by Diana Bjornskov

This article presents a market view for variable refrigerant flow (VRF) HVAC systems: how they work, how to commission them, and why they are on the rise today in new buildings and major renovations to help accomplish pandemic remedy, climate-focused goals, and energy efficiency improvements.

Here's an overview of the how and why, functional performance testing and commissioning for new and existing building systems, a look toward future opportunities for VRF systems application, followed by resources on VRF systems and technology.

How and Why Does VRF Work?
Most of us think of "flow" as a substance or process that is constant and continuous. In the case of HVAC building systems, varying the flow — whether air, water, refrigerant or electrons — can facilitate a building owner's requirements for meeting occupant health and comfort, efficiency, savings, and performance targets.

Since its invention in Japan 40 years ago, VRF technology has shown to be extremely efficient. It can either heat or cool (heat pump system), or simultaneously heat and cool (heat recovery system) where heat is extracted from an area that needs cooling to heat another area. In that scenario, refrigerant from the heating units is transferred to cooling units and vice versa.

VRF systems typically consist of multiple indoor air handling units, a [usually] outdoor inverter compressor, and low-temperature and high-temperature gas and pressure lines. VRF systems can be designed as ductless or as ducted, in which case air can be sent directly to the zonal handing units.

According to a report by Pacific Northwest National Laboratory (PNNL), VRF systems include advanced controls integrated with the units. These controls include self-diagnostics and monitoring points. In certain cases, VRFs can operate without a separate building automation system. However, they also can communicate with other building systems via non-proprietary BAS communication protocols.

Why is VRF gaining more traction now?
VRF was not introduced in the U.S. until the early 2000s. It has recently gained more attention among building project designers, owners and managers attracted to the technology's energy efficiency, installation flexibility, and temperature control capabilities, according to Joe Cefaly, Senior Manager of Applications with Mitsubishi Electric Trane HVAC US.

Drivers for the acceptance of VRF systems are evident in today's economy. Recent market conditions such as increased emphasis on zonal air conditioning and healthy ventilation, energy efficiency, climate change legislation and codes have caused VRF systems to become more widely recognized and applied than ever before.

Among the numerous reasons to incorporate VRF systems in new or retrofit project:

  1. Cleaner Ventilation. VRF supports the pandemic-related focus on healthy HVAC systems. VRF systems are designed to support customized air flow control in multiple, diverse building zones, with more energy efficiency and better occupant control of comfort.
  2. Energy Efficiency. VRFs generally incorporate a DC inverter on the compressor that supports variable motor speeds, allowing VRFs to operate only at the speed necessary to meet demand, permitting significant energy and cost savings when serving partial load conditions. VRF systems are popular options because they deliver variable capacity for the amount of conditioning needed to fulfill zonal demand.
  3. Performance Management. Monitoring of BAS/HVAC data allows for ongoing analytics that correlate building occupancy with systems performance standards set by facility management. Antonio Bouza, Technology Systems Optimization Manager of DOE's Building Technologies Office, points out that VRFs require different maintenance than standard RTUs, but once the staff is trained, maintenance is not more difficult, just different.
  4. Design of Building Space. The equipment takes up a small amount of interior space within each assigned zone, and can be physically configured so as not to intrude upon room design.
  5. Regulatory Requirements, e.g., Building Electrification and Embodied Carbon Standards for new construction; Building Performance Standards for existing buildings; federal, state and local mandates for benchmarking and proving efforts to reduce energy use and carbon emissions.
  6. Sustainability Commitments. Government and corporate voluntary commitments to sustainability in the built environment focus on lower carbon outcomes and reducing environmental impacts. Of (currently) 217 companies, including major players Amazon, JetBlue, Unilever and Microsoft that have joined The Climate Pledge to strive for net zero by 2040, many are building-related firms.
  7. Cost of VRF Systems. The potentially higher initial cost of implementing VRF systems can be offset by a lower cost of operation. In addition, the social and financial benefit to owners of improved air quality will likely override the cost of installation.

What's Different About Commissioning VRF Systems
Commissioning VRF systems follows the same logic path as the commissioning process for new construction or existing buildings, beginning with the OPR/BOD or CFR review and ending with facility turnover or ongoing commissioning post-occupancy.

The CxP will need to understand as much about the facility interior as the VRF system design. Recognizing certain potential piping problems in design that can lead to system failure, and avoiding conditions like draft areas and poor airflow, are uniquely specific with VRF. The CxP needs to have experience – both system-wide and by zone — and a commissioning plan starting with the basis of design and design review, and performing the complex functional testing during construction to integrate systems properly and avert operational problems.

An in-depth 1-hour live-recorded webinar, Commissioning of VRF/VRV and DOAS Systems, is currently available on the BCxA website for members and the public. The presentation by VRF expert Harry B. Koons III, LEED AP, CxA of Precis Commissioning, Inc., includes advantages and disadvantages of VRF, startup and controls integration, common performance issues, and Cx tasks by phase from predesign through delivery.

The chart below shows the steps that are included in new construction VRF commissioning.

Courtesy Harry B. Koons III, LEED AP, CxA, Precis Commissioning, Inc.

Market Opportunity Perspective
The Global Split Air Conditioning System Market, with VRF in the lead, is estimated at US$27.64 billion for 2021 and is expected to reach US$39.68 billion by 2026. Worldwide, all-electric heat pumps are the most popular technology for decarbonizing heating and cooling. VRF heat pumps and heat-recovery systems contribute to lower carbon footprints and benefit strategic electrification by reducing overall costs for commercial building owners, consumers and society.

A 2022 market research report examined the global status and development of the split air conditioning market, segmented by equipment type, market sector, geography, and other factors. The report explores recent significant developments by more than 20 leading players in this market, including Carrier, Daikin, Johnson Controls, Lennox, Mitsubishi, Sharp, Siemens, Toshiba, and others. Findings report that among equipment types, the VRF segment is expected to grow at the highest CAGR in the commercial market sector, with North America leading the market globally.

VRF systems are most effective and efficient for buildings with multiple floors, rooms, or zones, such as offices, healthcare and managed care facilities, hotels, schools, multifamily buildings, indoor agriculture and others; not every room in these facilities requires constant heating and cooling— especially now, when there are frequently unoccupied or variably-occupied building spaces.

VRF can contribute to the decarbonization of existing buildings. According to PNNL, "VRF is well suited to retrofit applications in older buildings because it can be added onto or replace existing equipment in limited space, where there is currently limited or no ductwork…"

The Future of VRF
The biggest HVAC technology change in the near future will relate to refrigerant, says CJ Corbet of Fujitsu General America. With technology advances, concerns about ozone depletion and global warming potential come into play. Refrigerants that can minimize the impact on the environment are becoming preferred alternatives to older versions.

VRF systems allow for on-demand comfort heating and cooling while providing the necessary airflow and air changes as prescribed in current industry standards. When used in conjunction with air-quality devices, such as mechanical and UV filtration and ionization, questions of health-related concerns can be alleviated.

With workplaces changing to adapt to fewer in-building employees and occupants, installed VRF systems can vary their speed to account for the heating and cooling demand of a varying occupancy. As companies start to bring people back into their buildings, a VRF system can adapt to anything from the minimum to maximum occupant levels.

Codes and Guidelines
In part due to the current pandemic, ASHRAE has produced an addendum to Guideline 41 Design, Installation and Commissioning of Variable Refrigerant Flow (VRF) Systems, approved on June 14, 2021. The addendum provides new, more specific requirements and accurate language on the energy modeling and commissioning of VRF systems.

Refrigerant system safety requirements for VRF design are available for manufacturers, design engineers, commissioning providers, facility managers and operators who need to stay current with new air conditioning and refrigerating requirements ASHRAE Standard 15 (packaged with Standard 34): Safety Standard for Refrigerant Systems and Designation and Classification of Refrigerants.  The most recent versions of these two standards were published in 2019, and precede the Covid-19 pandemic.

Ten Great VRF Resources

  1. Commissioning of VRF/VRV and DOAS Systems: 1-hour live-recorded webinar currently available on the BCxA website for members and the public.
  2. Variable Refrigerant Flow (VRF) Market Strategies Report: Northeast Energy Efficiency Partnerships (NEEP).
  3. Understanding Your Variable Refrigerant Flow (VRF) Options. Part 1, FacilitiesNet, 2022.
  4. How To Improve the Energy Efficiency of a VRF System, Part 2, FacilitiesNet, 2022.
  5. 6 Best Practices for VRF Systems, Part 3, FacilitiesNet, 2022.
  6. Control of VRF Systems, Automated Buildings.
  7. Global Split Air Conditioning System Market: Market survey and forecast, estimated at US$27.64 billion for 2021 and expected to reach US$39.68 billion by 2026, shows VRF in the lead.
  8. Variable Refrigerant Flow Systems: Report prepared for the U.S. GSA by Pacific Northwest National Laboratory.
  9. Comparative analysis of the VRF system and conventional HVAC systems, focused on life-cycle cost: Georgia Tech.
  10. EPA's HFC Phasedown: How Regulatory Heat is Advancing the Coolant Industry.

And, within this context, there is the future of how VRF systems will align with phasing down refrigerants … but that's another BCxA story!