BELGIUM: Daikin has introduced a new DWDC C series water-cooled centrifugal chiller designed for use with low GWP HFO refrigerant R1234ze(E).
This new design is specifically developed to satisfy the European and Middle East markets and will be available in a wide choice of cooling capacities and component combinations. The range has been developed to optimise energy efficiency and reduce operating costs. Maximizing performance at both full- and part-loads, the new dual compressor chillers, using a single refrigerant circuit design, are also available with R134a or R513A refrigerants.
Capacities are from 2100kW (600RT) up to 9000kW (2500RT) with both R134a and R513A and 1500kW (450RT) up to 6700kW (1900RT) with R1234ze at nominal AHRI conditions.
Daikin maintains that the new series allows virtually infinite combinations of heat exchangers, gears, and semi-hermetic motors to provide the exact required capacity, minimising the need for a costly step up to a larger-size chiller package.
The dual compressor DWDC C chillers are said to offer many benefits, including outstanding part-load efficiency, and system redundancy similar to two separate chillers, with a lower total installed cost. They can be equipped with a brand new and enhanced variable speed drive.
Daikin has ensured redundancy by having two of everything connected to the evaporator and condenser – two compressors, two lubrication systems, two control systems, and two starters. If any component on a compressor system fails, it can be removed or repaired without shutting down the other compressor and provides an automatic back-up with at least 60% of the chiller design capacity available on DWDC units.
Redundancy is also built into the distributed control system, which consists of a unit controller, a compressor controller for each compressor and an operator interface touch screen. The chiller will operate normally without the touch screen being functional, says Daikin. If a compressor controller is unavailable, the other compressor will operate normally and handle as much of the load as possible.
Lower inrush current
With DWDC C dual compressor chillers, there are two smaller motors – as compared to a single compressor chiller with one larger motor – which produce the same cooling capacity. The microprocessor control logic is built in such a way that when the second compressor is to be started, the first compressor is unloaded further and the second compressor startup is initiated. This starting method reduces the total inrush current of the dual compressor chillers. Additionally, if an emergency power back-up generator is utilised, this method can reduce the size of the generator.
For chillers operating at 60% and below load for DWDC’s, Daikin has programmed the unit controls to allow only one compressor to run, which results in lower run hours.
These chillers have a single-refrigerant circuit for the evaporator and condenser with two compressors running in parallel and are available in one, two or three-pass configurations. According to Daikin, their salient feature is that at single-compressor, part load operation, the running compressor can utilise the entire chiller’s heat transfer surface, providing outstanding part load performance.
The flexible control logic of the Daikin inverter drive maps exact performance curves at every condition to minimise speed and still deliver the required cooling capacity. This allows the DWDC C chillers to take advantage of off-design conditions to save energy for comfort cooling applications with variable loads – even for data centers with a constant heavy load, says Daikin.
Heat transfer performance is said to be improved thanks to the use of heat exchangers with flood-type technology and most advanced tube type in the market.
The DWDC C chiller’s layout has been developed in order to be ready for free-cooling operation and is customisable for marine application.
In addition, Daikin says its precision-engineered gear driven design allows for lighter components, less vibration, and ability to select gear ratios that will provide the optimum impeller speed whatever the application. Daikin’s compressors also reduce the discharge area as load decreases to maintain gas velocity and greatly reduce the tendency to stall or surge.