Adiabatic air/air cooling 2025: buildings and industry
- Cédric K
- Sep 8
- 7 min read
Adiabatic air/air cooling (buildings & industries) explained for 2025 efficiency, comfort, and resilience.
Many organisations now evaluate adiabatic (evaporative) air-to-air solutions to cut HVAC electricity use, reduce refrigerants, and maintain reliable cooling under rising heat stress. This guide covers how the technology works, where it excels, key design choices, water and hygiene management, integration with modern controls, and a step‑by‑step roadmap to deploy it in offices, logistics, manufacturing, and data centers.
At a glance
Cuts compressor runtime by leveraging the air’s wet-bulb potential; works best in hot‑dry and mixed climates.
Options include indirect evaporative units, hybrid AHUs/rooftops, and adiabatic pre‑cooling for dry coolers and chillers.
Typical goals: lower HVAC electricity use, improve PUE in data centers, stabilize process air temps, and reduce refrigerant risk.
Water, hygiene, and smart controls are design-critical; plan blowdown, filtration, and drift <0.001%.
2025-ready: integrate with BMS/IoT, monitor wet‑bulb/enthalpy, and align with Ecodesign and Legionella guidance.
Understanding adiabatic air-to-air cooling
How it works (direct, indirect, hybrid)
Adiabatic cooling removes heat as water evaporates into an airstream. In direct evaporative cooling (DEC), supply air contacts wetted media, approaching the ambient wet‑bulb temperature. In indirect evaporative cooling (IEC), evaporation happens in a secondary airstream and the supply air is cooled across an air‑to‑air heat exchanger—no moisture added to the occupied space. Hybrid systems combine IEC/DEC with mechanical cooling, staging compressors only when needed.
Every litre of water evaporated removes roughly 0.68 kWh of heat (latent heat of vaporization at ~30°C), a useful rule-of-thumb for sizing. See thermophysical data from NIST (2023).
Climate suitability and performance envelope
Performance depends on wet‑bulb depression (dry‑bulb minus wet‑bulb). The larger it is, the more cooling potential. Hot‑dry regions are ideal; mixed climates can still benefit for many hours annually, especially in shoulder seasons or at night. IEC units with 65–80% effectiveness can deliver supply air near the ambient wet‑bulb without adding moisture, making them attractive for comfort cooling, process air, and white‑space ventilation.
Example calculation: On a 35°C dry‑bulb / 20°C wet‑bulb day (typical hot‑dry afternoon), an IEC with 70% effectiveness can supply ≈ 35 − 0.70 × (35−20) ≈ 24.5°C air—without compressors. In humid conditions (small depression), savings shrink; a hybrid strategy covers those hours.
Hygiene, drift, and compliance
Modern adiabatic sections use high‑efficiency drift eliminators, non‑recirculating or well‑controlled recirculating water, and smart flush/bleed to manage dissolved solids. Specify materials compatible with treated water, implement periodic disinfection, and monitor biocide levels where applicable. Consult local codes and guidance on evaporative devices and Legionella risk, including risk assessments and written schemes of control.
Reference: UK HSE – Legionella and evaporative cooling systems
Where it delivers value in 2025
Commercial buildings: offices, retail, logistics, venues
Pre‑cool outside air for high-ventilation spaces, easing coil loads and downsizing compressors.
Improve comfort resilience during heatwaves with lower peak electricity draw.
For warehouses and event halls, DEC can be acceptable where slight humidity rise is tolerable; IEC suits offices and mixed‑use areas.
Data centers and telecom facilities
IEC and indirect/direct economizer modes dramatically reduce hours of mechanical cooling, lowering PUE and refrigerant use.
Integrates with free‑cooling coils, adiabatic dry coolers, and rear‑door or in‑row solutions to maintain thermal envelopes recommended by ASHRAE.
Controls prioritize air‑side economizer, then IEC, then compressive cooling as a last resort.
Reference: U.S. DOE Better Buildings – Energy efficiency in data centers and ASHRAE Thermal Guidelines – overview
Manufacturing and process environments
Make‑up air units with adiabatic sections stabilize supply temperatures for machining, food processing, wood, and print lines.
Adiabatic pre‑coolers on air‑cooled chillers and condensers lower condensing temperatures in summer, boosting EER and protecting throughput.
Dust or corrosive environments benefit from IEC (no added moisture to process air) and robust filtration.
Energy, water, and economics
Estimating cooling capacity and water use
A basic approach:
1) Quantify hours with sufficient wet‑bulb depression from local weather files.
2) Select effectiveness (η) based on technology (e.g., IEC 0.65–0.80).
3) Compute supply temperature approach and resulting sensible cooling to the space/process.
4) Water use (litres) ≈ Cooling load (kWh_th) / 0.68, adjusted for media efficiency, blowdown, and drift (target near-zero drift).
As a check: delivering 100 kWh_th of evaporative cooling requires roughly 147 L of net evaporation at ideal conditions, plus blowdown per water quality.
Energy savings and ROI drivers
Savings stem from fewer compressor hours, lower condenser temperatures, and higher economizer hours. ROI depends on climate, existing system efficiency, water cost/quality, and control sophistication. Typical accelerators: - Adiabatic pre‑cooling retrofits on existing dry coolers/chillers (often fastest payback). - IEC in facilities with high ventilation demand (offices, logistics, data halls). - Digital controls that maximize economizer/IEC hours and limit water when benefit is marginal.
If recent metered data are unavailable, build an hour‑by‑hour model using T_db/T_wb bins, utility tariffs, and water chemistry to estimate savings and OPEX.
Design and integration best practices
System architectures to consider
Standalone IEC AHUs: air‑to‑air heat exchangers with wet secondary circuits; supply stays dry.
Hybrid rooftop/air handlers: evaporative section ahead of coils; mechanical cooling stages as needed.
Adiabatic pre‑coolers: retrofit media or misting frames upstream of air‑cooled condensers/dry coolers (with drift eliminators and controls).
Modular units for telecom and edge sites: factory‑built, low‑touch maintenance, integrated filtration.
Controls, sensors, and digitalization
Use enthalpy-based changeover (not temperature only) to select economizer vs IEC vs DX.
Monitor T_db, T_wb (or RH), ΔP across media, conductivity/TDS, and drift status; trigger flush/bleed intelligently.
Predictive control with weather forecasts schedules water use for peak hours; anomaly detection flags fouling or pump faults.
Integrate with BMS and energy dashboards to verify savings, ensure alarms, and enable remote maintenance—aligned with a cyber‑secure, data‑driven operation.
Codes, standards, and 2025 context
Comfort and ventilation: consider ASHRAE 55 (thermal comfort) and 62.1 (ventilation) principles where applicable.
Data centers: align with ASHRAE allowable envelopes and economizer guidance.
EU Ecodesign: ventilation/air handling units must meet fan and heat recovery performance and efficiency labeling; check local transpositions.
Reference: EU Regulation 1253/2014 on ventilation units and CIBSE – Technical resources on evaporative cooling
Implementation roadmap (from audit to optimization)
1) Feasibility study: climate bin analysis, existing plant audit, process/IAQ constraints, water quality and discharge permits.
2) Concept design: choose IEC/DEC/hybrid or pre‑cool retrofit; define redundancy and hygiene strategy.
3) Controls strategy: enthalpy logic, staging, deadbands, frost/legionella protections, BMS points list.
4) Engineering and procurement: select media and heat exchangers, drift eliminators, pumps/valving, filtration, water treatment.
5) Pilot or phased rollout: validate performance and water use; adjust setpoints.
6) Commissioning: functional testing across modes, verification of alarms and blowdown, baseline metering.
7) Operate and optimize: seasonal tuning, predictive maintenance, KPI tracking (kWh saved, water per MWh_th, compressor hours).
For an integrated, end‑to‑end approach across energy, digital, and new tech, see our home page: score-grp.com.
Risk management and sustainability
Water stewardship
Specify make‑up water filtration and consider onsite treatment if hardness/TDS are high.
Meter water to each adiabatic section; track litres per MWh_th delivered.
Use smart blowdown tied to conductivity, not fixed timers, to cut waste while controlling scaling.
Health, safety, and maintenance
Implement a written scheme of control for biogrowth risk and keep logs.
Design for safe access to media and sumps; include isolation and drain‑down.
Train O&M teams on seasonal start‑up/shutdown, disinfection, and PPE.
Sustainability alignment
Reduces reliance on high‑GWP refrigerants by shifting cooling to air‑and‑water physics.
Scales with on‑site renewables (PV) and demand response; lower peak kW eases grid stress.
Supports ESG reporting with measurable KPIs: kWh avoided, peak demand reduction, water intensity.
FAQ
Is adiabatic cooling viable in humid climates?
It depends on the wet‑bulb depression. In very humid conditions, direct evaporative cooling (DEC) adds moisture and provides limited temperature drop; it may still suit high‑ventilation industrial halls. Indirect evaporative cooling (IEC) can be more suitable, as it cools supply air without adding moisture, but the benefit still shrinks as humidity rises. Many mixed climates offer hundreds to thousands of annual hours where IEC or adiabatic pre‑cooling meaningfully reduce compressor runtime. A site‑specific bin analysis using local weather files is the best way to quantify potential.
How much water does an adiabatic system use?
A practical rule: each litre of evaporated water removes about 0.68 kWh of heat. Real systems need additional water for blowdown to control scaling—typically managed via conductivity sensors. Water intensity is therefore a function of cooling delivered, media effectiveness, and water quality. For example, delivering 100 kWh_th of evaporative cooling ideally evaporates ~147 L; with prudent blowdown, total consumption may be higher. Metering each section and optimizing setpoints keep water per MWh_th low while preserving hygiene.
Does adiabatic cooling increase Legionella risk?
Properly designed and maintained systems keep risk low. Key measures include high‑efficiency drift eliminators to minimise aerosol carryover, appropriate water treatment, routine flushing/bleed, periodic disinfection, and a documented maintenance plan. Indirect systems further reduce exposure as supply air does not contact wetted components. Always follow local regulations and guidance on evaporative devices and water hygiene, and conduct a risk assessment. Reference materials from authorities such as the UK HSE provide practical controls and inspection schedules.
Can adiabatic pre‑cooling retrofit my existing chiller or dry cooler?
Yes. Retrofit frames with wetted media or controlled misting can be installed upstream of condenser coils or dry cooler intakes. By lowering intake air temperature during hot periods, compressors operate at lower condensing pressures, improving EER and reducing trips at peak. Critical points: robust controls (enable only when beneficial), drift eliminators, corrosion‑resistant materials, and water treatment. A short pilot on a representative bank of coils can validate savings and refine blowdown and staging logic before full rollout.
How do I model savings without overpromising?
Use hour‑by‑hour weather data (T_db and T_wb), your plant’s performance curves, and tariff structures. Simulate control sequences: economizer first, then IEC/DEC, then mechanical cooling. Include fan/pump penalties and water costs (with expected blowdown). For data centers, track PUE across modes and align with ASHRAE thermal envelopes. Validate assumptions with a small‑scale trial and metering—kWh, kW peak, water litres, and compressor hours. Document uncertainties and provide ranges, not single‑point estimates, to keep expectations realistic.
Remember
Adiabatic air-to-air solutions unlock compressor‑free or compressor‑light cooling for many hours each year.
IEC suits offices, data halls, and processes needing dry supply air; DEC fits tolerant, high‑ventilation spaces.
Water and hygiene are design‑critical—meter, monitor, and maintain to standards.
Smart, enthalpy‑based controls maximize savings and minimize water.
Retrofits on condensers/dry coolers often yield the fastest, low‑risk paybacks.
Ready to explore a feasibility study or pilot? Start the conversation at score-grp.com.
