Air Handling Units — Sizing, Selection & Procurement Guide
AHUs condition and distribute the air that reaches every occupied or process space. Selection drives IAQ, energy, humidity control and infection-control compliance — from packaged rooftops to hygienic pharma / hospital AHUs and clean-room recirc.
What it is & where it's used
An AHU is a factory-assembled cabinet containing fans, coils (cooling / heating), filters, dampers, heat-recovery devices and optionally humidification. Modular AHUs are engineered per project; packaged rooftops (RTU) integrate the refrigeration circuit.
- • Commercial buildings (offices, malls, hotels)
- • Hospitals, clean rooms, laboratories
- • Food processing (hygienic AHUs)
- • Industrial process ventilation
- • Data centre CRAH units
- • Ventilation + heating/cooling of occupied spaces
- • Process temperature and humidity control
- • Positive/negative pressurisation for infection control
- • Heat recovery for energy compliance
- • Centralised filtration and heat recovery drive 30–50% HVAC energy savings
- • Precise humidity and pressure control
- • EN 1886 leakage/hygiene classes for regulated environments
- • Requires ducting network — space and pressure-drop hungry
- • Filter and coil PM is non-negotiable for IAQ
- • Chilled-water / DX / gas piping to the AHU
Typical project sizes: 1,000 m³/h fan-coil unit up to 250,000 m³/h airport / factory AHU.
Modular Built-Up AHU vs Packaged Rooftop (RTU)
| Criterion | Modular Built-Up AHU | Packaged Rooftop (RTU) |
|---|---|---|
| Airflow range | 5,000–250,000 m³/h | 1,000–60,000 m³/h |
| Refrigeration | External chilled water or DX | Integrated DX + gas / heat pump |
| Heat recovery | Wheel, plate, run-around | Optional wheel / plate |
| Configurability | Fully custom sections | Standard menu |
| CAPEX per m³/h | USD 3–8 | USD 4–10 |
| Best for | Institutional, industrial, hygienic | Retail, warehouses, big-box, quick-install |
| Install complexity | High (piping + ducts + controls) | Low (crane-and-connect) |
How to evaluate
- 01Specify EN 1886 casing class — L1/T2/TB2 minimum for anything hospital / pharma / food.
- 02Insist on EC or IE4 direct-drive plug-fans — they cut fan energy 20–40% vs belt-driven.
- 03Add heat-recovery (rotary wheel 75–85% or plate 60–70%) unless local climate makes it uneconomic.
- 04Filter progression F7 → F9 for offices; H13/H14 for clean rooms; separate pre-filter + fine + HEPA layer.
- 05For pharma / hospital, hygienic AHUs with drainable coils, cleanable interior and full stainless drain pans.
- 06Include VFD / EC control, differential-pressure filter monitoring and CO₂-based demand ventilation.
- 07Confirm sound and vibration data at the neck — many AHUs fail commissioning acoustics.
Spec checklist
- Design supply airflow (m³/h or cfm)
- External and internal static pressure
- Cooling / heating coil duty (kW)
- Chilled / hot water temperatures and flow
- Filter progression and end-of-life ΔP
- Heat-recovery type and efficiency
- Humidification / dehumidification requirement
- Casing class (EN 1886)
- Acoustic limits at supply / return / casing
- BMS integration protocol
Investment & operating cost
- Standard modular AHU (10,000 m³/h)USD 25K – 55K
- Hygienic AHU pharma / hospital (10,000 m³/h)USD 55K – 110K
- Packaged rooftop (30 TR / ~15,000 m³/h)USD 40K – 90K
- Large custom AHU (60,000 m³/h)USD 150K – 350K
Indicative ranges. Actual quotations vary by country, scope, spec, freight and site conditions.
- • Airflow and static pressure
- • Casing class and material
- • Coil rows and heat recovery
- • Filtration level
- • Humidification technology
- • Custom acoustic / seismic requirements
- • UV-C in-duct disinfection
- • Adiabatic humidifiers
- • Bag/HEPA final filter
- • Energy meter package
- • Structural pad / roof steel
- • Ductwork and dampers
- • Chilled/hot water piping and BMS wiring
- • Condensate drainage
- • Fan electricity dominates OPEX
- • Filter change 2–4× per year
- • Coil cleaning annually
- • Monthly filter inspection
- • Quarterly belt / bearing check (if belt-driven)
- • Annual coil clean + eddy-current test
Before you request quotations
- Define production goals and daily throughput (kg/day)
- Confirm utilities: power (kVA), water, drainage, compressed air
- Define project scope (turnkey vs supply-only vs hybrid)
- Prepare site layout, floor plan and clear height
- Confirm local regulations (F-Gas, ATEX, HACCP, seismic code)
- Determine financing route (own cash, lease, bank loan, ECA)
- Create technical specification with U-values and setpoints
- Prepare RFQ and shortlist qualified international suppliers
Interactive evaluation matrix
Score each shortlisted supplier on the criteria below. All calculations run locally — nothing is sent to our servers.
| Criterion | |||
|---|---|---|---|
Price / Investment Turnkey CAPEX including installation, controls and commissioning. | |||
Warranty (years) Comprehensive, on major components (compressors, PLC, panels). | |||
Lead time (weeks) Ex-works or delivered to site including customs. | |||
Energy efficiency (SEC / COP) Lower SEC or higher COP is better. | |||
Local service & spare parts Response time, service partner in country, stocked spares. | |||
References / installed base Comparable capacity, region and application. | |||
Maintenance program Preventive maintenance plan, remote monitoring. | |||
Operator training On-site training days, documentation, language. | |||
Expandability Add capacity, modules or additional rooms later. | |||
Lifecycle cost (10y) CAPEX + energy + maintenance + refrigerant cost of ownership. | |||
| Total score | 0 / 50 | 0 / 50 | 0 / 50 |
Common questions
How do I size an AHU?
Start from ventilation code (ASHRAE 62.1 or EN 16798-1) for outside air, then add cooling load in kW to size coils, then confirm supply airflow from Q = load / (1.2 × 10 × ΔT). Get external static from ducted losses. Never oversize — poor part-load performance.
Is heat recovery always worth it?
In climates with >2,000 heating degree-days or >1,500 cooling degree-days, yes — payback is usually 2–5 years. Skip only in very mild coastal climates or 100% recirculating applications.
Modular AHU or packaged rooftop?
Choose packaged RTU for quick-install commercial / retail where a single-package DX plus gas heat is fine. Choose modular AHU for hospital / pharma / food / high-airflow projects that need custom coils, hygienic construction or wheel heat recovery.
Continue your planning
Receive structured, comparable quotations from qualified international suppliers — vendor-neutral. Add financing pre-qualification if the project requires equipment leasing, project loan or ECA-backed facility.