Variable refrigerant flow (VRF) and geothermal heat pumps often are seen as competing energy- efficient technologies. What many people don’t recognize is that you can combine these systems. Water-source VRF units can be connected to a geothermal loop field to make an ultra-efficient system, combining the best attributes of a VRF system and geothermal heat pumps.
VRF systems operate much like a four-pipe, fan-coil system, except that heat is generated by a heat pump. The heat pump circulates refrigerant directly to the fan coils instead of using water. VRF systems also provide a centralized compressor for ease of maintenance and to reduce noise; individual room temperature control; and packaged self-addressing controls. They also require minimum ceiling space and no floor space for the fan coils. Compared with an air-source VRF, a geothermal water-source VRF offers several advantages, including higher heating capacities, lower refrigerant volumes and no defrost cycle – mitigating concerns about the VRF heat pump not functioning during extremely cold weather.
Geothermal systems save energy by reducing the temperature difference the refrigerant compressor has to work against. Additionally, a geothermal system typically has lower fan and pump power and doesn’t waste energy for reheating like variable air-volume systems. Geothermal VRF takes all of these energy-saving features to the next level.
VRF ductless-ceiling cassettes reduce fan power even further. Centralized compressors allow shorter water pipe runs between the condenser and the well field, resulting in lower pumping power. The compressor in a VRF system uses permanent magnet motors and features variable speeds, which reduce the compressor’s energy use. The heat-recovery feature of VRF systems allows a single refrigeration cycle to cool one room and uses the rejected heat in another room. VRF systems take advantage of diversity by connecting more fan coils than the nominal condenser tonnage. This typically allows the installed tons of heat pumps to be reduced by up to 25 percent. This right-sizing further reduces pump power and improves part-load efficiency.
Geothermal VRF systems not only are energy efficient, but with proper design, they have been shown to be cost effective for a building’s life cycle.
For additional information regarding geothermal VRF systems, please contact Matt Slager at MSlager@hanson-inc.com.