COOL AT THE TOP - ECS CASE STUDY 2007
 
     
 

 

 

 

Summary

Our hypothesis that the wind speed at the top of the circular stairway in the Knight Library exceeds the ASHRAE standard of 40 fpm was confirmed. The air speed is noticeably stronger especially as you reach the vestibule on the third floor. While the airspeed always exceeds the ASHRAE standard, it is not at a consistent strength. From our data we are unable to find any correlations that would help us explain this phenomenon.

Consequently, we turned to Don Neets, one of the two facilities managers for the University of Oregon’s campus, for further explanation and to ease our curious minds. Don was impressed with our findings and felt he knew right away a possible explanation. He feels the system, AHU-6, located on the North side of the building is the most likely culprit and probably contributes greatly to the wind speed of the stairway. The exhaust fans of AHU-6 are never able to run at full capacity because they are located directly below reading room 101 and are extremely loud.  Therefore, the Knight library is always over pressurized.  This is because AHU-6 takes in more outside air than it can get rid of. The exhaust fan cannot run higher than 15% of the capacity even though they sometimes run the intake as high as 100%.  This air needs to go somewhere and in turn moves from a higher pressure to a lower pressure. Don believes that if we were to test the air circulation in the two main hallways that run past the check out counter on the main floor, we would also find air movement.

The circular stair is the only connection that links all four floors of the library besides the elevator shafts, but these are usually closed.  Therefore, the air movement we are seeing is being caused by a stack effect of all the extra pressure moving up through the stairwell.  The compression at the vestibule causes a larger velocity because the opening is the smallest the air encounters.

Don was quick to explain that this is just one reason why it is important not to cut the budget for the mechanical system.  Don explained that the North side of the building was the final stage in the Knight Library renovation. After three previous stages, the budget was getting tight and AHU-6 was put in, in order to save money.  This is why the fan system is so loud - it is a much cheaper system than what is found in the rest of the building.  The other interesting tidbit Don shared about AHU-6, was that another corner was cut in order to save money on duct work by not having a fully ducted system.  This would be a topic for further study because the effect of cutting this corner allows for a ten degree temperature difference in the air, from when air is taken in until it reaches the building.  This ten degree change is enough to make it so they can no longer use the outside air to cool the building. Instead, they must use a chiller to cool the air back down to what it was originally coming in at.  This causes an enormous waste of energy and money.