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Feature
A PLACE FOR VRF TECHNOLOGY
By Eamonn Ryan
VRF refers to a variable refrigerant flow air-conditioning system consisting of outdoor units connected with refrigerant piping to numerous indoor units .
VRF system provides precise capacity control in order
A to meet each zone ’ s demand . The control of the correct refrigerant amount and refrigerant temperature ensure the system operates at the optimum capacity for user comfort and energy saving .
Beswent Bester , Toshiba specifying engineer & head of Technical at AHI Carriers explains how it works : “ Each indoor unit has an array of thermistors for monitoring the refrigerant temperature and return air temperature . A modulating expansion device is also fitted to each indoor unit for modulating the flow and temperature of the refrigerant . The information accumulated from each indoor unit provides the outdoor unit with sufficient information in order to optimise the refrigerant flow and refrigerant temperature , satisfying the demand and efficiency requirements of the total building .
AHI Carriers
“ Not only can the outdoor unit provide capacity control , but the indoor units can also control capacity by implementing variable evaporating or condensing temperature control , avoiding frequent on / off switching of the indoor units and maintaining a more precise space temperature .
“ The outdoor units incorporate variable heat exchangers , such as a main HEX and sub HEX , which allows the outdoor unit to control the flow of refrigerant through the heat exchangers , to best match the local ambient condition and indoor demand . A VRF system relies heavily on the inverter technology incorporated in the equipment for compressor speed control , and fan motor speed control on both the indoor units and outdoor units . Older VRF equipment incorporated a fixed speed compressor and an inverter compressor . However , more and more suppliers moved to all inverter compressors .”
There are two main types of VRF systems :
• Heat Pump systems , which are also referred to as two-pipe systems .
• Heat Recovery systems , which are also referred to as threepipe systems .
Multiple VRF heat recovery systems with a central control . Multiple Light Commercial cassettes units , high wall units and ducted units which are also connected to the central controller .
AHI Carriers
Bester explains two VRF sub-categories :
• Mini VRF , which could be heat pump or heat recovery , and these systems normally cover a capacity range from 8kW to 35kW . These smaller capacities are generally used for light commercial and residential applications but are not limited to these applications .
• Air to water VRF is also an option and utilises a cooling tower and water flow for heat exchange on the outdoor unit . This type of system has a lower demand worldwide and not all suppliers can offer this option .
Numerous Teraco projects ranging from pre-treating fresh air to humidity control hybrid units . These projects utilised Light Commercial outdoor units and VRF outdoor units connected to custom built AHUs .
He describes the benefits as they apply to four different categories :
• The building owner
• End user / employees
• Operator
• Installers / maintenance contractors
“ From a building owner ’ s perspective there is an initial customer saving compared to a chiller plant , with architectural flexibility relating to the partitioning inside which can change at any stage
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RACA Journal I June 2023 www . refrigerationandaircon . co . za