Retrofitting with VRF
A variable refrigerant flow (VRF) system with heat recovery may be an energy efficient alternative for buildings with inefficient fans and leaky ductwork. Variable frequency drive motors allow a VRF system to adjust to a variety of loads. The refrigerant serves as both the heating and cooling medium that can be delivered to multiple fan-coil units from a single outdoor condensing unit.
An article in Buildings recommends taking three steps to determine if a VRF system is an appropriate retrofit option.
1. Evaluate building characteristics. Buildings with high energy use, especially those with VAV systems with electric reheat or other electric resistance heat, may be well suited to VRF systems. Facilities with limited space to add ductwork for additional cooling capacity may also be good candidates. The comparatively small size of VRF refrigerant lines makes them easier to install than ductwork.
The zonal capability of VRF fan units are well-suited to facilities with separated spaces, such as schools, lodging, multifamily, healthcare, some shopping centers and office buildings with numerous enclosed spaces and conference rooms. VRF systems are typically not appropriate for big box retail, warehouses and other facilities with large open spaces.
VRF systems are better suited in buildings located in extreme weather climates. The ideal building size for a VRF system is 10,000–100,000 square feet.
2. Perform an energy analysis. A building survey will reveal how, where and when the building uses and wastes energy. At least one year of detailed consumption data is recommended. The analysis will help determine how large the VRF system needs to be and estimate its efficiency and cost.
3. Assess lifecycle costs. Higher maintenance, repair and replacement costs for VRF systems may offset some of the energy cost savings, so detailed lifecycle costs should be estimated, according to the Buildings article.
Variable Refrigerant Flow Systems, a technology assessment prepared under GSA’s Green Proving Ground program, estimates that VRF systems can achieve 30 percent and higher HVAC energy cost savings over older inefficient systems and minimally code compliant conventional systems. However costs and energy savings for retrofit projects vary a great deal, so estimating typical ROI is not feasible.
Trane applications engineers discuss some of the challenges when applying a VRF system, such as complying with ASHRAE Standards 15 and 90.1, meeting the ventilation requirements of ASHRAE Standard 62.1, and zoning to maximize the benefit of heat recovery.
Photo via Shutterstock.
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