When your office’s overzealous air conditioner is creating a sub-arctic work environment, what measures will you take to keep warm? Will you go right to the thermostat, or do you put on a sweater, make some hot tea or perhaps even plug in a space heater? A Drexel engineer is looking at how these behaviors affect your thermal comfort and the office’s energy usage with the hope of informing future sustainable building design practices with you and your sweater in mind.
Jared Langevin, a doctoral student in the department of Civil, Architectural and Environmental Engineering, wants to know if you’re too hot or too cold in your office and what you do get comfortable. Langevin’s goal is to make a computer model for architects, engineers and building managers that accurately reflects how people adjust to their thermal environment on a daily basis.
Building a Better Model
Energy models predict the heating and cooling energy use per square foot as it relates to keeping a space at a pre-ordained “target temperature.” Architects and building engineers strive to incorporate design tactics such as better insulation, or natural lighting in hopes of maintaining the interior temperature of their buildings with minimal additional energy use for heating and cooling. Existing modeling software can simulate how these design factors will affect energy use, but their accuracy has often been a point of contention, as large discrepancies are sometimes seen between predicted and actual energy consumption outcomes. Langevin, who is part of the Building Science & Engineering Group at Drexel, contends that a significant part of the disparity could be due to a lack of consideration for the human factors that affect energy consumption.
“If some people are using heaters in the summer because they are so cold from the air-conditioning, might it be more efficient to use less air conditioning and provide desk fans – which use very little energy – for those who tend to be warmer, to ensure they are still comfortable? These are the sorts of basic questions that our model will help building managers and designers answer,” Langevin said.
To build and validate his model of office occupant behavior, Langevin collected occupant response data over the course of a yearlong study at the Friends Center, an office building in Center City Philadelphia that was recently renovated to give it a LEED Platinum rating –the best marks for sustainability that a building can receive from the U.S. Green Building Council.
For two weeks in each season, Langevin surveyed 24 people who work in the four-story, 58,000-square-foot building. Three times each day, the participants filled out a survey that asked questions about their comfort with the temperature of the office, their clothing and recent activities, and what -if anything- they did to adjust the thermal environment of their office.
At the same time, Langevin tracked data from multiple sensors he’d installed in each of the offices that recorded temperature, humidity, and air velocity, as well as the current states of fans or heaters (on or off) and nearby windows (open or closed).
“It’s important to establish the sequencing of ‘control actions,’” Langevin said. “If someone is cold, will they tend to put on a sweater first, or immediately turn up the thermostat?”
Oh, The Humanity!
While Langevin is still converting his findings into computer algorithms that will become part of energy modeling software, his initial analysis of the data has already yielded some surprising findings.
“In particular, we were a little surprised by the relatively infrequent adjustment of windows and thermostats in the building,” Langevin said. “While I think part of this is simply because the building is pretty well controlled and comfortable most of the time, we did see a very clear preference for more immediate and accessible adaptive actions, such as modifying clothing or turning on or off a fan and heater, during the course of the day.”
Langevin suspects that social pressures and niceties may also have something to do with this result.
“In addition to being convenient and effective, people reported that these actions rarely required asking anyone else’s permission, which seemed to make them more attractive. An exception to this finding is in the shared private offices, where people usually did have to ask their office mate before turning on a heater for example, perhaps because they felt the action would have a noticeable effect on the other person’s comfort.”
This is the sort of human behavior that can’t be accurately predicted or accounted for when designing or managing a building –at least not yet.
Langevin believes that the modeling program developed from his National Science Foundation-funded study could be used first as a tool by building managers to promote more efficient and effective operating strategies, and eventually could be used in the early stages of designing buildings for LEED certification. He will present the methods used to conduct the Friends Center study at the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ Indoor Air Quality conference in Vancouver this fall, and hopes to present key outcomes from the study and the behavior model as part of a green buildings tour of Friends Center at the National GreenBuild Conference in Philadelphia in November.