Low Energy Data Centre
Ventilation
Figure 1 : Hot/Cold aisle ventilation system
One of the main challenges of refrigerating server rooms is the control of air flow we have decided to choose a hot and cold aisle insulation so we could achieve the air control as well both good sides of each option. Such as lowering costs (initial and running costs for cooling) and preventing hot and cold air mixture that could compromise server eficiency.
What is a hot and cold aisle?
For optimizing refrigeration on your data centre economically and physically, these measures have been designed so you could make the best use of your money for your servers cooling.
It consists on building your server room with aisles and racks front looking to each other. This arrangement creates an insulation on both corridors and one of them drives cold air through the ground meanwhile the other does the same with hot exhaust air from the servers that will be collected via exhaust chimneys over hot aisles.
There are several variations for this measure such as only hot aisles or only cold aisles, even one with air coming from the cealing instead of from the ground. However we have chosen in our configuration to insulate both aisles, with cold air from the ground and hot air collection from the ceiling to guarantee a good air flow control and avoid air mixtures that could compromise some upper parts of the racks.
Figure 2 : Server aisle
Figure 3: Ventilation Formula
Ventilation Estimation
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For estimating temperatures that would come out of the servers we have used the shown equations. Dry air and water in suspension have been considered and input data of volume of air rates have been extracted from ASHRAE: 120CFM per KW of heat generated by the servers.
With this data in mind we could set our air cooling aims.
Other information and tools were also used such as a psychrometric chart and average relative humidity of air from Falkirk.
Simulation Model
For simulating the ventilation we have used information, equations and phychometric charts found on Fundamentals of Engineering Thermodinamics, by Moran Howerard and Shapiro, and ASHRAE EC9005A paper from june 2012.
The input from our simulation was the heat that was needed to be taken out per rack in Kw, in this case 6100Kw. After calculations considering vapour of water from the air (average relative humidity of 0.5), we could reach the temperature out of each rack of 34.74°C which can be used for heating office facilities If needed.
These results are critical for defining which cooling unit we might need for cooling air.
