Almost twenty years ago, and 10 miles north of Iowa City in North Liberty, IA, we opened the doors of my mechanical and electrical engineering firm, A&J Associates PC. I had always questioned traditional HVAC design concepts, and I knew there were new, exciting, engineering models that went well beyond standard industry practices. Everyone was starting to talk about how to save energy, and I wanted to better understand the benefits of systems like geothermal, radiant cooling and heating, and variable refrigerant flow (VRF) zoning systems.
I originally became interested in VRF zoning technology after reading a magazine article in 2003. The article made the case for extreme energy conservation by combining several energy-efficient concepts into one total building HVAC system. I agreed that a multifaceted approach to HVAC design would overcome the usual shortcomings of using just one HVAC concept (such as VAV):
- Poor air distribution
- Poor humidity control
- Poor acoustical requirements
- Poor use of plenum and shaft space, or a requirement for excessive plenum and shaft space
BUNDLING INTRIGUING NEW HVAC CONCEPTS
That same year, the U.S. Department of Energy (DOE) listed several HVAC technologies that had great theoretical potential for energy savings. I was intrigued. Buildings in America consume huge amounts of energy for cooling and heating — accounting for about half of the country’s total energy use — so the DOE suggested energy savings concepts that included both tried-and-true engineering technologies as well as some that were still being sketched on the drawing board.
The DOE outlined new concepts like the dedicated outdoor air system (DOAS), electronically commutated motors, enthalpy/energy recovery heat exchangers for building ventilation, improved and expanded duct sealing, occupancy-based environmental controls, radiant ceiling cooling and heating, heat pumps for cold climates, and VRF zoning systems.
I asked myself, why couldn’t we design a building HVAC system that incorporated many or all of these energy-saving ideas? After about five minutes of consideration, I concluded there was absolutely no reason these concepts could not be bundled into one HVAC solution.
At A&J, we first employed the bundling concept by using all of the above energy savings systems, except for the VRF zoning system, in two separate, new construction projects. We designed two brand-new buildings using radiant panel cooling and heating for the individual spaces. Both projects performed very well.
ENERGY TRANSFER: GETTING SERIOUS ABOUT VRF ZONING
Shortly after these projects were finished in 2007, Bruce Senti of Mitsubishi Electric [US Cooling & Heating Division, Suwanee, GA] and Paul Ebeling of the Davenport, IA, Trane office came to A&J for a show and tell about the Mitsubishi Electric VRF zoning system technology. Bruce and Paul explained that the system had been a popular source of energy savings in Europe and Asia for decades but was relatively new to the U.S. Most importantly, they convinced me that the Mitsubishi Electric CITY MULTI® VRF zoning system was cost competitive with conventional HVAC systems.
I was immediately drawn to the use of VRF zoning two-phase, change-of-state energy transfer, which is similar to steam heating. This mass- and heat-transfer mechanism had to be efficient and could be used effectively for both heating and cooling.
COMBINING WATER-SOURCE HEAT PUMPS WITH GEOTHERMAL
At A&J, we had long ago used horizontal-bore geothermal loop heat exchangers in our HVAC design to reduce the cost and energy consumption. I asked Bruce if Mitsubishi Electric would consider coupling its water cooled VRF zoning system with a heat exchanging geothermal loop.
We convinced them that the geothermal loop was no different than the company’s water cooled condensing units. They agreed that integration with the geothermal system would work. We used this system at a project we were working on for an Iowa school district, and it was very successful. For the project, we coupled an energy recovery cell with a Mitsubishi Electric ducted terminal unit to make a field-erected DOAS. The manufacturer liked the result so much that the company adopted the DOAS design that we developed and now offers it as a manufactured DOAS.
GREEN TECHNOLOGY FOR 107-YEAR OLD COURTHOUSE
A few weeks after this VRF zoning introduction with Bruce and Paul, I received a call to pay a visit to a striking 1907 Beaux Arts Courthouse in Muscatine County, IA.
The building had been exhibiting growing signs that the more than-30-year-old cooling and heating system would soon need to be replaced. Building personnel had found water in the basement from the old boilers, the pipes were starting to leak, the indoor units were loud, moldy, and fuzzy, and everyone disliked the huge, ugly condenser unit sitting prominently on the roof of the handsome Beaux Arts building, spoiling the view.
The Muscatine County Board of Supervisors wanted to save taxpayer dollars. Although county governments aren’t known for being on the cutting edge of technology, the Board was looking for ways to better manage county energy usage.
In 2002, the Board had authorized the construction of a 25,000-sq-ft county conservation learning center using a geothermal cooling and heating system. Several years later, the members had approved funding for replacing the century-old original windows throughout the courthouse. This effort brought grants from the DOE and the Iowa Office of Energy Independence, and it helped the courthouse become one of only a handful of courthouses in the U.S. to earn an Energy Star® certification. The Board had even invested in drilling a geothermal test well in anticipation of replacing its old energy system.
MAJOR COURTHOUSE UPGRADE CHALLENGES
The Muscatine County Courthouse HVAC upgrade presented some major challenges. First, this is an active courthouse, and the chambers could not afford to be shut down for even a day. Next, no roof- or grade-mounted equipment could be used because of aesthetic restrictions. The new indoor units had to blend well with the historic woodwork and other finishes within the courthouse. In addition, we had extremely limited shaft space within the historic structure itself. Humidity control in any Mississippi River town is extremely important and individual room control of temperature and humidity is essential. Finally, I had to keep construction costs under tight control.
WHY A VRF ZONING SYSTEM WAS RIGHT FOR THE COURTHOUSE
I considered both the Mitsubishi Electric two-pipe and a different three-pipe system for this project. For this project, I decided the two-pipe was the best for several reasons:
- First-cost advantage;
- Less piping and wiring to better fit the tight spaces;
- The compactness of the outdoor units and their ease of installation in the basement;
- Based on the past work, I knew we could integrate it with the existing geothermal campus loop field.
It also helped that the modular units could easily be taken down the stairs into the basement of the courthouse.
By connecting to the existing geothermal loop, backup heat would not be needed as it might with air source units. This VRF zoning system, which uses water instead of air as a heat-exchange medium, is superior to air cooled systems, especially in Iowa, where it’s not uncommon for winter temperatures to dip below -10ºF. I also knew the system’s dry mode would serve well in the months of July and August, which can make Iowa feel like a greenhouse.
Because of these hot, humid Iowa summers, I wanted to use the VRF zoning product, the aforementioned Mitsubishi Electric DOAS, which is designed to work with VRF zoning systems. The DOAS would supply outdoor ventilation air to the courthouse, delivering the proper amount of fresh air to each room, and it would provide ample dehumidification during the humid Iowa summers, without excessive reheat. The DOAS would also increase the VRF zoning system’s energy efficiency, because it preconditions outside air for introduction into the downstream HVAC units, lessening the load on the HVAC system.
All in all, I felt we were ready to overcome the installation challenges posed by the 107-yr-old building, even with its 24-in.-thick limestone walls. I told the Board that the gas-fired boiler supplying heat to the courthouse would be eliminated, providing the county with significant natural gas savings in the winter. But there was something even more significant — the VRF zoning system efficiencies coupled with the heat sync exchange of the campus geothermal field could serve both 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.
COURTHOUSE RECEIVES ENERGY STAR BUILDING CERTIFICATION
The Board knew it was time to replace the failing, outdated HVAC system, so I made a presentation showing the Board the basics of a closed-loop geothermal system and how smoothly it would work in tandem with the Mitsubishi Electric VRF zoning system. Emphasizing the potential for load sharing and shedding, energy storage and diversity, I was able to demonstrate to the Board how this multiple building use enhanced the savings potential possibility. I was also able to show them how this would be less expensive than replacing the current system with new boilers and chillers.
ORDERLY TRANSITION: JUDGES HOLDING COURT WITHOUT DISRUPTION
What could have been very disruptive construction happened harmoniously. The entire building is devoted to the courts and courtroom administration, and not one office lost a day of work. Judges were holding court while we were making this transition, and we could not afford to have a lot of banging and pounding during the installation of new equipment.
This smooth installation had a lot to do with the native intelligence of the VRF zoning system. The two-pipe simultaneous cooling and heating system translated to far fewer fittings on the refrigerant lines, which saved us a lot of labor and equipment costs. We were also able to remove the worn-out hot and cold water pipes and, for our vertical distribution, put down the new wiring and refrigerant lines in the old chase walls. Because the compressors of the water-source units are installed indoors, we did not have to drill through the thick limestone walls, which would have made quite a racket.
MANAGING ENERGY USE: SHARED ENERGY
There are so many benefits to this new design that it is hard to know where to begin. First of all, there is the historic preservation accommodation of this minimally intrusive approach. 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. The system’s dry mode has also had the intended effect on comfort during our humid summers.
The 100% inverter-driven compressor varies its speed to match the indoor cooling or heating demand also gives us energy-efficiency is significantly higher than that of a standard fixed-speed system when at partial loads or simultaneous heating/cooling.
Inside the buildings, the VRF zoning system heat pumps recover excess heat generation 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 heat pump system uses the shared energy to maintain the temperatures in the county 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 allows phenomenal overall campus energy savings. We sized the geothermal loop field to handle 450 gpm flow at the design heating and cooling load. 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 have been tremendous. This result is due in large part to the ability of the courthouse VRF zoning system to store and share heating and cooling energy for later use in the other building.
NEW JAIL ADDITION ADDS ZERO ENERGY COSTS
Because of the installation’s success, the Board decided that when systems need to be replaced in other Muscatine County facilities, the partnership of geothermal and Mitsubishi Electric VRF zoning systems would be the new standard. The Board recently hired my firm to design geothermal systems for two additional county-owned buildings.