What is Variable Refrigerant Flow (VRF)?

Variable Refrigerant Flow (VRF) is an HVAC technology that has been around for decades globally and is becoming more popular in the US market with ever tightening energy codes. But what is Variable Refrigerant Flow? Simply put, it is a way to efficiently distribute the cooling and heating from a single outdoor unit to multiple indoor zones while saving energy in the process.

VRF systems offer cooling and heating options for any sized space. However, due to the many system configurations available, figuring out if a VRF system is right for you can be challenging.

Here, we will walk you through the basics of VRF technology to help you make an informed decision about your HVAC needs.

What is VRF?

A VRF system (Variable Refrigerant Flow) is an air conditioning system that first became popular in Japan in the 1980s.  Unlike conventional systems that use a separate compressor system for each indoor unit, VRF allows a single compressor system to serve multiple indoor units. This allows the system to control temperatures in different parts of the building better and operate more efficiently overall.

Initially, the Japanese were looking for a more efficient way to heat and cool their factories, and they found that by using a system of multiple variable speed scroll compressors, they could achieve this goal.  Daikin released the first VRF system for use in Japan in 1982, although Daikin trademarked it as VRV (Variable Refrigerant Volume) at the time. The system quickly gained popularity due to its energy efficiency and flexibility, and it soon became available in other countries, although adoption in the United States has been rather slow in comparison to other countries.

However, VRF systems have become increasingly popular in the US in recent years, thanks to technological advances that have made them more reliable and easier to install. Today, VRF systems are used in various commercial, residential and industrial applications, from office buildings and hotels to factories, warehouses and even residences.

How Do VRF Systems Work?

In a typical VRF system, an outdoor unit contains one or more compressors that move refrigerant to the indoor units where it flows through a series of coils or heat exchangers to transfer the heating or cooling to the spaces served. The speed of the compressor(s) is controlled to only deliver the amount of refrigerant needed to meet the cumulative demands of the indoor units. As a result, the part load energy efficiency of the system is greatly enhanced with respect to a conventional on-off compressor system. 

The indoor piping distributes the refrigerant to the individual zones within the building, each of which has its own thermostat that controls the refrigerant flow to that particular unit based on the demand in the space. 

There are two main piping configurations for VRF systems:  2-pipe and 3-pipe systems. The 3-pipe system allow the indoor units to either heat or cool at any given time, regardless of what the other indoor units are doing. This also allows for energy recovery to occur, as the heat removed by the indoor units that are cooling can be transferred to the indoor units that need heating without any energy input from the compressors. As a result, a VRF system can provide heating and cooling to each zone independently, depending on the occupants’ needs, all while freely sharing the energy between zones.

Most 2-pipe systems only allow either heating or cooling to occur simultaneously on a single VRF system, however through the addition of branch circuit controllers, a 2-pipe system can also provide heating and cooling along with heat recovery, similar to a 3-pipe system. Several manufacturers have taken this approach.

Heat recovery type VRF systems are ideal for office buildings, hotels, schools, and other commercial applications where load sharing can result in significant energy savings.

Variable Refrigerant Flow System Applications

Mixed-use facilities

VRF systems are increasingly used in mixed-use facilities to provide efficient heating and cooling to diverse spaces. Mixed-use facilities are complex environments with many different types of spaces that must be kept at different temperatures. For example, retail spaces may need to be cooler than office spaces and residences can be all over the map depending on the occupant’s preferences. VRF systems make it possible to efficiently maintain different temperatures in different areas, sharing energy and saving money in the process.

Multi-story buildings

VRF systems are an energy-efficient and cost-effective alternative to traditional water based HVAC systems in multi-story buildings. They can be used for various applications, however they are particularly well-suited for use in high buildings due to their ability to “lift” the refrigerant to greater heights than is possible with conventional one-to-one refrigerant based HVAC systems.  

VRF systems use a centralized condensing unit system to serve multiple units and multiple floors. This allows for better temperature control, higher energy efficiency, and lower operating costs.  Additionally, VRF systems are smaller and less intrusive than traditional HVAC systems, making them ideal for retrofit applications or spaces where the floor-to-floor heights are tight.

Hospitality

The hospitality industry has long been an early adopter of new technologies, and VRF systems are no exception. The space savings, energy efficiency and heat recovery features of VRF make them ideally suited for hotels and resorts. VRF systems also tend to be quieter than conventional HVAC systems, which is another plus for the noise sensitive hospitality sector.

As more owners and developers look for ways to reduce energy costs and increase building efficiencies, VRF systems will likely become even more popular in the coming years.

VRF System Advantages

VRF systems offer several advantages over traditional DX split systems.

1. They offer a higher level of energy efficiency. Unlike traditional systems, which cycle on and off, a VRF system can operate continuously at part-load, resulting in a significantly higher overall operating efficiency.
2. VRF systems can be equipped with heat recovery, which allows heat extracted from one space to be used to condition other spaces in the system that are in need of heat and vice versa, increasing the overall system efficiency.
3. VRF systems are typically smaller and lighter weight than their DX counterparts, making them easier to install and transport, as well as preserving precious ceiling heights and floor space.
4. VRF systems offer a wide range of configurable options, allowing users to tailor the system to their specific needs.
5. VRF systems offer longer refrigerant piping run lengths and greater refrigerant “lift” heights.  They use a variable speed compressor to deliver the appropriate amount of refrigerant to the indoor units at any time.  This allows for longer piping lengths, as the compressor can adjust the volume of refrigerant flow, delivering the right amount of refrigerant at the appropriate pressure over greater distances.

As a result, VRF systems are more flexible and more efficient than traditional split systems and can provide greater comfort and better indoor air quality to the building occupants.  

VRF System Disadvantages

A Variable Refrigerant Flow system’s most apparent disadvantage is its higher initial cost compared to traditional split systems and many hydronic systems, like water source heat pumps (WSHP).  VRF systems have a higher initial investment cost for two primary reasons.

• Installing a VRF system is much more complicated and time-consuming than either split systems or hydronic systems. The piping systems are more complex, particularly for systems with heat recovery.  Since each indoor unit is controlled by its own zone controller and served by its small refrigerant loop, more materials and components are required for the installation, raising the initial cost.
  
• VRF systems use a much larger refrigerant volume than comparable DX or hydronic systems, driving up the initial cost of the system significantly. This increased refrigerant volume also increases the likelihood of the system violating ASHRAE 15 refrigerant volume requirements, requiring more independent VRF systems to stay within ASHRAE safety limitations.

Final thoughts

Variable Refrigerant Flow systems are widely used in the HVAC world today.  They offer many advantages over traditional systems, however they also have some limitations that need to be considered when designing a system. The initial cost of the systems is sometimes a driver that will lead to the use other system types, as is the availability of sufficient space to locate the banks of outdoor condensing units required. As with all building design decisions, it is best to hire the most qualified engineering and construction teams to ensure an outcome that meets the needs of your facility at the minimum overall ownership cost.

If you’re considering a VRF system for your next project, contact our experienced team at Schnackel Engineers to ensure it’s the right fit for your project.