Fall. Water Cooling Tower. PR Team Patrick Doyle, Patrick Moss, Raven Snyder ENGR 4350

Transcription

1 Fall 2013 Water Cooling Tower PR Team Patrick Doyle, Patrick Moss, Raven Snyder ENGR 4350

2 2 Letter of Transmittal To the Unit Operations for Chemical Engineers Laboratory, In the month of august group PR and one junior team began to investigate two types cooling methods used by some of the University of Tennessee at Chattanooga campus buildings. The locations selected for the testing were the Administrative building and Challenger Center. The report will cover all the aspects that took place prior to testing, data collection, results, and conclusions made during the first half of the semester. Sincerely, Group PR

3 3 Contents Letter of Transmittal.2 Introduction 4 Theory.4 Equipment...7 Procedure. 8 Data.. 9 Data Analysis.. 10 Conclusion Recommendations. References... Appendix

4 4 Introduction The objective for the group was to find which method of cooling used by the Administrative building and the Challenger Center is more energy efficient. The method of cooling used by the Administrative building it the use of a water cooling tower which located in the back of the building. The tower was operational so accurate measurement were taken. The Challenger Center uses the Trane Series R unit, which is a water cooled unit, and with the use of compressors, heat exchangers, and fans heat can be removed from the system to cool the building. By using the additional help of the junior team multiple attempts were made for data collection of each particular unit. Theory Cooling systems are used as a source of cooling for large areas of space with the intention of using as little amount of energy as possible. The Cooling Tower works by using water delivered from the building which contained a type of refrigerant. The water is used to cool the refrigerant, which in turn cools the building. The system pumps water to the top of the tower and is then allowed to freely fall inside the system. With the use of fans and honeycombed shaped grates, the air is driven upward out of the system and thus helping the water to change to vapor and exit the system with the feeling of moist air. Figure 1. Water Cooling Tower Diagram

5 5 By using the energy balance on the system you will be able to find the enthalpy of the air exiting the system. ¹º», º»» º ¹º», º»» ¹º», ºº º¹º», ºº ¹¹º»¹» ¹¹º»¹ Where Q= heat removed M=mass flow rate H=enthalpy The mass flow rate (M) can be derived from using the following: º º»¹»¹ M=mass flow rate H=enthalpy P=density V=volumetric flow rate Vavg.= average velocity of the fan entering/exiting system A= cross sectional area of the cooling tower fan Once all of these have been calculated the use of a psychometric chart will aid in calculating enthalpy (h)

6 Figure 2. Psychrometric Chart 6

7 7 Equipment The instruments used for the data collection were found in lab and are as follows: Anemometer -The anemometer was used to take the velocity of the fans exiting and entering the cooling tower. Data Logger-The multi functions of the data logger helped keep excellent track of the data collection at all times. The logger functions by connecting to the computer, and then setting the correct parameters prior to testing. Some of the functions used for the device were to store: the date, time, relative humidity, temperature, and dew points. Tape Measure -the tape measure was used to take the radius and the height of the fan Stopwatch -the stopwatch was used for timed intervals for the data logger and for the velocity of the air with the anemometer. Lab notebook-most essential tool for all activity s preformed inside the lab. Will be used to reference back to data and notes about projects

8 8 Procedure 1. Collect all equipment from lab 2. Insert data loggers into USB port and calibrate the device 3. Walk to the administrative building and locate the water cooling tower 4. Take measurements of the fan diameter and the height using the tape measure. 5. Use the anemometer and the stopwatch to calculate the air velocity of all the exiting and exiting the tower 6. Press activation button on the data logger and begin data collection on the exiting air of the tower. Use the stopwatch to time out five minutes and record the exact time of day the five minutes had taken place. 7. Repeat step 6 only now collecting the data on the air entering the system. Make sure to record the exact time of day. 8. Return to the lab and insert the data loggers back into the USB port and download the recent activity collected. 9. Using the times recorded in your lab notebook, match the times up with the data logger and save into excel format.

9 9 Data All data not found in the Data section may be found in the Appendix. Table 1: Admin Building Cooling Tower Air Enthalpy Data Table 2: Challenger Center Air Enthalpy Data

10 10 Data Analysis The data in found in Table 1 of the Data Section was initially calculated in kj/kg. When discussing air conditioning energy, BTU/lb are the appropriate English unit of measurement. Thus the data was then converted to units of BTU/lb. Once the units were in BTU/lb, proper data analysis can proceed. It is desired to know the energy loss of the administrative cooling tower per season (weather season). This process was done by first calculating the cross sectional area of the cylinder housing the fan on top of the cooling tower. This was found by using the following equation: Cross sectional area πr π 85.5in in 14.8 m Next the molecular weight of air was referenced, 28.8 g/mol or lb/mol, in order to cancel out the pounds from the enthalpy data provided in Table 1. BTU BTU tº lb mol BTU lb lb BTU mol BASIS BTU mol mol Given that the enthalpy has been converted to BTU energy units only (using a 1 mol basis), it is now possible to find the amount of BTUs per season are required for the administrative building air conditioner cooling tower. The velocity of the air coming out cooling tower fan was found to be 21.2 ft/s or 6.46 m/s. Given that the height of the tower was found to be 125 meters, it is now possible to find the BTU/season. Below shows how this is executed: BTU season BTU 14.8 m 1.25 m m s s hr 1000 hr BTU/season season

11 11 Conclusion The water cooling tower at the Administration Building is uses less energy while running than the cooling tower at the Challenger Center. While this is true, the Challenger Centers cooling tower cools air much quicker than the Admin Building. The Admin Building and the Challenger Center are approached the same way when calculating the energy balances. As stated earlier, the Challenger Center cooling tower is not as energy efficient as the Admin Building cooling tower. The Admin Building can however, cool more air faster due to the higher volumetric flow rate. When doing the energy balance, it was determined that the Admin Building water cooling tower operates at /»¹¹»ºº. The Challenger Center cooling tower operates at Recommendations The results obtained are as accurate as possible with the given equipment. If more accurate equipment were available, the results would be more precise. The measured data is extremely important in this experiment due to the fact that all of our results and calculations revolve around this initial data collection. If digital equipment gave us data from the actual piping and flow rates were given, the results would be much more precise.

12 12 References Boles, M. A. and Y. A. Gengel, Thermodynamics, Engineering Approach, 2 nd ed., McGraw Hill Book Company, St. Louis, MO, 1994, p

13 Appendix 13