Everything began with an idea from Prof. Dr. Beat Wellig, head of “CC Thermische Energiesysteme & Verfahrenstechnik“. He showed me how much the energy efficiency of our Enterprise Lab could be improved. Some drawings on a paper and a few calculations later he came up with a theoretically possible PUE value of 1.1. And ever since I’ve been committed to this idea.
In the mean time power efficiency has become a main topic in politics and research as well, so the time was right to launch a project showing how little change would be needed to achieve this goal. There are no energy consuming compression refrigeration machines and no gas refrigerant medium involved anymore. In fact the schematic below shows how simple the system can be kept. Remember the words of one of the great minds of the last century: “Keep things as simple as possible, but not simpler!” Albert Einstein
The main key in this kind of cooling system is the ability of the cooler sitting on top of the roof to cool down the water heated by the computer systems. This is not possible with ordinary coolers. Therefore we’ll use a so called hybrid dry cooler. It gets it’s cooling advantage by wetting of the heat exchangers and thus using convection and evaporation effects. This triples the performance compared to conventional dry operation. The second key is the use of ordinary water as a medium. To get the heat produced by the computer systems into the water we’re using cool racks – simple but efficient water cooled racks. Remember: No compression refrigeration machines, no gas refrigerant medium, no complicated and complex cooling systems. The image below shows how the hybrid cooler works:
- Fan drive
- Heat exchanger
- Air stream
- Primary circuit inlet
- Primary circuit outlet
- Primary circuit pump
- Heat source
- Make up water
- Low volume basin
- Primary circuit
- Blow down valve
- Wetting circuit
- Conductivity sensor
So what happens here?
The heat exchangers sitting at the top of the racks will “load” the water up to 33°C. This then must be cooled down by the cooler to 25°C. A small delta as this can only be achieved by this sort of hybrid dry coolers. The whole theory is based on the so called “wet bulb temperature” (german: Feuchtkugeltemperatur). This temperature is very beneficial in our latitudes. It reaches at most about 21°C. Letting our cooling system enough room to get the job done even on very hot summer days.
Improving the PUE value even further
Together with Erich Keller AG we’re trying hard to use the heat in winter time for heating the class rooms. The system must be simple (again) but effective. The cool racks will be modified with a flap blowing the heat into the room instead through the cooler on the top of the rack.
Picture: Lukas Gasser, Thermische Energiesysteme und Verfahrenstechnik