Turning Air Conditioner Condensate into a Sustainable Water Resource for Large Buildings

Original Authors: Amr Elbrashy, Kambiz Vafai, Abdullah Elshennawy, Manar Ayman, Ahmed Elgebaly, Maher Rashad

Original paper is accessible at: https://doi.org/10.1007/s11269-025-04203-9

This pioneering study explores a sustainable and underutilized water source: condensate water produced by air conditioners (ACs). Conducted at Horus University in New Damietta, Egypt, the research examines how 113 AC units across 3000 m² of campus infrastructure can generate thousands of liters of water daily — transforming what is typically wasted into a valuable environmental resource. The results demonstrate that condensate harvesting not only contributes to water security in arid climates but also offers a synergistic benefit with energy efficiency, making air conditioning systems dual-purpose devices for both cooling and water generation.

Key Highlights

• Quantified daily and seasonal condensate production from university AC networks.

• Analyzed the influence of climatic factors (temperature, humidity, dew point) on water yield.

• Assessed water quality against WHO standards for potential potable and non-potable uses.

• Evaluated economic feasibility and sustainability metrics for implementation in large institutions.

1. Introduction: Cooling Meets Water Harvesting

Air-water condensation — the process where moisture in the air transforms into liquid when cooled below its dew point — has long been observed but rarely optimized at scale. In regions like Egypt, where temperatures exceed 38 °C and humidity averages 70–75%, air conditioners continuously condense water as a byproduct of cooling indoor air.

The authors argue that this neglected resource can be harvested and reused for irrigation, cleaning, laboratory experiments, and — with proper treatment — drinking. A single AC unit can produce between 2 and 8 L of condensate daily, depending on operating hours and humidity conditions.

Their case study focuses on Horus University’s Faculty of Engineering, where a network of 113 split-type air conditioners was monitored for water yield, energy input, and feasibility of large-scale collection.

2. Methodology

Study Site and Climate

New Damietta City experiences a Mediterranean desert climate: hot, dry summers (up to 38 °C) and mild, humid winters (11–18 °C). Average summer relative humidity peaks at 75%, providing excellent conditions for condensation.

Building Setup

The university’s engineering complex includes 72 rooms with 113 AC units rated at 3–5 HP each, operating 7 hours daily. The system uses R-410A refrigerant and circulates 733 CFM of air per unit.

Human and Thermal Loads

Around 800 occupants contribute heat and moisture, creating an internal latent load of up to 120 kW. This increases humidity and, consequently, the condensation rate — especially during peak afternoon hours.

3. Mathematical and Economic Framework

The study develops psychrometric and thermodynamic models to quantify condensate generation.Key relationships include:

where:

• ωin​: indoor humidity ratio

• ωsup: supply air humidity ratio

The Economic Feasibility Quotient (EFQ) evaluates cost savings:

Findings show that condensate water is essentially free, since the AC units already operate for cooling; only collection and maintenance costs apply.

An Efficiency Quotient (EQ) compares actual to theoretical yield based on local psychrometric data, guiding design optimization.

4. Results and Discussion

4.1. Seasonal Water Yield

• March–May: Rising humidity increases daily condensate to ≈50 L per unit.

• June–August: Peak summer yields reach 51–56 L per unit per day, translating to ~6 m³/day for the entire building.

• September–November: Slight seasonal decline to 44–53 L/day, matching cooler temperatures.

Overall, annual production exceeds 1,500 m³, equivalent to the daily water needs of several households.

4.2. Influence of Indoor vs. Outdoor Conditions

• Indoor humidity: 64–74%

• Outdoor humidity: 53–61%

• Indoor dew point: 18–20 °C

• Outdoor dew point: 9–13 °C

The humidity gradient between indoor and outdoor air drives condensation efficiency. The dew point differential ensures constant moisture removal, even during fluctuating weather conditions.

4.3. Water Quality and Suitability

Condensate resembles distilled water but can accumulate minor contaminants (dust, metal ions, or microbes).A summary comparison with WHO standards shows:

Thus, the condensate is safe for non-potable applications and can be upgraded to potable through UV, carbon, or nanofiltration treatment.

5. Environmental and Economic Implications

Each liter of condensate reused offsets the demand for treated municipal water, helping institutions reduce costs and carbon footprint.For example:

• Daily yield: ~6 m³/day

• Potential annual saving: hundreds of dollars in water costs

• Payback period: typically < 1 year for collection infrastructure

By viewing condensate as a valuable byproduct rather than waste, the study bridges the gap between building energy systems and sustainable water management.

6. Outlook and Recommendations

Future development should focus on:

• Smart condensate networks that integrate multiple buildings for centralized storage.

• Solar-assisted sterilization and pH neutralization for low-cost treatment.

• IoT-based sensors to monitor water yield, quality, and system efficiency in real time.

This approach could transform urban campuses and corporate buildings into self-sustaining micro water plants, aligning with UN SDG 6 (Clean Water and Sanitation) and SDG 13 (Climate Action).

7. Conclusion

The study demonstrates that air conditioners, often criticized for high energy consumption, can simultaneously serve as micro water harvesters.At Horus University, 113 units produced nearly 6 m³ of water daily — enough to irrigate green spaces and support laboratory operations.

By scaling similar systems across educational, commercial, and residential buildings, we can recover thousands of cubic meters of clean water annually, advancing sustainability and climate resilience in water-scarce regions.