Shedding Light on VRF Misconceptions
Dispelling False Impressions
One of the most common misconceptions about VRF systems is that they are difficult to install, commission, and service, said Karl Gorbet, service manager, Panasonic Air Conditioning Group.
Ken Brown, senior training manager, Mitsubishi Electric Cooling & Heating, agreed that it’s a fallacy that VRF systems are difficult to install. He said that they are easy to install. “Ductwork is limited or not required at all, and the two-pipe system is extremely flexible. Mitsubishi Electric VRF zoning systems require only a 3-inch opening in the exterior of a building for the refrigerant lines and wiring to run through, connecting the indoor units to the outdoor units.”
He continued, “Some contractors might think that VRF zoning systems are difficult to maintain. On the contrary, Mitsubishi Electric VRF zoning systems need only minimal maintenance due to easily accessible filters, little or no ductwork to clean, and simple wiring between the indoor and outdoor units.”
The VRF zoning systems by the company permit an indoor unit to be serviced while other indoor units within the same piping system are still in operation, and the simple controls networks provide diagnostic information, making maintenance simpler, Brown added.
Other specific misconceptions exist about VRFs. According to Don C. Fort Sr., national training manager, air conditioning division, LG Electronics Systems, one wrong idea that contractors have about VRFs is that the liquid lines do not need to be insulated. Another erroneous belief about VRFs concern indoor unit takeoffs. “Many feel that Y-branch takeoffs to indoor units can be positioned in any convenient manner or that copper Ts can be substituted for manufactured Y-branches, but this is not the case. The rules must be followed closely,” said Fort.
Another incorrect idea that some contractors have about VRFs is in regard to wiring and controls. Fort said, “Some contractors feel that any type of control wire will work on a VRF low voltage control application. These are the same contractors who have continuous problems with system communication errors.”
The Scoop on VRFs
In addition to fighting misconceptions, VRF manufacturers are also promoting what HVAC contractors should know about VRFs.
Brown said that the fact that VRFs don’t need ductwork means that they’re more flexible in terms of what types of applications they can be installed in, e.g., a historical building.
Gorbet indicated that attention to piping is important. He observed, “Contractors with refrigeration experience tend to do a better installation because overall they pay more attention to their piping. Piping (correct sizing) and leak checking are important for all HVAC but especially for VRF.”
Fort pointed out that VRFs and traditional residential or commercial HVAC systems differ in regard to “rules of thumb relative to system refrigerant charging and what is normal related to expected subcooling and superheat values. The norm for VRF would be out of sync for unitary systems. Computer software must be relied upon to determine whether a VRF system is operating within design parameters or not.”
One similarity between VRFs and conventional HVAC units more often found in the U.S., all three experts agreed, is that contractors use load calculations in equipment sizing for VRFs, just like they’d use load calculations for sizing other types of equipment. Fort added, “Manual J load calculation is acceptable.”
Brown said that in applications that require multiple indoor units, zone and whole-building loads should be factored in to the equipment sizing calculations to size the indoor units.
He pointed out, as with traditional U.S. HVAC systems, “The load calculation is not the first and only step in sizing VRF zoning systems. Outdoor ambient temperatures should always be given consideration in the sizing process. The manufacturer’s technical manuals should be checked to see if the summer and/or winter design conditions will require a temperature correction factor to be applied. Most VRF zoning system manufacturers have a design software program available (such as Mitsubishi Electric’s Design Tool) that calculates adjusted capacities of the selected equipment based on the user’s input.”
When addressing fresh air changes and IAQ for VRF systems, the requirement is the same as for traditional U.S. HVAC systems, said Fort. He explained, “Separate outside air delivery systems capable of tempering fresh air complements VRF systems nicely. Mixed air temperature limits must be respected when delivering fresh air to a VRF IDU [indoor unit] when the design calls for bringing the outside air into the IDU airstream. However, a detached system would not be tightly bound to mixed air temperature limitation.”
On the subject of fresh air, IAQ, and VRFs, Gorbet remarked on an air handler’s role. “Outside air can be introduced if the air handler is sized to handle the additional sensible and latent load. Another potential problem is the variable-speed air handlers may not be able to maintain air exchanged when they slow down. In most cases, it is better to use a dedicated system such as Aaon.”
Courses, Of Course
To promote wider knowledge and understanding of VRF technology in the U.S., manufacturers that sell this equipment offer training courses for contractors.
Brown said that his company’s introductory course gives attendees an “in-depth understanding of the technologies used in the Mitsubishi Electric VRF zoning systems.” He added, “An in-depth functional study of the system is conducted as well as thorough discussion of the theories associated with properly applying, installing, commissioning, and troubleshooting Mitsubishi Electric VRF zoning systems.” The classes include concepts and theories that are covered in the classroom as well as hands-on practice.
Fort said that due to time constraints, LG Electronics’ introductory VRF course, “Installation Essentials,” has a prerequisite: “a good working knowledge of the basic refrigeration cycle.” Some of the topics the course includes are an overview of the company’s product offering, including controls; pre-installation considerations, including tools and equipment needed; piping installation; requirements for control and supply wiring; heat recovery box installation and setup; pressure testing and evacuation; as well as preparation for commissioning (with a hands-on lab).
Gorbet listed three main areas Panasonic Air Conditioning Group covers in its introductory VRF class: 1) installation (piping, power wiring, control wiring, and clearances and condensation removal), 2) commissioning (basic explanation of switch settings and auto addressing; leak checking and vacuum; operation, temperatures, and superheats; and factory computer software to verify equipment function and performance), and 3) service (basic explanation of error codes and where/how to retrieve them).
For a deeper comprehension of VRF technology and to gain the knowledge needed to install and service and maintain this type of system, training is essential, as it is with other new HVAC technology. Contractors who want to expand their knowledge base to cover VRF will find understanding VRF technology and the equipment is essential.
Sidebar: Information for All
Panasonic Air Conditioning Group, Mitsubishi Electric, and LG Electronics all offer training courses intended for technicians and contractors on how to install and service and maintain VRF systems. The following are among the other courses offered by VRF manufacturers:
• LG Electronics Systems Air Conditioning Division offers a one-day basic refrigeration course for sales and other nontechnical employees so they can learn how any a/c system works and what each component does.
• Panasonic Air Conditioning Group holds three day-long sales/application, installation/commissioning, and service courses once a month in Kennesaw, Ga. Online training and testing is also available.
• Mitsubishi Electric Cooling and Heating has a three-day course that focuses on its zoning systems and City Multi Controls Network, which is designed for distributors so they can understand and support the design and application of the systems. The company also offers a class on the control capabilities of the VRF product line. That course is offered for start-up personnel and salespeople.
Publication date: 11/19/2012