According to an analysis by the Umweltbundesamt (German federal environmental agency) in 2014, refrigeration alone accounts for 14% of Germany’s overall energy consumption, and is responsible for about five per cent of direct and indirect greenhouse gas emissions. In consideration of national and international climate protection goals, it is imperative that climate-friendliness in the refrigeration sector be improved. An important contribution can be made by using natural refrigerants, such as ammonia dimethyl ether (R723), which is particularly environment-friendly with an ozone-depleting potential (ODP) of zero and a global warming potential (GWP) of eight. It also offers great investment security for operators of refrigeration systems, since the refrigerant bans of the EU regulation on fluorinated greenhouse gases don’t apply to it.

A perfect fit for low refrigerating capacity ranges?
The refrigerant consists of 60% (by mass) of ammonia (R717) and 40% of dimethyl ether (RE170) – a propellant gas, whose refrigerant properties are similar to those of isobutane. Thanks to its azeotropic boiling behaviour, the mixture can be used like a mono-refrigerant. In other words, there is no concentration shift during evaporation or condensation. R723 is particularly efficient in the low-capacity range up to 100 kW. The circulating volume flow rate of the vapour phase is about 150% that of ammonia, which means acceptable pipe cross sections and flow velocities even for lower refrigerating capacities. Also, ammonia dimethyl ether has a higher volumetric refrigerating capacity than ammonia, so it is possible to obtain considerably higher refrigeration capacities with the same quantity of R723. In refrigerating systems tested with both ammonia and R723, the COP (coefficient of performance) improved by seven per cent when using the latter. Besides its energy efficiency, the azeotropic mixture also features a high performance coefficient and good oil solubility. “In principle, ammonia-based cooling systems can be filled and operated with R723,” says Bernd Kaltenbrunner, member of eurammon and CEO of KWN Engineering GmbH. “However, the individual application must always be taken into consideration – this is why the conversion should always be clarified with the individual component manufacturers.”

The performance is achieved with a fill quantity of merely 7.5kg of R723. The condensers are operated with the fully synthetic alkyl benzene oil

The energy efficiency of the azeotropic mixture is complemented by a high performance coefficient and a high level of oil solubility. A further great advantage results in the about 15K lower compression end temperature. This allows the piston compressors to reach a larger temperature stroke and enables the use of air-cooled condensers. R723 is also environment-friendly, cost-efficient, and readily available in sufficient amounts. R723 systems have been in use for many years. All components are available and sold as “ready to plug in” condensing units or chillers. “Another advantage is that the relevant authorities treat R723 cooling system like R717 systems and, therefore, do not require more extensive safety measures,” Kaltenbrunner says. Its low acquisition costs, reliability and future-proof nature make the natural refrigerant a popular choice for planners and operators of refrigerating systems.

An add-on for existing systems
These aspects were also in the focus of a project realised by eurammon member Th. WITT Kältemaschinenfabrik GmbH for Herrmannsdorfer Landwerkstätten, a food-producing company. The family-owned business from Bavaria, Germany, doesn’t only set great store by organic farming and food processing but also makes a point of pursuing a holistic sustainable subsistence strategy. This is why the company, when planning a new refrigerating system, looked into environment-friendly alternatives that were not only durable and energy-efficient but also used natural refrigerants. The idea was for a new cooling system to add to the capacity of the existing one, an ammonia-operated chilled-water system. Herrmannsdorfer Landwerkstätten also wanted the system to be reliable, safe and easy to maintain.

Against this background, Th. WITT Kältemaschinenfabrik installed a chilled-brine compact refrigeration unit, tailor-made for the specific requirements, charged with 20 kg of ammonia dimethyl ether. Using two reciprocating piston compressors, the system has a refrigeration capacity of 64 kW, and is equipped with an evaporator and two condenser fans. Thanks to the combination of R723 as a refrigerant and air-cooled condensation with EC fans, the refrigeration unit can reach a very high energy efficiency under both full and partial load. Despite being completely encased, the refrigerating system can be easily cleaned and serviced, thanks to removable side parts. Equipped with a UMTS modem and a W-LAN connection, the entire system can be monitored via the internet.

A special challenge for the planners and fitters was to install the system on the flat roof of the plant, because this required additional measures during assembly and installation

Lending support to meat processing
The refrigerant also played the leading part in a project of another eurammon member, HKT Huber-Kälte-Technik GmbH. The refrigeration engineering experts from Halfing, Bavaria, are currently supporting ABC Foodmachinery s.r.o., a company based in Bratislava, in a project for one of their clients from the meat-processing industry, and contributed an R723 refrigeration unit for the construction of a new external refrigerating system. The unit has a refrigeration capacity of 135 kW. At the same time, the cooling set is equipped with heat recovery as full condensation. Therefore, the maximum heating power is 180 kW. This performance is achieved with a fill quantity of merely 7.5kg of R723. The condensers are operated with the fully synthetic alkyl benzene oil.

Regarding the conceptual design of the system, two aspects were of particular importance to the client: energy efficiency and low operating costs. Also, the client wanted the new solution to use natural refrigerants, be durable and help reduce CO₂ emissions. A special challenge for the planners and fitters was to install the system on the flat roof of the plant, because this required additional measures during assembly and installation. With this newly installed cooling system, the client now possesses the region’s largest R723- based system for poultry production.

Low- and medium-range applications
Efficient, environment-friendly, energetically advantageous, cost-efficient, and readily available in sufficient amounts: The list of advantages for R723 is long and convincing. The natural refrigerant is especially efficient in the low and medium range of refrigeration capacity – a cooling solution for all kinds of requirements. R723 cooling systems are a good option to operate industrial cooling systems with a natural coolant. “Together with R744 and the hydrocarbons,” Kaltenbrunner says, “this gives us another option to use a more environment-friendly and climate-friendly system technology.”

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