DATA CENTRE COOLING
The second is a hybrid dry cooler that dissipates the heat of a data centre which, at external temperatures of over 34°C, sets its server rooms to a room temperature on a sliding scale up to a maximum 32°C. A year-round constant cooling load of 1,000kW was assumed as a basis.
Thanks to the hybrid dry cooling, the water consumption for the hybrid dry cooler from JAEGGI was reduced by more than 90% compared to the wet cooling tower.
The temperature “increase” in the data centre to maximum +32°C compared to +18°C in the production hall resulted in free cooling only having to be used for just short of three quarters of the year.
This reduced the number of operating hours of the refrigeration chiller thus lowering the operating costs of the hybrid dry cooler to 44% of the wet cooling tower reference taken as a comparison.
At another data centre that was studied, in Scandinavia, the refrigeration chiller only runs at 2% in sole operation. In this cooling system, hybrid dry coolers were connected in series with air-cooled refrigeration chillers and the system was operated at almost 60% exclusively through free cooling. During the rest of the time, the hybrid dry coolers cool the process fluid beforehand and the refrigeration chiller cools it afterwards, back down to the required temperature level.
Dispensing with the cold-water generator
In order to maximise the operating time of the free cooling operation, the required temperature level must be shifted in order to minimise losses at the data centre/dry cooler system separation at the plate heat exchanger.
At a data centre near Bern, this project was successfully implemented and the data centre works without a central refrigeration chiller. In the planning phase, the climatic conditions were not considered on the basis of statistical long- term data – as is standard practice. Instead, the system was dimensioned on the basis of the temperature data from 2003 with maximum summer heat. This year featured a significant shift of average temperatures into the higher temperature ranges, compared to the statistical average year.
With this additional underlying climatic deviation, an additional redundancy was built into the design and thus the operational reliability was further improved. We can also assume from this that this concept can be transferred without difficulty to the climatic conditions in Germany.
As the temperature level rises in the server room, the potential of free and hybrid cooling rises too – while operating costs fall.
Climate data comparison of Frankfurt and Bern (statistica and the year 2003). Geothermal cold reservoir
Another means of dispensing with a central refrigeration chiller is to use a natural cold sink. In the Netherlands, for example, it is possible to use groundwater aquifers as geothermal reservoirs.
Using this natural reservoir, the peak loads are shifted into times of the day or year when conventional cooling is possible, or put another way: coldness is harvested at climatically favourable times and stored geothermally. As statutory provisions demand an even thermal balance of the reservoir, the system is cooled at low external temperatures (1.5°C) through free cooling and the thermal reservoir is ‘charged’ with coldness.
Where technically possible, the hybrid coolers pre-cool the fluid between external temperatures of 14°C to 25°C, and the difference with respect to the desired temperature level is compensated via the low media temperature of the thermal reservoir. If the external temperatures rise above 25°C, the thermal reservoir alone serves as the cold reservoir.
Hybrid dry coolers from Jaeggi are optimised for the energy-efficient and cost-efficient operation of the overall system. Due to their large finned heat exchanger, they can be operated for most of the year without water and evaporation, purely as a dry cooler.
The operating costs of cooling are limited during dry operation to the energy consumption of the fans, media pumps and the control technology. Efficient fans whose speed is controlled via frequency converters are used to regulate the output of the hybrid cooler. By wetting the robust fins made from hard- rolled aluminium and fitted with louvres, the output of the hybrid cooler can be increased enormously at high external temperatures. As a result, when used in accordance with the specifications, the jaeggi type HTK hybrid coolers meet the hygiene requirements of the German VDI guideline 2047-2 and also comply fully with ACOP L8 and HSG274 Part one and thus also fulfil the strict requirements of sensitive sectors and applications.
36 November 2019
www.acr-news.com
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