Vrf System Advantages And Disadvantages Pdf


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This paper reviews the attributes of an emerging space conditioning technology; variable refrigerant flow VRF systems.

Variable refrigerant flow VRF systems are gaining in popularity and are used as an enhanced version of multi-split systems, featuring simultaneous heating and cooling as well as heat-recovery capabilities. Modern VRF systems provide some major advantages, such as zoning, individual temperature control, minimized ductwork, excluding the need for secondary fluids chilled-water or hot-water distribution , and associated costs. This all-electric technology consists of a single outdoor condensing unit, multiple indoor units serving various zones, refrigerant piping with branch selectors, and associated controls. VRF systems use RA refrigerant as the heat-transfer fluid and the working fluid, achieving a very high energy efficiency ratio EER of 15 to 20 and integrated energy efficiency ratio IEER of 17 to In recent years, gas heat pump technology has been increasingly used in certain applications where natural gas utilities offer incentives.

Back to basics: VRF systems

Variable refrigerant flow VRF systems are gaining in popularity and are used as an enhanced version of multi-split systems, featuring simultaneous heating and cooling as well as heat-recovery capabilities. Modern VRF systems provide some major advantages, such as zoning, individual temperature control, minimized ductwork, excluding the need for secondary fluids chilled-water or hot-water distribution , and associated costs.

This all-electric technology consists of a single outdoor condensing unit, multiple indoor units serving various zones, refrigerant piping with branch selectors, and associated controls.

VRF systems use RA refrigerant as the heat-transfer fluid and the working fluid, achieving a very high energy efficiency ratio EER of 15 to 20 and integrated energy efficiency ratio IEER of 17 to In recent years, gas heat pump technology has been increasingly used in certain applications where natural gas utilities offer incentives.

As a result, VRF systems can contribute a great number of points toward U. VRF systems are nontraditional HVAC systems, in comparison with conventional ducted systems circulating the air or chilled-water throughout the building. The term VRF indicates the ability of the system to vary and control the refrigerant flow through multiple evaporator coils to provide individual temperature control in various mechanical comfort zones.

Using direct expansion DX as part of the basic refrigeration cycle, VRF systems transfer the heat from the room directly to evaporator coils located within the conditioned space. The heat-transfer media, in this case, is the refrigerant, which delivers heating and cooling to various zones with less energy as compared with air or water.

VRF systems act as multi-split systems, connecting multiple indoor units with one centralized outdoor condensing unit assembly, providing simultaneous heating and cooling and heat recovery in various zones as follows:. Air-cooled , where multiple compressors are connected to a refrigerant-piping loop. Water-cooled , where multiple compressors are connected to a water-source loop, allowing the heat recovery between compressor units.

Various manufacturers have developed refrigerant-piping loop systems for different applications, such as:. Two-pipe systems , which are normally used in VRF heat pump applications to provide cooling or heating only during the same operating mode see Figure 2.

Branch-circuit controllers are used with two-pipe systems to perform the following functions:. Three-pipe systems , which are configured with a heating pipe, a cooling pipe, and a return pipe see Figure 3. Branch selectors are used with three-pipe systems to perform the same functions as two-pipe systems with the exception of separators. The VRF system is best suited for applications with simultaneous needs for cooling and heating during the same mode of operation.

Branch selectors are used as control devices directing the liquid refrigerant or gas refrigerant to particular zones requiring cooling or heating. In heat-recovery systems, the branch-circuit controller can take the heat recovered from the cooling zone and use it to warm up the room in heating mode. This way, the compressor cooling or heating requirements are reduced, which saves energy. Dedicated outside air units with energy recovery are used to provide ducted ventilation air directly to the space or indoor unit.

VRF systems require much less ceiling space than conventional systems because only the refrigerant piping and ducted outside ventilation air are accommodated.

Heat pump systems are used in restaurants, lobby areas, clubhouses, or religious facilities where there is a defined cooling or heating mode of operation. All indoor units will operate in either cooling or heating mode nonsimultaneous. Heat pump systems with heat recovery are used in historical buildings, schools, office buildings, assisted living facilities, hotels, banks, and other commercial buildings where simultaneous cooling and heating is a design requirement.

This addresses refrigerant capacities and possible leakage, especially if the system serves small rooms, which could cause oxygen depletion. VRF systems use refrigerant RA. As overall capacity is reduced, the system EER is increased significantly see Figure 5.

Learning objectives: Summarize the different types of variable refrigerant flow VRF systems available. Explain the pros and cons of using VRF systems in a commercial building application.

Identify the codes and standards that dictate the design and use of VRF systems. VRF system operation VRF systems are nontraditional HVAC systems, in comparison with conventional ducted systems circulating the air or chilled-water throughout the building. VRF systems act as multi-split systems, connecting multiple indoor units with one centralized outdoor condensing unit assembly, providing simultaneous heating and cooling and heat recovery in various zones as follows: The VRF heat pump system provides heating and cooling for all indoor units at a specific time see Figure 1 The VRF system provides nonsimultaneous cooling and heating at any time Heat-recovery systems provide simultaneous cooling and heating as well as heat recovery, transferring the energy from cooling zones to heating zones of the building.

All of the above features are accomplished by VRF-enhanced technology using: Variable-speed and capacity-modulated inverter duty compressors Outdoor fans with variable frequency drives motors Indoor units with electronically commutated motors ECM.

System types There are two different types of VRF systems: Air-cooled , where multiple compressors are connected to a refrigerant-piping loop. Various manufacturers have developed refrigerant-piping loop systems for different applications, such as: Two-pipe systems , which are normally used in VRF heat pump applications to provide cooling or heating only during the same operating mode see Figure 2.

Branch-circuit controllers are used with two-pipe systems to perform the following functions: Separate refrigerant into gas and liquid Ensure that zones in heating mode receive superheated gas Ensure that zones in cooling mode receive subcooled liquid Facilitate removal of heat from one zone and apply it to a different zone. Branch selectors perform a similar function as branch-circuit controllers, directing the superheated gas to heating zones and subcooled liquid to cooling zones.

Outside air ventilation Dedicated outside air units with energy recovery are used to provide ducted ventilation air directly to the space or indoor unit. VRF system applications Heat pump systems are used in restaurants, lobby areas, clubhouses, or religious facilities where there is a defined cooling or heating mode of operation. The disadvantages of VRF systems include: The need for a dedicated ventilation system to deliver the outside air to various zones Long refrigerant lines and a large number of branch connections could result in refrigerant leakage The need for condensate drain lines for each VRF indoor unit Use of supplemental heat may be required for a quick warm-up Compliance with maximum allowable refrigerant quantities within a given volume.

Variable refrigerant flow (VRF)

The answer can depend on many variables, including the building application, architecture and age, to name a few. The answer is important because it will determine how air conditioning and heat will simultaneously run throughout your building. So, where do you start? VRF technology is known for its ability to simultaneously heat and cool a space. A three-pipe system does just that, but the phase separation occurs in the outdoor unit — the traditional VRF system layout. These systems require three pipes to allow simultaneous distribution of hot gas and liquid refrigerant to multiple branch controllers.

Variable refrigerant flow VRF system installations are increasing as the heating and cooling source in hotels, schools, and multifamily residential buildings. The VRF industry is expected to grow by Unlike traditional central air conditioners, variable refrigerant flow systems do not rely on ductwork to carry conditioned air throughout a building. VRF units are considered to be enhanced versions of multi-split systems, including those that use heat pumps. A refrigerant, usually RA, is the working, heat-transfer fluid. The compressor heats or cools the refrigerant, which is then sent into the building to condition the air. A variable speed drive controls the compressor, allowing it to regulate and vary the flow of refrigerant through the multiple evaporator coils.


With a higher efficiency and increased controllability, the VRF system can help achieve a Refrigerant flow control is the key to many advantages as well as the The shortcomings of TXV are offset by the modern electronic expansion valve.


What Is Variable Refrigerant Flow?

Variable Refrigerant Flow VRF technology has been commonly used throughout the world for the past three decades, particularly in Asia and Europe. Increased energy efficiency, flexibility and the potential to offer a quick return on investment have been some of the key drivers for its new-found popularity in the United States since the turn of the century. In a VRF system, there generally is one outdoor condensing unit that connects with multiple indoor evaporating units. This refrigerant flow is adjusted through a pulse modulating valve PMV , which provides individualized comfort control to room occupants.

Welcome to the Energy Efficiency Program Library

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Is two- or three-pipe VRF system right for you?

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