Hydronics vs. VRFBy. Kyle DelPiano
When it comes to HVAC system design, carefully assess the options.
Some considerations when evaluating hydronics versus VRF
Concerns about the safety and viability of Variable Refrigerant Flow (VRF) in commercial building HVAC systems have persisted since the technology was introduced in the United States nearly 20 years ago. The most notable indictment against VRF systems to date is the Department of Defense (DOD) guidelines that ban or strongly discourage the use of VRF in military facilities.
Among the factors cited by the DOD in comparison of VRF and traditional HVAC systems: safety and operational considerations of running refrigerant lines through occupied spaces; system complexity and proprietary controls that can introduce operational, maintenance and cybersecurity challenges; and difficulty developing life-cycle costs analysis.
These and other considerations are relevant to building owners, architects, design engineers and others involved in commercial building HVAC system design, installation, operation and maintenance. As the industry continues its shift to sustainable building practices to maxi- mize building performance while minimizing environmental impact, the type of HVAC system is important in realizing energy-efficiency targets.
Hydronic systems and VRF systems are two heating and cooling methods often compared in terms of energy consumption and system performance. Hydronic systems provide water-based heating and cooling through pipes, ductwork and other components such as pumps, drives, controls, heat exchangers and valves. VRF systems use refrigerant as their cooling/heating medium, comprised of a main compressor unit connected through refrigerant lines to multiple indoor cassette units that can be individually controlled. When evaluating HVAC systems, factors such as safety and compliance, and costs related to serviceability and life cycle must be considered.
Safety and compliance
Since the 1970s, the U.S. Environ- mental Protection Agency (EPA) has issued major changes in regulations restricting and banning the use of cer- tain types of refrigerants. In 2016, the EPA revised the Section 608 rules of the Clean Air Act, which govern the handling, use and sale of refrigerants. Most notable is the regulation banning the use of hydrofluorocarbons such as R-410A in new chillers, rooftop units and VRF systems beginning in 2024. Under the updated rules, the EPA expanded the refrigerant management program, extending
the regulations to non-ozone- depleting substitutes such as hydrofluorocarbons. This action
lowers the allowable leak rate for comfort cooling and refrigeration appliances. It also incorporates industry best practices, such as verifying repairs and conducting annual leak inspections for systems that have lost a small amount of their refrigerant charge. While it’s possible for leaks to develop in both hydronic and VRF systems, a leak in a VRF system can be life-threat- ening. Refrigerant leaks can’t be detect- ed by sight or smell, making them hard to find and repair. In spaces with mini- mal ventilation, large concentrations of refrigerant gas in the air can put people at risk of asphyxiation.
The International Association of Plumbing and Mechanical Officials (IAPMO), along with ASHRAE, the international oversight organization for the HVAC industry, has set standards to ensure these systems are installed correctly. Hydronic systems with cooling units also use refrigerant, but the average system uses 66 to 75 percent less than a VRF system of the same size, according to the Hydronics Industry Alliance. Hydronic systems are not exempt from the ASHRAE and IAPMO codes, how- ever, the refrigerant is typically contained within a mechanical room, which, by code, is required to have the proper ventilation to manage a potential leak.
Cost and serviceability
In a March 2017 bulletin, the U.S. Army Corps of Engineers indicated that Air Force facilities will no longer permit VRF systems; while the Army will allow VRF systems, they will be strongly discouraged; and the Navy is not restricting VRF as long as systems comply with ASHRAE 15. In addition to safety concerns over refrigerants and serviceability of long refrigerant runs, the bulletin cited the proprietary nature of VRF systems go against established guidelines for HVAC systems.
Proprietary VRF systems require specialized technicians for installation and maintenance – which can drive up costs – compared to hydronic water systems designed with universal components that can be installed and serviced by any HVAC service technician. The initial cost of a hydronic system is generally lower, and systems offer a much wider range of flexibility for components, operation and maintenance, both in terms of parts and service.
Components in a hydronic system are factory made and tested, reducing failure rates after installation. Since VRF piping requires brazing and soldering on-site, the quality of the installation de- pends on the installer’s level of expertise. Installers also must be qualified to work with refrigerants under extremely high pressure and be knowledgeable about leak detection and ventilation requirements per ASHRAE 15. Additionally, each VRF manufacturer has a different protocol, further reducing the pool of qualified technicians for installation and maintenance.
VRF systems generally have a shorter life expectancy than hydronic systems. Hydronic systems often last 20 to 25 years, while VRF systems could need replacing 10 to 15 years after installation. The compressor in a VRF system is forced to work harder during heating cycles, reducing the life of the bearings and the compressor.
When specifying a system, it’s important to consider not only building size, but also the size of the HVAC system itself. Hydronic systems are better suited to handle buildings requiring 50 to 100 tons of cooling capacity or more. Hydronic systems also have the capacity to pump water efficiently over very long distances, such as a college campus or a high-rise office tower.
In contrast, system efficiency in VRF goes down based on the length of refrigerant pipe runs. Typically, refrigerant charge in a VRF system is 4 to 6 lbs of refrigerant per ton of cooling. To adhere to ASHRAE 15 requirements, the VRF system may need to be broken down into smaller refrigerant circuits, thus compromising the benefits of diverting loads.
VRF systems are generally limited to buildings fewer than 10 stories because the length of piping runs must be limited in order to carry refrigerants and oil through the building in accordance with manufacturer guidelines. Long lengths of piping can jeopardize performance of the unit if oil or refrigerant accumulates in the piping or migrates back to the unit.
As rising energy costs and a movement toward sustainability continue to drive changes in the commercial HVAC market, the technology and components of HVAC systems are constantly being re-evaluated. Those who influence system selections must be diligent in their analysis to ensure systems are code compliant, energy efficient and adaptable to future energy sources.
Kyle DelPiano is the Business Development Manager – CBS market for Xylem AWS. He holds a bachelor of science degree in polymer and fiber engineering from Auburn University. He has nearly 10 years of experience in the HVAC industry in a variety of sales and training roles. In addition, he is an active HIA-C and ASHRAE chapter member and is LEED AP certified.