Bachelor of Science
Denise A. McKahn
Geothermal energy, Ground source heat pumb, Vertical borehole heat exchangers, Campus heating system, Building energy simulation, Building modeling validation, Life cycle cost analysis, Building retrofit, Cost benefit analysis, Sustainable energy, Sustainable systems
Committed to becoming a carbon neutral campus by 2030, Smith College is transitioning towards geothermal energy for campus heating and cooling. Energy Consultants have been hired to conduct an economic and phasing analysis to prepare a district energy master plan. In conjunction with this planning effort, this thesis designed and evaluated the life cycle cost of a vertical ground source heat pump system for the Field House as a pilot demonstration project.
A building energy model of the Field House was constructed in Trace 700. A sensitivity analysis identiﬁed eight sensitive unknown design parameters, including wall construction, ventilation and inﬁltration rate, window, wall and ﬂoor u-factor and wall height. The model was validated with existing oil usage data. The calibrated model estimates a total annual energy consumption within 4% difference from the oil data.
With this model of building heating load, a ground-source heat pump (GSHP) was designed. The design included the calculation of ﬁve key parameters, namely the total and individual borehole ﬂow rate, borehole thermal resistance, total borehole length, number of boreholes and the power of the water and heat pumps. Two methods of borehole length calculation were compared, and a ﬁnal design was proposed that detailed three boreholes at 600 ft, with a ﬂow rate of 2.4 gpm per well coupled with three heat pumps of 0.6 tons.
A life cycle cost analysis was conducted over a period of thirty years for four design options, including (1) the existing oil-based system, (2) a GSHP system, (3) a GSHP system with medium level building retroﬁt and (4) a GSHP system with deep level building retroﬁt. While remaining on oil requires the least cost over the next 30 years, that solution does not meet our carbon neutrality goals and offsets are not being considered as a viable path. As a result, the GSHP only option ranked the least among the three remaining options in terms of the total converted present worth at year30, $285,000, closely followed by GSHP + Deep, which also reduced the annual heating demand by 28.9%. Economically, it is not worthwhile to retroﬁt a load bearing masonry building unless a deep retroﬁt is conducted.
Future work is recommended to improve system efﬁciency and reduce total life cycle cost. Speciﬁcally, work is identiﬁed in areas of thermal modeling to provide more accurate temperature proﬁle of the system. A PV system is also recommended to provide electricity for the geothermal system heat pumps. This framework provides a useful way to compare potential carbon tax policy frameworks
©2019 Xinyi Li. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.
Li, Xinyi, "Design and life cycle cost of a vertical ground source heat exchange system for the Smith College field house" (2019). Honors Project, Smith College, Northampton, MA.
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