Networks Europe Issue 13 January/February 2018 - Page 21

COOLING By Natascha Meyer, Product Manager for chillers, STULZ www.stulz.co.uk 21 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 TU"2FR&Fb6Ɩr66GFvW"67VFF2fVR6VB&R2v076&RRBV6VW&w2&WV&VBF&GV6RFRFW6&VB6Ɩr66GGfFvW2F6GfFvW06&6276&RvFFR6PW&FrBǒRW&FrB266FW&VBFW2BFR66VBbVff6V7F&VvWBFRV"ख&V66R&V6W6RBVf7GW&W'0W6RFR6R67VW'2f"FV 67VF2RrVWW&V7FF&BVW&wVff6V7&FU4TU"232"C2#4@vW&V'B7FBf"FRfvrFW6v&WFW'3W&FrBTU"f7F"WG6FRFVW&GW&PR23R +0"sRR323 +02SRC#R +0B#RR#2# +0vFFRU4TU"Bw277VVBFB6Ɩr66GFV7&V6W22FRWG6FRFVW&GW&Pf22FW&R2W72VVBf"6ƖrGfFvW2F6GfFvW06&6276&Rf"6WfW&W&FpG26Ɩr66G67FBFRFF6VG&RFR&fR77VF2FBv0ǒvFW"FVW&GW&W2&RB&V7B7V6f2'WB&VFVfVB֖7&66Rv&V6W6R6W"26W77FVB6vR6VB6vBGFW'22FR&W0FW&7F&WGvVVFRFfGV6VG2FRFP6&W76"f"WSWfVbFR6R6&W76 V'2F&R7FVB&F6W'2FR'FBFp2G2Vf&VBWfW'6W"2Wf&F"B6FV6W"2vV2FR6&W76"6vN( 2FRFffW&V6SFRWf&FFVW&GW&PB6FV6rFVW&GW&R&RFR&VfW&V6Rf&&W2f FRVW&w67VFBW&Fr&VfW"bFPwwrWGv&6WW&VvR6