Six years ago, Phoenix lay burning in the sun one day. It was 110 degrees Fahrenheit and I was the only person foolish enough to be out walking instead of moving by air-conditioned car. Arriving hot and parched at a bookstore, I opened the doors to be greeted by a blast of arctic air.
The coffee shop in which I sat down felt like it was freezing. Other customers, dressed in light summer wear for Phoenix summers, were shivering. We all chatted about how cold it was, so I went over to the coffee shop manager to see if the thermostat could be changed. He agreed wholeheartedly it was entirely too cold but reported that the temperature was decided and controlled not by the branch, but at the national headquarters.
As many people know, this is an extreme example of a common experience. Americans often find themselves in a store or office that’s too cold in summer or too hot in winter.
Obviously one can’t find a temperature that will please everyone all the time, but if lots of people are dissatisfied, this is a double dose of nonsense: Energy being wasted to make people uncomfortable. This led to the questions that would guide my research: What are the thermostat settings in commercial buildings and why are they set there? How much energy is wasted in making people uncomfortable?
In the end, I was surprised at how big the impact of poor thermal management in buildings is on our country’s energy consumption.
Making progress on my research questions went on hold until I was situated in a less extreme environment than Phoenix – Rochester, New York – when I started working with Ph.D. candidate Lourdes Gutierrez, who quickly uncovered many interesting things. One is that 42 percent of workers report being dissatisfied with the temperature in their offices, with 14 percent being very dissatisfied. Thus, there is a widespread problem with thermal comfort. Curiously, there is much less information available as to what thermostat settings are and how they are decided.
Lourdes also realized thermostat settings should vary by season and location. An office worker in Minnesota, for example, will wear heavier clothes in winter than one in Florida, so the thermostat in Minnesota can be set at a lower temperature.
We went on to analyze the national potential for energy savings from changing thermostat settings, by bumping them up in summer and down in winter by an amount appropriate for the local climate.
The first step was to figure out what winter and summer thermostat settings would ensure comfort for least 80 percent of occupants in 14 different U.S. cities. Eighty percent satisfaction is a typical compromise used by experts in thermal comfort. One result of our analysis was that in winter the thermostat could be safely set at 68F (20 degrees Celsius) in Minneapolis, while in Miami 72F (22C) is a better choice, since Miami-ites will be dressed lighter.
Next, we used energy simulation models to calculate the change in energy use with these new thermostat settings, compared with the typical year-round setting of 70F (21C). Not all buildings are set year-round at 70F, but it is considered a typical figure. There are many types of commercial buildings; we decided to focus on office buildings and restaurants as important, but tractable, types.
Our results, recently published in “Sustainable Cities and Society,” showed that the new thermostat settings could reduce 2.5 percent of energy use in U.S. office buildings and restaurants. National savings on utility bills would total US$600 million.
If other types of commercial buildings such as hotels and stores get similar savings as offices and restaurants, revised thermostat settings would reduce national carbon emissions by 0.3 percent. These saved carbon emissions are equivalent to the carbon pollution generated by four million automobiles in a year. This isn’t going to save the world from climate change, but it is a heck of a lot of carbon to be reduced while saving money and making people more comfortable.
Better data and monitoring
Where to go from here? We don’t claim to have the final answer on what thermostat settings should be and how much energy could be saved, as it’s a complicated question and will vary by building.
But we do argue these results highlight the need to rethink thermostat settings in offices, stores, restaurants and other commercial buildings. Managers should investigate what thermostat settings will make their customers and employees comfortable, considering the local climate. Dress code also plays a role: The closer employee clothing fits the outdoor environment, the more energy can be saved from moving thermostat settings closer to ambient.
There are a number of other obvious steps for improving the comfort of people in buildings, while using less energy. Energy auditors can advise building managers as to how much they could save with different thermostat settings. Governments can be more active in collecting data on indoor temperatures and thermostat settings in commercial buildings. And to all you building occupants out there: If you find your office, store or restaurant too cold in summer or warm in winter, let management know about it.
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