A Comparative Analysis of Lake Country Lutheran’s Current
Heating System and a Geothermal HVAC System
by
Daniel Radewahn
English 132 Student
for
Dr. Carma Stahnke
Associate Professor in General Studies
Milwaukee School of Engineering
Milwaukee, Wisconsin
May 8, 2009
Letter of Transmittal
May 8, 2009
9617 West Ruby Avenue
Wauwatosa, WI 53225
Dr. Stahnke
MSOE
General Studies Department
1025 North Broadway
Milwaukee, WI 53202
Dear Dr. Stahnke:
Here is my comparative analysis of Lake Country Lutheran’s current heating system and geothermal HVAC. In this report I compare these two systems and decide whether or not Lake Country Lutheran made the correct decision when choosing a more standard forced air HVAC system.
Geothermal heating and air conditioning is extremely efficient and can save consumers large amounts of money in operating costs. However, the up-front cost for these systems is very significant. While they pay for themselves over the long run, this can take anywhere from 10 to 30 years. A decision on whether or not to purchase a geothermal system must be well thought out and many factors must be researched.
I experienced minimal complications when assembling this report. Some of the information acquisition was tedious at times, such as touring the school’s facility, creating visuals from this tour, and acquiring sufficient information from the internet to support my topics.
Thank you for enabling and assisting me in the creation of this report. I am grateful for the additional knowledge I have attained on the topic of HVAC systems in the process, as well as the report writing experience I have gained. This will be extremely helpful in my continued education and throughout my career as a Mechanical Engineer.
Sincerely,
Daniel Radewahn
Table of Contents
Letter of Transmittal
Table of Figures
Abstract
Data Section
Introduction
What are geothermal HVAC systems?
What are the essential parts of a geothermal system?
How do all the parts fit together in a geothermal system?
What are the different types of geothermal systems?
Can a geothermal system be added to an existing building?
What are the benefits and drawbacks of geothermal?
What are the main parts of Lake Country Lutheran’s heating system?
How do these parts fit together in Lake Country Lutheran’s System?
Summary: How do the two systems compare?
Conclusion: Did Lake Country Lutheran make the correct decision?
Works Cited
Works Consulted
Table of Figures
Figure 1: Heat from Sun
Figure 2: Geothermal Loop
Figure 3: Typical Geothermal System
Figure 4: Pond Loop
Figure 5: LCLHS’s "Great Hall"
Figure 6: Rooftop Units
Figure 7: Energy Recovering Ventilators
Figure 8: Water boilers
Figure 9: Hot Water Pumps
Figure 10: Frequency Drive
Abstract
This report is a comparative analysis of Geothermal HVAC and a traditional forced air system which the Lake Country Lutheran building committee decided to install in the school’s new building. The information gathered for this report was accessed mainly through the internet, although a tour of the school’s heating system was also necessary. This report contains a detailed analysis of both geothermal HVAC and Lake Country Lutheran’s system, and concludes by addressing whether or not the school made the correct choice by eliminating geothermal from the building’s design.
Geothermal HVAC systems require very little energy to operate and rely on heat energy from the sun stored in the ground. Almost 50% of the energy from the sun is stored in the ground, representing about 500 times the energy used by the entire world in a year. Geothermal takes advantage of this fact to heat buildings. The building committee, when deciding which type of HVAC system to install, chose a more standard system using natural gas to heat and standard air conditioning to cool. The system they chose is not as energy efficient as geothermal, but provides a unique flexibility that geothermal could not offer.
One of the major drawbacks of geothermal is its enormous up-front cost. Based mainly on this and the flexibility of Lake Country Lutheran’s system, I concluded that the building committee made the correct decision when they chose not to install geothermal. The system they chose is fairly efficient compared to other standard systems. Even though geothermal systems eventually pay for themselves, they do not provide as many options as the school’s system, and are more complicated to run and maintain.
1
Data Section
Introduction
This report is a comparative analysis of Lake Country Lutheran’s heating system and a geothermal system. Lake Country Lutheran is a private high school located in Hartland, Wisconsin. The school has occupied numerous locations as it has grown, and in February, 2009, was moved into a brand new permanent facility. A Geothermal HVAC system was originally in the building’s plans, and a pond was constructed to accommodate this system. However, during the building design and construction process, the building committee decided to replace the geothermal system with a more conventional system to avoid the enormous up-from cost associated with a geothermal system. This report was created with the intent of analyzing the two systems and deciding if Lake Country Lutheran made the correct decision in replacing the geothermal system.
This report is directed toward the entire building committee at Lake Country Lutheran. However, my father, Mr. John Radewahn, was one of the main figures in the decision to avoid geothermal HVAC. Therefore, this report is directed more specifically toward him.
Several methods of research and inquiry were used to assemble this report. Internet sources were researched to obtain information and visuals pertaining to geothermal heating and cooling. These sources consisted of HVAC manufacturing companies’ websites who specialize in geothermal systems. These sources were readily available and provided a good deal of information on the topic of interest. The section of this report discussing Lake Country Lutheran’s system was based mostly on a tour of the school’s facility and a personal interview with Mr. Radewahn. The third type of source referenced in this report areweb sites that discuss HVAC systems in general.
The main points presented in this report pertain to two main topics: Geothermal HVAC and Lake Country Lutheran’s system. For each topic, I present the parts necessary for the system to operate and explain how they fit together. The report continues with a summary and comparison of the two systems. It concludesby addressing if the school made the correct decision, or if geothermal HVAC should have been installed instead.
What are geothermal HVAC systems?
Geothermal is a fairly new concept developed in the early 1970’s, which was a major breakthrough in the heating, ventilating, and air conditioning (HVAC) industry (“Geothermal Heating”). These systems take advantage of a simple temperature difference, using this difference to heat and cool buildings. In both heating and cooling seasons, geothermal systems simply exchange heat with the ground. The geothermal method of heating and cooling employs heat energy stored in the ground. It is estimated that 46-47% of the sun’s heat energy is stored by the earth (see Figure 1), which is approximately 500 times more energy than the entire earth consumes in a year (“About”).This heat energy from the sun is very important. It causes the temperature of the ground a few feet below the surface of the earth to remain fairly constant throughout the year. This is the case even in climates that experience substantial temperature fluctuation, such as Wisconsin (“Geothermal Heat Pumps”).
What are the essential parts of a geothermal system?
Geothermal heating systems are comprised of an extensive loop of tubing below the ground (See Figure 2). This tubing is placed below the frost-line of the particular region, which is usually about 3-5 feet below the surface. At this depth, the temperature remains fairly constant throughout the year, which allows the heat to be properly exchanged during both the heating and cooling seasons. Because the ground at this depth does not freeze during winter, its temperature will be higher than the air’s temperature, creating a proper exchange. During summer, the ground will be cooler than the air, and the heat will again make the desired transfer.
The proper tubing is essential to create an effective geothermal HVAC system. It must have the ability to exchange heat while at the same time remain non-permeable.Copper is a very effective heat exchanger, but is not used in all cases because of its high cost. Plastic is a viable and more cost-efficient substitute in many cases, as it is also a fairly efficient medium for heat transfer, yet does not allow the liquid to escape.
The liquid involved in a geothermal system is also very important. Even though it never comes in contact with any external surface, neither air nor ground, it is the most essential component of an efficient geothermal system. Usually a refrigerant-type product is used because of its ability to absorb and release heat.One website describes this process as follows: “A substance called arefrigerantcarries the heat from one area to another. When compressed, it is a high temperature, high-pressure liquid. If it is allowed to expand, it turns into a low temperature, low pressure gas. The gas then absorbs heat” (“Geothermal Heat Pumps”). The fluid in a geothermal system is very similar to that of a refrigerator (thus the name refrigerant), as they serve essentially the same purpose with their different systems.
Another important part of a geothermal HVAC system is its pumps. Three pumps are used in a typical geothermal system: a ground pump, which circulates the liquid through the ground loop; a heat pump, which transfers the heat in the liquid into the air; and a distribution pump or fan, which circulates the heat through the building using a standard duct system. Varying the speed of these pumps allows the system operator to change the temperature in the building. This aspect makes sense, because the faster the fluid is forced to flow, the more heat will be exchanged.
How do all the parts fit together in a geothermal system?
The entire geothermal system (see Figure 3) requires all the parts listed above: the tubing, liquid, pump, and also the ground, in which the tubing loop is buried. The tubing runs in a large loop through the ground, and is connected to the heat pump. During the winter, the liquid gains heat in the ground loop. This heat is extracted by the heat pump and transferred to the building via a standard duct system and the distribution pump. This distribution pump is very similar to the fan system used in typical HVAC systems. During the summer, the system works in the opposite manner.The heat pump transfers heat from the air to the liquid, and this heat is then transferred to the earth in the ground loop.
What are the different types of geothermal systems?
There are three types of geothermal systems. The least expensive and most commonly used system involves a horizontal placement of tubing in trenches 3-5 feet below the surface. The drawback of this system is it requires a sizeable amount of ground space, which is not present in many residential cases.
In cases where yard space is not available, a more expensive option is available. This is known as a vertical loop system, which employs a single loop of tubing traveling vertically in the ground. In addition to being more expensive, a vertical loop system is also more difficult to repair due to its great distance from the surface of the earth.
The final type of geothermal system employs a pond as a main method of heating and cooling. Pond systems are the least common due to the lack of open water areas near most buildings. These systems utilize the ground around and under the pond as a means of heat transfer. Usually the tubing apparatus is sunk into the pond where it becomes buried by settling dirt and other organic materials. Due to the amount of space available, and the fact that a pond was a required part of the school’s design, this type of geothermal system was considered during the selection process at Lake Country Lutheran.
Can a geothermal system be added to an existing building?
Because geothermal systems use ductwork similar to standard HVAC heating methods, geothermal can be added to buildings fairly simply, provided the building has a functional duct network. A ground loop must be added to the building, as well as the pumps required to run a geothermal system. In some cases, a distribution pump is already in place in the form of a fan, which can lower the installation cost.
If Mr. Radewahn decides to install a geothermal HVAC system at Lake Country Lutheran, he could also consider including a geothermal water heating system, which is a more efficient method of heating water compared to standard natural gas heaters. These are known as “desuperheaters.” During the summer months, the heat extracted from the building is used by these machines to heat water essentially for free. According to the Consumer Energy Center: “In the winter, the desuperheater can reduce water-heating costs by about half, while a conventional water heater meets the rest of the [building’s] needs” (“Geothermal Heat Pumps”).If this type of system were installed, it could save the school additional money on energy costs.
What are the benefits and drawbacks of geothermal?
Geothermal HVAC systems have many benefits, both to the consumer, and to society as a whole. One of the greatest impacts of geothermal systems relates totheir cost efficiency.The only energy consumed by the system is that required to operate the three pumps. Compared to standard HVAC systems, this can be very significant. According to JB Energy Solution, a company that installs geothermal systems: “Heating and cooling with geothermal heat pumps can easily cut energy bills by up to 75%. The only energy used in a heat pump system is for the system to run itself. The heating and cooling is done by moving heat energy from or to the earth, depending on the season. And the earth's energy is, of course, free”(“Geothermal”). Because of this efficiency, geothermal systems actually pay for themselves. Depending on the situation, this can be accomplished in approximately 10 to 20 years (“Geothermal Heat Pumps”). In the case of Lake Country Lutheran, it would probably be closer to 20 years, due to the massive up-front cost.
Another benefit of geothermal systems is their superior comfort compared to standard systems. Because geothermal systems are easier to control, they provide more even heating to the building and move a larger volume of air than fossil fuel systems. According to Energy Star, a government agency that sets standards for safe and efficient consumer products: “Because [geothermal HVAC systems] use the earth's natural heat, they are among the most efficient and comfortable heating and cooling technologies currently available.”(“Geothermal Heat Pumps for Consumers”).
Geothermal systems also benefit society as a whole. Fewer buildings using fossil fuels to heat and cool will ultimately cause the price of these fuels to fall,which in turn will reduce our dependence on foreign oil. In addition to being cost effective, geothermal systems are much cleaner and do not emit greenhouse gasses. Even though heat is transferred to the ground continually throughout the cooling season, this heat is not released into the atmosphere and does not produce greenhouse gases or any other pollutants (“Geothermal”).
Geothermal HVAC also has some drawbacks. The biggest liability is its enormous up-front cost. This was the main factor in the decision for Lake Country Lutheran to eliminate the system. The total cost to the school would have been close to $3 million, compared to the $1.5 million the school spent on its current system. Another drawback of geothermal is the maintenance involved. Because the loop is buried below the ground (or pond),tubing ruptures are very difficult to repair. The three pumps involved also include some maintenance, and last for about 35 years. This allows approximately 15 years between the time that the system pays for itself and the time the pumps must be replaced. While this is a positive factor, it does cut down on the system’s efficiency.
What are the main parts of Lake Country Lutheran’s heating system?
The HVAC system at Lake Country Lutheran High School is comprised of two separate systems. These two work together for maximum comfort and efficiency during the heating system, while only one is utilized during the cooling season. The rooftop units (RTUs) provide the bulk of the heating and all of the cooling to the school. As suggested by their name, these are large units located on the roof of the building. They contain two separate units, large units which provide the heat and air conditioning, and another special unit called energy recovering ventilators (ERVs).
The large units (Figure 6) contain a heating side used during the winter and a cooling side used primarily during the summer months. These two sides operate in a very similar fashion to standard residential heating and cooling units, with the heating side providing heat via natural gas, and the air conditioners operating with the use of a coolant loop and fans.