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VRF air-conditioning systems owe their growing popularity to their ability to meet a wide range of requirements, as Tony Nielsen explains. The primary function of all air-conditioning systems is to provide thermal comfort for building occupants. There is a wide range of system types available, staring with the basic window-fitted unit through to the very latest VRF (variable refrigerant flow) equipment. Deciding which system best suits the application will depend on several variables. For example, in a modern, design-conscious office the aesthetic requirements of the client may prove of greater importance than the number of control options they provide. While a client looking for the best life-cycle cost will need to balance capital cost with long-term operating costs, efficiency and predicted VRF systems provide cooling and heating using refrigerant (R407C or R410A) as the working fluid. There are two basic types of VRF system — cooling/heating-only and energy-recovery. Cooling/h

The inverter tag found on some air conditioners signifies the ability of the unit to continuously regulate its thermal power flow by altering the speed of the compressor in response to cooling demand. Traditional reverse-cycle air-conditioners use a heat pump that is either working at maximum capability or switched off, as the compressor's speed cannot be varied. In order to regulate temperature a thermistor is used to measure the ambient air temperature and switch the compressor on when the ambient air temperature is too far from the desired temperature Air-conditioners bearing the inverter tag use a variable-frequency drive to control the speed of the motor and thus the compressor. The variable-frequency drive uses a rectifier to convert the incoming AC current to DC and then uses pulse-width modulation of the DC current within an inverter to produce AC current of a desired frequency. The AC current is used to drive a brushless motor or an induction motor. As the speed of a b

Introduction Heating, ventilating, and air-conditioning (HVAC systems) account for 39% of the energy used in commercial buildings in the United States. Consequently, almost any business or government agency has the potential to realize significant savings by improving its control of HVAC operations and improving the efficiency of the system it uses. The use of high performance HVAC equipment can result in considerable energy, emissions, and cost savings (10%-40%). Whole building design coupled with an "extended comfort zone" can produce much greater savings (40%-70%). Extended comfort includes employing concepts such as providing warmer, but drier air using desiccant dehumidification in summer, or cooler air with warmer windows and warmer walls in winter. In addition, high-performance HVAC can provide increased user thermal comfort, and contribute to improved indoor environmental quality (IEQ). Given the range and complexity of the subject, this information should be vie