(32f) Energy Conservation Approach to Cooling Process By Employing Preheat Tank and Chilled Water Tanks

Energy conservation has been a hot topic worldwide. With the rapid growth of population and urbanization, the energy demand is increasing annually. According to the 2005 Annual Energy Review compiled by the Energy Information Administration (EIA) within the U.S. Department of Energy (DOE), the energy consumption in the United States including transportation, residential, and commercial end uses, shows a trend of increasing during the period of 1970 to 2005. Over the years from 1970 to 2004, total commercial end uses have an annual growth rate of 2.6 percent, and electricity consumption accounts for 76.2% of total commercial energy consumption. The HVAC system is an important process to provide comfortable temperatures, but demanding a large amount of energy and mainly contributing to the peak electricity consumption. The chilled water tank is a technology that can dramatically reduce the peak energy consumption with installation in traditional air conditioning systems, especially for the hot and humid climates. The preheat tank is a device used for heat recovery purposes that absorbs the heat from air flows to decrease the air temperature entering the chilled water tank and enhance the performance of cooling with even less energy requirements.

Our research utilizes the preheat tank and chilled water tank in commercial and conventional air conditioning systems to achieve energy conservation opportunities in Birmingham, Alabama. The preheat tank was installed to exchange heat with hot air, and the heated water can be used for lavatory and other purposes. The chilled water tank was set up to provide cooling with less energy consumption. The Generalized Fluid System Simulation Program (GFSSP) software was utilized to analyze the air conditioning system involving the heat recovery tank and chilled water tank. In addition, experiments were conducted in a small building at the University of Alabama at Birmingham campus with an installed small preheat tank and chilled water tank, respectively, to provide data needed for software programming. The energy consumption of the modified HVAC system was monitored to check the energy conservation rate. Some factors that may affect the performance of the modified system, include ambient temperature, humidity, water temperature in the tank, air conditioning set temperature, and dew point. The variables were recorded and analyzed in regression models to determine which factor(s) are significant for energy conservation. Moreover, covariance analysis was performed to determine the relationship between these factors. The results are expected to provide energy conservation for air conditioning systems, especially during the peak hours of energy consumption in hot and humid summer climates which is the typical weather condition in Birmingham, Alabama. Finally, the payback period was estimated by comparing energy bill savings and capital investment. The research can be extended to other southern states that experience hot and humid climates, such as Texas, Arizona, Georgia, and Florida.