Ohrid ’09: 2nd day key technical presentations

By Sabine Lobnig, May 11, 2009, 11:28 6 minute reading

Safety, efficiency, and new market opportunities for ammonia were among the topics of the technical papers presented at the second day of the 3rd International Conference on Ammonia Refrigeration Technology in the Republic of Macedonia. An overview of the key technical papers presented is provided in this final article.

An extensive list of 32 technical papers was presented at this year’s International Conference on Ammonia Refrigeration Technology conference in Ohrid, which attracted 95 ammonia refrigeration experts from 24 countries. Apart from subjects traditionally discussed, such as improving system energy efficiency and ensuring safe operation, discussions also covered new market possibilities and trends for ammonia through reducing the refrigerant charge and using ammonia in small systems.

The presentations

Semihermetic and Hermetic ammonia compressor packages, Nelson Mugabi, Mayekawa Mfg. Co.Ltd., Japan
In this paper Mugabi reports on the development of semi hermetic ammonia compressor packages coupled with interior permanent magnet motors (IPM). A corrosion resistant magnet for use with ammonia was developed and as a result IPM motors, with better efficiency and less bulky than the conventional induction motors were then also developed. He discusses how ammonia refrigeration systems with CO2 as a secondary refrigerant and with a 55 kW IPM motor as well as a scroll compressor for use with ammonia and with a 15 kW IPM motor have been successfully introduced into the market. Oil miscible with ammonia enabled the development of dry expansion systems. Combined with compact heat exchangers and electronic expansion valves, refrigerant charge was drastically reduced compared to conventional flooded systems. Even in flooded systems, tests showed that miscible oil offers better performance than immiscible oil and minimises refrigerant charge.

Low Charge Chillers Based on Microchannel HXs: Opportunity for Expanding Use of Ammonia, Pega Hrnjak, Professor and Co-Director, Air Conditioning and Refrigeration Center, University of Illinois, US
This paper discusses the charge reduction options in ammonia systems in general and in smaller, low charge chillers in particular, as a means of reducing risks, as well as improving system efficiency and performance. Hrnjak believes that smaller low charge ammonia systems, chillers in particular, used for refrigeration or air conditioning as a part of secondary loop or cascade system provide excellent potential for market penetration of ammonia. The main focus of the paper is charge reduction in heat exchangers and especially microchannel, for which it is shown that they can benefit air cooled ammonia chillers, as the charge would be significantly reduced while maintaining the same heat transfer capability, while also the external volume of the chiller could be reduced. Besides being compact, microchannel heat exchangers are also made from lightweight aluminum, features that make microchannel designs appropriate for use in the automobile industry. New developments in hermetic ammonia compressors by Mycom as well as ongoing work in low charge microchannel condensers and systems with ammonia at Creative Thermal Solutions are further presented.

Making the Case for Heat Pumps with Ammonia and Carbon Dioxide, Andy Pearson, Star Refrigeration Ltd., UK
This paper explains the different ways in which Perkins cycle devices, used to raise the quality of available heat in order to increase its value, are configured and sets out the reasons why they are gaining increased attention at the moment. The author explores the particular opportunities offered by the unusual properties of ammonia and carbon dioxide and considers the prospects for the long term adoption of this technology. Referring to heat pumps as “heat transformers”, Pearson maintains that these offer the opportunity to decouple factory operating costs from external influences. New materials, new equipment design, new processes and new operating cycles offer increased opportunities for process integration and the opportunity should be taken in designing a new facility to maximise the possible interconnections between processes. The investment in heat transformers is worthwhile if it helps to protect the production process from price uncertainty in the supply of energy.

Ammonia Refrigeration Safety Management, Mark Roxburgh, Mercury Technologies Ltd., UK
Roxburgh describes a programme consisting of a number of safety management tools for end-users of ammonia refrigeration systems in Europe that will allow the risk level associated with these systems to be reduced to as low as is reasonably practical. Unlike the US, guidance and requirements regarding safety management in Europe are fragmented throughout multiple national and international codes and standards. Mercury Technologies have, therefore, taken the broad, comprehensive model developed in the US by ASHRAE and IIAR and adapted it for use in EU countries. By carrying out a risk management assessment such as the one described, an owner can be certain that he is meeting all legislative responsibilities.

The Use of Strain Gauge Stress Monitoring Systems on Ammonia Refrigeration Pipework Affected by Underground Mining Surface Subsidence, Jonathan E Fryer, ISECO Consulting Services Pty Ltd, Australia
This paper discusses why flexibility analysis should be carried out on ammonia refrigeration piping systems in a site subjected to unusual ground subsidence, compares the predicted stresses with actual measured stress at a number of piping locations, shows how remedial action reduced actual stresses and provides lessons learnt from strain gauge installation and monitoring at an industrial food processing facility. The author concludes that all ammonia refrigeration piping systems should be subjected to a flexibility analysis, while where the designer has doubt regarding the ability of the system to comply, a comprehensive analysis should be made. The suitability and advantages of using Whesso PSA-5 Pipe Stress Software based on ASME B31.3 & B31.5 for modelling refrigeration pipe stresses under thermal and subsidence loadings is discussed. Finally, the paper discusses how the use of electric resistance strain gauging to measure refrigeration pipe stress changes in a site subjected to unusual ground subsidence has been proven workable.

A New Generation of Ammonia Unit Coolers, S. Filippini and U. Merlo, LU-VE SpA, Italy
The authors discuss how a new generation of coil geometry aimed at performing well under frost formation with proper use of the finned surface was developed thanks to the use of Computational Fluid Dynamics (CFD) Software and extensive testing in the LU-VE laboratory. The surface has several turbulators for perfect aerodynamic configuration. Particular attention was paid to their definitions and a micro-photographic evaluation of frost formation on finned turbulators was made clearly showing frost growth on finned surface. To demonstrate the advantages of using a tube with significantly reduced diameter, two new units in the LSA series (one with high ventilation and one with low ventilation) were compared to 2 market-reference products which are good representatives of the heat exchange matrices used in the ammonia refrigeration sector, the first using a traditional exchanger in galvanised iron, the other using stainless steel tubes and aluminium fins of geometry 50 x 50. The advantages include: i) greater capacity at equal surface area, ii) significant internal volume reduction at equal capacity and surface.

Selecting Evaporative Condensers for Optimum System Efficiency, Rob Vandenboer, Evapco Europe NV, Belgium
This paper reviews the relationship between the compressor and evaporative condenser in an ammonia refrigeration system in terms of system operation and energy consumption. In addition, examples are provided to demonstrate how system efficiency can be optimised by increasing the heat transfer surface area of the condenser and by developing the proper method of operating the condenser and compressor to reduce total energy consumption. The author proposes additional criteria when sizing evaporative condensers: 1) The optimum condensing temperature will yield the lowest energy consumption for the compressor and evaporative condenser; 2) A minimum ratio of base heat rejection per motor power (TR/kW) for an evaporative condenser will provide a starting point for evaluating the total system efficiency. In this way, the evaporative condenser is treated like most HVAC equipment in terms of energy efficiency. Using an efficiency rating for evaporative condensers will provide added energy savings beyond any improvements in system design or system operation.


By Sabine Lobnig

May 11, 2009, 11:28

Related stories

Sign up to our Newsletter

Fill in the details below