Sponsored by COMPRESSORS
The ESEER fi gure is representative for the seasonal annual chiller performance, taking into account the diff erent climatic conditions found within EU. It allows an analysis of the chiller energy consumption, considering realistic more operating conditions.
The more recent index used in the UK is the SEER which follows the same calculation method as ESEER however can look at more localised ambient weather data which for the UK can off er lower average ambient temperatures when compared with the ESEER. Also building bespoke part load data, if known, can be used in the SEER calculation. Considering the new effi ciency measurements, chillers and compressor technology had to improve at partial load and the industry demanded higher effi ciency performing chillers which has driven compressor technology to greater effi ciency targets.
Inverter screw technology
As partial load requirements were the key to overall compressor effi ciency, inverter technology was introduced so that at low load the compressor would no longer manage capacity control just through slide valve management with a fi xed compressor speed, but the compressor speed will vary depending on the load conditions.
Reducing the compressor speed with the use of the inverter signifi cantly increases the effi ciency of the unit and reduces power input required to meet the cooling demand.
Addition of Variable Volume Ratio The inverter compressor technology has been combined with Variable Volume Ratio technology (VVR), which allows to compressor to modify its own geometry, varying the condenser pressure charge to maintain the highest compression effi ciency. This works utilising the compressor slide valve arrangement, which is usually used for capacity control in fi xed speed compressors. The controller manages the operation of the movable slide into two possible positions (A or B), thus getting the variation of the compressor volume ratio and the discharge side geometry. The eff ect of these operations is the optimisation of the compressor effi ciency depending on the chiller working conditions, so whether at full load or partial load the slide valve will work with the inverter control to maximise performance and there is no compromise.
In addition to the high full load and part load effi ciencies that the inverter compressor
provides, there are secondary benefi ts to inverter control.
Low Inrush Current - limitation of the maximum absorbed current (LRA), since the inverter driven compressor can always be started up at low speed, for this reason the inverter chiller can be employed in commercial and industrial applications in which the prevention – of electricity absorption peaks of the system is a requirement.
High displacement power factor correction (>0.95 at all loads) – reduction of the absorbed current, since the inverter maintains a constant cosphi of the compressors to which it is connected, for this reason the inverter can allow building owners to avoid power factor penalties and decreases electrical losses in cables and transformers.
Low noise levels are partial load – with the compressor speed reducing at low load operation the unit noise level can be signifi cantly reduced by up to 12dB(A), this can off er low noise night time solutions without the requirement for secondary attenuation. Inverter compressor technology is leading
the effi ciency drive in chiller technology enhancements both on air cooled and water cooled applications with increased ESEERs up to 6.0 and 9.5 respectively.
17
TZ-B from DAPUK
T
he TZ-B air cooled inverter screw chiller utilises the latest technology to provide optimised
chiller performance and the highest effi ciency in its class.
The TZ-B covers cooling capacities
from 170kW up to 1.1MW, off ering outstanding energy performance across the range, with EER values up to 3.9 and ESEER values of up to 5.8.
With extra quiet operation down to 65dB(A) at 1m at full load, along with compact footprint utilising the latest microchannel condenser coils and full design fl exibility the new TZ-B can be used for a variety of applications from precision cooling needed for data centres to commercial comfort cooling applications.
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