Geothermal And VRF Provide Best Of Two Worlds
Ground-source heat pumps and variable-refrigerant flow zoning work together to save a lot of energy for an Ohio institution.
At Miami University's Elliott and Stoddard Halls in Oxford, Ohio, the combined energy efficiency of variable-refrigerant-flow (VRF) systems and ground-source heat pumps (GSHP) is clearly displayed. The solutions also made it possible to preserve the two ancient residence halls' original architectural integrity.
Elliott Hall, a three-story structure with 35 rooms, was constructed in 1825 as a men's residence hall for a cost of $7,000. Elliott, originally known as Old North, was built in the Federal style and based on Connecticut Hall at Yale University in New Haven, Connecticut. Nine years later, Miami constructed Stoddard (Old South), a second residence hall that was an exact replica of Elliott.
Over the succeeding years, the residence halls were refurbished, but more recently, Miami University ordered its physical facilities department to create a long-term utility master plan in order to expand its campus and reduce energy expenditures. Miami makes geothermal heating and cooling a focal point of its sustainability plans due to the generally stable temperatures (about 55 F) subsurface. By 2025, the university will no longer burn coal on its grounds.
Doug Hammerle, PE, Miami’s director of energy systems, said:
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Geothermal is very advantageous for our climate in Ohio, where heating and cooling loads are closely matched over the year. This helps balance the well-field temperature and maximize the efficiency of the system.- Doug Hammerle
The two oldest buildings on campus had their efficiency increased as part of Miami's utility master plan. The renovation of Elliott's and Stoddard's HVAC systems served as a striking example of Hammerle's company's dedication to sustainability. Hammerle turned to Brian Isaacs, director of corporate sales at Habegger Corp., Cincinnati, to discover the finest technology to supplement the geothermal system.
When Isaacs learned about Miami's sustainability initiatives and the special cooling and heating requirements for the university's two older buildings, he instantly thought of VRF zoning systems from Mitsubishi Electric, Suwanee, Georgia.
Isaacs arranged for a demonstration at a neighboring Mitsubishi Electric training facility with Hammerle and two regional engineering businesses. The senior partner of Heapy Engineering in Dayton, Ohio, Alec R. Carnes, PE, CEM, LEED AP BD+C, was a member of this group.
Hammerle was impressed, but the heat-recovery water-source units' capacity to simultaneously chill and heat was what truly won him over. On the 880-acre campus, he added, a central steam plant heats 90% of the buildings, and two central chiller facilities cool more than 50 large structures.
A current limitation with our two-pipe fan-coil system is they can do either heating or cooling but not both at the same time. This causes comfort control issues during mild weather. The Mitsubishi product solves this problem by being able to do both cooling and heating, irrespective of the temperature outside.- Doug Hammerle
Hammerle was particularly curious about the possibility of energy savings, particularly on the heating side. "A fossil fuel heating facility cannot achieve a COP [coefficient of performance] of 1, but geothermal and water-source heat pumps can achieve a COP of 10."
Hammerle requested a thorough energy modeling investigation from Heapy Engineering in order to confirm this. According to Heapy's model, a building's annual energy consumption is 43 kBTU/hour/square foot.
Hammerle should approve the Mitsubishi Electric VRF zoning system for Elliott and Stoddard halls, according to Carnes' recommendation. “This unique VRF, two-pipe option will enable Miami to maintain the historical and architectural integrity of these two legacy structures,” Carnes said.
The sidewalks enclosing the halls were covered with seventeen 600-foot-deep geothermal wells. 150 years ago, there were no modern footings, therefore there was no room for heat pumps in the hand-dug basements. Each building's attic has a mechanical area with convenient access for the three heat pumps and centralized controller.
The indoor units for each room are housed in special cabinets that were created to preserve the historic integrity. Hammerle said:
Geothermal heating and cooling replaced the coal-fired steam heat in Elliott and Stoddard halls, which were metered as a single unit. For the fiscal year 2010–2011, the buildings used 740,000 kBTU/hr of energy annually.
This amount decreased to 346,000 kBTU/hr after the geothermal installation, which represents a 61% reduction in energy usage compared to 2010. On campus, the oldest structures are currently the most energy-efficient.
“This new system has already saved us a ton of money and enables me to have many more satisfied customers,” Hammerle said. “I can say with certainty that VRF is my system of choice for all new outlying buildings on campus not tied into the central plant.”
“Renovation of any historic building is a complex undertaking requiring a balance between the original architecture and modern building systems,” Carnes said. “This was accomplished thanks to the installation flexibility of the VRF City Multi system. [It] allowed us to preserve this historic architecture and control energy efficiency, two goals important to Miami University.”