Variable-refrigerant-flow zoning and ground-source heat pumps combine to produce significant energy savings for an Ohio university.
The combined energy efficiency of variable-refrigerant-flow (VRF) systems and ground-source heat pumps (GSHP) is dramatically demonstrated at Miami University’s Elliott and Stoddard Halls in Oxford, OH. The systems also made it possible to maintain the architectural integrity of the two historical residence halls.
Three-story Elliott Hall was built for $7,000 in 1825 as a men’s residence hall with rooms for 35 students. Known then as Old North, Elliott was designed in the Federal style and modeled after Connecticut Hall at Yale University, New Haven, CT. Nine years later, Miami built a second residence hall, Stoddard (Old South), a mirror image of Elliott.
The residence halls were upgraded over the ensuing years, but more recently, to grow its campus and shrink energy costs, Miami tasked its physical facilities department to develop a long-range utility master plan. Because temperatures underground are relatively constant (around 55 F), Miami made geothermal heating and cooling a centerpiece of its sustainability strategies. The university is committed to ending on-campus coal burning by 2025.
“Geothermal is very advantageous for our climate in Ohio, where heating and cooling loads are closely matched over the year,” said Doug Hammerle, PE, Miami’s director of energy systems. “This helps balance the well-field temperature and maximize the efficiency of the system.”
The right heat-pump system
Miami’s utility master plan included improving the efficiency of the two oldest buildings on campus. “Updating Elliott’s and Stoddard’s HVAC systems was a dramatic showcase for demonstrating our commitment to sustainability,” Hammerle said. To find the best technology to complement the geothermal system, Hammerle turned to Brian Isaacs, director of corporate sales for Habegger Corp., Cincinnati.
When Isaacs learned of Miami’s sustainability goals and the unique needs for cooling and heating the university’s two older buildings, he immediately thought of VRF zoning systems from Mitsubishi Electric U.S. Cooling & Heating Division (Mitsubishi Electric), Suwanee, GA.
Isaacs invited Hammerle and two local engineering firms to a nearby Mitsubishi Electric training center for a demonstration. In this group was Alec R. Carnes, PE, CEM, LEED AP BD+C, senior principal, Heapy Engineering, Dayton, OH.
400% more energy efficient
Hammerle was impressed, but what really sold him was the simultaneous cooling and heating capability of the heat-recovery water-source units. He explained that 90% of the buildings on the 880-acre campus are heated by a central steam plant, and more than 50 major buildings are cooled by two central chiller plants. “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,” Hammerle said. “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.”
Hammerle was especially interested in the potential for energy savings—especially on the heating side. “It’s impossible for a fossil-fuel heating plant to hit a COP [coefficient of performance] of 1, whereas, with combined geothermal and water-source heat pumps, it’s possible to hit a COP of 10.”
To verify this, Hammerle asked Heapy Engineering for an extensive energy-modeling analysis. Heapy’s model showed a total building energy usage of 43 kBTU/hr./sq. ft./yr. Carnes recommended that Hammerle accept the Mitsubishi Electric VRF zoning system for Elliott and Stoddard halls. “This unique VRF, two-pipe option will enable Miami to maintain the historical and architectural integrity of these two legacy structures,” Carnes said.
61% drop in energy consumption
Seventeen 600-ft.-deep geothermal wells were placed under the sidewalks surrounding the halls. As modern footings were unknown 150 years ago, the hand-dug basements had no space for the heat pumps. An easy-to-access mechanical room was built into the attic of each building for the three heat pumps and centralized controller.
To maintain the architectural integrity, custom cabinets were designed and built to house the indoor units for each room. “These cabinets are beautiful,” Hammerle said. “None of this would have been possible without the two-pipe system design. The interior would have been severely cut up with a hydronic four-pipe system.”
Elliott and Stoddard halls switched from coal-fired steam heat to geothermal heating and cooling and were metered as one. The buildings showed annual energy usage of 740,000 kBTU/hr. for the 2010-2011 fiscal year. Following the geothermal installation, this number dropped to 346,000 kBTU/hr.—a 61% decrease in energy consumption compared with 2010. The oldest buildings on campus are now 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.”