FEATURE Data Centres By accurately monitoring these four delta Ts, data
centre managers can gain a better understanding of the factors affecting cooling ineffi ciency, which can then inform mitigation and improvement measures to fi ne 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 e.g. 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.
HUMIDITY
IT equipment can also be adversely affected by humidity; low levels increase the risk of static electricity, so spray or evaporative humidifi ers may be necessary. However, high levels of humidity are also to be avoided because they can result in condensation, and the corrosion of metallic equipment.
In cooler climates it may be possible to utilise colder outside air to cool data centre equipment in a process known as economisation. The water content of this outside air may be low, and since the relative humidity of air decreases when it is heated, the humidity level may fall below acceptable levels unless appropriate controls are in place. Different types of humidity measurement are
required, depending on the location and application. For example, relative humidity and dew point can be measured in rooms, spaces, ducts and
The WXT530-family
outdoors, whereas wet bulb temperatures would be necessary in cooling towers and evaporative humidifi ers, and enthalpy sensors may be required for airside economisers. Enthalpy expresses the total heat energy (sensible heat and latent heat) involved with thermodynamic changes. These calculated humidity parameters are typically available directly from advanced humidity sensors, such as Vaisala’s. The three most common sensor confi gurations
for airside economiser control are dry bulb, single enthalpy, and dual enthalpy. While dry bulb control is the simplest method, it may miss potential energy savings by not opening the economiser when the ambient temperature is slightly warmer but relatively dry. Dual enthalpy works in a similar way, except
that two enthalpy sensors are employed; one monitoring outdoor air, and the other return air.
The HMD60 Series
The economiser will run if the outdoor air enthalpy is less than the return enthalpy. Vaisala’s transmitters are designed specifi cally
for applications such as air conditioning and economisation; measuring humidity and temperature, with derived outputs for dew point, wet bulb temperature and enthalpy. Temperature measurements do not generally suffer from drift, but traditional humidity sensors do, so Vaisala’s humidity sensors employ HUMICAP technology which delivers long- term stability and insensitivity to interferences such as dust and condensation. These thin-fi lm capacitive humidity sensors have become the industry standard in applications where long- term accurate, reliable, maintenance-free humidity measurements are required. Air fl ow in ducts allow sensors to respond
quickly to changing conditions, whereas air movement in other spaces can be slow, so some data centres prefer to use dew point temperature as a humidity control parameter because it does not depend on the temperature of the sensor. Other sensors that may be deployed at data
centres measure differential pressure in ducts and between hot and cold aisles, as well as additional outdoor meteorological parameters such as air pressure, rainfall, wind speed and direction. These measurements can be undertaken by an automatic weather station, by individual sensors, or by one of Vaisala’s WXT530 instruments, which utilise solid state technologies to minimise operating and maintenance costs. Outdoor sensors should be placed in a location with free airfl ow, away from any surfaces that might radiate heat and disturb measurements. Naturally, outdoor measurements must be as accurate and reliable as indoor measurements, so Vaisala’s meteorological instruments provide the long-term reliability that is required in even the harshest environments.
Vaisala
www.irish-manufacturing.com
www.vaisala.com Irish Manufacturing September 2022 25
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