NATURAL REFRIGERANTS FOR TECHNOLOGY GROUP

Future-proof alternative

In the summer of 2019, Schott AG renewed a first chiller in Landshut. For the new process cooling, the company wanted to use the natural refrigerant propane (R290).

For the operator, the natural refrigerant offers a long-term and future-proof alternative to chemical options. Due to the F-Gas regulation (EU) No. 517/2014 and the phase-down decided therein, companies are exposed to a long-term incalculable risk for the operation of the plant. The step-by-step reduction of the amount of CO2 equivalent for refrigerants available on the market described in the phase-down, down to 21 percent in 2030, is already having a strong impact on refrigerant prices. Natural refrigerants are not affected by the F-Gas Regulation. Propane (R290) is characterized by its high energy efficiency, low pressure level and simple system handling during operation. In comparison to other HFO and HFC refrigerants, the naturally combustible gas is present in the atmosphere, so it is not an artificially generated foreign gas, for which any environmental damage is currently not foreseeable. Schott AG is an internationally operating technology group that is a leader in the fields of special glass and glass ceramics.

Air-cooled propane chiller

The propane (R290) chiller in its energy-efficient system configuration has a cooling capacity of 320 kW at 35 °C ambient temperature. It is equipped with two separate cooling circuits, a six-stage capacity control, six EC fans and an industrial PLC with 7″ touch display. The superheat control is done by electronic injection valves. Each refrigeration circuit is controlled, analyzed and monitored by numerous sensors and an intelligent control algorithm. When using propane as refrigerant, compressor manufacturers often specify a comparatively high total superheat. This is usually achieved by using a suction gas heat exchanger. However, especially at low ambient temperatures and reduced refrigerant mass flow, this heat exchanger loses its performance, which can quickly lead to a too low total superheat and thus to compressor damage. To avoid this, Skadec chillers detect evaporator and total superheat as standard. In combination with dynamic superheat control, this guarantees compressor protection. As a positive side-effect, it is also possible to reduce plate overheating at high ambient temperatures and thus operate the machine much more efficiently.

BMS software integrated in the chiller

In addition to the old chiller, part of the hydraulic system was also replaced. The high flow temperature of 10 °C can be completely covered by a 295 kW free cooler placed next to the chiller at an ambient temperature of +5 °C. At such high system temperatures, the use of free cooling is a sensible and sustainable decision that additionally improves the energy balance of the entire system. The hydraulic system has been designed in such a way that both individual operation of the chiller or free cooler and mixed operation (series connection) are possible. In this way, part of the required cooling capacity can be covered by the free cooling already in the transitional period. An innovative control algorithm calculates from which temperature spread the use of free cooling is actually worthwhile. In the original planning, a separate control cabinet was planned as the higher-level control of the entire system, consisting of a chiller, free cooler, three-way valve, redundant pump group for the primary circuit with glycol/water mixture and a redundant pump group for the secondary circuit in the building with the medium water. Through close cooperation between operator, planner, installer and machine manufacturer, the concept could be adapted in such a way that the control and monitoring of all mentioned components were integrated into the PLC of the chiller. The visualization can be operated in the building at the PC, by remote maintenance or directly at the machine. For service technicians and operating personnel, this makes everyday work much easier. The modular expandable programmable logic controller can be operated intuitively by plant engineers. Similar to modern smartphones, no comprehensive operating instructions are required. All process values and error messages are displayed in plain text in German. Depending on the operating status, the individual actuators and process values are highlighted in color. In the event of a malfunction, the cause can be localized at first glance. Service managers in the office can connect to the entire system and see the same visualization as the service technician on site at the factory. Changes in settings and programs can be updated via remote maintenance access. The connection to the Internet is made via network or also via a mobile phone card. Especially in case of malfunctions in the refrigeration process it is important that the operating behaviour can be traced in detail. This is where the powerful data logger integrated as standard helps, which stores all process values (60 to 80 units) in single-digit second intervals over a period of several years. Plant engineers can retrieve and analyze these values remotely before sending a service technician to the site.

Risk management

In the risk assessment prepared by the operator, the risks of outdoor installation with a very low refrigerant charge were considered. Access to the chiller is restricted and only trained personnel can access it. Furthermore, a propane gas sensor is installed inside the machine, which switches the system voltage-free via two switching stages. The EX-protected system components are supplied with a separate supply line. An integrated EX fan ventilates the housing and ensures that no explosive mixture can form. Any faults that occur are directly forwarded to the higher-level building control system. As an option, these can also be sent by e-mail.