Indirect-direct evaporative cooling (IDEC) pairs two complementary processes to deliver colder supply air with much lower energy use than refrigerant systems. The first stage cools sensibly without adding moisture and the second completes cooling by controlled evaporation; together they exceed single-stage evaporative cooler limits while keeping humidity in check. This two-stage path is most effective in arid climates where fresh-air ventilation and energy efficiency are priorities.  

Indirect stage:

Sensible pre-cooling and no moisture gain. Primary outdoor supply air flows through the dry side of a heat exchanger while a separate wetted airstream evaporates on the wet side; heat transfers through the exchanger walls and the supply air cools along a constant-humidity line. Lowering dry-bulb temperature before the adiabatic step reduces the load on the direct stage and preserves the ability to control indoor humidity.

Direct stage:

Adiabatic final cooling toward the wet-bulb. Pre-cooled primary air passes through wetted media where evaporative cooling lowers its temperature toward the wet-bulb of the primary stream; a small amount of moisture is added but the net result is a colder, relatively drier supply than single-stage evaporative cooler. Designers use controls to blend hybrid DX when needed during the most humid hours, preserving capacity and indoor humidity limits.

“The future of cooling isn’t about working harder — it’s about cooling smarter. IDEC replaces compressor dependency with physics, delivering fresh air, lower temperatures, and dramatically lower energy consumption. ” Eng. Wali Khan

Energy and operating cost comparison

IDEC can operate around 0.22 kW/ton versus a DX refrigerant baseline near 1.0 kW/ton in dry conditions. That gap corresponds to roughly 60–83% energy savings versus DX depending on wet-bulb, staging and controls. When outdoor wet-bulb rises, IDEC capacity and effective EER decline; plan hybrid DX staging when sustained wet-bulbs exceed about 26°C (78°F). For guidance on understanding wet-bulb temperatures and how they affect cooling performance, consult resources that explain wet-bulb impacts on evaporative systems.

Use the formula, annual kWh saved = (kW/ton_DX − kW/ton_IDEC) × tons × annual hours to estimate site savings, then multiply by tariff to get annual cost saved.

Example: 500 tons, 3,000 hours/year, tariff $0.10/ kWh, DX = 1.0 kW/ton, IDEC = 0.22 kW/ton.
Savings: (1.00 − 0.22) × 500 = 390 kW; annual kWh saved = 390 × 3,000 = 1,170,000 kWh; annual cost saved = 1,170,000 × 0.10 = $117,000.

Build sensitivity tables for tariff, hours and wet-bulb to show realistic payback ranges for your project.

Water, maintenance and lifecycle costs

Water use is the primary trade-off for IDEC and should be modelled early in project planning. Expect measurable evaporation on the order of cubic meters per day for medium commercial installations; for example, a 100-kW cooling requirement running 12 hours may evaporate roughly 1–3 m3/day depending on wet-bulb and system effectiveness. Verify local water quality, supply reliability and treatment needs up front because poor make-up water shortens media life and increases maintenance. For an overview of commercial and industrial evaporative cooling considerations, industry resources can help size make-up and treatment systems.

Service tasks for IDEC focus on media replacement, sanitization and pump, valve and basin checks; typical pad replacement intervals are 1–3 years with monthly to quarterly mechanical inspections. By contrast, DX requires refrigeration-circuit servicing, leak detection and certified technician support, so spare-part costs and local skill availability often favor IDEC in markets where refrigeration expertise is scarce.

Energy cost typically dominates OPEX, so lifecycle economics frequently favors evaporative strategies.  Capital costs for IDEC are often similar or slightly lower than rooftop DX at scale, while ongoing O&M and energy savings drive paybacks commonly in the 2–4 year range under representative assumptions. Local tariffs, operating hours, humid-season hybridization and water treatment choices are the main variables that move that range.

Comfort, humidity and climate suitability

IDEC delivers 100% fresh, filtered outdoor air and lower energy use in suitable climates, with a modest increase in indoor relative humidity. The direct stage typically raises indoor RH by about 2–5 percentage points relative to the pre-cooled stream, and in dry climates that added moisture often improves 

perceived comfort by reducing eye and skin dryness. For spaces that are humidity-sensitive, designers should weigh the trade-off or provide hybrid DX for dehumidification during peak-humid periods.

Performance is strongest where outdoor wet-bulb remains low to moderate; as a rule of thumb, IDEC efficiency is highest below roughly 18–26°C (66–78°F) wet-bulb depending on unit design and staging.  Above that range capacity and effectiveness decline and a hybrid DX backup should be considered to manage latent loads. For humidity-sensitive manufacturing, high latent-load process spaces and tightly recirculated rooms that require low RH for product quality, DX dehumidification remains the reliable choice.

High-value IDEC targets include facilities that need large volumes of fresh air and can tolerate modest humidity: warehouses, light industrial plants, large open-plan retail, many commercial office floors and certain data halls designed with staged redundancy. For specific retail sector guidance see HVAC and IDEC Solutions for shopping malls and other Industries solutions. When specified for arid or semi-arid regions, IDEC using indirect cooling followed by the direct stage delivers lower supply temperatures with controlled moisture addition and predictable operating costs.

Case study: Windmason Arabia retrofit and measured savings

Project snapshot: a retrofit near Riyadh for a food-processing and light-manufacturing facility with a design cooling load of about 200 tons. The baseline plant used multiple DX rooftop units and AHUs; scope included a full IDEC retrofit and local training for operations staff. The measured results below follow the assumptions used to reproduce the math. The project used the IDEC Supercool, 2 Stage Indirect-Direct Evaporative Cooler platform as the packaged solution for the retrofit.

  1. Baseline power: 200 ton × 1.0 kW/ton = 200 kW. Annual energy = 200 kW × 3,500 h = 700,000 kWh.
  2. IDEC power: 200 ton × 0.22 kW/ton = 44 kW. Annual energy = 44 kW × 3,500 h = 154,000 kWh.
  3. Annual energy saved = 700,000 − 154,000 = 546,000 kWh.
  4. Percent reduction = 546,000 / 700,000 ≈ 78%.
  5. Annual cost saved = 546,000 kWh × SAR 0.18/kWh = SAR 98,280 per year.

Measured results matched expectations: annual kWh saved ≈ 546,000 kWh and annual savings ≈ SAR 98,280. Payback depends on CapEx and scope; using representative retrofit ranges (SAR 350,000–SAR 700,000 including equipment, installation, controls and water treatment) yields a simple payback between roughly 1 to 2 years. These economics become more attractive once lifecycle energy savings and lower O&M are included.

Quick decision checklist and next steps

Before committing to full design, run this seven-question screen to identify whether IDEC deserves deeper study. If four or more answers are affirmative, plan a pilot or staged retrofit to validate savings and comfort under real operating conditions.  

  1. Is your local design humidity and temperature profile favorable for evaporative cooling?

Check seasonal wet-bulb levels and long-term humidity trends to confirm suitability.

  1. Do you require significant fresh-air ventilation for indoor air quality?

IDEC supplies 100% outside air  which can simplify HVAC layouts where high ventilation rates are required.

  1. Are operating hours high enough to monetise lower energy consumption?

Longer runtime shortens simple payback and amplifies lifecycle savings.

  1. Is reliable make-up water and basic treatment available on site?

Water quality and supply reliability affect media life and ongoing maintenance costs.

  1. Are there humidity-sensitive processes or occupants indoors?

If so, a hybrid DX arrangement or spot dehumidification may be necessary to protect processes and comfort.

  1. Can you accept modest rises in relative humidity or add hybrid DX for peak periods?

Designers can sequence controls to limit humidity increases and bring in DX during the most humid hours.

  1. Do you prefer local manufacturing and turnkey delivery to speed commissioning? Windmason Arabia provides local manufacture and full-service delivery that shortens lead times and supports rapid commissioning.

Next technical steps: Run an hourly cooling-load profile, map humidity and enthalpy distributions, and model kW/ton scenarios for IDEC versus DX across peak and shoulder periods. Include a DEC comparison where relevant to benchmark simple evaporative options and design a hybrid DX fallback for the most humid hours so performance never degrades. A staged pilot or partial retrofit is recommended to capture measured performance before full rollout.

Windmason Arabia provides turnkey support, including site survey, local manufacture, AI-optimized controls and a 12-month measured performance guarantee to back the ROI.

Contact Windmason Arabia to request a complimentary site screening or an ROI model; Windmason engineering team will convert your checklist answers into a clear specification and next steps.

How does IDEC indirect direct evaporative cooling compared to traditional AC units: Final takeaways

IDEC can deliver the cooling you need while using a fraction of the electricity and supplying 100% fresh air. By separating sensible and adiabatic cooling, IDEC reaches lower supply temperatures without compressor work; in appropriate climates expect up to about 85% energy savings and significant peak- demand reductions for large facilities. 

The trade-offs are predictable: measurable water use, balanced against lower energy bills and simpler mechanicals. For an accessible overview of evaporative cooling vs air conditioning trade-offs, industry comparisons can help stakeholders decide. To quantify savings for your site and confirm alignment with Vision 2030 targets, schedule a site assessment and ROI comparison with Windmason Arabia’s engineering team or review IDEC a Sustainable Cooling Solution.