Sustainable Refrigeration and Heat Pump Technology Conference - part 2

By team, Jun 18, 2010, 13:29 4 minute reading

This second article reporting on the ‘Sustainable Refrigeration and Heat Pump Technology’ Conference taking place this week at the campus of the Royal Institute of Technology, Stockholm, provides an overview of first-day presentations that focused on CO2 commercial refrigeration, including on integrated waste heat recovery systems for CO2 systems and the development of a transcritical R744 soft serve ice cream making machine.

Development Challenges in CO2 Commercial Refrigeration Systems, B. Olsommer, Carrier Kältetechnik GmbH

Medium temperature (MT) CO2 systems using a transcritical cycle for supermarkets are now offered as standard solutions by Carrier, while the market also requires further energy saving solutions through high efficient integrated heating systems. Waste heat reclaim for heating is already mandatory in Switzerland for example. In that respect, Olsommer presented on energy efficient integrated waste heat recovery systems for CO2 refrigeration. CO2 systems have advantages over conventional refrigerant systems, as, for example, they provide higher discharge temperature, which enables higher secondary medium outlet temperature such as tap water at temperature of 70°C and higher. Furthermore, in transcritical operation, the cooling of the CO2 occurs without the usual latent heat of the condensation process. The continuous CO2 temperature change allows for the installation and controls of two separate heat recovery units in series for two separate water loops, one of which can be used for tap water while the other serves the heating system.

Olsommer presented schematics of the heat recovery modules, consisting of heat exchangers, standard water/brine pumps, CO2 motor-actuated valves and instrumentations for the water/brine and CO2 loops. A smart control system enables a safe and energy efficient operation of the refrigeration and heat reclaim system, with the objective to minimise the sum of electrical and fossil consumptions while securing the cooling capacity. The system allows for up to 86% of waste heat recovered thanks to optimal pressure adjustment, which fulfils 60-100% of supermarket heating demand and therefore allows for substantial reductions in electricity bills compared to systems heating with electricity. Bypassing the gas cooler would enable 100% waste heat recovery into usable heat and this is the way that Carrier will go in the future.

The paper by Olsommer also discusses new non-return safety valves that has been developed to avoid any CO2 discharge in the supermarket area during service. These are installed upstream and downstream of each cabinet group, replacing the functionality of the existing shut off and service pressure relief valves. During system shut downs these valves allow the isolated components to “burp” CO2 when the pressures exceed the pressures in the adjacent lines into the piping system, which is then vented into the medium pressure section and cooled by the low-cost auxiliary cooling system on the receiver or through the main pressure relief valve at the suction side. This valve combination can be placed at all positions where a serviceable area is necessary.

Development of a Transcritical R744 Soft Serve Ice Cream Making Machine, C. Zilio, Università degli Studi di Padova

Zilio presented preliminary results regarding a transcritical R744 soft serve ice cream making machine developed for manufacturer CARPIGIANI and compared it to a baseline R404A “off the shelf” optimised unit (30 L; dispense at -7°C). He explained that the cylinder wall temperature constraint and stringent sanitation requirements posed some design constraints. Moreover, the face area and volume had to be maintained, as well as the same fin spacing, same fan and same air plenum. A two stage semihermetic reciprocating compressor as well as a single throttling for the cylinder and reservoir were chosen. Regarding the air heat exchangers design, the gas cooler, intercooler and evaporator were integrated into one component.

The results indicate that using R744 for this type of application is a viable solution: The R744 unit achieved a constant -7 to -7.5 degrees, while the baseline equipment presented some increase in temperatures. Moreover, in the cylinder side R744 was found somewhat faster. For pasteurization, R744 featured small improvements compared to R404A, for cooldown it was more efficient, while for production the performance was the same as the one of the baseline system.

In the last phase of the project, further optimisation and pre-industrialisation of the system will be carried out. When asked by the audience about the cost implications, the presenter maintained that CARPIGIANI are happy about costs. Indeed the reservoir and cylinder and hence the costs of these components are the same as for the baseline system, while electronics for R744 are widely available. More importantly, as the unit is almost completely in stainless steel for sanitation reasons, the refrigeration circuit is less important for the overall cost. When asked about the need for training technicians to work with the system, he assessed that training for CO2 is indeed needed for all CO2 applications including ice cream machines, bottle coolers etc. Pointing to the need of training of technicians in general, he also noted that in Italy venting f-gases is a common practice. 


By team (@r744)

Jun 18, 2010, 13:29

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