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  • Forsspac Team

An introduction to PUE and Energy Budgeting


Over a series of short articles, we will be talking about energy budgeting and PUE calculation for designers of the Building Services for Data Centres.


This first article serves as an introduction to the subject and will be followed by articles dedicated to:


  • Energy Budgeting

  • Data Hall Air Conditioning

  • Power System Losses

  • Non-IT space loads

  • Building Infrastructure Systems


Establishing the Power Usage Effectiveness (PUE) Target

Developers and operators of Data Centres generally obsess over the PUE their Data Centre is achieving. Apart from being a badge of distinction, it shows how energy efficient the Data Centre is, how costly to run and how well it is meeting Environmental targets. Business wise, power costs money so less power loss means higher profits. This is particularly relevant in 2022 and into the foreseeable future as we face a global energy cost crisis.


It is very important to establish the PUE target before design commences as this directly impacts the systems and plant selected and the commercial budget for Data Centre construction.


In a well designed Data Centre, most of the power is used for the IT equipment in the data hall racks. The lower the PUE, the higher the % of power used by the IT racks. A low PUE can only be achieved therefore, if the systems and plant serving the data halls are very efficient and in particular the Air Conditioning system which is the second highest power consumer in the Data Centre.


That said, the Non-IT loads also need to be controlled which include: Electrical reticulation and harmonic losses, ventilation power, lighting and auxiliary systems.


If 69% of the power is used by the IT equipment in the data halls and 31% to support this (Air conditioning, ventilation, lighting, system losses etc..) then the PUE is 1.45 (1/0.69). This is a reasonable design target PUE if like me, you are working in a tropical environment such as the Philippines, using water cooled chiller water systems for the Data Centre Air Conditioning. If DX type air cooling systems are used then the PUE can be much higher.


How Energy Efficient will the Data Centre be?

Designing to a given PUE at 100% load does not mean that it will automatically be achieved, nor does it establish part load PUE. Factors such as day 1 loads, plant build out, rack power variance, power factor and harmonic control, ambient conditions, and in particular operation / maintenance, impact the actual PUE achieved which will vary over time. Some of these factors are within the control of the Designer and need to be considered during design.


The articles that follow in this series will develop the overall picture of how and where energy is used and how to work out whether your target PUE is achievable.


If you wish to speak to one of our experts on Energy Budgeting and PUE calculation, get in touch.