Feature
2020 will see global data centre capacity exceed 6.8 zettabytes – all in need of continual cooling where this function alone accounts for up to 40 % of operational costs .
Hybrid technology with both DX and CW mediums can off a mix of cost effectiveness and the efficiency whilst still meeting a high tier rating .
“ Further to what has already been mentioned , configurations could also be designed according to hot / cold isles principles or
contained areas where cooling is focused on a particular area in the space rather than that cooling an entire room unnecessarily , in-row cooling , air handlers and ducted solutions . Use of any of the methods mentioned are primarily driven by the building and what you have to work with – this can be an existing building or new building , open spaces or confined spaces . Suppliers then have similar equipment commonly referred to as CRAC units – computer room air conditioning or CRAH – computer room air handling . Some installations incorporate combination solutions as well . You can have a water-cooled CRAC unit with an economiser coil so when the water is cold enough it works like a chilled water unit , but if it ’ s not cold enough it uses a compressor to pull down . You may also get a unit that is an air-cooled DX type with a chilled water coil ,” adds Frans Jooste , director at Intramech .
Jooste continues , “ With the many different configurations , and what we find in particular , is that the system selection is also often heavily weighted and driven by the client – and ties into the secrecy in data centre designs . Having a unique combination or setup that can save up to thousands of kW in cooling costs monthly , makes the client more competitive on cost to the market . This can equate to millions of Rands annually across a couple of sites , so keeping the methods applied under wraps , naturally maintains certain advantages .”
While many designs are based solely on the required amount of net sensible cooling and inlet rack temperature , air leakage rates through a raised floor , rack capture index , correct airflow distribution , supply airflow from the cooling unit , correct cooling unit control philosophy and a rack population strategy must be also be included in the design .
“ Rack population strategy is so important as a DC is gradually populated over time . Therefore , the maximum load within the data centre is not present upon the first day of operation . The correct type of cooling strategy to deal with low part load operations must also be selected and implemented to ensure the cooling units are still able to provide an energy efficient solution whilst operating without any critical alarms ,” notes Michael Young , engineer and trainer within data centre cooling at My HVAC Coach .
Since energy consumption is such an important aspect in data centre cooling , CW systems too employ the use of hybrid free cooling and hybrid adiabatic free cooling type of principals . DX systems employ compressor and fan speed modulation to account for varying loads but more advanced systems now employ water cooled DX systems that are coupled to dry coolers that can also provide an indirect type of cooling system for operations during low ambient conditions .
“ As Frans Jooste alluded to , all suppliers utilise the same thermodynamic principals and cooling technology within their cooling systems but the key differentiator between each supplier is energy consumption , quality , price and redundancy of the cooling unit . Energy consumption between each brand of cooling system is influenced by the complex process of constantly matching the required cooling load of the DC with the cooling operations of the system ,” adds Young .
Because of the heat load in a DC and concentration of heat , the correct amount of air to move the heat out quickly is required in order for you to be able to maintain the targeted temperature range , but further to this , the Uptime Institute specifies that when there is a power or a generator failure , the temperature rise within 15 minutes of the failure must not be greater than 5C .
“ You may think 15 minutes is a lot and 5C is little , but once you exit the environment conditions , for you to be able to capture the generated heat in that time and cool it down again is going to take quite a long time . It is therefore imperative for designers to also take into account the temperature rise factor . In addition , designers must consider the changeover when a power failure does occur and that the cooling equipment will not reach capacity again instantaneously , including allowances for that inertia in a temperature rise situation in their planning ,” notes Soluade .
FILTRATION , HUMIDITY AND AIR QUALITY FACTORS “ Air is essentially what needs to be controlled and managed in data centre operation as dust can be sucked into servers and cause various malfunctions . Humidity control too is a critical design requirement . Should there not be sufficient humidity the air quality affects the volume of air required per appliance and
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RACA Journal I January 2021 www . hvacronline . co . za