“Its not the heat, it’s the humidity”, Gareth French, director at Humideco, considers the issue of humidity control in the data centre and introduces some new approaches to tackle the problem, which at the same time greatly reduce energy consumption. Although an important consideration, data centre humidity is often an afterthought when compared to temperature, and there is much debate within the industry about the optimum level. It’s well known that by keeping room humidity between certain limits, the risk of data loss and equipment damage through electrostatic discharge can be alleviated, as well as preventing energy from being wasted. Also acknowledged is that large fluctuations in humidity can offer the potential for condensation, and cause circuit boards to expand and contract, bringing the possibility of damaged circuitry.

The humidity level we refer to is more accurately termed “relative humidity”, which is the percentage saturation of air with water vapour, at a given temperature. But as air passes through a server, its temperature increases, and correspondingly its relative humidity decreases, although the actual moisture content of the air remains the same. Some schools of thought therefore believe that the actual moisture content, or absolute humidity, should be the important factor.

But what are the right limits of humidity for a data centre ?  Go online and you will see many differing viewpoints, with opinions varying from as wide as 5% to 95%. The generally accepted ‘ideal’ range is between 40% to 60%; but this can also depend on the method of cooling employed in the data centre, and the ambient conditions in the region.
Most people agree that stability is the key and to achieve this means taking control of humidity across the entire facility, through reliable humidity measurement and controllable humidification equipment.

Historically, CRAC units have incorporated a humidification function, based on electrically generated steam, with units featuring a display of room humidity, with an adjustable set point. But steam humidifier units are both energy and maintenance intensive, and they add heat into an environment that is predominantly cooled – so the energy equation doesn’t really stack up in practice. When a data centre has looked to reduce energy, and particularly now with the CRC initiative in force, an easy answer has been to reduce the number of individual CRAC unit humidifiers in use, or to switch off these completely and seek an alternative method.

A common design in data centres is to utilise a central air handling unit, incorporating a steam humidifier, to supply tempered fresh air at a controlled level of humidity, to all rooms in the data centre. However, these rooms are often operating under different conditions, for different clients, often with different views and requirements. Couple this with the fact that many steam humidifers do not provide particularly accurately controlled steam output, so the actual relative humidity can vary greatly from room to room. Most of the data centres we visit have low volumes of fresh air introduced into the individual rooms, and where cooling demands are high, it becomes impossible to achieve the desired room humidity via the fresh air.

This means that many data centres operate with widely varying humidity levels throughout different rooms, with a great deal of energy being needlessly consumed by the humidification units, often operating in conflict with cooling equipment.

As a company, Humideco have taken a close look at the requirements in data centres, and as an example of a solution provided for a large London data centre, we have recently provided low energy “ultrasonic” underfloor units, throughout the facility. The initial benefit of this approach is a 93% energy saving over steam humidification, with the humidified air being delivered exactly where it is needed, from a fully contained unit, with no visible mist. The individual needs in each room are reliably and accurately met, with a further benefit being that  ultrasonic humidifers require virtually no maintenance, with no cylinders or scale to contend with.

Where CRAC units operate with raised chilled water temperatures, the same benefits can be achieved with ultrasonic “in-room” units. Here, the units stand vertically within the room and the fully evaporated humidified air is delivered at high level, with no visible mist.

When steam humidifiers are being replaced with ultrasonic humidifiers, as well as providing a more accurate solution, the energy savings result in payback within a short period of time, typically between 1 and 2 years.