A Feasibility Study of Potential Energy Savings
at the Pettit National Ice Center (PNIC)
Revised Quarterly Progress Report
Dr. Kevin J. Renken, Associate Professor
Dr. John R. Reisel, Associate Professor
Mr. B. Andrew Price, Instructor
University of Wisconsin-Milwaukee
Mechanical Engineering Department
Energy Conversion Efficiency Laboratory (ECEL)
3200 N. Cramer Street
Milwaukee, Wisconsin 53211
Tel.: (414) 229-5755; E-mail: email@example.com
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Our primary objectives for the project have not changed from our original proposal. The main objective remains to determine if the waste heat from the ice-making compressor system can be effectively used to reduce energy costs at PNIC and/or the State Fair Park's Youth Center. Currently, the waste heat from the compressor system is being disposed of via a condensing tower on the center's roof, while a separate two-boiler system is being employed to keep the skating area at 55}F and the offices, shops, locker rooms, concession areas at around 72}F. The PNIC has a monthly natural gas bill of approximately $7K (see attached). Our second objective is to evaluate potential on-site alternative methods to generate electricity. Currently, the PNIC has a monthly electric bill of approximately $25K (see attached). Our final objective of the project is to use this feasibility study as an educational tool in our Mechanical Engineering Department capstone design course. Here, we plan on having our senior mechanical engineering undergraduates work on the first two objectives of the project so that they can apply their educational experience to a real problem.
Mr. B. Andrew Price was incorporated into the project to add his expertise to that of the principal investigators, thereby making the project team stronger. Mr. Price is the primary instructor of our 612-496 Senior Design Project course, and will be using this project in the Spring 2002 offering of that course. Mr. Price, who is expecting his Ph.D. in Mechanical Engineering from the University of Iowa, also has expertise in the area of control of HVAC systems. His addition eliminated the need for hiring a graduate project assistant in this area.
612-496 is the Mechanical Engineering Department's capstone course in design. The senior mechanical engineering students work in design teams (typically 4-6) in collaboration with college faculty and industrial sponsors. With this project, we will have the undergraduates work with Drs. Reisel and Renken, Mr. Price, and Mr. James Gulczynski (Director of Facility & Operations at PNIC).
The course objectives are to allow the students to (1) apply relevant topics from earlier courses to their senior design project, (2) critically evaluate designs using engineering criteria, (3) demonstrate an ability to identify and specify design requirements from general problem descriptions, (4) systematically develop a design from concept to prototype, (5) clearly communicate design ideas and information, and (6) demonstrate the ability to facilitate their learning by identifying design issues and questions that require additional investigation and formulation of appropriate course of action.
The PNIC feasibility study provides two ideal projects in the HVAC area for the Spring 2002 semester. One student group will be asked to provide alternative designs for a heat recovery system for the rejected heat of the compressor system at the PNIC. In order to keep the problem open-ended in nature (which is of great educational value), the design group will be given the problem statement, architectural drawings, mechanical manuals, and a small budget for S&E, and will participate in site visits to facilitate their understanding of the project. The second group of students will be requested to design and compare alternative sources of on-site power generation at PNIC. The student team will be given power and heating requirements, industrial contacts, and again a small budget for S&E. This team will also be involved with site visits to better understand their problem and limitations. They will be expected to perform a life-cycle analysis of wind power, solar energy, and fuel cell technology to determine if any of these technologies are feasible applications for this facility.
The co-PIs obtained the following information from our meeting with Mr. James Gulczynski, Director of Facility & Operations at the PNIC.
Currently, the PNIC operates with a system of eight compressors. Six are used for ice-making purposes and the other two are used for air conditioning. The normal operation continuously uses only four compressors from October to February when the center is heavily utilized. During the months between March and September, only three compressors are normally operating. A portion of the waste heat produced by the compressor system is utilized by the center's snow pit (~ 1 MBtu/hr) which melts the snow dumped by the Zamboni machines after resurfacing. A subfloor frost deterrent heating system is operated once a year and utilizes approximately 170,000 Btu/hr. The remaining heat is rejected to the environment by a rooftop evaporative condenser system. This system is rated at 12.5 MBtu/hr.
Our initial assessment to utilize the wasted energy includes four possible alternatives. The first is to use the rejected heat as a preheat to the current supply air used in the HVAC system so that boiler operation and hence, natural gas usage is reduced. Currently the heating system is using cool indoor air as the supply air.
The second alternative is to use the rejected heat as a means of heating the hot water supply at the facility. The PNIC contains both washrooms, locker rooms, offices, and concessions that utilize hot water.
The third preliminary design would use the heat in a heat-recovery system that would heat the facility. The ice skating area is required to be at 55}F to offset the 22}F ice temperature. The remaining parts of the facility require normal operating temperatures of 72}F. As part of the initial design, it is anticipated that a thermal storage system would have to be employed to store the large amounts of heat. A more detailed investigation on this alternative is being considered.
The fourth possible design would involve the State Fair Park's Youth Center which is in close proximity to the PNIC. In this alternative design, the rejected heat would be transferred to the Youth Center via a tunnel for hot water heat and/or space heating.
1) Wind Power
An initial analysis of power production using wind energy has been performed. The initial analysis is based on estimated average annual wind speeds for Milwaukee, Wisconsin. The average wind speed for Milwaukee is based on a wind classification of 3, as shown in Fig. 1. A wind classification of 3 relates to average wind speeds of 6.7 m/s. The average wind speed is converted to bins of wind speed using a Waybill distribution (Rohatgi, J.S., 1994, Wind Characteristics, an Analysis for the Generation of Wind Power, Alternative Energy Institute, West Texas A&M University). The bins of wind speed are compared to the wind turbine power curves to estimate the possible power that could be produced at the site in a year's time. For example, a Zond 750-50 wind turbine would produce 1,150,000 kW-h of power in one year with an average wind speed of 6.7 m/s and a typical Weibull distribution. The energy estimation will be improved by examining the site to determine the effects caused by local terrain, and comparing the energy demand with the time of production.
Fig. 1. Average wind speed classification for Wisconsin.
The installation of a wind turbine at the PNIC to offset electricity costs is seen as a potentially attractive option. The relatively flat, unobstructed grounds near the facility, coupled with the proximity to Lake Michigan, which induces substantial localized winds, presents a site that offers a number of benefits for the use of wind power. As wind turbines are relatively inexpensive pieces of electricity-generation equipment, this option has moved to the forefront of our considerations.
In addition to the advantages listed above, the use of a wind turbine at PNIC could encourage more installations in the state to use wind power. The high visibility nature of a wind turbine just off of I-94 would provide a substantial amount of exposure for the technique.
One concern that often appears when a wind turbine is to be installed is the noise of the equipment. However, with the large amount of nonresidential area near to the facility, the siting of the equipment should allow for the minimization of the disturbance to the population in the surrounding area.
A disadvantage of wind power is that it is not constant. Therefore, wind power would not completely replace the consumption of utility-produced electricity. Further analysis of the site data will allow us to determine the cost savings possible even with sporadic wind power generation.
2) Solar Energy
Initial assessment of the PNIC site for the use of solar power suggests that the site is not ideally located for substantial electricity production from photovoltaics. The availability of sunny and mostly sunny days, when photovoltaic electricity production is at its highest, is moderate at the site. In comparison, wind energy is much more readily available than solar energy.
However, the PNIC facility does offer a large rooftop space which could be used for the installation of a large array of photovoltaic cells. Therefore, on sunny days, a substantial amount of electricity could be generated on site from solar energy. Further study is planned to determine how the economics of this will appear in a typical year.
3) Fuel Cells
It has been popular to tout the advantages of fuel cells for electricity generation in recent years. Fuel cells have been pushed as a clean power alternative. In addition, as non heat-engine power generation devices, the efficiency of the fuel cells is not limited by the familiar Carnot expressions which impose a Second Law of Thermodynamics limit to the efficiency of conventional power plants. The combination of potentially CO2 emission-free electricity generation and very high efficiencies have caused much focus to be placed on the development of fuel cells recently.
Unfortunately, the reality has not yet caught up to the hype for fuel cells. Currently, fuel cells still suffer from problems related to the poisoning of the catalyst with carbon. As the most common fuels are hydrocarbons, the use of hydrocarbons in fuel cells typically require a reformer to separate the hydrogen from the carbon, directing the hydrogen to the fuel cell for power generation. During this process, something must still be done with the carbon to prevent it from contributing to CO2 emissions. In addition, the reformation process requires energy, which uses a considerable portion of the electricity produced by the fuel cell, thereby reducing the overall efficiency. A different source of hydrogen to power fuel cells at PNIC would avoid this problem, but such a source is not readily available. Fuel cells, though, could be sized to satisfy the entire electrical needs of the PNIC, and would not be subject to fluctuations in weather conditions. At this time, further investigation is needed to determine the feasibility of fuel cell utilization.
4) Micro Gas Turbines
Micro gas turbines are small-scale gas turbine electricity generation systems that are designed to provide power for factories, small businesses, or similar settings. These devices use modern gas turbine technology, similar to that found in large-scale gas turbine power plants, but at a small scale suitable for satisfying localized power needs. These systems have good efficiency, and have the advantage of removing the facility from the utility power grid. This would greatly reduce, or eliminate, the PNIC electricity costs. However, the natural gas bill would increase, as the devices operate by burning natural gas. Therefore, a recommendation on the use of micro gas turbines will be based on a careful economic analysis, to determine if any operational costs savings exist, and if they offset the capital equipment cost.
As described above, the focus of this portion of the project will be the economic viability of each of these technologies. There is no question that if the meteorological conditions are favorable enough, the electricity costs at PNIC can be reduced, although not eliminated, by the use of one or more of these technologies. The determining factor in the recommendations is whether the operational cost savings from these technologies justifies the capital costs of equipment installation.
If these technologies do not appear to be economically viable, more focus will be placed on micro gas turbine. Finally, if micro gas turbines are not a feasible option, stationary fuel cell technology will be considered. As discussed above, while both of these technologies have the potential to remove eliminate the need to buy any electricity from the utilities, they do add fuel costs.
Fig. 2. Photo of snow pit.
Fig. 3. Photo of PNIC compressor system.
Fig. 4. Photo of rooftop condensing tower.
Fig. 5. Photo of current HVAC ductwork at PNIC.
Fig. 6. Photo of PNIC HVAC room.
Fig. 7. Photo of nearby Wisconsin State Fair Park Youth Center.