Variable refrigerant flow

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Variable refrigerant flow (VRF), also known as variable refrigerant volume (VRV), is an HVAC technology invented by Daikin Industries, Ltd. in 1982. [1] Similar to ductless mini-split systems, VRFs use refrigerant as the primary cooling and heating medium, and are usually less complex than conventional chiller-based systems. This refrigerant is conditioned by one or more condensing units (which may be outdoors or indoors, water or air cooled), and is circulated within the building to multiple indoor units. [2] VRF systems, unlike conventional chiller-based systems, allow for varying degrees of cooling in more specific areas (because there are no large air handlers, only smaller indoor units), may supply hot water in a heat recovery configuration without affecting efficiency, [3] and switch to heating mode (heat pump) during winter without additional equipment, all of which may allow for reduced energy consumption. Also, air handlers and large ducts are not used which can reduce the height above a dropped ceiling as well as structural impact as VRF uses smaller penetrations for refrigerant pipes instead of ducts. [4]

Contents

Description

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 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] [5] This also results in greater control of the building's interior temperature by the building's occupants. The lower start-up power of VRF's DC inverter compressors and their inherent DC power requirements also allow VRF solar-powered heat pumps to be run using DC-providing solar panels.

VRFs come in two system formats, two pipe and three pipe systems. In a heat pump two 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, Carrier and LG whose systems are able to do this with a two pipe system using a branch circuit (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. [6] In heat recovery VRF systems, some of the indoor units may be in cooling mode while others are in heating mode, reducing energy consumption. If the coefficient of performance in cooling mode of a system is 3, and the coefficient of performance in heating mode is 4, then heat recovery performance can reach more than 7. While it is unlikely that this balance of cooling and heating demand will happen often throughout the year, energy efficiency can be greatly improved when the scenario occurs. [7]

VRF systems may be air or water cooled. If air cooled, VRF condensing units are exposed to outside air and may be outdoors, and condensing units are the size of large refrigerators, since they need to contain a large condenser (heat exchanger) which has a large surface area to transfer heat to the surrounding air, because air doesn't have a high heat capacity [8] and has a low density, volumetric thermal capacity and thermal conductivity thus needing to transfer heat into a large amount of air volume at once. If water cooled, the condensing units are placed indoors and are much smaller and cooled with water by a closed type or circuit cooling tower or dry cooler.

Japan

VRF systems have been used in Japan since the 1980s. By 2007, in Japan, VRFs are used in 50% of midsize office buildings (up to 70,000 ft2 or 6,500 m2) and 33% of large commercial buildings (more than 70,000 ft2 or 6,500 m2). [6]

Home automation integration

There are dedicated gateways that connect VRFs with home automation and building management systems (BMS) 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. [9] [10]

Primary manufacturers

Japan:

Korea:

India:

Bangladesh:

Italy:

United States:

France:

China/Other:

Related Research Articles

<span class="mw-page-title-main">Heating, ventilation, and air conditioning</span> Technology of indoor and vehicular environmental comfort

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.

<span class="mw-page-title-main">Heat pump</span> System that transfers heat from one space to another

A heat pump is a device that uses work to transfer heat from a cool space to a warm space by transferring thermal energy using a refrigeration cycle, cooling the cool space and warming the warm space. In cold weather, a heat pump can move heat from the cool outdoors to warm a house; the pump may also be designed to move heat from the house to the warmer outdoors in warm weather. As they transfer heat rather than generating heat, they are more energy-efficient than other ways of heating or cooling a home.

<span class="mw-page-title-main">Heat exchanger</span> Equipment used to transfer heat between fluids

A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. Another example is the heat sink, which is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant.

<span class="mw-page-title-main">Chiller</span> Machine that removes heat from a liquid coolant via vapor compression

A chiller is a machine that removes heat from a liquid coolant via a vapor-compression, absorption refrigeration, or absorption refrigeration cycles. This liquid can then be circulated through a heat exchanger to cool equipment, or another process stream. As a necessary by-product, refrigeration creates waste heat that must be exhausted to ambience, or for greater efficiency, recovered for heating purposes. Vapor compression chillers may use any of a number of different types of compressors. Most common today are the hermetic scroll, semi-hermetic screw, or centrifugal compressors. The condensing side of the chiller can be either air or water cooled. Even when liquid cooled, the chiller is often cooled by an induced or forced draft cooling tower. Absorption and adsorption chillers require a heat source to function.

<span class="mw-page-title-main">Heat recovery ventilation</span> Method of reusing thermal energy in a building

Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR) or energy recovery ventilation (ERV), is a ventilation system that recovers energy by operating between two air sources at different temperatures. It is used to reduce the heating and cooling demands of buildings.

<span class="mw-page-title-main">Air handler</span> Device used to regulate and circulate air as part of an HVAC system

An air handler, or air handling unit, is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, furnace or A/C elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system that distributes the conditioned air through the building and returns it to the AHU, sometimes exhausting air to the atmosphere and bringing in fresh air. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork

<span class="mw-page-title-main">Absorption refrigerator</span> Refrigerator that uses a heat source

An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling process. Solar energy, burning a fossil fuel, waste heat from factories, and district heating systems are examples of convenient heat sources that can be used. An absorption refrigerator uses two coolants: the first coolant performs evaporative cooling and then is absorbed into the second coolant; heat is needed to reset the two coolants to their initial states. Absorption refrigerators are commonly used in recreational vehicles (RVs), campers, and caravans because the heat required to power them can be provided by a propane fuel burner, by a low-voltage DC electric heater or by a mains-powered electric heater. Absorption refrigerators can also be used to air-condition buildings using the waste heat from a gas turbine or water heater in the building. Using waste heat from a gas turbine makes the turbine very efficient because it first produces electricity, then hot water, and finally, air-conditioning—trigeneration.

<span class="mw-page-title-main">Vapor-compression refrigeration</span> Refrigeration process

Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Cascade refrigeration systems may also be implemented using two compressors.

<span class="mw-page-title-main">Absorption heat pump</span> Heat pump driven by thermal energy

An absorption heat pump (AHP) is a heat pump driven by thermal energy such as combustion of natural gas, steam solar-heated water, air or geothermal-heated water differently from compression heat pumps that are driven by mechanical energy. AHPs are more complex and require larger units compared to compression heat pumps. In particular, the lower electricity demand of such heat pumps is related to the liquid pumping only. Their applications are restricted to those cases when electricity is extremely expensive or a large amount of unutilized heat at suitable temperatures is available and when the cooling or heating output has a greater value than heat input consumed. Absorption refrigerators also work on the same principle, but are not reversible and cannot serve as a heat source.

<span class="mw-page-title-main">Air source heat pump</span> Most common type of heat pump

An air source heat pump (ASHP) is a heat pump that can absorb heat from air outside a building and release it inside; it uses the same vapor-compression refrigeration process and much the same equipment as an air conditioner, but in the opposite direction. ASHPs are the most common type of heat pump and, usually being smaller, tend to be used to heat individual houses or flats rather than blocks, districts or industrial processes.

<span class="mw-page-title-main">Air conditioning</span> Cooling of air in an enclosed space

Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior environment and in some cases also strictly controlling the humidity of internal air. Air conditioning can be achieved using a mechanical 'air conditioner' or by other methods, including passive cooling and ventilative cooling. Air conditioning is a member of a family of systems and techniques that provide heating, ventilation, and air conditioning (HVAC). Heat pumps are similar in many ways to air conditioners, but use a reversing valve to allow them both to heat and to cool an enclosed space.

<span class="mw-page-title-main">Water heat recycling</span> Use of a heat exchanger to recover energy and reuse heat from drain water

Water heat recycling is the use of a heat exchanger to recover energy and reuse heat from drain water from various activities such as dish-washing, clothes washing and especially showers. The technology is used to reduce primary energy consumption for water heating.

<span class="mw-page-title-main">Fan coil unit</span> HVAC device

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<span class="mw-page-title-main">Chilled water</span> Cooling commodity

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HVAC is a major sub discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.

<span class="mw-page-title-main">Dedicated outdoor air system</span>

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Daikin Applied Americas is a corporation that designs, manufacturers and sells heating, ventilation, and air conditioning (HVAC) products, systems, parts and services for commercial buildings. Since 2006, McQuay has been a subsidiary of Daikin Industries, Ltd. McQuay world headquarters are located in Minneapolis, Minnesota, United States. Products are sold by a global network of sales representatives and distributors.

In air conditioning, an inverter compressor is a compressor that is operated with an inverter.

The Glossary of Geothermal Heating and Cooling provides definitions of many terms used within the Geothermal heat pump industry. The terms in this glossary may be used by industry professionals, for education materials, and by the general public.

References

  1. 1 2 Thornton, Brian (December 2012). Variable Refrigerant Flow Systems (PDF). General Services Administration (Report). US Federal Government. Archived from the original (PDF) on 2022-01-20. Retrieved 2013-08-06.
  2. ↑ "VRF – "Reason to choose VRF HVAC Technology" – 22-7 Website" . Retrieved 2019-09-05.
  3. ↑ "Introduction of Heat Recovery Chiller Control and Water System Design" (PDF). Retrieved 2024-01-13.
  4. ↑ Felt, Justin (2017-12-21). "The Emergence of VRF as a Viable HVAC Option". Buildings. Endeavor Business Media. Archived from the original on 2023-02-10.
  5. ↑ "Variable Refrigerant Flow".
  6. 1 2 Goetzler (April 2007). "Variable Refrigerant Flow Systems". ASHRAE Journal: 24–31.
  7. ↑ Rostamabadi, Mehrdad (2017). VRF HVAC Systems. Shafaf.
  8. ↑ GF. Hundy, A.R. Trott, T.C. Welch, Chapter 6 - Condensers and Cooling Towers, Editor(s): G.F. Hundy, A.R. Trott, T.C. Welch, Refrigeration, Air Conditioning and Heat Pumps (Fifth Edition), Butterworth-Heinemann, 2016, Pages 99-120, ISBN 9780081006474, https://doi.org/10.1016/B978-0-08-100647-4.00006-1
  9. ↑ "Cool Automation's CoolMasterNet Features IP Connectivity, Multi-Brand HVAC Support". CE Pro. Retrieved 16 November 2015.
  10. ↑ "Air Condition Repair". Tuesday, 10 August 2021
  11. ↑ "Toshiba Carrier Global | Air conditioner for residential, commercial and industrial uses". www.toshiba-carrier.co.jp.
  12. ↑ "AHI Carrier Contacts". www.ahi-toshiba.com.
  13. ↑ "Toshiba Carrier Ductless Heat Pump System - RAS-LAV/LKV | Carrier - Home Comfort". Carrier.
  14. ↑ "Toshiba Carrier Variable Refrigerant Flow Systems | Carrier Commercial Systems North America". Carrier.
  15. ↑ "VRF IFM Series". waltonbd.com. Retrieved 2023-07-19.
  16. ↑ "VRF: Bosch Enters the Market". rac. 15 January 2016.
  17. ↑ "Bosch enters VRF". Cooling Post. April 1, 2015.
  18. ↑ "VRF systems | Products |". Buderus.

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