ENVS 102 Lab Term Project Jim Harrell

Transcription

1 ENVS 2 Lab Term Project Jim Harrell The project for this semester was to investigate the potential of solar energy to heat water effectively with the intent to use this heated water for every day uses. This water could be used for washing things such as clothes, utensils, bathing or possibly a hot tub. With this hot tub as an example, we attempted to build a tank of water and then heat the water by creating a thermal syphon. By experimenting with different factors in design, such as size, volume of water or insulation, we could test the effects these had on water temperatures. A passive solar water heater is a heating system without the use of an electrical pump to create a flow of water. It consists of a tank of water with a re-entry and exit port. The water leaves the exit port where it flows through a plastic tube into a solar heat collecting plate. This plate is made from copper pipe sandwiched between metal sheets that is placed in a thin wooden box painted black and enclosed with a sheet of plexiglass. The sun shines through the plexiglass and hits the black plate and heats the water in the tubes by conduction (contact with the heated metal). The plexiglass traps the heat inside of the box. As the water heats, it passes through the tubes and flows back to the tank by convection. When molecules are heated, they rise. This is convection. Here the heated water rises from the tubes in the plate back through a re-entry port into the tank which is placed on a surface higher than the thermal solar collector plate therefore creating the thermal syphon. In our project, we drilled holes in our tank for re-entry ports. These holes started from the bottom of the tank and went straight up the side of the tank, spaced approximately every 3-4 inches. Each 3-4 inches of height equaled the volume of 1 liter of water. Each week, the re-entry hose was attached to a different port starting from the bottom and ending at the top port. The tank was designed to have temperature probes installed to the other 4 re-entry ports to monitor the changes of temperature at each level and register that data on a computer every minutes for the week-long period. Our investigation was to look at changes in temperature at the different levels of the tank and analyze which re-entry port was the most effective in heating the water throughout the entire tank. Since heat rises we could assume that the lowest levels of re-entry would be more effective because the heated water would rise and disperse throughout the tank. This is a quality that would be desirable in a use such as a passive solar heated hot tub. It is possible that re-entry at the lower level however could be less effective because the energy would be dispersed more rapidly throughout the tank. In the mid-range reentry, the energy could also be dispersed evenly but might leave the lower level cooler because of rising heated molecules. When the re-entry is at the top, the highest temperatures might be achieved but again, the lower levels could have the lowest temperatures, which, in the use of a hot tub, would be uncomfortable. With the data we 1

2 recorded, a series of graphs were produced and analyzed to see which of these scenarios might be proven. The first set of graphs displays the full weeks of data for each of the 4 temperature readings and also indicates the re-entry level for that week. The results for each day vary in temperature due to cloud cover. The earlier weeks readings show higher overall temperatures due to the time of year, with one temperature reaching as high as 4 degrees Celsius. The overall high temperatures average degrees Celsius. Overall lows averaged degrees Celsius. As the season progresses and the intensity of sunlight diminish, the average temperatures tend to be lower. To account for this, the next set of graphs focus on the 2 days of each week that provided the best conditions for testing (sunny days). These graphs show the 12 hour period, approximately 9: AM 9: PM, where the heating process would happen and displays the temperature change at each level. The first week of readings, October -22, show a sharp increase in temperature at the probe directly above the re-entry port. As this input of heated water rises, the other temperature readings also increase in order as this bubble of warm water rises to the top of the tank. As the input water temperature decreases, the temperature readings decrease again, in order from bottom to top, as the water rises to the top. The following week, October 22-29, the weather was cloudy most of the week. Here, the probe readings run parallel with no large increase above the re-entry port (second to the bottom). Again, temperatures increase or decrease from bottom to top with the highest temperatures at the top, possibly because of the rising warm water. Week three, October 29-November, had lots of sunshine and the data showed a consistent increase of temperatures. Again, the readings run parallel with higher temperatures at the upper levels. Week four, November -12, stays consistent with this trend. As might be expected, temperatures remained highest at the top of the tank. Week five, November 12-26, breaks this trend. The re-entry level was at the top port and the temperature readings are almost completely reversed with higher temperatures at the lower levels of the tank, particularly at the next to the bottom probe. This reversal in the trend is somewhat of a mystery but I feel that the temperature in the greenhouse may have influenced the readings by conduction. Cooler, exterior temperatures could be transferred through the tank wall creating a core of warmer water insulated from the tank wall. The last set of graphs display the average increase of temperatures at each reading level for each week that the re-entry level changed. There are temperatures for each graph which represent each week. This is the average increase for those 2 days of each week as indicated on the prior graph. As there are only 4 probes, there are only 4 graphs. As the re-entry level moves up that probe is moved to the level below. For instance, when we changed from the bottom re-entry to the next port up, the probe was moved to the bottom port. This cycle continues throughout the project until the re-entry tube was placed in the top port. Despite a very high increase in temperature in the next-tobottom probe during the first week, the highest increase in average temperature occurs when the re-entry is located at the middle port. This indicates an even distribution of energy throughout the tank, suggesting that this middle port of re-entry would be the best for this thermal syphon. 2

3 Due to limited time and data this conclusion is not completely borne out by the data collected in this project. The varied temperature readings were not predicted and cannot be conclusively explained and may be due to weather conditions and/or design and external environmental factors. Conclusive results would require further experimentation. In terms of passive water heating for a hot tub, significant temperatures can be gained but I believe that obtaining the most effective re-entry would require experimentation with a much larger tank and thermal mass to simulate actual conditions. BIBLIOGRAPHY John I. Yellott, Solar heating and cooling, in AccessScience@McGraw-Hill, Retrieved September 17, 7 From DOI.36/

4 Mother Earth News. Build An Integral Passive Solar Water Heater. Retrieved September 17, 7, From printarticle.aspx?id=69348 Dieckmann, L., Selby, B., Wright, R. & Wright, S. (198). The Hawkweed Group Passive Solar House Book. Chicago: Rand McNally &Company. El Paso Solar Energy Association. Passive Solar Water Heating. Retrieved September 17, 7, From Australian Academy of Science, NOVA Science in the News. Harnessing direct solar energy a progress report. Retrieved September 17, 7, From cience.org.au/nova//act6.htm Bainbridge, D.A. (1981) The Integral Passive Solar Water Heater Book: Breadboxes, batchers, and other types of solar water heaters. The Passive Solar Institute. U.S. Department of Energy. Energy Efficiency and Renewable Energy Solar EnergyTechnologies Program. Retrieved September 17, 7, From The Sietch Clean Power Projects. Hot Water from the Sun. Retrieved September 17, 7, From projects/solarthermalpanel/index.htm 4

5 T emperature(celsius) 7Oct.to22- Bottom Entry Next to bottom T ime(hour) M iddle Next to top Top

6 T emperature(celsius) Tues. Oct T ime(hours) Next to bottom M iddle Next to top To 6

7 T eperature(celsius) Wed. Oct T ime(hours) Next to bottom M iddle Next to top T 7

8 TeperatureCelsius) 7Oct.22to29-NB Entry 3 3 Series1 Series2 Time(H ours) Series3 Series4 8

9 T eperature(celsius) Sun. Oct.28 3 T ime(hours) Bottom M iddle Next to top Top 9

10 Teperature(Celsius) M on. Oct.29 3 T ime(h ours) Bottom M iddle N ext to top Top

11 Temperature(Celsius) 7Oct.29toNov.- M iddle Entry 3 3 Bottom Next Time(H to bottom ours) M iddle Top 11

12 T emperature(celsius) T ues. Oct T ime(hours) Bottom Next to bottom Next to top Top 12

13 T emperature(celsius) Wed. Oct T ime(hours) Bottom Next to bottom Next to top Top 13

14 Temperature(Celsius) 7Nov.to12-NT Entry 3 Bottom N ext Time(H to bottom ours) M iddle Top 14

15 Temperature(Celsius) T ues.nov Time(H ours)

16 T emperature(celsius) Sun. Nov.11 3 T ime(hours) Bottom Ne to bottomxt M iddle Top 16

17 Temperature(Celsius) 7Nov.19to26-T op Entry 3 Time(H ours) Bottom Next to bottom M iddle Next to top 17

18 T emperature(celsius) Fri. Nov.23 3 Time(H ours) Bottom N ext to bottom M iddle N ext to top 18

19 Temperature(Celsius) Sat.Nov Time(H ours) Bottom Next to bottom M iddle Next to to 19

20 Increase in T emp.(celsius) Delta T B,N B,M,N T,T-Entry

21 Increase in T emp.(celsius) Delta T B,NB,M,NT,T-Entry 21

22 Increase in Temp.(Celsius) Delta T B,N B.M,N T,T-Entry 22

23 Increase in Temp.(Celsius) Delta T B,N B,M,N T,T-Entry 23