Comparison between VAV and VRV system

HVAC stands for heating, ventilation, and air conditioning. This system provides heating and cooling to residential and commercial buildings. You can find HVAC systems anywhere from single-family homes to submarines where they provide the means for environmental comfort. Becoming more and more popular in new construction, these systems use fresh air from outdoors to provide high indoor air quality. The V in HVAC, or ventilation, is the process of replacing or exchanging air within a space. This provides a better quality of air indoors and involves the removal of moisture, smoke, odors, heat, dust, airborne bacteria, carbon dioxide, and other gases as well as temperature control and oxygen replenishment.

VAV System

VRV/VRF System

VAV system

VAV, variable air volume, systems work by varying the airflow in a building at a constant temperature, which is the opposite workings of a CAV system that varies the temperature at a constant airflow. For larger commercial buildings, whether it be a five-story office building or a shopping mall, this is a pronounced advantage as it allows better temperature control. With buildings of these sizes, individual control is a necessity and accomplished via a main VAV/airbox, zones, ductwork, and dampers. How this works is that the supply air temperature remains constant, and the airflow rate fluctuates to accommodate the loss-and-gain heating patterns of each connected zone.

VRV system

VRV is a technology that alternates the refrigerant volume in a system to match a building’s precise requirements. Only a minimum amount of energy is required for a system to maintain set temperatures, and ensure that it automatically shuts off when no occupants are detected in a room. This unique mechanism achieves more sustainability in the long run, as end users save on energy costs while reducing their system’s carbon emissions.

With up to 64 indoor units connected to 1 outdoor unit, the VRV system operates similar to a Multi-Split system. Each individual indoor unit determines the capacity it needs based on the current indoor temperature and requested temperature from the remote control (set point).

Comparative Analysis

Building energy simulation has been conducted on a reference building in Gurgaon, India. Two examples with different HVAC systems are modeled and simulated to compare the energy consumption of both the cases. EUI of each case is compared i.e Energy use intensity (kWh/m2/yr).
Building envelope values:
U-value of glass: 1.57 W/m2 K, SHGC of glass: 0.25, U-value of roof: 0.05 W/m2 K, U-value of walls: 0.3 W/m2 K

Fig. Graph showing EUI for VAV and VRV systems for reference building

Conclusion

It is observed that VRF system has less energy consumption as compared to VAV system in a cooling-dominated climate such as Gurugram mainly due to the flexibility of operation and controls. The part-time-part-space operation mode of the VRF systems allows occupants to turn on the air conditioner only when needed and occupied, resulting in much less operation time, while the full-time-full-space operation mode of the VAV systems operated with a fixed schedule, which is less flexible(VAV boxes cannot be turned off even when space does not need air-conditioning)and leads to much longer operation time.