Development of a Web-based Decision Tool for Selection of Distributed Energy Resources and Systems (DERS) for Moving College and Corporate Campuses Toward Net-Zero Energy
Net-Zero energy buildings are currently being built, and they no longer consist of small demonstration projects but rather large commercial and institutional buildings. However, achieving a “net-zero energy building” concept for existing buildings has its challenges in an urban environment where private and/or public space around the building considered is limited, in addition to the inherent energy challenges associated with urban multi-story buildings. While the most achievable task would be energy efficiency improvements in the operation of the building electrical and mechanical systems, examples of integration of renewable heat and electrical power systems on college and corporate campuses are abundant. The integration of renewable energy systems on urban campuses presents significant logistical challenges. For instance, the available roof area may not be enough to produce a substantial amount of photovoltaic power for the buildings under consideration.
In this investigation, two students enrolled in an independent study Mechanical Engineering course at the Milwaukee School of Engineering (MSOE) developed a web-based a Distributed Energy Resources and Systems (DERS) decision guidance modeling tool that can be used by facilities directors on college or corporate campuses. Their work was augmented by an undergraduate engineering student who was employed as a research assistant during the following summer. The tool allows the following user-defined input, priorities, and constraints to generate a recommended suite of distributed energy resources that best meet the requirements of the user:
• electrical and thermal load distribution on campus
• geographical location
• user objectives (moving toward a net-zero energy campus, a net zero carbon campus, or minimization of energy costs)
• capital resources available
The model uses ambient weather data, system performance parameters, and capital costs of distributed energy resources to make recommendations on the distributed energy system configuration. The tool enables the user to identify and analyze practical technologies that can be adopted for an existing campus in moving toward a net-zero energy goal.
For calculations of solar photovoltaic (solar PV) system output, the solar irradiance and ambient temperature are used in conjunction with an estimated cell temperature correction along with rule-of-thumb derating factors (e.g. electrical losses, dirt losses, etc.). Solar thermal system output is estimated using the f-chart analysis approach which utilizes local solar irradiance data, ambient temperature, thermal load of the building, and typical performance parameters of flat plate solar thermal collectors. Combined Heat and Power (CHP) system output is estimated using design guidelines provided by the US Department of Energy’s Midwest Combined Heat and Power Applications Center. The decision tool outputs the following parameters:
• Annual thermal energy output
• Annual electrical energy output
• Number of solar PV panels
• Number of solar thermal panels
• Size of the CHP system
• Internal rate of return on the total initial capital investment
Currently, the tool uses an iterative method in MATLAB to optimize the configuration of distributed energy systems as measured by the internal rate of return (IRR) realized from the initial capital investment. Future work will focus on expanding the capabilities of the tool so the user can identify the optimum configuration as measured by the amount of off-site energy purchased (thus moving toward net-zero energy), and/or by the amount of carbon emissions generated (moving toward net-zero carbon).
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