Analysis Of Cost And Energy Performance Of Geothermal Heat Pump Systems In Southern Louisiana

Duran Tapia, Claudia de Lourdes, “Analysis of Cost and Energy Performance of Geothermal Heat Pump Systems in Southern Louisiana” (2017). LSU Master’s Theses. 4504. https://digitalcommons.lsu.edu/gradschool_theses/4504

This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master’s Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact gradetd@lsu.edu.

Claudia de Lourdes Duran Tapia‘s one-hundred-seventy page thesis about ground-source heating and cooling systems. Mark Schultz, President of Earth River Geothermal and his web developer, Michael A. Loftus will be gathering energy consumption data and systems data from clients throughout 2020 in order to produce a report similar in format for Central Maryland.

Claudia de Lourdes Duran Tapia, Louisiana State University and Agricultural and Mechanical College, claudiaduran_21 [at] hotmail.com.

A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in Construction Management in

The Bert S. Turner Department of Construction Management by

Claudia de Lourdes Duran Tapia B.S., University of New Orleans, 2015 August 2017

Acknowledgments

I am grateful for the Bert S. Turner Department of Construction Management at Louisiana State University for funding this research. I would like to especially thank Dr. Christofer Harper for giving me the opportunity to pursue this degree and for his constant support and guidance throughout this endeavor. Also, I would like to thank Dr. Yimin Zhu and Dr. Chao Wang for their valuable assistance during this research project. This research would not have been possible without the participation of several consultants, non-profit organizations, and each of the homeowners and contractors who shared their knowledge and experience of working with geothermal heat pumps.

My gratitude to my graduate colleagues in the Construction Management Department, whose friendship and invaluable support helped me to enjoy this year of graduate school. I cannot be more thankful to my father, Jorge Duran Camacho, only the smartest, hardworking engineer and generous man I have ever met. I want to especially thank my mother, Claudia, who dedicated years of her life to take care of me and my siblings Gabriela and Jorge, her unconditional love and support has motivated me to always look forward even in the toughest moments.

Finally, I would like to thank Luis de Grau, who shared with me his passion for green building and encouraged me from the beginning of this journey. Thank you, Lord, for all your blessings, especially for my old friends and the new friends I have made in LSU because they made me feel less far from home and no matter where I go, I will always carry them in my heart.

TABLE OF CONTENTS

ACKNOWLEDGMENTS ABSTRACT

CHAPTER 1: INTRODUCTION 1.2. Background 1.2. Report Organization

CHAPTER 2: LITERATURE REVIEW 2.1. Overview of 2.2. Geothermal Heat Pump System Components 2.3. Standards and Certifications 2.4. Geothermal Heat Pump Market Overview 2.5. Other Ground-Source Thermal Technology 2.6. Performance and Cost Data

CHAPTER 3: METHODOLOGY 3.1. Define Scope of Work 3.2. Conduct Literature Review 3.3. Develop Case Study Protocol 3.4. Conduct Case Studies 3.5. Analyze Case Study Data 3.6. Discussion and Conclusions

CHAPTER 4: ANALYSIS 4.1. Case Study 1 4.2. Case Study 2 4.3. Case Study 3 4.4. Case Study 4

CHAPTER 5: DISCUSSION 5.1. Case Study 1 (GH1 and CH1) 5.2. Case Study 2 (GH2) 5.3. Case Study 3 (GH3 and CH3) 5.4. Case Study 4 (GH4) 5.5. Comparison of Case Studies

CHAPTER 6: CONCLUSIONS 6.1. Primary Results and Conclusions 6.2. Limitations 6.3. Future Research

REFERENCES

APPENDIX A. GEOTHERMAL CASE STUDY PROTOCOL QUESTIONNAIRE APPENDIX B. CONVENTIONAL CASE STUDY PROTOCOL QUESTIONNAIRE APPENDIX C. CONVENTIONAL HVAC SYSTEM QUOTE SHEET APPENDIX D. AVERAGE COST ELECTRICITY AND NATURAL GAS FOR RESIDENCES IN LOUISIANA APPENDIX E. PAYBACK PERIOD CALCULATIONS VITA

ABSTRACT

In the last three decades of the geothermal heat pump (GHP) industry, there has been an urge to present data, especially performance and itemized installation cost, as a plan to reduce the lack of knowledge and trust towards GHP systems for heating and cooling. The potential of GHPs in hot and humid climates is significant [Tao and Zhu, 2012]. However, past research efforts have demonstrated this potential through the use of simulation rather than real-time data. Therefore, the scope of work for this research is to investigate GHP system applications for residential buildings in areas with hot and humid climates. Based on the scope of work, the objective of this research is to determine the cost, energy performance, and the payback period of GHP systems using real data collected from residences in southern Louisiana.

To achieve this objective, the research answered the following questions: RQ1: How do geothermal heat pump systems perform in terms of energy usage and costs in hot and humid climates when compared to traditional HVAC systems? RQ2: What is the payback period for installing a GHP system in hot and humid climates for a residential dwelling?

A case study protocol was developed to collect building information, HVAC installation cost, financial incentive, energy usage, and end-user satisfaction data from residential buildings in Louisiana, three with GHP systems and two with conventional air-source systems. The electricity consumption and usage cost between the samples were compared using ANOVA in SPSS.

This study concludes that tax credits can make GHP systems more affordable to average size households as the payback period can be four times longer without the tax credits, (note: this the thesis focuses on data obtained from Louisiana, a southern state within the United States where cold weather is rarely forecasted. although the contractor base for GHPs in southern Louisiana is in its infancy, homeowners feel more satisfied with the performance of a GHP system than with the performance of a conventional air-source system.

CHAPTER 1: INTRODUCTION

1.2. Background

Energy is necessary for almost all facets of human existence: oil and gas for cooking and heating; electricity for cooling, lighting, appliances and machines; gasoline and diesel fuel for transportation; and a mix of energy supplies for a myriad of other purposes [2008 APS Energy report]. In terms of economics, energy is key to macroeconomic growth. In most cases, energy consumption increases as societies become more developed and their standard of living increases. The United States, for example, with the highest per capita gross domestic product reported by the World Bank, consumed 97.8 quads (1 quad=1015 Btu) of energy in 2010 which represented 19% of all global consumption, making the US the second-largest share after China [2011 Buildings Energy Data Book, p.1-7].

Americans spend 90% of their time indoors, working, living, shopping and entertaining in buildings that consume enormous amounts of energy. Since most of their energy comes directly or indirectly from fossil fuels, buildings are responsible for large quantities of greenhouse gas (GHG) emissions [2008 APS Energy Report]. According to the U.S. Energy Information Administration (EIA), in 2010 the building sector consumed 40% of total primary energy but consumed 74% of all electricity usage.

Heating Ventilating and Air Conditioning (HVAC) systems are typically one of the largest components of building energy consumption, accounting for 42% of residential primary energy use and 32% of commercial building primary energy use [2011 Buildings Energy Data Book, tables 2.1.6 and 3.1.5]. Yet, a large fraction of the energy delivered to buildings is wasted because of inefficient building technologies and systems [2008 APS Energy Report]. In order to improve energy efficiency and savings, new technologies and systems must be explored, particularly on the HVAC side of energy consumption. The U.S. Department of Energy Building Technologies Program (DOE-BTP) identified geothermal heat pumps as one such high-impact technology that can substantially reduce energy consumption and peak electrical demand in residential and commercial buildings.

Geothermal Heat Pumps (GHP), also known as Ground-Source Heat Pumps (GSHP) are among the most efficient, with annual energy consumption as little as half that of conventional systems. When compared to a stereotypical Air-Source Heat Pump (ASHP) or typical furnace with a split-system air conditioner, the primary energy savings are in the range of 30% to 60%. In addition, for many commercial and residential applications, GHPs also provide water heating via a desuperheater [2012 DOE-BTP R&D Roadmap].

While GHPs are more energy-efficient compared to the best available ASHPs and forced-air furnace systems, national impacts also depend on likely market penetrations of each alternative. Multiple studies identified three key barriers that inhibit GHP widespread industry growth:

High first cost for ground loops Low market awareness and lack of knowledge/trust in GHP benefits, and… Infrastructure limitations including a limited number of qualified installers.

The purpose of this study is to address the second identified key barrier, especially in U.S. Southern states, by developing an economic feasibility analysis to compare the energy performance and cost of GHP systems with other conventional air-source HVAC systems installed in residential buildings in Southern Louisiana to determine the benefits and challenges of GHPs in climates that experience higher cooling loads that heating loads. This research employs utility and monitored data of actual GHP systems to calculate the payback period on the investment of such systems. The study will compare the payback period obtained with and without considering the Federal residential tax credit.

To address the purpose of this research, this thesis is organized into six chapters and altogether describes the work that has been completed in order to achieve the objectives and answers the research questions for this research project. The following information briefly describes the contents of each chapter:

1.2. Report Organization

Chapter 1, the current chapter, provides a background of building energy consumption and introduces GHPs as well as the benefits and barriers of GHPs in the United States market. This chapter also briefly explains the motivation that precedes this research, the purpose and the main tasks.

Chapter 2 presents a substantial collection of literature review, which contains the most important basic theory behind GHP systems. The content of this chapter is meant to expand the knowledge that homeowners or any person have in regards to non-conventional HVAC systems. This chapter attempts to clarify certain common misinterpretations of GHP system applications/limitations, particularly, applications based on geography and climate. Chapter 2 also highlights the difference between this study and previous similar research projects and how this difference intends to improve the body of knowledge.

Chapter 3 describes the methodology used for this research. The third chapter provides the detailed steps for conducting this research from the initial literature review through the analysis and discussion of results and conclusions.

Chapter 4 summarizes the general information of each case study and analyzes the information collected in each case study from surveys (Appendix A) and interviews.

Chapter 4 additionally presents the results of the statistical tests and payback period return on investment evaluation conducted based on the energy usage and cost data collected from each case study.

Chapter 5 discusses the results obtained in the analyses presented in the previous chapter. The author utilizes this section to provide insight from the results observed in each case the study, especially in cases where the system design was determined to be non-ideal for the the facility, oversized, or unnecessarily complex. The discussion goes beyond numbers and presents information that highlights specific components of GHP systems in residential homes found in southern Louisiana as well as the perceived satisfaction in using a GHP system.

Chapter 6 provides a brief summary of the knowledge gained from this study as well as reviewing the goals achieved and lessons learned in conducting this research project. This chapter presents the conclusions and limitations of this study and suggests possible future research.

CHAPTER 2: LITERATURE REVIEW

2.1. Overview

Geothermal energy or geothermal heat is the thermal energy stored below the surface of Earth. Geothermal heat recovered from different depths below the surface provides unique and different possibilities of utilization. Among the advantages of geothermal energy is that the source does not depend on the weather and is available 24 hours per day and 7 days a week. Consumed geothermal energy is renewed and replenished from the internal planetary reservoir and is unlimited from a human perspective if used sustainably. Using renewable energy resources sustainably means that the rate of consumption is equal or smaller to the rate of renewing the process [Stober and Bucher, 2013].

Geothermal energy is used in three main ways: electricity generation, direct heating, and indirect heating and cooling via geothermal heat pumps (GHPs). These three processes use high, medium, and low temperature resources, respectively. High and medium temperature resources are usually the product of thermal flows produced by the molten core of the Earth, which collects in areas of water or rock. Low temperature resources are near ambient temperature and are mostly attributable to solar energy absorbed at the ground level and ambient air. High and medium temperature thermal resources are often deep within the earth, and the depth affects whether they can be exploited economically as drilling and other extraction costs can increase substantially when drilling at great depths [Self et al., 2012]. Low temperature geothermal resources are abundant and can be extracted and utilized in most locations around the world. Extracting such thermal energy is relatively simple because the depths involved are normally small. Heat pumps extract low temperature thermal energy and raise the temperature to that required for practical use [Self et al., 2012].

In terms of using geothermal energy, indirect heating and cooling using GHP technology is not the same technology as geothermal power generation, also known as enhanced geothermal systems (EGS), in which the extreme heat of subsurface geological processes is used to produce steam and ultimately to generate electricity. Nor is it the same as the direct use of geothermal heat, in which moderate-temperature geothermal sources such as hot springs are used directly to heat greenhouses, aquaculture ponds, and other agricultural facilities. GHP systems use the only renewable energy resource that (a) is available at most building’s point of use, (b) is available on demand, (c) cannot normally be depleted (assuming proper design), and (d) are potentially affordable [Liu, 2010].

The biggest difference between GHP and conventional space conditioning and water heating systems is that, instead of rejecting heat from the buildings to the ambient air (in cooling mode) and extracting heat from fossil fuel combustion, electricity, or the ambient air (in space and/or water heating modes), a GHP rejects heat to or extracts heat from various ground resources, including the earth, surface water, recycled gray water, sewage treatment plant effluent, stormwater retention basins, harvested rainwater, and water from subsurface aquifers– either alone or in combination with conventional heat addition and rejection devices in a hybrid configuration [Liu, 2010].

GHPs are becoming more common as the costs of energy and equipment maintenance rise. When properly designed and installed, GHPs not only reduce energy use, but lower maintenance costs and extend equipment life since they have no exposed outdoor equipment. They are very simple devices and have only a slight difference from traditional heat pumps [Kavanaugh, 2006].

Finances of course are a key issue. Although GHPs need considerable initial investment (higher than common HVAC systems), in theory the overall performance is more favorable. The higher installation cost is due to the additional ground and site work (usually drilling and completion activities) and components (heat pump, connections, and distributors). On the other hand, running costs for GHPs are generally low, as usage is mainly electricity for operating the heat pumps and circulation pumps [Rybach, 2012].

Current GHP research and development efforts focus on reducing installation costs through advanced design and installation configurations and approaches. Additionally, many organizations, including the Department of Energy-Building Technologies Program (DOE-BTP), are focusing efforts on innovative financing approaches to defer or reduce upfront costs.

2.2. Geothermal Heat Pump System Components

A GHP system, in its most basic elements, consists of a ground loop, a heat pump, and a heating/cooling distribution system. This section will review the basic principles of the airconditioner and the fundamentals of heat pumps, along with introducing the various types of ground loops and the different configurations available.

2.2.1. Indoor Components

2.2.1.1. Heat Pump

To understand how GHPs work we need to start from the basics: the air-conditioner. The air-conditioner, also known as the refrigeration cycle, consists of several primary components and four primary functions as shown in Figure 2.1.

Figure 2.1 - Simple Vapor-Compression Refrigeration Cycle

Figure 2.1. Simple Vapor-Compression Refrigeration Cycle (Adapted from: Kavanaugh, 2006)

The compressor (shown between points 1 and 2 in Figure 2.1), driven by an electric motor, is typically located outdoors, and “sucks” the refrigerant from point 4 through tubing in the evaporator coil. This action causes the liquid refrigerant to evaporate and become cold (≈45°F). The evaporating refrigerant inside the tubes cools the air being circulated over the outside of the tubes and fins by the indoor fan. In order to move the refrigerant from point 1 to point 2, it must be raised to a higher pressure by the compressor. The compressor causes the refrigerant to become a hot and high pressure vapor. The hot refrigerant vapor is sent through the tubing inside the condenser. Outdoor air circulated by a fan cools the refrigerant and causes it to return to a liquid (condense). Even though the outside air may be warm (80-100°F) it is cooler than the hot refrigerant (100-160°F). The warm liquid leaving the condenser at point 3 passes through an expansion valve device which lowers the refrigerant pressure before it returns to point 4 to repeat the cycle [Kavanaugh, 2006]. In water cooled or geothermal systems, a pump is used rather than an outdoor fan. Figure 2.2 shows the primary components of a water source air-conditioner followed by a description of the cooling-only cycle.

Figure 2.2 - Water Source Air Conditioner

Figure 2.2. Water Source Air Conditioner (Adapted from: Kavanaugh, 2006)

The cycle of a water source-air conditioner in cooling-only mode is basically the same as the one described on the previous page except for the location of the compressor and the replacement of the outdoor fan with a pump. In this case, the compressor is located indoors and the use of a pump changes the process from points 2 to 3.

After the refrigerant is compressed, the hot and high-pressure refrigerant vapor is sent through the outside tubing of a tube-inside-tube water coil condenser. Water is circulated by the pump through the condenser coil and outdoor water loop (ground loop, lake loop or water well) and cools the refrigerant causing it to return to a liquid (condense).

The water is typically 50°F to 90°F and is cooler than the hot refrigerant (90°F to 140°F). The liquid refrigerant leaving the condenser from point 3 passes through an expansion device which lowers the refrigerant pressure before it returns to point 4 to repeat cycle [, Kavanaugh, 2006]. Heat naturally flows “downhill”, from higher to lower temperatures. A heat pump is a machine which causes the heat to flow in a direction opposite to its natural tendency or “uphill” in terms of temperature. Because work must be done to accomplish this, the name heat “pump” is used to describe the device. In reality, a heat pump is nothing more than a refrigeration unit. Any refrigeration device (window air conditioner, refrigerator, freezer, etc.) moves heat from a space and discharges that heat at higher temperatures. One primary difference between a heat pump and a refrigeration unit is that heat pumps are reversible and can provide either heating or cooling to the space [Rafferty, 2001].

A heat pump is merely an air-conditioner with extra four-way reversing valve that allows the condenser (hot coil) and evaporator (cold coil) to reverse places in winter. Figure 2.3 and Figure 2.4 shows the reversing valve in heating mode and cooling mode respectively. The valve permits the refrigerant to travel from the indoor air coil to the compressor while in cooling mode and from the water coil to the compressor while in heating mode.

In heating mode, the reversing valve slides to a position that routes the hot refrigerant from the compressor through the top port to the indoor air coil (now the condenser) through the right bottom part of the reversing valve. Thus the air circulated by the indoor fan will be heated. After passing through the expansion device, the refrigerant enters the outdoor coil at a low temperature. Because the temperature of the refrigerant is low, heat can be transferred from the water to the refrigerant inside the evaporator [Kavanaugh, 2006].

Figure 2.3 - Heating Cycle

Figure 2.3. Heating Cycle (Adapted from: Oklahoma State University)

Figure 2.4 - Cooling Cycle

Figure 2.4. Cooling Cycle (Adapted from: Oklahoma State University)

The advantage of using water from the ground or lake/pond is that backup heat is often unnecessary. If the water loop is connected to a properly sized ground or lake coil loop, the heating efficiency is exceptionally high when compared to conventional systems. Figure 2.5 presents a more anatomically correct diagram of a “water-to-air” heat pump. Note that an additional heat recovery coil or desuperheater can also be added to the GHP unit to partially heat domestic hot water (DHW) with waste heat in the summer and with excess heating capacity in the winter [Kavanaugh, 2006].

However, the heat pump only produces DHW when it is running for either space heating or cooling purposes. The percentage of annual DHW needs met depends upon the run time of the heat pump and DHW usage patterns in a facility. The largest savings occur in applications where the heat pump runs a large number of hours, particularly in cooling mode, and where alternative water heating is by electric resistance. The capacity of the desuperheater is directly related to the heat pump capacity. For an average family size (3.5 persons) with a 3-Ton heat pump, the annual savings on DHW would be in the range of 25% (colder climates) to 35% (warmer climates) or about $100 – $150 per year at $0.08/KWh [Rafferty, 2001].

Figure 2.5 - Ground-Source Geothermal Heat Pump Unit

Figure 2.5. Ground-Source “Geothermal” Heat Pump Unit (Adapted from: Kavanaugh, 2006)

One of the most important characteristics of heat pumps, particularly in the context of home heating/cooling, is that the efficiency of the unit and the energy required to operate it are directly related to the temperatures between which it operates. In cooling, the inlet fluid temperature should be as low as possible to reduce heat pump energy consumption. While in heating mode the inlet fluid temperature should be as high as possible. In other words, the temperature lift across the heat pump which is the difference between the source and load temperatures should be minimized. This is important because it forms the basis for the efficiency advantage of GHPs over air-source heat pumps (ASHPs).

An ASHP must remove heat from cold outside air in the winter and deliver heat to hot outside air in the summer. In contrast, the GHP retrieves heat from relatively warm soil (or groundwater) in the winter and delivers heat to the same relatively cool soil (or groundwater) in the summer. As a result, GHP, regardless of the season is always pumping the heat over a shorter temperature distance than the ASHP. This leads to higher efficiency and lower energy use. The most commonly used GHP unit is the single package water-to-air heat pump as shown in Figure 2.6. All of the components are contained in a single enclosure about the size of a small gas furnace. The single package design is a major advantage over the so-called split system used for ASHP. The lack of an outside unit reduces the amount of refrigerant required and the potential for leaks, which results in a major enhancement to reliability.

Virtually all GHP units use refrigerant R-22 which is considered a transition refrigerant with an ozone depletion value (ODP) of 0.05. High efficiency equipment generally contains a high efficiency compressor, larger air coil, higher efficiency fan motor, and sometimes, a larger refrigerant-to-water heat exchanger. Manufacturers also offer split systems, water-to-water heat pumps, multi-speed compressors, dual compressor, and rooftop versions of this equipment to suit various applications [Rafferty, 2001].

Figure 2.6 - Single Package Water-to-Air Heat Pump

Figure 2.6. Single Package Water-to-Air Heat Pump (Source: WaterFurnace)

2.2.1.2. Distribution System

The second indoor component of a geothermal system is the distribution system that is responsible for moving conditioned air from the heat pump throughout the home. The typical thermal output system in a residential application transfer heat to either a forced air heating/cooling system (a “water-to-air” system), or to a hydronic system for radiant heating, pool heating, or domestic water heating (a “water-to-water” system).

A typical residential system has a 3-ton (36,000 Btu/hr) thermal capacity. Depending on the layout of a given building and the nature of the heating/cooling loads, the building may use either a distributed architecture or a centralized architecture. A distributed architecture uses many small units, each one serving a specific zone or subset of the building space, while a centralized architecture uses fewer and higher capacity units in combination with a traditional distribution system [Goetzler et al., 2012].

Whether it is a forced air or radiant system, an efficient HVAC distribution system is very important for a high performance geothermal system. For radiant systems, pipes must be properly sized, have proper spacing, and have a good thermal connection with the room. For air distribution systems, ducts must be tightly sealed and efficient [Home Owner Guide to Geothermal Heat Pump Systems, Ground Energy Support].

2.2.1.3. System Controls

The most basic type of control system is a heating and cooling thermostat. Programmable thermostats, also called setback thermostats, can be energy savers for homes by automatically adjusting the temperature setting when people are sleeping or not at home. Most of the common Wi-Fi thermostats (e.g. Ecobee®, Nest®) are compatible with geothermal heat pumps. The thermostat selected should be designed for the particular heating and cooling equipment it will be controlling, otherwise it could actually increase energy bills.

A thermostat should be located centrally within the house or zone on an interior wall. It should not receive direct sunlight or be near a heat-producing appliance. A good location is often 4 to 5 feet above the floor in an interior hallway near a return air grille. The interior wall should be well sealed at the top and bottom to prevent circulation of cool air in winter or hot air in summer [Louisiana Department of Natural Resources, 2010].

2.2.2. Outdoor Components

2.2.2.1. Ground Heat Exchanger

Unlike an ASHP with its outside coil and fan, a GHP also called Ground-Source Heat Pump (GSHP), relies on fluid-filled pipes buried beneath the earth as a source of heating in winter and cooling in summer. In heating mode, the GHP pulls heat from the earth and transfers this heat to the indoor air or water, and in cooling mode the heat pump pulls heat from the indoor air and rejects the heat into the ground. This transfer of heat is called Geo-Exchange. The primary undisturbed temperature of the ground heat source is given by the thermal properties (heat conductivity and heat capacity) and hydraulic properties (water and air content) of the subsurface. High porosity and void content of the ground typically reduce the heat conductivity. For example, if the groundwater table is low and the ground is in the vadose (unsaturated) zone instead of the saturated zone, the voids are filled with air instead of water which decreases the heat conductivity of the system [Stober and Bucher, 2013].

Therefore, it is important for engineers to perform a ground thermal conductivity test prior to starting the design of the ground heat exchanger (GHX). In general, steadily flowing groundwater can be expected to be beneficial to the thermal performance of closed-loop ground heat exchangers. The transfer of heat away from the borehole field via a fluid flow will alleviate the possible buildup of heat around the boreholes over time [Chiasson et al., 2000]. The climatic conditions at a home’s location also affect the temperature of the ground heat source. However, a few feet below the surface of the earth the ground remains at a relatively constant temperature all year round. Depending on the latitude of a location, ground temperatures can range from 45 F (7 °C) to 75 F (21 °C). Similar to a cave, the ground temperature is warmer than the air above it during the winter and cooler than the air in the summer [U.S. Department of Energy].

Eliminating the outside equipment means higher efficiency, less maintenance, greater equipment life, less noise, and stronger resilience [Gregor, 2012]. The buried piping in geothermal systems usually has a 25-year warranty. Most experts believe the piping will last longer, because it is made of durable plastic with heat-sealed connections, and the circulating fluid typically has an anticorrosive additive. The actual costs of GHPs vary according to the difficulty of installing the ground loops as well as the size and features of the equipment. Proper installation of the geothermal loops is essential for high performance and the longevity of the system. Therefore, qualified and experienced geothermal heat pump contractors should be used for installation [Louisiana Department of Natural Resources, 2010].

2.2.2.2. Type of Ground Loop

Ground source heat pumps are generally classified by the type of ground loop. Selection of one over another type of ground loop depends mostly on the site characteristics, local regulations, and contractor availability.

Closed-loop heat pumps, also known as ground-coupled heat pumps (GCHPs), are the most common system type. Energy transfer in a GCHP involves four media: indoor air, the refrigerant gas, water in the loop, and the earth mass. Energy must pass through three heat exchangers: the indoor air-to-refrigerant coil, the refrigerant-to-water coil, and the water-to-earth pipe wall.

In the cooling mode, thermal energy flows from the indoor air to the refrigerant, to the loop water, and to the earth. Electric energy that powers the compressor enters the refrigerant gas as heat of compression and sensible heat from the motor and passes on to the earth. The total heat rejected to the earth is the sum of the heat absorbed from the indoor space plus the electrical energy needed to power the compressor.

In heating mode, the compressor heat energy goes into the indoor space along with the heat absorbed from the earth. For every unit of electrical energy needed to drive the heat pump compressor, three to four additional units of heat energy are absorbed from the earth [Braud, 1992]. The Ground heat exchanger (GHX) loop pipe material is typically high-density polyethylene (HDPE). The heat pump controller operates the pumps to circulate the water/refrigerant solution throughout the GHX as necessary to meet the required heating or cooling load. In colder climates, water is usually mixed with refrigerant to prevent the water from freezing. Closed-loop GHXs can have either a vertical, horizontal, or slinky-like configurations, which are laid in the ground or occasionally in a pond or lake. The vertical configuration consists of a loop that runs down the length of a vertical borehole and returns to the top. Each ton of capacity typically requires a single borehole of approximately 150 to 220 feet deep [Rafferty, 2008]. The vertical loop has a smaller ground surface area requirement, typically 200-400 ft² (5- 10 m²/kW), which makes it more feasible for smaller properties but it adds on significant drilling costs to the total installation cost of the system [ASHRAE, 1995].

The major advantage of a vertical loop configuration is that it places the loop in a much more thermally stable zone as the deeper the boreholes, the ground temperature is more consistent. Thermal advantages of the vertical configuration over the horizontal configuration are less of a factor in moderate climates. The more extreme the climate, either in heating or cooling, the greater the advantage of the vertical system [Valizade, 2013].

Horizontal loops lie in trenches four to six feet deep and require 125 to 300 feet of trench per ton of cooling/heating capacity delivered [Rafferty, 2008]. This type of configuration usually represents a less expensive option since it involves less digging. On the other hand, it requires much more space and the ground temperature is more exposed to seasonal fluctuations. The length of pipe necessary is a function of system size, climate, soil/rock thermal characteristics and loop type. The ground surface area for a typical horizontal loop ranges from 2000 ft² to 3500 ft² per ton (50-90 m²/kW) [ASHRAE, 1995].

A variation of the horizontal loop is the spiral or “slinky” loop configuration in which the piping is laid out in an overlapping circular fashion. This configuration requires less ground area but more pipe length and pumping energy than a basic horizontal setup [Valizade, 2013]. Figure 2.7 shows the three different loop configurations, vertical, horizontal and slinky, within the same category of GCHPs. Figure 2.7. Closed-Loop or Ground-Coupled Heat Pumps (GCHP) (Adapted from: Kavanaugh and Rafferty, 1997)

Figure 2.7 - Closed-Loop or Ground-Coupled Heat Pumps (GCHP)

Open-loop systems, also known as ground-water heat pumps (GWHP), pump ground water from a well into the heat pump’s heat exchanger and then re-inject the water back to the aquifer via a second well. In some applications, regulations allow the building owner to reject water into an existing body of surface water, thereby avoiding the need for an injection well.

Surface disposal is the least expensive option; but, even if a disposal well is required, the capital cost is likely to be much less than the cost of a closed loop ground coupled heat pump system. Water quality is also an important issue. Since the water is used directly in the heat pump, the issue of corrosion and/or scaling can be a problem. If the water is hard (>100 ppm of calcium carbonate) or contains hydrogen sulfide, a closed loop system would be a better choice. If the water is good quality and the house is to be served by a well for domestic water, serious consideration should be given to the open loop approach. Figure 2.8 shows the two configurations for GWHPs, one as a two well and the other as a single well with surface disposal [Goetzler et al., 2012]. Figure 2.8. Open-Loop or Groundwater Heat Pumps (GWHP) (Adapted from: Kavanaugh and Rafferty, 1997)

Pond/lake configurations, also known as surface-water heat pumps (SWHP), can use either open-loop or closed-loop architectures. The latter often uses a submerged “slinky” configuration to exchange heat with the water at the bottom of a pond or lake [Goetzler et al., 2012] as shown in Figure 2.9. Figure 2.9. Lake/Pond or Surface Water Heat Pumps (SWHP) (Adapted from: Kavanaugh and Rafferty, 1997)Figure 2.9 - Lake Pond or Surface Water Heat Pumps (SWHP)

Direct Exchange (DX), also known as Direct GeoExchange (DGX) systems are a niche form of closed-loop system that circulate refrigerant from the heat pump directly through buried metal tubing instead of using a secondary glycol/water loop. Advanced DX systems are generally more efficient than systems that use a conventional ground loop. This efficiency gain is due to the lack of a water-circulation pump, which directly reduces electricity consumption, and the lack of a water-to-refrigerant heat exchanger, which decreases the temperature lift. DX loops are also appealing due to lower installation costs. The ground loop itself is smaller and requires less land area. However, DX systems present many technical challenges for designers, installers and building owners. For example, underground leaks of refrigerant pose serious performance and environmental concerns, in addition to the high cost and complexity of locating and repairing such leaks [Goetzler et al., 2012].

Figure 2.8 - Open-Loop or Groundwater Heat Pumps (GWHP)

Estimates indicate that for offices and other similar building types, hybrid systems may provide benefits across the majority of climate regions. Hybrid configurations use a ground loop to meet the entirety of the smaller load in terms of heating and cooling load (most U.S. commercial applications are cooling-dominated). Figure 2.10 shows an example schematic of a hybrid system that utilizes a cooling tower to supplement the ground loop during the cooling season.

Figure 2.10 - Schematic of Hybrid GHP

Figure 2.10. Schematic of Hybrid GHP (Adapted from: Goetzler et al., 2012)

Some large buildings now have systems that use a variety of alternative ground-heatexchanger architectures, including flooded-mine water, municipal wastewater systems, standing column wells, and combinations of various water sources. Despite the need for custom engineering design for each system, utilizing such alternative heat sinks/sources enables greater energy savings and reduces overall costs [Goetzler et al., 2012]. Table 2.1 summarizes the type of ground loops available for GHP systems.

Table 2.1 - Summary of Type of Loop for GHXs

* Hybrid systems can use any type of loop (usually supplement system with cooling tower)

2.2.3. Equipment Sizing

Typically, energy efficient homes require less demand for heating and cooling; so cost savings may be realized by installing units that are properly sized to meet the load requirements. Because energy bills in more efficient homes are typically lower, high efficiency systems may not provide as much annual savings on energy bills and may not be as cost effective as compared to less efficient houses.

It is important to size GHP systems properly as oversized equipment cost more to install, can waste energy and increase energy bills, and may decrease comfort such as providing inadequate dehumidification [Louisiana Department of Natural Resources, 2010]. Therefore, use a sizing procedure such as:

Calculations in Manual J published by the Air Conditioning Contractors Association. Procedures developed by the American Society of Heating, Refrigeration, and Air

Conditioning Engineers (ASHRAE). Software procedures developed by electrical or gas utilities, the U.S. Department of Energy, HVAC equipment manufacturers, or private software companies.

The heating and cooling load calculations rely on the size and type of construction for each component of the building envelope, as well as the heat given off by the lights, people, and equipment inside the house. If a zoned heating and cooling system is used, the loads in each zone should be calculated separately.

Proper sizing also includes designing the cooling system to provide adequate dehumidification. In humid climate, such as the Southern United States, it is critical to calculate the latent load (the amount of dehumidification needed for the home). If the latent load is ignored, the home may become uncomfortable due to excess humidity. The Sensible Heating Fraction (SHF) designates the portion of the cooling load for reducing indoor temperatures (sensible cooling).

For example, in a HVAC unit with a 0.75 SHF, 75% of the energy expended by the unit goes towards cooling indoor air. The remaining 25% goes towards latent heat removal or taking moisture out of the air in the home. Many homes in places such as Louisiana have design SHFs of approximately 0.7, that is, 70% of the cooling will be sensible and 30% latent. Systems that deliver less than 30% latent cooling may fail to provide adequate dehumidification in summer [Louisiana Department of Natural Resources, 2010]. Additionally, the size of the system will dictate the size of the Ground Heat Exchanger (GHX).

2.3. Standards and Certifications

2.3.1. Performance Ratings

All heat pumps are rated by the American Refrigerant Institute (ARI). For GHPs, results are published every six months in the Directory of Certified Applied Air Conditioning Products. Cooling performance is defined by the index EER which means Energy Efficiency Ratio. The EER is the cooling effect produced by the unit (in Btu/hr) divided by the electrical input (in Watts), which measures the number of Btu’s removed by one Watt of electricity (Btu/Wh). Electrical input includes operating the compressor and fans, and a “pumping” allowance (for the groundwater or ground loop).

Heating performance is defined by the coefficient of performance (COP). COP is the heating affect produced by the unit (in Btu/hr) divided by the energy equivalent of the electrical input (in Btu/hr) resulting in a dimensionless value. COP also includes allowance for pumping. Both the COP and EER values for GHPs are valid only at the specific test conditions used in the rating.

COP and EER are single point values and therefore cannot be directly compared to seasonal values such as the seasonal energy efficiency ratio (SEER) or the heating seasonal performance factor (HSPF), which are published for air-source equipment. Table 2.2 summarizes typical installed costs for GSHPs and ASHP at typical and best efficiency levels [Rafferty, 2001].

Table 2.2. Typical and Best Efficiency Levels and Installation Cost of GSHP and ASHP (Source: Cooperman et al., 2012)

Table 2.2 - Typical and Best Efficiency Levels and Installation Cost of GSHP and ASHP

2.3.2. Heat Pump Efficiency Standards

There are a few industry standards that specify the minimum energy efficiencies of GSHP units in ground water and ground loop applications, including ASHRAE standards 90.1 (2010) and 189 (2010), as well as the Energy Star standards of the Environmental Protection Agency (EPA).

Heat pump efficiencies shall be measured in accordance with the ISO/AHRI/ASHRAE

Standard 13256-1 (for water-to-air heat pumps) and 13256-2 (for water-to-water heat pumps). Federal and local governments adopt the minimum efficiencies specified in these standards in their related building energy efficiency codes, procurement requirements, and/or qualifications for financial incentives.

For example, the Energy Star certification is a prerequisite for obtaining the federal tax credits for GSHP installations. The Energy Star minimum efficiency requirements for GSHP equipment at various applications are listed in Table 2.3. Currently, more than 3,600 GSHP models have been certified by the ENERGY STAR® standard.

Table 2.3. ENERGY STAR Minimum Efficiency Requirements of GSHP Equipment  Source: www.energystar.gov)

Table 2.3 - ENERGY STAR Minimum Efficiency Requirements of GSHP Equipment

2.3.3. System Design and Performance Evaluation Standards

The International Ground Source Heat Pump Association (IGSHPA), located at Oklahoma State University, originally developed and maintains a series of manuals and tools for the design and installation of GSHP or GHP systems that use closed-loop (horizontal or vertical) GHXs for residential and light commercial buildings. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has published several guides on the design, operation, and commissioning of commercial GHP systems. ASHRAE also maintains a chapter dedicated to the application of GHP technologies in its Handbook of HVAC Applications [ASHRAE, 2011].

The National Ground Water Association (NGWA) has published guidelines for the construction of vertical boreholes for closed-loop GHP systems, the scope of which includes loop field design, test holes and samples, borehole construction, piping, borehole grouting, loop field identification, and permanent loop piping decommissioning [NGWA, 2009]. These publications have been widely accepted by the United States GSHP industry. Properly sizing the closed-loop GHX is very important as this component represents a significant share of the overall system cost. The sizing methodology needs to account for many factors, including the heat rejection and extraction loads, the physical layout of the GHX, the thermal properties of soil/rock formation at the job site, and the thermal properties of the grouting material. Several software programs are used in the U.S. to size closed-loop vertical borehole GHXs, including GLHEPRO, GlheCal, EES, GLD, and GeoDesigner. These software programs require the user to provide building heating and cooling loads at design conditions and estimates of the cumulative loads.

In addition, these software programs cannot perform a comprehensive energy analysis of a whole building with a GHP system. There are a few integrated simulation tools, such as eQUEST, TRNSYS, and EnergyPLUS, that can be used in sizing the GHX and optimizing the design of GHP systems [Liu et al., 2015].

2.3.4. Professional Certification Standards

Proper professional licenses or certifications are usually required in the U.S. to design and install GHP systems, especially for commercial projects. In all states, it is required that designers of GHP systems must be registered Professional Engineers, and in some states they must also be accredited by IGSHPA as Certified Geo Exchange Designers (CGD). Many states require that ground loop installers be IGSHPA-accredited installers and/or drillers and that the installer of the indoor portion of the GHP system be an HVAC technician certified by the Air-Conditioning Contractors of America. Recently, the Geothermal Exchange Organization developed the first national certification standard for all the disciplines involved in GSHP projects [Liu et al., 2015].

2.4. Geothermal Heat Pump Market Overview

2.4.1. Global Market Development

The growing awareness and popularity of GHPs has had a significant impact on the direct-use of geothermal energy. The installed capacity grew 1.51 times from 1995 through 2015 at a compound annual rate of 8.65%. This is due, in part, to better reporting and the ability of geothermal heat pumps to utilize groundwater or ground coupled sources anywhere in the world.

Table 2.4 provides the five leading countries in terms of installed capacity in thermal megawatts

(MWt) of heat pumps. The leading countries in terms of annual energy use in Terajoules per year

(TJ/year) with heat pumps are: China, USA, Sweden, Finland, and Germany [Lund et al., 2015].

Table 2.4. Worldwide Leaders in the Installation of GHPs (Source: Lund and Boyd, 2015)

Table 2.4 - Worldwide Leaders in the Installation of GHPs

Around US$ 20 billion were reported as invested in geothermal energy by 49 countries during the period 2010-2014, for both direct use and power, doubled the amount from 2005 to 2009 for 46 countries. The average was US$ 407 million per country, with countries investing over US$ 500 million (or US$ 100 million per year) being: Turkey, Kenya, China, Thailand, USA, Switzerland, New Zealand, Australia, Italy and South Korean (in descending order).

In terms of categories of investment: 28.3% was for electric power utilization in 16 countries, 21.8% was for direct-use in 32 countries, 25.6% was for field development including production drilling and surface equipment in 32 countries, and 24.4% was for R&D including surface exploration and exploratory drilling in 48 countries [Lund et al., 2015]. In regards to U.S. geographical distribution, GHPs are used in all 50 states and the District of Columbia. About 52% of domestic GHPs shipments went to ten states: Florida, Illinois, Indiana, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, and Texas. The split between the cumulative residential and commercial GHPs applications by 2012 is 3.5:1 [Navigant Consulting, 2013]. It is estimated that 75% of residential applications are in new construction and 25% in retrofits of existing homes [Ellis, 2008].

A recent Navigant Research report (2013) indicates that the United States represented 29% of global GHP installations by capacity with 13,564 MWt (3.9 million tons) installed in This corresponds to roughly 199 million m² (2.14 billion ft²) of building floor space [Liu et al, 2016].

In the United States, there are 27 known domestic manufacturers of GHP equipment [US EIA, 2010]. Small packaged or split water-to-air heat pump units with cooling capacities ranging from 0.5 to 20 tons (1.74 – 70 kW) are most common in the United States. The efficiency and applicability of GHP units have been improved in recent years as a result of a number of technological advancements, including inverter-compressor technology with communicating controls, along with improvements and refinements to refrigerant coils and to all aspects of variable-speed motors [US EIA, 2010 and Liu et al., 2015]

A report issued by Priority Metrics Group (2009) estimated that the GHP market in the United States was approximately $3.7 billion in 2009, which includes the costs for design, equipment, and installation. A few surveys [Kavanaugh 1989, Huttrer 1994, Kavanaugh et al. 1995, and Kavanaugh et al. 2012] have been conducted in the U.S. to collect cost information for GHP systems. According to the study [Kavanaugh et al., 2012], the average cost of a commercial GHP system increased by 129% from 1995 to 2012. This same study determined that the cost increase (177%) for the interior portion of the GHP system (including the heat pump and other major equipment, controls, piping, and ductwork) exceeded the cost increase for the closed-loop portion (52%) over the 17 year period.

The typical price, in 2006 dollars, of a GHP system installed in a new home is in the range of $3000-5000 per ton; the average price for large-scale housing retrofits of GHP systems is $4600 per ton [DOD, 2007]. The simple payback period for a GHP retrofit project in the United States is usually 8-14 years [DOD, 2007 and Liu, 2010]. For new construction, the payback period is shorter than retrofits, as a payback period of 5 years or more is common [Hughes, 2008].

The cost of a GHP system in the U.S. is about 2-3 times higher than similar GHP system in China. In China, the GHP industry has experienced explosive growth since 2005 due to strong promotion and financial incentives offered by the Chinese central government for renewable energy technologies such as GHPs. The cumulative building floor space conditioned by GHP systems in China grew from zero to 4.3 billion square feet in just one decade. The high growth rate may even increase in the future because of increased mandatory requirements and governmental investment in fighting the severe air pollution found in China [Liu et al., 2015].

2.4.2. Status of U.S. GHP Industry

The U.S. GHP industry began to take shape in the early 1970s by general contracting and manufacturing entrepreneurs. The GHP industry includes manufacturers of water-source (geothermal) heat pumps, HDPE piping and fittings, circulating pumps, and specialty components, as well as the design infrastructure, an installation infrastructure, and various electric utilities. Currently these infrastructures only exist in some localities, and elsewhere customers lack access to the technology [Hughes, 2008]. The small group of manufacturers presented in Table 2.5 is believed to produce most GHP units. Other major brands, such as Carrier, participate in the GHP market by sourcing water-source heat pump units from other manufacturers. The manufacturing base for HDPE pipe is large and well-established. Circulating pumps, propylene glycol antifreeze, plate heat exchangers, fluid coolers, and many other products used in GHP systems are already massproduced to serve markets much larger than the GHP market [Liu, 2010].

Table 2.5. GHPs and HDPE Pipe Manufacturers

The economic impact of ground-coupled technology is truly unique. It is not sophisticated, high technology. It is good for local business. A new trade – ground loop contracting is needed to provide the ground-coupling. Bore drilling gives work to small water well drillers. Pipe installation, trenching, and other loop work use small contractors and local labor. The dollars the customer invests in ground-coupling feed the local economy instead of paying for a new large distant electric power plant [Braud, 1992].

Some regions of the country have their own regional geothermal professional organizations. Members of these organizations, presented in Table 2.6 are committed to furthering their industry.

Table 2.6. Regional Geothermal Professional Organizations

Table 2.6 - Regional Geothermal Professional Organizations

As seen in the previous table, there is no regional geothermal professional organization representing southern states, even though from a scientific and technical point of view the potential for wide applications of GHP systems in hot and humid climate is significant [Tao and Zhu, 2012]. The IGSHPA provides access to their business directory of accredited installers, designers, and contractors. Table 2.7 summarizes the information found in the IGSHPA database for US southern states.

The number of accredited installers in the state of Louisiana is the second lowest after Mississippi, and in huge disadvantage compared to Texas. These results illustrate the lack of knowledge that HVAC contractors, as much as building owners, have in GHP systems and therefore the inevitable poor market competition within the HVAC industry in Louisiana.

Table 2.7. IGSHPA Business Directory for U.S. Southern States

Table 2.7 - IGSHPA Business Directory for U.S. Southern States

State Accredited Installer Trainer Certified GeoExchange Designer Vertical Loop Installer Certified Geothermal Inspector

In regards to academia, there is not much evidence of previous research work of GHPs in Louisiana, except by an independent study (1998) prepared for the U.S. Department of Energy by Oak Ridge National Laboratory. The study is about the installation of over 4,000 GHPs at the U.S. Army’s Fort Polk military base in Leesville, LA; the world’s largest installation of GHPs at the time (1996).

Smaller and less detailed case studies of GHPs in Louisiana can be found in research work of Braud (1992) and Smilie (1984). Harry J. Braud was a professor in the department of Agricultural Engineering at Louisiana State University, Baton Rouge. Most of his geothermal research publications are from the late 80s and early 90s. Nevertheless, the design of GHPs as well as the market barriers described in the study published by professor Braud has remained very much the same.

In the past decades research efforts regarding GHPs in Louisiana has decreased to almost zero. This might be one of the main reasons for the low awareness of the applications of GHPs in Louisiana, thus, for the low market penetration in this state. Hughes study (2008) surveyed GHP industry experts and were asked to respond the question: What are the key barriers to rapid growth of the GHP industry? The most important identified barrier was the high first cost of GHPs to consumers and the given solution was to assemble independent, statistically valid, hard data on the costs and benefits of GHPs.

Given the need for data, a new sector in the GHP industry emerged. This relatively new sector is composed by companies that specialize in web-based GHP monitoring to track system performance. Ground Energy Support, for instance, developed a monitoring system called GxTrackerTM that monitors the basic operations of geothermal heating and cooling system and displays this real-time information online. The purpose of a monitoring system is to enable homeowners to insure that the heat pump system is providing the optimal return on investment.

2.4.3. Key Barriers

Initial cost and long payback periods clearly limit GHP system acceptance in many markets. Currently in commercial markets, GHPs are primarily limited to institutional customers (e.g., federal, state, and local governments and K-12 schools) that take the lifecycle view of a GHP system. In residential markets, GHPs are limited to a small subset of newly constructed homes that the builder plans to occupy and thus wants to equip with the best available system, and to home retrofits in which the owner plans to occupy the premises long enough to justify the investment [Liu, 2010].

While loop cost appears to be a major reason for higher first cost, the $5,400 “indoor” equipment cost should be approximately the same as the $4,000 typical first cost of a conventional system given the essentially equal complexity of the equipment and installation [Kavanaugh and Gilbreath, 1995]. Many new HVAC market entrants require additional resources and/or knowledge for safe and correct installation. Without knowledge of, and experience with, of GHP systems and equipment, installers are hesitant to advertise and sell such systems. Furthermore, inexperienced designers tend to oversize GHP systems and/or add excessive backup capacity to provide a larger safety margin, but doing so unnecessarily increases their cost [Liu, 2010].

The lack of public awareness and trust in non-conventional HVAC systems directly leads to low motivation to invest in GHP systems. Given the large proportion of unmotivated consumers and inexperienced design and installation professionals, the GHP supply chain must educate consumers and even provide extra technical assistance for the design and installation of GHP systems. These extra selling and training costs are then included in the prices of GHP products [Liu, 2010].

Reductions in GHP system cost, improvements in installation quality, greater competition, and improved market penetration have occurred primarily in the areas that have been involved with GHPs for several years. The first cost of GHPs in areas that do not have established contractors and designers is often prohibitively high. These relatively high costs cannot be economically justified by many potential customers. Thus, the GHP industry in these areas does not develop sufficiently to support loop and HVAC contractors who will invest in the equipment and training necessary to install GHPs effectively [Kavanaugh and Gilbreath, 1995]. Consumers who make purchase decisions based primarily on first cost will not be likely candidates for purchase of higher cost equipment that can save them on operating costs. While part of this barrier can be overcome through greater consumer education and awareness of energy benefits, first-cost barriers must also be addressed directly [Goetzler et al., 2014]. Recommendations are to concentrate on reducing the cost of the components with the greatest potential (heat pumps, indoor installation, and pumps) instead of overemphasize low36 cost loops at the expense of quality. GHP manufacturers have to find a way to reduce costs in order to become more competitive compared to high efficient air-source systems. Additional suggestions are to involve experienced contractors in loop research & development for affordable housing projects [Kavanaugh and Gilbreath, 1995].

2.4.4. Policies and Incentives

State and Federal government organizations typically use tax incentives, such as property and sales tax incentives, and tax credits to offset the costs of purchasing, installing, and/or owning a geothermal heating and cooling system. The residential renewable energy tax credit established by The Energy Policy Act of 2005, initially applied to solar-electric systems, solar water heating systems and fuel cells. However, the Energy Improvement and Extension Act of 2008 extended the tax credit to small wind-energy systems and geothermal heat pumps, effective as of January 1, 2008. The credit was further enhanced in February 2009 by The American Recovery and Reinvestment Act of 2009, which removed the maximum amount for all eligible technologies (except fuel cells), placed in service after 2008 [DSIRE, 2017].

In 2015, the US federal government extended similar tax credits for commercial and residential solar energy installation, but for geothermal heat pumps and other clean energy technologies stopped at the end of December 2016. According to Doug Dougherty, President of the Geothermal Exchange Organization (GEO), geothermal heat pumps are 100% ‘Made in the USA’ with American-made components manufactured and installed by American workers. Without reinstatement and extension of federal tax credits, the entire geothermal supply chain, including manufacturers, distributors, dealers, contractors, installers, drillers – plus all the families and small businesses that they support – will all see loss of investments and jobs [GeoExchange, 2017].

The geothermal industry is currently working towards the reinstitute and extension of commercial and residential installation tax credits geothermal heat pumps through 2021. Table 2.8 presents a few federal policies in place that apply to geothermal heating and cooling technologies (ground source heat pumps, direct-use). Additionally, the Database of State Incentives for Renewables and Efficiency (DSIRE) contains further information on state, local, utility, and federal incentives and policies that support renewable energy and energy efficiency,

Table 2.8. Current Federal Policies for Geothermal Technologies (Source: National Renewable Energy Laboratory, www.nrel.gov)

Table 2.8 - Current Federal Policies for Geothermal Technologies - table 1

Table 2.8 - Current Federal Policies for Geothermal Technologies - table 2

Current Policy Description Applicable Technology

Energy Policy Act of 2005 Residential Renewable Energy Tax Credit 30% residential renewable energy tax credit applies to ground source heat pumps. Effective January 1, 2008 – December 31, 2016. Ground Source Heat Pump Grants/Loans/Loan Guarantees Geothermal projects can receive U.S. Department of Energy Tribal Energy Program grants and U.S. Department of Agriculture Rural Energy for America Program grants. Federal government has been authorized to provide loan guarantees for geothermal energy projects under Title XVII of Energy Policy Act of 2005.

Direct-use, Ground Source Heat Pump Investment Tax Credit 10% investment tax credit for all expenditures on geothermal equipment except those required for transmission. No expiration date. Direct-use, Ground Source Heat Pump Table cont’d. 38 Current Policy Description Applicable Technology Investment Tax Credit/Cash Grant Program Section 1603 of Recovery Act allows taxable entities developing geothermal projects to take the 10% corporate investment tax credit as a cash grant. Direct-use, Ground Source Heat Pump Modified Accelerated Cost Recovery System An IRS-implemented incentive that allows for accelerated depreciation on a 5-year tax schedule. Direct-use, Ground Source Heat Pump Recovery Act Research and Demonstration Recovery Act provides $350 million for geothermal research and demonstration. $50 million available for ground source heat pump demonstration projects. Direct-use, Ground Source Heat Pump

2.4.5. System Financing

High upfront costs continue to be a significant barrier to achieving potential monetary and energy savings from energy efficiency investments across the building sector. Over the past several decades, a number of innovative energy efficiency financing programs have emerged with the intent of reducing the upfront costs for energy efficiency improvements and assisting owners in the residential and commercial building sectors in achieving greater energy savings [ACEEE, 2011].

There are five major energy efficiency finance models prevalent today in the United States:

1) The energy savings performance contract (ESPC) model implemented by an energy service company (ESCO); 2) The energy services agreement (ESA) model; 3) The managed energy services agreement (MESA) model; 4) The property assessed clean energy (PACE) model; and 5) On-bill financing and on-bill repayment (OBF/OBR) approaches [WSGR, 2012].

While many energy efficiency finance options exist, these five models are among those attracting significant interest from both private-sector and public-sector stakeholders. Table 2.9 below summarizes the five emerging energy efficiency finance models.

Table 2.9. Energy Efficiency Finance Models (Source: WSGR, 2012)

Table 2.9 - Energy Efficiency Finance Models

*Municipalities, Universities, Schools and Hospitals (MUSH) market

PACE and On-Bill Finance and Repayment (OBF/OBR) are the only models that target the residential segment. Very few ESCOs work in the residential market, and those that do target larger multi-family and public housing facilities.

Property Assessed Clean Energy (PACE) was developed in 2007 and is an innovative financing mechanism that enables low-cost, long-term funding for energy efficiency, renewable energy and water conservation projects, including geothermal. Depending on local legislation, PACE can be used for commercial, nonprofit and residential properties. Interested property owners evaluate measures that achieve energy savings and receive 100% financing. PACE financing is repaid as an assessment on the property’s regular tax bill for up to 20 years, and is processed the same way as other local public benefit assessments have been for decades. Figure 2.11 shows the basic structure of a PACE model.

Figure 2.11 - Basic PACE Structure

Figure 2.11. Basic PACE Structure (Source: WSGR, 2012)

Energy projects are permanently affixed to a property, meaning that the benefits and obligations can be transferred to a new owner upon sale. Moreover, the annual energy savings for a PACE project usually exceeds the annual assessment payment, so property owners are cash flow positive immediately [www.pacenation.us].

On-Bill Financing for Energy Improvements is another program that is starting to gain in popularity. In this program, electric utilities finance energy improvements and in much the same way as PACE, the cost is spread out over a period of up to 20 years, providing impressive net positive benefits.

2.5. Other Ground-Source Thermal Technology

Thermoactive piles, also known as energy piles, are foundation piles equipped with heat exchanger piping. The piles are installed in ground with poor load-bearing properties. The energy piles use the ground beneath buildings as heat source or sink, according to the season. Concrete has a good thermal conductivity and thermal storage capacity, which makes it an ideal medium as an energy absorber (heat exchanger).

To use these properties for energy foundations, high-density polyethylene plastic pipes of 20 or 25 mm diameter, with 2.0 or 2.3 mm wall thickness respectively, are installed within the concrete. They are placed to form several individual closed coils or loops, which circulate a heat carrier fluid (heat transfer medium) of either water, water with antifreeze (mainly glycol), or a saline solution. The plastic piping can be fixed to the reinforcement cages of the energy foundation in a plant or on the site.

There is no limitation to the depth of piles or diaphragm walls as far as the installation of energy absorber systems is concerned. The energy potential increases with depth: hence deeper foundations are advantageous. The economically minimum length of piles, barrettes or diaphragm wall panels is about 20 ft. [Brandl, 2006]. Khan et al. (2014) performed a study on energy foundation design in south Louisiana using the envelope features of a four-story building and LEED software.

2.6. Performance and Cost Data

The U.S. Department of Energy and the Environmental Protection Agency (EPA) are two federal government institutions that categorize geothermal or ground source heat pump systems as the most efficient, comfortable and environmentally friendly technology for space heating and cooling. Yet, one drawback is that the installation cost of a geothermal system is higher than that of an air-source system of similar heating and cooling capacity. However, the additional costs are claimed to be returned in the form of energy savings within 5 to 10 years. American leaders in geothermal heat pump manufacturing state that along with a proper lifestyle and insulation, homeowners can reduce utility bills up to 70% resulting in a more attractive payback period of 2 to 3 years.

The residential renewable energy tax credit program for geothermal heat pumps expired on December 31, 2016. The reason for this decision is not publicly known. On the other hand, the lack of trust in GHP benefits by consumers, policymakers and regulators can be gradually overcome with the availability of costs and performance data of GHP systems using a representative sample of building applications. [Tao and Zhu, 2012] used simulation program TRNSYS/EnergyPlus in their research paper, Analysis of Energy, Environmental and Life Cycle Cost Reduction Potential of Ground Source Heat Pumps (GSHP) in Hot and Humid Climate, to develop baseline building models and generate pre-retrofit data. Although simulation programs support data collection and analysis, assumed parameters not always coincide with reality. For example, the lighting, equipment schedule and weather data.

Other assumptions valid in simulation but that hardly occur in real life include, boreholes uniformly placed in the cylinder storage, perfectly constant temperatures (no saturation or heat accumulation over periods of time), and overall neglects human error in every possible aspect of the installation. Steve Kavanaugh, Ph.D., Fellow ASHRAE, in his journal article Long Term Performance of GHP Systems, Part 7: Achieving Quality insists in the lack of information especially itemized cost details on recent HVAC system costs and service life. This type of information is very important, and ASHRAE research efforts need to focus more on field surveys that collect performance and cost data for all types of HVAC systems [Kavanaugh, 2013]. Kavanaugh also suggests a framework for possible formats to be included in an “engineering portfolio”.

The idea of an engineering portfolio is to present a succinct listing of results to show how well primary goals have been achieved in previous geothermal projects. Some important information that should be shown in an engineering portfolio are building characteristics and energy conservation features, energy rating, mechanical system cost, and occupant satisfaction.

CHAPTER 3: METHODOLOGY

The content of this chapter describes the research methodology used to conduct this study on the installation and use of GHPs for residential facilities in southern Louisiana. The objective for this research is to determine the cost and energy performance, as well as the payback period return on investment of geothermal heat pump systems using real data collected from residences in southern Louisiana. To achieve this objective, the research will answer the following questions:

RQ1: How do geothermal heat pump systems perform in terms of energy usage and costs in hot and humid climates when compared to traditional HVAC systems?

RQ2: What is the payback period for installing a GHP system in hot and humid climates for a residential dwelling?

To address these questions and to achieve the objectives of this research, Figure 3.1 illustrates the research methodology, which is discussed in the sections below.

Figure 3.1 - Research Methodology

Figure 3.1. Research Methodology

3.1. Define Scope of Work

The focus of this research is to investigate GHP system applications in climates that experience high temperatures and high humidity, which includes the southern Louisiana area.

Based on a report in 2010 by the US. Energy Information Administration (EIA), GHP applications are more concentrated in areas with a cold climate and high population density. With fewer applications found in hot and humid climates, more research is needed in GHP systems used in these climate areas of the US. Further, this study investigated residential buildings rather than commercial buildings as GHP systems in southern Louisiana are difficult to find. The lack of GHP knowledge and contractor base limits GHP system applications more to residences than commercial facilities.

In terms of energy and cost performance of GHP systems, initial cost and energy usage and cost data was collected from residential homes found in New Orleans, Louisiana. Electricity energy usage and cost data was collected for 32 to 42 months from each case study residence via monitoring systems and monthly energy bills from utility companies. A lifecycle assessment of costs was not performed as the GHP systems investigated were installed in 2008 or later, meaning relatively little, if any, maintenance costs were collected from the case study residences. Also, federal incentives such as tax credits were included in the cost analysis. On the other hand, mortgages and other financing programs were not considered due to the variation in financing available to homeowners and difficulty to collect this type of information from homeowners.

3.2. Conduct Literature Review

To begin the research literature review, the author investigated the current status of energy consumption across the building sector, and found GHPs to be one of the emerging technologies with the potential to increase the efficiency of energy usage in residential buildings. The market development of GHPs was also investigated, especially in regions with hot and humid climates. From there, key barriers were identified and measured. Past research work that addressed key barriers such as lack of knowledge/trust towards GHPs were reviewed.

The author realized the benefits on collecting real, current data of cost and performance from installed GHPs, instead of been generated and extracted from computer simulations as in most research studies. Thus, examples of geothermal field surveys were searched and modified for Louisiana residential case studies. The majority of the literature review has been summarized in chapter 2 of this thesis.

3.3. Develop Case Study Protocol

A case study protocol was created and refined based on the intent of this research, using as reference the information from the literature review and the following two reports: Survey and Analysis of Maintenance and Service Costs in Commercial Building Geothermal Systems prepared by Caneta Research Inc. for the Geothermal Exchange Organization, and Analysis of Energy, Environmental and Life Cycle Cost Reduction Potential of Ground Source Heat Pumps (GSHP) in Hot and Humid Climate, prepared by [Tao and Zhu, 2012] from Florida International University for the U.S. Department of Energy.

The protocol, as shown in Appendix A, captures the actual conditions of the residence in question. The protocol provides a method to collect technical and non-technical data required for costs and benefits evaluation of GHP and conventional HVAC systems. Technical data will be employed in quantitative analysis to evaluate the energy savings compared to conventional airsource systems and to calculate the payback period to determine the return a homeowner can expect on their investment into a geothermal heat pump system. Non-technical data will be employed in a qualitative evaluation of end-user satisfaction and psychological barriers to considering and installing GHP systems in southern Louisiana.

3.4. Conduct Case Studies

The data collection process utilizes case studies of actual residential homes using geothermal heat pump systems for heating and cooling purposes found in southern Louisiana. The data collection includes identifying potential homes and homeowner participants, contacting potential participants, gathering geothermal system data from the homes with geothermal heat pump systems, gathering conventional HVAC system data from homes with similar characteristics as the geothermal heat pump system homes for comparison, and analyzing the consumption, cost, and satisfaction data collected from each case.

3.4.1. Identify Potential Participants

Sources that usually provide information on GHP system designers, installers and dealers are: ground source heat pump organizations (IGSHPA, GEOEXCHANGE, etc.), GHP manufacturers, HVAC contractors, and MEP engineering firms, Leadership in Energy and Environmental Design (LEED) projects and non-profit organizations involved in developing sustainable buildings. As this research was performed at Louisiana State University, LSU has an on-campus sustainable home laboratory called the LaHouse Home and Landscape Resource Center.

LaHouse is a resource center and a research-based showcase of home solutions that works closely with local mechanical contractors and other sectors involved in the construction of buildings. LaHouse includes a geothermal heat pump system for heating and cooling loads. Working with LaHouse staff, the researcher collected contact information for homes in southern Louisiana that have geothermal heat pump systems installed for heating and cooling. In addition, the researcher explored non-profit home developers and builders that are or have been working in areas devastated by hurricane Katrina in New Orleans. Two non-profit agencies in New Orleans have been developing sustainable homes, which include alternative energy sources such as geothermal and solar. Each non-profit organization was contacted and information was collected for potential homes with geothermal heat pump systems for use in this study.

3.4.2. Contact Potential Participants

Using the information from LaHouse and the two non-profit organizations, each of the homeowners were contacted via email that included a description of the project, the project goals and objectives, and potential outcomes and benefits. A reminder email was sent two weeks after initial contact if the researcher did not hear back from the potential participants. After receiving responses from the electronic invitation, teleconferences with the homeowners that accepted the participation request were scheduled in order to clarify breadth and width of the project, type of data needed, and roles and expectations on collaboration. After gaining approval from a homeowner, the researcher provided the case study protocol survey to the homeowner to be completed. A total of four homes with geothermal heat pump systems agreed to participate in this study.

3.4.3. Gather Geothermal System Data

The geothermal case study protocol survey prepared for this study is presented in Appendix A. The survey includes six sections:

Building information: Includes the basic information of the residence such as location, type of residence, year constructed, floor area, number of floors, number of occupants, types of light bulbs and number of light bulbs, and type and number of appliances. This section also collected the specific details of the framing and insulation used for walls, roofs, and floors, as well as details on the windows of the structure. GHP system general information: Includes HVAC installation date, type of system, type of loop along with the details of the system such as header diameters and length of pipe installed.

GHP system installation cost: A breakdown of the installation costs for the system. The costs were divided into two parts: ground loop costs and system costs. Each of the costs breakdowns includes the type of material, the quantity of material, cost of the material, and labor costs to install the materials. GHP system maintenance cost: Labor and material costs for scheduled and unscheduled maintenance of the geothermal HVAC system. Available metered data: The electricity usage data (kWh) and gas usage data (CCF) for each case. This information is used in the analysis of consumption, cost, and payback period.

Occupant satisfaction: The overall perception of how satisfied homeowners were of their installed geothermal system in regards to cooling season comfort, heating season comfort, indoor air quality, acoustics, maintenance, and thermostat settings. Each question was ranked using a 5-point Likert scale that ranged from very satisfied (5) to very dissatisfied (1).

As part of the survey, the author offered a non-disclosure agreement which is committed

to protect the participant’s identity and information used in this study. In other words, all the responses were coded and kept confidential. Homeowners were encouraged to complete the survey with as much detail as possible. During the allotted time to complete the survey (two weeks) considerable follow up was necessary. Questions that remained empty such as itemized installation costs, for instance, were answered with the assistance of the GHP system designer/installer.

Additionally, follow up in-person meetings took place to review the case study protocol survey and to collect any other needed information for this study. Participants in this project were met with once or twice for data validation but most importantly to acknowledge the motivation for installing GHPs in their homes. On-site visits supported additional information of the building and helped to obtain a better understanding of the operation and the settings of the GHP systems.

3.4.4. Gather Conventional HVAC System Data

Once the geothermal heat pump system homeowners agreed to participate, the researcher collected the building information using the case study protocol questionnaire. Then, the researcher identified similar homes with conventional HVAC systems and contacted these homeowners via email to see if they would participate in the study.

The case study protocol for conventional HVAC system homes, shown in Appendix B, includes the same six sections as the geothermal case study protocol questionnaire, except that the questions and cost data is in regards to the conventional HVAC system rather than a GHP system. In addition to the cost data provided by the homeowners, quotes were also requested to A/C contractors for reference. The quote sheet developed and distributed to HVAC contractors is provided in appendix C.

3.4.5. Comparison Requirements

In order to compare the actual consumption and cost of a residential geothermal heat pump system to a home with a conventional heat pump system, the researcher had to find homes with conventional HVAC systems that have similar building envelope and characteristics to the GHP system homes in terms of the following aspects:

Type of home Size of the home in square footage Location of the home Year constructed Number of floors Number of occupants Framing structure Insulation used

3.5. Analyze Case Study Data

The first step in the analysis is to determine if the collected data is statistically the same. To do this, an analysis of variance (ANOVA) was implemented. The analysis included the following steps and was conducted using the energy consumption data and the energy cost data for each case sample.

Determine the descriptive statistics for each sample (mean, standard deviation, variance, minimum, maximum, and range).

Test data for normality using MVP Stats statistical program. Test for homogeneity of variance in SPSS using ADA (normal distribution) or ADM (non-normal distribution) values calculated in MVP Stats. Test the mean values using a one-way ANOVA (established homogeneity of variance) or Welch ANOVA (lack of homogeneity of variance) in SPSS.

To obtain the energy cost, electricity and gas usage had to be converted to dollars. The electricity usage (kWh) was multiplied by the average retail price for electricity for Louisiana residential (cents/kWh) costs divided by 100 to obtain electricity cost in dollars. The retail price of electricity in Louisiana was obtained from the U.S. Energy Information Administration official website (www.eia.gov). The gas usage was multiplied.

Then, for each case study, the payback period was calculated by creating a table containing installation (materials and labor) costs along with the usage costs. The payback period, or “break even” point, in which the installation costs and usage costs for the GHP system equal the installation costs and usage costs for the conventional system, was calculated. The payback period provides information on the return on investment period in terms of how long it will take for the initial investment in the GHP system to become more cost effective than a conventional system, taking into consideration the cost of installation and usage costs for the GHP system. Results of the statistical tests and payback period of each case study are presented in chapter 4.

3.6. Discussion and Conclusions

Case studies were discussed independently and cross-compared based on the results from the analysis and occupant satisfaction, and how the contractor base for GHPs in southern Louisiana affected the performance and cost of the GHP systems from the case studies. The discussion of results is found in chapter 5 with conclusions stated in chapter 6.

CHAPTER 4: ANALYSIS

This study collected technical and non-technical data from three homes with GHP systems in operation for 32 to 42 months (GH1, GH2, and GH3). GH2 was retrofitted with geothermal and the rest were new construction. A fourth home with a GHP system was surveyed (GH4). However, collecting specific information on the system as well as accurate cost data proved to be difficult due to the particular situation experienced in this home. Despite the fact that the information was incomplete and not validated, the author considered this particular case useful as an example for best practices to homeowners that consider investing in a GHP system in southern Louisiana.

Table 4.1 summarizes the basic building information and ground loop dimensions of the geothermal samples in the case studies. GH4 has no well or pipe information available. Then, Table 4.2 outlines the basic building information for the conventional HVAC system homes (CH1, CH2, and CH3). It is important to note that CH2 is the same home as GH2 since this sample was retrofitted with a geothermal heat pump system. Using the information collected from the survey shown in Appendix A, the sections below presents both samples (geothermal and conventional systems) included within each case study. The analysis conducted for each case study is presented, with discussions of the findings presented in chapter 5.

Table 4.1. General Information of the Residences with GHP Systems Residence

Table 4.1 - General Information of the Residences with GHP Systems

Table 4.2. General Information of the Residences with Conventional HVAC Systems

Table 4.2 - General Information of the Residences with Conventional HVAC Systems

4.1. Case Study 1

The sections below describe the two sample homes, GH1 and CH1, included with case study 1.

4.1.1. General Information

GH1 is a single-family house on pile/pier foundation built in 2008 in New Orleans, LA. It is a two story, 3-bedroom residence with a conditioned floor area of 1,268 square ft. The building is designed for a total of four occupants and currently is being used as a model home and information center. The overall design of the building complies with a Platinum Certification Level according to the U.S. Green Building Council’s Leadership in Energy & Environmental Design (LEED). The home also has an energy rating certificate granted by Energy Star® that shows a Home Energy Rating System (HERS) Index of 13 or 87% better efficient home comparison.

The construction of GH1 as well as the installed technologies is meant to increase the energy efficiency. Among these technologies the most noticeable are the geothermal heat pump system, 5.3 kW solar electric photovoltaic system, green roof, rain water harvesting tank, and access to real-time information of utility data (water and electricity consumption) through a cloud-based building management platform. The owner of this building received federal incentives for the installation of energy efficient equipment.

CH1 is a single-family house on pile/pier foundation built in 2009 in New Orleans, LA. It is a two story, 3-bedroom building with a conditioned floor area of 1,120 square ft. The residence has a total of three occupants and it is also certified by Energy Star®. The home received the Energy Star certification in 2010, and it is rated with a HERS Index of 17 or 83% better efficient home comparison.

To achieve this energy efficiency, CH1 owns a couple of energy star appliances as well as an electric air source heat pump, 3.0kW solar electric photovoltaic system, and access to realtime information of utility data (water and electricity consumption) through a cloud-based building management platform. The owner of this building received federal incentives for the installation of energy efficient equipment. The following paragraphs will describe the type of material and level of insulation of GH1 and CH1 shell components: interior wall, exterior wall, roof, floor, and windows. In addition to this, other features such as lights & appliance, mechanical (HVAC) system costs, electricity consumption and gas consumption will be reviewed in order to calculate the payback period or return on investment of the geothermal heat pump system installed in GH1.

4.1.2. Building Shell Features

The building shell information includes the framing structure for walls, roofs, and floors, the insulation for walls, roofs, and floors, and window information. The framing material and type of insulation were gathered from blueprints and construction document specifications. Table 4.3 presents the building shell for GH1 and Table 4.4 presents the building shell for CH1.

Table 4.3. Building Shell Features of GH1

Table 4.3 - Building Shell Features of GH1

Table 4.4 - Building Shell Features of CH1

According to GH1 homeowner the house has 29 lightbulbs. Additionally, their Energy Star® home energy rating certificate shows that the building has approximately 75 percent Fluorescent CFL and 25 percent Fluorescent Pin-Based lights. The energy certificate also describes the electricity consumption of the refrigerator in (kWh/yr) to be approximately 485; the dishwasher energy factor as 0.63; the fuel for the clothes dryer and range/oven is natural gas; and the ceiling fan (cmf/Watt) to be zero.

Per the CH1 homeowner, the house has 20 lightbulbs. Additionally, their Energy Star® home energy rating certificate shows that the building has approximately 70 percent Fluorescent CFL and 30 percent Fluorescent Pin-Based lights. The energy certificate also describes the electricity consumption of the refrigerator in (kWh/yr) to be approximately 388; the dishwasher energy factor as 0.46; the fuel for the clothes dryer and range/oven is natural gas; and the ceiling fan (cmf/Watt) to be zero.

To better understand a building’s energy consumption, homeowners were also asked to list the quantity of appliances used in their residence. Table 4.5 outlines the type and number of appliances found in GH1 and CH1. Table 4.5. Appliance Quantities of GH1 and CH1

Table 4.5 - Appliance Quantities of GH1 and CH1 1

Table 4.5 - Appliance Quantities of GH1 and CH1 2

4.1.4. Mechanical Features

GH1 uses a geothermal heat pump system to supply heating and cooling to the house. The installation of the HVAC system was finished in January, 2009. The geothermal heat pump system uses a closed-loop ground heat exchanger. Due to the proximity of the construction site to a levee, there is a limitation in the depth of digging. Therefore, the geothermal pipes are buried horizontally in the backyard in a slinky loop configuration at a minimum of 4 feet below the ground surface as shown in Figure 4.1. The material of the pipes is PEX, which stands for Crosslinked Polyethylene, and the grouting material used for backfilling is bentonite. The spiral of the loop has a typical diameter of 4 ft. and the distance between the trenches is a minimum of 8 ft. The diameter of the water loop pipe is ¾ inches and the diameter of the ground loop header is 1-1/4 inches. The total length of buried piping is approximately 954 ft. The horizontal PEX slinky coils are connected the rainwater harvesting storage tank as shown in Figure 4.2. Additionally, as a backup, the system has a cooling tower that runs an additional loop to keep the rainwater tank cool if needed.

Figure 4.1. GH1 Ground Loop Installation

Figure 4.1 - GH1 Ground Loop Installation

Figure 4.2 - Rainwater Harvesting Tank Used In GH1

Figure 4.2. Rainwater Harvesting Tank used in GH1

The geothermal heat pump unit manufacturer is WaterFurnace®. It is an N-5 Series waterto- air heat pump with a 3-ton capacity of heating and cooling. The model nomenclature NDV026A111CBL indicates that the equipment has a dual-stage compressor, vertical cabinet configuration, unit capacity of 026 MBTUH (≈1,000 BTU/hr), voltage of 208-230V, hot water generation, variable speed electronically commutated motor (ECM) blower, copper water coil, bottom (vertical) discharge air configuration, and left return air configuration.

According to the building plans and specifications package provided by owner, the heat pump unit compressor in cooling mode has 25,800 Total Btu/hr, 19,010 Sensible Btu/hr, and 19.3 EER. While in heating mode it has 27,040 Total Btu/hr and 4.1 COP. The system has also a desuperheater in line from the water heater. The geothermal system pre-heats the water as long as it is running, for this reason the building also has an instant water heater fueled by natural gas with an efficiency rating of 0.90.

The cooling tower is a SHINWA SBC-2ES vertical as shown in Figure 4.3. The fan motor is 115 Volt, 50 Watts, and the water flow is 6.0 gpm. The entering water temperature (EWT) is 90°F and the leaving water temperature is 80°F. The ambient wet bulb temperature is set as 95°F, and the operating weight is 80 lbs. The cooling tower pump is closed-coupled, direct driven, and is located under the deck. The pump operates at 115 Volt, 6.0 gpm, 20 head ft, 1750 rpm, and a minimum of 1/15 hp. A second pump is used for condenser water and is located in the mechanical room on the second story. It operates at 115 Volt, 6.0 gpm, 75 head ft, 1750 rpm, and a minimum of ¼ hp.

Figure 4.3. Cooling Tower used in GH1

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