High-efficient cooling of server rooms – Sparkassen-IT Calw

The Sparkassen-IT GmbH & Co. KG, a subsidiary of the German bank, Sparkasse Pforzheim Calw, maintains a broad-band network with a connection length of some 800 km in the northern Black Forrest area. The network comprises a fiber optic network of the highest grade and allows huge volumes of data to be transferred using extremely high bandwidths. Since June 2016, the newly installed computing center in Calw has hosted both own and customers’ servers.

The task specified by Sparkassen-IT in Calw was to cool a high-efficiency data center with a maximum refrigeration capacity of 35 kW and a cold aisle temperature of 25 °C.

What was special about this application was the stepwise increasing of the cooling requirement during the server room ramp-up.

As solution the server racks were installed between the cold and warm aisles. The chilled air is fed to the servers via side coolers. An eChiller provides the cooling. A conventional chiller with a HFC refrigerant is installed asthe required redundancy. The server room is connected to the chiller via a hydonic system and redundant pumps. The servers are cooled solely via the eChiller.

Here, the challenge was to provide the initial refrigeration capacity of 8 to 10 kW, corresponding to about 20 to 25 % of the maximum chiller capacity,. This was accomplished using a thermal storage. The chart below illustrates the progression of generated cooling load from commencement from July 2016 to February 2017.


Cooling Capacity

Cooling capacity from 1 July 2016 until 21 February 2017


The next chart shows the generated cooling load over a one-week period. The cooling requirement fluctuates only marginally by approximately 3 kW and is thus independent of day, night or weekend operation.


Weekly cooling capacity

Cooling capacity throughout a week


Energy footprint:

During the period from July 2016 to February 2017 (approx. 5640 h), the eChiller produced around 80 MWh of cooling energy. The eChiller consumed around 4 MWh of electricity for cooling. Among other factors, this was a result of the unit operating predominantly in free-cooling mode with a electrical energy of approx. 300 W as of October, making the eChiller approximately six times more efficient than the redundant HFC unit.