EVALUATION OF LOW TEMPERATURE GROUND COUPLED VERTICAL HEAT EXCHANGER IN SOUTH LOUISIANA Md Adnan Khan, E.I.T Jay Wang, Ph.D.; P.E. Louisiana Tech University 1

What is geothermal energy It’s a clean and sustainable form of energy. The concept is getting energy from the temperature difference between soil and atmosphere. Energy can be extracted in many ways. This paper only describes close loop vertical heat exchanger installed in building pile. This method is very applicable and economical even in small to medium residential buildings. Louisiana has a huge potential to explore its untapped geothermal energy 2

How it works Fig 1. A schematic diagram of energy pile heat exchanger in summer (left) and winter (right) 3

KEY PARAMETERS IN DESIGN OF ENERGY PILE 4

Soil Temperature Figure 2. Mean annual earth temperature in Fahrenheit scale at individual stations, superimposed on well-water temperature contours [1] 5

Summary of Design Parameters Building LocationNew Orleans Total number of energy pile 16 Energy pile spacing8.53m Concrete thermal conductivity 1.38 W/m-K Soil thermal conductivity1.47 W/m-K Soil temperature C Fluid inlet temperature for heating 36 0 C Fluid outlet temperature for cooling C Fluid circulation pump1492-Watt, 85% efficient Fluid typeWater (100% by weight) Fluid discharge0.757×10-3 m 3 /s Minimum fluid velocity0.61 m/s U-tube typeSDR 11 (40 mm) No of U-tubeOne U-tube in one pile Energy pile diameter0.33m Annual running time for cooling load at peak load 21.89% Annual running time for heating load at peak load 57% Table 1. Design parameters of New Orleans building 6

Energy Pile Design Fig 3. Energy pile model using GLD 2012 industrial version 7

COST AND CO 2 EMISSION BY DIFFERENT ENERGY SOURCES 8

Cost and CO 2 emission comparison Type of energy source Ratio of the cost to geothermal energy cost Ratio of emission compare to geothermal energy Natural Gas Propane Oil electric heat Geothermal1.0 Table 2. Annual energy cost by different sources of energy 9

SENSITIVITY ANALYSIS OF DESIGN PARAMETERS 10

Soil Temperature Design soil Temperature is 19.4° Celsius (67°F). As the temperature gap is increasing within a certain range the pile length is decreasing up to 20%. Fig 4. Effect of ground soil temperature on the required pile length 11

Soil Thermal Conductivity Design soil thermal conductivity is 1.5 W/m-k More soil thermal conductivity means less overall pile length. Fig 5. Effect of soil thermal conductivity on the required pile length 12

Concrete thermal conductivity Design concrete thermal conductivity is 1.38 W/m-k. In industry specialized thermally enhanced concrete is available with thermal conductivity as much as 1.85 W/m-k. Using that specialized concrete can reduce pile length as much as 15%. Fig 6. Effect of concrete thermal conductivity on the required pile length 13

Pile Diameter Reduction of pile length means less surface area for heat transfer. So using slender pile will increase the pile length to get the same exchange of heat transfer. Fig 7. Effect of pile diameter on the required pile length 14

U-tube Diameter Heat carrying medium in this system is the circulating fluid inside the U-tube. So less amount U-tube diameter will result in less surface area to heat transfer. The result is increase in pile length. Fig 8. Effect of U-tube diameter on the required pile length 15

U-tube Orientation U-tube placed along the outer wall has more exposure to heat transfer with the soil. Close together placement of U-tube will increase the pile length by 10%. Fig 9. Possible U-tube orientation in energy pile Fig 10. Effect of U-tube orientation on the required pile length 16

Acknowledgement The research was funded by The National Science Foundation (NSF) and the Louisiana Board of Regents (BOR) at the program of EPSCoR-Pfund under the contract No. LEQSF (2012)-PFUND-286. The support and assistance of the BOR personnel are gratefully acknowledged. 17

Reference [1] Virginia Department of Mines Minerals and Energy. (2012, January 22). Earth Temperature and Site Geology. Available:

THANK YOU! 19