Montana State University

MSU chamber teaches engineering students how to design for comfort

February 21, 2012 -- By Evelyn Boswell, MSU News Service


Craig Rohwer twirls a sling psychrometer to take temperatures inside a chamber used by upper-level engineering students at MSU. (MSU photo by Kelly Gorham).    High-Res Available

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Tel: (406) 994-4571
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BOZEMAN - As the temperature neared 102 and humidity soared, three engineering students began to sweat in the name of science in an underground chamber at Montana State University.

"Welcome to the Deep South," said Craig Rohwer of Fairbanks, Alaska.

"This is what South Carolina felt like last summer," said Tanner Miller of Townsend.

Rohwer, Miller and Matt Oliver, of Missoula -- all MSU seniors in mechanical engineering technology - ran their shoes across the floor and felt the walls of MSU's psychrometric chamber to see if the surfaces were sticky yet. If they were, it would indicate that the air was saturated with moisture and life was growing increasingly uncomfortable in this 13-by-16-foot room in the basement of the EPS Building.

The exercise occurs every spring as part of Kevin Amende's Thermal Processes Lab, and it's designed to show upper-level students the importance of keeping people comfortable in their homes and offices and how it feels when they're not, said Amende, adjunct assistant professor in the Department of Mechanical and Industrial Engineering.

The exercise is also meant to familiarize students with the psychrometric chart, a tool used by anyone who goes into the heating, ventilation and air conditioning (HVAC) industry, Amende added.

Engineers who design a heating system, for example, record temperatures, humidity and air flow in a room, then mark those points on the psychrometric chart. If the intersection of those points falls inside the designated "comfort zone," the room's occupants are happy. If it lies outside the comfort zone, the engineers need to make some adjustments.

"Not everyone can be made completely comfortable by one set of conditions, but a fairly clear understanding of what is involved in providing comfort to most of the occupants in a controlled space has been developed," Amende tells his students.

Comfort level depends on the interaction of temperatures, moisture and air flow, Amende added.

On this particular day, Rohwer and Tanner each twirled a sling psychrometer to take the wet bulb and dry bulb readings inside the psychrometric chamber. A psychrometer looks like a short magic wand that's broken in the middle. The operator holds one end so the other end twirls. The dry bulb temperature is the air temperature without moisture. The wet bulb temperature indicates moisture in the air. Swinging the instruments creates air flow.

Cloth material, called a wet bulb sock, covers the end of the thermometer, Amende said. When air flows across the wet sock, it cools it down based on how much moisture is in the air.

"An easy way to think of this is to imagine wearing a wet swimsuit traveling across a lake (pretty cold even if it is 90 degrees outside)," Amende said. "If the swimsuit is dry, you don't feel nearly as cold."

"It's an HVAC party favor," Rohwer said of the spinning psychrometers.

At the same time, Oliver pointed an infrared thermometer at the chamber's floor, walls, ceiling, door and window. When Miller pulled over a chair, Oliver told him to be careful. The chair was 84 degrees.

"It's about to be 100," Miller said as he sat down.

Oliver passed along all the readings via walkie-talkie to fellow student Tadhg O'Rourke, who sat outside the chamber with doctoral student Chantz Denowh and adjunct instructor Adam Weisenstein.

Weisenstein used a computer to monitor and change conditions inside the chamber. He added steam at times. Other times, he added heat.

O'Rourke -- a senior in mechanical engineering technology from Swarthmore, Penn. - recorded Oliver's report every three minutes. In the process, he observed the relationship between temperatures and the saturation point, predicted when condensation would occur and finally felt he understood how condensation and saturation work.

"This lab really helped me clear that up," O'Rourke said.

Weisenstein said the psychrometrics exercise is popular with students. In fact, "I ask students every year what lab they gained the most from. This is usually No. 1 or No. 2 because they can physically see what's going on," he said.

Amende said the psychrometric chamber and the HVAC Lab that houses it also lead to some "pretty cool job opportunities" for undergraduate researchers who work in the lab. Amende currently employs five undergraduates and a doctoral student in the lab. Most of the time the psychrometric chamber is used to test HVAC equipment and conduct research projects related to the HVAC field. Some of those projects are related to AAON, an HVAC manufacturing company based in Tulsa, Okla., and founded by Winifred native and MSU alumnus Norm Asbjornson. A long-time supporter of small Montana schools and MSU, Asbjornson donated more than $600,000 in cash, equipment and technical advice to create the HVAC laboratory. AAON also gives research grants to the College of Engineering on a continuing basis.

"The Asbjornson Laboratory remains a truly unique and state-of-the-art facility in the world of HVAC design and research," said Robert Marley, dean of the College of Engineering. "As such, it provides a tremendous opportunity for our students to gain that valuable hands-on experience. Together with other opportunities in energy-related instruction and research at MSU, these students are in very high demand both nationally and internationally. "

Rohwer, Miller and Oliver left the psychrometric chamber after they finished relaying their readings to O'Rourke.

"That was a lot of fun, but I wouldn't want to do it again," said Rohwer, who is more used to the climate in Alaska than Georgia.

But before he left class for the day, Rohwer asked Amende if he might be able to use the chamber to conduct his senior capstone project on evaluating the insulation performance of windows. Rohwer said new windows typically carry a sticker that labels certain performance measures. His team wants to make a device that will measure and compare performances of any existing window.

The psychrometric lab will help because it contains a small port between two chambers, Rohwer said. He wants to simulate a typical indoor environment in one chamber and a cool evening in the other. That will allow his capstone team to calibrate their equipment against a window with known performance values.

Hopefully, they will then be able to test any window with reasonable accuracy.

"That window from the 1950s may be costing you hundreds of dollars a year in heating or cooling losses," Rohwer said. "This system could quantify that, and see if replacing the window is cost effective."

Evelyn Boswell, (406) 994-5135 or evelynb@montana.edu