CPD Programme
Turbocompressor vs screw compressor in air cooled chillers application (ESEER Comparison)
10 9 8 7 6 5 4 3 2 1 0
x
TMA with New Evap System
TMA with EC Fans
TMA with AC Fans
Screw Compressor
air cooled chiller with evaporative cooling and a typical air cooled screw chiller. Data from a 500kW air cooled centrifugal chiller with evaporative cooling indicate a 26kW saving in power consumption compared to the same chiller without the evaporative cooling, and a saving of 52kW over a screw compressor chiller. There is a requirement for between 360 and 490 l/h of make up water for the evaporative cooling system. The overall annual running cost for the enhanced chiller is £16,000, a reduction of £3,200 over the non enhanced centrifugal chiller and a reduction of £10,600 over a screw compressor chiller.
25 50 Part Load % Figure 3: Efficiency comparison between turbo and screw compressor
Turbocompressor vs screw compressor in air cooled chillers application (Energy cost/year)
40,000,0 30,000,0
TMA with New Evap System TMA with EC fans TMA with AC fans Screw Compressor
75 100
Application to data centre air conditioning Data centres are an application of building services where it is being proposed that the whole project be built from pre- manufactured, pre-assembled components (in fact, not just the services, but the complete building). Known as ITPACs (IT pre-assembled components) the modules are not containers in the traditional sense, but are pre-configured, manufactured components, pre-assembled and delivered to any site around the world. As part of this scheme, modular cooling plant in 300kW packages is being developed and produced. The air cooled chiller section can include
20,000,0 10,000,0 0,0 Cost/Year Part load % Figure 4: Annual energy cost comparison
true. The more humid, and hence the higher the wet bulb temperature of, the ambient air, the less dry bulb reduction will occur. • Cassette contact factor: Looking at the psychrometric chart, if the saturation were 100%, the air entering the condenser coil would have a dry bulb temperature equal to the wet bulb temperature. In reality the efficiency, or contact factor
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will be 85% to 90% so the dry bulb temperature of the air leaving the cassette will practically ‘approach’ but not get as low as the wet bulb temperature.
Enhanced performance data Figures 3 and 4 illustrate operating efficiencies in terms of the EER(Energy Efficiency Ratio) and Energy costs between the new centrifugal
References: 1. Air Conditioning Systems – Design, Commissioning and Maintenance, Legg RC, Batsford, 1991
2. Refrigeration and Air Conditioning, McGraw Hill, Stoecker and Jones
3. Geoclima: Evaporative systems 4. Geoclima: Turbomiser performance data 5. DataCentreDynamics Focus, April/May 2010 ‘The new future of data centres’
July 2010 CIBSE Journal 57 Delta Cost
the evaporative cooling cassettes for improved performance. Conditioned air is ducted from the air handling unit section to discharge under-floor in the data centre sections and ducted from high level back to the air handling unit/fresh air intake. Further enhancements to the air handling package include an adiabatic heat exchange unit in the return air section, with sensible heat transfer to the fresh air supply providing initially free cooling from the outside ambient, then adiabatic cooling, then liquid pressure amplification(LPA) free cooling and finally mechanical cooling from the centrifugal compressor. © Terry Welch, Steve Chaplin
Energy Cost/Year (€/Year)
EER
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