Judged To Be Efficient
Integrated VRF and geothermal systems save energy for an historical courthouse.
The Beaux Arts-style courthouse in Muscatine, IA, uses a VRF/geothermal integrated HVAC system from Mitsubishi Electric Cooling & Heating.
Searching for green
The County Board of Supervisors wanted to learn more about going green and knew it was time to replace the courthouse’s failing, outdated HVAC system. A proposal from Vic Amoroso, a 40-year HVAC design engineer and president of A&J Associates PC, North Liberty, IA, caught their attention. Amoroso explained the basics of a closed-loop geothermal system and how smoothly it would work in tandem with a variable-refrigerant-flow (VRF) zoning system from Mitsubishi Electric Cooling & Heating, Suwanee, GA.
Bruce Senti, an independent sales representative from Mitsubishi Electric, explained to Amoroso how the VRF zoning water-source system would interface with a geothermal field. “Our new W-series modular units perfectly combine the energy effectiveness of geothermal systems with the excellent efficiencies of our VRF zoning technology,” said Senti. “These new units are 30% smaller than previous models and can be easily transported down the stairs into the basement of the courthouse. By connecting to the geothermal loop, backup heat would not be needed as it might with air-source units.” The system, which uses water instead of air as a heat-exchange medium, is superior to air-cooled systems, especially in Iowa, where it is not uncommon for winter temperatures to dip below –10 F. The system’s dry mode is effective for the months of July and August, which can make Iowa feel like a greenhouse.
The courthouse is listed on the National Register of Historic Places and now boasts an updated HVAC system that saves energy and money.
Because of the hot, humid Iowa summers, Senti recommended another key VRF zoning product, a Mitsubishi Electric City Multi dedicated outdoor air system (DOAS). The DOAS would supply outdoor ventilation air to the courthouse, delivering the proper amount of fresh air to each room, and also provide ample dehumidification without excessive reheat. The DOAS would also increase the VRF zoning system’s energy efficiency because it pre-conditions outside air for introduction into the downstream HVAC units, reducing the load on the HVAC system.
The fact that the DOAS and the VRF zoning system were designed to work together was appealing to Senti. “The DOAS from Mitsubishi Electric was very convenient for us,” he said. “Because the outdoor-air system and the VRF system were manufactured by the same company, we didn’t have to cobble together a system with components from different manufacturers that might decrease the system’s energy efficiency. Additionally, this system combination provided us with a one-stop shop regarding parts, warranties, installation, service, and repair.”
Amoroso was interested in the VRF zoning system because its engineering design would overcome the installation challenges posed by the 105-year-old building with its 24-inch-thick limestone walls. The gas-fired boiler supplying heat to the courthouse would be eliminated, providing the county with significant natural-gas savings in the winter. But Amoroso also saw something even more significant—the VRF zoning system efficiencies, coupled with the heat-sync exchange of the campus geothermal field, could serve the courthouse and the new jail addition across the street. The geothermal campus was a hybrid, closed-loop system with 60 vertical and 40 horizontal wells. Amoroso’s presentation to the board convinced the members that this was the right decision.
Order in the court
The transition to the new system was smooth, with not one courthouse office losing a day of work. Judges even held court during the transition. Mechanical contractor Heath Allard, president of Climate River Valley, Eldridge, IA, said, “This smooth installation had a lot to do with the native intelligence of the Mitsubishi Electric VRF zoning system design. Because it’s the industry’s only two-pipe system, there are far fewer fittings on the refrigerant lines, which saved us a lot of labor and equipment costs. Because the W2-series units are installed indoors, we did not have to drill through the thick limestone walls, which would have made quite a racket.”
VRF equipment from Mitsubishi Electric Cooling & Heating, Suwanee, GA, installed at the Muscatine (IA) County Courthouse includes:
“There are so many benefits to this new system it is hard to know where to begin,” Amoroso said. “First of all, there is the historic preservation accommodation of this technology, which is the least intrusive, less destructive factor of this two-pipe system. There is the super-quiet aspect of all the indoor units, ideal for an office environment: It’s so quiet, people often ask if it is operating. There is the system’s remarkable ‘dry mode’ setting, which has great impact on indoor comfort during our humid summers. Then, there is the unique 100% inverter-driven compressor that varies its speed to match the indoor cooling or heating demand. This is great engineering. When the system is operating at partial load, the energy efficiency is significantly higher than that of a standard fixed-speed system.”
Inside the buildings, the VRF zoning-system heat pumps recover excess heat and reuse it to heat cold spots and to warm water. When the building temperatures are satisfied, the excess heat is then shared with the second building served by the campus geothermal loop. The second building’s heat-pump system uses the shared energy to maintain the temperatures in the jail addition. If both building temperatures are satisfied, then the excess heat is transferred to the loop field to be stored for later use. This use of a single energy unit provides overall campus energy savings.
“We sized the geothermal loop field to handle 450 gallons/minute flow at the design heating and cooling load,” Amoroso continued. “The geothermal pumps are variable speed and adjust to what is needed in the overall campus balance. We have observed this past summer that the field can handle the campus system heat-transfer requirement with just 20% of the design flow. The savings in pumping energy alone has been tremendous. This result is due in large part to the ability of the courthouse VRF zoning system to share and save heating and cooling energy for use in the other building and for storing for later use.”
“We are all thrilled with the performance of this technology partnership,” Seright said. “As budget director, I can tell you the clearest proof of the success of our decision came when the 30,000-sq.-ft. new jail addition came online and was tied into the campus geothermal field between both buildings. The energy bill did not move up one tick! That’s amazing proof of how this technology works.”
“Perhaps best of all, we were able to remove that hideous chiller on the courthouse’s roof that spoiled its classic lines,” she continued. “The diminutive demands of this VRF zoning system have helped us bring back the grandeur of our courthouse.”