Variable refrigerant flow (VRF) is an HVAC technology invented in Japan by Daikin company in 1982.[1] Like ductless minisplits VRFs use refrigerant as the cooling and heating medium. This refrigerant is conditioned by a single outdoor condensing unit, and is circulated within the building to multiple fan-coil units (FCUs). VRFs are typically installed with an Air conditioner inverter which adds a DC inverter to the compressor in order to support variable motor speed and thus variable refrigerant flow rather than simply perform on/off operation. By operating at varying speeds, VRF units work only at the needed rate allowing for substantial energy savings at partial-load conditions. Heat recovery VRF technology allows individual indoor units to heat or cool as required, while the compressor load benefits from the internal heat recovery. Energy savings of up to 55% are predicted over comparable unitary equipment.[1] [2] This also results in greater control of the building's interior temperature by the building's occupants.

VRFs come in two system formats, two pipe and three pipe systems. In a heat pump 2 pipe system all of the zones must either be all in cooling or all in heating. Heat Recovery (HR) systems have the ability to simultaneously heat certain zones while cooling others; this is usually done through a three pipe design, with the exception of Mitsubishi which is able to do this with a 2 pipe system using a BC controller to the individual indoor evaporator zones. In this case the heat extracted from zones requiring cooling is put to use in the zones requiring heating. This is made possible because the heating unit is functioning as a condenser, providing sub-cooled liquid back into the line that is being used for cooling. While the heat recovery system has a greater initial cost, it allows for better zoned thermal control of a building and overall greater efficiencies. VRF systems have been used in Japan since the 1980s. Currently, in Japan, VRFs are used in 50% of midsize office buildings (up to 70,000 ft2 or 6,500 m2) and 33% large commercial buildings (more than 70,000 ft2 or 6,500 m2).

Today, there are dedicated gateways that connect VRFs with Home Automation and BMS (Building Management Systems) controllers for centralized control and monitoring. In addition, such gateway solutions are capable of providing remote control operation of all HVAC indoor units over the internet incorporating a simple and friendly user interface.HOME > Eco Changes > Multi-zone HVAC system Mitsubishi Electric's cools and heats different rooms simultaneously. Eco Changes for a greener tomorrow Room temperatures differ even in the same building, according to the amount of sunlight that reaches into the room and the direction the windows face. In such offices, Mitsubishi Electric's City Multi R2-Series Variable Refrigerant Flow (VRF) System offers an ideal solution. In addition to controlling the entire building, the R2-Series simultaneously cools and heats different zones in the building. This means an optimum temperature can be set for each room according to the amount of sunlight it receives, the number of people who use the room, the number of electronic appliances that are used in the room, and other such specific conditions.

For example, you can set the system to provide cooling in machine rooms and west-facing rooms where temperatures tend to be high, and provide heating in offices that receive little sunlight or window-less conference rooms. Furthermore, the R2-Series uses just two pipes, something that no other manufacturer in the industry can do, to significantly save on pipe installations. There is no doubt the R2-Series is the perfect multi-zone HVAC system for future offices. Flexible cooling and heating settings enable HVAC operations suited to the actual status of each room, such as room temperature and purpose.gas furnace and ac unit City Multi R2-Series Two-pipe Simultaneous Cooling and Heating HVAC Systemsplit unit ac maintenance Mitsubishi Electric has developed a multi-zone HVAC system that provides simultaneous cooling and heating to satisfy customers who seek solutions to a large number of individual needs. home ac unit compressor

By connecting the required number of indoor units to an R2-Series outdoor unit, each room can be cooled or heated as desired. Moreover, through the use of the Branch Circuit (BC) Controller, which is equipped with a gas-liquid separation function and a flow dividing function, differing phases of refrigerants are circulated between indoor units with differing demands, for effective energy recovery. The industry's only two-pipe simultaneous cooling and heating system saves on materials and installation. The industry's only* two-pipe simultaneous cooling and heating system has fewer pipe connections compared to the three-pipe system, and offers greater system stability. It also uses less copper pipes and insulation, and contributes to the sustainable development of the environment. Comparison of pipe connections Rebirth of Maryland's Largest Stone Mill (1866) Giving an old mill new life. Simultaneous Heating & Cooling An overview of Eco Changes and how we're helping create a greener tomorrow.

Ah, so what exactly is this hidden flaw? "My HVAC guy put a zoned system in my house and told me it was the cat's pajamas," you may be thinking about now. Or maybe your HVAC installer described it as the bee's knees, the eel's ankle, or the elephant's instep. However they described it, there's one piece they absolutely should NOT have installed. First of all, let's be precise in our language and clear up exactly what we're talking about. The word zoning is used in more than one way in the context of heating and air conditioning systems in a house. First, larger houses are always zoned. That is, they have more than one thermostat so you can control the conditions separately in different parts of the house. If you have a two-story house, for example, you probably have at least two thermostats — one upstairs and one downstairs. The other way that the term 'zoning' is used is to describe a single duct system attached to a single HVAC system that serves multiple zones. In most homes, each thermostat is connected to its own heating and cooling system.

The home is zoned, but the HVAC system is not. In a 'zoned system,' a single heating and air conditioning system is controlled by multiple thermostats in multiple zones. "Come on, man, just tell me what the flaw is!" In the photo above, the three green lights are part of three zone dampers that control the flow of air to three separate zones. Depending on the needs of the house, any combination of 1, 2, or 3 zone dampers may be open and sending conditioned air to their respective zones. If only 1 or 2 of the zones are calling for air, most air handlers will create extra static pressure because 1 or 2 of the pathways are closed off. Enter the bypass duct, shown at right. When the system is running but not all zone dampers are open, the bypass duct—in theory—is supposed to relieve the extra pressure and maintain good air flow throughout the duct system. At the Affordable Comfort conference this year, I went to a talk on zoned duct systems where John Proctor and Rick Chitwood discussed the pros and cons of these systems.

Proctor's take is basically that zoned systems are horrible and shouldn't be used. Chitwood likes them and says when done right, they provide exceptional performance. On one point, though, they both agreed: Bypass ducts should never be used. Here are three reasons why: Throwing cold air directly into the return plenum reduces the temperature of the air coming in to be cooled. That makes the evaporator coil get colder, and the colder it gets, the less efficient it becomes. The bypass duct steals air. Even with all three zone dampers open, the bypass duct has a big pressure difference across it, and air is lazy. It'll cheat and take the path of least resistance whenever possible, in this case the bypass duct. Not only is a colder evaporator coil less efficient, it's also more likely to freeze up, as the condensation it collects eventually drops below the freezing point. (And if you think a bypass duct is bad for air flow, a frozen coil is way worse. It's really hard to push air through a solid block of ice.)