MECH 4010 Design Project I

Team #1

Chilled Engineering Systems

Design Final Report -Design and Analysis of an Ice Pond Refrigeration SystemTeam Members:

Derek Britten B00196127

Roger Connolly B00196560

Ben Francis B00145217

Adam Trudeau B00146132

Steve Vines B00143285

Submitted to: Dr. Murat Koksal and the Dalhousie Mechanical Engineering Faculty

Date: December 3rd, 2004

Table of Contents

11.Introduction

32.History

43.Design Requirements

43.1 Size:

43.2 Ice Making

43.3 Testing

53.4 Ergonomics/Human Factors/Safety:

53.5 Aesthetics:

53.6 Cost and Materials:

53.7 Timing/Deadlines:

63.8Deliverables:

63.9Intellectual Property:

74.System Components

95.Ice Pond Structural Design

95.1 Design Options

135.2 Selected Ice Pond Design

145.3 Budget for Ice Pond Structural Design

156.Ice Pond Heat Exchanger

156.1 Design Options

206.2 Design Comparison

206.3 Heat Exchanger Design

206.3.1 Heat Transfer Calculations

226.3.2 Ethylene Glycol Mixture

236.3.3 Heat Exchanger Length

246.3.4 Copper Pipe Characteristics

246.3.5 Final Design

256.4 Budget

267.0 Ice Pond Cover

267.1 Designs

297.2 Selected Design

307.3 Bill of Materials

318.0Insulation

318.1 Sub-Floor Insulation

328.2 Reservoir Wall Insulation

348.3 Reservoir Cover Insulation

348.4 Connector Pipe Insulation

358.5 Budget

369.0Ice Making System

369.1 Design Options

429.2 Selected Ice Making System

439.3 Freezing Time Plot

4510.0Ice Making Plan

4711.0Load Testing

4912.0Conclusion and Future Goals

5113.0References

List of Figures7Figure 1 - System Diagram

10Figure 2 - Rectangular Pond with Sloped Walls

10Figure 3 - Rectangular Pond with Sloped Floor and Protective Grate

11Figure 4 - Circular Pond with Wedging Structure

12Figure 5 - Circular Pond with Base Support

13Figure 6 - Circular Pond with Wood/Steel Support Structure

16Figure 7 - Ice Pond HX Option One

17Figure 8 - Ice Pond HX Option Two (American Radiant 2003)

18Figure 9 - Ice Pond HX Option Three

19Figure 10 - Ice Pond HX Option Four

21Figure 11 - Heat Transfer Diagram

23Figure 12 - Heat Exchanger Length Comparison for Material

25Figure 13 - Heat Exchanger Final Design, Laid in the Pond

27Figure 14- Option 1

28Figure 15- Square Cover

28Figure 16- Bottom View of Square Cover

28Figure 17- Round Cover

28Figure 18- Round Cover Open

40Figure 20 - Nozzles and PVC Piping System

41Figure 21 - Plot of Drop Height versus Ambient Temperature for Various Droplet Sizes

44Figure 22 - Plot of Freezing Time versus Depth of Water for Various Ambient Temperatures

List of Tables13Table 1 - Ice Pond Structural Design Comparison

14Table 2 - Budget for Ice Pond Structural Design

20Table 3 - Ice Pond Heat Exchanger Comparison

22Table 4 - FCU Characteristics (AZ Parts Master 2004)

22Table 5 - Freezing Temperatures for EG Solutions (Engineering Tool 2004)

23Table 6 - Exchanger Length compared to %EG in Working Fluid

24Table 7 - Heat Exchanger Length Compared to Inner Diameter

25Table 8 - Budget for the Heat Exchanger System

29Table 9 - Ice Pond Cover Comparison

35Table 10 - Budget for Insulation

42Table 11 - Comparison Table for Ice Making System

AbstractThe storage of ice created in the winter for use in the summer has been used for over 2000 years. Only in recent years has it been considered for the use of air conditioning in the summer months.

Group 1, called Chilled Engineering Systems , is designing an Ice Pond Refrigeration System that will be used to test the effectiveness of a refrigeration system based on using the heat of fusion of water to provide air conditioning to a given space. This will then be compared to a conventional vapor compression system to show the benefits of a system of this type. This report outlines the first half of the final year design project of Group 1, called Chilled Engineering Systems. The design process includes design requirements, design criteria, brainstorming solutions, design refinement and finally a selected design. There are several sub-systems that needed to be designed and each sub-system will be described in this manner.

Initial calculations have shown that the reservoir selected in this design can hold approximately 8 m3 of ice. While this is an admittedly modest number, it will be suitable for the goal of this project, which is to evaluate the efficiency of such a system. This volume of ice has a cooling potential of 2.7 GJ. A detailed budget has estimated this project to cost approximately $4000.00 CAD.Future work includes building the working model, filling the reservoir with ice and performing a series of tests to gather data. This data will be analyzed and applied to a full-sized application for greenhouse and food cold storage purposes.

1. Introduction

The objective of this project is to evaluate the effectiveness of using an ice pond cooling system to absorb a heat load. To meet this objective, Chilled Engineering Systems will design and build a refrigeration system using ice produced and stored in a thermally insulated reservoir, or ice pond. The system will be tested for performance evaluation and data gathered will be used for a techno-economic analysis for possible greenhouse and food preservation applications. Accurate measurements of cooling load provided and ice consumed to produce this load will be required to give a realistic estimation of an overall efficiency. The system could potentially replace a conventional vapor compression refrigeration cycle at a temperature range of 3C - 10C.The heat transferring system is composed of two heat exchangers, a pump and a closed copper piping loop in which a mixture of ethylene glycol and water is circulated as a working fluid. The heat exchanger located in the ice pond will cool the working fluid in the loop. The fluid is circulated using a pump to the other heat exchanger, located in the simulated load, where the fluid will cool the ambient air. The cool air is then distributed throughout the load by a fan through a manifold. The ice will be produced in winter when the ambient temperature is below 0C. An ice making system will be used to make ice that has low porosity and therefore higher cooling capacity. The ice will be stored in the ice pond until the summer, when it is needed.

The main design components discussed include the ice making system, the ice pond design, the pond heat exchanger and the load heat exchanger. Each component design option is compared using a list of criteria for that component, ranked from 1 to 5, 5 being the best. The design with the highest score was selected.

The majority of the construction of this project should be completed by mid January. This is the coldest part of the year and therefore should be taken advantage of to make ice. Making ice at this time will give the shortest production times and allow more time for testing. If need be, more ice will be created in February for a second round of testing.2. History

The use of ice pond refrigeration technology dates back many centuries. For more than two thousand years people have been exploiting the cold temperatures of winter for use in the summer in cooling applications such as food storage. Organic waste has been used to insulate the ice during the hot seasons of the year. This clean method of refrigeration can still be found today in many parts of the world.

It was not until the late 1970s that ice pond refrigeration research began. Universities, such as Princeton and Illinois State Universities, as well as institutions like Public Works Canada and Commonwealth Edison Company were at the forefront of the research.

Several commercial ice ponds were later developed by NOVA, Inc., a company started by Theodore Taylor. The ice ponds produced by NOVA take full advantage of the natural weather cycles of North America. The cold nighttime air of winter is used to freeze water in a reservoir. These ice ponds of winter use less than 10% of the energy required by conventional refrigeration systems and have paid themselves off in one to three years of operation.

The first automated ice pond was built in Japan in the late 1990s. This design used nozzles that would engage automatically when the temperature and weather conditions permitted efficient ice making. This ice pond was used to cool produce. The reservoir size was approximately 1000m3, producing ice with a porosity of around 25%. They were able to obtain an overall efficiency of 41% - 47%, meaning that 41% - 47% of the heat of fusion of the ice was converted to useful air conditioning.3. Design RequirementsThe main goal of this project is to determine how much cooling can be produced for a given volume of ice. In doing so, the cost of an ice pond system will be evaluated not only for the prototype, but for a larger scale. We will design and build one complete system that could be used for a variety of applications such as greenhouse cooling, food storage cooling and residential cooling. Using the test results from this prototype, the feasibility of a full scale system will be evaluated. The budget for this project must be less than $5000 CAD.Chilled Engineering Systems will deliver to the client a completed prototype with the testing results as promised. Also, an accurate estimation of the size, cost, and performance of a scaled-up system to allow for some comparisons to traditional cooling systems will be performed. This will require some accurate calculations and cost analysis of the full scale system.

4. System ComponentsThe Ice Pond System is composed of several subsystems, as shown in figure 1.

Figure 1 - System Diagram

The main systems are as follows: Reservoir (Ice Pond),

This is where the ice is to be stored and insulated. Also needed for the reservoir is an insulated cover to protect from snow, rain and any warm days that could melt the ice and lower the efficiency of the system Insulation

The reservoir must also be insulated on the sides and the bottom to prevent any sources of thermal energy external to the system from entering Ice Making System

This is the method that will be employed to introduce the water to the ice pond Ice Pond Heat Exchanger This heat exchanger will be responsible for cooling the working fluid that is entering the pond from the load. Its dimensions are a critical aspect of the entire system

Load

The load is the part of the system from which heat will be transferred. The load is to simulate the environment that would be cooled by the full scale application. The following sections are detailed summaries of the design process, from initial ideas to refined designs. Sample calculations are found in the appendices.5. Ice Pond Structural Design

Several criteria have been evaluated to make the selection for the appropriate ice pond design. The structure must be able to support the weight of approximately 10 cubic meters of ice (about 9 tonnes) and must protect the heat exchanger (located at the bottom) from potential movement of the ice block. To aid with the structural support of the mass of ice and with the insulation of the reservoir, the pond could be partially buried in the ground. This can be applied to any of the design options, but is undesirable due to the added labor involved with burying the pond. The design must be simple to construct, inexpensive and functional.

5.1 Design Options

Several Designs were considered for this part of the system. The following sections outline these designs.Option 1: Rectangular Pond with Sloped Walls

The pond would be a rectangular shape with the walls of the pond angled to help support the weight of the ice block. The angled walls also direct the melt water to the heat exchanger located on the flat surface at the bottom of the pond.

This type of design is advantageous for a few reasons. It is a simple design due to its square shape. There are no complex angles to construct. The sloped edges of the pond serve two purposes. They direct the melt water toward the heat exchanger located at the bottom of the pool, increasing the effectiveness of the heat exchanger. They also provide some support to the ice block. The heavy mass of ice is wedged between the sloped edges, partially supporting the weight of the ice.

Figure 2 - Rectangular Pond with Sloped WallsThe main disadvantage of this design involves the protection of the heat exchanger. The sloped walls do provide some protection, but there is no guarantee that the heat exchanger will be completely protected. As the ice block melts, the wedging effect of the sloped walls may become less advantageous.

Option 2: Rectangular Pond with Sloped Floor and Protective Grate

This option uses one sloped floor to support the ice and to direct the melt water to the heat exchanger on a flat surface at the bottom of the pond. The heat exchanger is protected by a steel grate that will also help support the ice block.

There are several advantages to this design. The main advantage is that the ice block is totally supported with absolutely no stress on the heat exchanger. This is accomplished while ensuring improved effectiveness of the heat exchanger.

The disadvantages arise from the incorporation of the steel grate. The support of the steel grate may introduce unwanted point loads on the base of the ice pond.

Figure 3 - Rectangular Pond with Sloped Floor and Protective GrateOption 3: Circular Pond with Wedging Structure

This pond is circular shaped with a wedging structure to help support the mass of ice with minimum stress to the heat exchanger. The wedging structure consists of steel channel inserted at an angle along the radius of the pond, from the wall to the bottom of the pond. The channel will approximate a cone shaped wedge. The main advantage to this design lies in the circular shape. It evenly distributes the load along the wall with no points of stress concentration. The wedging structure acts the same as the sloped walls of Option 1 & 2, providing support to the mass of ice to help protect the heat exchanger.

The major negative aspect of the design is introduced by the channel. Just as in Option 2, the channel introduces point loads that will affect the strength of the pond. Also, connecting the channel to the wall and base of the pool would be very difficult without altering the watertight aspect of the pond.

Figure 4 - Circular Pond with Wedging StructureOption 4: Circular Pond with Wooden Base SupportThis design is very similar to Option 3, but instead of the steel channels wedging the ice block, 4 x 4 lengths of wood will be placed alongside the heat exchanger pipes. The 4 x 4 beams will be slightly taller than the heat exchanger pipes so the mass of ice will rest on them and not the pipes. To maintain melt water circulation, holes will be drilled through the lengths of wood.Again, the circular shape of the pond evenly distributes the load along the wall with no points of stress concentration. The wooden beams fully support the mass of ice and do not introduce unwanted point loads on the pond structure. The construction of the supports is extremely simple.

However, the introduction of the lengths of wood between the heat exchanger pipes greatly impedes the circulation of the melt water. Another disadvantage of using the wooden supports is their buoyancy force. After the ice block has melted, there will be nothing holding down the supports and they will start floating around in the pond. In order to fix them to the pond, some alterations would have to be made to the base of the pool, which is undesirable.

Figure 5 - Circular Pond with Base SupportOption 5: Circular Pond with Wood/Steel Support StructureThis design utilizes both wood and steel components to support the mass of ice, and protect and elevate the heat exchanger. A steel member is fastened to a wooden member of the same length through small wooden spacers. The gaps created by the small wooden spacers are used as passages for the heat exchanger piping to go through.

The wooden member on the bottom of the structure elevates the piping to maximize the amount of surface area exposed to the melt water, thus improving the efficiency of the heat exchanger. The next advantage to this design involves the use of the steel members. They will combat the buoyant forces of the wood and will work to hold down the structure. The required volume of steel is also much smaller than that of the wood, so there is more space available to make ice if required. The last main advantage is that the heat exchanger pipes are completely protected by the structure.

The only disadvantage to using this design is the fact that the steel may be expensive to use. However, the steel will work against the buoyancy force of the wood, eliminating the need to physically fasten the structure to the pool. This largely outweighs the cost of implementing the steel.

Figure 6 - Circular Pond with Wood/Steel Support Structure

5.2 Selected Ice Pond Design

The following table weighs the different aspects of each option. Each design was scored out of 5 based on the different desired criterions.

Table 1 - Ice Pond Structural Design Comparison

CriterionOption 1Option 2Option 3Option 4Option 5

Cost32154

Functionality34235

Ease of Construction32245

Scalability55355

Adequate Support34455

Protection of Heat Exchanger24355

Total1921152729

Based on the evaluation table, Option 5 is the best design for the ice pond. A circular above ground pool can be purchased very inexpensively, to cut down on costs and construction. It is designed to hold the required amount of water as well. The design also adequately, simply and relatively cheaply protects the heat exchanger and is very easy to scale to a full size application. For these reasons, Option 5 will be used for the ice pond. For a detailed design and calculations, please refer to Appendix A5.3 Budget for Ice Pond Structural Design

Table 2 - Budget for Ice Pond Structural Design

Ice Pond Structural SupportQuantityUnit CostHSTTotal Cost

1/4" x 4" mild steel flat bar (ft)60 $ 3.00 $ 0.45 $ 207.00

5/4"x4"x16' PT (piece)4 $ 8.32 $ 1.25 $ 38.27

2"x4"x16' PT (piece)2 $ 10.20 $ 1.53 $ 23.46

Wood Screws (2.25in)60 $ - $ -

Total $ 268.73

The Ice Pond Structural Design is an important component of the project. It will protect the heat exchanger, and will promote a more effective heat exchange by maximizing the surface area of piping exposed to the melt water. However, it is a simple design with minimal construction required.

6. Ice Pond Heat ExchangerFour design options will be compared to select the final heat exchanger (HX) design. Each design will be given an overview and analyzed based on a set of criteria. A comparison will be done rating each option to the given criterion. From this comparison, the best HX design will be determined and chosen.

The four HX options will be compared based on functionality, durability, ease of construction and cost. The HX should have a high rate of heat transfer, reducing overall length and increasing efficiency. Durability is important as well, as it is not to fail during testing. Ease of construction was a factor to allow setup of the system in a timely manner. With faster system setup comes a longer period for ice making and testing. It is important to keep cost as low as reasonably possible.6.1 Design OptionsOption One

The first option does not use a heat exchanger at all. This is an open loop system that circulates the melt directly as the working fluid for the FCU . Baffles would be installed in the reservoir to allow for more cooling time of re-circulated water. The baffles would create a longer path for the water to travel, thus increasing heat transfer. A conceptual drawing of option one is shown in Figure 7The main disadvantage of the open melt water system is its functionality during the proposed testing period. For the testing period, the ambient temperature will be around -6C. To prevent freezing in the pipes traveling from the pond to the load, an additive such as ethylene glycol (EG) would be needed. If an EG mixture is introduced into the open system, the ice will melt at an accelerated rate. This will dramatically skew testing results of ice melting in relation to the cooling provided. If this system were to be tested in warmer temperatures, it would benefit from directly using the melt water. This is opposed to all of the other options that use a HX, adding thermal resistance and reducing overall heat transfer.

Figure 7 - Ice Pond HX Option OneThe open melt water system does rank high in the remaining areas of durability, ease of construction and cost. With the removal of the HX from the ice pond, there is no chance of HX failure. Also there is less overall construction and associated costs.

For a full scale ice pond refrigeration system, this is an excellent solution. For the scaled model, this is not a viable option. There are high risks of the system not working during testing periods.

Option Two

For option two, the HX piping material would be Kitec. Kitec piping is a combination of an aluminum core with interior and exterior plastic layers. A benefit of Kitec is that it can be easily bent into the desired shape in long piece of tubing. Figure 8 shows the flexibility of this material.

Figure 8 - Ice Pond HX Option Two (American Radiant 2003)The main advantage of Kitec is the inherent ease of construction. Kitec piping can be bent by hand. It is possible that only one long piece of Kitec would be needed. It is also slightly cheaper than copper. 3/4 Kitec piping is $0.99/ft compared to 3/4 copper piping which is $1.14/ft for size M and $1.39/ft for size L. The cost of fittings for the Kitec material is slightly more expensive per piece, but since only a few would be needed, the overall cost of the fittings would be reduced.A disadvantage of Kitec is its value of thermal conductivity; kKitec = 0.43W/mK (Kitec nd). Kitec is normally used with radiant in-floor heating. The principal behind radiant in-floor heating is to transfer heat by radiation from a hot circulated medium to a much colder surrounding. The temperature difference between the working fluid and the ambient environment is approximately 20C or less, and radiation is therefore neglected. The majority of the heat transfer is in the form of conduction, which is directly proportional to the thermal conductivity, k. The thermal conductivity of copper, kcopper = 403.34W/mK, which is 938 times greater than that of Kitec (Incropera 2004). Kitec piping requires 18% more length than that of copper piping to have equivalent heat transfer.

Another disadvantage is the forming of the Kitec. A general guideline is that the minimum bending radius is to be 5 times greater than the radius of the pipe to avoid kinking. This minimizes the length of pipe that can be fit into the pool. Also, since Kitec can be shaped by hand, it is a strong possibility that it could be crushed and destroyed by the ice. Option Three

The third option uses a closed loop, single pass copper pipe HX. The HX will cover a large area of the ice reservoirs bottom, promoting an even melting of the ice. One possible layout for the single pass unit can be seen below in figure 9.

Figure 9 - Ice Pond HX Option ThreeOption Four

This option uses a closed loop, double pass copper pipe heat exchanger. This system was examined to determine if the heat transfer could be increased over the single pass system. This setup would also allow for a more even melting of the ice due to the distribution of the copper piping. A layout for the double pass HX is shown in figure 10.Options 3 and 4 or compared together since they are very similar. Both options use copper piping without fins. The fins could be easily damaged by shifting ice.

Figure 10 - Ice Pond HX Option FourOne advantage of a copper HX design is that copper is much stronger than Kitec. It would be able to handle forces placed on it from the ice much better than the Kitec. The heat transfer is much greater than the Kitec because of the increased thermal conductivity. Although the construction will be more time consuming, it is not too labour intensive and was not a deciding factor.The major difference of the single pass to double pass HX is the required length to achieve the necessary heat transfer. The double pass HX was considered in the attempt to reduce the length of the HX by increasing the efficiency of the heat transfer. It was found through calculations (see Appendix B ) that the double pass simply doubles the length of copper pipe needed since the flow is laminar. When the fluid is separated into two streams, both will require the same amount of piping length to achieve the desired temperature reduction.

6.2 Design Comparison

In comparing the four possible options, a rating was developed to determine the best solution. For each criterion the three possibilities were rated from one to ten, ten being the best. If the options were equivalent for a particular criterion, an equivalent score was awarded. The option that attained the highest score was determined to be the best solution. Table 3 below shows the compared results:

Table 3 - Ice Pond Heat Exchanger Comparison

CriterionOption 1Option 2Option 3Option 4

Functionality0354

Durability5244

Ease of Construction4443

Cost5432

Total14141613

As shown, option 3, the single pass copper pipe HX, was selected as the final design. It accumulated the highest score and is most suitable for the testing period. As a note, if this selection was to be completed for the full scale design, option one, the open loop model, would have been chosen.

6.3 Heat Exchanger Design

With the selection of a general design, several elements must be decided upon to reach the HXs final design. The first element is the percentage of EG to be mixed into the water medium, lowering its overall freezing temperature. The second will be to choose an appropriate cooper pipe size and wall thickness. With these elements chosen, a final pipe length can be determined and a HX layout can be created. As a comparison, the required lengths of options two, three and four will be found.6.3.1 Heat Transfer CalculationsThere are three heat transfer resistances when cooling the working fluid using the ice: internal flow convection (hmix) inside the HX, conduction through the pipe wall (kcopper), and the free convection (hmw). The free convection is the heat transfer that occurs in the melt water between the piping and the ice. Figure 11 below shows a diagram of this heat transfer process:

Figure 11 - Heat Transfer DiagramTo determine the length of the HX, a load and FCU was initially picked. Primarily, the energy available in 8000kg of ice was found to be 2.672 GJ. It was assumed that the system would be able to extract 30% of this energy and would completely melt the ice over a two week testing period. This gave an average cooling load of 662.7W. Comparing this load to commercial available units, a FCU was picked for calculations. AZ Parts Masters smallest one, FCU-310cfm (Left Hand) gave the characteristics shown in table 4:

Table 4 - FCU Characteristics (AZ Parts Master 2004)

The FCU values were taken with the resistance found in the HT diagram from figure 11. From this, the needed length of the HX is calculated with Newtons Law of cooling (Incropera 2002). The calculation is completed with the equation below:

A sample calculation for calculating the length of the HX can be found in Appendix #. All calculations for length followed this procedure.

6.3.2 Ethylene Glycol Mixture

The importance of adding EG is to reduce the freezing temperature of the working fluid so that the pipes in the refrigeration system do not freeze. Table 5 below gives the freezing point for a range of EG solutions:

Table 5 - Freezing Temperatures for EG Solutions (Engineering Tool 2004)Ethylene Glycol Solution(% by volume)0102030405060

Freezing Point Temperature(oF)3223142-13-36-70

(oC)0-3-8-16-25-37-55

During the testing period, which will be in late February or early March, the average daily minimum will be -6C. A comparison for overall HX length using this temperature was done. When using the single pass copper HX design the following results in table 7 were found:

Table 6 - Exchanger Length compared to %EG in Working Fluid

The 20% EG solution has only needs an extra 2m of length for the needed heat transfer. Considering the daily minimum testing temperature, it was deemed acceptable to use the 20% EG solution in the working fluid.

6.3.3 Heat Exchanger LengthThe following analysis was done with a 20% EG solution as the working fluid. The results are shown in figure 12 below:

Figure 12 - Heat Exchanger Length Comparison for Material

The single pass copper HX was found to have the highest efficiency. Along with its high durability in being able to handling the ices adverse forces, it was concluded to be the selected HX.

6.3.4 Copper Pipe Characteristics

The Nominal pipe size of the HX was chosen by making them comparable to the FCUs connectors. These have an outer diameter (Do) = 3/4 and inner diameter (Di) = 5/8 = 0.625. The most equivalent FCU is the 5/8 copper pipe, but as this is not commercially available, another size is necessary. The next two closest sizes are 1/2 and 3/4. When these were compared with length it was found that as the nominal size increases the necessary pipe length decreases. From this the 3/4 copper pipe was chosen.

With the nominal pipe size chosen, the Di was still to be determined. The pipe schedule for 3/4 copper gives three possibilities for Di. These are K=0.745, L = 0.785 and M = 0.811 (Johns 2003). When these diameters were compared to length, changes in the results are shown in table 7 were found:

Table 7 - Heat Exchanger Length Compared to Inner Diameter

As there is no significant change in the length of the HX, a thicker pipe wall would be preferred to stand up against the stresses placed on the HX by the ice. Due to the commercial availability of sizes L and M, L was selected because it has thicker walls.6.3.5 Final Design

The HX will be a single pass design, made from 3/4 L copper piping. There will be 14 passes across the bottom of the pond with a 6 spacing between centers. The total length of piping inside the pool is 42.1 m (138.2 ft.), neglecting the inlet and outlet pipe lengths. The pipes will be supported from below by a wooden/steel support structure (see section 5). The ice above it will also be supported by this structure, to prevent damage to the HX. The working fluid of the system will be a solution of 20% EG and 80% H2O. A drawing of the HX in the support structure and ice reservoir is shown in figure 13.

Figure 13 - Heat Exchanger Final Design, Laid in the PondPlease refer to engineering drawing HX-01 for the HXs component list and drawing HX-02 for its dimensions in Appendix B.

6.4 BudgetTable 8 gives the budget estimating the cost for the HX system:

Table 8 - Budget for the Heat Exchanger System

7.0 Ice Pond Cover

There are several reasons why it is necessary to cover the ice pond. The primary reason is to insulate the ice so that it does not melt during the summer months. However, it is also crucial to cover the pond in the winter to protect the ice from the melting effects of rain, sleet, snow and the occasional warm day. Also, since testing will be done in the winter, additional cooling of the pond is undesirable, and needs to be minimized.7.1 Designs

Several things were considered in the selection of the ice pond cover. As with all the other components, cost, functionality and ease of construction were considered. For this case functionality meant that the cover would not interfere with the ice making process and access to the pond was still available. Other criteria considered were the ability of the cover to handle the typical Halifax snow load (1.8 kPa) and the overall aesthetics of the cover.

Option 1

The first option was to use a tent like structure to protect the pond from precipitation. This tent would have been covered with a tarp, which could be adjusted to permit air flow to increase convection heat transfer during the ice making process. This structure would not have any insulation effects, so in order to insulate the pond sawdust would be placed over the ice after the ice making process was completed. As an alternative to sawdust, a polystyrene cover could be used on a smaller scale, but this would not suit an industrial scale ice pond.

An advantage of this design is that an ice making system could be suspended from the structure, if that system is used (see section 9). The structure also provides shelter for the entire system from rain, snow, wind, and other environmental factors. The structure would be designed to be able to carry the maximum snow loads experienced in Halifax. Depending on the design of the walls of the structure, they could be removed to increase the air flow, as previously mentioned.

Figure 14- Option 1

This option also has many disadvantages. The main disadvantage is cost. It would need to be a large structure, at least 4m x 4m, and would also need to be very tall to allow for the suspension of the ice making/nozzle system. With this option also being the largest, it would have the most time consuming construction as well.Option 2

Option 2 is a square cover that would be placed on the top of the pond and supported from the ground. This structure would be made in two pieces to reduce the weight and allow for easier removal. Extruded polystyrene and wooden cross members would be attached to the bottom of the cover giving it sufficient insulation and strength. Also, vapor barrier would be used to protect the ice from precipitation.

This design is easily constructed due to its shape. It is supported from the ground, not the pool walls and can therefore be designed to support heavy loads. With the shape of this design, it is also easy to attach insulation. It is also very inexpensive when compared to the first option.

Unfortunately this design is very heavy. An initial estimate states that each side would weigh approximately 72kg. It would need to be removed each time that ice is made since it completely covers the pool. It is also a waste of material since its shape is not the same as the pool.Figure 15- Square CoverFigure 16- Bottom View of Square Cover

Option 3

Option 3 is a round cover that seals to the top of the ice pond. This cover would be supported by the ground and insulated using polystyrene. Vapor barrier would prevent precipitation from entering the pool and the plywood joints will also be sealed with silicon. Like option 2, the cover would be made in two pieces to allow for easier removal, but it would also be hinged to allow for quick access.

Figure 17- Round CoverFigure 18- Round Cover Open

This design is more attractive that the second one because it can be removed or opened easily. Its shape also allows for easy placement of a gasket material to make an air-tight seal. It is the least expensive option since it does not waste material and it is also the most visually appealing

Due to the round shape, this will be more difficult to construct than the square cover. The benefits of this shape outweigh the increased construction difficulty. Snow will have to be removed to open the cover, and the hinges may freeze and need to be thawed. This design weighs approximately 60 kg, which is lighter than the square option, but still quite heavy.7.2 Selected DesignAs seen from the evaluation table, the design that best suits the criteria is Option 3. The hinged, round cover design will be the cheapest, lightest and most aesthetically pleasing design. It is not scalable for an industrial design, but this of little consequence because the cover does not directly affect the quality of ice. In an industrial application option 1 would be a better choice and budget numbers for fabricating a full sized model of the tent will still be obtained for the final report due in April. Calculations made for the sizing of the cover are presented in Appendix C.Table 9 - Ice Pond Cover Comparison

Criteria:Option 1Option 2Option 3

Cost355

Functionality534

Ease of Construction354

Handle Snow loads544

Aesthetics435

Total /25202022

7.3 Bill of Materials

Pool LidQuantityUnit CostHSTTotal Cost

1/2"x4'x8' Pressure Treated Plywood7$ 45.88$ 6.88$ 369.33

4"x4"x16" PT (piece)3$ 19.42$ 2.91$ 67.00

2"x4"x16" PT (piece)10$ 10.20$ 1.53$ 117.30

2"x2"x10' PT (piece4$ 5.00$ 0.75$ 23.00

Vapor Barrier (ft2)120$ 0.50$ 0.08$ 69.00

Truss plates72$ 0.50$ 0.08$ 41.40

Hinges (unit)4$ 15.00$ 2.25$ 69.00

Galvanized Nails (4.5in/ 2kg)1$ 9.99$ 1.50$ 11.49

Total$ 767.53

The round cover is scheduled to be built in December immediately after the pool is constructed. It will be removed during ice making to allow for air flow to increase heat transfer and closed when ice is not being made to prevent melting. The total cost is estimated at $970. 8.0 InsulationMinimizing heat transfer to the ice from the surroundings was an important issue for this project. If the energy were transferred to the ice not only from the heat exchanger but also from the ground and surrounding air, the ice would melt much more quickly and therefore data would be inaccurate. Also, if testing is to take place during February, ambient temperature will actually be lower than that of the ice, resulting in excess cooling and altering efficiency calculations.

In order to minimize any heat transfer of this sort, it was decided to install insulation on all parts of the ice reservoir, including underneath the bottom, around the sides and on the cover over top. The potential heat transfer magnitude for each of these parts varies, therefore different types of insulation were selected for the different areas.

8.1 Sub-Floor Insulation

In general, the underground temperature remains constant through the course of the year. It was determined, though, that the temperature at the surface of the ground is subject to change with varying above ground temperatures. On this principle, the temperature of the ground surface during summer was approximated to be at the temperature of the surrounding air. For this reason, it was deemed necessary to insulate the reservoir floor for potential heat transfer from the ground up.

Due to the fact that this insulation would be supporting the weight of the entire ice pond structure (including ice/meltwater), as well as space constraints, the selection for this insulation was limited. After consideration of these parameters, extruded polystyrene foam insulation was selected based on its ability to support sizeable weight and its adequate thermal resistance.

The thermal resistance of the panels is calculated by:

Where:Rtot = thermal resistanceL = width of insulation

k = thermal conductivity

Ac = area of heat transfer

The pool liner is quite thin and therefore the thermal resistance can be neglected. Thus,

WThe heat loss through the panels during February testing is calculated by:

WWhere:q = total heat transfer

Tground = ground surface temperature

Tice = ice temperature

8.2 Reservoir Wall Insulation

The wall of the ice pond posed a large surface area through which heat could transfer to the ice. As the wall is made of thin steel, the method of attaching a given insulation was not clear. There could be no protrusions through the wall for sealing purposes and there are no other obvious extensions on which to attach the insulation. The other parameter affecting the wall insulation is that it will be exposed to the outdoor elements, unless a structure is built around it, which seemed an excessive measure to protect the insulation.

Consultation was sought from insulation experts at various companies. After multiple conversations, it was determined that polyurethane spray insulation would be the best choice for this application. It is a somewhat newer technology in insulation with a variety of good qualities such as:

Versatile to be applied to almost any surface area

Weather resistant

Stops leaks

High insulation efficiency

Lightweight

Guildfords Inc. was found to be the only contractor in the area to supply this type of insulation.

The calculations for the heat transfer through the polyurethane are as follows:

EMBED Equation.3 Where:Rtot = total thermal resistanceL = width of insulation

k = thermal conductivity

Ac = area of heat transfer (through wall)

The thermal resistance of the liner could be neglected reducing the equation to:

K/WAnd the overall heat transfer is calculated using the following equation:

WWhere:q = total heat transfer

Tamb = ambient temperature

Tice = ice temperature

The negative value indicates that the heat transfer will occur from the ice to the surroundings. This extra cooling will be accounted for in final efficiency calculations.

The machine used to apply the spray can only be operated by a certified technician; therefore this job had to be left to the contractor. The cost of the entire job was originally quoted at $1500, but after further talks regarding the nature of the project and the funding available, Guildfords was able to reduce the quote to about $500, or possibly even donate the insulation if they are given sufficient notice.

8.3 Reservoir Cover Insulation

The approach taken to insulate this cover was to apply extruded polystyrene panels between the studs, much like in the walls of a house. Extruded polystyrene insulation was chosen due to its ability to fit in the various sizes between wooden studs. In order to protect the reservoir from moisture, vapour barrier will be installed above this insulation.

The analysis of the overall thermal resistance of the cover is slightly more involved than in the other cases, as the insulation is only between the studs, not covering the entire surface area. Therefore, thermal resistance will be provided by the wooden beams in parallel with the insulation, and this was taken into account in the calculations.

8.4 Connector Pipe Insulation

As the pipes connecting the heat exchanger to the inside load will be run outside, there is a large opportunity for heat transfer. For the purposes of this project, this could mean heat transfer from the pipes to the surroundings during spring testing or from the surroundings to the pipes during actual summer usage.

To insulate the connector pipes, standard expanded polyethylene pipe insulation was selected due to its ease of installation and appropriate size for the application. Based on the standard sizes of pipe insulation, the following calculations were made for the heat loss from the pipes.

Total thermal resistance per unit length of pipe:

Rate of heat transfer per unit length of pipe:

8.5 BudgetTable 10 - Budget for Insulation

The actual unit costs of all of the insulating materials were obtained, with the exception of the polyurethane spray. As this is a contract job that may be done at a significantly reduced price, an estimate of $300 is being used until further notice.

9.0Ice Making SystemSeveral ideas were considered in the design of the ice making system. It had to be easy to build, reliable and provide consistent ice making. Cost was also an important factor as a full scale ice making system could become expensive to construct as well as to run. Another criterion was the porosity of the ice that is formed; porous ice responds more quickly to the initial loading but has less total cooling capacity due to air bubbles.

The quality of ice produced will be mentioned numerous times throughout this section. For the sake of simplicity, the different terms will be explained now. The porosity of the ice is a measure of the volume of air trapped within the ice. A low porosity ice block means that the ice has very few air bubbles. This type of ice has the largest heat of fusion value, approximately 334 kJ/kg. As the porosity of the ice increases, the heat of fusion decreases because of the low specific heat capacity of air. This ice melts much quicker than the low porosity block, however.

The seemingly obvious choice is to make ice with low porosity. This is true for the majority of the ice. Our design requires that the heat exchanger be surrounded in water. For a given load, the high porosity ice will melt first and be the first to completely immerse the heat exchanger in water. Therefore, high porosity ice is required around the heat exchanger. Once the heat exchanger has been immersed in this type of ice, the low porosity ice is required.9.1 Design Options

The following section outlines the different options for this system, with advantages and disadvantages for each design.

Option 1 Filling pond with water

The basic idea of this design is to fill the pond with water all at once and allow it to freeze. This would be accomplished by using a nozzle and hose. There are many advantages to using an inherently simple system such as this one. The main advantage comes from the fact that it is such a simple system. There are no problems with reliability, manufacturing, or design complexity. The hose and nozzle are cheap and can be purchased anywhere.

Another advantage of this system is that it creates the lowest porosity block of all the designs. It is a very solid block with the highest heat of fusion and therefore the highest cooling potential.

One disadvantage of this design is the quality of ice immediately surrounding the heat exchanger. It would be low porosity and unresponsive to the initial loading from the working fluid. This means that the first time that the system is used, it would take a long time until the room experienced some cooling.

A major disadvantage to this design is the expansion of the ice. With such a large volume of water, the water will tend to freeze at the surface initially, like in a pond or lake. The water that freezes first will also freeze to the side of the pool and will want to stay there. As the water below freezes, it will try to expand vertically and laterally. This will stress the pool wall and also the heat exchanger. This stress could cause the pool to fail and when the ice began to melt, all of the water would be lost. With the heat exchanger also in jeopardy from this design, other options had to be considered.Option 2 Successive Ice Layering using Hand-Held Hose and Nozzle

This idea is similar to Option 1, except that it is done in many stages. A predetermined volume of water is sprayed into the reservoir and allowed to freeze. When the water freezes, the next volume of water will be sprayed in. This process continues until the pond is completely frozen.The volume of water to be sprayed into the pool is a direct function of the outdoor temperature and wind velocity. During a cold day, the ambient conditions would be exploited and more water would be sprayed into the pool to maximize ice production for that day and make up for days with particularly poor ice production.This system has all of the same advantages as option number 1 it is simple, cheap and reliable. This system has its own advantages over the first option, however. We are able to control ice making better with this system. On a warmer day, for example, during a snowstorm when it is not uncommon for the temperature to be above zero, we can simply close the lid and rely on the insulation of the cover and sides to prevent the ice from melting inside. We wouldnt spray any water at this time since it would only act to melt the ice already present.

The expansion problems with the first option are not a problem with this system. With small volumes of water sprayed, the water will still freeze on the top and bottom first with the sides to freeze next, but there would be a much smaller volume of water trapped in the middle. The ice would tend to expand vertically only, with little to no lateral expansion.

This option has the same disadvantages as the first option too, but they are more manageable with this method, for example, the quality of ice immediately surrounding the heat exchanger. When ice production begins, it is assumed that there will be snow on the ground. If snow from the ground is placed to surround the heat exchanger, and then water is sprayed in, the desired porous ice will be made. Once the heat exchanger is completely covered in ice, we will make ice using only water. This way, the advantages of both types of ice will be used.

The main disadvantage from this design is the need for constant attention from an operator. The ice will need to be checked several times per day to verify that the water is freezing at the predicted rates, or determine if it is freezing faster or slower. Adjustments to the calculations will need to be made if there are any large discrepancies.

Option 3 Snow making machine

This option involves using a snow making machine to create a snow and water (slush) mixture. This could be pumped directly into the ice pond which will be at or near 0C, so it will freeze quickly. The way in which slush would be pumped into the reservoir would be similar to Option 2 incremental volumes until the entire reservoir is frozen.

The main advantage of this system is that it would have freezing times that are a lot less than water injection methods since the mixture is already partially frozen and it is at zero degrees at the time of injection. There would also be minimal melting of the ice alreadyin the reservoir. There would be very minimal expansion of the mixture when it froze since it is already partially frozen.

The main disadvantage of this system is the quality of ice produced. It is a very porous mixture and would have a lot lower cooling capacity than the other two options already discussed. It is also a lot more costly than the other two ideas. Not only would a costly snow making machine be purchased, but power would also be supplied to the unit during the entire ice making process. Modifications would also need to be made to the reservoir structure to allow for the unit to be incorporated.

Option 4 Nozzle and Hose system

This idea consists of suspending a hose and nozzle system over the ice pond. The nozzles would be attached to a PVC piping frame that serves to circulate the water. Pressure from municipal tap water would be sufficient to circulate water through this system. The nozzles would atomize the water and allow for heat transfer from the water droplets to the cold ambient air. The height from which the nozzles would release the water would be adjustable via a pulley system. A frame/structure would be built around the pond from which this system would be suspended. Depending on ambient conditions, the height would be varied such that the water would be about 1 - 2C when contacting Figure 20 - Nozzles and PVC Piping System

the existing ice. This would ensure that the droplets dispersed slightly evenly over the surface before they froze.The main advantage of this design is that it would be fast at making ice. The variable height would ensure that the water is a maximum of 1C - 2C and minimize the melting of the ice already in the reservoir when the water comes into contact with it. The low flow rate means that the water could freeze within a short period of time of being injected. With the low flow rates and pressures would be used, 6 nozzles would be needed to ensure that the surface was covered with water.

To demonstrate the heat transfer between the droplets and the air, calculations were performed using principles of heat transfer such as external flow around a sphere and heat transfer approximation by the lumped sum capacitance method. The terminal velocity of the drop falling through the air was also determined. For an example of the detailed calculations, please refer to Appendix D.

On the following page is the plot of Drop Height versus Ambient Temperature for a range of droplet sizes (sphere diameter).

As an example of the calculations performed, a droplet of diameter equal to .3mm falling through air at -10C needs approximately .295 s to cool from an assumed initial temperature of 10C. With a terminal velocity of 2.95 m/s, it would need to be sprayed from the nozzle at a height of .87m. This point is shown on figure 21. This result assumes that the droplet is ejected from the nozzle at its terminal velocity.

Ice could be produced at various porosities by varying the drop height of the droplets. If the droplets were 0C or partially frozen as they hit the surface, higher porosity ice would be produced since air would be trapped during freezing. This would be used for the first stage of freezing, and then like the other designs, low porosity ice would be produced to fill the rest of the pond. The constant ice making would allow only vertical expansion and no expansion laterally.

Figure 21 - Plot of Drop Height versus Ambient Temperature for Various Droplet SizesThe main concern with this design is the extremely low flow rates required. This problem is magnified by the fact that 6 nozzles are needed to achieve the desired spray area. With low temperatures, even with a constant flow, the nozzles could freeze at the opening, or the water could even in the PVC piping. This would mean that the whole system would have to be disassembled and brought inside to allow the ice to melt.

9.2 Selected Ice Making System

A comparison of the different designs was carried out on this system in the same way as it was for the other components. The result is shown in table 11.Table 11 - Comparison Table for Ice Making System

CriterionOption 1Option 2Option 3Option 4

Cost5523

Functionality3545

Ease of

Construction5543

Scalability2244

Ice Quality

Control4444

Expansion1445

Total20252224

Option 2, the hose and nozzle with intermittent spraying, was selected due to its excellent overall performance compared to the other designs. A close second was the nozzle with variable height.

Option 2 was felt to be best suited to the small scale of this project. It is the most simple, the cheapest and the easiest to build. These are all important criteria. It excels in functionality and expansion over the most similar alternative, filling the pond all at once. It is more functional because we can control the porosity of the ice surrounding the heat exchanger. This means that when the system is first turned on, it will respond quickly.

Option 4 was felt to be best suited to a full scale application. The reason why it was not chosen for this design was the concern of the system freezing up in extreme cold weather. The flow rate of the water to provide constant freezing is not known exactly, but is one the order of 100ml per minute. When this is divided by 6 nozzles, the flow rate per nozzle is around 17ml 20ml per minute. Nozzles commercially available for this flow rate with the municipal tap pressure have extremely low flow rates because they are meant to atomize the water. From calculations performed, the atomized water would freeze into snow almost immediately after being sprayed from the nozzle. Eventually the nozzle itself would become frozen.

This made the application of nozzles very difficult for this project. In order to prevent the water from freezing before it hit the surface, the droplet size had to be increased. A number of sources were contacted with the following criteria:

Operating pressure: 50 psi

Volumetric Flow Rate: < .2L/min

Average Droplet Size: .25 - .375mm diameter

There were no nozzles that met these criteria. The reason why this design is more applicable to a full size system is that the flow rate would be much higher. This would prevent freezing and give proper flow rates.

9.3 Freezing Time Plot

There were several assumptions made in order to make this calculation. The first assumption was that the heat transfer coefficient between the water and the air is 56W/m2K [Fusion Engineering and Design 54, 2001]. This value is for stagnant air and water. Because of this assumption, any wind that is present will decrease the freezing time for the water added. The black line represents the 12 hour mark. This states that for a given volume of water at a given temperature, that much ice will be produced in 12 hours. Water was assumed to hit the surface at 10C, and cause little to no melting of the ice already there. This is a valid assumption since the heat of fusion of ice is approximately 82.5 times greater than the specific heat capacity of water.

A detailed sample calculation can be found in Appendix D. As a general result, it will be possible to freeze around 3 inches of water in a 24 hour period at the average temperature in January of -6C. This corresponds to the reservoir being filled with ice in approximately 2 weeks, assuming that there are no particularly warm periods during the freezing time.

Figure 22 - Plot of Freezing Time versus Depth of Water for Various Ambient Temperatures10.0Ice Making PlanThe consensus from Environment Canada and the Weather Network is that the average daily temperature in January and February is -5C to -6C. This permits ice production to be completed in approximately 2 weeks, with no unusually warm periods. With warmer weather, however, this time will increase.

To ensure that the reservoir is completely filled with ice when it comes time to perform testing on the system, ice production needs to begin no later than the 3rd week of January. This will give at least 5 weeks during which ice can be made. This leaves a lot of room for error, abnormally warm conditions and any other problems that may be encountered that are not foreseen now.

The current plan for making ice is to spray the water into the reservoir at night and leave the insulated top open. This serves a dual purpose, as long as there is no precipitation forecasted for that night. The open top will expose the reservoir to a low temperature and will decrease the temperature inside the reservoir since it will still be at an elevated temperature from the elevated daytime temperatures. It will also allow any wind to circulate inside the pond, increasing the freezing rates.

During cold days the insulated lid will remain open. This is to allow for heat transfer from the water to the ambient. If the lid is closed during a cold day, this prevents the heat from leaving the system. The pool will be monitored for ice production and if this strategy is not working as well as predicted, changes will be made to allow for better production.

The following night, if all of the water from the previous day has been frozen, a new amount of water will be sprayed into the pool. The amount will be determined from the plot discussed in detail in the Ice Making System section, section 8. If all of the water has not frozen, an estimate of the remaining volume of water will be made and subtracted from the amount of water that would have been put in if all of the water had been converted to ice. This new volume will be the volume to be added that night.

During days where the temperature is above or around 0C, the lid will be closed, preventing melting of the ice. Any water that is inside the pool during these days will not freeze, but since it will be at 0C, it will also not cause melting of the ice. Once the temperature has decreased below zero, the lid will be re-opened to allow ice production to continue.

This process will continue until the entire reservoir is filled with ice. At this point, the lid will be closed and left closed for testing.11.0 Load TestingThe current testing plan calls for the system to be tested by providing cooling to Lab C152 of the Mechanical Engineering Building. This room has dimensions of 7.8m x 7.2m x 3.0m, which is a total volume of 168.48 m3. In actual operation, the system would be used in the summer when the temperature inside would be elevated because of the warm ambient conditions outside. Assuming an efficiency of 30%, the system will be able to provide an average cooling rate of 660W for 2 weeks. This estimate is based on previous attempts of ice pond refrigeration systems in Japan. The system can be run constantly for the 2 weeks, or can be run intermittently with higher cooling rates for shorter periods of time.

As previously mentioned in the report, a FCU will be used to cool the lab. The FCU will automatically turn on when the temperature in the room exceeds the maximum value, and will cool the room until the temperature reaches the minimum. This will create a sinusoidal temperature in the room. Ideally the FCU will be able to cool the room faster than the heaters are able to heat the room. The FCU cooling power will be approximately 2 kW. At 2 kW, it will overpower the heater and be able to lower the temperature in the room. By not being used constantly, it will provide the average cooling rate desired.To create a load for the system, a resistance heater with a variable setting will be used. If the heaters supply a given load and the room temperature is kept constant at the temperature that would occur without heating (in the summer), the cooling load is equal to the heating load.

The heat losses for the room can be determined by measuring the temperature with the heaters on and then again with them off. Since the temperature the room would reach with out losses can be calculated, then the rate of heat loss can be found.

It has not yet been determined how the climate in the lab is controlled. Ideally, the ventilation and air conditioning provided by Dalhousies Systems would be turned off. This would leave the ice pond refrigeration system and simulated load to completely control the climate. This is likely, as the room has its own thermostat. This can be set at the minimum value of 13C and the heating system will be inactive above this temperature. Testing will be carried out in mid-December to verify this.

12.0 Conclusion and Future GoalsThere are still aspects of this project yet to be determined by Chilled Engineering Systems.A definite test plan needs to be determined. This is due to the fact that the FCU selection is dependant upon the test plan and the maximum cooling power that is to be provided to the lab. Once the test plan has been determined, the FCU can be selected.

With the general equations determined for the HX length, the next step is to match the heat transfer from a load to that of the ice reservoir. The load will represent the heat added to a room during a summer day. The rooms target temperature will be set at 20C and the outdoor ambient will be 30C. With a load found, an appropriate FCU based on heat transfer rate and flow rate will be balanced out against a HX. Initial variables in the HX will be its pipe length, nominal diameter and the flow rate. The heat transfer rate equation will be compared with to ensure that the desired temperature change can be obtained.The pump selection has not been made yet either. The pump selection depends on the FCU. For a given cooling rate, the FCU has a pre-determined flow rate. If the flow rate is exceeded, the working fluid does not have enough time to absorb energy from the coils. If the working fluid rate is too low, the fluid absorbs the necessary amount of heat, but in a longer than expected time. This lowers the cooling rate.

Construction of the ice pond has already commenced with the placement of the foundation. Over the Christmas break, the remainder of the system will be assembled. This includes fabrication of the heat exchanger, the pool, the support structure, the cover and installation of the fan coil unit. The piping system will also be implemented, including the pump to circulate the working fluid.

Once the model is completed and all of the soldered connections have been pressure tested to ensure that there are no leaks, the ice making will begin. Ice making will continue until the required amount of ice has been produced, totaling 8 m3. This mass of ice will be sealed from the weather using the fabricated cover, storing it until it is time for testing.

With the measured data and subsequent calculations, the model will be applied to a real life scenario. The present method of cooling will be compared to the cooling ability of the ice pond refrigeration system.Although no testing has been completed, Chilled Engineering Systems is confident that the selected overall design is the appropriate one for this project. All aspects have been considered and the best selection based upon functionality, cost, and other important criteria have been selected.

13.0 ReferencesFaherty, K. & Williamson, T. (1995). Wood Engineering and Construction Handbook (2nd ed.). US: McGraw-Hill Inc.

Hibbeler, R. (2000). Mechanics of Materials (4th ed.). New Jersey: Prentice Hall.

American Radiant Technologies and Supplies Inc. (2004). Radiant Heating. Retrieved November 30, 2004, from http://www.americanradiant.com/kitec.shtmAZ Parts Master. (2004). Fan Coil Units Ceiling. Retrieved November 9, 2004, from

http://www.azpartsmaster.com/shopazp/Fan%20Coil%20Units%20-%20Ceiling.htmlEngineering Tool Box, The. (2004). Ethylene Glycol Heat-Transfer Fluid. Retrieved November 8, 2004, from http://www.engineeringtoolbox.com/24_146.html

Environment Canada. (2004). Canadian Climate Normals 1971 2000. Retrieved November 8, 2004, from http://www.climate.weatheroffice.ec.gc.ca/Incropera, F. & DeWitt, D. (2002). Introduction to Heat Transfer (4th ed.). New York: John Wiley & Sons Inc.

Johns, W. (2003). Notes on Pipe. Retrieved November 8, 2004, from

http://www.gizmology.net/pipe.htmKitec. (nd). Thermal Properties. Retrieved November 30, 2004 from

http://www.kitecpipe.com/prop2.htmMarshall, T & Girard, C (2001). Modeling of ice formation and condensation on a cryogenic surface, from Fusion Engineering and Design, Vol 54. North Holland

Inc. Brodkey, R & Hershey, H (1988) Transport Phenomena A United ApproachIncropera, F. & DeWitt, D. (2002). Introduction to Heat Transfer (4th ed.). New York: John Wiley & Sons Inc.Parker, Harry. (1979). Simplified Design of Structural Wood (3rd ed.).Toronto: John Wiley & Sons Inc.Appendix A

Ice Pond Structure and SupportTo obtain the required dimensions of the structure, the following calculations were performed:

Determining the Load

Total Length of SupportsThe following lengths and positions were chosen for the supports. The lengths were added together to find the total length of the support.

Figure 6: Lengths of Support Members

Material Selection and Material Properties

The steel members for the top of the supports were chosen to be by 4 flat bar. The heat exchanger pipe diameter was chosen to be 7/8 so the space should be at least one inch in height. Therefore, the spacers were chosen to be 2 by 4 blocks of wood, approximately 3 in length. The bottom members were selected as 1 by 4 lengths of wood.

The maximum allowable bending stress and the density for steel were approximated as 16000 psi and 7800 kg/m^3, respectively (Milton 2004). The loading scheme for the structure is as follows:

Figure 7: Loading Configuration for Steel Members

Calculating Distance Between Spacers

For the above loading, the equation for maximum allowable bending stress is:

(Hibbeler 2000)

Where w is the load per unit length, L is the length between spacers, b is the width of the beam, and h is the height of the beam. Therefore,

As a further safety factor, L was chosen to be 12. Using this spacing and ensuring that the ends of each member were also supported, the layout for the spacers consists of sixty spacers and is as follows:

Figure 8: Array of 2" by 4" Spacers

Buoyancy ForceTo ensure that the buoyancy force was not a problem, a comparison of the densities of each material was applied. The specific gravity of Eastern Spruce was used as 0.41 (Faherty 1995). The calculations were performed as follows:

Volume of Wood:

2 by 4:

1 by 4:

Total Volume

Volume of Steel:

by 4:

Density Difference:

The above calculation states that 25 kg are required to keep the wooden portion of the structure from floating. Using the steel member gives 69 kg holding the wooden portion down. Therefore, the support structure will remain on the floor of the pool.

Fastening Design

A wood screw will be used to fasten the steel members to the 2 by 4 and 1 by 4. The Screw will pass through a small hole in the steel member, completely through the 2 by 4, and finally into the 1 by 4. The screw will not pass entirely through the 1 by 4 to ensure that the screw does not puncture the watertight seal of the pond.

Figure 9: Wood Screw Fastening Design

5.4 Construction Sequence

The construction of the ice pond has already commenced. Step one of laying the foundation for the pond was completed on November 18, 2004. The next step is to lay the insulation on top of this foundation. The pond itself will then be built over this base.

The pond is an above ground pool purchased from a commercial supplier, which consists of a water tight liner and a steel frame. The ice support structure will be built inside of this pool.

The ice support structure will be built on site. The 1 by 4 blocks of wood will be laid in position on top of the pool liner in the base of the pond. Next, the 2 by 4 spacers will be positioned according to the array explained in the Refined Design section. Once these spacers are in place, the steel members will be placed on top of the spacers and will be tacked to the spacers and 1 by 4.

Appendix BIce Pond Heat Exchanger

Heat Exchanger LengthThis section outlines the calculation used to determine the heat exchanger (HX) length. From this, characteristics such as pipe material and wall thickness were determined with the length comparison. To determine each characteristic, all other variables were held constant.

Fan Coil Unit Characteristics

Primarily, a comparable fan coil unit (FCU) for our system was chosen for some of its fluid characteristics. The characteristics of the FCU-1070cfm (Left Hand) from AZ Parts Master are shown below.

Where:

= Volumetric flow rate of air

= Heat transfer rate

= Volumetric flow rate of fluid

The suggested q of the FCU uses pure H20 as the working fluid. For our application the working fluid will consist of a 20% EG / 80% H20 mixture which will produce a smaller q. This is acceptable because as the q decreases, so will the length of needed pipe.Pipe Size

The size of the pipe was picked in comparison to the FCUs connector size.

FCU Connection Size: Do = 3/4, Di = 5/8 = 0.625

Copper Pipe: 3/4 L, Do = 7/8 = 0.022225m, Di =0.785 = 0.019939m

Where:

Do = Outer Diameter

Di = Inner Diameter

Heat Transfer Convection Coefficient for EG/H2O Mixture (h20%)

To determine h20%, a mean temperature (Tm) of the fluid mixture is needed to find the fluids properties. It was assumed that the inlet temperature (Ti) is 25C and the outlet temperature (To) would be 5C.

Where:

= Inner cross sectional area

Where:

= Velocity of fluid

Where:

= Density of fluid

Where:

= Reynolds number for flow in a circular tube

As > 2300 the flow is laminar and the appropriate Nusselt number is to be picked. requires a fully developed laminar flow with a uniform pipe surface temperature. The other available value was and requires a uniform heat flux. The lower value of the two is the conservative number as when decreases the HX length increases. As the mean pipe temperature was used in all of the calculations the uniform surface pipe temperature was accepted. Therefore was chosen.

Where:

= Thermal conductivity of fluid

Finding Heat Transfer Coefficient for Melt Water for Free Convection (hmw)To determine hmw, an average temperature of the melt water (Tmw) between the pipes surface (Ts) and the temperature of the ice (Tice) is needed. For the calculation to be completed, Ts was assumed to equal Tm.

Where:

= Thermal conductivity of melt water

= Thermal expansion coefficient

= Specific volume

= Prandtl number

= Absolute viscosity

= Specific heat

= Gravity

= Kinematic viscosity

= Thermal diffusivity

Where:

= Rayleigh number for free convection

Determining HX LengthNow that all of the needed resistance variables have been calculated, the Newtons Law of Cooling Equation can be rearranged to find length (L).

Appendix CIce Pond Protective Cover

Calculations

Several Calculations were made with various wood sizes and support locations. This section details the calculations necessary for the final design, but not all the other designs that similar calculations were carried out for.

Center Beam

The following calculation is to check if the middle support is strong enough to hold entire weight of one side of the cover. This is necessary because when the cover is open its weight will be concentrated at the two hinges. This calculation is to make sure that the deflection and bending stress will not be too large.

Assumptions:

The weight was assumed to be 200 lbs for the 6ft x 12ft section. This is a very conservative value as the actual weight of the wood will be about 130lb.

The weight of snow was neglected as it would be shoveled off before opening the cover.

The hinges were considered as point loads.

Since the maximum deflection is less than the allowable deflection, the 4x4 will not fail due to deflection.

EMBED Equation.3 The max allowable bending stress for spruce is 435psi, so this member will not fail due to bending stress.

Rafter Spacing

The rafter spacing was chosen as 24 inches for inch plywood was chosen from Table 17-2 of Simplified Design of Structural Wood (Parker, 1979). The snow load typically used for calculations in Halifax, Nova Scotia is 1.8kPa (Elieen Redmon, personal communication, Nov 2004). Table 17-2 states that the chosen arrangement will support a live load of 50lb/ft2, which is 1.33 times the Halifax snow load. The following calculation checks this arrangement for deflection for the longest rafter.

Assumptions:

The density of spruce is 0.016204lb/in2.

The maximum snow load in Halifax is 1.8kPa (0.26114psi= P). This corresponds to about 3ft of compacted snow.

Plywood can be considered part of the beam when finding the Moment of Inertia, I.

As expected the deflection is within allowable limits for the longest rafter, and thus all the rafters are within the deflection limits.

Construction

The pool cover is a basic wood structure and will be constructed by Chilled Engineering Systems. It will not be constructed until the pool is fully assembled and the exact dimensions of the assembled pool are known. Please refer to the drawing series IP-01 for the dimensions and details.

As for fasteners, nails will be installed every six inches to fix the rafters to the plywood. In addition, each rafter will be fastened to the outside frame by shear connectors. The shear connectors that will be used are known as truss plates and are commonly found in this sort of application. These can be bent to fit any angle which will be useful when fastening the rafters to the round part of the frame.

Figure C1-Truss Plate (www.gov.on.ca, 2002)

The round frame is essentially to properly seal the cover to the ice pond. A gasket material will be fixed to the top of the pool frame and it will make contact with round frame. The gasket material will be a self adhering weather-stripping.

Appendix DIce Making Systems

This section outlines calculations made to determine the height from which the droplets would need to be released for a temperature of 0C when it hit the surface of the ice. The lumped sum capacitance method is used, which assumes that there is no temperature gradient in the droplet of water (i.e. the droplet has perfect conduction). This is a valid assumption since the droplet size is so small. The droplet is also assumed to be a perfect sphere.

As a sample calculation, the required drop height for a droplet of diameter .30mm, initially at 10C, with an ambient temperature of -10C will be shown.

First the terminal velocity of the droplet is determined (from Transport Phenomena A United Approach, P.590):

Where:

ut = Terminal velocity of the water dropletrp = water droplet radius

p = density of water droplet

= density of air

= absolute viscosity of air

Once the terminal velocity has been calculated, the Reynolds Number for the sphere falling in air can be determined by:

Where:

dp = Diameter of the sphere

U = Terminal velocity

= Density of air

= absolute viscosity of air

Using the Reynolds Number and Prandtls Number, a correlation can be used to find the heat transfer coefficient:

Where:

hp = Heat transfer coefficient from the droplet to the ambient air

k = Thermal conductivity of the air

NPr = Prandtls Number of the air at the given condition

With the heat transfer coefficient now known, the lumped sum capacitance method can be used. A rearranged formula to solve for time is as follows:

Where:

= Density of water

V = Volume of the water in the sphere

Cp = Thermal capacitance of the water

As = Total surface area of the droplet of water

Ti = Initial temperature of the water

T = Ambient temperature

T = Final temperature of the water

Now that the time required to cool a droplet from 10C to 0C is known, along with the terminal velocity, the drop height can be easily obtained:

A spreadsheet analysis was carried out to create the plots shown in the main body of this report.

This section is an example of the calculations carried out to determine the quantity of water to be frozen for given conditions, assuming no wind. Because of the assumptions mentioned in section 9, the calculations for this were able to be based upon Newtons Law of Cooling:

Where

Q = heat transfer rate (W)

h = heat transfer coefficient (W/m2K)

A = Area over which the heat transfer occurs

T = Twater - T

This equation was used to calculate the time required to cool the water from its initial temperature to 0, and then to remove the heat from the water to freeze it. As previously mentioned, h = 56W/m2K for all of the heat transfer scenarios.

To calculate the amount of heat to be removed from the water, the following equation was used:

Where

Q = Amount of heat (J)

mw = Mass of waterCp,w = Specific Heat of water

T = Twater - T

The amount of heat to be removed from water at 0 to cause the phase change to ice is:

Where

Q = amount of heat (J)

mw = mass of waterHfus = Heat of fusion of water (334.44 J/g)

As a sample calculation, the time required to freeze 1 inch of water initially at 10C to ice, with ambient air conditions of -10C, will be used.

A spreadsheet analysis was carried out to create the plot shown in the main body of this report.Appendix EOverall Budget

Dec. 6, 2004

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