VRF/VRV HVAC Systems | Working principle and benefits | HVAC 11

Introduction to VRF Systems

This section provides an introduction to Variable Refrigerant Flow (VRF) systems and their working principles.

What is VRF?

• VRF, also known as Variable Refrigerant Volume (VRV), is an HVAC technology invented by Daikin Industries in 1982.

• VRF systems circulate only the minimum amount of refrigerant needed during a single heating or cooling period.

• This technology allows for individual control of multiple air conditioning zones.

Growth of VRF Systems

• In 1982, Daikin introduced VRF technology, which was later adopted by other manufacturers who marketed it as VRF due to trademark restrictions.

• By 1987, VRF systems reached Europe, and by the early 2000s, they entered the USA market.

• In Japan, by 2007, VRF systems were installed in 50% of mid-size office buildings and 33% of large commercial buildings.

• China currently accounts for 67% of the global VRF market.

Components of a Typical VRF System

• A typical VRF system consists of an outdoor unit, several indoor units, refrigerant piping with copper distributors and pipes (ref net joints), and communication wiring.

• Each indoor unit has its own wired control panel for individual control. Wireless remotes and centralized controllers are also possible.

How Does a VRF HVAC System Work?

This section explains the operation logic and power consumption regulation in a VRF system.

Operation Logic

• The operation logic in a VRF system is proprietary to each manufacturer.

• The system takes inputs from users (desired comfort temperature) and surroundings (outside ambient temperature) to implement its logic for optimal power consumption.

Example of System Operation

• Initially, the system is in a standstill condition with everything turned off.

• When a user turns on an indoor unit, the outdoor unit starts working and adjusts the compressor's output based on the requirements from all the indoors.

• The system constantly recalculates and adjusts power consumption based on demand from indoor units and prevailing conditions.

Inverter Driven Scroll Compressor

• Modern VRF systems use inverter-driven scroll compressors.

• These compressors adjust their speed to match variations in cooling or heating load.

• The capacity control range can be as low as 6% to 100%.

• Higher cooling demand increases the input frequency of the compressor, while lower demand reduces it.

Working Principle of Inverter Scroll Compressors

This section explains how inverter scroll compressors work and their relationship between speed, capacity, and voltage.

Speed and Capacity Relationship

• The relation between speed and capacity is almost linear for scroll compressors.

• Double the speed results in almost double the capacity for high cooling demand.

Voltage Supply for Different Frequencies

• To run the compressor at higher frequencies than the power supply frequency (e.g., 230 volts, 50 hertz), a higher voltage must be supplied to the motor.

• For example, supplying 415 volts at 50 hertz allows achieving maximum required cooling capacity using 90 hertz for scroll compressor speed.

Graphical Representation of Scroll Compressor Voltage, Capacity, and Speed Relationship

This section presents a graph illustrating how scroll compressor voltage relates to capacity and speeds between 30 and 90 hertz.

New Section

This section discusses the benefits of inverter technology and how it improves the efficiency and performance of HVAC systems.

Inverter Technology

• With inverter technology, a large capacity compressor operating at variable speed replaces three small compressors in a standard solution.

• In a conventional HVAC system, the compressor runs at maximum operation load until the desired temperature is reached and then turns off until cooling is required again. On the other hand, an inverter compressor continues to run but only uses the required amount of energy to maintain the desired temperature.

• The variable speed operation of an inverter compressor not only makes it more efficient but also maintains more precise temperatures. This results in fewer maintenance calls and a longer lifespan for the motor itself.

New Section

This section explains the different types of VRF (Variable Refrigerant Flow) systems - cooling only systems, heat pump systems, and heat recovery systems.

VRF System Types

• Cooling-only systems can only cool and do not provide heating.

• Heat pump systems allow heating or cooling in all indoor units but not simultaneous heating and cooling. Each indoor unit can either heat or cool but not both at the same time.

• Heat recovery systems allow heating and cooling in all indoor terminal devices simultaneously. These are the most sophisticated VRF systems where each outdoor air-cooled condenser is connected via three pipes to an indoor heat recovery unit.

New Section

This section describes how a VRF heat recovery system works by connecting outdoor condensers with indoor heat recovery units.

VRF Heat Recovery System

• In a VRF heat recovery system, each outdoor air-cooled condenser is connected via three pipes to an indoor heat recovery unit.

• The three pipes include a high-pressure gas refrigerant line for heating, a high-pressure liquid refrigerant line for cooling, and a low-pressure gas suction line for return to the outdoor unit.

• Each indoor heat recovery unit works together with the indoor terminal units and respective thermostats in each zone to determine if they require heating or cooling. In heating mode, the indoor terminal unit acts like a condenser, while in cooling mode, it acts like an evaporator.

New Section

This section introduces hybrid VRF systems that use water instead of refrigerant between the hybrid branch circuit controller and the indoor units.

Hybrid VRF Systems

• Hybrid VRF is a unique two-pipe heat recovery VRF system that replaces refrigerant with water between the hybrid branch circuit controller and the indoor units.

• The hybrid branch controller (HBC) acts as the brains of the system and is connected to the outdoor heat recovery unit via traditional refrigerant piping. It consists of heat exchangers, inverter-driven pumps, and valve blocks.

• The key difference between traditional VRF systems and hybrid VRF systems is that leak detection is not required in hybrid VRF systems as they use water instead of refrigerant in occupied spaces. This makes them compliant with F-gas regulations and eliminates risks associated with refrigerant leaks.

New Section

This section highlights some advantages of VRF systems including individual temperature control, design flexibility, and energy efficiency.

Advantages of VRF Systems

• VRF systems allow individual temperature control in each room, responding individually to fluctuations in space load conditions. The system automatically adjusts the refrigerant flow to suit the requirements of each room.

• VRF systems offer design flexibility as a single condensing unit can be connected to a wide range of indoor units with varying capacities and configurations such as ducted or ductless options. Multiple indoor units can be supplied by a single condensing unit.

• VRF systems use variable speed compressors with inverter technology, resulting in energy efficiency and potential energy savings of 30% to 40% compared to package or split systems.