Two of my favorite (and most efficient) technologies can actually be combined to form an uber-efficient HVAC system. Both Mitsubishi and Daikin have provided water-cooled condensing units as part of their US line-up for several years. However, only recently has this technology been refined through plate and frame heat exchangers and control logic to perform optimally with geothermal ground loop heat exchangers. Mitubishi’s WR2 series (heat recovery) and WY series (heat pump) along with Daikin’s VRV-WIII series can combine the benefits of variable speed inverter compressor technology and geothermal heat pump efficiency. Add to this the additional benefit of being able to install multiple types of ductless, ducted and concealed indoor evaporators and you have one of the most flexible and highly efficient solutions for a green building project. Because of the system’s flexibility, it can be designed into new building and retrofit mechanical schemes (see Mitsubishi schematic).
Unfortunately, as these systems are only available in larger sizes of 6 tons and up and only available in 3 phase, they are not yet a viable option for single family homes. However, we are seeing these systems specified on multiple dwelling residential projects like apartment buildings and condominiums. For the most part, this is really primarily a commercial option that can deliver added points for LEED buildings and deliver the ultimate in sustainable design. Existing ground source heat pumps on the market provide dual speed for their premium models (like the WaterFurnace Envision line), but there has not been a variable speed inverter compressor option available to the market. In redeveloping their water-cooled condensing unit lines to accommodate the geothermal market, these VRF/VRV manufacturer’s have provided a significant boost in efficiency. Based upon an energy modeling study for assisted living facilities in various cities across the country, it was proven that this type of hybrid VRF-Geothermal installation provides on average a 37% efficiency increase over VRF air-cooled heat pumps. Although VRF/Geothermal is still a costly initial installation versus established fossil fuel and air-cooled systems, emerging energy efficiency technology experts are now touting ground-source variable refrigerant flow heat pumps as an affordable energy option.
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