(538d) Ranking Energy Efficiency of UAB Buildings and Quantitative Determination of Heat Transfer Reduction From Setback Schemes

As energy costs nationwide are increasing and the economy was knocked for a loop by the perfect financial storm of last fall, sales are down meaning less state revenue is generated from consumer spending. Facing a deficit, enormous pressure has been placed on UAB Facilities Management to find ways to reduce energy expenditure, and one key method is to reduce the amounts of resources that people within buildings use, including light, heat, and water. These measures also contribute less to global warming due to a reduction in coal burning. The Civil, Construction, and Environmental Engineering Department of UAB was contracted to perform occupancy surveys in a large number of buildings across campus in after-hours on weekdays, and on weekends. The goal of these surveys was to find out how efficiently building utilities were used, by counting the number of people occupying each room, and by noting whether lights have been left on if the room is unoccupied. Other ?low hanging fruit? such as incandescent lighting, vending machines, freely-running water, and other non-efficient energy usages was also noted. This data was used to make overall recommendations to Facilities Management and building deans of measures they can take in order to reduce energy costs. Academic buildings that do not have large amounts of literature, for example, can withstand a 7-hour setback of air conditioning and dehumidification systems from 10:00 p.m. to 5:00 a.m. on weeknights, and possibly longer on weekends (48 hours from 6:00 p.m. on Friday to 6:00 p.m. on Sunday, for example). As for lighting, usage of lights only when the room is occupied or when natural lighting is unavailable is a favorable change at the building dean's discretion, but more long-term measures include motion sensors and layered lighting systems, as well as restricting access to certain floors at certain times of day. These measures have achieved favorable results in buildings where they have been implemented.

The costs of operating each building at a large college campus like UAB include a number of key utilities, including electricity, water, and natural gas. Some are cyclical in nature depending on season, but most are steadily increasing. For one sample building, the Humanities building, the costs of each utility has been shown to increase by $14.22 per megawatt, increase by $0.76 per 100 cubic feet, and decrease by $0.08 per 100 cubic feet, respectively from 2006 to 2007. Global warming concerns today are increasing, and the main culprit is carbon dioxide, to the tune nearly 6 billion tons emitted by energy-related sources into the atmosphere each year (Energy Information Administration, 2008). Since coal combustion generated 57% of the electricity in Alabama in 2005 (Birmingham Newschart, 2007), and burning 12 kg of coal produces 44 kg of carbon dioxide, (Carnegie Mellon University, 2003), control of electricity usage is proven to reduce coal combustion, and thus decrease production of carbon dioxides which contribute greatly to global warming.

The goal of the study was to determine how efficient each building was in terms of energy use by its occupants. A total of 14 buildings were covered by this study. Each entire building that was surveyed in 2007 was surveyed roughly every two hours on weeknights from 6:15 p.m. to 12:15 p.m. and on weekends from 7:00 a.m. to 11:00 p.m. A little more freedom was granted with the buildings surveyed in 2008, so they were surveyed at varying times, roughly every two hours 5 p.m. to 9 or 11 p.m. on weeknights and every 2-3 hours 9 a.m. to 9 p.m. on weekends. As each room was surveyed, a symbol was recorded for that room for that nominal time: if the room was occupied, the number of occupants was recorded, and if not, the percentage of lights on in the room was estimated and recorded as follows: ?P? for 1-50%, and a zero with a slash through it (Ø) for 51-100%. The time period covered by each study is roughly 6 hours on weeknights and 16 hours on weekends (a total of 62 hours) for 2007 studies, and 4-6 hours on weeknights and 12 hours on weekends (a total of 44-54 hours) for 2008 studies, or that portion thereof in which the building was open (HUC, Sterne, Lister Hill), By taking the cost of the resources that were expended during the month of the study, prorating it for the actual after-hours time period covered by each study, and dividing it by the average number of occupants witnessed over all studies, an expenditure per member figure can be calculated. A comparison of this will determine which buildings are being used less efficiently during this period. In addition, a qualitative judgment can be made about what time each weeknight HVAC systems can be set back, which varies from building to building, based on at which point occupancy tapers off significantly. Finally, a comparison of the number of fully lit rooms against the number of rooms that could be surveyed should give an idea of what buildings have the worst problem with lights being left on when rooms are not in use.

From the survey data, as well as some utility bill data from the period of 2006 to 2008, three key parameters can be determined that each provide a crude measure of each building's relative energy efficiency. These criteria are: after-hours utility cost per occupant (CPO); percent of building fully lit in after-hours; and utility cost per gross square foot. Classroom buildings tended to be on the low range in CPO, due mainly to the fact that they have higher average after hours occupancy, while research-oriented buildings were occupied often by fewer than 5 people in after hours, and thus their CPOs tend to be upwards of $480; thus, they are far more expensive to operate in their benefits to each occupant. The percentage of the building that is fully lit in after-hours tends to randomly fluctuate between classroom and research rooms based on the bias of the researcher as to what constituted a fully lit room. The utility cost per GSF is just that, and is a parameter which does not rely on any survey's results. It follows that, like with CPO, it tends to favor libraries, administrative buildings, and classroom buildings, while research facilities perform poorly. However, that does not mean that there are no exceptions, as the Scrushy building, which is the second-best in terms of cost per gross square foot, is the worst in terms of after-hours CPO. All 11 buildings for which each parameter could be determined were ranked 1 to 11, and the buildings with the lowest scores can be termed ideal models for how buildings should operate, while the ones with the highest scores appear to need some work. Lister Hill Library is the only one with a score less than ten, and HUC, which was determined by the team to be ?an ideal model for how a building to operate? scored an 11. Five buildings had scores in the 20s: Ryals; UBOB; Hoehn; Scrushy; and Worrell. By this analysis, it appears these buildings could use some work in making them utility-efficient.

It turns out that in the literature of some earlier surveys by George A. Jackins from 1981, the overall heat transfer coefficient U, and the area A of the walls and roof was determined. As mentioned previously, by setting back the HVAC systems to minimum levels when the occupancy of the building tapers off, a certain amount of energy can be saved. An estimate of the amount of heating or air conditioning that is required to heat the room in each season can be determined quantitatively by taking an average of the temperatures at each hour of the 24-hour daily cycle, subtracting the room temperature (72°F), and inserting this as the temperature term in the overall heat-transfer equation Q=UADT, the heat transfer at every hour within the day in each season can be determined. Then, by replacing the room temperature with a setback temperature of 55°F in colder weather and 85°F in warmer weather when the building is unoccupied, a savings of heat transfer can be determined. For a 5-day work week, this is about 40% in extreme seasons but 67% in temperate ones, and in a 4-day week scenario, as has been proposed for UAB, these percentages increase to 45-50% and 75%, respectively.

References

1. Birmingham Newschart. (2007, April 15). State Leads Nuclear Comeback. The Birmingham News .

2. Carnegie Mellon University. (2003). Environmental Decision Making, Science, and Technology: Science Notes: Chemistry of Fossil Fuels. Retrieved August 3, 2008, from http://telstar.ote.cmu.edu/environ/m3/s3/09fossil.shtml

3. Energy Information Administration. (2008, May). Greenhouse Gases, Climate Change, and Energy. Retrieved August 3, 2008, from http://www.eia.doe.gov/bookshelf/brochures/greenhouse/Chapter1.htm