Excessive AC is a Hot Topic in the U.S.

A recent New York Times article, “Enduring Summer’s Deep Freeze,” described a scenario we’re unfortunately all to familiar with in the summer: over-air-conditioned buildings. While a blast of cold air may provide welcomed relief from a triple-digit-temperature day as you walk into a convenience store, many office workers can attest that sitting in an over-air-conditioned space for long periods of time is less than comfortable (and can lead to decreased productivity and morale).

There is a fine line between a brief, refreshing, cool blast of air and prolonged exposure leaving individuals chilled enough to resort to individual space heaters or blankets in summer just to warm up. Bloomingdale’s has even started advertising “summer cashmere”—oxymoron that it is—to those of us who suffer from excessively cooled indoor environments: “from overactive ACs to seaside breeze, we’re really feeling our ultra-cozy cashmere.” This “blast the AC” strategy is rampant in the U.S. and has become part of our office and commercial culture. A recent Washington Post article highlights the excess of our cooling compared to the rest of the world: “While indoors, Europeans wear sweaters in winter, while American wear sweaters in summer.”

Let’s not diminish the importance of being comfortable, however, but rather simply discredit the concept of excessive air conditioning as the best mechanism to achieve comfort. In fact, multiple studies have proven that providing some cooling increases working productivity and happiness.


Not surprisingly, there is a mountain of research around air conditioning and the health, comfort, and well being of building occupants. People have a comfort range in which they maximize their productivity simply through the absence of discomfort (such as sweating or shivering). Also, at a building or societal level, the term comfort is used to describe the average levels for individuals. A recent article in Energy Manager Today points out that even industry organizations such as ASHRAE use an average of more than 1,000 subjects to create their thermal comfort standard.

As summer temperatures reach their highest points, the idea of dictating comfort as an “average” becomes increasingly polarizing, particularly between men and women. For example, how often have you seen two colleagues occupying the same workspace with the same temperature and one has a space heater under their desk? Ultimately, it is an individual’s personal comfort that is actually important, not the thermostat’s setting on the wall. As anyone working in an office can tell you, what is considered comfortable varies greatly from person to person.


The U.S. building industry needs to break the incumbent standard of relying on energy-inefficient centralized heating and cooling systems to meet everyone’s comfort needs. Ironically, with our currently fossil-fueled grid, we are actually warming the planet by making our buildings cooler due to the 100 million tons of carbon dioxide the U.S. releases each year because of our obsession with cool indoor environments. In fact, air conditioners are so pervasive in the U.S that AC units consume about five percent of all the electricity nationally produced.

We should instead follow the logic behind the 80-20 rule by using central systems to get a building’s comfort “most of the way” generally and utilize individual heating and cooling controls to meet everyone’s comfort needs specifically. This approach allows comfort to be personalized to each occupant while saving energy by not over-conditioning a space. RMI will showcase this thermal comfort approach in our under-construction Innovation Center—a 15,610-square-foot office in Basalt, Colo.—with a pioneering approach to thermal comfort.


Set points commonly range from 70 to 76 degrees F in commercial buildings, but the Innovation Center will have an expanded range spanning 64 to 82 degrees F. Those six extra degrees on the high side, while seemingly insignificant, provide tremendous opportunities to save energy by avoiding excessive AC.

Just looking at these temperatures, people’s gut reactions are that they will be uncomfortable. However, temperature is just one factor controlling your comfort. Think of how much cooler you feel when the humidity is low or a fan blows on you. The absolute temperature may be high, but you can still perceive the temperature to be cooler. Six factors ultimately determine how humans feel in a space, and how our staff will specifically feel comfortable in the new office:

  1. Air velocity using ceiling fans and personal fans
  2. Air temperature through natural ventilation
  3. Surface temperature from cooling thermal mass in the floors and wall overnight
  4. Occupants’ activity level designing the space to be comfortable for all of the possible activities
  5. Humidity taking advantage of Colorado semi-arid climate
  6. Occupants’ clothing level encouraging occupants to dress comfortably

Conditioning people to feel comfortable through these variables proves far more efficient than conditioning the space those people occupy.


With this mentality, and through integrated design, our design team entirely eliminated a centralized cooling system from the new building. While focusing on all six variables is not seen in most buildings, it is actually based off an established approach using ASHRAE 55, a professional standard for thermal environment conditions focused on human occupancy. However, many owners and contractors perceive additional risk implementing this approach due to an over-simplified gut instinct after looking at the temperature ranges. Therefore, it is crucial to engage everyone from the occupants to designers and contractors up front so they understand and are comfortable looking at all six variables.

Chris McClurg, a senior associate at Rocky Mountain Institute who coordinated the thermal comfort strategy at the Innovation Center, believes this is the approach buildings will take in the future. She says: “Once the team is able to step away from the standard rules of thumb and gut checks by openly discussing the risks and benefits of this approach, they can focus on providing enhanced personal comfort where energy savings are almost a secondary benefit.”


The Innovation Center will employ several personal comfort technologies, including a cutting-edge personal heating and cooling chair (imagine having an adjustable heated car seat as your own personal desk chair, but one that has fans to cool too!), which help eliminate mechanical systems. For example, a super-efficiency ceiling fan can provide the same cooling effect as an air conditioning system but at the fraction of the cost or energy. But why fan an entire area when you can provide air movement directly to an individual through personal fan? A room doesn’t need to be comfortable—people need to feel comfortable.

RMI will also utilize personal USB-powered fans to regulate airspeed directly to individuals, another important factor in warm weather. Accessories like radiant underfoot pads or heated mouse pads also help in the coldest weather. We’ll also encourage low-tech comfort solutions, such as inviting everyone, from staff to visitors, to dress seasonally appropriately and rely on old-fashioned common sense—and just plain fashion. There is no question that a critical mechanism to widely implement a “seasonal dress policy” is a national cultural a shift in business dress codes.


In the new building, the only mechanical systems are for ventilation and localized backup heating equivalent to roughly 13 hairdryers. By accounting for all the thermal comfort variables, the building’s mechanical room was reduced by 200 square feet, compared to traditional buildings, because of the lack of additional equipment.

This is all made possible through passive, integrative design. The building is a passive, climatically responsive showcase for cold regions, highlighting proper orientation, a highly insulative envelope, exceptional daylighting, solar gain and shading strategies, natural ventilation, thermal mass, and nighttime flush.

With a predicted energy use intensity of just 17 kBtu per square foot, the Innovation Center will be the most-efficient building in the coldest climate zone in the U.S. (including solar PV, the building will be net zero, producing as much or more energy than it uses annually).


The Innovation Center will immediately be put to the test, opening this winter where average temperatures in Basalt range from 6 to 33 degrees F in the month of December. A crucial first step will be to train staff members on ways that occupant behavior will make or break our ambitious performance goals.  And sure, the Innovation Center is being built in the Colorado Rockies at 7,000 feet elevation (ASHRAE Climate Zone 7), where heating is the primary concern rather than cooling. It doesn’t get as hot as a sweltering summer day in Dallas or Phoenix, but the same thermal comfort strategy principles apply for both heating and cooling.

The Innovation Center managed to eliminate our cooling system; other high-performance buildings in different climates have similarly eliminated their heating systems. While this is a small achievement, it is invaluable to achieve high performance or net-zero energy building statutes, both of which are rapidly-growing classifications. And most importantly, by providing the means for each occupant to be comfortable year round, employees and visitors of the Innovation Center will be healthier, happier, and more productive.

So if you do find yourself swinging through Aspen’s Roaring Fork Valley next summer, and you’re looking for a respite from a hot, sunny day in Colorado’s mountains, stop by and visit our new Innovation Center. Our comfortable staff will welcome you…