MECH!4692! Final!Report:! Off8Grid!Winnipeg!! BedandBreakfast!bibeauel/research/... · MECH!4692!...

MECH 4692 Final Report:

Off-‐Grid Winnipeg Bed and Breakfast

University of Manitoba 2011-‐04-‐11

Mitch Smith 6843751

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Table of Contents List of Tables ............................................................................................................................. 3 List of Figures ............................................................................................................................ 3 1.0 Executive Summary ...................................................................................................... 4 2.0 Introduction .................................................................................................................... 5 3.0 Assumptions ................................................................................................................... 6

3.1 Electricity ................................................................................................................................................ 6 3.2 Natural Gas ............................................................................................................................................. 7 3.3 Gasoline ................................................................................................................................................... 7 3.4 Anaerobic Digestion ........................................................................................................................... 7 3.5 Thermal Tank ........................................................................................................................................ 8

4.0 Mathematical Models ................................................................................................... 9 4.1 Energy Loads ......................................................................................................................................... 9 4.2 Weather Analysis .............................................................................................................................. 12 4.3 Anaerobic Digester – CHP ............................................................................................................. 13 4.4 Thermal Tank ..................................................................................................................................... 15

5.0 Results ............................................................................................................................ 16 5.1 Anaerobic Digester – CHP ............................................................................................................. 16 5.2 Thermal Tank ..................................................................................................................................... 18 5.3 Greenhouse Gases ............................................................................................................................ 19 5.4 Cost ......................................................................................................................................................... 21

6.0 Conclusion .................................................................................................................... 23 Bibliography ........................................................................................................................... 24

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List of Tables Table 1. Design Parameters .................................................................................................................. 5 Table 2. Energy Consumption of Bed and Breakfast .................................................................. 5 Table 3. Electrical Load Usage Breakdown ................................................................................... 6 Table 4. Digester Performance -‐ Thermal and Electrical Distribution ............................. 16 Table 5. Digester Performance -‐ Natural Gas Distribution .................................................... 17 Table 6. Results for Thermal Tank Analysis ................................................................................ 18 Table 7. Business as Usual GHG Emissions .................................................................................. 19 Table 8. CO2 Emissions after renewable energy implementation ...................................... 19 Table 9. Business as Usual Cost Breakdown ................................................................................ 21 Table 10. Present Value of a Series of Annuities per Unit Time .......................................... 21 Table 11. After Renewable Cost Breakdown with 5 digesters ............................................. 22 Table 12. After Renewable Cost Breakdown with 3 digesters ............................................. 23

List of Figures Figure 1. Electrical Load per Year .................................................................................................... 10 Figure 2. Natural Gas Load per Year ............................................................................................... 11 Figure 3. Gasoline Load per Year ...................................................................................................... 11 Figure 4. Overall kWhr per Year ....................................................................................................... 12 Figure 5. Average Annual Temperature for Winnipeg ............................................................ 13 Figure 6. 24-‐hour Breakdown of Average Temperature on August 8 in Winnipeg .... 13 Figure 7. Excerpt from Fisher et al. .................................................................................................. 14 Figure 8. Snapshot of GUI showing Thermal Tank Heating Loads ..................................... 15 Figure 9. System Results -‐ Thermal ................................................................................................. 17 Figure 10. System Results -‐ Electrical ............................................................................................. 18 Figure 11. Yearly CO2 Emissions for 'Business as Usual' and 'After Renewable' ........ 20 Figure 12. CO2 Emissions for March 25 ........................................................................................ 20

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1.0 Executive Summary An anaerobic digestion system with a thermal storage system has been proposed for an off-‐grid renewable energy bed and breakfast. This system will see the use of four ‘Dachs Mini-‐CHP’ cogeneration units capable of producing 5.5 kWe and 12.5 kWth at full load. These will be powered by biogas generated from 3 swine manure digesters, each with a volume of 54.3 m3, generating a total of 512 m3 of methane a day. The digesters will be couple to a 163 m3 reserve manure tank, as well as an 18 m3 thermal tank for storing excess heat. To account for excess methane and heat from the cogeneration units, both a flare and a radiator will be incorporated into the design. This system operates in the thermophilic region with a temperature of 50oc and a hydraulic retention time of 1 week for ease of maintenance. Volatile solids of the manure entering should remain around 75 g/L, but can be adjusted at a cost of natural gas production per hydraulic retention time. The energy loads were divided into daily usages based on a number of assumptions, and further parasitic loads for the heating of the digester and thermal tank were added into the total energy required. From all this, the system was sized to the dimensions above. Over the year, the digesters are able to produce enough natural gas to fulfill the 100000 m3 of natural gas load, send 48052 m3 of gas to the cogeneration units, with an excess of 38698 m3, which is to be flared. The electrical loads are fulfilled outside of a total of 19920 kW, which is only a 14% requirement from Manitoba Hydro in comparison to the full load. There will be reverse metering throughout the year, but this value represents an overall load. With R-‐16 insulation on all tanks, a loss from the thermal tank of 11657 kWhr/year and a loss from the digesters of 40540 kWhr/yr is realized. Greenhouse gas emissions were calculated for the ‘business as usual’ model, at a total of 223719 kg of CO2 per year. The addition of the system increases the CO2 emissions to 408786 kg, but considering this is removing the emission on methane to atmosphere, a total equivalent reduction of 3513682 kg CO2, as it is part of the natural carbon cycle. Finally, installation of this system will be slightly smaller than what would have been optimal, as costs are quite substantial for this project. For a 3-‐digester, 4-‐cogeneration install, a total projected present worth cost of $315641.13 was estimated. This is equivalent to roughly 20 years of utility costs, therefore yielding a 20-‐year payback period. This technology is very stable in the sense that it doesn’t depend on weather patterns in order to perform, and is able to provide the required heating load the most efficiently in comparison to the other, electrical based renewable energy systems. Anaerobic digestion has been utilized in treating human feces in water treatment plants for a long time, so this technology is proven. It will be an excellent choice for implementation into this bed and breakfast project.

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2.0 Introduction

It is common knowledge that energy is a very cheap resource in Manitoba, as our energy rates are among the lowest per kW-‐hr in the world. Having this luxury makes the use of renewable energy a very difficult decision when planning out large buildings and infrastructure, as their prices are still not competitive enough economically. This is a plenty good reason continue to develop novel types of renewable energy resources, as having cheap energy available to all parts of the world will help humanity in its entirety. With the discovery and increasing usage of fossil fuels in the last century, cheap energy has been available, but a cost to the environment. As well, it has a limited supply, and we are quickly approaching its bounds. Therefore, finding cheap energy sources is important, but we have to make sure that it will not harm the environment, and that it will last. Renewable energy is the solution. Implementation of various types of renewable energy systems has been proposed for a bed and breakfast to be located in southern Manitoba. A list of criteria was provided for design parameters, and below is a valid subset of the list for this specific design.

Table 1. Design Parameters Maximum Utility Usage 50% Purchase Price of Power $0.06/kW-‐hr Selling Price of Power $0.06/kW-‐hr

From these values, the most important to meet is the 50% maximum utility

usage rate. To better quantify this goal, the energy requirements must be analyzed. From the supplied information, the specific energy types have all been converted to similar units to show a better comparison.

Table 2. Energy Consumption of Bed and Breakfast

Energy Type Energy Consumed Energy Consumed Electricity 18000 kW-‐hr/yr 64800 MJ Electricity 18000 kW-‐hr/yr 64800 MJ Electricity 18000 kW-‐hr/yr 64800 MJ Electricity 18000 kW-‐hr/yr 64800 MJ Electricity 18000 kW-‐hr/yr 64800 MJ Electricity 18000 kW-‐hr/yr 64800 MJ Electricity 36000 kW-‐hr/yr 129600 MJ Electricity 36000 kW-‐hr/yr 129600 MJ Natural Gas 80000 m3/yr 814705 MJ Natural Gas 20000 m3/yr 3258819 MJ Gasoline 1000 L/year 36051 MJ Gasoline 2400 L/year 86523 MJ

From this chart, and knowledge of the use of each of these energy types, 3 of

the 4 highest usages are used for heating, and the two highest are natural gas demand. It is therefore inherent that when designing the renewable energy system,

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the focus should be on providing heat, or fuel, rather than reproducing electricity for the building.

The design selection for this project is focused on methane production, using swine manure in an anaerobic digestion system. This methane will serve two purposes: to supply the household and greenhouse natural gas loads of 100 000 m3 total per year, as well as to be run in a combined heat and power cycle, or micro cogeneration, to provide electricity and external heat, which will be used for hot water generation. To better constrain the system design, assumptions for each step of the project must be outlined.

3.0 Assumptions

The majority of assumptions made during the design process will outlined in this section. Less important assumptions used during calculations will be made in the appendices.

3.1 Electricity The electricity use of this building is rather high, but not high enough to warrant dedicated electricity production. In breaking down energy loads to daily-‐allotted values, the following assumptions were made.

Table 3. Electrical Load Usage Breakdown Refrigeration Distributed evenly throughout the year and per day Freezing Distributed evenly throughout the year and per day Lighting Distributed evenly throughout the year during hours awake and sun is

set Appliances Distributed evenly throughout year during hours awake Computers/Electronics Distributed evenly throughout year during hours awake Air Circulation Used in parallel with heating – distributed evenly between November

1 and April 1 Air Conditioning Used in summer only – distributed evenly between June 21 and

September 22 Hot Water Heating Removed from electrical load – powered by cogeneration unit

To perform much of the cost analysis it is will be assumed that there are no

demand charges in terms of volt-‐amperes, and that costs per kW-‐hr will be fixed at the price listed above. With reverse metering, it is an equal give and take system where energy produced is paid the same amount as energy used.

Finally, the proposed system has electrical output, and will be assumed to provide either full rated power, or be off, and provide nothing. The cogeneration units selected are able to perform within a certain range, but for simplicity in controls it is assumed to be an ‘on’ or ‘off’ piece of equipment.

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3.2 Natural Gas Natural gas usage is spread out in a linear trend throughout the fall, winter and spring months. Again, prices will be considered constant, with no demand charges if needed, and a cost of $0.2108/m3 will be used for costing [Hydro]. Summer was assumed to start, temperature-‐wise on June 1 and end on its typical day of September 22. Heating increases linearly until December 31, where it then begins to fall linearly to June 1. The slope of each line and y-‐intercepts are found by assuming the area under the combined curves to equal the total usage throughout the year. This will be further explained in the mathematical models section for energy loads. The model designed for the bed and breakfast supplies its own self-‐generated natural gas for use in the building. It is already known that biogas only provides ~70% methane, but this is already accounted for in the biogas model, and therefore may be neglected [1] [2]. Biogas also contains CO2 and trace amounts of ammonia (NH3) and hydrogen sulfide (H2S). As the last two may be very harmful to humans as well as equipment, a gas scrubbing system must in place to clean the biogas if it is being burned in the home in an air furnace. Since boilers have been described in the definition of the heating loads, this should not be a problem as long as stainless steel is used for the combustion chamber and pipes, and the effluent gases are vented away from the home.

3.3 Gasoline Through the investigation of the energy requirements of the bed and breakfast, the gasoline usage is small percentage of the energy use, and from the beginning was not going to be chosen for replacement with renewable energy. Assumptions were still made on its yearly distribution. Through research it has been found that fuel usage for the typical Canadian is 1.4 times more in the summer than the winter [3]. Therefore a sinusoidal model was created having a peak value 1.4 times higher during the summer than during the winter, and total area under the curve equal to total gasoline usage. This will be further explained in the model section. Finally, as gas prices fluctuate daily, a standardized value of $1.00/L will be used for the costing section of the report.

3.4 Anaerobic Digestion The entire anaerobic digestion system is simple in its inputs and outputs, but overall is quite a complex series of events. Typical manure is allowed to flow into lagoons from hog barns with bacteria breaking it down into more simple components, which are eventually spread onto fields as compost. By providing heat to the manure in a controlled manner, it is possible to culture the bacteria into higher counts, able to break down the manure faster and more efficiently. Luckily, methane is a byproduct of this reaction, and therefore the source of this design.

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First off, a model to describe these phenomena has been selected which has been derived from empirical correlations. It has been deemed accurate for a baseline model, but would have to be refined to meet the specific criteria of this location, and possibly the age of the hogs from which the manure is received. As well, the temperature range with which the model is described transfers through 3 different types of bacteria, being the psychrophiles, mesophiles and thermophiles. As it takes time for these bacteria to culture and switch between one set and another, it is assumed that a steady state must be achieved for whatever temperature is going to be selected, and the design would not change following that As per the model itself, a number of restrictions were laid out in the beginning, completely dependent on the research. Temperature ranges are only valid between 20-‐60oc for the digester, and a hydraulic retention time between 5 and 30 days. HRTs have been found longer in cold climate situations such as Manitoba, but this is utilizing the very cold psychrophilic range, and large volume long retention times benefit from these conditions. The plan here is to utilize a slightly higher temperature, meaning a lower retention time and higher gas production. Finally, the volatile solids content has been restricted to a range between 10-‐120 g/L as methane extraction will be very low on the low end of the range, and the model utilized in this system is not valid outside of the higher range [2].

The number of reactors is limited to 5 as any more becomes to cumbersome for installation as well as providing an abundance of energy to the house, much of which would become wasted. It is also chosen that the maximum number of cogeneration units used at once would be 4, as this correlates with the average electrical load if divided into the year. Also, costs become an important factor to consider if any more are required.

To provide a means of measuring the heat loss, some type of R-‐value was assigned to the tanks. An R-‐16 spray on polyurethane insulation has be specified for the tanks [4].

Piping, pumps, controls and installation have been omitted from the design as it would prove to complex at this point in time to utilize this, and the layout would be highly dependent on the land and house/greenhouse layout.

3.5 Thermal Tank The thermal tank will be used as a thermal storage device for excess heat produced by the cogeneration units. This device is very basic, as it works on the principle of storing hot water in a tank for future use. It will be very similar to a radiator, except since the goal is to store the heat, it will have to be able to be disconnected. It is planned that the thermal tank will be placed outdoors with the digesters, as it will be decently large in size. Insulation on this tank will follow the same R-‐16 value specified for the digester tanks, and the same assumption of a perfectly insulated base will apply. Heat transfer through the tank will follow the same temperature difference as explained above. Pumping loads required for this device will be consumed in the anaerobic digester system

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4.0 Mathematical Models Explained in this section will be the models devised for the energy loads, the weather analysis and the two specified designs being the anaerobic digester featuring combined heat and power, and the thermal energy storage tank.

4.1 Energy Loads The energy loads were separated into 3 distinct Excel sheets, for each of the 3

types. As explained earlier for electricity, the freezer, refrigeration, appliances, hot water and electronics were separated evenly through the year by dividing their energy load by 365 to obtain a daily value. The hot water load was calculated here just for organization, but it is still omitted from the electrical energy load as the thermal tank supplies it. The lighting load is spread equally over the time awake and time the sun is not in the sky. With 6:30am and 11:30pm chosen as time to wake up and sleep, the following formula was utilized. =IF($I$16-C27>0,0,ABS($I$16-C27))*24+IF($I$17-D27>0,ABS($I$17-D27),0)*24

This code sums the hours in any specific day, by checking if a person awakes before sunrise and stays up past sunset. Summing these values for a year amounts to 1824 hours of lighting required, which is then divided into the lighting energy load, and multiplied into each days lighting requirement to give an overall daily energy load for lighting. Air conditioning is divided evenly into what was deemed summer days, running from summer solstice on June 21 to fall equinox on September 22. The number of days during this period was divided into the total air conditioning load, and was considered the average daily value. The final electrical load is the fan, which was displaced in the same manner as the natural gas loads explain later. The load is to maximized at December 31 and January 1, and taper off to zero from January 1 to June 1, and start from zero going to a maximum from September 22 to December 31. The area under the curve would be equal to the total energy load. Two linear lines were solved for to come up with these values. Their equations are

!"#$ !"# !"!!"#!!"#$(!"ℎ!) = −0.94984 !"##$%& !"# − 1 + 142.95108 !"#$ !"# !"!!"#$!!"#(!"ℎ!) = 1.43426 !"##$%& !"# − 265 + 0.71713 Natural gas usage followed the same model as the fan equation, using the

same beginning and ending days for its linearization. First the natural gas was converted from m3 to kWhr using its density of 0.78 kg/m3, HHV of 52.225 MJ/kg and 3.6 MJ/kWhr. The linear equation for energy demand per day for the greenhouse was calculated as,

!"#$ !"# !"!!"#!!"#$(!"ℎ!) = −47.7680 !"##$%& !"# − 1 + 7189.0838

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!"#$ !"# !"!!"#$!!"#(!"ℎ!) = 72.19678 !"##$%& !"# − 265 + 36.06048 The household used ¼ the amount of energy as the greenhouse, so the final

value for each day for the greenhouse was divided by 4 to gain the household daily energy load. These values were summed together to find the total kWhr per day, as well as converted back to m3 of natural gas for use in the anaerobic digestion model.

Finally, the gasoline usage followed a sinusoidal curve as mentioned above. Using the density of 0.7747 kg/L and HHV of 46.536 MJ/kg with the same 3.6MJ/kWhr value, the equation for the sinusoidal functions for the car and truck are

!"# !"# !"!!"# ! = −0.45662 cos360 !"#365 + 2.7397

!"# !"# !"!!"#$% ! = −1.09488cos360 !"#365 + 6.56926

These values were converted to kWhr following this, but were left in litres

for the final summary as no system was implemented to change them to renewable, so a simple representation of how much fuel used in a certain time frame is sufficient.

Below are the results of the energy breakdown for each of the three energy sources as well as the total overall energy load.

Figure 1. Electrical Load per Year

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Figure 2. Natural Gas Load per Year

Figure 3. Gasoline Load per Year

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Figure 4. Overall kWhr per Year

4.2 Weather Analysis Using the weather data proved very cumbersome, as there were almost half a million data points, so only the last 3 years worth of data was utilized in the analysis. As the overall system only requires temperature, it seemed more computationally favourable to only bring in the temperature values rather than every column of data. The dates and temperature values were input into columns, and the date information was separated into its year, month, day and hour sections using the ‘RIGHT’ and ‘LEFT’ functions of Excel. This was able to pull certain data points out to give each of the individual time steps mentioned above. As the temperature was given in T x 102 oc, a quick divide by 10 was performed to get the appropriate temperature. The basic formula used to separate the data points into average daily values is shown below, for January 1. {=SUM(IF(($D$4:$D$35067=MONTH(L4))*($E$4:$E$35067=DAY(L4))*($H$4:$H$35067<80),$H$4:$H$35067,0))/SUM(IF(($D$4:$D$35067=MONTH(L4))*($E$4:$E$35067=DAY(L4))*($H$4:$H$35067<80,1,0))} What this code does is perform an array summation over the entire set of data such that it pulls only specific data for the specified month and day, summing the values, then dividing it by the number of values summed. As this is an array formula, it requires a CTRL+SHIFT+Enter to work properly. The same type of formula was used to provide a 24 hour temperature display for any given day, specified in the Summary Page of the Excel sheet. One important note in this code is the temperature value being less than 80oc. As corrupted values in the data were displayed as 99, this helped reduce error in the annual average temperature chart,

0.00

1000.00

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7000.00

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18-‐Nov 07-‐Jan 26-‐Feb 17-‐Apr 06-‐Jun 26-‐Jul 14-‐Sep 03-‐Nov 23-‐Dec 11-‐Feb

Total kWhr per Year

Time (days)

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while still including all temperature values. The average temperature displayed annually and for August 8 for a 24-‐hour breakdown.

Figure 5. Average Annual Temperature for Winnipeg

Figure 6. 24-‐hour Breakdown of Average Temperature on August 8 in Winnipeg

4.3 Anaerobic Digester – CHP The digestion model requires a number of inputs to produce results. First the size and number of cogeneration units is specified, in the form of cylindrical tanks. A

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limit of 5 digesters is imposed as any more would be redundant for this project, and produce abundant amounts of natural gas. From here, the empirical formulas used to define the model as shown in the following excerpt from a paper by Fisher et al [2].

Figure 7. Excerpt from Fisher et al.

Therefore this model is capable of providing the gas production per unit volume of digester for various hydraulic retention times and volatile solid concentrations. This model was limited to a reactor temperature of 35oc with only a single μm value. Another study was able to provide a relation for this value as a function of temperature [5].

!" = 0.013 ! − 0.129

So to obtain a methane production value, the temperature and volatile solid content are first utilized in the above equation as well as the kinetic parameter equation listed in the excerpt. These values are then plugged into the initial two formulas to obtain the overall methane production. Having a constant production of methane each day, and the overall methane load required each day, a difference was calculated for each day. If the value was negative, this would mean required utility gas, and this circumstance was not completed in time for this report. The positive gas flow however has been accounted for. Excess gas is utilized in one of two ways. If there is enough on a certain day to power a cogeneration unit at full capacity, it is burned in the unit to provide heat and power. All excess is sent to the flare. Therefore the utilization of gas increases in steps as cogeneration unit has enough gas to be able to provide full operating loads.

The electricity is sent to the household, where if there is too much, it is sent to the grid in reverse metering at cost, and if it is not enough, the house pulls back on the grid for the remainder. The heat is separated in a number of ways. First, an energy loss for each day is performed using the outdoor temperature, the digester temperature, the resistance value of the insulation placed on the digester and the

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surface area of the tank exposed to the environment. This energy load is the primary load to be fulfilled, and must be fulfilled whether or not it must use utility natural gas. If there is excess heat after this, it goes into the thermal tank, which also has the same energy loss as the digester tanks due to environmental losses. It also has the losses due to the hot water energy load from the house. Finally, if there is any remainder heat, it is sent to an external radiator, to be shed to the environment.

Many of the Excel formula used in this model are the same as in the previously defined models, and for the sake of brevity, will not be included in this section.

4.4 Thermal Tank The thermal tank uses the same principles as the methods above by discretizing the year by day, and solving for an effective heat loss or gain for each day. As the cogeneration units supply water at 80oc, and for simplicity sake, it was chosen to leave the thermal tank at this temperature. The tank is rectangular in shape with a chosen size of 3 x 3 x 2 m tall, giving a total volume of 18 m3. Using the same R-‐16 insulation as specified for the digester and reserve tanks, the same temperature difference according to a specific average daily temperature and the 80oc tank temperature, and calculating the surface area open to heat transfer as 33 m2, heat loss though the boundary may be calculated. It must be noted that the total heat required as an input from the thermal output of the cogeneration units must be the heat loss through the tank boundary as well as the heating load from the hot water. These two values are summed and made equal to the heat going into the digester, as seen in the Excel Summary Page.

Figure 8. Snapshot of GUI showing Thermal Tank Heating Loads

The same array-‐based Excel formulae are used to generate the monthly values in the summary section, and ‘VLOOKUP’ was used for the daily values in the table. As with the other models, yearly was a summation of the daily values, and hourly was found by dividing the daily value by 24.

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5.0 Results The results of this analysis are shown for the digester and thermal tank themselves, as well as a basic cost analysis and environmental analysis in the form of greenhouse gas emissions.

5.1 Anaerobic Digester – CHP Using anaerobic digestion with cogeneration is a very attractive renewable energy source as it is capable of harnessing copious amounts of natural gas. The final model selected was using 3 reactors with a series of 4 cogeneration units by Dachs. with a hydraulic retention time of 7 days, volatile solids of 75 g/L and a digester temperature in the thermophilic range of 50oc. By changing each of these values, and previous knowledge, it was known that a higher temperature would yield higher gas production, and would be able to utilize a higher volatile solids concentration. The 7-‐day HRT was chosen to help with the turnaround of fresh manure into the digester, without flooding the thermophiles out, but also provide a very accessible maintenance schedule, performed on a weekly basis. A list of monthly data is shown below.

Table 4. Digester Performance -‐ Thermal and Electrical Distribution

Month

Thermal Energy Produced (kWhr)

Electrical Energy Produced (kWhr)

Heat Lost by Digesters (kWhr)

Heat to Thermal Tank (kWhr)

Heat Lost by Thermal Tank (kWhr)

Heat from Radiator (kWhr)

January 0.00 0.00 4888.06 4298.60 1241.06 -‐6129.12 February 0.00 0.00 4053.79 3819.86 1058.22 -‐5112.01 March 15000.00 6600.00 4015.15 4146.99 1089.45 9895.39 April 35100.00 15444.00 3193.52 3893.01 934.10 30972.37 May 37200.00 16368.00 2822.14 3939.79 882.25 33495.60 June 36000.00 15840.00 2482.02 3769.43 810.53 32707.45 July 37200.00 16368.00 2263.99 3842.84 785.31 34150.70 August 37200.00 16368.00 2297.11 3848.60 791.06 34111.82 September 36000.00 15840.00 2705.97 3808.33 849.43 32444.61 October 37200.00 16368.00 3332.74 4028.47 970.93 32896.32 November 11100.00 4884.00 3751.17 3989.86 1030.96 6317.87 December 0.00 0.00 4734.24 4271.88 1214.35 -‐5948.59 Total 282000.00 124080.00 40539.91 47657.66 11657.66 229802.43

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Table 5. Digester Performance -‐ Natural Gas Distribution

Month

Natural Gas Produced (m3)

Natural Gas to Cogen (m3)

Natural Gas to House (m3)

Natural Gas to Flare (m3)

January 15863.86 0.00 22165.64 -‐6301.78 February 14328.65 0.00 15661.86 -‐1333.21 March 15863.86 2556.00 12514.18 793.68 April 15352.13 5981.04 7282.13 2088.96 May 15863.86 6338.88 2535.55 6989.43 June 15352.13 6134.40 0.00 9217.73 July 15863.86 6338.88 0.00 9524.98 August 15863.86 6338.88 0.00 9524.98 September 15352.13 6134.40 251.26 8966.46 October 15863.86 6338.88 5810.30 3714.69 November 15352.13 1891.44 12920.49 540.20 December 15863.86 0.00 20892.04 -‐5028.18 Total 186784.20 48052.80 100033.45 38697.95

It is important to note that the negative values for gas to the flare represent and are equal to the intake from the utility of natural gas, but the controls were too difficult to implement into the model to counteract this, and have been omitted. By using the utility gas the negative values in the heat to radiator column would also be turned to zero. These values are also graphically represented to get a better feel for the system as a whole.

Figure 9. System Results -‐ Thermal

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Figure 10. System Results -‐ Electrical

The first graph shows the large portion of heat required to heat the house. The stepped portions represent the powering on of each individual cogeneration unit, and can also be seen in the purple “Total Heat from Flare” data. In the second graph, electricity is take from grid for the winter months, but is able to be returned to the grid in the summer months, yielding a still negative, but much lower need for utility electricity.

5.2 Thermal Tank The thermal tank was designed such that it will always provide enough heat to supply the household with hot water. The tank itself will consume energy as it is placed outside and will experience heat losses due to temperature differences. Using the criteria listed, a summation of the heat losses for each month as well as an annual value are listed in the table below.

Table 6. Results for Thermal Tank Analysis

Month Heat Loss (kWhr)

Hot Water Heating Load (kWhr)

Total Heat to Thermal Tank (kWhr)

January 1241 3058 4299 February 1058 2762 3820 March 1089 3058 4147 April 934 2959 3893 May 882 3058 3940 June 811 2959 3769 July 785 3058 3843 August 791 3058 3849

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September 849 2959 3808 October 971 3058 4028 November 1031 2959 3990 December 1214 3058 4272 Annual 11658 36000 47658

It may be advantageous in the future to utilize some of the extra heat in this thermal tank by increasing it in size and using it as a backup for the thermal energy required to heat the digesters, as there is some natural gas usage in the coldest months of the year as supplementary fuel.

5.3 Greenhouse Gases Greenhouse gas emission will be divided into two distinct cases, being the ‘business as usual’ case, without any added technology, and the ‘after renewable case’, using the anaerobic digesters as an energy source. First, the ‘business as usual’ case is modeled for all CO2 emissions. The CO2 emissions will be presented from each energy form and calculated in their entirety.

Table 7. Business as Usual GHG Emissions

Electricity 1080 kg CO2 Natural Gas 214500 kg CO2 Gasoline 8139 kg CO2 Total 223719 kg CO2

From the amount of each energy source as some common knowledge, it was obvious that natural gas would provide the highest source of CO2 emissions. Renewable energy systems must not only provide near unlimited sources of energy, but also reduce effects on the environment in comparison to fossil fuels. The proposed system still uses natural gas, but is removing it from a source, which is a higher GHG producer than the combustion of fossil fuels. Anaerobic digestion occurs naturally in manure lagoons, releasing the natural gas to atmosphere, rather than capturing and combusting it. Methane is known to be 21 times worse as a greenhouse gas than CO2, therefore an equivalent 21kg CO2 per kg of methane. Using the system data of total methane captured from the digesters, and the equivalent CO2 reduction, it may be concluded that this technology vastly decreases the emission of greenhouse gases to the atmosphere.

Table 8. CO2 Emissions after renewable energy implementation

Business As Usual 223719 kg CO2 After Renewable 408786 kg CO2 Equivalent CO2 3922468 kg CO2 Total Reduction 3513682 kg CO2

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In the Excel model, a yearly and daily CO2 emission plot was created to show how they vary with the system throughout the year. An example for March 25 is shown along with the yearly distribution below.

Figure 11. Yearly CO2 Emissions for 'Business as Usual' and 'After Renewable'

Figure 12. CO2 Emissions for March 25

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5.4 Cost

Provision of a cost report is in the form a very basic break-‐even analysis. First a benchmark must be calculated using the cost of power to begin with, which will be known as the ‘business as usual’ model. The following table shows a breakdown of this cost.

Table 9. Business as Usual Cost Breakdown Energy Type Cost/ Unit Energy Consumed per Year Total Cost per Year Electricity $0.06 / kWhr 180000 kWhr $10800.00 Natural Gas $0.2108 / m3 100000 m3 $21080.00 Gasoline $1.00 / L 3400 L $3400 Total $35280.00

As both the ‘business as usual’ and ‘after renewable’ models both require constant O&M costs, they will be assumed to be equal and be negated from the rest of the analysis. This will also help to show a better comparison between the energy sources only, rather than also including auxiliary costs in the calculations. As the comparison is between a series of annuities and a large initial capital expenditure, a net present value calculation will be used to compare the results. For the ‘business as usual’ model, the following equation was used, and values for various time intervals are shown below. It must also be noted that the cost of capital was derived from the Government of Canada as a fixed rate equal to that of a single-‐family mortgage from a local vendor plus 3%. From CIBC, this value came out to 9.35% [6] [7].

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Table 10. Present Value of a Series of Annuities per Unit Time

Life Span (years) Present Value ($) 5 -‐$135,989.69 10 -‐$222,968.22 15 -‐$278,599.38 20 -‐$314,180.88 25 -‐$336,938.67 30 -‐$351,494.48 35 -‐$360,804.33 40 -‐$366,758.87 45 -‐$370,567.37 50 -‐$373,003.28

If one were to keep going with this trend, the present value would maximize at a value of $377,326.20, which is a commonly known economic occurrence in long term annuities. It will be assumed that if our costs for the ‘after renewable’ model

Prof. E. Bibeau

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are higher than this value, that the project will be deemed too expensive and that changes must be made in order to make it more attractive. For the ‘after renewable’ costing model, a number of assumptions were made. The cost of capital will remain the same for consistency. The tanks for construction would cost $1/gal of capacity, which is on par with many industrial quotes. This was also met with a zero discount on multiple unit purchases, as there would be a multiple quantity for almost all components. The pumps required are not known for size, but an estimate based on previous experience was made. Piping and the radiator costs were also made this way. The installation was chosen to cost 75% of the total capital cost of all equipment required. Finally, rebates from Manitoba Hydro were given as $0.30/m3 of natural gas saved and $0.15/kWhr electricity saved. As we did not exceed their limits as per their website, the full dollar value is returned to us. This led to the following cost breakdown.

Table 11. After Renewable Cost Breakdown with 5 digesters

Item Cost / Unit Qty Total Cost Cogen Unit $28,968.00 4 $115,872.00 Digester Tank $14,341.03 5 $71,705.17 Reserve Tank $71,705.17 1 $71,705.17 Thermal Tank $4,755.10 1 $4,755.10 Piping $20,000.00 $20,000.00 Pumps $10,000.00 $10,000.00 Radiator $10,000.00 $10,000.00 Installation/Maintenance $228,028.08 $228,028.08 Hydro Gas Rebate -‐$30,000.00 -‐$30,000.00 Hydro Electrical Rebate -‐$27,000.00 -‐$27,000.00 Reverse Metering $0.06 36576 -‐$2,194.56 Total $472,870.95

Comparing the two total costs, it is obvious that this project would never pay for itself, and that modifying of this optimum case would be necessary to make it viable for the prospective client. By reducing the number of digesters to 3, maintaining the same values for everything else, the price of the entire system would fall to a payback of just over 20 years. Payments would be on par for the 20 years of utility costs, with the 21st year as upkeep only. It would not longer be 100% off grid, as electrical load is now required, as well as natural gas load during peak heating periods. This may be combatted with a storage source of the excess natural gas during off-‐peak periods, but this will also introduce additional costs.

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Table 12. After Renewable Cost Breakdown with 3 digesters

Item Cost / Unit Qty Total Cost Cogen Unit $28,968.00 4 $115,872.00 Digester Tank $8,604.62 3 $25,813.86 Reserve Tank $25,813.86 1 $25,813.86 Thermal Tank $4,755.10 1 $4,755.10 Piping $20,000.00 $20,000.00 Pumps $10,000.00 $10,000.00 Radiator $10,000.00 $10,000.00 Installation/Maintenance $159,191.11 $159,191.11 Hydro Gas Rebate -‐$30,000.00 -‐$30,000.00 Hydro Electrical Rebate -‐$27,000.00 -‐$27,000.00 Reverse Metering $0.06 -‐19920.00 $1,195.20 Total $315,641.13

6.0 Conclusion This project, though expensive, will provide its owner with a highly renewable source of energy to replace the natural gas and electrical loads of the bed and breakfast. It provides the best energy per cost in comparison to wind and solar energy devices for this region, as the utility supplied electricity prices are very competitive.

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Bibliography [1] K. J. Chae, Am Jang, S.K. Yim, and In Kim, "The effects of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure," Bioresource Technology, vol. 99, pp. 1-‐6, 2008.

[2] J.R. Fischer, E.L. Iannotti, and J.H. Porter, "Anaerobic Digestion of Swine Manure at Various Influent Solids Concentrations," Agricultural Wases, vol. 11, pp. 157-‐166, 1984.

[3] National Resources Canada. (1996, September) Personal: Transportation -‐ 6 -‐ Fuel Consumption Ratio. [Online]. http://oee.nrcan.gc.ca/publications/infosource/pub/energy_use/NAPVUS/NAPVUSch6.cfm?attr=8

[4] Hanson Tank Pressure Vessels. (2011, April) Hanson Tanks. [Online]. http://hansontank.us/r16-‐insulation.html

[5] D.T. Hill, "Simplified Monod Kinetics of Methane Fermentation of Animal Wastes," Agricultural Wastes, vol. 5, pp. 1-‐16, 1983.

[6] Government of Canada. (2011, April) Canada Small Business Financing Program. [Online]. http://www.ic.gc.ca/eic/site/csbfp-‐pfpec.nsf/eng/h_la02855.html

[7] CIBC. (2011, April) CIBC Fixed Rate Open Mortgage. [Online]. https://www.cibc.com/ca/mortgages/fixed-‐rate-‐open-‐mortg.html

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