REFRIGERANTS
Field trials with propane
GEA Bock has invested in air-conditioning technology to prepare for future summers with extreme temperatures.
F
or a year now, a system operating with propane has been providing extra cooling capacity for maximum air-conditioned comfort in offices. It has also created the ideal testing environment for an in-house development: the HG66e HC semi-hermetic hydrocarbon compressor. Following the successful trial, the HG66e HC is now going into full production.
Sometimes when the compressor test beds at GEA Bock GmbH (Frickenhausen) were working to capacity during the summer, it wasn’t just the engineers who were sweating. Up to a year ago, a single system removed heat from the Compressor Test Centre as well as from the administration building. And the test beds always had priority, so compressor tests could be carried out under the required conditions.
If the Test Centre required a large amount of cooling capacity, in extreme cases this was at the expense of air-conditioning elsewhere. This only happened on a few summer days, but the air-conditioning system, which had been designed with some cooling capacity reserves, was depleted on those occasions. In view of the rising output requirements in the compressor test areas and increasingly frequent summer hot spells, it became essential to convert or expand the air-conditioning system. To avoid worsening climate change, which has been the cause of hotter summers in recent years, GEA Bock placed great emphasis on having an efficient and environmentally- friendly solution. Synthetic refrigerants with
46 March 2019
high greenhouse effect (GWP, Global Warming Potential) were taboo. As a supplier of compressors for air-conditioning and cooling systems, our in-house system also had to have a flagship character: a natural refrigerant was therefore a must.
“Since the main heat load arises in the summer months, propylene and propane were the obvious refrigerants,” says Manuel Fröschle, manager for application engineering at GEA Bock and a specialist in natural refrigerants. Systems with these refrigerants also work very efficiently at high ambient temperatures. The choice was finally made in favour of the R290 refrigerant, otherwise known as propane.
GEA Bock has several suction-gas-cooled compressors for hydrocarbons in its product range. The seven sizes (at that time) with 24 capacity stages from 5.4 to 279.8 m³/h (50 Hz) meant that a suitable compressor could easily be found. “To meet the required 132 kilowatt cooling capacity for the new system, we first selected two frequency-controlled HG56e HC compressors, which harmonised perfectly with the Futron compact chillers,” says the product manager.
The plan was to operate two identical brine chillers at 6 °C forward flow temperature and 12 °C return temperature to air condition the administration building. The redundant solution allows for optimum operation under partial-load conditions. It also allows performance of maintenance during transitional periods between the seasons,
without having to shut the air-conditioning down completely. The old system from then on would only cool the compressor test areas. Later, there was one notable change in detail to the basic planning: since a prototype of the new HG66e/1340-4 HC could be provided before the brine chillers were installed, it was integrated into the system. Like the smaller HG56e HC, the new compressor is a six- cylinder model, with output between this series and the HG88 HC models. With a displacement of 116.5 m3/h to 180 m3/h (50 Hz), it closes the gap in the range offered. The ultimately installed solution uses an HG56e HC and, in parallel, the prototype of the HG66e HC. Apart from the change of compressor, the originally planned concept for the system was retained. Controlling output via frequency or switching off the cylinder head “The ability to subject our first HG66e HC to a field test on our own premises was very appealing,” says Mr Fröschle. The new compressor is not only somewhat larger, it also offers more output and benefits from the mexxFlow valve plate: the combination of a flow-perfected double ring fin design for the valve plate and a cylinder head custom-built for it increases the compressor’s efficiency significantly. For the HG66e HC, output is adjusted by means of a frequency converter, while for the HG56e HC output is controlled by switching off the cylinder head.
Since the thermal energy in the building is dissipated by means of a brine circuit through a heat exchanger, the safety-related aspects
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