Conventional Direct Expansion Air-Conditioners offer no modulation in response to changes in the space load conditions. Their compressor operation is simple on-off type, making it difficult to maintain desirable indoor conditions.
With Variable Refrigerant Flow (VRF) Technology, it is now possible to connect multiple Indoor Units with single Outdoor Unit. Compressor is Inverter Driven or Digital Scroll type. This compressor reduces its speed and hence electricity consumed in response to actual demand from room temperature setting or from reduced quantity of Indoor Units in operation. Both ductless and ducted Indoor Units can be connected to common refrigerant lines from Outdoor Units.
Major advantage of this type of system is its Energy Efficiency. As Air Conditioning loads for any type of building is at its peak only 1% of the time, rest of the time system is required to operate at part load conditions. A system which operates at part load conditions with proportionate Energy Savings is always a desirable one in Air Conditioning application. A VRF Outdoor which is connected to say eight Indoor Units will consume around fifty percent of its full rated energy if out of eight only four units are in operation at a particular instant.
Another added advantage is the smaller footprint of Outdoor Unit and minimum space required for Indoor Refrigerant Piping run. VRF Units can be operated in heating/ cooling or simultaneous heating and cooling mode. These systems come with sophisticated electronic controls and are easy to commission and operate.
Maintenance cost is substantially less than a comparable Chiller System. Normal maintenance includes changing filters and cleaning coils. VRF heat pumps may operate at ambient temperatures as low as -18°C, but their efficiency drops off considerably at low temperatures.
As VRF Systems use variable speed compressors with wide capacity modulation capabilities, they can maintain precise temperature control generally within ±1°F, with independent controls and set points in each zone.
This type of system is easily adaptable to changes in room layout: extra indoor unit can be added. Units with different styles and capacities can be installed according to interior design; system automatically and effectively controls each unit to provide individual comfortable working or living environment.
For buildings requiring simultaneous heating and cooling, heat recovery VRF systems can be used. These systems circulate refrigerant between zones, transferring heat from the indoor units of zones being cooled to those of zones being heated. Each manufacturer has its own proprietary design, but most use a three pipe system (liquid, suction, discharge) and special valving arrangement.