Comfort AHU
People-centered air
A lobby moving from 23 C to 25 C is usually a comfort complaint, not a production failure.
Air Handling Unit Selection
Comfort AHU vs Process AHU: Selection Criteria for Humidity, Filtration and Process Risk
Comfort AHU vs process AHU selection starts with the consequence of losing control. A comfort AHU protects people, while a process AHU protects production, storage or technical performance.
Choose Comfort AHU
Human comfort is the target
Temperature, fresh air, indoor air quality, noise and energy use drive selection.
Choose Process AHU
Production conditions matter
Humidity, pressure, filtration, contamination and uptime affect product or equipment risk.
Hybrid Rule
Define process first
If both people and process matter, set the process limit first, then add comfort constraints.
Core Difference: People Load vs Process Load
Scope boundary: this is a duty-classification and engineering selection guide, not an AHU supplier catalogue. Use the air handling unit supplier page for product range and configuration options; use this page to decide whether humidity tolerance, filtration, pressure, cleanability and downtime risk require a process-duty unit.
A comfort AHU protects occupant comfort and indoor air quality. It is sized around occupancy, ventilation rate, envelope heat gain, solar load, lighting, equipment heat, acoustic limits and building schedules.
A process AHU protects a technical condition. It is sized around process heat and moisture load, required room pressure, particle target, contaminant control, operating hours, product sensitivity and downtime risk.
Ventilation and indoor air quality coordination is commonly referenced to ASHRAE 62.1, filter classification is addressed by ISO 16890, and cleanroom air cleanliness classification is addressed by ISO 14644-1.
Process AHU
Product-centered air
A process room drifting from 45% RH to 60% RH can affect coating, powder handling, electronics, packaging or storage stability.
Selection Matrix for Comfort and Process AHUs
This matrix gives a buyer-level comparison before detailed coil, fan and control selection. Use it to decide whether a standard comfort AHU is enough or whether a process AHU specification is needed.
Main target
Comfort AHU
Human comfort and IAQ.
Process AHU
Product, process or technical condition.
Buyer rule
State which failure costs more: discomfort or process loss.
Airflow basis
Comfort AHU
Occupancy, cooling load and fresh air.
Process AHU
Process exhaust, heat, moisture, pressure or ACH.
Buyer rule
State m3/h and calculation basis.
Humidity band
Comfort AHU
Broad RH target, such as 40-60% RH.
Process AHU
Tight RH target, such as 45-55% RH.
Buyer rule
State RH tolerance before coil selection.
Filtration
Comfort AHU
Pre-filter plus medium filter.
Process AHU
Multi-stage filter or HEPA where required.
Buyer rule
State ISO 16890 or ISO 14644 target.
Operating schedule
Comfort AHU
Building schedule, often 8-16 hours per day.
Process AHU
Production schedule, sometimes 24 hours per day.
Buyer rule
State uptime and standby requirement.
The process AHU column is stricter because air is part of the production environment. Higher filtration increases pressure drop, tighter humidity control changes coil and reheat requirements, and pressure control needs stable dampers, sensors and commissioning.
Worked Example: Fresh Air and Process Airflow
A simple airflow split shows why comfort and process AHUs diverge even when the total airflow is the same. Assume two rooms each need 20000 m3/h total supply airflow.
| Input | Comfort office AHU | Process production AHU |
|---|---|---|
| Total supply airflow | 20000 m3/h | 20000 m3/h |
| Fresh-air ratio | 20% | 80% |
| Fresh-air volume | 4000 m3/h | 16000 m3/h |
| Return-air volume | 16000 m3/h | 4000 m3/h |
| Cooling coil duty | Lower outdoor-air load | Higher outdoor-air and moisture load |
| Filter pressure allowance | Medium filter allowance | Multi-stage filter final pressure allowance |
Fresh-air volume = total supply airflow x fresh-air ratio
Comfort AHU = 20000 x 0.20 = 4000 m3/h
Process AHU = 20000 x 0.80 = 16000 m3/hRecommendation: the process AHU needs a different coil and fan selection because outdoor air adds sensible load, latent load and filter pressure. Do not reuse the comfort AHU coil model for the process room without recalculating entering-air condition and final filter pressure.
Filtration, Humidity and Casing Decisions
Filtration is the first major split between comfort and process AHUs. Comfort projects usually need dust control, occupant IAQ and filter maintenance access. Process projects need a defined particle, product or equipment protection target.
ISO 14644-2 specifies monitoring requirements for cleanroom or clean-zone performance related to airborne particle concentration, while ISO 14644-1 classifies air cleanliness by particle concentration.
Filter targetUse ISO 16890 for general ventilation filter classification; use ISO 14644 logic for cleanroom or clean-zone requirements.
Humidity bandState the exact RH band and alarm limit. “Humidity control” is too vague for a process AHU.
Coil and reheatProcess dew-point control may require deeper cooling plus reheat or seasonal humidification.
Casing and drainageState leakage class, drain-pan material, access doors, insulation, cleanability and corrosion protection.
RFQ Data and Specification Checklist
A comfort AHU RFQ should describe the building load and comfort target. A process AHU RFQ should describe the air condition that protects production. The second RFQ needs more measured limits.
For engineering support, send your airflow, external static pressure, air conditions, filtration target and process description when you request a quote from SongXin. If the AHU needs modular sections or supplier-side configuration support, use SongXin’s air handling unit supplier guide together with this comparison.
When the AHU uses chilled water, coordinate coil duty, water temperature and operating hours with the air-cooled screw chiller product range or SongXin’s air-cooled screw chiller supplier guide before finalizing the AHU selection.
| RFQ item | Comfort AHU data | Process AHU data |
|---|---|---|
| Application | Office, mall, hotel, school or public building | Production, laboratory, storage, clean zone or equipment room |
| Airflow | m3/h and fresh-air ratio | m3/h, exhaust balance and pressure target |
| Temperature | Indoor comfort setpoint | Product or process temperature band |
| Humidity | Comfort RH target | Minimum, maximum and alarm RH values |
| Filtration | ISO 16890 filter class | ISO 16890, ISO 14644 or project particle target |
| Coil | Chilled-water, hot-water, steam, DX or electric | Coil plus reheat, humidifier or dehumidification requirement |
| Controls | BMS, VFD, temperature sensor and filter alarm | BMS plus humidity, pressure, filter and process interlock alarms |
| Maintenance | 1-3 month filter access plan | 1 month inspection plan for critical or dusty process rooms |
AHU typeComfort, process or hybrid duty stated clearly.
AirflowDesign m3/h and external static pressure stated.
Coil dutyEntering and leaving air conditions, water or DX conditions and kW capacity stated.
FiltrationISO 16890 or ISO 14644 basis stated with final pressure allowance.
HumidityRH target and tolerance stated, such as 45-55% RH for a process room.
CasingEN 1886 or project casing class, insulation and leakage requirement stated.
ControlsTemperature, humidity, pressure, filter alarm and BMS points stated.
MaintenanceFilter, coil, drain pan and fan access stated before production.
Common Mistakes
01
Selecting process AHU by comfort airflow rules
The same 20000 m3/h airflow can mean very different coil duty if one unit handles 20% fresh air and the other handles 80% fresh air.
02
Giving humidity target without tolerance
State the allowed band, alarm point, seasonal range and whether the process needs dehumidification, humidification or both.
03
Using clean-filter pressure in a process AHU
Final filter pressure matters because loaded filters reduce airflow and room pressure. Include dirty-filter pressure allowance and a differential-pressure switch or gauge.
04
Ignoring access and cleaning
A process AHU needs filter pull space, coil cleaning access, drain-pan cleaning, fan service access and sensor calibration access.
FAQ
These FAQ answers use the same AHU performance, filtration and clean-zone basis referenced above under EN 1886, EN 13053, ISO 16890, ISO 14644-1 and ISO 14644-2.
What is the difference between a comfort AHU and a process AHU?
A comfort AHU is selected mainly for people, with priorities such as temperature, fresh air, noise and indoor air quality. A process AHU is selected for production or technical conditions, with priorities such as humidity band, filtration, pressure control, cleanability and uptime. The same airflow number does not make the two units equivalent.
When should I choose a process AHU?
Choose a process AHU when air conditions affect product quality, equipment reliability, storage stability, contamination control or production uptime. Typical examples include manufacturing rooms, laboratories, clean zones, coating areas, drying processes and sensitive storage. State the temperature, humidity, filtration, pressure and operating schedule before asking for a price.
Is a comfort AHU enough for a factory?
A comfort AHU is enough for factory offices, staff areas and support rooms where human comfort is the main target. Production areas need a process AHU when dust, moisture, heat, fumes, pressure or product sensitivity affects the result. A mixed factory project might use comfort AHUs for people spaces and process AHUs for technical rooms.
What filtration standard should I use for a process AHU?
Use ISO 16890 when the goal is general ventilation filter classification. Use ISO 14644 logic when the space is a cleanroom or clean zone where airborne particle concentration is part of the process requirement. The RFQ should state filter stages, final pressure drop, access side and monitoring method, not only a filter name.
What data should I send for comfort AHU vs process AHU selection?
Send airflow, external static pressure, fresh-air ratio, room function, temperature band, humidity band, filter target, cooling and heating source, casing requirement, operating hours, control points and maintenance access. For a process AHU, also send process heat, moisture load, exhaust requirement, pressure target and contamination-control requirement.
Need comfort or process AHU selection support?
Send airflow, external static pressure, air conditions, filtration target and process description. SongXin can help define the AHU duty before quotation.
Review Record
Technical review: SongXin HVAC Engineering Team, comfort and process AHU selection review, 2026-07-13.
Sources
- ASHRAE Standard 62.1 and 62.2 overview, ashrae.org
- ISO 16890-1:2016, “Air filters for general ventilation – Part 1,” iso.org
- ISO 14644-1:2015, “Cleanrooms and associated controlled environments – Part 1,” iso.org
- ISO 14644-2:2015, “Cleanrooms and associated controlled environments – Part 2,” iso.org
- BS EN 1886:2025 summary, “Ventilation for buildings – Air handling units – Mechanical performance,” thenbs.com