The scale is impressive: close to 80 kilometres of compressed air lines, a supply coverage area of approximately 350,000 square metres throughout a large section of Erlangen’s city centre, around 8000 take-off points for medical gases and a compressed air network of epic proportions hidden underground – the University Clinic in Erlangen, Germany, is a showcase example of how highly efficient, premium quality compressed air can be supplied over long distances.
For Wolfgang Emrich, of the Technical Services Department at the University Clinic of Erlangen, it is a proud achievement. What he and his team have accomplished over the past 15 years is a true masterpiece of compressed air engineering; not just in terms of efficiency, reliability and energy savings, but also with regards to building technology and the actual layout of the air distribution network. A total of 24 medical clinics with university outpatient departments are spread across large parts of Erlangen’s city centre – yet are still interconnected with one another.
Respiration with compressed air
The compressed air generated at the University Clinic of Erlangen falls into the category of medical gases and is therefore classed as a pharmaceutical. This is because, contrary to popular belief, patient respiration does not routinely involve oxygen, but rather medical grade compressed air. Pure oxygen for any length of time would be too aggressive for the respiratory tract, whilst compressed air comes closest to natural breathing air. However, for all medical applications – such as the powering of surgical tools in the operating theatre for example – compressed air must be produced, regularly monitored and documented in accordance with the Pharmacopoeia (the standards for quality, testing and storage of medicinal products). In addition to these standards, other special requirements regarding clinics and hospitals also apply. Operational reliability and the maintenance of required air purity are of paramount importance because patients, from premature infants to centenarians in different care and nursing facilities (from normal wards up to intensive care units and operating theatres), require a dependable source of quality compressed air 24 hours a day, 365 days a year. So, even in the event of faults, emergencies and any number of other potential difficulties, this medical product remains available as efficiently and economically as ever.
Deciding on a new direction
Before the University Clinic of Erlangen began to modernise its compressed air supply system about 15 years ago, each medical building had its own compressed air station, including the back-up machines that are so necessary in the medical field. But this meant that systems could not be operated at optimum capacity, and maintenance was highly demanding. Moreover, crucial consumption and energy data, pressures and other operational information could not be centrally collected and evaluated. This resulted in high energy and maintenance costs, which would only have continued to increase, since the technical requirements for compressed air quality assurance had also dramatically increased over time. Therefore, the University Clinic of Erlangen decided to radically rethink its approach to its medical compressed air supply.
Clarity through analysis
The first step was to carry out a detailed ‘Air Demand Analysis’ (ADA) to pinpoint exactly where and what air demand occurred and, subsequently, to determine where potential compressed air stations should be located. Analysis was also performed to determine whether there were possibilities for integration between the individual systems. After the necessary data had been collected, it quickly became apparent that dramatic energy and maintenance cost savings could be achieved by integrating the individual compressor stations into an interconnected system.
Consequently, work began to link the various buildings of the University Clinic via a subterranean network. The result of that initiative today is an approximately 80 km long air distribution network. Since it must meet ISO/DIS Standard 7396-1, the 76 mm main distribution piping is made from copper. Moreover, total pressure loss in this large network amounts to only 0.1 bar, or a maximum of 0.2 bar when the connected consuming equipment is included.
Whilst the compressors still have a decentralised layout as before, the systems are now concentrated at four main locations. This approach has clear advantages should any buildings, or parts of a building in the clinic complex, for example, experience a system outage due to fire, a power failure or similar such cause. All sections of the clinic can be individually isolated and switched off at different levels. Therefore, should one section experience a fault, compressors in other stations are immediately activated in order to ensure that no area of the expansive clinic complex experiences a shortfall in compressed air quality or volume. In this way compressed air delivery is 100 percent assured, even if technical issues do occur.
The compressor stations themselves boast state-of-the-art technology and design. In addition to the compressors, they are equipped with so-called desiccant dryers tailored for use in the pharmaceutical sector, which feature integrated activated carbon adsorbers and catalysts. Each of these systems is constantly monitored and can be switched off individually in the event of a fault. A master control system (in this case the Sigma Air Manager, or SAM for short) was installed to synchronise the individual components and stations. Over the years it has been continuously kept up to date with the very latest advances in technology via software updates. The compressors themselves all feature integrated compressor controllers (Sigma Control) and can therefore be optimally monitored. Thanks to existing bus systems, even older compressor systems dating back to 1994 – some having notched up approximately 80,000 operating hours – could be integrated into the network. Needless to say, these veteran workhorses will soon enjoy their well-deserved retirement.
The pipework itself was, in most cases, integrated in the underground service passages between the clinics. In certain cases, however, it also had to be installed beneath the streets, a task that was accomplished relatively easily with modern pipe laying techniques.
Quality always a key consideration
The quality of the compressed air is continuously monitored and recorded in the same way as compressed air production efficiency. Amongst other data, energy consumption, required delivery volumes, pressures and pressure dew points are logged. Using a mobile quality measuring instrument developed by the Technical Service Department of the University Clinic (for which the University Clinic also holds the patent), not only can the air quality be tested in the immediate area of the compressed air station, but the parameters set by standard N ISO 7396-1: 2014-06 can also be measured at each individual take-off point. Every take-off point is equipped with a barcode, and the respective quality measurement for that take-off point can be allocated and archived using a barcode scanner. The retention period for this data is subject to the Medical Devices Directive (MDD). The central compressor controller then outputs the data to a centralised control system, which monitors compressor operation of all clinics. The on-duty operator is consequently informed immediately and directly should a fault actually occur.
The compressor rooms themselves were designed with generous access space to make maintenance and service work as easy as possible. All rooms are equipped with an optimised ventilation system with back-up, which ensures that compressor operation can continue uninterrupted for extended periods of time, even if one of the ventilation systems does fail. Even though the new system uses fewer compressors than before, compressed air supply reliability has increased and, as a result, meets the requirements of ISO 7396-1 N: 2014-06 and the Pharmacopoeia by a wide margin. Decisive factors underlying this achievement are the interconnected air distribution lines between the individual clinics and the master controller, which manages the entire system.