Ammonia Refrigeration Technology

International Conference
- Ohrid 2011 -

 

ABSTRACTS


OPPORTUNITIES FOR COMBINED HEATING AND COOLING
Andy Pearson

Star Refrigeration Ltd,
Thornliebank, Glasgow, G46 8JW, UK

The concept of heat pumps was first suggested over 150 years ago, and heat recovery from industrial systems and chillers for air-conditioning or process cooling has been used occasionally. However the significant opportunities to combine requirements for heating and cooling have not been exploited to anything like their full potential so far. This paper explains some of the metrics used to assess these systems, including discussion of the shortcomings of the existing methods, and proposes adoption of a common approach to system assessment. The paper then explores some of the opportunities for combined heating and cooling and addresses some of the barriers to adoption of this technology.
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DESIGNING AMMONIA SYSTEMS FOR MAINTENANCE AND SAFETY
Gary Webster

Kraft Foods Global, Inc.,
Madison, Wisconsin, USA

The goal of design and maintenance is to account for the safety of workers and the nearby community given the inherent risks of ammonia. Properly designed, maintained, and operated, these systems can be safe. The examples provided in this paper highlight protective ways of meeting this goal, though there may be similarly protective alternate ways of designing, maintaining, and/or operating an ammonia system.
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LOW CHARGED HERMETIC AMMONIA CHILLERS ARE EXCELLENT OPPORTUNITY FOR AIR CONDITIONING AND INDIRECT REFRIGERATION
Pega Hrnjak

Professor and Co-Director, Air Conditioning and Refrigeration Center,
University of Illinois, Urbana Champaign,
President, Creative Thermal Solutions

This article discusses the options for expanding use of ammonia in densely populated areas by utilizing low charge chillers for air conditioning, refrigeration or high side of the cascade system. The focus is on charge reduction in heat exchangers, especially microchannel condensers, along with use of newly developed hermetic compressors.
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TWO-PHASE FLOW AND BOILING OF AMMONIA IN HORIZONTAL SMOOTH TUBES
John R. Thome, Ricardo J. Da Silva Lima

Ecole Polytechnique Federale de Lausanne (EPFL), Station 9,
CH-1015 Lausanne, Switzerland

The lecture will address our experimental work on observing flow patterns and measuring heat transfer coefficients and two-phase pressure drops for evaporating ammonia flows in a horizontal tube over a range of mass fluxes and saturation temperatures. Some images of the flows will be presented to demonstrate several representative flow regimes. The measured results are discussed with respect to the influence of flow patterns and are also compared to some leading prediction methods. Ideas for future work on ammonia flow boiling are also addressed.
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RECENT DEVELOPMENTS IN PLATE EXCHANGERS – AMMONIA/CARBON DIOXIDE CASCADE CONDENSERS
Zahid Ayub, M. Sultan Khan, Amir Jokar, Tariq S. Khan, Neil Hayes

Isotherm, Inc.,
Arlington, Texas, USA

The use of carbon dioxide and ammonia in low temperature cascade systems is gaining momentum in the industrial refrigeration market. The use of plate exchanger as cascade condenser is a viable option due to the high thermal efficiency and smaller foot print characteristics of such exchangers. There is lack of reliable data in open literature on condensation of carbon dioxide and evaporation of ammonia in such heat exchangers. This paper presents the latest research on condensation of carbon dioxide and evaporation of ammonia in various corrugation angle plate exchangers at different saturation temperature and heat/ mass flux. The data are reduced to generalized empirical correlations to be used as design tool by engineers. It also discusses the mechanical aspects of plate exchanges and their suitability in cascade systems.
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DRY & SPRAY TECHNOLOGY: HIGH EFFICIENT HEAT EXCHANGER FOR LIQUID COOLER, CO2 GAS COOLER, NH3 CONDENSER
Stefano Filippini
LU-VE SpA
21040 Uboldo, Varese, Italy

The new range of large capacity dry coolers and condensers, based on the DRY and SPRAY operating principle, are the result of intense research and development carried out at the laboratories of the LU-VE Group under the supervision of noted scientific consultants from Politecnico di Milano University.
The DRY and SPRAY products represent the most advanced point in the development of dissipaters capable of exchanging great quantities of heat at low temperature, near that of the dry bulb air temperature. The objective underlying the research was to create a product that has the lowest possible impact on the environment and therefore able to allow heat exchange temperatures near the ambient temperature (guaranteeing high COP of the installation) combined with low ventilation consumption.
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AIR-COOLED CONDENSERS IN NH3 REFRIGERATING PLANTS AS AN ALTERNATIVE TO EVAPORATIVE CONDENSERS
Josef Riha, Heinz Jackmann

Guentner AG & Co. KG,
Hans-Guentner-Strasse 2-6, 82256 Fuerstenfeldbruck, Germany

Ammonia plants are designed very often only with evaporative condensers; the designers of these plants frequently forget that the option of using air-cooled condensers exists. The reason for this is mostly that the designers only concentrate on the design point of the plant, on compressor energy consumption and on the operating costs in this point. Their thinking, however, is slowly starting to change and in the last years there was an increased use of air-cooled condensers in NH3 refrigerating plants.
Air-cooled condensers require less maintenance, no water for cooling or chemicals for water treatment are needed. We tried to find answers to the following questions:
- Are state-of-the-art air-cooled condensers the better option compared to evaporative condensers?
- Which influence do increasing water, wastewater and energy prices have on the operating costs of different systems?
- Which influence does the location of the plant (ambient temperature distribution during the whole year) have on the operating costs?
We have analysed these relationships and will give you an overview of the results we obtained. The conclusion is that air-cooled condensers are a real economical alternative to evaporative condensers.
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COMPACT, ENERGY EFFICIENT, LOW CHARGE AMMONIA EVAPORATOR WITH SEPARATOR VESSEL
Rolf Christensen*, Bjorn Sollie
**
*Alfa Laval AB, Rudeboksv.1, 221 00, Lund, Sweden
**Sollie AB, Nordmannavagen 46, 224 75 Lund, Sweden

The paper deals with possibilities to obtain low Ammonia plant charges by minimizing the charge in the evaporator and separator vessel. The focus is on compact exchangers used for ammonia systems like semi-welded and AlfaNova plate heat exchangers. The charge of liquid in different parts of the system are discussed focusing on the evaporator and separator vessel parts such as drop leg, oil pot, inlet and outlet ports in the evaporator, evaporator channels and wet return line as well as the separator vessel itself. The influence of circulation rate and the impact on the charge is discussed with respect to different control methods. The importance of balancing the pressure drop in the wet return line and the evaporator by selecting the control level to obtain correct circulation rate and thus minimizing the charge is also discussed for systems using level controls. A brief discussion is held on the liquid hold up in the evaporator.

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TWO-PHASE FLOW HEAT TRANSFER DURING NH3 VAPORIZATION IN HORIZONTAL SMOOTH MINICHANNELS
Kwang-Il Choi, Maulana Rifaldi, Jong-Taek Oh*, Kiyoshi Saito, Jong Soo Jeong

Department of Refrigeration Engineering, Chonnam National University,
San 96-1, Dunduk-dong, Yeosu, Chonnam 550-749, Republic of Korea

An experimental study of convective boiling heat transfer was conducted with NH3 in horizontal smooth minichannels. The experimental facilities were used to collect data with rigorous study and development. The test section is made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm; the length is 2000 mm each. The minichannels are uniformly heated by applying an electric current directly to the single tubes; all components are well insulated to prevent heat loss. Local heat transfer coefficients are obtained for a heat flux of 10-80 kW/m2, a mass flux of 50-800 kg/m2s, saturation temperatures of 0, 5, and 10 °C and quality of up to 1.0. Nucleate boiling heat transfer contributions are predominant, especially at the low quality region. The reduction of heat transfer coefficients occurred at areas of lower vapor quality with a rise of heat flux, mass flux and saturation temperature, and with smaller inner tube diameters. Laminar flow appears in minichannel flows. A new boiling heat transfer coefficient correlation for NH3 was developed with 9.79% MD and -3.57% AD.
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AMMONIA HEAT PUMP PACKAGE USING WASTE HEAT AS SOURCE
Shuji Fukano, Takanori Kudo, Noriyuki Arata

Mayekawa Mfg. Co.Ltd.,
3-14-15 Botan, Koto-Ku, Tokyo 135-8482, Japan

Not only environmental concerns that make ammonia, one of the oldest refrigerants in industrial use so attractive among old and new users, its excellent thermal properties enables design and installation of systems with high COPs as compared to HFCs. The main disadvantage of ammonia, however, is toxicity, smell and flammability. For this reason, most ammonia refrigeration systems are of indirect type using secondary refrigerants.
A lot of processes in industry as well as district heat supply centers that require heat between 65 °C and 85 °C., use fossil fuels. Particularly, in industrial process, there is a lot of unused waste heat that can be reused as a heat source for heat pumps. Use of waste heat in heat pump applications not only reduces use of fossil fuel but also contributes to energy conservation.
This paper reports on the development and case study applications of ammonia heat pump packages that use heat sources such as condenser sink heat from existing refrigeration plants, exhaust heat from industrial plants, renewable geothermal energy among others to produce hot water with a maximum temperature of 85 °C.
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INDUSTRIAL AMMONIA HEAT PUMPS AND THEIR CHALLENGES
Alexander C. Pachai

Johnson Controls,
Christian X’s Vej 201, 8270 Hoejbjerg, Denmark

Industrial heat pumps systems based on ammonia (NH3) as a refrigerant have gained a lot of attention. In fact ammonia has proven to be an efficient heat pump fluid. The challenge to produce a new heat pump is not without pitfalls and should be considered very carefully. The paper covers considerations taken when designing and planning production of heat pumps for industrial applications.
Main focus is off course including the whole cycle but a lot of attention has to be put on the selection of measures on how to obtain in the most efficient way all heat from the cycle. Also possible heat sources are discussed. There are a number of low hanging fruits that are very often not included in the considerations.
How can heat pumps be used in plants where there is also used other sources for heating such as gas and oil? Are ammonia heat pumps competitive with these systems?
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UTILIZATION OF INDUSTRIAL LOW-GRADE WASTE HEAT BY MEANS OF NEW EMERGING HIGH-TEMPERATURE HEAT PUMPS
P. Brondum*, M. Markussen*, L. Reinholdt**
*Grontmij | Carl Bro A/S, Dusager 12. DK-8200 Aarhus N, Denmark
**Teknologisk Institut, Kongsvang Alle 29, DK-8000 Aarhus C, Denmark

A project supported by the Danish Energy Agency has the objective to accelerate the implementation of new large (> 500 kW) high-temperature heat pumps by means of full-scale demonstration.
High temperature is here defined as above 85 °C water temperature. In this project only natural refrigerants are investigated.
Although many other factors besides heat pump technology influence the feasibility of such technology, these new products will through the combination of high output temperature, refrigerant type and size of commercially available heat pumps, dismantle some of the existing heat pump barriers.
First phase is to examine 4 different suitable refrigerants (and unit types):
• R717 in a Vilter/Star unit.
• Hybrid (combination of R717 and R718)
• R744
• R718
The purpose of this examination is to make a map of which refrigerant is preferable for given conditions.
The project group consists of the Danish Technological Institute (DTI), Industrimontage, Arla Foods, Thise Dairy, Århus Abattoir, SPX AVP and Grontmij | Carl Bro.
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DESIGN AND TEST OF A DOMESTIC HEAT PUMP WITH AMMONIA AS REFRIGERANT
Behzad Monfared, Bjorn Palm
Royal Institute of Technology,
Brinellvagen 68, Stockholm, 10044, Sweden

Among alternative refrigerants, ammonia with zero Ozone Depleting Potential (ODP) and Global Warming Potential (GWP), and favorable thermodynamic properties is a sensible choice as a replacement for the synthetic refrigerants, which are powerful greenhouse gases.
In this paper, the results of experiments done on a new ammonia water-to-water heat pump prototype at different evaporation temperatures and compressor speeds are reported. The heat pump is designed to deliver 7 kW heat at evaporation temperature of -5°C and condensation temperature of 40°C. The hot discharge gas from compressor is utilized to provide sanitary hot water, and the rest of the heat is used for preheating the tap water and space heating of a single-family house. The compact design of the heat pump helps reducing the refrigerant charge. To reduce the charge further and to prevent oil accumulation at the bottom of evaporator, a minichannel aluminum heat exchanger is used as evaporator.
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THE USE OF THE GWP INDICATOR IN REFRIGERANT SELECTION
Lambert Kuijpers
Technische Universiteit,
Eindhoven, The Netherlands

Today there is more interest than ever in the metrics of the GWP and climate indicators than ever. The EC F-gas Directive requiring suitable refrigerants for mobile air conditioning in Europe below a GWP 150 limit, the emphasis on the low GWP of natural refrigerants, the development of low-GWP unsaturated HFCs (also called “HFOs”) as alternatives for saturated HFCs, the explicit mentioning of climate friendly alternatives for HCFCs in the manufacturing conversion in developing countries, this all has caused that the metric GWP and the definition “low-GWP” and “high-GWP” have entered the discussion on refrigerant and equipment selection. If available and applicable, substitution of HCFCs in developing countries should preferably be to low-GWP alternatives and policy has directed substitution plans to be subject to environmental considerations including climate, with a possible financial “bonus”. This paper aims at the clarification of the GWP as an indicator via the radiative forcing parameter. It describes relevant Decisions of the Parties to the Montreal Protocol on climate relevance and on low-GWP technologies and refers to studies that have tried to define where the limit for “low-GWP” could be. It summarises the aspects of indicators used for equipment operation. It then summarises the climate impact of the 2007 decided HCFC phase-out and presents some concluding remarks on the use of “low-GWP” in relation to natural refrigerants and how equipment refrigerant choice optimisation could be done.
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THE CLIMATE IMPERATIVE OF BASING POLICIES ON THE 20 YEAR GWP OF HFC REFRIGERANTS
(Discussion paper)
Janos Mate (Greenpeace International)
David Kanter (Princeton University PhD Candidate)

The intent of this paper is to reignite the discussion on the climate benefits of basing policies on the 20 year global warming potential (GWP) of refrigerants rather than on the current standard of 100 year GWP. The following is discussed:
• The need for a global phase out of HFCs,
• The rationale for basing policies on the 20 year GWP of HFC refrigerants,
• The classification system of refrigerants as having HIGH or LOW GWP needs to be simple, functional and reflect a high level of environmental ambition,
• Further required research regarding the climate benefits of using the 20 year GWP of HFC refrigerants.
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ENERGY AND CO2-EMISSION REDUCTION IN INDUSTRIAL AMMONIA REFRIGERATION: AN END-USER PERSPECTIVE
Rene Van Gerwen

Unilever Engineering Services,
Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands

Unilever, one of the largest fast moving consumer goods companies in the world, is also one of the largest end-users of industrial refrigeration. Unilever publically launched their Sustainable Living Plan at the end of 2010: Whilst aiming to double the growth of the company, the goal is to halve the impact on water, waste and greenhouse gases (GHG) per consumer use across the lifecycle of the products. Manufacturing sites represent only 3% of the greenhouse gas footprint; however Unilever is directly responsible for this. The manufacturing carbon footprint, requires a robust implementation plan which has been developed, including concepts for new ‘’green’’ factories and production lines, production process improvements, use of renewable energies, and improvements in existing manufacturing sites. Supporting benchmarking techniques have been investigated, but currently appear not to be practical as main improvement driver for existing manufacturing sites due to the wide variability of parameters. A sophisticated system using a large number of detailed improvement levers has been chosen as most appropriate to drive improvement. An assessment in each manufacturing site of current status on each lever, using a scoring scale of four stages of excellence, results in qualitative and quantitative improvement potentials for each lever. For industrial refrigeration energy and GHG, ten improvement levers have been identified, and saving potentials quantified. These levers cover the whole improvement range, from minimising refrigeration loads, optimising operational conditions and settings, advanced control strategies, efficient designs and components, refrigeration system heat recovery, up to implementing advanced energy-efficient technologies like heat pumps for upgrading condenser heat, or the use of tri-generation.
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LOW CHARGE AMMONIA AIR-COOLED CHILLERS WITH MICROCHANNEL CONDENSER
F. Aloisio, G. Del Gobbo

ZUDEK srl,
Strada per i Laghetti 9, Muggia, 34015, Italy

This paper shows a case of study for the methods and solution to reduce ammonia charge in an air cooled chiller for air conditioning application (water 11°C/6°C) till 900 kW of cooling capacity, having at the same time high efficiency, for air ambient condition from -20°C to +45°C. Aluminium microchannel condenser and flooded evaporator are used to achieve this result. To optimize the performance in partload condition, screw and reciprocating compressors used have variable speed control while fans for condensation are operated by permanent magnets motors equipped with VFD.
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A CONCEPTUAL STUDY OF AN INVERSE NH3 TO CO2 CASCADE FOR SIMULTANEOUS COOLING AND HEATING
Klaas Visser

KAV Consulting Pty Ltd,
PO Box 1146, Kangaroo Flat, Vic, 3555, Australia

It is a well known principle that the COP of refrigeration compressors is inversely proportional to their compression ratio. Applying this principle to a cascade system where the ammonia refrigerant condensing is effected by evaporating CO2, i.e. the reverse of a conventional CO2 to ammonia cascade, means that the COP of the ammonia compressor will increase with a reducing Saturated Condensing Temperature (SCT). It also means that the CO2 Saturated Suction Temperature (SST) will need to reduce at the same time to effect the condensing of the ammonia at a lower SCT. Thus the COP of the CO2 compressor reduces as the ammonia compressor COP increases and vice versa. Herein lies an energy consumption optimization problem. There is a point where the combined energy consumption of the two compressors is a minimum. Attention is also drawn to the sharply reduced energy consumption of the first stage cascade ammonia compressor, which performs a cooling function at a much increased COP due to the reduced SCT, and the reduction in parasitic energy consumption of the evaporative condenser fans and pump and the consequent reduction in cooling water consumption. Frequently CO2 global warming emissions are also reduced. The overall thermodynamic efficiency of the system may be further enhanced by pre-heating the water to be heated by heat recovery from the ammonia compressor discharge.
The advent of CO2 compressors with SST of +15°C and discharge pressures up to 140 bar opens the prospect of retrofitting efficient CO2 heat pumps to existing ammonia refrigeration systems at food processing plants. This also offers the prospect to build highly efficient CO2 refrigeration systems with a heat pump stage at high SST which is the SCT of the first stage refrigeration plant. This aspect is also examined briefly.
Finally, the CO2 heating systems are compared with single and two stage heat pumps added to the discharge of industrial two stage ammonia refrigeration plants.

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ENERGY SAVING TECHNOLOGIES IN AMMONIA REFRIGERATION APPLICATIONS USING WELL DESIGNED PUMP CIRCULATION SYSTEMS
Ramesh Paranjpey

ARTI
Pune, India

This paper presents a case study of refrigeration plant designed for a customer in India, using liquid ammonia pump circulation system. At the time of designing and selecting the equipment for this particular project the author had to struggle to get satisfactory design guidelines. The detailed information is not readily available on whether to use hand expansion valves or flow control valves, what is the ideal pump discharge pressure, what should be the temperature difference between inlet and outlet of evaporator, how to adjust optimum flow etc and it forms part of the system design. This paper is presented with a view, to give some readily available guidelines for the people who wish to design efficient pump recirculation systems. This paper is based on the design of actual system already commissioned and working satisfactorily for last 4 years.
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SAFE USE OF AMMONIA AS A REFRIGERANT IN URBAN AREAS
Hans T. Haukås

Consulting engineer,
Lingavegen 225, N-5630 Strandebarm, Norway

Non-industrial use of ammonia as a refrigerant has shown an increasing trend during the last 10-15 years, especially in the Nordic countries, along with increasing pressure on the HFCs. Ammonia use in populated areas requires additional safety issues to be addressed. In the paper a strategy for safe use of ammonia is discussed, including methods for minimising ammonia release and methods to minimise the consequences of a release. Provided that realistic release scenarios are analysed and relevant measures taken to minimise identified hazards, it is the author's opinion that ammonia can be safely used for practically any purpose where it is found of interest technically.
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ROMANIA – AMMONIA TRADITIONAL USER - BARRIERS & OPPORTUNITIES EU REFRIGERATION AND AIR CONDITIONING LEGISLATION IMPLEMENTATION
Gratiela M. Tarlea

Technical University of Civil Engineering,
Bd. Pache Protopopescu nr. 66, Bucharest, 021414, Romania

This paper presents a study of the Romanian line up to the environment, refrigeration and air-conditioning EU legislation with the recommendation of using ammonia as a very eco-efficient alternative.
The establishment of a second version of Code of Practice (CoP 2) in this field is part of the work presentation. The CoP 2 was developed and finally agreed upon by relevant representatives from the trade and relevant authorities.
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ECONOMIC OPTIMISATION OF REFRIGERATION SYSTEMS AT THE DESIGN PHASE
Jakub Pietrzak

ZC FROST,
ul. Wojska Polskiego 4, 89-430 Kamien Krajenski, Poland

During design process of refrigeration installation, the designer, in consultation with the investor, chooses between higher investment expenditure, allowing in the future for decrease in exploitation cost of the system, and cheaper solutions at the manufacturing phase but more expensive during operation. This kind of dilemma also occurs at the phase of system modernization. The final choice is made on the economic grounds. The choice and application of economic criteria in order to determine the purpose of incurring additional costs for changes in the designed or already working installation will be called economic optimisation.
In this article the author presents potential areas being subject to economic optimisation. The areas of high risk in the refrigeration system must be analysed from the perspective of subsequent exploitation and service costs. Respective criteria that facilitate taking investment decision will be also formulated.

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ELIMINATION OF WET RETURN LINES IN AMMONIA SYSTEMS
A. Monsted, C. Madsen, L. Reinholdt, P. Schneider
Danish Technological Institute,
Kongvangs Alle 29, 8000 Aarhus C, Denmark

The objective of this project is to reduce the energy consumption in industrial refrigeration and freezing systems that use ammonia as refrigerant by removing the pressure loss in the wet return from flooded evaporators.
The target is to reduce the energy consumption by 10% compared to existing systems corresponding to energy savings of 30 GWh/year in Denmark alone. The project aims at industrial refrigeration and freezing systems, and the project propose new methods to lower the energy consumption by introducing new technology in new as well as existing systems.
Project objectives:
- Determine future ammonia low-temperature plant design
- Reduce energy consumption
- Increase evaporator efficiency
- Reduce pressure loss by eliminating the wet return line
Ammonia properties in low-temperature applications:
- 0.1 bar pressure loss in the suction line corresponds to 2K at te=-35°C
- 2K improvement on the suction temperature gives a COP improvement of approximately 8% for a one-stage ammonia compressor.
Apart from eliminating the pressure loss, the optimisation could also increase the evaporator capacity and significantly reduce the necessary ammonia charge in the system. Laboratory tests and measurements were carried out during 2009 and 2010.
This paper only describes part of the work that has been carried out in the course of the project and selected results are shown for the plate heat exchanger only.
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A THERMODYNAMIC APPROACH OF MECHANICAL VAPOR COMPRESSION REFRIGERATION COP INCREASE
Mihail-Dan Staicovici

S.C. VE & IPAE S.R.L., 81 B Mihai Eminescu str., fl. 4, apt. 9, 020 072 Bucuresti 2, Romania

Part I: METHODS AND IDEAL LIMITS
The two-part work proposes two new thermodynamic methods for compression cooling cycle effectiveness increase. Both stem of recovering the discharge gas heat. The first converts it in mechanical work (TWRC) which diminishes the initial cycle work input, while the second (TTRC) converts it in cooling effect, which is added to cycle initial one. In this work, both methods principles are schematically presented and theirs ideal thermodynamic limits are made known by two proved theorems. They show the TWRC method ideal application leads to the isothermic compression, while the TTRC one ideally performs better then TWRC.

Part II: THERMAL TO WORK RECOVERY METHOD APPLICATIONS

The work proposes the TWRC thermodynamic method for increasing compression refrigeration cycles effectiveness. The method application is illustrated by schemes running with single, two-stage and multi-stage compression, for the air conditioning, normal and industrial refrigeration. According to the proposal, the compression refrigeration should stimulate the compressor operation with high temperature discharge gas and the conversion of its heat into work, rather than using an additional compression work for limiting the discharge gas temperature, as it is happening today in the two-and multi-stage refrigeration. The schemes operation have been modeled. The model results emphasize a reasonable feasibility of the single-stage, but the three-stage and especially the two-stage compression are the most feasible, enjoying a great potential in the refrigeration COP increase, and therefore in the primary energy savings and carbon footprint reduction (~ 50 to 100 percent and more).
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THERMODYNAMIC PROPERTIES OF AMMONIA BY MOLECULAR SIMULATION
J. Vrabec*, G. Guevara-Carrion**, C. Engin**, T. Merker**, B. Eckl**, H. Hasse**

*University of Paderborn, Warburger Str. 100, 33098 Paderborn, Germany,
**University of Kaiserslautern, Erwin-Schrodinger-Strasse 44, 67663 Kaiserslautern, Germany

The success of process design in chemical engineering and energy technology depends on the availability and accuracy of thermodynamic properties. In recent years, molecular modeling and simulation has become a promising tool to accurately predict thermodynamic properties of fluids. Thermodynamic data can accurately be predicted with molecular models that are based on quantum chemical calculations and are optimized to vapor-liquid equilibrium (VLE) data only. This approach is applied to ammonia here, studying a wide range of properties and thermodynamic conditions. In addition to static properties, the self-diffusion coefficient, shear viscosity and the thermal conductivity are determined. The employed molecular model is based on one Lennard-Jones site and four point charges. Furthermore, the influence of the intramolecular degrees of freedom on the VLE is studied, showing that angle bending plays an unexpectedly large role in the liquid state, because of a significantly enhanced dipole moment.
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EXPERIMENTAL INVESTIGATION OF A NEW RESORPTION CYCLE USING AMMONIA AS REFRIGERANT
K. Helle*, M. Morschel*, S. Peil*, T. Weimer**, S. Haep*

*Institut fur Energie- und Umwelttechnik e.V. IUTA, Bliersheimer Str. 60, 47229 Duisburg, Germany
**Makatec GmbH Siemenstr. 3, 71149 Bondorf, Germany

Using the resorption principle and two solvent loops a new advanced absorption chiller with 1-2 kW cooling power has been developed. In contrast to classical absorption design strategies the hot ammonia gas is not condensed but absorbed in a second solvent loop. Instead of evaporation the absorbed ammonia is desorbed to produce cooling energy. Using two solvent loops a rectification is avoided. The reduced pressure compared with pure ammonia evaporation allows for the application of commercially available and inexpensive plastic raw materials. The construction method makes compact plants possible, thus enabling mobile applications in near future.
Design and experimental results of a prototype with 1-2 kW cooling power will be presented along with the start-up strategy and process stability. Its advantages over existing technology will be discussed.
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A NEW AMMONIA/LITHIUM NITRATE ABSORPTION CHILLER FOR SOLAR COOLING APPLICATIONS
M. Zamora, M. Bourouis, M. Valles, A. Coronas

CREVER-Universitat Rovira i Virgili,
Av. Països Catalans, 26 – 43007 Tarragona, Spain

The ammonia/lithium nitrate mixture has been proposed in the open literature as a suitable pair for absorption cooling systems driven by low-temperature heat sources, which makes it an interesting option for residential solar cooling applications using flat panels. This working pair presents a lower risk of crystallization than water/lithium bromide at high temperatures in the absorber and condenser, allowing safety operation of the chiller at high heat rejection temperatures. This is essential for hot climates such as the Mediterranean in which high solar radiation and high cooling demand are coincident at the same daily hour with high ambient temperatures.
A new small capacity absorption chiller prototype using ammonia/lithium nitrate as the working mixture has been designed at the Rovira i Virgili University in Tarragona (Spain). A water-cooled and an air-cooled compact prototypes have been manufactured and tested in a test bench. A patent has been applied for the configuration of the new absorption chiller using brazed plate heat exchangers (BPHE) in the main components and ammonia/lithium nitrate as the working fluid together with a new design of the solution distributor in the absorber and the integration of a finned tube heat exchanger dry-cooler for the condenser and absorber heat rejection.
This paper reports the cooling capacity and COP measurements in the test bench of both prototypes under the following test conditions: medium heat rejection temperature between 30 and 41°C, chilled water temperature of 8°C and 15°C, and driving hot water temperature at 85, 90 and 95°C.

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THE FORMATION OF NON-CONDENSABLE GASES IN AMMONIA/WATER ABSORPTION HEAT PUMPS MADE OF STAINLESS STEEL - LITERATURE REVIEW AND EXPERIMENTAL INVESTIGATION
H. Moser, G. Zotter, O. Kotenko, R. Rieberer
Institute of Thermal Engineering, Graz University of Technology,
Inffeldgasse 25/B, Graz, 8010, Austria

Highly efficient ammonia/water absorption heat pumping (AHP) processes (e.g. the GAX-process) require a high desorption temperature level of e.g. 200°C and above. At these conditions the formation of non-condensable gases can take place, which can be dedicated to two chemical processes: corrosion of steel and thermal decomposition of ammonia.
Within a research project the possible use of stainless steel components at high temperature level has been investigated. Tests with an absorption/desorption test rig operating at temperatures up to 290°C as well as corrosion tests using autoclaves at temperatures up to 220°C have been performed. The produced non-condensable gas has been analysed using gas-phase chromatography in order to identify the responsible chemical process.
The results show a large initial corrosion rate which decreases with time. This may be explained by a passivation process of the steel surface. At all tests the carbon steel (ST37) autoclaves has shown significant lower corrosion rates compared to the stainless steel components. Regarding the thermal decomposition no dissociation products has been detected up to a temperature level of 290°C.

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THERMAL CONDUCTIVITY OF AMMONIA-WATER
Y. Cuenca, A. Vernet, M. Valles

University Rovira Virgili,
Avda. Països Catalans 26, Tarragona, 43007, Spain

In the last years there has been an increasing interest in energy saving and protecting the environment. Due to these factors the use of NH3-H2O absorption refrigeration systems driven by waste heat or solar thermal energy has been favoured. Many researchers have investigated how to enhance the absorber performance since it is the most critical component in the cycle. To calculate heat and mass flow rates in the absorber it is necessary to know the thermal conductivity of the NH3-H2O. Usually, thermal conductivity of ammonia solutions at different concentration (from 20 to 60 %) and at temperatures ranging from 35 to 50ºC are needed. Unfortunately, the experimental data available from the literature shows remarkable inconsistencies.
In this study, a transient hot wire apparatus was set to measure thermal conductivity of NH3-H2O. The measurements were made with a platinum wire coated with a Teflon insulation layer. The measured values of thermal conductivity were compared with data reported in the literature. The reliability and accuracy of the experimental method was confirmed with measurements on pure Water and Water-Lithium Nitrate with well known thermal conductivity values.
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USING AMMONIA-WATER ABSORPTION COOLING SUBSYSTEM IN BCCHP
V. Popa*, C.L. Popa*, Al. Serban
**
*“Dunarea de Jos” University, 47 Domneasca Street, Galati, 800008, Romania
**Transilvania University, 29 Eroilor Avenue; Brasov, 500036, Romania

Building combined cooling heating and power (BCCHP) systems tend to become a good alternative solution for energy demands. For a good efficiency of the system, it is indicated to use renewable energy source. In this paper a trigeneration system for a detached house, including the option of so- called solar cooling with solar collectors, is presented. Pellets and solar energy will be used for activating the system. The different alternatives for system structure are presented. For cooling demands an absorption ammonia-water chiller is adopted. A detailed structure of the system is presented. The purpose of this work is to demonstrate that thermally activated cooling technologies are attractive alternatives that not only serve the need for air-conditioning, refrigeration, and augmenting prime movers, but also can meet the demand for energy conservation and environmental protection.
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