Technique Sharing

Green Concept

PUE is the standard used to calculate Data Center energy efficiency.

The calculation method is Total Facility Energy divided by IT Equipment Energy.

The lower the PUE value, means more energy efficient Data Center.

It also means saving more cost for enterprise.


For a 100 kW power usage Data Center as an example,

if city power cost NT$2.5 per kWh, then this Data Center will need to pay NT$131.4 million annually for electricity cost in order to operate.

Consider the PUE for this Data Center is 2.5, IT Equipment Energy is 40kW and non-IT equipment (ex: CRAC) will be 60kW.

However, when PUE decrease to 1.5, non-IT Equipment Energy will decrease to 33.34kW,  the annual electricity cost decrease to NT$730,146.


In other word, by decreasing PUE by 1, enterprise will save NT$583,854 cost annually .

Although lower PUE means lower enterprise operation cost, but this will need a lot of energy saving design and techniques to achieve.


For instance, the most common seen "Hot/Cold Aisle" design (below diagram)

Above diagram's blue arrow represent the flow of cold air ; red arrow represent hot air.


This design concept is based on:

Install the cabinet racks so all the hot air produced by IT equipment can be centralized in one aisle to avoid the mixing of cold/hot air, and be able to control the air flow.

By that, it is possible to adjust higher Data Center environment temperature setting, reduce the need for CRAC to produce cold air.

In other word, CRAC will reduce operation need (ex: compressor) ; decrease electricity cost.


A more enhance method, for example, as below:

we called it "Closed" cold/hot air aisle.

It will centralize cold or hot air in a certain aisle more precisely.

Reducing energy (cooling) wasting.

It also can collocate with other auxiliary equipment or design to achieve greater energy saving effect. For example: use Evaporating Cooling to reduce air conditioning cost.


The design concept is:

Use cooling water to take away the heat produced by Data Center. Then reuse the hot water generated, through the cooling tower to perform heat exchange with the cold air in atmosphere, to achieve cooling purpose.

This way, it is unnecessary to pay extra electricity cost to cool the hot water.

From this Free Cooling Method to reduce the CRAC electricity cost.