Executive Overview
Air Handling Units (AHUs) in Dholera Special Investment Region (DSIR) industrial facilities must deliver outdoor air and recirculated air at defined purity levels to protect product quality, worker health, and process equipment. Under the DSIRDA General Development Control Regulations (GDCR) 2023 Chapter 12.3 (HVAC and Ventilation), NBC 2016 Part 8 Section 2, ISO 16890:2016 (air filters for general ventilation — classification), ASHRAE 52.2 (MERV ratings), and GPCB ambient air quality norms, all industrial AHUs in DSIR must be designed with multi-stage filtration matched to the occupancy class and process sensitivity.
Dholera’s ambient air carries high particulate loads from Gujarat’s alluvial plains and nearby construction dust — PM10 routinely exceeds 80 µg/m³ during summer. An undersized or wrongly specified filter bank fails prematurely, collapses differential pressure, trips fans, and causes indoor air quality non-compliance.
1. Regulatory Framework
| Code / Standard | Scope |
|---|---|
| DSIRDA GDCR 2023 Chapter 12.3 | HVAC filtration norms for industrial occupancies |
| NBC 2016 Part 8 Section 2 | Air quality and ventilation rates |
| ISO 16890-1:2016 | Filter classification by ePM1, ePM2.5, ePM10 |
| ASHRAE 52.2-2017 | MERV rating method |
| ASHRAE 62.1-2022 | Ventilation for acceptable indoor air quality |
| IS 8183 | Bonded mineral wool for duct insulation |
| GPCB Ambient Air Quality | Permissible PM2.5 and PM10 limits |
| ECBC 2017 | Energy-efficient fan and filter system requirements |
DSIRDA GDCR 2023 Clause 12.3.1 mandates a minimum two-stage filtration for all AHUs serving industrial occupancies — a pre-filter stage (minimum ISO Coarse 65% / MERV 7) and a secondary filter stage (minimum ISO ePM2.5 50% / MERV 13) for general manufacturing. Pharmaceutical and electronics clean zones require additional HEPA stages.
2. Filter Classification Systems
2.1 ISO 16890 Classification (Current International Standard)
| ISO Class | Particle Size Target | Min Efficiency |
|---|---|---|
| ISO Coarse | PM10 > 50% | ≥ 50% arrestance |
| ISO ePM10 | PM10 | ≥ 50% for PM10 |
| ISO ePM2.5 | PM2.5 | ≥ 50% for PM2.5 |
| ISO ePM1 | PM1.0 | ≥ 50% for PM1.0 |
Sub-classifications: ISO ePM2.5 50%, 60%, 70%, 80%, 85%, 90%, 95% based on tested efficiency at the given particle size.
2.2 ASHRAE MERV Equivalency (legacy, still widely used on equipment nameplates)
| MERV | ISO 16890 Equivalent | Filter Type | Application |
|---|---|---|---|
| 5–6 | ISO Coarse ≥ 50% | Panel/washable | Pre-filter, coarse |
| 7–8 | ISO Coarse ≥ 65% | Pleated panel | Pre-filter standard |
| 9–10 | ISO ePM10 50%–65% | Bag filter | Intermediate |
| 11–12 | ISO ePM2.5 50%–65% | Bag/pocket filter | Secondary |
| 13–14 | ISO ePM1 50%–75% | Rigid cassette | Fine secondary |
| 15–16 | ISO ePM1 ≥ 85% | Semi-HEPA | Near-HEPA |
| 17–20 | HEPA / ULPA | High-efficiency panels | Clean rooms |
3. DSIRDA Filtration Requirement by Occupancy Type
| Occupancy | Stage 1 (Pre-filter) | Stage 2 (Secondary) | Stage 3 (Final) |
|---|---|---|---|
| General manufacturing | ISO Coarse 65% / MERV 8 | ISO ePM2.5 50% / MERV 11 | — |
| Auto-components / light engineering | ISO Coarse 65% / MERV 8 | ISO ePM2.5 65% / MERV 13 | — |
| Electronics assembly | ISO ePM10 50% / MERV 10 | ISO ePM1 50% / MERV 14 | HEPA H13 (EN 1822) |
| Pharmaceutical (non-sterile) | ISO Coarse 65% / MERV 8 | ISO ePM1 65% / MERV 14 | HEPA H14 |
| Pharmaceutical (sterile / ISO 5) | ISO Coarse 65% / MERV 8 | ISO ePM1 85% / MERV 15 | ULPA U15 |
| Food processing | ISO Coarse 65% / MERV 8 | ISO ePM2.5 65% / MERV 13 | HEPA H13 (final zone) |
| Data centre / server room | ISO Coarse 65% / MERV 8 | ISO ePM1 50% / MERV 13 | — |
4. Filter Stage Design and Specifications
4.1 Pre-Filter (Stage 1)
| Parameter | Specification |
|---|---|
| Type | Synthetic panel filter, washable or disposable |
| Media | Polyester or glass fibre mat |
| Frame | Galvanised steel or ABS plastic |
| Nominal face velocity | 2.0–2.5 m/s |
| Initial pressure drop | ≤ 30 Pa at rated airflow |
| Final (change-out) ΔP | ≤ 100–150 Pa (per filter manufacturers’ data) |
| Service interval | Monthly inspection; replace at ΔP limit or 3 months |
4.2 Bag / Pocket Filter (Stage 2)
| Parameter | Specification |
|---|---|
| Type | Mini-pleat bag, 6–8 pockets |
| Depth | 360–600 mm |
| Media | Micro-glass fibre or synthetic high-loft |
| Nominal face velocity | 2.0–2.5 m/s |
| Initial pressure drop | ≤ 80 Pa (MERV 11–13) |
| Final ΔP (change-out) | ≤ 250 Pa |
| Service interval | 6–12 months depending on dust load |
4.3 HEPA Final Filter (Stage 3 — where applicable)
| Parameter | Specification |
|---|---|
| Classification | H13 (EN 1822): ≥ 99.95% at MPPS; H14: ≥ 99.995% |
| Face velocity | 0.45–1.0 m/s (lower for longer life) |
| Initial ΔP | ≤ 150 Pa at rated face velocity |
| Final ΔP (change-out) | ≤ 450 Pa |
| Leak test | DOP/DEHS scan test per ISO 14644-3 after installation |
| Frame | Aluminium; gasket compression rated |
5. Pressure Drop Monitoring — DSIRDA Requirement
“` AHU FILTER SECTION — INSTRUMENTATION
[Pre-filter G4]──[Magnehelic 0-100Pa]──[Stage 2 F7/F9]──[Magnehelic 0-250Pa]──[HEPA H13]──[Magnehelic 0-500Pa] │ BMS alarm output ◄────────────────────────────────────┘ (alert at 80% of final ΔP) “`
DSIRDA GDCR 2023 Clause 12.3.4 mandates: – Magnehelic or digital differential pressure gauge across each filter stage – BMS (Building Management System) alarm at ≥ 80% of final ΔP limit – Filter log to be maintained and available for DSIRDA inspection (change-out dates, recorded ΔP readings)
6. Filter Energy Efficiency (ECBC 2017 / DSIRDA Mandate)
DSIRDA GDCR 2023 aligns with ECBC 2017 provisions for AHU fan power:
| AHU Size | Max Fan Specific Power (FSP) |
|---|---|
| < 1000 L/s | 2.0 W/(L/s) |
| 1000–5000 L/s | 1.6 W/(L/s) |
| > 5000 L/s | 1.4 W/(L/s) |
Higher filter efficiency = higher pressure drop = higher fan energy. DSIRDA requires VFD (Variable Frequency Drive) on all AHU fans > 7.5 kW to compensate for rising filter ΔP over time and maintain constant airflow without excessive energy.
6.1 Filter Selection for Energy Balance
| Filter Stage | Clean ΔP | Dirty ΔP | Contribution to Fan Power |
|---|---|---|---|
| Pre-filter G4 | 25 Pa | 100 Pa | ~5% of total |
| Bag filter F7 | 60 Pa | 200 Pa | ~25% of total |
| Rigid cassette F9 | 90 Pa | 300 Pa | ~35% of total |
| HEPA H13 | 150 Pa | 450 Pa | ~50% of total |
Design at average dirty ΔP (clean + final / 2) for energy calculations per ECBC 2017 guidelines.
7. Filter Change-Out and Disposal
7.1 Change-Out Procedure
- Shut AHU and lock-out/tag-out (LOTO)
- Don PPE: N95 mask, nitrile gloves, disposable coveralls
- Insert new filter before removing old (maintain seal continuity in pharmaceutical zones)
- Bag old filter in heavy-duty polythene immediately — double-bag
- Record: filter type, MERV/ISO class, date, ΔP at change-out, technician name
7.2 Disposal Classification (DSIRDA / GPCB)
| Filter Type | Waste Category | Disposal Method |
|---|---|---|
| Pre-filter (clean dust) | General solid waste | DSIRDA-approved landfill |
| Bag filter (industrial dust, non-hazardous) | Schedule II solid waste | DSIRDA licensed transport |
| HEPA (pharmaceutical process air) | Hazardous waste Schedule I | Incineration via GPCB-authorised facility |
| HEPA (radioactive/toxic process) | Hazardous waste special | CEA-licensed disposal |
8. AHU Filter Section Sizing — Worked Example
Scenario: 5000 m² auto-component manufacturing hall, Dholera SIR Design supply airflow: 50,000 m³/h (ACH = 4) Required filtration: ISO Coarse 65% (pre) + ISO ePM2.5 65% / MERV 13 (secondary)
Step 1 — Face velocity: Target 2.2 m/s Step 2 — Filter face area: A = Q / v = (50,000/3600) / 2.2 = 6.3 m² Step 3 — Filter bank: Use 25 panels of 610 mm × 610 mm per stage (standard 24″ × 24″ nominal) Step 4 — ΔP at design: Pre-filter 30 Pa clean + Bag filter 80 Pa clean = 110 Pa total clean Step 5 — Fan selection: At average dirty ΔP ~200 Pa total system, select fan with adequate static pressure
FAQ
What is the minimum filter specification required for an AHU serving general manufacturing in Dholera SIR?
DSIRDA GDCR 2023 Clause 12.3.1 mandates a minimum two-stage filtration for general manufacturing AHUs: Stage 1 — ISO Coarse 65% (MERV 8) pre-filter, and Stage 2 — ISO ePM2.5 50% (MERV 11) secondary filter. Auto-component and light engineering facilities require the secondary stage upgraded to MERV 13 (ISO ePM2.5 65%).Is a HEPA filter mandatory for all industrial AHUs in Dholera?
No. HEPA (H13/H14 per EN 1822) filters are mandatory only for electronics assembly, pharmaceutical (non-sterile and sterile), and food processing final-zone AHUs per DSIRDA GDCR 2023. General manufacturing and data centres are served by MERV 11–14 bag/cassette filters without HEPA.What pressure drop monitoring is required for AHU filter banks in Dholera industrial buildings?
DSIRDA GDCR 2023 Clause 12.3.4 requires a Magnehelic or digital differential pressure gauge across each filter stage, with BMS alarm set at 80% of the final change-out ΔP limit. A filter change-out log (dates, ΔP readings, filter grades) must be maintained on-site for DSIRDA inspection.Are VFDs mandatory on AHU fans in Dholera industrial buildings?
Yes. DSIRDA GDCR 2023 aligned with ECBC 2017 mandates Variable Frequency Drives (VFDs) on all AHU fan motors exceeding 7.5 kW. VFDs compensate for rising filter pressure drop over the filter’s service life, maintaining constant airflow at lower energy consumption.How should used HEPA filters from pharmaceutical AHUs be disposed of in Dholera SIR?
Used HEPA filters from pharmaceutical process air streams are classified as hazardous waste (Schedule I) under GPCB regulations. They must be double-bagged immediately, transported by a DSIRDA-licensed waste carrier, and incinerated at a GPCB-authorised high-temperature incineration facility. A waste manifest must be maintained for regulatory inspection.Download Dholera SIR 2026 Investor’s Kit
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