Variable Air Variable Refrigerant Flow System

Combines the benefits of VAV and VRF systems to provide a highly efficient HVAC system

This HVAC system combines the efficiencies of Variable Air Volume (VAV) and Variable Refrigerant Flow (VRF) systems, simultaneously providing the advantages of both systems. Heating, ventilation, and air conditioning (HVAC) systems are responsible for heating and cooling, and controlling the humidity and purity of the air in an enclosed space. Currently, Variable Air Volume (VAV) and Variable Refrigerant Flow (VRF) systems are popular and widely used HVAC systems.

VAV systems regulate the supply air volume-flow rate using a damper to match the variation of the space-cooling load and maintain the zone air temperature at the set temperature. On the other hand, a VRF is a refrigerant system varying the refrigerant flow rate and temperature to cool down the room with the help of a variable speed compressor and electronic expansion valves (EEV). The EEV uses information received from thermistor sensors in each indoor unit to enable precise control of refrigerant flow variation, providing exact amounts of heating or cooling in each space. VRF systems hold an impressive capacity control range, providing approximately 20-50% higher energy efficiency than traditional VAV systems. However, there is a current movement to increase the efficiency of HVAC systems beyond those of VRF and VAV technologies.

Researchers at the University of Florida have developed the Variable Air Variable Refrigerant Flow (VAVRF) system. This new HVAC system combines the efficiencies of both VAV and VRF systems. The design allows for simultaneous variations of the air volume in conditioned spaces and the refrigerant flow and temperature, increasing efficiencies beyond the conventional VRF and VAV systems.

Application

HVAC system combines the benefits of Variable Air Volume (VAV) and Variable Refrigerant Flow (VRF) technologies, providing higher efficiencies and energy savings than traditional HVAC systems

Advantages

• VAVRF combines the benefits of both VAV and VRF, increasing efficiencies beyond those of conventional VRF and VAV systems
• The VAVRF can be packaged as a single unit with centralized airflow, reducing cost and energy usage and improving air cleaning and control
• Does not need multiple fans in all indoor units, reducing energy use, cost, and need for invasive indoor maintenance on indoor units
• Indoor units have fewer moving parts, leading to fewer breakdowns
• Modulates airflow to broader ranges using the integral damper, providing better airflow controls than traditional HVAC systems
• Unlike a traditional VRF unit, VAVRF units can be equipped with several high-performance technologies, such as economizers, UV filters, bipolar ionization, HEPA or other ULPA filters, humidifiers, preheat coils, indirect gas heating, enthalpy wheels, air-air heat recovery, etc.
• Ability to replace old traditional VAV packaged units with more efficient VAVRF packaged units, reusing existing ductwork with the advantages of efficient VRF technology
• Indoor unit designs can be low voltage (24V-48V) and don’t require an electrical contractor to wire them unlike VRF Indoor units, reducing project cost
• Having localized filters in the central units unlike VRF indoor units leads to higher indoor environmental quality (IEQ), as the filters are replaced more regularly compared to individual VRF indoor units. VAVRF units can also employ other IEQ measures such as bipolar ionization, UF, etc. which is cost prohibitive in VRF units on most projects
• Better humidity controls are achieved by VAVRF systems compared to both VAV and VRF systems

Technology

This Variable Air Variable Refrigerant Flow (VAVRF) system depicts an innovative HVAC system, combining the benefits of both VAV and VRF technologies simultaneously. In contrast to VRF systems, consisting of several indoor units with individual fans for providing air movement, the VAVRF system encompasses a central ventilation Air Handling Unit (AHU) responsible for this task. The AHU is a VAV system with supply, relief, ventilation, return, and mixing sections. A VRF-type system handles the heating and cooling of air from the unit supplies into the building using ductwork. Each zone has a volume-modulating air damper (VAVRF indoor unit), maintaining a predetermined volume of air flowing through it. A VRF coil inside this unit provides heating or cooling in response to the space thermostat, and a few usual heat recovery/branch controller boxes serve multiple VRF coils. The VAVRF system's easy packaging and centralized airflow lead to savings in energy and cost, better air cleaning, and improved control.