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The monitoring and evaluation of geothermal systems

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Title:
The monitoring and evaluation of geothermal systems
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English
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Maynard, Whitney
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University of South Florida
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Subjects / Keywords:
Heat pump
Soil
Air conditioning
Energy
Dissertations, Academic -- Civil & Environmental Eng -- Masters -- USF   ( lcsh )
Genre:
non-fiction   ( marcgt )

Notes

Abstract:
ABSTRACT: With the heightened importance of green engineering in today's society, harnessing the Earth's internal energy has become ever more important. Specifically, the use of geothermal heat pumps as a means of heating and cooling homes and municipal buildings is on the rise. However, due to the high cost of installation and limited amount of research conducted, geothermal systems in the State of Florida have yet to meet their potential as an alternative heating and cooling source. With Florida's relatively constant ground temperature of 72°F, an above average temperature gradient for both heating and cooling of indoor areas is provided. To this end, this thesis investigates different geothermal systems and their ability to utilize ground energy storage. To conduct this research, four different geothermal systems were installed and monitored over a period of one year. Testing of the installed systems monitored not only overall efficiency, but also the soils reaction to heightened energy input. Conclusions and recommendations are made as general design parameters for vertical column geothermal well systems in the state of Florida.
Thesis:
Thesis (MSCE)--University of South Florida, 2010.
Bibliography:
Includes bibliographical references.
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Mode of access: World Wide Web.
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System requirements: World Wide Web browser and PDF reader.
Statement of Responsibility:
by Whitney Maynard.
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Title from PDF of title page.
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Document formatted into pages; contains X pages.

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ABSTRACT: With the heightened importance of green engineering in today's society, harnessing the Earth's internal energy has become ever more important. Specifically, the use of geothermal heat pumps as a means of heating and cooling homes and municipal buildings is on the rise. However, due to the high cost of installation and limited amount of research conducted, geothermal systems in the State of Florida have yet to meet their potential as an alternative heating and cooling source. With Florida's relatively constant ground temperature of 72F, an above average temperature gradient for both heating and cooling of indoor areas is provided. To this end, this thesis investigates different geothermal systems and their ability to utilize ground energy storage. To conduct this research, four different geothermal systems were installed and monitored over a period of one year. Testing of the installed systems monitored not only overall efficiency, but also the soils reaction to heightened energy input. Conclusions and recommendations are made as general design parameters for vertical column geothermal well systems in the state of Florida.
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The Monitoring and Evaluation of Geothermal Systems by Whitney E. Maynard A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil and Environmental Engineering C ollege of Engineering University of South Florida Major Professor: A. G ray Mullins, Ph.D. Rajan Sen, Ph.D. Michael Stokes, Ph.D. Date of Approval: October 22 2010 Keywords: heat pump, soil, air conditioning, energy Copyright 2010 Whitney E. Ma ynard

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i Table of Contents List of Tables ................................ ................................ ................................ ..................... iii List of Figures ................................ ................................ ................................ .................... iv A BSTRACT ................................ ................................ ................................ ....................... ix Chapter 1 Introduction ................................ ................................ ................................ ........ 1 1.1 Problem Statement ................................ ................................ ................................ .... 1 1.2 Thesis Organization ................................ ................................ ................................ .. 3 Chapter 2 Background ................................ ................................ ................................ ........ 4 2.1 Air Conditioning Basics ................................ ................................ ............................ 4 2.2 Energy Efficiency Ratings ................................ ................................ ........................ 7 2.2.1 Conventional Air Cooled Heat Pump System ................................ ................... 7 2.2.2 Ground Source Heat Pump (GSHP) System ................................ ...................... 9 2.3 Background on Geothermal Energy ................................ ................................ ....... 10 2.3.1 Ground Coupled Heat Pumps (GCHP) ................................ ............................ 12 2.3.2 Groundwater Heat Pumps (GWHP) ................................ ................................ 15 2.3.3 Surface Water Heat Pumps (SWHP) ................................ ............................... 16 2.4 Thermal Relations hips ................................ ................................ ............................ 17 2.4.1 Heat Diffusion ................................ ................................ ................................ .. 18 Chapter 3 Instrumentation and Monitoring ................................ ................................ ...... 21

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ii 3.1 Site Exploration ................................ ................................ ................................ ...... 23 3.2 System A Geothermal Well ................................ ................................ ................. 25 3.2.1 Instrumentation ................................ ................................ ................................ 25 3.2.2 Monitoring ................................ ................................ ................................ ....... 27 3.3 System B Geo Slinky above the Water Table ................................ ...................... 28 3.3.1. Instrumentation ................................ ................................ ............................... 29 3.3.2 Monitoring ................................ ................................ ................................ ....... 30 3.4 System C Geo Slinky below the Water Table ................................ ..................... 30 3.4.1 Instrumentation ................................ ................................ ................................ 30 3.4.2. Monitoring ................................ ................................ ................................ ...... 31 3.5 System D Geothermal Basement ................................ ................................ ......... 32 3.5.1 Instrumentation ................................ ................................ ................................ 32 3.5.2 Monitoring ................................ ................................ ................................ ....... 33 Chapter 4 Results ................................ ................................ ................................ .............. 50 4.1 System A Vertical Column Geothermal Well ................................ ..................... 51 4.2 System D Geothermal Basement ................................ ................................ ......... 57 Chapter 5 C onclusions ................................ ................................ ................................ ...... 61 5.1 Computing Required Energy ................................ ................................ .................. 61 References ................................ ................................ ................................ ......................... 67 App endices ................................ ................................ ................................ ........................ 69 Appendix A Field Data ................................ ................................ ................................ 70

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iii List of Tables Table 2.1: Testing Requirements for C alculation of EER Value ................................ ....... 9 Table 2.2: Testing Requirements for Calculation of COP Rating ................................ .... 10 Table 2.3: Thermal Values for Common Materials ................................ .......................... 18 Table 5.1: Unit Energy Losses for Homes and Buildings ................................ ................ 62 Table 5.2: Home Depot Recommended Energy Input for a Given Area .......................... 62

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iv List of Figures Figure 1.1: General Schematic of a Geothermal System. ................................ ................... 2 Figure 1 .2: Annual Ground Temperature Variation ................................ ........................... 2 Figure 2.1: Conventional Heat Pump Cooling Cycle ................................ ....................... 6 Figure 2.2: Convention Heat Pump Heating Cycle ................................ .......................... 6 Figure 2.3: Energy Savings Based on SEER Rating ................................ .......................... 8 Figure 2.4: Three Different Categories of Geothermal Heat Pu mps ................................ 12 Figure 2.5: Vertical Loop GCHP ................................ ................................ ...................... 13 Figure 2.6: Horizontal Loop GCHP ................................ ................................ .................. 14 Figure 2.7: Geothermal Geo Slinky System ................................ ................................ ..... 15 Figure 2.8: Open System GWHP ................................ ................................ ...................... 16 Figure 2.9: Open System GWHP with D ischarge into Pond ................................ ............ 16 Figure 2.10: Surface Water Heat Pump System ................................ ............................... 17 Figure 3.1: Site Locator on Map of Florida ................................ ................................ ...... 21 Figure 3.2: Site Locator on Map of Hillsborough County ................................ ................ 22 Figure 3.3: Site Overview ................................ ................................ ................................ 23 Figure 3.4: B 1 Soil Profile ................................ ................................ ............................... 24 Figure 3.5: B 2 Soil Profile ................................ ................................ ............................... 24 Figure 3.6: Pump and Heater S etup ................................ ................................ .................. 34 Figure 3.7: Schematic of System A ................................ ................................ .................. 34

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v Figure 3.8: Overview of System A Layout ................................ ................................ ....... 35 Figure 3.9: Individual 10" Diameter Geothermal Well ................................ .................... 35 Figure 3.10: Plug System Used for Thermocouple Bundle Placed within the Well ........ 36 Figure 3.11: Installed Thermocouple ................................ ................................ ................ 36 Figure 3.12: System A Instrumentation Scheme ................................ .............................. 37 Figure 3.1 3: CPT Truck with Rod Pushing Thermocouple Bundle into the Ground ....... 38 Figure 3.14: Thermocouple Bundle ................................ ................................ .................. 38 Figure 3.15: Nut and Bo lt Set Attached to Bottom of Thermocouple Bundle ................. 39 Figure 3.16: Removal of CPT Rod as Thermocouple Remains in Ground ...................... 39 Figure 3.17: Installed Thermocouple 10 inches From Well ................................ ............. 40 Figure 3.18: Finished Installation of Thermocouples ................................ ....................... 40 Figure 3.19: Omega Pa ddle Wheel Flow Meter ................................ ............................... 41 Figure 3.20: Systems A and B Monitoring Setup ................................ ............................. 41 Figure 3.21: Geo Slinky Used in Systems B and C ................................ .......................... 42 Figure 3.22: System B Instrumentation Scheme ................................ .............................. 42 Figure 3.23: Installation of System B ................................ ................................ ............... 43 Figure 3.24: Installation of Thermocouples on System B ................................ ................ 43 Figure 3.25: Installation of System C ................................ ................................ ............... 44 Figure 3.26: System C Geo Slinky Below Water Level ................................ ................... 44 Figure 3.27: System C Instrumentation Scheme ................................ .............................. 45 Figure 3.28: System C Monitoring Setup ................................ ................................ ......... 45 Figure 3.29: System D Basement Walls Constructed ................................ ....................... 46 Figure 3.30: System D Basement Floor Cast ................................ ................................ .... 46

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vi Figure 3.31: System D Completed Structure ................................ ................................ .... 47 Figure 3.32: U shaped Piping Placed within Basement Walls ................................ ......... 47 Figure 3.33: System D Temperature Sensor L ocations ................................ .................... 48 Figure 3.34: Installed Thermocouple on System D ................................ .......................... 48 Figure 3.35: Close up of System D DAS System ................................ ............................. 49 Figure 3.36: Monitoring Setup for System D ................................ ................................ ... 49 Figure 4.1: F low Comparison between Systems A and D ................................ ................ 50 Figure 4.2: Inflow, Outflow, Air Temperature and Flow Rate for System A .................. 51 Figure 4.3: Overall Change in Temperature from Inflow to Outflow for System A ........ 52 Figure 4.4: Ground Temperature Profile 10 inches From Well for System A ................. 53 Figure 4.5: Local Soil Temperature Comparison 6 Feet below Ground for System A .... 54 Figure 4.6: Normal Seasonal Temperature Profile ................................ ........................... 55 Figure 4.7: Change in Soil Temperature 10 inches From Well for System A ................. 55 Figure 4.8 : T soil Profile for System A at Start up ................................ ........................... 56 Figure 4.9: T soil Profile for Syste m A after System Start Up ................................ ......... 56 Figure 4.10: Energy Input into Soil for System A ................................ ............................ 57 Figure 4.11: Inflow, Outflow, Air Temperature and Flow Rate for System D ................ 58 Figure 4.12: Outflow Temperature of Each Induvidual Well for System D .................... 59 Figure 4.13: Overall Change in Temperature from Inflow to Outflow for System D ...... 59 Figure 4.14: Energy Input into Soil for System D ................................ ............................ 60 Figure 5.1: Monthly Energy Requirement for T of 20 F ................................ ................ 63 Figure 5.2: Monthly Energy Requirement as a Function of T ................................ ........ 64 Figure 5.3: Summer Energy Cost Based on Indoor Temperature of 78 F ........................ 64

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vii Figure 5.4: Cooling Cost in a 2000 SF Home with Respect to Thermostat Setting ......... 65 Figure 5.5: Number of Geothermal Wells for Various Temperature Gradients ............... 66 Figure 5.6: Number of Geothermal Well Based on Average Summer Conditions .......... 66 Figure A.1: Ground Temperature Profile 20 inches From Well for System A ................ 70 Figure A.2: Ground Temperature Profile 40 inches From Well for System A ................ 70 Figure A.3: Ground Temperature Profile 80 inches From Well for System A ................ 71 Figure A.4: Groun d Temperature Profile 160 inches From Well for System A .............. 71 Figure A.5: Local Soil Temperature Comparison 12 Feet below Ground for System A 72 Figure A.6: Local Soil Temperature Comparison 18 Feet below Ground for System A 72 Figure A.7: Seasonal Ground Temperature Profile 10 inches from Well ........................ 73 Figure A.8: Seasonal Ground Temperature Profile 20 inches from Well ........................ 73 Figure A.9: Seasonal Ground Temperature Profile 40 inches from Well ........................ 74 Figure A.10: Seasonal Ground Temperature Profile 80 inches from Well ...................... 74 Figure A.11: Change in Soil Temperature 20 inches From Well for S ystem A ............. 75 Figure A.12: Change in Soil Temperature 40 inches From Well for System A ............. 75 Figure A.13: Change in Soil Temperature 80 inches From Well for System A ............. 76 Figure A.14: T soil Profile for System A after 3 Days of System Flow ........................... 77 Figure A.15: T soil Profile for System A after 6 Days of System Flow ........................... 77 Figure A.16: T soil Profile for System A after 9 Days of System Flow ........................... 78 Figure A.17: T soil Profile for System A after 12 Days of System Flow ......................... 78 Figure A.18: T soil Profile for System A after 15 Days of System Flow ......................... 79 Figure A.19: T soil Profile for System A after 18 Days of System Flow ......................... 79 Figure A.20: T soil Profile for System A after 21 Days of System Flow ......................... 80

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viii Figure A.21: T soil Profile for System A after 24 Days of System Flow ......................... 80 Figure A.22: T soil Profile for System A after 27 Days of System Flow ......................... 81 Figure A.23: T soil Profile for System A after 30 Days of Syste m Flow ......................... 81 Figure A.24: Change in Temperature across Loop 1 of System D ................................ ... 82 Figure A.25: Change in Temperature across Loop 2 of Sy stem D ................................ ... 82 Figure A.26: Change in Temperature across Loop 3 of System D ................................ ... 83 Figure A.27: Change in Temperature across Loop 4 of Sy stem D ................................ ... 83 Figure A.28: Change in Temperature across Loop 5 of System D ................................ ... 84 Figure A.29: Change in Temperature across Loop 6 of Sy stem D ................................ ... 84 Figure A.30: Change in Temperature across Loop 7 of System D ................................ ... 85 Figure A.31: Change in Temperature across Loop 8 of Sy stem D ................................ ... 85 Figure A.32: Monthly Energy Requirement for T of 5 F ................................ ............... 86 Figure A.33: Monthly Energy Requirement for T of 10 F ................................ ............. 86 Figure A.34: Monthly Energy Requirement for T of 15 F ................................ ............. 87

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ix The Monitoring and Evaluation of Geothermal Systems Whitney E. Maynard ABSTRACT With the height ened importance of green engineering in today's society harnessing the Earth's internal energy has become ever more important. Specifically the use of geothermal heat pumps as a means of heating and cooling homes and municipal buildings is on the rise. However, d ue to the high cost of installation and limited amount of research conducted, geothermal systems in the State of Florida have yet to meet their potential as an alternati ve heating and cooling source. With Florida's relatively constant ground te mperature of 72 F, an above average temperature gradient for both heating and cooling of indoor areas is provided To this end, this thesis investigates different geothermal systems and their ability to utilize ground energy storage. To conduct this re search, four different geothermal systems were installed and monitored over a period of one year. Testing of the installed systems monitored not only overall efficiency, but also the soils reaction to heightened energy input. Conclusions and recommendati ons are made as general design parameters for vertical column geothermal well systems in the state of Florida.

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1 Chapter 1 Introduction 1.1 Problem Statement Geothermal energy is described as the thermal energy obtained from the subsurface of the ea rth by means of a heat exchange system. Dating back to the early twentieth century, this process has been utilized as a primary source of heat for residential homes and large industrial buildings. More recently, methods to provide cooling through similar systems have gained much needed attention. Such systems operate by bathing an air conditioner condenser core in water extracted from a geothermal system, rather than the conventional method of having air blown across it. The water that is returned from the condenser core is then re circulated into the geothermal system and the process repeats. This results in better system efficiency, as the conductivity and specific heat of water are much greater than that of air. See Figure 1.1 for a general schemati c of the system. Specifically in the state of Florida, there is a significant heat exchange gradient for both heating and cooling systems due to the ground's subsurface maintaining a year round temperature of approximately 72 F (Figure 1.2). In the summer months, when temperatures reach over 100 F, the geothermal system could possibly extract water at temperatures lower than that of ambient air, therefore requiring less energy by the condenser core to achieve a desired indoor air temperature. Furthermore, in the winter months, when temperatures drop to under 40 F, the geothermal system could recover the

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2 heat that was stored in the ground throughout the summer months and use it to heat the reverse cycle evaporator core. Figure 1.1: General Schematic of a Geothermal S ystem. Figure 1 2: Annual Ground Temperature Variation

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3 While it is clear that geothermal energy is better for the environment, the high installation costs have hindered its incorporation into all new construction. Furthermore, the lack o f exact values for overall system efficiency has further inhibited its marketability. 1.2 Thesis Organization This thesis investigates four different geothermal systems that, if effective, can significantly reduce installation costs while increasing its marketability in Florida. It is organized into four ensuing chapters. Chapter 2 discusses the concepts which will be applied in the systems that will be evaluated throughout this thesis as well as past instances where similar systems have been utilized. It will also cover conventional heating and cooling systems and the theory of thermal conductivity as it pertains to this particular project. Chapter 3 of this thesis will describe, in depth, the four different types of systems that were utilized for thi s project, their installation, overall site layout, and soil conditions. Also discussed in great detail are the monitoring schematics of each system as well as the data collection. A summary of results will be included in Chapter 4 which compare each syst ems overall efficiency through graphical presentation of the data. Finally, Chapter 5 will contain the conclusions and recommendations.

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4 Chapter 2 Background A thorough literature review was conducted to initiate and focus the scope of this Thesis. The following topics will be discussed in detail throughout this chapter: the basic refrigeration cycle, air conditioner efficiency rating systems, the history of geothermal systems, and finally, a section covering basic thermal properties of soil. 2.1 A ir Conditioning Basics Refrigerant based cooling systems function based on thermodynamic heat absorption as a high pressure gas rapidly expands. Therein, all gases have the potential of providing cooling when passed through an orifice or expansion valve f rom high to low pressure. The amount of energy absorption is dependent on the gas; the most popular being FREON, of which there are multiple formulations. Alternate systems using ammonia gas are similarly effective, but require more robust systems to con tain the caustic contents. In all systems, the refrigerant is re circulated going through the following stages ( Figure 2 1 ): 1 Starting as a gas the refrigerant is compressed into a liquid. Due to the energy required for this process, the resultant is a very hot liquid. 2 The heated liquid is then piped, typically through an air cooled, fan forced radiator that transfers its heat energy, into the surrounding air producing hot air (usually outdoors). The result is a cooled liquid.

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5 3 The cooled liqui d is then piped indoors and then through an orifice, or expansion valve, which essentially sprays the refrigerant (high to low pressure transformation) into an evaporator core, which is another fan forced radiator. 4 The cold refrigerant passes through the piping of the evaporator core while the warm air passes over the cold pipes. The cooled air passing through and leaving the evaporator core is the desired product for air conditioning or refrigeration systems. The evaporator core cannot drop below t he freezing point of water or the humidity in the air will freeze on the radiating vanes thus blocking air flow. As a result, the entire system is charged with sufficient gas/liquid pressure to ensure that the drop in pressure across the orifice/expansion valve will not be too efficient to cause freezing. 5 Finally, the refrigerant gas, now warmed by the evaporator core, is piped back to the compressor and process starts over. The only difference between heating and cooling in the above processes is wh ere the condensing and expansion occurs. For normal air conditioning, the evaporator core is indoors and the condenser core is outdoors; for reverse cycle (heat pump) systems the evaporator core is outdoors and condenser core is indoors. As the evaporato r core cannot be operated near or below freezing, the possible heat exchange at low outdoor temperatures (near or below freezing) is greatly diminished. Typical systems become too inefficient to operate at temperatures below 40¡F. Figure 2. 2 shows a gener al schematic for the reverse cycle heating process.

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6 Figure 2.1: Conventional Heat Pump Cooling Cycle ( http://www.allenhvacpro.com ) Figure 2.2: Convention Heat Pump Heating Cycle ( http://www.allenhvacpro.com ) Due to the relative warm climate in Florida, HVAC systems can be equipped with the heating module know as a heat pump or reverse cycle system. These systems essentially cool the outdoors while heating the des ired indoor facility. These systems are not widely used throughout the rest of the country due to poor performance during

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7 extreme low temperature conditions. However, when geothermal heat exchangers are used, it is possible to use heat pumps during extre me low temperature conditions. 2.2 Energy Efficiency Ratings Energy efficiency ratings were established by the Department of Energy as a means of comparing all heating, ventilating, and air conditioning (HVAC) units of the same type. Unfortunately, when c onsidering system efficiency, the conventional air cooled heat pump systems are not comparable to ground source heat pump systems. Thi s is because air cooled system efficiency ratings are based over an entire cooling season, as opposed to at a single outd oor temperature for the ground source systems [1] The following section discusses in detail the different rating systems that are used to evaluate the energy efficiency of common HVAC systems. 2.2.1 Conventional Air Cooled Heat Pump System 2.2.1.1 SEER Rating The Seasonal Energy Efficiency Rating (SEER) is a rating system established to determine the level of efficiency of an air conditioning system in the cooling season. In general, the higher the SEER number, the more efficient the system, and therefo re, the lower the amount of electricity required to meet standard cooling demands. The general equation for calculating SEER ratings is described below. Reference the ANSI/AHRI Standard 220/240 2008 Section 4.1 for detailed calculation steps [2].

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8 Acco rding to a bulletin published by the Consumer Energy Center, prior to 1992, the average SEER rating of an air conditioner was 6.0 However, beginning in 1992 the federal government required a minimum rating of SEER 10 on all new air conditioner installati ons. This standard was again changed in January 2006, and required a minimum SEER 13 on all new air conditioner installations [3]. Figure 2.3: Energy Savings Based on SEER Rating ( http://www.heatpumpreview.net ) 2.2.1.2 HSPF Rating The Heating Seasonal Performance Factor (HSPF) is a measurement of efficiency similar to the SEER rating; only this value measures the efficiency of the system over an entire heating season rather than a cooling season. The HSPF ra ting is defined by the following: Detailed steps for calculating the HSPF efficiency factor can be found in section 4.2 of the ANSI/AHRI Standard 220/240 2008 [2].

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9 2.2.2 Ground Source Heat Pump (GSHP) System A GSHP as defined by the U.S Environmental Pro tection Agency is an electrically powered system that tap[s] the stored energy of the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings." The GSHP varies fro m the traditional air cooled heat pump in that it is creating its energy from the ground rather than the ambient outdoor air. This proves to be more efficient due to the approximately constant subsurface temperature of the ground. Subsequently, the effic iency rating system for the GSHP is not comparable to the traditional air cooled systems. The following section covers in detail the different efficiency rating systems for the GSHP. 2.2.2.1 EER Rating The Energy Efficiency Rating (EER) is a value used t o determine the cooling efficiency of a ground source heat pump under regulated temperature conditions. The Air Conditioning, Heating, and Refrigeration Institute (AHRI) developed standard testing conditions for calculating the EER rating of any GSHP syst em. Table 2.1 illustrates the testing requirements established by the AHRI Standard 330 1998 [4]. Under the specified conditions, the EER value is calculated as the ratio of cooling capacity (Btu/hr) to power input (W). Table 2.1: Testing Requirements for Calculation of EER Value Air Temperature Fluid temperature Passing over indoor evaporator Outdoor Returning from geothermal system Fluid Flow Rate 80¡F 80¡F 77¡F specified by manufacturer

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10 2.2.2.2 COP Rating The Coefficient of Perform ance (COP) is a rating system used to establish the heating efficiency of a ground source heat pump. This rating system is calculated as the ratio of heating capacity (Btu/hr) to power input (W). Table 2.2 illustrates the AHRI standard rating conditions [4]. Table 2.2: Testing Requirements for Calculation of COP Rating Air Temperature Fluid temperature Passing over indoor condenser Outdoor Returning from geothermal system Fluid Flow Rate 70¡F 70¡F 32¡F specified in Standard Rating Cooling Test 2.3 Background on Geothermal Energy The term geothermal stems from "geo" referring to the earth and "therme" referring to heat. Ergo, geothermal systems work by extracting heat from the earth to heat the insides of buildings. In the simplest o f forms, this technology dates back as far as the 18 th century when geothermal energy from hot springs was used for bathing and cooking. Beginning in the 19 th century, direct uses of geothermal energy, by means of space heating and usable electricity beca me possible [5]. A general timeline following the advancements in geothermal technology is as follows: 1892 The world's first geothermal district heating system was installed in Boise, Idaho. Heated water was extracted from the earth and pumped through a series of pipes to heat downtown buildings.

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11 1904 Geothermal power production was trialed in Larderello, Italy. Steam escaping from the Earth was used as an electric power producer. 1920's Turbine driven geothermal power production from the Geyser's (hot springs) of San Francisco, California began. 1960 Large scale power production began at the Geyser's in California. The geothermal power plant produced 11 MW of net power. 1980's Three more heating districts were added in Boise, Idaho. Geother mal technology reached several areas around the world [5]. Following the energy crisis in the late 1970's, research and development targeting ways to use geothermal energy accelerated. Not only were there advancements made to better geothermal heating, bu t ideas of utilizing geothermal systems for cooling also became of interest. The outcome was a geothermal heat pump that works by bathing the condenser core in cool water in lieu of blown air resulting in reduced condenser core dimensions and increased ef fectiveness. To date, three different types of geothermal systems have gained much interest and acceptance in society (Figure 2.4). The following sections describe in detail each differing system.

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12 Figure 2.4: Three Different Categories of Geothermal Hea t Pumps [1] 2.3.1 Ground Coupled Heat Pumps (GCHP) Ground coupled heat pumps, also known as closed loop heat pumps, work as a pressurized system that re circulates a coolant (like water or glycol/water mixture) through a heat exchanger and is then passed t hrough a series of looped pipes that are installed in foundation elements to either cool or warm the coolant. In these systems the heat exchanger takes the place of the "outdoor" condenser core for air conditioning systems or the evaporator core for rever se cycle systems. Condenser, evaporator, or radiator cores are air based heat exchangers; however, by convention, heat exchangers refer to liquid bathed cores that exchange heat from the liquid coolant with the refrigerant or vice versa. GCHP systems exc hange geothermal energy by the process of heat dissipation into the ground. In the summer months, the heat that is generated by the condenser core is transferred to the coolant that re circulates through the closed loop

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13 system; as the heated coolant circu lates through the geo foundation, the heat naturally dissipates into the cooler surrounding soil. The geothermal energy that is stored in the surrounding soil throughout the summer months can then be recovered during the winter months as the cooled coolan t (from reverse cycle function) circulates through the system. Overall, there are three different forms of this system: the vertical loop system, horizontal loop system, and slinky system [6]. The vertical loop system is typically used in situations wher e limited land is available for use. As shown in Figure 2.5, the vertical loop system consists of high density polyethylene piping that is looped in boreholes drilled as much as 200 to 300 feet below ground and 15 to 20 feet apart. The amount of borehole s needed depends on the surrounding soil type, but typically one to two boreholes can support a one ton air conditioning system [5]. Figure 2.5: Vertical Loop GCHP [5] Horizontal loop systems perform in the same manner as the vertical loop systems. H owever, the piping loops are laid in a horizontal fashion approximately 4 to 10 feet

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14 below ground and spaced approximately 6 to 12 feet apart. While this option requires less intricate drilling techniques, and therefore costs less to install, it requires the greatest amount of land surface. A typical horizontal loop system covers approximately 1,500 to 3,000 square foot, depending on the soil type, to provide for a one ton air conditioning system. Figure 2.6 provides an illustration of this system [5]. Figure 2.6: Horizontal Loop GCHP ( www.canadamenergy.com/en/solution ) The third form of ground coupled heat pump is the slinky system. This system is a slight variation of the horizontal loop GCHP in that it requires 3 to 5 times less land area for instal lation. The slinky system consists of a series of overlapping circular piping loops laid in trenches approximately 5 to 10 feet below ground (Figure 2.7). Because the system can accommodate more piping per unit length of trench, there is more surface are a available to dissipate or recover heat from the surrounding soil. This results in the reduction of required land area to 500 to 800 square feet to provide for a one ton air conditioner [5].

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15 Figure 2.7: Geothermal Geo Slinky System ( http://www.searsheatingcooling.com ) 2.3.2 Groundwater Heat Pumps (GWHP) The groundwater heat pumps, also known as open loop heat pumps, extract ground water from the earth for use as a geothermal cooling and or heating agen t. The system works by pumping ground water from a nearby well that is then passed through a heat exchanger where the energy transfer takes place. The resulting water is then injected back into the aquifer or into a nearby pond. Systems that discharge water back into the aquifer must utilize two separate wells. To ensure that water does not flow between the two wells, they must be spaced approximately 200 to 600 feet apart depending of the surrounding soil type. The production wells, those which extra ct ground water, can also vary widely in depth based on the local soil strata. Figures 2.8 and 2.9 demonstrate both types of groundwater heat pumps [5].

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16 Figure 2.8: Open System GWHP [5] Figure 2.9: Open System GWHP with Discharge into Pond [5] 2.3. 3 Surface Water Heat Pumps (SWHP) Surface water heat pumps use local ponds or inland bays as the geothermal source. These systems can be either closed or open systems, and are typically similar to a ground source system in configuration. The closed syst em utilizes the same piping layout as the closed loop slinky, but is placed in a local body of water rather than the foundation. Pond or Lake

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17 This system works my by means of heat dissipation between the slinky and the local body of water. The open system SWHP is s imilar to the groundwater heat pump. For this system to operate efficiently, water is pumped from the bottom of a pond or bay, approximately 30 feet below water level, passed through a heat exchanger and then discharged back into the same body of water. Figure 2.10 illustrates the typical open system SWHP layout. Figure 2.10: Surface Water Heat Pump System [5] 2.4 Thermal Relationships Thermal conductivity and heat transfer are the basis by which the geothermal heat pump was developed. Due to the drast ic difference in thermal conductivity and specific heat between air and water, the heat transfer that occurs in the condensing stage is much more efficient when water is the transfer medium. Table 2.3 lists thermal properties for a few common materials. W hen comparing air to water the conductivity (rate of heat diffusion) is 25 times higher and the specific heat (energy storage) is over 5 times higher. Therefore, by

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18 bathing the condenser core in water in lieu of blown air the net result is system efficien cies that are orders of magnitude higher for the same size condenser core. Table 2.3: Thermal Values for Common Materials [9] Material Thermal Conductivity (W/m K) Specific Heat (J/kg K) Air at STP 0.024 775 Water 0.6 4184 Sand 2.2 1500 Steel 14 470 2.4.1 Heat Diffusion Just as important as the efficiency of the geothermal heat pump is the dissipation of heat into the soil foundation and the amount of energy that can be stored and maintained in the foundation. The following section discusses the essential thermal properties needed for computation of these values. Conduction, convection, and radiation are the framework by which heat flow through soil occurs. Of these three mechanisms conduction is the most effective means of heat transport. Cond uctive heat flow, also classified by thermal conductivity, is defined as the heat flow passing through a unit area given a unit temperature gradient. Thermal conductivity, can be calculated using the following equation: (2 1 ) This value c an be estimated by the geometric mean of the thermal conductivity of the individual matrix components: solids, water, and air. Thermal conductivity of soil minerals range from 2 to 8 W/m C (for clay to quartz, respectively); although dependent on temperat ure and relative humidity, water is roughly 0.6 W/m C and air, 0.03 W/m C.

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19 For a saturated soil, the thermal conductivity can be determined using equation (2 2) where n represents the vo lumetric fraction of water [7, 8 ]. (2 2 ) Likewise, the t hermal conductivity of the solids is related to the fraction of quartz or sand, q in the soil and is determined using equation (2 3). The subscript o denotes other soil minerals. (2 3) The heat capacity of the soil can be determined bas ed on the volumetric fraction of solids, water, and air wherein the heat capacity of each component is defined as the heat required to raise the temperature of a unit volume of material one degree C. The heat capacity is actually the product of the mass sp ecific heat, c (cal/g C), and the dry density of the soil, r (g/cm 3 ). By defining X i as the volumetric fraction of each component, equation (2 4) can be used to determine the effective specific heat of the soil matrix where C s C w and C a represents the hea t capacity of the solids, water, and air, respectively. (2 4)

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20 The reluctance of the soil to be heated ( C ) along with the abilit y to conduct heat ( ) are two conflicting parameters that affect heat dissipation in the surrounding soils. A denser material requires more ene rgy to warm, while also being a bette r conductor. This conflict combines in to an additional parameter, the diff usivity of the material This parameter is defined as the ratio of thermal conductivity to the heat capacity as shown in the following equation. (2 5 ) While computation of these thermal properties is precise and valuable, recent advancements in soil p roperty algorithms has made it possible to determine the thermal conductivity and heat capacity from boring logs whereby the soil type and blow count are used to estimate sand content and density [10].

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21 Chapter 3 Instrumentation and Monitoring The primary focus of this research project was to perform a series o f instrumented tests to verify the concept of developing an economical method to enhance the efficiency of HVAC systems. Four different systems were constructed and tested at Coastal Caisson Corp oration in Odessa Florida (Figures 3.1 and 3.2) Figure 3.1: Site Locator on Map of Florida

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22 Figure 3.2: Site Locator on Map of Hillsborough County Because this research project was implemented to test only geothermal efficiency, no HVAC system was provided as the actual heat exchanger for the system. However, to mimic each system as it would be used in residential and commercial buildings, a Titan tankless water heater coupled with a 2.5 gallon per minute, # inch water pump was used to supply both heat and flow to all four systems (Figure 3.6). Chapter 3 of this report describes each system in detail and outlines the individual instrumentation and monitoring schemes.

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23 3.1 Site Exploration Coastal Caisson Corporation designated an area at the ir storage yard for all four systems to be installed and tested. Figure 3.3 shows the site overview with designated system locations. Figure 3.3: Site Overview Standard penetration tests were performed at two different locations within th e site. Figure 3.3 illustrates each boring log location relative to the four installed systems. Prior to Coastal Caisson owning this property, the site was a local landfill. This condition caused many soil samples to be omitted due to encountering trash and debris. Figures 3.4 and 3.5 show a summary of their findings.

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24 Figure 3.4: B 1 Soil Profile Figure 3.5: B 2 Soil Profile

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25 3.2 System A Geothermal Well The design for the vertical column geothermal well was based on the ability to retrofit this concept to any ho me or business application. As shown in Figure 3.7, the geothermal well system consists of a closed re circulating system, made up of a series of 19 foot long, # inch Polyvinyl Chloride (PVC) pipe encased by a 20 foot long 10 inch diameter steel pipe, pl aced vertically into the ground. The system works by pumping hot water, at up to 2.5 gallons per minute, into the top of the steel well and allowing it to be cooled by the surrounding soil as it slowly sinks to the bottom of the well. The cooled water t hen exits the well through the smaller, thermally insulated PVC pipe. For this particular application, 10 wells were constructed in series to optimize the systems maximum effectiveness (Figures 3.8). Finally, the system was instrumented with numerous tem perature sensors to verify the cooling effect of the system and monitor the dissipation of heat into the surrounding soil. 3.2.1 Instrumentation To monitor all aspects of the geothermal well system, thermocouple type temperature sensors were installed at many different locations within the wells as well as in the soil surrounding the wells. These sensors were Omega brand, type T (copper/constantan) thermocouples. Installation of the thermocouples is described in the following section. To monitor the ove rall change in temperature achieved by the system, thermocouples were placed at the inflow and outflow location of each individual well (Figure 3.9). Thermocouples were also installed at depths of 1, 6, 12, and 18 feet within the first well of the series to measure the gradual change in water temperature as it flowed

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26 through the well. To ensure the system would remain enclosed and not leak water, thermocouples were installed through plugs that were pre fabricated on the top of the well at the appropriate measurement locations. The thermocouples were secured into the threaded plug so that it could easily be removed or repaired. To fabricate the thermocouple plugs, a small hole was drilled out of the center of a standard male pipe plug and the thermocouple was pushed approximately 4 inches through it. To ensure the plug would not leak, the remaining opening in the center of the plug was sealed with epoxy Figures 3.10 and 3.11 show a sample plug prior to installation and after respectively. To monitor th e heat dissipation of the geothermal well into the surrounding soil, five series of thermocouple bundles were placed at various locations away from the first well of the series to measure instantaneous ground temperature. The temperature sensors were inst alled at distances 10, 20, 40, 80, and 160 inches away from the well corresponding to 1, 2, 4, 8,and 16 well diameters away from the edge of the well. At each location, four different thermocouples were installed at depths of 1, 6, 12, and 18 feet below g round level. Se e Figure 3.12 for a diagram of the instrumentation layout. To ensure the thermocouples were installed in their proper position at each radial distance from the well, a Cone Penetration Test (CPT) Truck was utilize d ( Figure 3.13) This inst allation technique minimized soil disturbance and assured accurate verticality of each bundle. Four thermocouples, one at each appropriate depth, were bundled together ( Figure 3.14 ) and passed through the CPT rod. Once the thermocouple bundle passed thro ugh the end of the rod, it was attached to a nut and bolt set ( Figure 3.15 ) that plugged the bottom

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27 of the rod and served as a disposable drive tip. Once prepared, the rod was pushed 18 feet into the ground using the hydraulically driven CPT device. As t he rod was removed from the ground, the nut and bolt set caught in the soil, leaving the thermocouple wires in their exact location (Figure 3.16 ). This procedure was repeated at all radial distances from the well. Figure 3.17 shows the first thermocouple bundle installed 10 inches away from the well. Each wire bundle was extended and buried in a shallow trench leading back to the data collector (Figure 3.18). Finally, an Omega Paddle Wheel Flow Sensor (Figure 3.19) was installed on the inflow pipe to moni tor the rate of water flowing through the well system. 3.2.2 Monitoring Data from the installed temperature and flow gauges was monitored and stored using a Campbell Scientific Data Acquisition Systems (DAS) as shown in Figure 3.20. The DAS for this parti cular arrangement consisted of the following devices: (1) 16 x 18 inch Weather Resistant Enclosure (1) PS100 12V Power Supply and Wall Charger (1) CR1000 Measurement and Control Datalogger (2) AM25T 25 Channel Solid State Multiplexers (1) Airlink RavenXT V CDMA Cellular Digital Modem (1) 800 MHz Wave Whip Cellular Antenna Connection between the gauges and the system was accomplished by wiring each thermocouple into an AM25 T Multiplexer. Each AM25 T can accommodate 25 channels, and therefore 2 multiplexer devices were required to monitor all of this systems temperature and flow gauges. The CR1000 was programmed to record an average reading from each gauge every 15 minutes. The collection devices were housed in a

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28 fiberglass, weather resistant enclosure an d powered by a 12V re chargeable battery. The enclosure was stored in the on site shed where the water heater and pump were housed complete with electrical power. Communication with the system from a remote location was made available through the use of an Airlink Raven Cellular Modem, powered by Verizon. The modem was wired into the CR1000 control system via an RS 232 cable which then transferred all of the stored data from the CR1000 to a host computer via the Internet. This allowed for the systems da ta to be collected remotely without physically connecting to the CR1000 which would have required frequent site visits. Data was transmitted hourly. 3.3 System B Geo Slinky above the Water Table This system is currently used in the industry and was ins talled and monitored as a comparison for the vertical column geothermal well and the geothermal basement The system was comprised of approximately 750 feet of # inch high density polyethylene piping coiled at a 10 inch pitch to make up a 60 foot long geo thermal coil field (Figure 3.21 ). The geothermal coil, also known as a Geo Slinky, was installed 3 feet below ground level (Figure 3.22), which positioned it above the water table where the soil was not fully saturated. Similar to the other four systems, hot water could be pumped into the entrance of the coil and slowly cooled by the surrounding soil as it circulates. The Geo Slinky was monitored similarly to the geothermal well to capture the overall efficiency and effect of the system on the surroundin g soil.

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29 3.3.1. Instrumentation Monitoring this system required the installation of thermocouples on the inflow pipe, outflow pipe, and below the ground near the Geo Slinky. For this particular system, thermocouples were installed at three locations along the geothermal coil to measure the vertical dissipation of heat into the surrounding soil as well as the effects of daily temperature fluctuations on the systems efficiency. Ground temperature thermocouples were placed at quarter points, 15, 30, and 45 fe et, from the inflow location of the Geo Slinky. At each quarter point, five thermocouples were bundled together and placed at depths of 1, 2, 3, 4, and 5 feet below ground level to monitor instantaneous ground temperatures (Figure 3.22). Thermocouples in stalled on the inflow and outflow pipes were fastened to the outside of the piping at each location for easy access. Installation of ground temperature thermocouples was done in conjunction with the Geo Slinky's installation. Prior to installation, thre e thermocouple bundles, consisting of five different thermocouples, one at each assigned depth, were prepared for easy on site installation. As see in Figure 3.23 a trench was made 3 feet below ground level and the coiled piping was laid inside. Before the trench was back filled with soil, the thermocouples were placed in the ground. To ensure proper installation of the thermocouples, each thermocouple bundle was securely fastened to a 5 foot long wooden stake with the deepest thermocouple fastened at t he bottom. Because the coil was installed 3 feet below ground level, each stake was embedded 2 feet below the coil to ensure that the 4 and 5 foot depth thermocouple elevations would be correct. Figure 3.24 shows the installed thermocouples.

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30 Finally, an Omega Paddle Wheel Flow Sensor (Figure 3.19 ) was installed on the inflow pipe to monitor the rate of water flowing into the well system. 3.3.2 Monitoring Campbell Scientific control devices were used to monitor this system. Due to the close proximity to S ystem A and the on site shed, the System B data was monitored and stored using the System A CR1000 Control System. An additional AM25 T Multiplexer was used to collect average readings every 15 minutes from each installed temperature and flow gauge on Sys tem B. The data was collected by the System A CR1000 and transferred to the host computer on the same schedule as System A. Figure 3.20 shows the AM25 T that makes up the monitoring scheme for System B. 3.4 System C Geo Slinky below the Water Table Sy stem C was installed as a modified version of System B. The system consisted of the exact same Geo Slinky used in System B, but installed at a depth of 8 feet, which placed it below the water table and in a location where the soil surrounding it was compl etely saturated (Figures 3.25 and 3.26). 3.4.1 Instrumentation In order to compare this system to System B an identical instrumentation scheme was implemented. Per this condition, thermocouples were installed at quarter locations, 15, 30, and 45 ft, from the inflow location of the Geo Slinky. At each quarter point, 5 thermocouples were installed at depths of 6, 7, 8, 9, and 10 feet. Just as with System B,

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31 thermocouples installed on the inflow and outflow pipes were fastened to the outside of the piping at each location. F igure 3.27 shows this instrumentation scheme. Unlike System B, instrumentation of the ground temperature thermocouples was done following installation of the Geo Slinky. In this case, 2 inch PVC pipes were jetted in at each quarter poi nt location as a guide for thermocouple installation. The PVC pipe was installed 10 feet into the ground. Installation was completed by simply dropping each thermocouple bundle, consisting of a thermocouple at every foot from 6 to 10 feet, into the appro priate PVC pipe until it was at the correct depth. The PVC was then pulled from the ground leaving the thermocouple bundle in place. Some soil disturbance likely resulted from this installation process, but it assured no damage to the slinky would occur from the CPT installation method. 3.4.2. Monitoring The monitoring setup for this particular system consisted of the same devices used in System A; however, there was no direct power source available to the monitoring enclosure. To compensate for this iss ue, a 20 Watt Solar Panel was installed to provide power to the system. To store the energy created by the solar panel, an additional 24 amp hr, 12V rechargeable battery was also installed within the enclosure. Figure 3.28 shows the monitoring setup.

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32 3 .5 System D Geothermal Basement This concept was constructed as a test subject for Coastal Basement Corporation (CBC). Their development of an underground, watertight basement that can be constructed in high water table locations provided the opportunit y of integrating a geothermal system within the basement walls of any home or business at the time of construction. Figure s 3.29 through 3.31 show the installation process. The system comprises of a series of U shaped pipes (Figure 3.32) that are install ed within the basement panel walls. The geothermal basement works by pumping the hot water exiting the geothermal HVAC system into the U shaped piping constructed within the basement walls. As the hot water slowly flows through the pipes, the heat of the liquid will naturally dissipate into the surrounding concrete/soil mixed walls and the outer undisturbed soil. The effect on internal basement temperature could also be assessed by this program. 3.5.1 Instrumentation Similar to the other systems, flow r ate and temperature of the coolant was measured using a paddle wheel flow sensor and thermocouples, respectively. The flow sensor was installed at the inflow location before the piping entered the basement walls. The instantaneous water temperature at th e beginning and end of every one of 9 loops was measured (Figure 3.33). A total of 18 thermocouples were installed while maintaining a watertight seal. In order to do this, a half inch steel plug was installed at each thermocouple location The thermoco uple was secured into the threaded plug so that it could easily be removed or repaired. Installation of these thermocouples followed

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33 the same steps as used in System A for inflow and outflow temperature. Figures 3.10 and 3.34 show the plug prior to inst allation and installed. 3.5.2 Monitoring The monitoring setup for this system was initially installed using the same devices as used in System A and consisted of the following: (1) 16 x 18 inch Weather Resistant Enclosure (1) PS100 12V Power Supply and Wall Charger (1) CR1000 Measurement and Control Datalogger (1) AM25T 25 Channel Solid State Multiplexers (1) Airlink RavenXTV CDMA Cellular Digital Modem (1) 800 MHz Wave Whip Cellular Antenna However, the location of the control system proved to have li ttle to no Verizon cellular service and was unable to connect to the host computer. To eliminate this issue, a 800 MHz 9 dBd Directional Antenna was installed above the control device which replaced the 800 MHz Whip Antenna. For this system, electrical p ower was supplied from the basement building. Figure 3.35 and 3.36 show the systems monitoring setup.

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34 Figure 3.6: Pump and Heater Setup Figure 3.7: Schematic of System A

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35 Figur e 3.8: Overview of System A L ayout Figure 3.9: Individual 10" Diame ter Geothermal W ell

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36 Figure 3.10: Plug System Used for Thermocouple Bundle Placed within the W ell Figure 3.11: Installed Thermocouple

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37 Figure 3.12 : System A Instrumentation Scheme

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38 Figure 3.13 : CPT Truck with Rod Pushing T her mocouple Bundle into the Ground Figure 3.14: Thermocouple Bundle

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39 Figure 3.15: Nut and Bolt Set Attached to Bottom of Thermocouple Bundle Figure 3.16 : Removal of CPT R od as Thermocouple Remains in Ground

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40 Figure 3.17: Installed Thermocouple 10 inches From Well F igure 3.18 : Finished I nstallation of T hermocouples

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41 Figure 3.19: Omega Paddle Wheel Flow Meter Figure 3.20 : System s A and B Monitoring S etup

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42 Figure 3.21: Geo Slinky Used in Systems B and C Figure 3.22: System B Instrumentation Scheme

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43 Figure 3.23: Installation of System B Figure 3.24: Installation of Thermocouples on System B

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44 Figure 3.25: Installation of System C Figure 3.26: System C Geo Slinky Below Water Level

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45 Figure 3.27 : System C Instrumentation Scheme Figure 3.28: System C Monitoring Setup

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46 Figure 3.29: System D Basement Walls Constructed Figure 3.30: System D Basement Floor Cast

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47 Figure 3.31: System D Completed Structure Figure 3.32: U shaped Piping Placed within Basement Walls

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48 Figure 3.33: System D Temp erature Sensor Locations (highlighted in yellow) Figure 3.34: Installed Thermocouple on System D

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49 Figure 3.35: Close up of System D DAS System Figure 3.36: Monitoring Setup for System D Antenna

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50 Chapter 4 Results The time frame of this thesis was s uch that only systems A and D were tested throughout the project period. The evaluation of Systems B and C were suspended until a later date. Given that a single pump provided flow to both systems A and D with only one or the other running at a time; th ere were limited instances when flow was supplied to both systems simultaneously. Figure 4.1 shows the distribution of flow throughout the project period. Figure 4.1: Flow Comparison between Systems A and D The following sections discuss in detail the results from the data collected for the vertical column geothermal well (Sys. A) and the geothermal basement (Sys. B).

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51 4.1 System A Vertical Column Geothermal Well At the onset of this study only the first well of the 10 well system was instrumented. Monitoring of this single 10 inch diameter well began June 17, 2009. The initial program was based on a flow rate and inflow temperature of 1 gallon per minute and 100¡F, respectively. Figure 4.2 shows the basic data collected from this well over the 14 month monitoring period. The inflow temperature, outflow temperature, air temperature and flow rate are all compared. Unfortunately, due to pump failure, water leaks, and/or power outages which are evident by zero flow rates, there were numerous long te rm interruptions in flow. Figure 4.3 more clearly displays the ability for this system to dissipate heat into the surrounding soil strata through just one of the 10 geothermal wells. Figure 4.2: Inflow, Outflow, Air Temperature and Flow Rate for Syste m A

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52 Figure 4.3: Overall Change in Temperature from Inflow to Outflow for System A Data collected from the installed ground temperature sensors was used to provide a graphical analysis of the soil reaction to heightened temperatures levels. Figure 4.4 illustrates ground temperatures 10 inches away from the well at various depths versus time. Flow rate is also plotted in relation to ground temperature to show the immediate and long term reaction to changes in flow rate. Baseline soil temperature measur ements were taken for 1 month prior to the system start up which commenced on July 13, 2009. This most clearly shown by the drastic change in the temperature/time slope of the lower three thermocouple traces. The upper most thermocouple (0 1 ft depth) wa s clearly influenced by the transient air temperature and was virtually unaffected by the well heat source. The upward temperature trends during the baseline measurement period are keeping with seasonal warming and as a consequence are more pronounced in the upper gages (soil layers). At a depth of 18 feet no appreciable increase was noted. Other

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53 information noted in this graphical analysis is (1) the soils ability to recover during prolonged periods of no flow and (2) how the ground temperatures invert as the seasonal air temperature falls below the 72 73¡F steady state soil temperature. Ground temperature traces for the thermocouple bundles placed 20, 40, 80, and 160 inches from the well are prepared and are displayed in Appendix A, Figures A. 1 A. 4 Figure 4.4: Ground Temperature Profile 10 inches From Well for System A By rearranging the data from Figure 4.4 and the similar data from Appendix A (Figures A.1 A.4), Figure 4.5 shows the ground temperature data relative to a specific radial distance f rom the geothermal well. This particular figure compares the soil temperature 6 feet below ground from all the instrumented locations away from the well. Figure 4.5 captures two significant trends: 1) The highest soil temperatures closer to the geothermal w ell (1D or 10 inches) and a decreasing effect out to 16D, or 160 inches.

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54 2) The soils ability to recover (dissipate an elevated temperature) after system flow is discontinued. This type graph was also prepared for depths of 12 and 18 feet and can be found in Appendix A, Figures A. 5 and A. 6 Figure 4.5: Local Soil Temperature Comparison 6 Feet below Ground for System A It can be noted in Figure 4.5 that the soil temperatures 160 inches, or 16D, from the well represent the normal seasonal temperature for that depth with no effect from the geothermal well. Figure 4.6 shows the normal seasonal temperature profile obtained from the 16D thermocouple bundle. The temperature profiles from the 1D, 2D, 4D, and 8D bundles can be found in Appendix, Figures A.7 through A.10. Given that, Figure 4.7 shows the change in soil temperature 10 inches from the well relative to the soil temperatures 160 inches from the well. Similar to the Figure 4.4 and 4.5 graphs, Figure 4.6 was reproduced for all remaining well distances (2 D, 4D, and 8D) and are likewise presented in Appendix A, Figures A.11 through A.13.

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55 Figure 4.6: Normal Seasonal Temperature Profile Figure 4.7: Change in Soil Temperature 10 inches From Well for System A

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56 The following graphical analysis (Figures 4.9 and 4.10) presents the change in soil temperature at each radial location from the well compared to the soil temperature 160 inches from the well. In this particular analysis, the change in soil temperature ( T soil ) is plotted with respect to depth below ground for a specific moment in time. Figure 4.9 plots the T soil the day before system start up and Figure 4.10 plots the same data after 33 consecutive days of system flow. The temperature profile reflects the warmer inflow location (at the top) and that the cooler outflow (at the bottom) is still effectively dissipating heat. Plots were prepared for every third day of system flow up to the 33 day maximum and can be found in Appendix A, Figures A.14 23. Figure 4.8: T soil Profile for System A at Start up Figure 4.9: T soil Profile for System A after 33 Days of System Flow

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57 Figure 4.10 shows the energy dissipated into the soil surrounding the system as a function of time. Periods of zero energy input ind icate regions of no flow. Figure 4.10: Energy Input into Soil for System A 4.2 System D Geothermal Basement Monitoring of the geothermal basement system began October 15, 2009 and flow was initiated November 2, 2009. Similar to the testing scheme fo llowed in System A System D targeted an initial program based on a flow rate and inflow temperature of 1 gallon per minute and 100 F, respectively. However, do to the long travel distance from the on site shed (location of pump and heater) to the inflow location of System D, temperature losses made it difficult to reach the targeted inflow temperature. Figure 4.11 illustrates the overall system performance (from first to last well loop) throughout the 12 month testing period.

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58 Figure 4.11: Inflow, Out flow, Air Temperature and Flow Rate for System D Figure 4.12 shows the liquid coolant (water) temperature as it exits each individual loop. Flow rate is also plotted in relation to the coolant temperature. Portions of the graph with no flow have been om itted and are blank to those time periods. An alternate form of graphical analysis performed on System D is displayed in Figure 4.13 and compares the overall change in temperature from inflow to outflow to flow rate and time. This type of graph was also prepared for each individual loop in the system and can be found in the Appendix, Figure A.24 A.31. Finally, Figure 4.14 shows the energy dissipated to the basement walls for both the entire system and just the first of the nine loops in the basement seri es.

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59 Figure 4.12: Outflow Temperature of Each Induvidual Well for System D Figure 4.13: Overall Change in Temperature from Inflow to Outflow for System D

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60 Figure 4.14: Energy Input into Soil for System D

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61 Chapter 5 Conclusions Geothermal s ystems have long been recognized as an energy efficient means of heating and cooling homes, businesses, and municipal buildings. Nevertheless, the initially higher cost of these systems have dissuaded most buyers despite the long term cost savings and a b etter that modest rate of return on the upfront expense. Recent State and Federal incentive programs (as well as the cost or energy savings in technologies) have brought geothermal to the forefront with the intent on creating encouraging markets for both providers and consumers alike. This study explored four possible configurations for ground based heat diffusion wells; the results, however, are focused on the use and efficiency of vertical well systems which are easily adaptable to both new and existing (retrofit) structures. This chapter concludes the study by summarizing the findings as they pertain to recommended methods for designing vertical column geothermal well fields. 5.1 Computing Required Energy The energy required to heat or cool a struct ure is dependent of the target internal temperature, the outdoor temperature, and the qualitative insulative properties of the walls, windows, ceiling, and doors. The desired indoor temperature is a personal preference, but power companies often recommend winter and summer limits that provide reasonable comfort and cost effectiveness. For instance, Florida Power and Light recommends values of 68 F and 78 F for winter and summer months, respectively [11].

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62 The difference between the target indoor temperatu re and the actual outdoor temperature sets up a thermal gradient on the walls, ceiling, windows and doors whereby energy is lost. Table 5.1 provides ranges of values for these surfaces. Table 5.1: Unit Energy Losses for Homes and Buildings [12] Unit Energ y Loss Values Windows 0.37 0.79 BTU/hr ft 2 ¡F Doors 0.15 0.61 BTU/hr ft 2 ¡F Walls 0.06 0.27 BTU/hr ft 2 ¡F Ceiling 0.02 0.17 BTU/hr ft 2 ¡F Numerous references and do it yourself websites provide rules of thumb for selecting the BTU requireme nts for various sized indoor structures. In general, two parameters are needed: the square footage (assuming and 8 ft ceiling height) and an assumed insulation quality (varying from good to none). From this a duty cycle, or run time, of 40 50% is assumed and then required BTU/hr for a given building is provided. Table 5.2 shows recommended values for selecting an appropriate air conditioner in the form of BTU/hr. Table 5.2: Home Depot Recommended Energy Input for a Given Area [13] Conditioning Area in S q. Ft. BTU's Needed 100 5,200 200 6,000 300 7,500 400 10,000 500 12,000 750 15,000 1,000 18,000 1,250 24,000 1,500 28,000

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63 Using these guidelines and values from Table 5.1 a design parameter can be established identifying the amount of energy that would be discharged to a geothermal well system on the basis of square footage and change in temperature, T, between the indoor space and the outside temperature. Depending on the insulation quality, this value ranges from 0.1 0.7 BTU/hr/SF/ F for good to poor insulation, respectively. Figure 5.1 shows the effect of insulation on required energy input (BTU/month) and monthly electric cost for an average T of 20 F. This analysis was also performed for T of 5 F, 10 F, and 15 F and can be found in Appendix A, Figure A.32 A.34. Figure 5.1: Monthly Energy Requirement for T of 20 F Using the computed average values shown in Figure 5.1, monthly energy requirements for a series of T values were computed and are shown in Figure 5.2. This Figure al lows for easy estimation of both cost and energy input based on a particular building size and/or particular indoor/outdoor temperature gradient.

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64 Using the Florida Power and Light recommended thermostat settings, Figure 5.3 shows those periods of time wh en the outdoor temperature exceed the recommended thermostat setting (summer and winter) and the estimated cooling costs for a 2000 square foot home. The resulting average cooling costs from Figure 5.3 is approximately $55 per month assuming a 6 month sum mer season. Figure 5.2: Monthly Energy Requirement as a Function of T Figure 5.3: Summer Energy Cost Based on Indoor Temperature of 78 F

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65 If the assumed summer threshold values are varied to reflect personal comfort instead of economy (thermostat set lower than 78 F), then the associated increase in cooling costs can be estimated using Figure 5.4. Figure 5.4: Cooling Cost in a 2000 SF Home with Respect to Thermostat Setting Finally, using the calculated energy input into the soil for System A (Figure 4.10), a well analysis was performed to approximate the amount of geothermal wells needed to cool a home. Using an average en ergy input of 1100 BTU/hr with a design well depth of 20 feet spaced at 25 feet on center Figure 5.5 compares the number of required geothermal wells to various indoor/outdoor temperature gradients and indoor square footage. Assuming that the indoor/outdoor temperature gradient, T, averages 12.5 F throughout the summer season, an approximates total number of 20 foot geothe rmal wells for any home between 1000 and 4000 square feet can be found in Figure 5.6. Following a complete analysis of all four installed geothermal systems, recommendations suggesting which geothermal sys tem is most efficient could be made.

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66 Figure 5 .5: Number of Geothermal Wells for Various Temperature Gradients Figure 5.6: Number of Geothermal Well Based on Average Summer Conditions

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67 References [1] Rafferty, K. (1997). "An Information Survival Kit for the Prospective Residential Geotherma l Heat Pump Owner," Geo Heat Center Bulletin, pp 1 3. [2] Air Conditioning, Heating, and Refrigeration Institute. (2008). Performance Rating of Unitary Air Conditioning and Air Source Heat Pump Equipment. ANSI/AHRI Standard 210/240 Vol. Arlington, VA. [3 ] Rating a Unit's Efficiency. California Energy Commission. 2006. Web. < http://www.consumerenergycenter.org/home/heating_cooling/heating_cooling.ht ml >. [4] Air Conditioning, Heati ng, and Refrigeration Institute. (1998). Standard for Ground Source Closed Loop Heat Pumps. AHRI Standard 330 Vol. Arlington, VA:. [5] Tabak, John. (2009). Solar and Geothermal Energy [Electronic Resource]. New York: Infobase Publishing. [6] Ground Loop Configuration and Installation. Virginia Tech.Web. < http://www.geo4va.vt.edu/A2/A2.htm >. [7] Johansen, O. (1975). "Thermal Conductivity of Soils and Rocks," Proce edings of the Sixth International Congress of the Foundation Francaised'EtudesNordigues, Vol. 2, pp.407 420. [8] Duarte, A., Campos, T., Araruna, J., and Filho, P. (2006). "Thermal Properties of Unsaturated Soils," Unsaturated Soils, GSP, ASCE, pp. 1707 1 718. [9] Farouki, O. (1966). "Physical Properties of Granular Materials with Reference to Thermal Resistivity," Highway Research Record 128, National Research Council, Washington, DC, pp 25 44. [10] Pauly, Nicole (2010). "Thermal Conductivity of Soils f rom the Analysis of Boring Logs," Master's Thesis, University of South Florida, December. [11] Top 10 Savings Tips: Efficient Ways to Conserve Energy. Florida Power and Light Company.Web. < http://www.fpl.com/residential/energy_saving/resources_tips/top_tips.shtml >.

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68 [12] Ndiaye, Demba, and Kamiel Gabriel. "Principal Component Analysis of the Electricity Consumption in Residential Dwellings." Energy and Buil dings In Press, Accepted ManuscriptPrint. [13] Air Conditioning Calculator. Home Depot USA, Inc. 2010. Web. < http://www.homedepot.com/webapp/wcs/stores/servlet/THDCalcRoomACView? metric=false&storeId=10051&langId= 1&catalogId=10053 >.

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69 Appendices

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70 Appendix A Field Data Figure A.1: Ground Temperature Profile 20 inches From Well for System A F igure A.2: Ground Temperature Profile 40 inches From Well for System A

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71 Appendix A: (Continued) Figure A.3: Ground Temperature Profile 80 inches From Well for System A ` Figure A.4: Ground Temperature Profile 160 inches From Well for System A #

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72 Appen dix A: (Continued) # Figure A.5: Local Soil Temperature Comparison 12 Feet below Ground for System A Figure A.6: Local Soil Temperature Comparison 18 Feet below Ground for System A

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73 Appendix A: (Continued) Figure A.7: Seasonal Ground Temperature Profile 10 inches from Well Figure A.8: Seasonal Ground Temperature Profile 20 inches from Well

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74 Appendix A: (Continued) Figure A.9: Seasonal Ground Temperature Profile 40 inches from Well Figure A.10: Seasonal Ground Te mperature Profile 80 inches from Well

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75 Appendix A: (Continued) Figure A.11: Change in Soil Temperature 20 inches From Well for System A Figure A.12: Change in Soil Temperature 40 inches From Well for System A

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76 Appendix A: (Continued) Fig ure A.13: Change in Soil Temperature 80 inches From Well for System A

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77 Appendix A: (Continued) Figure A.14: T soil Profile for System A after 3 Days of System Flow Figure A.15: T soil Profile for System A after 6 Days of System Flow

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78 Appendix A: (Continued) Figure A.16: T soil Profile for System A after 9 Days of System Flow Figure A.17: T soil Profile for System A after 12 Days of System Flow

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79 Appendix A: (Continued) Figure A.18: T soil Profile for System A after 15 Days of System Flow Figure A.19: T soil Profile for System A after 18 Days of System Flow

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80 Appendix A: (Continued) Figure A.20: T soil Profile for System A after 21 Days of System Flow Figure A.21: T soil Profile for System A after 24 Days of System Flow

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81 Appendix A: (Continued) Figure A.22: T soil Profile for System A after 27 Days of System Flo w Figure A.23: T soil Profile for System A after 30 Days of System Flow

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82 Appendix A: (Continued) Figure A.24: Change in Temperature across Loop 1 of System D Figure A.25: Change in Temperature across Loop 2 of System D

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83 Append ix A: (Continued) Figure A.26: Change in Temperature across Loop 3 of System D Figure A.27: Change in Temperature across Loop 4 of System D

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84 Appendix A: (Continued) Figure A.28: Change in Temperature across Loop 5 of System D Figure A.29: C hange in Temperature across Loop 6 of System D

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85 Appendix A: (Continued) Figure A.30: Change in Temperature across Loop 7 of System D Figure A.31: Change in Temperature across Loop 8 of System D

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86 Appendix A: (Continued) Figure A.32: Monthly Energ y Requirement for T of 5 F Figure A.33: Monthly Energy Requirement for T of 10 F

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87 Appendix A: (Continued) Figure A.34: Monthly Energy Requirement for T of 15 F