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What is an Energy Budget?


In this article we will be looking at what we mean by an Energy Budget and what this means in relation to designing to achieve a target Power Usage Effectiveness (PUE).


The target PUE is the basis for energy budgeting. The PUE tells us how much of the energy being consumed by the Data Centre will be used to support the IT loads. This in turn points us in the direction of the technologies to use which determines final cost to build.


The Energy Budget also establishes the Non-IT power allocation and in what systems this power is to be used.


Energy Budget Vs PUE.

How the Energy Budget relates to the PUE is a straightforward calculation.


Let’s say the target PUE is 1.5. For every Watt of IT power consumed by the IT equipment in the data hall racks, the Non-IT power W/W(IT) must be no more than 0.5Watts.


Putting this into the normal language of Data Centres. If you are designing for 10MW of IT loads, the Non-IT loads must be at or below 5MW, making the total power demand of the Data Centre 15 MW when at full capacity.


Here is a breakdown of what must be considered when designing to achieve a target PUE for the Energy Budget.


System Losses

All of the power going into the Data Centre is subject to system losses. From simple I2R losses in the transformers, power reticulation and distribution equipment, to Power Factor and complex harmonic losses.


The selection of Transformers, UPS’s, Harmonic Filtration Systems etc.. and sizing of power reticulation impact the system energy losses and build costs. These losses are a major contributor to Non-IT power consumption.


Non-IT Loads

Non-IT Loads cover all other areas and infrastructure of the Data Centre and include Battery Rooms, UPS rooms, Pump rooms, Chiller Rooms, various offices and the ancillary systems.


Loads include operation of other plant and equipment, lighting and small power for office equipment and systems.


In the next Article we will look at the Air Conditioning and Ventilation Non-IT loads to consider in establishing an Energy Budget.


Rob. I would like to keep the ACMV to the next article as previously shown


I can look at redrafting the next article to make it a bit longer if that is appropriate


Air Conditioning and Ventilation of the IT Loads.

All of the power going into the IT racks, is emitted as heat from those racks and must be removed from the data halls to be discharged outside the building using an Air Conditioning System.


There are generally very limited opportunities for “free” cooling through ventilation unless the Data Centre is located in a cold climate area.


Air Conditioning and Ventilation for System Losses.

All system losses are emitted as heat into the air either directly or indirectly and need to be removed either by Air Conditioning or preferably by Ventilation.



Air Conditioning and Ventilation for Non-IT Loads.

These loads are both sensible and latent.


The latent heat load is driven by the ambient conditions which require pre-conditioning of outdoor air before supplying it to the occupied spaces.


Sensible heat load is direct heat output from the operating Non-IT loads, occupants; including equipment the Air Conditioning and Ventilation plant itself.


If you would like more information regarding Energy Budgeting, get in touch with our expert team.


The following articles will look at the specifics of Data Hall Air Conditioning, Non-IT spaces, Infrastructure and Power System Losses.