3 Mechanical System Redesign

Transcription

1 3 Mechanical System Redesign 3.1 Considered Alternatives The MAC building offered many opportunities to change the existing design and explore an alternative different than the solution the original design team chose. The building is not typical in the sense that it does not just have office spaces or fitness spaces. The building has multiple spaces including a gymnasium, offices, locker rooms, conference rooms, and suites. The diversity in the type of spaces gives the designers an opportunity to consider different systems. The schedules of the building offer the designers a unique challenge within the design. The gymnasium and the offices are at peak load at different times during a day. Considering the unique building spaces and schedules there were some design alternatives that were considered and later rejected after further investigation. Some of these considered redesigns are provided below. An initial idea for the building was to replace the existing mechanical system with a dedicated outdoor air system (DOAS) along with a parallel ceiling radiant panel system. The DOAS system would have taken advantage of using an enthalpy wheel and sensible wheel to lower the energy costs in the cooling coil and reheat coil of the system. The system would have allowed for a smaller duct system throughout the building. Furthermore, the air handling units could be smaller, since the air supplied to the space is on a ventilation requirement basis. Smaller air handling units would help with the already restricted mechanical spaces. DOAS would have been a good proposal for the office and conference spaces within the building; however, the building has such a variety of spaces that DOAS did not seem to fit the criteria within all the spaces. For instance, the locker rooms have showers and therefore the latent load within the room would be high which would be conducive to condensation on the panels. Furthermore, the radiant ceiling panels would need to be integrated into the design with the architects approval. Therefore, this option did not seem like a viable option for the MAC building. Also, this topic has been researched a number of times the last few semester so it was determined that it would be more educationally beneficial to study a different topic. - Page 14 -

2 A second idea for the building was to add indirect evaporative cooling to the supply side of the air stream. The idea behind this was to lower the load on the cooling coil by initially cooling the supplied air. Initially this was thought to be economically beneficial by lowering the load on the cooling coil but since the wet bulb temperature is relatively high the supply air temperature would not be reduced enough to justify its first cost. Furthermore, this topic was not in depth enough to rationalize spending an entire semester researching the topic. The mechanical load on the chillers was considered to be cut by using geothermal heat pumps to provide the cooling in the summer and also provide part of the heating required during the winter months. The initial idea was to use a vertical ground coupled heat pump cycle. According to ASHRAE Applications handbook, the approximate groundwater temperature is 56F. This option was disregarded for a few reasons. To receive the 900 tons of cooling the building needs, the number of holes that would be needed was a cause for concern. Also, the geology study of the area to determine the water table and temperature was not available with the material given for this project. Ultimately the location of the vertical bore holes on the limited surrounding space of the campus deterred this idea from developing into a proposal. The last option was to consider altering the design of the building in order to make the building LEED credited on some level. Technical Assignment 2 goes into further detail on the current design of the building and how many points it would be awarded with the current design. This would give the opportunity to explore numerous options to obtain points. The LEED guideline gives five categories where a building can be analyzed and designed to become a more sustainable building. Initial thought gave the idea of having a rainwater catching system along with low flush fixtures to help the building become more water efficient. The mechanical system would be analyzed to become more efficient. Overall, there is a lot that can be learned from trying to make the MAC building a LEED certifiable building but the scope of the project would be more focused on the building as a whole instead of the mechanical system. Therefore, analyzing the - Page 15 -

3 changes that would need to be made to make the building LEED was determined to be to radical of a changed warranted for this project. These alternatives are all viable options to explore for the MAC building, although none of the options can solve the power problems that currently exist with the building. Some of the above options will lower the energy requirements for the building but it is unlikely to be lower the power requirements enough for the existing power lines to be able to support the MAC building. 3.2 Proposed Goals, Scope, and Justification The major function of the redesign for the s mechanical system is to redesign the system to be able to be built with the existing power conditions that the university is experiencing. Since Monmouth University is located within a residential power grid in New Jersey, the overall glaring issue that could not be avoided is the fact that the building can not be built because the surrounding power lines do not have the capacity to support the addition of the building. To support the overall goal of allowing the MAC building to be built with the existing power restraint, the unique problem presented itself a challenging but logical solution to produce the power locally. After further investigation, the major mechanical alteration to the building will be the addition of combined heat and power (CHP), also known as cogeneration. This could be applied to the building using natural gas as the prime mover within a micro generator to produce the power. The power produced would be enough to supplement the buildings power needs so the existing power lines would not need to be increased. Furthermore, the exhaust from the power generation plant would be used in some form to produce hot water, steam, and/or chilled water. There are two methods that will need to be explored to determine the major concern for the CHP system. The CHP system will be optimized to provide the peak load of operation for either the peak electrical load or the peak thermal load. The difference - Page 16 -

4 between the two is that the peak electrical loads main design is to meet the peak electrical load while the other, peak thermal load, is designed to meet the peak thermal load of the building. There will be a few different natural gas turbines examined as the principle CHP design. The exhaust heat will then be used to power an absorption chiller that will supply the building with its chilled water. Additionally, the remaining exhaust will be used in place of the boilers to heat the water. Along with the CHP, the system will use operate with a chilled water thermal storage system. This system will produce chilled water throughout the day and night and the water that is not being used in the coils will be stored in a thermal storage tank. Thermal storage is used to level the load on the absorption chillers so the chillers will not need to be sized for the peak demand of the building for one hour but for the peak demand of the building for one day. The storage tank will discharge the stored chilled water during peak periods of the year. This will allow the chillers to be smaller in size allowing them to not need as much waste heat from the generator. Furthermore, this will allow more of the waste heat from the generation cycle to be used for another application. This addition will make the CHP system more efficient since the waste heat is always being used to run the chillers. Without thermal energy storage, the chillers would not be run at a consistent load and therefore the efficiency of the CHP system would lower. The remaining waste heat from the generation plant will be used to produce hot water. The hot water will be used to preheat or reheat the existing air in the HVAC system. In addition, the hot water will be used for showers within the locker rooms of the facility. In conclusion, the mechanical system redesign will try to optimize the system. This will be achieved by supplying the building with the needed electrical and thermal load; having the over produced electricity or thermal output either sold back to the campus or exhausted to the atmosphere respectively. The consistent load of the chillers due to the thermal storage offers an advantage to the overall efficiency as well as the ability to have smaller chillers. Overall, the redesigned mechanical system will replace or minimize the existing designed boilers, chillers, and electrical needs from the utility. - Page 17 -

5 The proposed redesigned is expected to allow the building to be built. The major focus and justification for the system that is being proposed is that the building will no longer need to wait until the utility supplies the power lines needed to support the addition of the building. The building can provide its own power and any extra power that is supplied can be sold back to the campus at the rate the power utility is charging the university. 3.3 Mechanical Load Calculations There are many aspects of a building that need to be known to properly design a combined heat and power system. One aspect of the building is the load profiles of the building. Both the thermal, heating and cooling, and electrical load profiles are needed to properly design a CHP system. Load profiles can include many different time periods being referenced including a typical day, workday, weekday, weekend, holiday, monthly, seasonal, yearly, hourly, and design day. The best data to design a CHP system is using hourly data over a yearlong period; this allows the most accurate and complete data to analyze the building for the peak period. A few graphs are included in the Appendix that represents the hourly data for the MAC building. Carrier s Hourly Analysis Program (HAP) was used to find the hourly loads. HAP is an energy simulation program that determines the energy used throughout the year. The program is arranged to calculate the loads that occur in different spaces. Each space is designed separately and the combination of all the spaces makes up the whole building. Within the spaces design parameters, the electricity used to power the lights and other equipment is accounted for in the calculation. Furthermore, it calculates the heating and cooling load for each designated space within the building. The simulation determines the heating and cooling loads using a large number of parameters including the outside temperatures, relative humidity, solar load, elevation, location, envelope materials, as well as many others. HAP was used to find the electrical, cooling, and heating design loads for the building. These calculated loads were broken down into the design day and peak for each of the - Page 18 -

6 loads. The design days were analyzed to determine the required size of the CHP system to meet either the thermal or electrical loads. The design day calculations are provided in the Appendix. 3.4 Prime Mover Selection A prime mover is a device that converts energy into electricity. Prime movers include but are not limited to, engines, turbines, and water wheels. There were many different prime movers researched to power the MAC building. The turbines that were investigated were too large to justify implementing into the MAC building. On the other hand, the micro turbines that were explored were too small to apply to the MAC building. After much consideration an internal combustion engine was the best option. The HESS 375 micro generator will be used to power the MAC building. The generator produces 375 kilowatts of electricity while also providing hot water to be used for thermal processes. The generator is rated to be 34.5 percent efficient at making electricity. The generator can be incorporated to run in parallel with the utility grid or can be run completely separate of the Figure 3.1 Hess 375 Micro-Generator electric utility. The rejected heat can be captured and used for thermal processes. The thermal efficiency of the thermal process is rated to be 50.6 percent. The thermal output can come in various forms including, hot water, 15 psi steam, 125 psi steam, and exhaust. The MAC building will incorporate two of these forms, the hot water and exhaust. Hot water will be produced and used to run the thermal loads of the building, but when hot water is not needed a diverter valve will exhaust the heat out the system. The efficiency of the system goes down as more heat is being exhausted into the atmosphere, thus the thermal - Page 19 -

7 efficiency of 50.6 percent can be misleading if you are not able to utilize the rejected heat into the system. The MAC building will be designed with either two or three micro generators run in parallel to supply the appropriate amount of electrical and thermal load. 3.5 Absorption Chillers Most chillers use electricity to produce chilled water but an absorption chiller uses a different source of energy to generate the chilled water. An absorption chiller uses heat as its electricity to produce the chilled water. Lithium bromide and water or ammonia and water are the working fluids within the absorption chiller. They typically have capacities of between 50 and 2000 tons. The produced chilled water is based of the amount of heat that is available. The input heat can be in a variety of different forms including, exhaust, hot water, steam, natural gas, oil, as well as other thermal heat sources. Absorption chillers come in different classifications including direct-fired and indirectfired. A direct-fired unit uses a chemical transformation, combustion, from the natural gas or oil to produce the required heat for absorption chiller. An indirect-fired unit uses hot water or steam as the required source of heat. In addition, there are different types of absorption chillers that can be used. The two main types available today are the single-stage and double-stage absorption chillers; there is a threestage absorption chiller that is under development. The coefficient of performance, COP, of an absorption chiller does not lose performance at part load conditions and in some cases the COP can even increase at part load. Figure 3.2 Cention Hot Water Absorption Chiller - Page 20 -

8 The CHP for the MAC building system will use hot water from the micro-generator to power the absorption chiller. The amount of hot water needed is directly related to the size of the chiller. As long as the electricity produced is enough to meet the building s peak electrical demand, the system will be designed to meet the cooling load. Since the MAC building s CHP system is designed to handle the cooling thermal load, thermal storage can be implemented to lower the peak cooling demand. By lowering the peak cooling demand, there will be a more consistent amount waste heat needed instead of having spikes during short periods throughout the year. Thermal storage can be implemented as long as there is enough power being produced to handle the requirements of the building. 3.6 Thermal Storage There will need to be a large amount of waste heat needed to run the absorptions chillers at the peak load. A method of lowering the peak cooling load is to install a thermal storage tank unit. Thermal storage will lower the peak load required by shifting some of the chilled water needed for the peak load operation onto off peak times. The required amount of waste heat needed for the absorption chiller can be lowered by introducing a thermal storage system into the CHP plant. After load leveling the design cooling day, the focus was directed to the electrical demand to verify that enough electricity will be produced to meet the electrical demand on the peak electrical design day. Since the two main focuses of the CHP system are electricity and chilled water, it was determined that load leveling the cooling side of the system is the best method to keep the system as small as possible as well as producing enough electricity for the building. The following graph represents the MAC buildings design day along with the load profile when thermal storage is implemented into the system. - Page 21 -

9 Load Profile for Design Day Tons Charge Thermal Storage Discharge Thermal Storage Without Thermal Storage With Thermal Storage Hour Figure 3.3 Thermal Storage Design Day Graph There are many different ways to implement thermal storage into the MAC building. The two types of thermal storage that were explored were latent and sensible storage. Latent storage is when the chiller produces a chilled solution that runs through a tank and creates ice for use later. The ice is created during low loads and then discharged during the higher loads. Ice storage takes advantage of both the latent and sensible properties of the ice. There is energy that is released during the phase change from the solid to liquid, latent part, and energy from the change in temperature of the liquid, sensible part. Sensible storage is when there is energy that is released just during the temperature change of the stored liquid, there is no phase change. The MAC building will implement a sensible storage system. This system was chosen to allow the absorption chiller to constantly produce the same temperature water without needing to lower the temperatures to create ice. Absorption chillers would need to use ammonia to be able to allow the system to lower the temperature enough to create ice. The sensible storage tank will be a stratified chilled water tank. A stratified tank is when - Page 22 -

10 the warm water and cold water do not mix but are separated by a boundary layer due to the differences in the densities of the water. The cold water is added to or drawn from the bottom of the tank while the warm water can be added or drawn from the top of the tank. The picture shows a stratified chilled water tank along with the thermocline which is the Figure 3.4 Stratified Storage Tank separation of the cold and warmer water temperatures. The size of the tank depends on the amount of thermal energy needed to be stored within the tank. The sample calculation below is representative of the thermal storage tank that is needed for the MAC building on the design day without the addition of enthalpy wheels. To determine the amount of water needed a general equation was used. The S represents the require amount of storage in ton-hours, the figure of merit or FoM is a reflection on the amount of heat gain on the stored water, the change in temperature is the change in the discharge and charged temperature S[ ton h] Volume( gal) FoM T[ F] ton h Volume( gal) [ F] Volume( gal) 330,000( gallons) After determining the size of the tank, there needs to be a system for which the tank will charge and discharge the stored chilled water. During the time period when the facility needs the stored chilled water, the thermal storage tank will discharge the needed capacity from the bottom of the storage tank. Thus, the water that is received in the top of the tank is warmer and less dense. On the other hand, the opposite occurs when the tank is being charged. The water from the top of the tank is taken and run through the chiller and then reintroduced into the thermal storage tank at the bottom of the tank with the colder, denser water. The following schematic shows the different sequences of - Page 23 -

11 operation. The blue schematic displays the sequence as the system is charging the thermal storage tanks; therefore, the second schematic is when the thermal storage tank is discharging. Figure 3.5 Thermal Storage Tank Charging Schematic Figure 3.6 Thermal Storage Tank Discharging Schematic - Page 24 -

12 3.7 Enthalpy Wheels Enthalpy wheels offer an increase in savings by using the exhaust air to either pre-cool or preheat the ventilation air before it reaches the cooling coil or heating coil. During winter applications an enthalpy wheel will preheat and humidify the ventilation air. On the other hand, during summer applications the enthalpy wheel will pre-cool and dehumidify the ventilation air. There will be a preheat coil before the enthalpy wheel to raise the outdoor air temperature to 32F to ensure that the wheel Figure 3.7 Enthalpy Wheel does not freeze. The figure below shows the winter and summer applications for the enthalpy wheel. The enthalpy wheel is an aluminum wheel that is coated in a desiccant molecular sieve to allow for catch and release water vapor. Figure 3.8 Enthalpy Wheel for Summer(Blue) and Winter(Orange) Conditions The MAC building can implement the design of an enthalpy wheel for the two air handling units serving the gymnasium. These units are 100 percent outdoor air units that serve cfm of air. These two units account for a major portion of the heating and cooling requirements during the year. By integrating an enthalpy wheel into the two gymnasium air handling units the amount of cooling and heating required went down - Page 25 -

13 drastically. The following table shows the MAC buildings design with and without an enthalpy wheel. Peak Cooling Peak Heating Tons MBH Without Enthalpy Wheel With Enthalpy Wheel Table 3.1 Load Changes due to an Enthalpy Wheel 3.8 Combined Heat and Power Design Considerations Cogeneration is the process of converting chemical energy into two useful forms of energy through a prime mover. The prime mover is the combustion system that transforms chemical energy into useful energy. Cogeneration typically uses combustion to drive a shaft to do some mechanical work and then uses the waste heat for another process. The efficiency of the electrical and thermal energy process is increased by using the waste heat. The cogeneration system can be transformed into a trigeneration system with the addition of absorption chillers. Trigeneration produces three useful energy sources, electrical, hot water or steam, and chilled water through an absorption chiller. The intent of a cogeneration or trigeneration system is to utilize the input energy to produce the most output energy available. Furthermore, cogeneration plants are intended to run at higher efficiencies which will result in lower fuel costs. During a life cycle analysis, the lower costs of energy can pay for the increased first costs in the additional equipment. Figure 3.9 Combined Heat and Power Applications - Page 26 -

14 One of the first factors that need to be considered is to analyze the locations spark gap. A spark gap is the difference between the price of electricity and the price of natural gas, or other fuel, based on the same units. A CHP design is considered a good application if the spark spread is greater than $12/MMBtu. As can be seen in the table below, Monmouth University has a spark spread that is greater than $16/MMBtu. Therefore, the MAC building is a good application to further study the feasibility of a CHP design. The cost data found in the table below will be further explained in the cost analysis section of this report. Location Monmouth County, New Jersey Electric $ $/kwh Natural Gas $7.95 $/MMBtu Electric $24.44 $/MMBTU Natural Gas $7.95 $/MMBTU Spark Gap $16.49 $/MMBTU Table 3.2 Spark Gap for Monmouth University The CHP system can be designed for three different purposes in mind; electrical load, heating load, and cooling load. One primary design is to meet the electrical demand for the building; another design method is to meet the heating demand; and the third is to design the system to meet the cooling demand. A CHP system that is designed to meet the peak electrical load will provide the building with the appropriate power requirements during the peak electrical hour; the waste heat during the power generation is used to produce part or all of the thermal requirements. A second and third design alternative is to base the design off the heating or cooling requirements of the building. Using these alternatives, the primary application of the CHP system will use the exhaust heat to produce a designed amount of heating or cooling; as a result, the production of electricity will be based off of the thermal output of the CHP system and not the electrical load profile of the building. Another design consideration is to have the CHP system designed to meet the buildings thermal or electrical base load. A base load configuration is designed to meet the - Page 27 -

15 minimum electrical or thermal load of the building. By having a CHP system operating on a base load condition the part-load operation can be abolished. Using base load operation will result in smaller CHP equipment than if the building was designed to meet the peak demand load. Another method is to have the system sized to the site s base load electrical or thermal load, and then have the CHP system track the load profile to produce the required load. This allows the site to produce the required thermal or electrical load during all hours of operation. Consequently, the CHP system will need to be designed to meet the peak loads. The peak load of the building will only be met at a very small percentage of time during the year, thus the CHP system will be running at part load for a large part of the time. A third method was studied to see if it was a viable option for the MAC building. This option is much like the first option but instead of producing the minimum amount of electricity or thermal the procedure will be to constantly produce the maximum amount of the designed needed load. The excess electricity can be sold back to the grid at a rate determined by the utility provider. This rate is usually a lot less than what the utility would originally charge the customer, unless the CHP system is producing a lot more electricity than is needed. On a thermal side of things, the building can implement thermal storage to store some of the excess thermal energy produced. These considerations are a few ways to design a CHP system. The combinations of all the design alternatives were considered in the MAC building to determine the best solution for the CHP design. The third solution was determined to be the best application for the MAC building. After careful consideration, there were six different designs that were considered for the MAC building. A table following the description of the design alternatives gives a graphic representation of the different components within the system. - Page 28 -

16 Design Alternative 1 The first design was based off the thermal load profile for the cooling load of the MAC building. Since the system is based off the cooling load, the system will be designed to use the waste heat from the combustion process and run it through an absorption chiller to meet the peak cooling load. This was determined after a study was done which concluded that if the CHP design was based off of the peak electrical profile the rejected heat would not be sufficient to run the absorption chiller during peak load operation. The MAC building offers a unique situation since it is on a campus. Do to this unique situation; the excess electricity that will be produced by the micro-generator can be connected back to the other university buildings. The excess electricity will be sold to the campus at the rate the university would be buying it from the utility. Additionally, the waste heat will also be used to produce hot water through a heat exchanger when the absorption chiller does not need all the rejected heat. An additional boiler will be added to produce the hot water when there is not enough hot water from the heat exchanger. Therefore the system will be integrated to be a trigeneration system that combines to produce heating, cooling, and electricity. The specific of the system are three Hess 375 kilowatt micro-generator connected. The thermal output will be in the form of hot water that will be run through a Cention absorption chiller. The absorption chiller rejects the hot water at a temperature still high enough to run through a heat exchanger to get the additional heating required for the building. Following the heat exchanger is a boiler that will be used when there is not enough heat rejected from the absorption chiller. The boiler will also be used to heat the water before it goes through the micro-generator if the return water is not at the nominal temperature. The following is a schematic of the hot water loop within the first design consideration. There are temperatures and flow rates associated with the different locations throughout the system. There were some key parts that were not shown including pumps and valves. - Page 29 -

17 Figure 3.10 Hot Water CHP Flow Schematic for Design Alternative 1 Design Alternative 2 The first design alternative led to the consideration of a second system consideration. The first alternative produces a lot of waste heat that will only be used during peak times of the system. Therefore, for most of the year there will be a large amount of waste heat that is not going to be used. Overall, this will lower the efficiency of the system. The second alternative was designed to use two Hess 375 kilowatt micro-generators. The thermal output from the micro-generators will be able to run the absorption chillers for most of the year. Like the first design consideration, a boiler will be added before the micro-generators; therefore, for the small percentage of the year where the microgenerators do not reject enough heat to run the absorption chillers the boilers will pick up the additional load required. This system will also have a heat exchanger to produce the hot water needed for heating the building. Compared to the first alternative this system will use the boiler more often; on the other hand, it will be more efficient because it can utilize more of the waste heat during the off peak conditions. The following is a schematic of the hot water loop within the second design consideration. There are - Page 30 -

18 temperatures and flow rates associated with the different locations throughout the system. There were some key parts that were not shown including pumps and valves. Figure 3.11 Hot Water CHP Flow Schematic for Design Alternative 2 Design Alternative 3 The second design alternative led to the consideration of a third system design. The second system was designed to use all the waste heat from the micro-generators during the peak conditions. Additionally, a boiler was added to create the additional heat during the peak cooling load periods. Therefore, there was a lot of heat being produced by the micro-generator and boiler to meet the peak cooling days. The third alternative is to determine the maximum amount of cooling that can be done by two Hess 375 kilowatt micro-generators. After this is determined, an additional electric chiller will be added to meet the peak loads. It was determined that the absorption chiller could produce approximately 250 tons of cooling based off the two micro-generators. Therefore, the electric chiller will need to produce the additional 200 tons of cooling for the design day. The MAC building requires more than 250 tons of cooling for approximately 60 days during the year. Furthermore, the two micro-generators will be - Page 31 -

19 producing enough electricity to run the electric chillers during the peak operating day. This coincides with the objective of not needing any power from the utility provider. The third alternative will still need a boiler to provide heating during the peak days when the micro-generators do not produce enough heat. This application will not need the boiler as much since there is an electric chiller. The following is a schematic of the hot water loop within the third design consideration. There are temperatures and flow rates associated with the different locations throughout the system. There were some key parts that were not shown including pumps and valves. Figure 3.12 Hot Water CHP Flow Schematic for Design Alternative 3 Design Alternative 4, 5, and 6 Design alternative 4, 5, and 6 were similar to design alternatives 1, 2, and 3, respectively. The last three design alternatives included an enthalpy wheel in two of the eleven air handling units. The enthalpy wheels were placed in the two air handling units that serve the gymnasium. Both of these air handling units are 100% outdoor air and require cfm during the design periods. The additions of the enthalpy wheels are to lower the design day requirements for the chillers. Ideally by adding the enthalpy wheels to the air - Page 32 -

20 side of the system it will in turn lower the required cooling coil demand for the design day. By lowering the cooling demand, the thermal storage tank can be reduced. On the other hand, by incorporating the enthalpy wheels into the system it will lower the required heat and cooling load. This will lower the amount of waste heat needed from the micro-generators. In the end, the total efficiency will be reduced due to the fact that less of the thermal exhaust heat will be used in the building. The following table is a list of the redesigned mechanical components along with the original designed components. Conventional System 1 System 2 System 3 CHP System 4 System 5 System 6 Mechanical System Components Thermal Electrical Heating Chilled Water Storage Utility Service Emergency Generator 3 - Hess Microgenerators 2 - Hess Microgenerators 2 - Hess Microgenerators 3 - Hess Microgenerators 2 - Hess Microgenerators 2 - Hess Microgenerators Boiler HX + Boiler HX + Boiler HX + Boiler HX HX + Boiler HX + Boiler ton Centrifugal Chillers ton Absorption Chiller ton Absorption Chiller ton Absorption Chiller ton Centrifugal Chiller ton Absorption Chiller ton Absorption Chiller ton Absorption Chiller 1-80 ton Packaged Chiller Table 3.3 Mechanical System Components None 330,000 Gallon Tank 330,000 Gallon Tank 330,000 Gallon Tank 198,000 Gallon Tank 198,000 Gallon Tank 198,000 Gallon Tank Air Side None None None None cfm Enthalpy Wheels cfm Enthalpy Wheels cfm Enthalpy Wheels Overall The six systems were all based on the cooling load. This could be done since the systems can produce additional electricity which could be sold back to the campus. Without this special situation economically it might have been better to design from an electrical load - Page 33 -

21 profile. Furthermore, all six systems produced enough electricity to operate the MAC building without any utility power needed. The systems efficiencies were determined by combining the electric efficiency and the thermal efficiency. The system efficiencies were all over 48 percent. The Hess 375 kilowatt micro-generators claim to have combined efficiencies of approximately 86 percent but the designed system for the MAC building did not use the entire thermal output. During the times when the building was not using the entire thermal output from the micro-generators, the system would divert the production of hot water to exhaust the unused heat. There would be an excess amount of hot water if the micro-generator did not divert the production of hot water to exhaust. The hot water would need to be cooled in some way before entering the micro-generator again. The following table illustrates the efficiencies of all the systems. Fuel Fuel Used Consumed Electricity Thermal System Efficiency MMBtu kw MBH Electric Thermal Total Conventional 43,616 3,253,260 6,613, % 80.0% 40.6% System 1 100,652 9,855,000 20,302, % 20.2% 53.6% System 2 67,102 6,570,000 18,212, % 27.1% 60.5% System 3 67,102 6,570,000 18,657, % 27.8% 61.2% System 4 100,652 9,855,000 15,604, % 15.5% 48.9% System 5 67,102 6,570,000 15,002, % 22.4% 55.8% System 6 67,102 6,570,000 15,271, % 22.8% 56.2% CHP 3.9 Emissions and Fuel Saving Table 3.4 Systems Efficiencies Since CHP systems produce at least two sources of energy at the same time the emissions produced are significantly lower. A conventional building will use electricity from the utility and then the heat from some on-site boiler. The utility and the boilers are both producing emissions. A CHP system produces both electricity and heat with a single source of emissions. Furthermore, the emissions from a CHP system are far less than that of the conventional method. - Page 34 -

22 To determine the actual emissions output of the building there were a few factors that needed to be determined. First the building needed to be analyzed to determine how much heat and electricity were going to be used. Next the emissions for the production of the electricity and the heat needed to be determined. In the appendix, a table provides the percentage breakdown of energy sources used to create the electricity for the utility serving the Monmouth Campus. The following table, courtesy of Dr. Freihaut, provides the emissions that are being used by the building on a per kilowatt-hour basis. lbm Pollutant j /kwh Jersey Central Power and Light (JCP&L) Fuel % Energy Mix Particulates SO 2 /kwh NO x /kwh CO 2 /kwh Coal E E E E-01 Oil E E E E-02 Nat. Gas E E E E-01 Nuclear E E E E+00 Hydro/Wind E E E E+00 Totals E E E E-01 USA Average E E E E+00 Table 3.5 Emissions for JCP&L and Nationwide Averages The following table shows the difference in the amount of emissions that are produced for the conventional system as well as the six other systems. The table represents both the electrical emissions from the power plant or the micro-generator depending on the system as well as the boiler emissions. The table is normalized to show the amount of emissions that is produced per megawatt-hour of energy used. As can be seen, the microgenerator offers a large amount of saving on the emissions in all categories but carbon dioxide. Jersey Central Power and Light acquires 42 percent of their electricity from Nuclear which does not give off any carbon dioxide which will in turn account for the lower CO 2 emissions. The larger amounts of particulates, SO2, and NOX of the conventional system is because the conventional production uses oil and coal which give off a lot more emissions than a natural gas micro-generator. Along with the Jersey Central Power and Light emissions, the average emissions for the United States is given to represent how the CHP system is compared to the United States average. - Page 35 -

23 Total Emissions Calculated from Electricity and Natural Gas per MWh Total Particulates SO 2 NO X CO CO 2 MWh lbm/10 3 lbm/10 3 lbm/10 3 lbm/10 3 lbm Conventional , NA 243 USA Average , , NA 339 System System System System System System CHP Table 3.6 Emission per MWh of Energy Produced By using the waste heat of a micro-generator to produce heat, there is less fossil fuels being consumed. A conventional system uses an energy source, fossil fuels, to produce the electricity provided by the utility and then some type of on-site heat generation equipment using another fossil fuel. A combined heat and power system uses one source to provide both the electricity and heat. The combined heat and power system that was designed for this project included an additional boiler to generate the heat that the CHP system would not generate. The following table represents the amount of fossil fuel being consumed by the building. The amount of fuel used in the CHP design is greater than the conventional design, but this is justified since it is providing more electricity and thermal energy. Since the amount of fuel being consumes is not a great representation of which system is actually using less fossil fuels, the systems were normalized to provide the amount of Btu s of fuel it takes to create 1 kwh of used energy. The fossil fuel used in the conventional system is more than all the other systems. The last column compares the amount of fuel used in the conventional system to each of the new designs. For instance, System 1 uses 82.8 percent as much fuel per kwh compared to the conventional system. - Page 36 -

24 CHP End Energy Use Btu of Fuel Fuel Needed Fuel Consumed Electricity Thermal Used per kwh Useful Energy Compared to Conventional MMBtu kw MBH Btu/kWh Method Conventional 43,616 3,253,260 8,267,328 7, % System 1 100,915 9,855,000 20,302,724 6, % System 2 69,978 6,570,000 18,212,176 5, % System 3 67,662 6,570,000 18,657,333 5, % System 4 100,652 9,855,000 15,604,492 6, % System 5 67,855 6,570,000 15,002,077 6, % System 6 67,437 6,570,000 15,271,698 6, % Table 3.7 Fossil Fuel Usage A CHP system can save more than just money. As seen above, the implementation of a CHP system will reduce the emissions and the fossil fuel consumption. This is a valuable consideration when considering the world today. Pollution is increasingly getting worse and there is talk of running out of fossil fuels in the future. Monmouth University can take strives to show its focus on the environment by reducing the amount of pollution the MAC building is creating and reducing the amount of fossil fuel it consumes using a CHP system Mechanical Depth Conclusion There are many factors that need to be analyzed when picking a system. After analyzing the six redesigned alternatives and the conventional system design, the best system that is proposed without taking cost considerations into account is the 3 rd system. Cost considerations will be accounted for in a later section. This system incorporates two Hess micro generator systems that provide hot water and electricity to the absorption and screw chillers. The major criteria when designing this trigeneration system was the system efficiency, emissions, and fossil fuel savings. The 3 rd system uses all of the waste heat in the absorption chillers for approximately 16 percent of the year. Furthermore, the system has the highest efficiency when analyzing the amount of fuel it converts to useful energy whether that is thermal or electrical. The efficiency is 61.2 percent. The actual efficiency should increase by using more of the thermal output of hot water for showers and sinks. - Page 37 -

25 The emissions of all the CHP systems were much lower than the conventional design in all categories except carbon dioxide. Carbon dioxide was low because the utility gets a large portion of the electricity from nuclear power plants which do not give off pollution in the form we are calculating. The CHP systems were all very similar when analyzing the system on emissions per megawatt hour as was done above. This can be justified because they were all designed using the same prime mover with the only variation being the amount the boiler is being used. The table below is a total amount of emissions the building is producing for each of the systems. Total Emissions Calculated from Electricity and Natural Gas Total Particulates SO 2 NO X CO CO 2 MWh lbm lbm lbm lbm lbm Conventional 13,267 1,318 14,769 9,855 NA 3,226,746 USA Average 13,267 2,158 24,540 14,768 NA 4,491,768 System 1 29, ,593 18,371 11,776,382 System 2 20, ,194 12,771 7,851,445 System 3 19, ,081 12,322 7,850,996 System 4 29, ,580 18,320 11,776,331 System 5 19, ,090 12,359 7,851,033 System 6 19, ,070 12,278 7,850,952 CHP Table 3.8 Total Emissions With the exception of the 6 th system, the 3 rd system uses the least amount of fossil fuel to produce useful energy. This is a direct relationship to the efficiency of the system but is a different way of analyzing it. The last graph in section 3.9 shows that system 3 will use 72.4 percent as much fuel as a typical conventional system. Moreover, the fuel saving in the table is per kwh that is used. The conventional case of the MAC building consumes 5,191,593 kwh of energy per year. The yearly savings of fossil fuel is enormous. - Page 38 -