Techno-Smart Heating and Cooling Solutions
If you’re a building owner, you’ve no doubt started to research the new variable refrigerant flow (VRF) technology for heating and cooling solutions—if you haven’t already installed it. Sometimes called “ductless HVAC,” VRF has emerged over the past decade with large-scale implementation throughout Asia and Europe because of its precise thermal control, absence of ductwork, smaller footprints for central systems, and fewer unsightly HVAC units, coupled with improved efficiencies. These advantages have propelled the technology into the United States, but many developers and owners still have questions.
Why is VRF on the rise?
In general, the flexibility of VRF systems supports broad application of the technology in most markets. Well-informed owners understand that while the VRF system itself may cost more than traditional solutions, it can still reduce overall first-costs due to smaller footprints for HVAC systems. That, in turn, offers the potential to convert that square footage into leasable or programmable space. Energy-use expectations of building developers and owners continue to rise, and project teams are pushing for creative solutions in both new construction and adaptive-reuse to minimize first cost, increase efficiency, and maintain superior thermal comfort. Engineers and owners are realizing that this technology can provide a wide range of benefits for solving complex problems in building design.
Who should use it?
A broad range of market types using VRF in the U.S. includes high-rise office, multi-family residential, hotels, schools, and more. VRF is also an excellent solution in historic building renovations due to smaller equipment requirements that fit into older designs with little room to accommodate bulky systems and ductwork. VRF may not be a good fit for buildings in colder climates due to capacity issues when the outside air temperature is low. In this situation, a heated mechanical penthouse space or an over-sized system would be needed to compensate for that load. And in building types with more complex mechanical needs such as labs or hospitals, other load-intensive specialized systems make more sense.
How does VRF work?
At the heart of VRF’s efficiency lies a direct expansion (DX) heat transfer. DX systems rely on refrigerant as the primary means of heat transfer. In the case of VRF, refrigerant pumps through a building to smaller terminal units, using valves and controls to mete out specified amounts of refrigerant. Those terminal units ensure the exact amount of heat, or coolant, serves each zone via small circulating fans and thermostat controls to modulate precisely the amount of heating or cooling a space receives. Terminal units may be networked to branch-selector boxes, which, in certain VRF systems, send either heating or cooling to the different thermal zones of the building. All of these components form a network, via refrigeration piping, to a central condenser unit system. These units house the compressors, condenser unit fans, and central controls that are the heart of the VRF system.
What are the options?
VRF systems come in both two-pipe and three-pipe configurations, with heat recovery. The two-pipe system can be set in heating or cooling mode, but not both at the same time. The technology is ideal for buildings with similar solar exposures such as condominiums or hotel facilities, and schools with loaded corridors and a similar floor plate throughout the building.
Alternatively, three-pipe systems offer more flexibility at a higher cost, as they simultaneously deliver heating and cooling to different thermal zones of the building, in addition to the efficiencies of heat recovery. For example, during the cooler months, recovered heat, rejected from the core of the interior can heat the colder, exposed exterior space. This allows energy to be moved around the building instead of being wasted, resulting in much higher overall system efficiencies.
These VRF configurations give design teams options for implementing the technology in different applications. Two-pipe systems and three-pipe systems both have nuances associated with applying the technology, and it is imperative that the design engineer achieve a balance between cost and efficiency.
What are the potential challenges with VRF technology?
VRF systems are considered one of the most flexible and efficient technologies to provide precise thermal control and increase operational efficiencies. However, like any emerging technology, there are some hurdles to overcome to best manage the learning curve for design engineers, contractors, owners, and facility operators. While it is important for the design team to select quality HVAC system options, it’s equally important to find the right group of experienced contractors to install the system, to engage owners who understand the system, and to invest time in training facility managers in the new technology. This is crucial to avoiding poor installation and maintenance of the system.
VRF is changing the way we stay comfortable inside our buildings. Researching the options, managing expectations, and right-sizing solutions will ensure successful projects bound to save money and energy in the long-term life-cycle of a building.