RACA Journal I September 2023 29
Feature
HOW HUMIDIFIERS ARE USED IN DATA CENTRES Supplied by Humidair
Humidity control in data centre environments has come a long way over the years . From the early computers which used punched cards that needed humidification to maintain the physical properties of the card to magnetic tape data storage that needed a level of humidity to prevent dust and debris adhering to the reels .
As technology has evolved so has the need for data centre humidification . The main reason to humidify data halls has been to combat electrostatic discharge ( ESD ) that can damage sensitive electronics . However , servers have now evolved to minimise the risk of damage from ESD , reducing the need for humidification of data halls .
This led ASHRAE ( American Society of Heating , Refrigerating and Air-Conditioning Engineers ) to change its recommended guidelines on the acceptable lower level of humidity in data centres in 2008 . Previously the recommended humidity level included a minimum of 40 % RH ( relative humidity ) but was reduced and is now measured in dew point rather than RH as studies suggested absolute humidity has a greater impact on ESD . The new recommended lower limit is a line from 18 ° C dry bulb temperature and 5.5 ° C dew-point temperature to 27 ° C dry-bulb temperature and a 5.5 ° C dew-point temperature . Over this range of dry-bulb temperatures and a 5.5 ° C dew point , the recommended RH varies from approximately 25to 45 %.
The reduction in the minimum recommended humidity level has resulted in a fewer number of hours per year when humidification ( and its associated energy use ) to combat ESD is necessary . However , humidification is still be needed in winter months when cold outside temperatures result a very low internal humidity and increase the potential risks from ESD .
Traditionally , electrode boiler steam humidifiers incorporated in the CRAC ( Computer Room Air Conditioning ) units have been used to combat ESD in data centres . However , this type of humidifier has a high energy consumption and maintenance requirement , giving it a high overall operating cost . More recently , low energy cold water humidifiers have been used in innovative energy saving strategies .
For instance , in 2008 the Fujitsu data centre in North London employed spray humidifiers to prevent ESD by preheating the cold , saturated , fresh air to 30 ° C with heat recovered from the data halls . Heating the incoming air allowed it to absorb more moisture and after humidification with the low energy JetSpray humidifier , it was returned to a room supply temperature of 17 ° C at an optimum 50 % ± 10 % RH . The energy cost saving of using a JetSpray humidifier combined with heat recovery , compared to a steam humidifier was around UK £ 35 000 a year .
RACA Journal I September 2023 29