geothermal energy fall 2011 final...

Cornell University Sustainable Design | Geothermal Energy Subteam | Fall 2011 Final Deliverable

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Geothermal Energy

Fall 2011 Final Deliverable

Cornell University Sustainable Design

Sustainability Research Facility

Team Members:

Ruhani Arya

Wendy Gu

Cameron Lancaster

Katherine Mayer

Julia Mertz

Jonathan Newman

Rachel Silverman

Jason Wright

Faculty Advisor:

Dr. Jeff Tester


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Table of Contents

Introduction ..................................................................................................................................... 1

Design Considerations ..................................................................................................................... 1

Types of Geothermal Systems ..................................................................................................... 1

Soil Analysis .................................................................................................................................. 2

Drilling .......................................................................................................................................... 6

Next Steps ................................................................................................................................ 9

Materials .................................................................................................................................... 10

Piping ..................................................................................................................................... 10

Refrigerant ............................................................................................................................. 11

Heat Pump(s) .............................................................................................................................. 14

Two different heat pump units .............................................................................................. 15

Desuperheater ....................................................................................................................... 16

Sizing calculations .................................................................................................................. 16

Sizing estimates ..................................................................................................................... 20

Next Steps .............................................................................................................................. 20

Radiant Floor Heating ................................................................................................................ 21

Maintenance & Controls ............................................................................................................ 27

Analysis .......................................................................................................................................... 32

Software ..................................................................................................................................... 32

Energy Estimates ........................................................................................................................ 32

Cost Estimates ............................................................................................................................ 33

Conclusions .................................................................................................................................... 34

Recommendations ..................................................................................................................... 34

Timeline ...................................................................................................................................... 35

External Contacts ........................................................................................................................... 36

Appendix ........................................................................................................................................ 37

References ..................................................................................................................................... 38


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Introduction

The goal of a geothermal system is to use the constant ground temperature stored within the ground to heat and/or cool a space and/or generate electricity. To accomplish this, a geothermal system involves piping within the ground with a fluid with high thermal properties, or a refrigerant, running within to transfer heat. In the winter, this system brings the heat stored in the ground to the surface and storing, which in combination with a heat pump, is then used to heat a space. The refrigerant returns back through this ground piping system, or the ground loop, to be re-heated. In the summer, the system runs in reverse, allowing the colder temperature of the ground to be again brought to the surface to cool a space [1, 2].

Figure 1. Geothermal map of the United States. [3]

As a subteam, we were motivated to explore the possibility of a geothermal system for the SRF because of the possibilities for research and innovation, building on the concept of the SRF as a living laboratory, as well as Ithaca’s greater feasibility for geothermal systems. The Ithaca region is unique because it has a higher than normal ground temperature than the majority of the Northeast, a fact that becomes more evident as you drill further down, as Figure 1 displays [3].

Design Considerations

Types of Geothermal Systems

There are two main types of geothermal systems: open and closed loop system. An open loop system involved drilling two bore holes deep, which would be the majority of the costs of the system, into the ground, tapping into an aquifer below that must be present for this type of geothermal system. This aquifer acts as a source of heat transfer, as water is drawn up into the building to heat or cool it and then after it has run through the piping of the building it will be returned to the aquifer. While this system is effective, it could alter the temperature of the


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aquifer, especially should the amount of water in the aquifer drop which would also decrease the efficiency of the geothermal system. Finally, this type of geothermal system is associated with a higher rate of pipe corrosion over time because of small particulates that may be drawn through the pipework from the aquifer [1, 2].

Figure 2. Diagram of an open loop geothermal system [4]

The other type of geothermal systems is a closed loop system, which has two variations: horizontal and vertical loop systems. Horizontal closed loop systems involve a trench dug roughly 5-7 feet beneath the ground to house the piping. This method requires a lot of space to prevent interference between the pipes as well as altering the ground temperature of the region. Additionally, this system requires more space and piping over its vertical alternative to fulfill the same heating load because the temperature at this depth is lower. However, without the costs of drilling, a horizontal closed loop system is also much cheaper. A closed, vertical loop system involves drilling a few boreholes deep into the ground to draw from the warmer temperature there. While this drilling is costly and makes a vertical closed loop system more costly, the entire system involves less piping, refrigerant, and space to meet a given heating load [1, 2].

Figure 3. Vertical Closed Loop geothermal system with two boreholes [4]

Soil Analysis

As the sun’s energy travels to Earth, the ground absorbs a major portion of the energy, creating an abundant energy supply. The system transfers energy with the soil, rendering the soil an extremely important factor in the overall efficiency and design of the system.


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While the temperature of the air fluctuates greatly throughout the year, the soil temperature is nearly constant. Six feet below the surface, the temperature of the soil, on average, is a constant 50-55 degrees Fahrenheit [11]. Soil’s consistent temperature is what makes geothermal heating and cooling reliable and efficient. In the summer, the soil is a lower temperature than the air, allowing for cooling, while in the winter it is at a warmer temperature, permitting heating. Although soil temperatures remain fairly constant, there are a number of factors that affect the temperature: air temperature, soil type, vegetative cover, and moisture or the presence of water [11].

There are four major materials that compose soil: minerals, rock, clay and sand [9]. The composition of the soil mainly affects the ground’s thermal conductivity, the rate at which it transfers heat. The higher the thermal conductivity is, the faster the system can transfer energy and the more efficient it is. The presence of water can also have an intense effect on the thermal conductivity of soil and if it discovered during drilling, must be accounted for in the design of the loops. Nevertheless, soil thermal conductivity usually falls within the range of producing 25-70 watts per meter, although the exact value varies site to site [9].

Table 1. Thermal conductivity values. [5]


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The thermal conductivity, as determined by the geology of the site, affects the design of the system. A more efficient soil requires less piping to complete the necessary heat exchange, allowing for shallower wells to be drilled and less loops to be implemented. Table 1 is a chart of thermal conductivity values for all major soil types The value for the thermal conductivity can then be used to estimate the efficiency of the soil, based on Figure 4[9], where lambda is in units of W/mK. A thermal conductivity value can correspond to a range of expected heat delivery. The exact value for the expected heat delivery can only be determined through testing the exact site and determining its exact composition. The average value of thermal conductivity corresponds to an expected heat delivery value of 35-45 watts/meter, but it is usually assumed to be on the lower end at 35 – overestimating will produce a system incapable of its job, while underestimating will always provide a system that can complete its task [9].

Figure 4. Relating thermal conductivity (lambda) to watts/meter [9]

In order to provide the most accurate estimates and values for our system, many steps were taken to find soil information relevant to our site. After a meeting with many grad students, a full soil test was determined unnecessary. Rarely are soil tests conducted on a new site, for they are very expensive and for preliminary designs estimates are accurate enough. Soil information for nearby sites can be found from case studies or local companies that have already implemented geothermal systems. A soil test ruled out, we began searching for data from local sources. A meeting was set up with University Planner Mina Amundsen to obtain soil data from Cornell’s campus. It was discovered such data does exist, but it has not yet been passed on to our team. Similarly, attempts to contact local companies have been slow to come to fruition. Thus, we have not been able to find in-depth soil data; however, case studies from local towns, have allowed us to estimate the type of soil we will encounter. Research from a soil survey in Binghamton, New York, shows that their soil is mainly loam [8]. Similar data was found by the United States Department of Agriculture, when a soil survey was conducted in Honeoye, NY (figure 5) [13]. Though this is not the most accurate information, for our preliminary designs, it is a valid estimate to assume our soil is loamy as well.


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Figure 5. Honeoye soil profile [13]

Loamy soil is a combination of sand, silt and clay in fairly equal ratios [15]. An examination of figure 2 shows that loam is not present. Thus, its closest present relative, water saturated clay/silt, is used for our data. With a thermal conductivity value of 1.7, water saturated clay/silt is a very average soil composition [15]. Further analysis using figure 4, shows that the estimated heat delivery for our system will fall between 32 and 43 watts/meter. Erring on the side of caution, we chose to work with 32 watts/meter as a rough estimate of our system’s heat delivery capacity. This value determines the efficiency of our system, which will determine the design of the system: the length and number of loops, affecting the drilling requirement.

Soil Thermal Conductivity

(Btu/(hr ft ⁰F))

Number of U-Tubes Effective Depth of U-Tubes

(vert. feet)

Total U-Tube Vert. Length

(vert. feet)

0.55 16 199 3,180

0.7 15 188 2,820

0.85 14 187 2,620

1.0 12 202 2,420

1.2 12 188 2,260

1.35 12 180 2,160

1.5 10 212 2,120

Table 2. Example of how geothermal parameters can be estimated based on thermal conductivity. [6]


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Drilling

Energy is drawn out of the soil by transferring its heat to a fluid flowing through tubing positioned in shallow rings or deep wells. For spatial reasons, our system will be a vertical closed loop, meaning large U pipes will be placed into the soil to generate energy (figure 6). These tubes are place in boreholes, a narrow hole drilled into the earth. Two pipes or one loop is placed in each borehole. The boreholes can be drilled in a number of manners, usually determined by the soil, the depth and the contractor hired to drill the hole.

Figure 6. Schematic diagram of a borehole. [3]

In a vertical loop system, numerous boreholes are often drilled and they must be placed correctly to achieve the highest efficiency possible. If boreholes are placed too close together, two major complications can occur. First, during drilling, a drill bit may not drill completely vertically and one runs the risk of drilling into another borehole if they are placed too closely [12]. The second difficultly is far more likely and involves thermal linking of two boreholes. The pipes in the boreholes transfer heat between the soil and the fluid running within them, possibly causing temporary temperature alterations in the soil. If two wells are drilled in close proximity they can link together thermally and interact, ruining their efficiency [9]. Thermal linking is more likely in deep systems and in systems with unbalanced heating and cooling loads [12]. The International Ground Source Heat Pump Association recommends separating boreholes by at least 10 – 15 feet, while another source recommends a similar 6 meters [9] [14]. It is also recommended to not place boreholes near a building to avoid interactions between the two and for maintenance use. It is recommended to place the wells at least 5 meters from a building.


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The width of boreholes and piping is another variable that must be considered when designing a system. Advance software is used to determine exact dimensions for both. Yet, recommended values provide ranges for both. The width of a borehole usually falls between 125 mm and 150 mm, while the width of the actual piping is 32 mm to 40 mm (figure 6). The length of piping varies tremendously within systems, but for our system will be fairly shallow (a couple hundred meters in depth).

There are two major methods of drilling used to create the boreholes: cable tool (percussion) drilling and rotary drilling. Cable tool drilling is performed by a heavy drill bit being lifted and dropped repeatedly. The heavy bit crushes the rock formations, which are carried away, creating a borehole (figure 7). Cable tool drilling is most useful for tough formations, for it is capable or drilling through nearly any formation. However, it is extremely slow. Fluids are pumped in to mix with the debris and every 5 to 10 feet the wet slurry must be bailed out. Also, casing must be placed in as the drilling occurs to prevent cave-ins, which increases the drilling time even further [7].

Figure 7. Cable tool drilling. [7]

Rotary drilling is far more common for drilling typical boreholes. Conventional rotary drilling uses a tricone roller drill bit and drills by rotating the drill collar and drill pipe, which rotate the bit (figure 8). The rock is cut through creating shards and debris. Drilling fluids are poured down the drill and pumped up to carry away debris as the drill continues to function [7]. Often, casing is placed into the hole during rotary drilling to ensure stability of the hole, but it is not always necessary. It is up to the contractor to determine the best course of action. Many other slight variations on conventional rotary drilling exist such as top-head drives or downhole hammer drilling, though for our system these other types are irrelevant [7]. Similarly, many experimental methods of drilling exist, but they concentrate on deep system (kilometers deep) drilling, and thus are impractical for our system.


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Figure 8. Rotary drilling. [7]

Deciding what method of drilling to employ for a given system relies on a number of factors. First, the soil type of the site is a major deciding factor. Figure 9 shows a number of drilling methods and the soils with which they work best. Another major factor is the contractor hired for the job. Not every company has access to every drilling method or experience with them all. Contractors are limited to certain drilling methods based on their own capability. Finally, the cost of a method is a determining factor. Figure 10 illuminates the large cost of drilling, making it financially significant to consider the cost of a drilling method.

Figure 9. Recommended drilling methods. [13]


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Figure 10. Cost of boreholes by component. [7]

Beyond the method of drilling, a drilling fluid must be chosen. The drilling fluid is used to cool off the drill bit because of the intense frictional heat, remove any cuttings away from the bit and transport them out of the well through the annulus. There are three common fluids used: water-based (mud), air-based (mist) and oil-based (used only for petroleum drilling) [7]. Since it is the most productive and common, our drill will most likely use a mud compound as its fluid. Muds are composed of Bentonite, water and numerous other agents, which are added in small amounts to change the fluids properties based on the drilling conditions. The density of the fluid affects its efficiency, for a denser fluid can better carry away materials from the drill bit, while it also increases the drilling pressure, speeding up the process. However, more dense muds can also push through cracks in the rocks more easily, creating more lost circulation (lost fluids) that must be replaced. The average density is 9 lb/gal, but decreasing the density even further is desirable [7]. Viscosity also affects the efficiency of the mud. Viscosity is the measurement of the time it takes the fluid to form a gel. The recommended value is 32-38 seconds per quart [7].

Based on our assumption that our site will contain loamy soil and figure 9, we will most likely use direct or conventional rotary drilling with mud. For our type of soil – clay, silt and sand – direct rotary drilling is the most economic and the fastest method. Also, the width of our piping must be calculated using advanced software. RETScreen, our preliminary software analysis assumes our piping width to be 31.8 mm, the smallest pipes possible in the recommended scale [10]. Yet, once again the final drilling and fluid decision is a choice of the contractor’s, for it depends on their expertise and equipment.

Next Steps

The next steps to be completed before installation can commence include a possible test borehole and finding a contractor and company to employ. When preliminary designs have been completed, a test borehole to ensure accurate data may become very useful and worth the financial cost. A test borehole is a miniature well used to collect data before the final design is completed and implemented [12]. A well is drilled with a diameter smaller than a functional borehole (4.828 in.) [7]. A wire-line is used to load the drill rod into the test borehole, which drills by rotating. A new core barrel is loaded in and filled with dirt every 10 feet, producing a replica of the soil as it appears in the ground, providing accurate and detailed data of the site [7].


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Also, steps should be taken to contact possible companies who would complete the drilling for us. From the companies, information from localized wells could also be retrieved, improving our data, without an expensive soil test. Before deciding which contractor to hire, a number of factors should be considered. We need a contractor with access to a type of drilling which functions well with the type of soil at our site. Also, we need a contractor with a lot of experience. There is a lot that can go wrong when drilling boreholes and we need a contractor who we trust will know what to do. The price of the contractor should also be taken into consideration. Once a contractor and company has be chosen, they will begin there tests and in discussion with our sub team will decide the best course of action for installing the boreholes.

Materials

Piping

In any geothermal system, the piping used must be able to fully allow the transfer of heat from the ground into the geothermal system itself. After conducting research on what type of piping works best to meet this requirement, we discovered that a type of polyethylene piping is best because it is extremely efficient and is also the most commonly used piping in geothermal systems [17]. Polyethylene piping efficiently transfers heat because it can easily absorb and retain it, maintaining a desired temperature by not allowing heat to escape despite readily taking in heat to raise the temperature of the substance within, or vice versa for cooling.

Figure 11. Polyethylene Piping for Interior Loop [21]

Another reason for using polyethylene piping is that it is currently the only type of piping used in geothermal systems. Polyethylene piping is easy to bend and manipulate unlike other solid types of piping such as steel, copper, or aluminum. This manipulation ability allows the heat transfer liquid used in the system to flow better and have a lower viscosity. Lower viscosity and better flow are extremely important because the solution needs to be able to travel around the loops of the system with ease. If the solution had difficulty moving through the loops, the system would not be able to effectively bring heat from the ground to heat or cool a space, inhibiting the system from working to its full potential.


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Figure 12. Polyethylene Piping in a horizontal, closed loop trench for a geothermal system [22]

For our system, we should use High-Density Polyethylene instead of low or regular polyethylene piping because it provides extra insulation for our refrigerant in the system. Although this extra insulation limits the piping’s manipulation abilities, it greatly reduces the risk of our refrigerant freezing even if the temperature at the ground’s surface is colder than the normal freezing point of the refrigerant.

Overall, there are few downsides to using polyethylene piping. However, one downside to polyethylene piping is that it is not resistant to corrosion from oxidizing acids, ketones, and chlorinated hydrocarbons [20]. Fortunately, this downside would not be relevant in our geothermal system for two reasons. First, we are not planning on using any of these within our geothermal system, preventing system degradation. Second, these substances are not normally found in the ground or in the building near the components of our geothermal system, and if they were present in the ground or building, it would be in extremely small amounts that would have very little effect on the system’s effective lifespan.

Refrigerant

Within the geothermal system, a liquid or mixture must be able to easily transfer the ground’s temperature to heat or cool a building or area. Therefore, it is necessary to choose a liquid or mixture that has a relatively high heat capacity, allowing it to efficiently transfer and maintain the heat that will maximize the effectiveness of our system. As shown in the picture to the right, the liquid must also be able to flow easily through the geothermal system and be non-toxic to living things and the environment in case it were to accidentally leak from the pipes into the ground or building. The fluid used would need to meet government issued toxicity levels for a college campus, the town of Ithaca’s toxicity regulations, and the team’s, since our goals center on sustainability. Finally, our refrigerant should be relatively resistant to cold, having a low freezing point. Although we could protect the refrigerant from freezing by increasing its flow rate through the pipes, limiting its exposure to the brief segment of the piping exposed to the coldest temperature near the ground’s surface, this would require a greater energy input and might affect the ground temperature.


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Figure 13. Heating and cooling mode variations visible in the interior/ground loop within a typical geothermal system [23]

Using these guidelines, we discovered that alcohols and water were the best types of heat transfer liquids. Based on our research on the fluids, the positives and negatives of each liquid are listed below:

Positives Negatives Heat Capacity (Jcm-3

K-1

)

Methanol

Flows well (low viscosity)

Good freeze protection down to 15 °F

Highly flammable

Poisonous to humans and animals

1.962

Ethanol Good freeze protection

Transfers heat well

Highly flammable


1.925

Glycols

Low freezing point

Freezing point depressant

High boiling point

Poisonous to humans and animals by themselves

2.36

Perfluorinated carbon

Non-flammable

Thermally stable over a broad range of temperatures


~1.958

Water High boiling point

Great transfer of heat High freezing point 4.1260

Table 3. Refrigerant possibilities. [16, 18, 25]

Therefore, we decided that although methanol, ethanol, and perfluorinated carbon are all superb heat transfer liquids, they are too toxic to be used in the geothermal system. For each of these liquids, the risks of potential harm to the environment and those living within it were far


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greater than the benefits of having a great heat transfer liquid. As a result, we researched potential mixtures with water for these three solutions, yet they were still going to be too toxic for our use. However, we found that ethylene glycol was the perfect heat transfer liquid when mixed with water because while ethylene glycol is poisonous alone if consumed, when mixed with a large amount of water, its toxicity is almost nothing. According to Lytron’s “Application Notes”:

“Dow Chemical recommends a minimum concentration of 25-30% EGW [Ethylene Glycol and Water]. At this minimum concentration, the ethylene glycol also serves as a bacteriacide and fungicide. With recirculating chillers, a solution of 30% ethylene glycol will result in only about a 3% drop in thermal performance over using water alone but will provide corrosion protection as well as freeze protection down to -15°C (5°F).” [19]

Therefore, to maintain both a safe and efficient heat transfer liquid, there must be a mixture with a concentration of 25-30% Ethylene Glycol and Water (EGW). Our mixture must have anywhere from 75-80% of water and 20-25% ethylene glycol because this combination will be the best liquid available for heat transfer since it will maintain the high thermal performance associated with water. It will also prevent some of the concerns associated with a system in Ithaca, or that the fluid would freeze within the system during the winter. However, in the future our subteam will need to test this liquid in a model geothermal system to truly examine its efficiency and its functionality during cold temperatures.

Figure 14. Heating mode as visible in the ground loop within a building’s geothermal system [24]

In some geothermal systems there is only one type of liquid and piping used for the loops located in the ground loop and the building’s interior loop. However, in this system it is best to use two different types of liquids and piping in the outside and inside loops. Although the proposed mixture of ethylene glycol and water is the best non-toxic heat transfer liquid for cold environments that we have found and is commonly used in both loops, it is safer and cheaper to use water in the inside loop. Water is an overall better refrigerant than ethylene glycol when


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freezing concerns are not a factor because of its thermal properties that allow it to transfer and maintain heat more efficiently. Since the internal loop of the building will not be exposed to freezing temperatures, we do can safely use water in this interior loop without decreasing the efficiency of the system. As for piping, it would be best to use the High-Density Polyethylene in the exterior loop, to protect and insulate the refrigerant within, and normal polyethylene pipes in the loops within the building. This will allow for more flexibility in our manipulation of the piping within the building, an important requirement for the building’s modularity.

Heat Pump(s)

Heat pumps are basically regular mechanical pumps that are used for refrigeration and air conditioning but with a reversing valve installed in them, so that they can both cool and heat a system.

Geothermal Heat Pump systems are comprised of individual packaged units that transfer heat via water loops. Each unit can be used in either heating or cooling mode year-round and loop temperature is maintained via an earth-coupled loop. Ground source heat pumps, or rather ground coupled heat pumps (water to water pumps preferably, which means a hydronic heating system), have three main parts-

1) The ground loop (with water or a mixture of water and ethylene glycol). 2) The heat pump itself. 3) Distribution system installed inside the building.

Figure 15. Heat pump as attached to piping and building. (RETScreen)

A typical heat pump unit is shown in Figure 16.


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Figure 16. Heat pump system diagram. [26]

How is our Ground Source heat pump system different from regular heat pump systems?

Two different heat pump units

We plan to use two different heat pumps but a common fluid loop for both the pumps. This arrangement is normally utilized in supermarkets and other places where some areas of the building might require cooling to lower temperatures while the other areas might need heating or if different areas of the building require heating to widely different temperatures (Like for example, in our building we might want the room with the anaerobic digester to be a higher temperature always). This would be very beneficial for the following reasons-

1) Large buildings often have simultaneous heating and cooling loads: for example, the core of the building may need cooling while perimeter areas need heating. The common building loop can transfer heat from cooling loads to heating loads, reducing the demand on the earth connection and improving efficiency.

2) Climate control is simplified and occupant comfort is improved, since each heat pump affects only the space in its vicinity. Controls can be local, rather than part of a complex building-wide system.

3) The common building loop transfers heat using a liquid, which permits it to be much more compact than the ducting required by air distribution systems tied to conventional central heating plants; space is freed up for more productive uses.

The disadvantages might be-

1) Cost of the equipment increases. 2) More storage space required.


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Desuperheater

We plan to install a desuperheater that provides domestic hot water when the compressor of a heat pump is operating. The desuperheater is a small auxiliary heat exchanger at the compressor outlet. It transfers excess heat from the compressed gas to water that circulates to a hot water tank. In the summer, the desuperheater uses the excess heat that would otherwise be expelled to the ground. Therefore, when the geothermal heat pump runs frequently during the summer, it can heat all of your water. During the fall, winter, and spring—when the desuperheater isn't producing as much excess heat—you'll need to rely more on your storage or demand water heater to heat the water. During the cooling season, when air-conditioning runs frequently, a desuperheater may provide all/any hot water needed for the building, thus preventing any wastage of water too.

Sizing calculations

A large part of the geothermal system involves making calculations for the heat exchanger. These methods are crucial in determining the mass flow rates of the refrigerant and hydronic fluid which will be necessary in sizing the heat exchanger so that we can meet the heating and cooling load of the SRF effectively [27]. A large portion of the research encompassed learning the methods used to determine these values. Because the current operating conditions are unknown, the explanation of calculations below will involve arbitrary numbers chosen as possible operating conditions.

The selected geothermal system for the SRF includes a vertical, closed loop system that heats the SRF through a hydronic heating system, which can be used to heat water for the building or maintain a desired temperature within the building. For our calculations, we assumed that the hydronic heating system uses water as its fluid and transfers heat perfectly. As a sample calculation, we also assumed that the SRF’s heat load dedicated to warming water or another liquid for certain purposes within the building would be roughly 60,000 Btu/h. This amount is most likely higher than the SRF’s actual heated water needs because the water would mainly be for labs and other activities rather than for daily living.

Thus using the formula the Q=mcΔT , the mass flow rate of hydronic fluid needed to provide this heat is calculated where m is the mass flow rate of hydronic fluid and Δ T is the temperature difference of the hydronic fluid after heat transfer and before heat transfer. For

our purposes, we assume that the hydronic system operates at 200 and the hydronic fluid

discharges at a temperature of 150 . Knowing the heat capacity of water, Cp, we can calculate the mass flow rate of the hydronic system [29].


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Suppose this hydronic system is also used to heat the space inside the facility. To find the mass flow rate needed for these loops of the hydronic system, we apply the same concept as above. In the winter, the facility will be maintained at a relatively constant temperature of around 68°F. Assuming that the peak heating load to maintain this temperature is 40,000 btu/h, that the temperature after heat transfer is 100 °F, and that the hydronic system operates at 200 ° F, we again calculate the mass flow rate needed through these loops [29].

Though in this analysis the peak heating loads for each purpose were set at 60,000 Btu/h and 40,000 btu/h as basic, sample calculations, the peak heating load should be determined after assessing many factors of the facility. Although the energy storage team reported an estimate of 2 kwh as the monthly energy goal for the facility, what proportion of this energy will be used for various aspects of the facility remains unknown.

In our system, the ground loops provide heat to the hydronic heating system. The general process is as follows: a compressor compresses the refrigerant to a higher pressure, thus increasing the temperature of the refrigerant and the heat exchanger will then condense the refrigerant. Using an expansion valve, the pressure will be lowered to its initial pressure and temperature, consistent with the ground loop. Finally, through this ground loop, the heat is transferred to the refrigerant, which vaporizes again, carrying the heat up into the hydronic system and allowing the cycle to repeat.

Additional information required to determine the size the heat pump is the mass flow rate of refrigerant needed to run through the ground loops. Again using the previous example as the basis for this analysis, the total heating load for the facility is determined to be 100,000 Btu/h

Heating load calculation [29]:

Assuming that the refrigerant, or water, needs to be heated from 50 °F to 212 °F to effectively carry out the process, a pressure enthalpy diagram can be used to calculate the necessary mass flow rate of the refrigerant. On the pressure enthalpy diagram in Appendix A, the refrigerant from points labeled one to two, the saturated refrigerant in vapor form is isoentropically compressed and therefore heated. It can be assumed that the entropy does not change during this compression. From step two to step three, the refrigerant condenses to a saturated liquid. The heat is transferred to the hydronic system during this process. This is shown as point three, which resides on the left side of the saturation bubble at that specific temperature and pressure. Noting the enthalpy at this point three to be 260 Btu/lb and the enthalpy at point two to be 1675 Btu/h, the difference can be taken between these points, thus determining the


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enthalpy of the refrigerant 212 °F. From point three to point four, the enthalpy is constant but the pressure decreases due to the expansion of the refrigerant as it passes through an expansion valve. Cooling also occurs during this expansion until the refrigerant at point four has the same temperature as the refrigerant originally had at point one. From point 4 to point 1 the refrigerant is evaporated. Taking the enthalpy difference between point 4 and 1 we obtain the enthalpy of the refrigerant at 50 °F. Knowing that the total heating load needed for the hydronic heating system is 100,000 Btu/h from our example, we can use this formula to calculate the refrigerant’s mass flow rate needed to flow through the ground loop. In the calculations below, Q is the heating load whereas ΔH is the change in enthalpy between the two respective temperatures.

Enthalpy at 212 °F [29]:

Enthalpy at 50°F:

Mass flow rate of Refrigerant[27]:

The diagrams below provide a clearer explanation of how the Pressure Enthalpy diagram in Appendix A corresponds to the heat pump process:

A

compressor

energy in

B

condenser

heat outC

expansion

valve

D

evaporator

heat in

Figure 17. System diagram [31]


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Figure 18. Enthalpy diagram [31]

As the geothermal subteam makes more progress in its research, definite specifications can be used through the calculations outlined above to accurately estimate the necessary size of the heat exchanger. Once again the actual heating load for our facility is expected to be about 3,000 to 12,000 kwh/month. This is equivalent to about 14217 Btu/h to 56809 Btu/h so the example used in this report is higher. The different temperatures that the refrigerant will operate at will also need to be determined but will require more analysis of the climate, soil, and other factors. Once more definite specifications for the facility are determined, these general calculations can be used to find the corresponding mass flow rates needed to run the hydronic and ground loop system at the desired heat load. Further research is also needed to calculate how many shells our heat exchanger should have. The geothermal team will further investigate this area to perform the needed calculations.

In addition to researching methods to size the heat exchanger, we also analyzed how the heat pump should be included within the facility. Using two heat pumps in the SRF seems to be more efficient for our purposes as well as more innovative, keeping with the goals of using the facility as a living laboratory. One larger heat pump may not adequately meet the needs of all areas of the facility. Two heat pumps can be used to thoroughly harness the energy of our system and direct it towards areas within the facility. By using two heat pumps, the geothermal system can be operated at different temperatures, which is advantageous if certain parts of the facility require different heating and cooling needs, such as the anaerobic digester, which needs a higher room temperature. The two pump system is also novel for further geothermal research. The efficiency of running the pumps at different temperatures and different refrigeration enthalpies can be tested as the coefficient of performance of the pump is related to enthalpy. In addition, in the future, we could change out one of the heat pumps for a different type of heat pump, allowing for an efficiency comparison between the two pumps that would clearly determine the more effective model. The same conceptual calculations outlined in this report can be applied to calculating mass flow rates through the proposed two heat pumps system for the SRF.


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Sizing estimates

A number of calculations for calculating the peak heating and cooling load were also done using software from RETScreen, for the understanding of which the following terms would come handy [28]:

1) EER- defines cooling efficiencies of unitary heat pump systems, that is, heat removed to the total input of energy applied.

2) SEER- same as EER, but on a national seasonal average, example- if the instantaneous rating for a system ranges from 10 EER to 20 EER, it may settle in at a seasonal rating of 15 SEER.

3) COP- ratio of useful heat energy acquired by the total heating applied.

The following are the assumptions and drawbacks of the calculations-

1) Building area that would require heating and cooling was assumed to be 372 square meters (4000 square feet) to avoid any over assumption.

2) The seasonal efficiency was assumed to be 90%.

3) The heating load was taken to be 55 Btu per square foot and the cooling load as 467 square footage per ton.

4) A ‘waterfurnace’ heat pump is used with COP as 3.6.

5) Some information from the ‘Chatham Airport in Canada’ database was used to complete the calculations, because of the similarity of the climatic conditions.

6) The ‘Financial Analysis’ and ‘Emission analysis’ could not be done due to the unavailability of certain information.

What this software provides us-

1) Peak heating load (64 kW) and peak cooling load (30kW).

2) Base case system load characteristics graphs for all months of the year, that is, how much of energy would be required every month to heat/cool.

3) Annual fuel consumption and fuel cost.

Next Steps

1) Once we get more concrete information about the exact building area available and what kind of temperatures would be needed in different areas of the building, we can calculate the exact size of the heat pumps required.

2) When we have an even better idea of things like ventilation, location and size and material of doors and windows, ductwork etc. we’ll be in a better position to calculate the heating and cooling losses- and that would aid in calculating the peak heating and cooling loads. This can be done with the completion of a ‘Manual N- Commercial Load Calculation for Small Commercial Buildings’, which is a worksheet used by professionals for the same purposes.

3) It should also be verified that the building has a capacity to handle the demands of the two separate heat pump systems, whether it is practically sound to use two pumps in a


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commercial building of a small size and also which areas of the building will be served by which heat pump.

Radiant Floor Heating

In selecting a heating and cooling system, we had a few baseline design needs and system goals. These included sustainability or energy efficiency, modularity, thermal comfort, and compatibility with a geothermal heat pump as well as the Haworth raised access floor system and other unique potential features of the building. In trying to meet these goals, we encountered many design challenges that do not exist in a traditional heating and cooling system.

Our first challenge was to create a single system that could operate reversibly as a heating and cooling system, with a heating system in effect below 68°F and cooling above 78°F, for example. An integrated system does already exist in the form of forced-air heating and cooling. In this system, a refrigerant is heated or cooled by a central furnace or air conditioner. Air is passed across the pipes holding the refrigerant, causing the air to heat or cool, after which it is forced out to different rooms in the building by a network of blowers and vents.

Figure 19. Heat Flow in a Forced Air System [31]

However, we had to reject this system because it would not be compatible with several of our baseline design needs. First, a forced air system is one of the least sustainable options because it is not very efficient in the way it distributes heat. Heat is expelled through vents in the ceiling, and because heat rises, the entire room must be heated from the top down before the lower, occupied level of the room reaches a comfortable temperature. The presence of dust in the ducts and vents can also decrease the indoor air quality. Heat transfer occurs very indirectly (boiler to refrigerant to duct to room for heating, and the reverse for cooling), so a forced air system operates on a very large temperature differential. This means that a large quantity of heat is lost to exhaust, and the system’s thermodynamic efficiency is very low. Additionally, a forced air system does not work well with modularity. We could not place any ducts in the moveable walls, and we would not be able to rearrange ducts or vents based on the changing wall positions, disabling us from heating and cooling reshaped rooms effectively and from heating or cooling different rooms to different temperatures.


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Figure 20. Baseboard Heating System [32]

In the interest of sustainability and modularity, we also rejected several other less common heating and cooling systems. Baseboard heating and chilled beam cooling both consist of pipes running along the perimeter of the room carrying hot or cold water. These systems are not the most efficient because heating and cooling starts at the edges of the room, so the room must be heated or cooled from the outside in before the occupants are comfortable. The two systems also restrict modularity because they are installed based on permanent wall arrangements and cannot be moved or rearranged. Rooms composed completely of movable walls will, therefore, be much more difficult to heat to a comfortable temperature.

Figure 21. Radiant Heating System [34]

Again, taking into consideration the efficiency and sustainability of the system as well as compatibility with modularity, we decided that a radiant heating and cooling system would best suit our needs. Radiant heating systems are widely used and are reported to yield a greater thermal comfort level than forced air systems. Although radiant cooling systems are not very common yet, the Center for the Built Environment conducted experiments showing that these systems may yield “an energy reduction of 21-25% during the peak cooling months, and peak electricity demand reduction of 27%, and also improved occupant thermal comfort” [33]. Radiant heating and cooling systems are based on the idea of directly heating or cooling the floor of the building so the heat can then radiate out of the floor into the room or vice versa. This system is very efficient because it heats or cools the room from the floor up, so the lower part of the room can be kept at a comfortable temperature without wasting energy on regulating the temperature in the upper part of the room or the outer sides that are not occupied. Additionally, radiant heating and cooling is compatible with modularity because it does not require ducts or any other equipment to be installed in the walls. The system lies entirely in the floor, so it will not constrain the motion of the walls or limit the rearrangement of space in the building.


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Figure 22. Forced Air versus Radiant Heating [35]

After deciding upon radiant heating and cooling, we had to select the method of installation and the type of system. There are two methods of installation: wet and dry. In a wet installation, a slab of concrete is poured, the system is embedded in the wet concrete, and then the floor is installed on top of the concrete. The single slab of concrete spans the entire floor and acts as a thermal mass. We immediately rejected this installation method for two reasons. First, this system would preclude maintaining different rooms at different temperatures because the entire concrete slab would be in thermal equilibrium. Second, it would be impossible to access the pipes for maintenance or to change the system in any way if it were embedded in a concrete slab. As a result, we decided on a dry installation, in which the heating and cooling system is installed in the plenum under the raised access floor. This floor, which will be provided by Haworth, will consist of an architectural floor supported by pedestals, on top of a concrete subfloor. The pedestals can be adjusted to set the floor 12-18 inches in height above the concrete subfloor. The airspace between these two floors, known as the plenum, will house electric wiring and controls, plumbing, and heating and air conditioning. The advantages of running these systems under the floor rather than through the walls are that the walls become free to detach and move, and the systems are easily accessible for changes or maintenance through nodes in the floor. A dry installation will allow for easy access to the heating and air conditioning system through these nodes, will be compatible with a raised access floor, and will allow for different parts of the building to be heated independently of each other.


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Figure 23. Dry Installation and Compatibility with Raised Access Floor [36]

The three types of radiant heating and cooling systems are electric, air, and hydronic. An electric system, in which electric cables are built into the floor, was eliminated because the use of a geothermal heat pump replaces the need for fuel or electricity as a source of heat. An air system, in which hot or cool air is pumped up through the floors, was also rejected based on the U.S. Department of Energy’s statements that air-heated radiant floors are “not cost-effective” and “not recommended” [37]. Additionally, our discussion with Professor Tester’s graduate students revealed that underfloor cooling is not very comfortable for the occupants because it gets cold very quickly and there will be constant, cold drafts. As a result, we chose to use a hydronic system, in which heated or cooled water runs through pipes laid out under the floor. This system is ideal for use with a geothermal heat pump, and the U.S. Department of Energy recommends hydronic heating as the most cost-effective system in climates with high heating demands [37].

Following the selection of a dry installation and a hydronic system, the next challenge faced was how to integrate the heating and cooling system with the Haworth raised access floor, which had already been donated and is expected to serve as an essential component of the SRF. The under-floor air system designed by Haworth is an air-based rather than hydronic radiant heating and cooling system. The system is primarily designed for data centers and other buildings that have very high cooling demands due to overheating equipment. For our purposes, under-floor air is not necessary and might endanger occupants’ thermal comfort, so we decided not to use Haworth’s suggested system with their raised access floors.


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Figure 24. Haworth Under-floor Air [31]

In researching precedents of dry installation of hydronic radiant heating and cooling systems under raised access floors, we discovered the Warmafloor system. Warmafloor is a company based in the United Kingdom that designs a wide range of under-floor heating and cooling systems for different types of floors, including raised access floors. The raised access floor system is a hydronic, radiant heating and cooling system with a dry installation. It can be added on to a preexisting raised access floor by simply clipping panels onto the pedestals supporting the raised access floor and then laying pipe down in the panels. The panel dimensions match the spacing of the Haworth pedestals (every 2 feet), and the single system can operate in heating or cooling mode interchangeably.

Figure 25. Warmafloor System, side view [36]


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Additionally, the Warmafloor system is extremely modular. Different areas of the building can be heated or cooled to different temperatures by regulating the velocity of the fluid flow in each pipe since each room or area of the building can be heated or cooled by a separate loop of underfloor pipe. These pipes are then connected through an inlet in the Warmafloor manifold, a device that has gauges to measure the temperature and pressure of the fluid coming through each inlet. This device can be used to set automatically adjust the fluid flow rate in each loop based on various temperature measurements. This manifold is entirely modular and can have anywhere between 1 and 12 ports depending on the number of desired loops and another manifold could be installed to accommodate more loops. Additionally, if room arrangements change, the piping can be reconfigured by simply sliding the pipes out of the brackets, unclipping and repositioning the panels, and laying the piping back down in the panels in the desired configuration.

Figure 26. Warmafloor System manifold [41]

Warmafloor states that their system is compatible with a geothermal heat pump, and they provide the following data regarding heating and cooling capacities:

“Heating- the Warmafloor RAF system can provide radiant heating between 50- 80Wm²at a flow temperature of 45 - 60°C (104-149°F)

Cooling – Using a flow temperature of 13°C the system can provide up to 25Wm² from the floor surface. If used in conjunction with Plenum Ventilation and standard grilled floor panels, this can be increased to 35- 40 wm² ” [36]

At this refrigerant temperature, the floor will be warmed to a temperature range of 23-32°C (73.4-89.6°F). The flow temperature of the refrigerant and the performance coefficient of the heating and cooling system are inversely related, so we should try to reduce the required flow


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temperature in order to maximize efficiency and reduce energy consumption. Warmafloor suggests two such measures: reducing the spacing between pipes to increase the output, and using a floor covering such as tile that has little or no resistance to heat flow, a component that is already a part of the Haworth raised access floors donated [38]. The main concern we had regarding the Warmafloor system was that the heat radiating from the underfloor pipes might damage or interfere with the other systems, such as electricity or plumbing, which will also be installed under the raised access floor. However, upon examining the Warmafloor system, we discovered that the panels holding the pipes are foil-faced polystyrene. As visible in Figure 8, each insulation panel is only 100mm in width with a 300 mm (about 1 foot) space between panels, leaving room to access the other underfloor systems. Additionally, if more space is ever required, the panels can be unclipped and temporarily removed. This material has a very high R value because the polystyrene acts as an insulator, while the foil lining reflects the heat up through the floor and blocks it from entering the under-floor plenum.

Figure 27. Foil-faced Polystyrene [40]

Looking to the future, the team should research quantitative data pertaining to the Haworth floor and should consult with Warmafloor once this data is obtained. The modular subteam already has an established relationship with Haworth as well as a few brochures from Haworth with more detailed information, so questions about the Haworth system should be directed toward the modular subteam. The required data includes the dimensions of the under-floor pedestals, the material and R-values of the floor tiles, and technical drawings of the system. After this data has been obtained, the team should provide this data to Warmafloor, so that Warmafloor can evaluate the compatibility of the two systems. Contact with a Warmafloor representative (Malcolm Jaques, <[email protected]>) has already been established through Rachel Happen, a member of the business team. Following consultation with Warmafloor, the team could also request sample heating modules from Warmafloor in order to conduct tests with the Haworth flooring system in the HVL next semester.

Maintenance & Controls

Proper maintenance and control of the geothermal heating and cooling system in the SRF is essential. Maintenance refers to work, whether routine or emergency, that must be done to keep the geothermal HVAC system in optimal operating condition. The controls system will provide a way to keep tabs on different components of the system to ensure that they are functioning properly.


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In order to perform maintenance, we must configure the geothermal system so that we are able to access components of the system without compromising either the system itself or any other structural or functional elements of the SRF. The SRF plans to use Haworth, Inc. Raised Access Flooring, as shown in the picture below. This type of flooring will enable workers ample space to conduct any necessary work to the pipes that will be placed under the floor to transport the heated or cooled water, depending on the mode of the heat pump. It is very important to be able to access these pipes with ease because they could encounter issues as they will be transporting fluid with potentially very varied temperatures and this might cause damage or require adaptations to the network or the materials.

Figure 28. Example of an access point for the Haworth flooring [32]

The SRF will have two heat pumps. These will likely be located in the basement of the SRF and access to these heat pumps to perform maintenance should not be an issue. Since both pumps will be operating simultaneously to support the heating or cooling load of the SRF, if one of the pumps should be shut down for maintenance, vital operations that require heating or cooling will not be compromised because these loads can be transferred to the still-functioning heat pump.

Another consideration for maintenance is the concern of pressure drops. The pressure in the freon loop from the Heat Pump to the Air Handler, a typical component of heat pumps could fall to low levels which could be dangerous [42]. In this case, the presence of two heat pumps provides an important safety aspect. Additional potential, although unlikely, pressure concerns include those in the underground loops of the system since they are very difficult to fix but generally only occur in the first year or so after installation. Such pressure changes are dependent on underground pressures that result from the earth’s movements, and so cannot be controlled. As a result, we would install simple pressure gauges to monitor the pressure within at various points throughout the piping. These monitors can be read at their locations or connected to the computer monitoring system.


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Figure 29. Example of a geothermal system with radiant floor heating [43]

Within a geothermal system, changes in temperature are the most important thing to monitor so that we can adjust individual room’s temperature to a desired level and because we use it to base our changes to the system’s flow rate. As a result, we would require temperature sensors not only within various points in the pipes themselves but also spread throughout the building in individual rooms and within the piping of the interior loop. Currently, conventional monitoring of geothermal heating and cooling systems is a network of however many temperature sensors are deemed necessary with each wired to analog input channels, which are connected to a computer and allow these readings to be viewed and monitored. If the number of temperature monitoring sites is relatively few, this setup is proven effective, which is why it is the conventional approach. However, since the SRF will serve as a living laboratory and require more temperature sensors, a digital sensor system would be a better approach.

One potential digital monitoring system for the SRF is the Web Energy Logger (WEL). The WEL uses a 1-Wire system to connect temperature sensors, contact closures, and current monitors to the HVAC central control center [44]. With this system, you can monitor 100 points or more and keep track of the data at different locations efficiently because each sensor is assigned its own unique address and it calculates the temperature at its location before sending it on to the central computer for further interpretation. In contrast, an analog system would simply send signals along and would require interpretation immediately upon their arrival to the central system. Therefore, a digital system has less “noise” and is more procise, with the 1-wire sensors accurate to +/- 0.5 °C which an analog system could not match. However, this system is limited to only two current monitors [43].

To further describe the 1-Wire network, it is based on the idea that a single pair of wires can transmit power and data between a set of cooperating network components. This is achieved using low-power devices that can extract enough power from the data-line during the "1" state of the line [43]. Dallas Semiconductor produces these temperature sensors that cost $2.09 each when 1000 or more are purchased, which is more than our system would need but gives a rough estimate of their cost. Key features of these sensors are given below. [43]


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Figure 30. Web Energy Logger [45]

Key Features of DS18S20-PAR: [45]

(6) 1-Wire sensors ready to be installed

Unique 1-Wire interface requires only one port pin for communication

Derives power from data line ("Parasite Power")—does not need a local power supply

multi-drop capability simplifies distributed temperature sensing applications

requires no external components

±0.5°C Accuracy from -10°C to +85°C

Measures temperatures from -55°C to +100°C (-67°F to +212°F)

9-Bit thermometer resolution

Converts temperature in 750ms (max.)

User-definable non-volatile temperature alarm settings

Alarm search command identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition)

Software compatible with the DS1822-PAR

Ideal for use in remote sensing applications (e.g., temperature probes) that do not have a local power source

An advantage to using the 1-Wire system with the sensors described above is that the sensors read and convert the temperature locally, a convenience not available with analog sensors. In order to read the temperature sensors, a Serial Port adapter is required, which will connect directly to the computer. The data from these particular devices can then be displayed, charted, and logged on the screen so that they are easy to interpret and monitor.

http://www.ourcoolhouse.com/images/hvac/1wire_sensors.jpg


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Figure 31. Screen shot of the WEL monitoring technique in use [43]

The graphic shows the geothermal ground loop, the domestic hot water circuit, the four ground zones, and the ducted air path, including the energy recovery ventilator. The computer screen of this user also displays the house floor-plan with air temperature zones. Both air and water temperatures were recorded; air temperatures are shown in the top graph and water temperatures in the lower right.

Figure 32. One way of mounting the 1-Wire temperature sensors to the pipes, which were copper in this case [43]

The 1-Wire system looks to be promising largely due to the minimized wiring required. However, in order to display the desired data, we will need to figure out how to program the DS18S20 temperature sensors. In addition, we might add flow sensors, which the sensors subteam would help us develop and would check for leaks, if we are going to use flow sensors, these will be included on an analog wiring system because there are not products on the market that measure flow and also hook up to the 1-Wire system. The SRF will need more temperature sensors than flow sensors, though, so it could be viable to have both a 1-Wire system for temperature and a conventional system for flow. As for the flow sensors themselves, which will alert us if leaking is occurring in the piping, we have asked the sensors team how to develop these but have no design as of now and that is an aim for next semester.


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Analysis

Software

In order to design and determine the sizing of a geothermal system, modeling software can be employed to make complicated calculations far simpler and more accurate. In determining which software to begin with for our preliminary design two factors were considered: difficulty and cost. Our top two choices of software were initially COMSOL and Ground Loop Design (GLD). GLD is a powerful geothermal design software that is used by companies and contractors. Unfortunately, the software costs thousands of dollars, which does not fit into our budget. As our team does not contain a computer science major, any program we used would have to be learned from scratch. COMSOL was thus eliminated, for it is not made to design geothermal systems without advanced programming skills.

The next round of software options came from Professor Tester’s grad students and consists of software that is much simpler and only used for preliminary design, what we desire. The list includes: eQUEST, EnergyPlus, TRNSYS, EnergyGauge USA, GLHEPRO, EED, RETScreen and GeoStar. After examining each of them thoroughly, the final decision came down to a financial one. Only EnergyPlus and RETScreen were free options. Ultimately RETScreen was chosen because of its straightforward input interface and simplicity, though it still provides useful preliminary data and design.

RETScreen is an analysis program that determines system requirements based on user inputs. Using a case study template from an office warehouse in Canada, we employed the software to calculate the necessary length of our piping. To fit the system to our site as accurately as possible, some input values were altered while others were kept constant. The first input option is the climate, which was set to Ithaca/Tompkins Co. The next part of the program is the “Load and Network” section, which deals with the heating and cooling loads of the building. Since we do not have exact sizes for the building the square footage of the case study was keep constant. The average heating and cooling loads were also kept constant. The case study values will serve as an upper limit, for our building will contain high tech insulation, demanding less energy to heat or cool the building (overestimation is always preferable). In the “Energy Model” section all input values were kept constant. The capacity of our heat exchanger had not been determined yet, so the case studies capacity was used. Finally on the “Tools” page the data found from early sections was compiled along with the temperature of the ground based on the climate data to determine the piping requirements for our vertical closed loop system.

As the team moves forward to the next semester with a preliminary design and copious information about all aspects of the system, a more advanced design should be created using, if possible, GLD. It is the preferred software for geothermal design, with the best user capabilities and the best results. Though it is expensive, if the team would like to produce a final design capable of being implemented, the information learned from RETScreen and our research must be further analyzed.

Energy Estimates

Once all the data has been inputted, RETScreen combines it with their assumptions and undergoes calculations to deliver the outputs. The first output calculated is the heating and cooling loads. The averages of each month are plotted on a graph (figure 22). Since the area


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under each curve is fairly equal, our system will be balanced, which allows it to maintain its efficiency without disturbing the ground temperatures.

Figure 33. RETScreen system load analysis.

The Energy Model determines whether or not the system is capable of supplying all of the heating and cooling to a building or if a backup system is necessary. Our system was designed to completely supply the building and this analysis confirms it will have the capability, based on our input values. The final and most important page is the ground heat exchanger analysis. Based on our heat pumps capacity and our heating and cooling the software calculates the length of the piping. Our system requires 1,491 m of piping. This would most likely be split into multiple boreholes and loops. For example our system may consist of 7 wells, each about 200 m deep. The software gives us a basic idea of the design of our system; however, it is very elementary. Most data is estimations, and the system is most likely a large overestimate of our actual requirements. Also, RETScreen does not optimize the system based on the number of wells and their depth, but only gives a total piping length. As more data surfaces it can easily be plugged into the program and the results will be recalculated and updated.

Cost Estimates

Installation prices vary depending on the type of loop system, with vertical loop systems being substantially more expensive due to increased drilling depth. Estimates for similar heating and cooling loads indicate that installation of a geothermal system for the SRF will cost between $20,000 and $25,000.[46]

This translates to a payback range from 2-10 years, assuming current conventional energy costs. The variation largely stems from environmental and seasonal factors, as well as variations in actual energy load in the SRF. The lifetime of the system ranges from 18-23 years, although this can be increased with effective maintenance.[46] The cost of replacement is also less than the initial installation cost because boreholes can be reused.


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Conclusions

Recommendations

Based on our research throughout the semester, we recommend a closed loop, vertical geothermal system because of its space efficiency and capacity to provide for a larger heating and cooling load. We recommend that this system be installed using rotary drilling because it is the cheapest and fastest method available for normal soil conditions. As for the piping and refrigerant used in the system, we propose a combination of Ethylene Glycol (25- 30%) and Water (70-75%) and High-Density Polyethylene piping for the external, ground loop to protect the system against inefficiencies due to extreme cold while accounting for safety concerns and maintaining efficient heat exchange within the system along with modularity, respectively. For the internal loop, which will not experience the same cold temperatures, we propose using water and normal Polyethylene piping for a more efficient and safe heat transfer and increased modularity.

We also propose that the system entail two heat pumps, whose requirements and size can be determined using the sample calculations that we reported. By having two heat pumps, this allows separate areas of the building to be heated at very different temperatures, the heating and cooling demand to be met more efficiently, and for future testing and heat pump model comparisons. Additionally, these pumps could potentially operate as an additional safety feature with one pump meeting the most high priority heating and cooling needs, such as research, within the building should maintenance or issues arise for the other heat pump. These heat pumps will serve to both heat and cool the SRF, with the goal being to meet the building’s entire heating and cooling demands. We also recommend expanding the scope of our software usage to include GLD in addition to RETScreen for any final design.

This geothermal system should also incorporate a hydronic, underfloor system to effectively heat and cool the different areas of the facility. By having a dry, underfloor installation of this system, the SRF can be heated and cooled comfortably and efficiently while maintaining the most modularity possible and protecting the other systems that will be installed underfloor, namely wiring. We recommend further work with Warmafloor and the use of their Manifold system to effectively moderate the various temperatures of each space and to adapt the hydronic system so that it can work with the Haworth raised access floors while maintaining maximum modularity and efficiency.

Finally, we recommend monitoring pressure drops, temperature, and refrigerant flow using simple pressure gauges throughout the piping, many 1-Wire temperature sensors throughout the piping and the building, and flow sensors, which we want to work with the sensors team to develop, respectively. We recommend using a digital monitoring system, such as the Web Energy Logger (WEL) because of its increased accuracy and less “noise.”


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Timeline

We plan to accomplish tasks in Spring 2011 according to the following timeline:

January-March

- Continue talks with Ramtech Engineering (Syracuse, NY), which reached out to us and indicated a desire to help.

- Get Haworth specifics from Modular to beginning working with Warmafloor to evaluate the compatibility of the two systems.

- Procure materials for the piping and refrigerant combination.

March-May

- Request sample heating modules from Warmafloor in order to conduct tests with the Haworth flooring system in the HVL.

- Work with sensors to develop flow sensors that will alert us to leaks within the system and test their effectiveness.

- Overall: construct a model geothermal system with 2 heat pumps to test the efficiency and functionality of the system, refrigerant, monitors, and controls at various temperatures.

- Update RETScreen analysis to consider new developments.


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External Contacts

Mina Amundsen (University Planner)

Ed Wilson (Facilities & Sustainable Energy Team Manager, Cornell Sustainable Campus)

Don Bruce Fox ([email protected]), Maciej Lukawski ([email protected]), Koenraad Beckers ([email protected]) (Dr. Tester’s grad students)

Elbert Chang (Former student of Dr. Tester)

The Thomas Group (Ithaca, NY)

Ramtech Engineers of Syracuse (www.ramtechengineers.com)

Oxford Piping Inc. (http://www.oxfordplasticsinc.com/geothermalheating.htm)

Warmafloor (http://www.warmafloor.co.uk/)


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Appendix

[A] Enthalpy Curve. [Annotations added, original image available online at http://whitebrooksolutions.com/documents/P-HDiagram_Water.pdf]


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References

[1] Union of Concerned Scientists. “How Geothermal Energy Works.”16 Dec 2009, accessed 15 Dec 2011. <http://www.ucsusa.org/clean_energy/technology_and_impacts/energy_technologies/how-geothermal-energy-works.html>

[2] United States Department of Energy. “Geothermal.” Accessed 15 Dec 2011. <http://energy.gov/science-innovation/energy-sources/renewable-energy/geothermal>

[3] Center for Environmental Innovation and Leadership. “U.S. has large geothermal resources, but recent growth is slower than wind or solar.” 22 Nov 2011, accessed 15 Dec 2011. <http://www.ceileadership.org/index.php/energy-efficiency-and-renewable-energy/4834>

[4] Triterra. “Open Loop Geothermal System.” Accessed 15 Dec 2011. <triterra.us>.

[5] Bell, Frederic Gladstone. Engineering geology and construction. Taylor & Francis, 2004. Pg.8

[6] Geo4VA (Special Energy Project funded by the U.S. Department of Energy's State Energy Program through the Virginia Department of Mines, Minerals, and Energy at Virginia Tech), “Earth Temperature and Site Geology.” Accessed 13 Dec 2011. <http://www.geo4va.vt.edu/A1/A1.htm>

[7] Culver, Gene. "Chapter 6: Drilling and Well Construction." Klamath Falls, OR: Print.

[8] Fippin, Elmer, and William Carter. Soil Survey of the Binghamton Area, New York. 1905.

[9] "Geothermal Boreholes, Ground Source Heat Pumps." Synergy Boreholes. Synergy Boreholes and Systems LTD., 2011. Web. 3 Dec 2011. <http://www.synergyboreholes.co.uk>

[10] "Ground-Source Heat Pump Project Analysis." RETScreen Engineering & Cases Textbook. Canada: Minister of Natural Resources Canada, 2005. Print.

[11] "How it Works." GeoThermal. Alliant Energy, 2011. Web. 3 Dec 2011. <http://www.alliantenergygeothermal.com/index.htm>.

[12] McCray, Kevin. “Guidelines For The Construction Of Vertical Boreholes For Closed Loop Heat Pump Systems.” Westerville, OH:

[13] U.S. Department of Agriculture. Honeoye -- New York State Soil.

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