Where Should I Locate Temperature & Humidity Sensors in my Server Room or Data Centre?

It’s a question that we are often asked by our customers and whilst the location will depend largely on the specific installation and user requirements, we’ve put together this short article to share some of the knowledge we have built up over the years.

Firstly, it is necessary to decide if you would like to monitor temperature and humidity conditions within each of your individual racks or if you would prefer to monitor the ambient room conditions. Both approaches will generate useful information which can be used to provide an accurate insight into environmental conditions and warnings in the event of Air Conditioning failure. It is, however, worth remembering that the in-rack and in-room conditions could be very different – the equipment in your racks may be working in a very different environment to what a sensor outside of the rack may be reporting.

In-rack Sensor Placement

Through experiments that we have conducted in-house, we have seen that the temperature within a single rack (in a non-temperature controlled environment) may vary by as much as 9.5°C, with the top of the rack being the hottest and the bottom the coolest. In instances like this you may choose to place your temperature sensor at the top of the rack to provide a ‘worst case’ reading or you could install the sensor at the middle to provide an average reading.

It is important to know how air moves throughout your rack. This will depend on your specific rack and cooling setup. Unless you specifically want to monitor the temperature of the cool air entering (or the warm air exiting) your racks it is best practice to avoid direct airflow over temperature and humidity sensors. Direct airflow over the sensor chip can cause false readings for both the temperature and humidity and values tend to fluctuate more in these positions causing false and/or frequent alarms.

To provide the highest level of protection multiple sensors can even be placed around a rack, with different alarm thresholds set for each location, to provide you with a definitive map of in-rack conditions. In some instances it may be beneficial to locate a sensor adjacent to hardware that is susceptible to temperature or humidity fluctuations.

In-room Sensor Placement

For customers who choose to place the temperature/humidity sensor outside of the rack to measure in-room conditions there are a similar range of considerations. Again, it is important to avoid direct airflow but, depending on the location, you may also need to avoid direct sunlight or other environmental factors such as doors which are frequently opened and closed.

In these situations it may be useful to trial different locations over set periods of time to see which locations provide you with a reliable and stable reading that is also sensitive enough to changing conditions in order to provide an alert should thresholds be breached.

Temperature & Humidity Thresholds

The thresholds you choose will also be dependent on your setup. You may wish to followed recognised guidelines such as those provided by ASHRAE – a .pdf can be found here . ASHRAE recommend an operating temperature of 18-32°C and a humidity of 40-60%* though other bodies recommend both smaller and larger operating ranges!

Whilst these temperatures are of course optimal, it can be difficult to maintain in some circumstances. What we’d suggest is that you run your device and sensors in-situ for a few days and note the typical peaks and troughs and then set your thresholds around these.

If you have any questions, please contact our Support Team.

*ASHRAE recommended levels as of July 2017

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