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Home » The sensor requirements of data centres – Part 1

The sensor requirements of data centres – Part 1

Data centre owners and managers are acutely aware of the need for better energy efficiency. With responsibility for around 1% of global electricity consumption, the sector is heavily affected by turbulence in energy costs, so there is a very strong demand for energy efficiency.

Around 60% of a data centre’s energy requirements are driven by its IT infrastructure.Photo by Vaisala
Around 60% of a data centre’s energy requirements are driven by its IT infrastructure.Photo by Vaisala

At the same time, governments around the world are looking to energy hungry industries for opportunities to reduce the use of fossil fuels and lower greenhouse gas emissions.

Around 60% 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 efficient. However, there are good opportunities for energy efficiency in the other 40% of energy demand; the majority of which comes from a data centre’s cooling and air-conditioning systems.

Efficient temperature and humidity control is important for the optimal functioning of IT infrastructure. In many modern facilities 99.999% 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 efficiency measures, effective energy management relies on the availability of accurate, reliable, continuous monitoring data. So, for data centres, what must be measured? And where?


Cooling and air conditioning are 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 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 sufficient 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 sufficient number of sensors, it is also therefore important for air flow and cooling to be optimally distributed throughout the server room.

Most data centres will need to monitor ‘delta T’ – which is commonly defined 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 (1) that need to be monitored if cooling operations are to be as efficient 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. This is 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 inefficiency in air flow management.

So, the four delta Ts are the temperature differences:

Before and after the IT equipment

  • Before and after the coolers
  • Between air leaving the coolers and air entering the IT equipment
  • Between air leaving the IT equipment and air entering the coolers

By accurately monitoring these four delta Ts, data centre managers can gain a better understanding of the factors affecting cooling inefficiency, which can then inform mitigation and improvement measures to fine tune data centre performance.

In dry climates evaporative cooling is effective at dissipating heat. In cold climates direct cooling with dry, cold air can be used. In recent years, liquid cooling solutions have become popular because they are more effective at removing heat. To support this trend, Vaisala has developed a new high-quality sensor for measuring cooling / heating liquid temperatures. The Vaisala TMI110 is an immersion temperature transmitter offering a fast response with high levels of accuracy. TMI110 is an addition to the extensive HVAC product offering, including for example the ever-popular HMD60 for air ducts, HMT120 for indoor air measurements, and state of the art Indigo platform for most precise measurements in data centres.