The Unseen Energy Drain: How Humidity, Not Just Heat, is Overburdening Our Air Conditioners

By Green Matters Staff

The hum of an air conditioner is a familiar soundtrack to sweltering summer days. For most, the primary function of this ubiquitous technology is to combat rising temperatures. However, according to engineer Jagan Pillai, the 2026 International Energy Innovator of the Year, the true energy adversary in our quest for cool comfort isn’t the mercury on the thermometer, but the invisible moisture in the air: humidity. This often-overlooked factor, Pillai argues, is responsible for a significant, yet surprisingly wasteful, portion of the energy consumed by our cooling systems.

The "Feels Like" Factor: Understanding Humidity’s Impact

On a sticky summer afternoon, a glance at a weather app reveals two critical numbers: the actual temperature and the "feels like" temperature. The disparity between these figures is a direct manifestation of humidity at work. Our bodies possess an innate cooling mechanism: sweating. As perspiration evaporates from our skin, it carries away heat, thus lowering our body temperature. However, when the atmosphere is already saturated with moisture, this evaporation process is significantly hampered. Sweat lingers, and the body’s natural cooling system becomes less effective, leading to that pervasive feeling of being hot and sticky, even if the thermometer doesn’t reflect extreme heat. A 90-degree Fahrenheit day in a humid climate can thus feel considerably hotter, sometimes exceeding 100 degrees Fahrenheit.

This same phenomenon, Pillai explains, is the hidden culprit behind the immense energy demands of air conditioning. "Most people think an air conditioner’s job is to make air cold," Pillai states. "In a humid city, a huge part of its job is making air dry, and the way we do that is surprisingly wasteful." His assertion is backed by scientific evidence. A 2018 study published in Scientific Reports indicated that moisture removal accounts for approximately 30 percent of the total air-conditioning cooling load, a figure that escalates considerably in tropical and subtropical regions.

The Overcooling Conundrum: A Paradox of Comfort

The fundamental principle at play is the dew point – the temperature at which air becomes saturated with water vapor and condensation begins to occur. Air has a finite capacity to hold moisture. As air is cooled, its ability to retain water vapor diminishes. When it reaches its dew point, any excess moisture transforms from a gaseous state into liquid water. This is why dew forms on grass during cool summer mornings, and why a chilled glass of water "sweats" on a humid day.

"Nearly every conventional air conditioner, from a window unit to the giant chiller plants that cool office towers, dries air the same way: it chills the air below its dew point so the moisture condenses out and drains away," Pillai elaborates. This method, while effective for dehumidification, necessitates cooling the air to temperatures far below what is comfortable for occupants. In many large buildings, this problem is compounded by a subsequent step: reheating the overly cooled air to a more palatable temperature before it enters the occupied spaces.

This practice of overcooling carries a significant energy penalty. Research from the Lawrence Berkeley National Laboratory has demonstrated that even a modest increase in the chilled-water supply temperature can lead to substantial improvements in operational efficiency. Specifically, raising the chilled-water supply temperature by one degree Fahrenheit can enhance the efficiency of centrifugal chillers by approximately 1 to 2 percent. For instance, supplying water at 55°F instead of 40°F could boost a chiller’s efficiency by an impressive 15 to 30 percent, depending on operating conditions and the system’s ability to still meet cooling and humidity demands.

The tangible, and often humorous, consequence of this overcooling is the sight of office workers bundled in sweaters during the peak of summer. A 2021 study in Scientific Reports highlighted that indoor temperatures in U.S. offices have frequently been found to be lower in summer than in winter. This phenomenon isn’t merely an inconvenience; it represents a substantial economic inefficiency. An earlier estimate from 2015 suggested that overcooling U.S. commercial buildings results in an annual waste of approximately $10 billion in electricity. "That sweater is a symptom," Pillai asserts. "In many buildings, the air is cold because the system had to make it cold to dry it. Comfort was never the goal. Humidity control was, and we paid for it twice."

A Decades-Long Pursuit: Decoupling Cooling and Dehumidification

Jagan Pillai, also recognized as a 2025 ACEEE Champion of Energy Efficiency in Industry, has dedicated nearly two decades of his career to addressing this fundamental flaw in conventional air conditioning systems. His central thesis is straightforward: "Temperature and humidity are different problems," he explains. "If you can remove moisture another way, you don’t have to overcool anything. You cool the air just enough to be comfortable."

One promising avenue for separating these two functions lies in the use of desiccants. These are materials, akin to the silica gel packets found in new shoe boxes, that have the inherent property of absorbing moisture directly from the air. In a desiccant-based system, the air is first dried, allowing the subsequent cooling equipment to operate at warmer, more efficient temperatures.

However, desiccant systems present their own challenges. Once a desiccant material becomes saturated with moisture, it requires a regeneration process – typically involving heat – to restore its absorptive capacity. Pillai’s innovative approach to this challenge involves harnessing waste heat that buildings are already expelling. By integrating desiccant dehumidification with heat recovery technologies, the energy required for regeneration can be significantly minimized, often utilizing otherwise discarded thermal energy.

Another hurdle for desiccant systems has been their evaluation against conventional metrics. Traditionally, their performance has been judged against a single, extreme "design day" scenario, representing the hottest and most humid conditions anticipated. During his tenure as Practice Leader for Energy and Analytics at the sustainability design firm Atelier Ten, Pillai pioneered a more holistic methodology. This approach analyzes a building’s performance across every hour of the year, rather than focusing solely on peak conditions. By understanding the building’s actual, moment-to-moment needs, dehumidification strategies can be dynamically adjusted for optimal efficiency.

This innovative methodology has been instrumental in the design of some of New York University’s most sustainable buildings. At the Center for Urban Science and Progress at 370 Jay Street in Brooklyn, Pillai’s analysis informed a design that integrated desiccant dehumidification, heat recovery, on-site power generation, and thermal energy storage. This multifaceted approach was designed to significantly reduce peak electricity demand. Atelier Ten reported that this project achieved LEED Platinum Core and Shell and LEED Gold Commercial Interiors certification, with an estimated 50 percent reduction in energy costs attributed to the combined strategies.

Similarly, at NYU’s John A. Paulson Center at 181 Mercer Street in Manhattan, a LEED Gold-certified building, the desiccant system is regenerated using waste heat from NYU’s campus cogeneration plant. Combined with other advanced systems such as displacement ventilation, decoupled systems, and enthalpy recovery, this strategy contributed to an impressive 46 percent reduction in energy costs, according to Atelier Ten.

The Urgency of the Humidity Crisis

The importance of Pillai’s work is amplified by current global climate trends. Heat waves are not only becoming more frequent and intense but also more humid. This intensifying humidity directly correlates with increased demand for air conditioning, placing unprecedented strain on power grids. "Efficiency used to be about the utility bill," Pillai observes. "Now it’s about whether the grid can keep up on the worst afternoon of the summer. Every kilowatt we don’t need at that moment matters."

Emerging material science offers further promise for scaling these advanced dehumidification techniques. Metal-organic frameworks (MOFs), for instance, are a class of highly porous crystalline materials with an exceptional capacity for capturing water vapor. A 2018 experimental study demonstrated the potential of coating heat exchangers with specific MOFs to remove moisture without overcooling the air. This system utilized residual condenser heat for regeneration, showcasing a pathway towards more efficient cooling and drying with potential for broader applications. While further development and real-world testing are necessary to confirm performance across diverse building environments, Pillai emphasizes that the ultimate test lies in a technology’s ability to perform reliably under the full spectrum of conditions a building experiences throughout an entire year.

What This Means for Your Home and Beyond

The principles Pillai champions are not confined to large commercial buildings; they have direct implications for residential comfort and energy consumption as well. An oversized air conditioner in a home, for example, can cool a room rapidly but shut off before adequately removing moisture. This results in a space that feels cold but clammy, prompting occupants to further lower the thermostat in an attempt to achieve comfort, thereby consuming more energy without a corresponding improvement in feel.

"Comfort isn’t just a number on the thermostat," Pillai reiterates. "Get the humidity right, and you can run warmer, use less energy, and actually feel better." As the demand for cooling continues to rise globally, Pillai’s focus on humidity as a central element in energy efficiency discussions is becoming increasingly critical. By decoupling the processes of moisture removal and temperature control, a viable path is emerging to reduce unnecessary cooling loads while simultaneously enhancing occupant comfort. The ultimate goal is pragmatic: to create buildings that are not only more energy-efficient but also provide a demonstrably better and more comfortable environment for the people within them.