Propane is a tried and tested refrigerant and is increasingly in demand, says eurammon, the joint European initiative of companies, institutions and individuals who advocate an increased use of natural refrigerants. It supports its arguments with case studies.
At the end of June, the Environment Committee of the European Parliament recommended a faster and stricter reduction of F-gases (fluorinated greenhouse gases) than expected, by operators. This more than ever brings into focus natural refrigerants, such as the hydrocarbon propane. Despite specific safety standards, propane applications are easy to implement and are increasingly popular with planners and engineers, who consciously seek new refrigeration systems and a sustainable solution in terms of environmental protection and energy efficiency.
Propane does not contribute to the greenhouse effect and has a very low global warming potential. Another advantage is the short payback period due to low energy consumption and operating costs. The following case studies from eurammon members show the areas where propane is particularly suitable.
City of Lübbecke uses environmentally friendly cooling
The Stadtwerke Lübbecke (public utilities) turned to Wilhelm Schriefer with the desire for a new refrigeration plant which provided both air conditioning to the building and reliable cooling to the server room. The plant engineers were to find an environmentally friendly solution with a cooling unit whose refrigerant ideally did not increase ozone depletion or global warming.
After a thorough examination, the choice fell on a brine chiller unit with the natural refrigerant propane. The chemical properties of the hydrocarbon were considered in the project planning. Based on the estimated refrigerant charging amount of 2.5 kilogrammes, a concept was created to deal with safety measures. This included the outdoor installation of the system on the roof of the Lübbecke municipal administrative building.
A high level of pre-assembly facilitated the setup of the compact housing, which covered, in addition to the water chiller, all other components, water supply connections, safety system and the controller. Apart from the basic components, such as condensers and evaporators, the plant engineers opted for the special R290 version of a semi-hermetic reciprocating compressor from HKT Huber Kälte-Technik.
Pressure controllers (for low and high pressure, respectively) and a safety high pressure limiter were also used in the system. A vacuum heat exchanger increased the efficiency of the system, since an increased enthalpy difference for the same amount of refrigerant could absorb more heat energy. The cost savings resulting from this helped pay back the purchase price of the heat exchanger within a year.
Besides the ecological advantages of the system, the overall cost benefits were impressive. “Regardless of all political debates, the stated arguments explicitly speak for this comprehensively sustainable technology. It is particularly noteworthy that the low operating costs compensate for initial extra costs in less than three years,” says Karl Huber, the Managing Director of HKT Huber-Kältetechnik-GmbH.
German supermarket chain opts for integral cooling and heating systems
The innovative, compact unit supplied to a renowned German supermarket chain was to meet the latest environmental standards and at the same time be cost efficient. The goal was to develop a prefabricated unit which provided for the generation of the required cooling for refrigeration units and cold storage rooms, air conditioning of the sales area and the heat supply of a floor heating, including the electrical equipment for the entire supermarket.
Futron provided the concept and developed the new unit together with thermofin. “Convincing arguments for the use of propane as refrigerant included the high energy-efficiency ratio, the low pressure level and pressurised gas end temperature, as well as the relatively low price,” explains Willy Löffler, a senior official at thermofin.
The compact unit comprised both the refrigeration system with 130 kW cooling capacity for cooling and a heat pump with 40 kW heating capacity. The refrigeration units and cold storage rooms were cooled indirectly with propylene glycol as secondary refrigerant. The need for low temperature was supplemented by an additional cooling unit as a CO2 cascade system.
An additional evaporator circuit in the lamellar blocks of the air-cooled condenser brought the heat from the ambient air to the floor heating. The low energy consumption of the system and the positive effect in terms of environmental protection were quite impressive. The characteristics of propane reduced the CO2 equivalent of the refrigerant from 9.07 t to nearly 0.
“The prototype of the integral system has even surpassed the expectations of our customers,” says Willy Löffler. “There are now more than 200 systems in operation, which demonstrates that propane is absolutely qualified for mass production today.”
Cascade system cools hops in the Hallertau region
As one of the world’s largest hop traders with its own production, Hopsteiner based in Mainburg (Hallertau) relies on natural cooling. Their old R404a refrigeration system was to be replaced by a larger cold brine system with 130 kW.
To process the sticky hop cones mechanically, it needed temperatures as low as -35˚C. Based on this, Robert Baust of Robert Schiessl presented a cascade system with CO2 and propane. The decisive factor was the future-proof, environmentally friendly overall package solution with low operating costs. Moreover, the investment costs balanced out in a short time, thanks to the statutory subsidies.
Since 2009, the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) has been funding the renovation of old refrigeration plants and the construction of new systems by up to 25% of the costs, provided all the prescribed guidelines, such as the use of natural refrigerants, the compliance with a specific TEWI value or a fixed annual power consumption are observed.
To avoid dangerous situations in the event of propane leakage, it was also necessary to take special safety precautions while designing the complex propane/CO2 cascade system, in addition to accommodating the specific characteristics of the refrigerant. Six Bitzer semi-hermetic reciprocating compressors were installed in total, which were designed for propane and subcritical CO2 applications.
The planner also decided to use new microchannel technology from Güntner – a desuperheater for R744, a condenser and a subcooler for R290. These components were made of aluminium and belonged to a new series, which was specially approved for inflammable refrigerants like propane. The key argument was, however, the extremely low refrigerant charge, thanks to this technology.
Despite the subcoolers, a charge of only 44 kilogrammes was needed for the R290 section of the refrigeration plant. Due to all these special components, the system proved to be very efficient and kept the operating costs low. Additional energy benefits were created by speed-controlled compressors with frequency converters and electronic injection valves. The operator was delighted to report remarkable COP values, which were as high as 2.3 at a brine temperature of -38˚C.
“Hopsteiner is so satisfied with the concept that the company has already ordered a second cold brine system with 100kW, of course, with propane,” says Robert Baust of Schiessl.
Other application areas for propane
These practical examples demonstrate that propane systems are environmentally friendly and energy efficient. It is already feasible to make individual customised systems as well as standard series production models.
Today, propane is already established in medium and small capacities up to 100 kW (as in heat pumps or air conditioners in the food retail sector), as well as in logistic cooling with refrigerating capacities of up to 300 kW. The high efficiency of propane applications is a decisive argument to persuade engineers and operators to go for the environmentally friendly alternative.