pressure differences set the air balance. Qualification tests then prove the result. Air-change rates are an outcome of that calculation and a recovery test, so a table value is only a first guess.

What do cleanroom classes actually limit?

A class is a limit on airborne particles per cubic metre at stated sizes and room states. For drug manufacture, the revised Schedule M to the Drugs Rules, 1945 (notified by G.S.R. 922(E), 28 December 2023) gives four grades for sterile products and says classification follows ISO standards. The table reproduces its particle limits and ISO equivalents. Outside pharma, such as electronics, medical devices or food packing, the product or customer specification names an ISO 14644-1 class and the same logic applies; Schedule M binds only drug manufacture.

Schedule M describes Grade A as the local zone for high-risk operations such as filling, normally under unidirectional airflow, and Grade B as the background to Grade A. Grades C and D serve less critical steps. The MEP consequence is that the grade of each room, at rest and in operation, belongs in the design basis before any duct is sized. For a pharma-specific design basis, see our note on GMP cleanroom basics.

How are air changes decided?

Not from a table. Schedule M says only that the number of air changes needed to reach grades B, C and D shall be appropriate for the size of the room and the equipment and personnel in it. The supply airflow is the largest of four requirements, each calculated:

• Cleanliness and recovery. Enough filtered air to dilute the particles that people and process generate, and to bring the room back to its at-rest class after operations. Schedule M gives a guidance recovery period of about 15 to 20 minutes and a test that shows particle concentration falling by a factor of 100.
• Heat load. Equipment, lighting, people and envelope gains, which in a process room can exceed the particle requirement.
• Pressure. Air that leaks out through doors, pass-boxes and wall gaps to keep the room above its neighbour.
• Fresh air and exhaust. Occupant fresh air plus any local exhaust the process needs.

Unidirectional zones follow a velocity rule instead: Schedule M gives 0.36 to 0.54 m/s as a guidance value at a test position 15 to 30 cm below the terminal filter, shown by airflow visualisation tests. Ask any designer who quotes an air-change figure for the calculation behind it; the figure alone tells you nothing about recovery or pressure.

How is a pressure cascade designed?

The principle is that air moves from cleaner to less clean rooms. For sterile areas Schedule M asks for a filtered air supply that holds positive pressure relative to lower-grade surroundings under all operating conditions, with adjacent rooms of different grade at a differential of approximately 10 to 15 Pa as a guidance value. Its oral solid dosage section adds rules that decide detailing:

• Pressure ranges of neighbouring rooms must not overlap. Its example, 5 to 15 Pa in one room and 15 to 30 Pa in the next, can fail when one room sits at its top limit and the other at its bottom limit.
• Pressure instruments are calibrated and qualified, read out in the room with alert and action limits, and linked to an alarm set from a risk analysis. A warning system must signal failure of the air supply.
• Airlocks may be cascade, sink or bubble types. Doors open towards the high-pressure side with self-closers, and doors of an airlock are interlocked or indicated where a risk assessment says so.
• The building must accommodate the cascade, with sealed ceilings and walls, close-fitting doors and sealed light fittings.

In design terms this means pressure-independent supply and return control, tight envelope details, room-by-room leakage estimates and a control sequence for AHU failure that does not invert the cascade.

What utilities and power does a cleanroom need?

The AHUs only hold class while chilled water, power and controls are available, so the support systems are designed to the same criticality as the room. Decide which rooms must hold class through a single AHU or chiller failure, and draw the redundancy to match. Typical lines to settle in the design basis are:

• Chilled water and dehumidification capacity with the redundancy the product risk justifies.
• Power distribution with separate feeders for critical loads, and DG or UPS cover sized for fans, controls and monitoring, not only for the lights.
• Process utilities where the process uses them, such as compressed air, nitrogen, vacuum and purified water, each with its own quality limits and test points.
• A monitoring system that records pressure, temperature, humidity and particle counts, with alarms and trend logs that the qualification tests can use.

Our cleanroom and process cooling page lists the HVAC scope, and the MEPF cost calculator gives an order-of-magnitude budget before the design basis is fixed.

What does qualification require from the design?

Schedule M defines qualification as documentary evidence in stages: design qualification shows the premises, utilities and equipment were designed to good manufacturing practice, installation qualification shows they were built to the design, operational qualification shows they operate to it, and performance qualification or process validation shows the process meets specification. It adds that significant changes need requalification and that the programme is not a one-off.

The design team's job is to make those tests passable. Schedule M recommends installed HEPA filter leak tests every six months and not beyond twelve, so filter housings need test ports and access. Classification needs sample locations and a particle counter route. Pressure gauges must be calibratable. Smoke studies need clear views of unidirectional zones. Drawings should convert into as-built records without rework.

How Secured Engineers helps

We design HVAC, electrical, plumbing, fire and ELV in-house and coordinate them in one drawing set; Fire NOC, CEIG and DISCOM filings are done in-house, and MEPF and solar can sit under one contract. We are executing the complete MEPF package with a solar plant for a multi-storey pharmaceutical formulations facility in Ludhiana, in execution as of October 2026. We work from Noida (Delhi NCR) and Ludhiana, across 535+ projects in 18+ states, with 89.77% repeat clients.

If you have a cleanroom layout, a vendor's HVAC proposal or a draft design basis, send it for a technical review against the grade, pressure and utility requirements before it is priced. See our MEP design and approvals service, message us on WhatsApp, call +91 70099 85817 or ask for a free proposal.