Customized Air Conditioning: Is It Really Efficient?

Feb. 19, 2016

How GSA reduced hot and cold complaints by 59%.

Saving energy and maximizing thermal comfort – achieving both of these goals at once seems impossible. However, a potential solution – socially driven HVAC optimization – has emerged. This user-based control system earned rave reviews from occupants in a recent test, with 83% claiming greater thermal satisfaction. Meanwhile, the facility saved roughly 20% on cooling costs.

How It Works

Rather than relying on a thermostat, socially driven HVAC optimization uses software on each occupant’s computer or handheld device to determine whether the user is too hot, too cold or comfortable. The feedback is sent to the building automation system, which triggers a large flow of conditioned air into the space to provide instant relief. After a short period, the airflow and temperature revert to an energy-saving mode while waiting for more feedback.

Over time, the system analyzes feedback trends to determine how best to keep occupants comfortable while saving energy. It also learns how to relax temperature setpoints in unoccupied spaces.

The technology is designed for variable air volume (VAV) systems that are controlled by digital energy management tools, though it can also be paired with other types of HVAC.

Successes and Hurdles

The socially driven HVAC technology was installed in the Federal Building and U.S. Courthouse in Phoenix in March 2014. The eight-floor facility is home to about 350 occupants and covers 289,000 square feet. Like about 50% of GSA’s portfolio, this building has a VAV system controlled by digital energy management. It also features a wide variety of tenant spaces to help evaluate the technology’s usefulness thoroughly, as well as a robust BAS system. Occupant surveys before installation and five months after deployment were used to determine comfort.

Over the summer, the system noted an average rise of 2 degrees F., from 75 to 77. This helped save energy during the cooling season while maintaining comfort.
Because the solution is subscription-based, a typical payback calculation doesn’t apply, GSA notes. Instead, the report compares the annual energy cost savings and square footage to the subscription cost to determine a “break even” threshold at which the technology pays for itself. The vendor provided a subscription range of 12-60 cents per square foot per year depending on the size, complexity and duration of the service.

GSA calculates the break even point of the subscription cost for large office buildings at roughly 9-16 cents per square foot depending on the climate zone. The Phoenix courthouse would likely save an estimated $6,700 in energy costs annually if the technology was used all year, GSA finds – a significant savings, but not enough to justify the annual subscription costs for this facility. However, the cost savings doesn’t include the decreased use of personal space heaters and fans. Staff described the value vs. energy cost as “a night and day difference.” The building was already meeting its energy requirements before the installation, but the technology could be a useful tool in a suite of energy savings programs, GSA says.

 “The socially driven HVAC technology should be considered for facilities where thermal comfort is a priority,” GSA notes in the report, stating that the technology’s economic viability is unclear. “It will be most effective in facilities with high energy costs, narrow deadbands (the range in which neither heating nor cooling is turned on), and a significant portion of space that is only intermittently occupied.”

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