ShareNew evaporative cooling system for more energy efficient data centres
A dew point cooling system, which is an indirect evaporative cooling system that approaches the dew point, has reduced the electricity consumption of a UK data centre by 80%.
According to a review article, evaporative cooling air-conditioning systems help improve the energy efficiency of data centres, measured using the Power Usage Effectiveness (PUE) standard. Evaporative cooling air-conditioning technology can reduce the annual PUE of a data centre to below 1.25. [1] It should be noted that the signatories to the EU Climate Neutral Data Centre Pact must achieve an annual PUE target of 1.3 in cold climates and 1.4 in warm climates by January 1, 2025.
Conventional evaporative cooling systems
There are two types of conventional evaporative cooling systems: direct evaporative cooling and indirect evaporative cooling. Direct evaporative cooling systems humidify and cool the air in data centres based on the following principle: outdoor air is introduced in the data centre where it comes into direct contact with water contained in a saturated porous medium. The water evaporates into the air, thereby lowering its temperature and increasing the humidity. [1, 2] The cooling system uses a portion of the server room return air to control the humidity level of the supply air and avoid the presence of condensation, which can affect IT equipment. [1]
Indirect evaporative cooling systems provide cooling without humidification. In this case, the air used to cool the data centre first passes through a heat exchanger placed in an evaporatively cooled, enclosed space. [2]
Dew point indirect evaporative cooling
In recent years, a new type of indirect evaporative cooling system, known as the dew-point cooling, has emerged. It is based on the “Maisotsenko cycle (M-cycle)”, which was developed to reduce the supply air temperature compared with conventional indirect evaporative cooling systems. The M-cycle is able to cool the air below the wet bulb temperature (the limit for conventional evaporative cooling) and approach the dew-point temperature. [3]
The dew point is the temperature at which dew forms (i.e. condensation). It is the temperature to which the air must be cooled at constant pressure to reach saturation (i.e. 100% relative humidity). Any further cooling produces condensation rather than lowering the air temperature. [4, 5]
A heat exchanger for dew-point cooling comprises several alternate wet and dry channels. [3] In a dew point indirect evaporative cooling system, some of the primary outdoor air is allowed into the wet channel before entering the heat exchanger, so that the wet bulb temperature of this secondary air after cooling will be further reduced. [1]
Dew point cooling system in a data centre [6]
A team of researchers at the University of Hull, UK have developed a high-performance dew point cooling system that can produce cold air at a temperature below the wet bulb temperature of the inlet air.
The researchers tested their technology in Hull City Council’s data centre, using a 100kW cooling system. From early August to the end of October 2021, the system reduced the electricity consumption for cooling the building by 80%, saving the city council £149 ($200) per day, or £54,000 ($73,000) per year. The data centre’s carbon footprint has therefore been reduced by the equivalent of 82.5 tonnes of CO2 emissions per year.
For more information on evaporative cooling, an IIR Informatory Note is available for download on FRIDOC: https://iifiir.org/en/fridoc/138322
Sources
[1] Chu, J., & Huang, X. (2021). Research status and development trends of evaporative cooling air-conditioning technology in data centers. Energy and Built Environment. https://doi.org/10.1016/j.enbenv.2021.08.004
[2] Evaporative Cooling, 27th IIR Informatory Note. https://iifiir.org/en/fridoc/138322
[3] Cui, X., Chua, K. J., Yang, W. M., Ng, K. C., Thu, K., & Nguyen, V. T. (2014). Studying the performance of an improved dew-point evaporative design for cooling application. Applied Thermal Engineering, 63(2), 624-633. https://doi.org/10.1016/j.applthermaleng.2013.11.070
[4] Dew Point vs Humidity. https://www.weather.gov/arx/why_dewpoint_vs_humidity
[5] https://labomat.eu/fr/faq-essais-de-corrosion/708-qu-est-ce-que-le-point-de-rosee-.html