FEATURE Data Centres
The sensor requirements of data centres
D
ata centre owners and managers are acutely aware of the need for better energy effi ciency. Around 60 per cent of
a data centre’s energy requirements are driven by its IT infrastructure, so there are energy reduction opportunities in (usually new) equipment that is more energy effi cient. However, there are good opportunities for energy effi ciency in the other 40 per cent of energy demand; the majority of which comes from a data centre’s cooling and air- conditioning systems. Effi cient temperature and humidity control
is important for the optimal functioning of IT infrastructure. In many modern facilities 99.999 per cent uptime is expected; representing annual downtime of just a few minutes. These extremely high levels of performance are necessary because of the importance and value of the data and processes being handled by the IT infrastructure. In common with all good process effi ciency
measures, effective energy management relies on the availability of accurate, reliable, continuous monitoring data. So, for data centres, what must be measured? And where?
TEMPERATURE
Cooling and air conditioning is necessary to remove the heat generated by IT equipment; to avoid over-heating and prevent failures. It is therefore necessary to monitor temperature in the aisles and racks, as well as in all spaces, ducts in the ventilation system, cooling system
24 September 2022 Irish Manufacturing
pipes, and outdoors. Naturally, it is vital that the measurement locations are truly representative and that the network of sensors is able to detect any potential cold- or hot-spots. Larger data halls can be more challenging to monitor because they have a greater potential for spatial temperature variability, so it is important that there are suffi cient numbers of temperature sensors to ensure that all servers are monitored. Some servers may be close to a cooling unit and others may be further away; some may be at the bottom of a rack, and others higher up, so there is potential for three-dimensional variability. In addition to a suffi cient number of sensors, it is also
HMT120 with probe
therefore important for air fl ow and cooling to be optimally distributed throughout the server room. Most data centres will need to monitor ‘delta T’ – which is commonly defi ned as the temperature difference between hot and cold aisles. However, in reality, the situation is more complex because there are actually four different delta Ts that need to be monitored if cooling operations are to be as effi cient as possible. The most obvious delta T is the temperature
difference in air before and after it passes through the IT equipment. The second frequently measured delta T is the temperature difference across the cooling equipment. However, in reality, the temperature of the air leaving the coolers is rarely the same as the air arriving at the IT equipment, usually because of issues such as obstructions, vortices, pressure differentials, air pockets etc that cause cold air and warm air to mix. Similarly, the temperature of the air leaving the IT equipment is frequently cooler by the time it enters the coolers. This is usually because cooled air mixes with the warmed air for a variety of reasons; all of which indicate ineffi ciency in air fl ow management. So, the four delta Ts are the temperature
differences, as outlined below: 1. Before and after the IT equipment 2. Before and after the coolers 3. Between air leaving the coolers and air entering the IT equipment
4. Between air leaving the IT equipment and air entering the coolers
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