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COOLING
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By Natascha Meyer , Product Manager for chillers , STULZ
www . stulz . co . uk
How to compare chillers for data centre applications using technical data that can be easily verified
Every planner / consultant or customer is familiar with this problem . Once the decision to purchase a system has been made , the tendering process begins and you are confronted with the major task of weighing up which product is most suitable for this project .
Before we get started , we should first be clear about what our main focus is . What are the most important factors for my project ? Is the focus on capital expenditure ( CapEx ), operating expenditure ( OpEx ), noise levels , or the easiest possible integration in an existing system ? Comparing capital expenditure is relatively straightforward . However , it ’ s very important to ensure that both machines can feature the same equipment . Does the standard version of a chiller have something to offer that is only available as an optional extra in the other model ?
Where integration is concerned , the key aspect is a collaboration with the manufacturer , and how flexible they are . Here , comparisons are already getting more difficult . However , it ’ s clear that some manufacturers are more flexible than others . In this context , flexibility means far more than simply adding to the standard range of options ; it could involve a larger compressor with the same footprint , the adaptation of load entry points , specific electrical requirements , and a great deal more .
Once we ’ ve gathered documentation for the same basic configuration from two or more manufacturers , the great comparison of technical data can commence . Defined KPIs such as EER and ESEER are a popular means of comparison . But how meaningful are these really ? To gain more clarity , let ’ s first define what these two values are actually about . See right for an explanation of how they are calculated :
Both these KPIs only provide limited information on the efficiency of a chiller in a data centre . One alternative would be a comparison of operating expenditure over the year as a whole , including all project specific data . This method is based on a weather profile at the respective location , so it takes into account behaviour over a broad temperature range , and all operating modes ( DX , MIX , FC ). When comparing operating expenditure , it ’ s important to ensure that calculations are based on the same temperature profile . Otherwise , significant discrepancies may occur . A lot of operating hours at cold temperatures considerably improve the statistics .
Can I rely on the technical data , or can I shed more light on them ? Occasionally , we need to question the technical data . A closer look makes sense whenever the difference in price is considerable and the technical data are very similar .
Which components are installed ? First of all , we need to verify which components from which manufacturers have been installed . There will be a lot of overlap . But even here , it ’ s worth putting this under the
Energy Efficiency Ratio ( EER )
Cooling capacity Power consumption
EER is the ratio of cooling capacity to power consumption . This value should be as high as possible ( i . e . not much energy is required to produce the desired cooling capacity ).
Advantages
Comparison is possible with the same operating point .
Advantages
Comparison is possible for several operating points .
Disadvantages
Only one operating point is considered .
Does not take account of efficiency throughout the year .
Imprecise , because not all manufacturers use the same consumers for their calculations ( e . g . pump ).
European Standard Energy Efficiency Ratio ( ESEER ) = 0.03 A + 0.33 B + 0.41 C + 0.23D whereby A-D stand for the following design parameters :
Operating point EER factor Outside temperature A- 100 % 0.03 35 ° C B- 75 % 0.33 30 ° C C- 50 % 0.41 25 ° C D- 25 % 0.23 20 ° C
With the ESEER , it ' s assumed that cooling capacity decreases as the outside temperature falls , as there is less need for cooling .
Disadvantages
microscope . Why ? Because a chiller is a complex system , not a single component . So what matters is the harmonious interaction between the individual components . Take the compressor , for example : even if the same compressor appears to be installed in both chillers , the important thing is its environment . Every chiller has an evaporator and a condenser , as well as the compressor .
So what ’ s the difference ? The evaporation temperature and condensing temperature are the reference variables for the energy consumption and operating behaviour of the
Cooling capacity constant in the data centre .
The above assumptions do not always apply .
Water temperatures are not project-specific , but predefined . www . networkseuropemagazine . com