19-02-2013, 09:40 AM
Splitting up the compressed air network and using a frequency controlled compressor
Introduction
The hospital in this case is a medium-sized institution that uses both medical and
technical compressed air.
Present situation
The present compressed air installation comprises three compressors of 37 kW
each. These compressors produce all the compressed air, without any splitting
up into medical and technical. The surgical instruments require a pressure of 11
bar, so that all the compressed air – both medical and technical – is produced at
this pressure. The air is dried by absorption drying.
The compressors make use of ON/OFF regulation, without any frequency
regulation. The percentage of time at zero load is 45% on average. At zero load
the compressors do not produce any compressed air, but they continue to
consume up to 25% of their rated power.
For the purposes of this case study the following consumption figures are used:
• Annual consumption of medical compressed air : 142 000 Nm3/year
• Annual consumption of technical compressed air : 820 000 Nm3/year
Proposal
By splitting the compressed air network into medical and technical compressed
air the technical part can be produced at a lower pressure of 6 bar, with lower
quality requirements. It was also proposed to install an additional two
compressors (one for each network), with frequency regulation, thus reducing the
zero load consumption to a minimum. Two of the present compressors were to
be kept as a backup for the medical compressed air, in order to ensure the
necessary redundancy. The third compressor was to be used to provide the
baseload for the technical compressed air, with the frequency-controlled
compressor dealing with the variations in compressed air consumption.
Estimated savings & investment
The savings were achieved by lowering the pressure, reducing the energy
consumption at zero load and making savings on drying and cleaning the
technical compressed air.