2013 IIAR Technical Papers
 Colorado Springs, CO
35th Annual Meeting

Prospects of Ammonia Based Ocean Thermal Energy Conversion (OTEC) Systems
Author:  Zahid Ayub, PhD, P.E. and Samuel Sami PhD, P.E.

This paper explores the potential use of ammonia in Ocean Thermal Energy Conversion (OTEC). Different types of advanced heat transfer equipment are discussed for use as vaporizer, condenser and regenerator. Pros and cons of each option are briefly discussed. An overall comparison between ammonia and R-134a based system is presented using a low temperature Rankine cycle.

A comparative analysis of various components of the cycle using ammonia and R-134a under the same input conditions at the evaporator and condenser showed that ammonia has better heat recovery efficiency compared to R-134a. Furthermore, the ammonia cycle has significantly less mass flow rate compared to R-134a, which results in much smaller system compared to that of R-134a.
Ammonia in Traditional HFC Territory: How Does It Compare?
Author: Stefan S. Jensen

During the lead-up to the historic passing of the Carbon Tax Bill in the Australian Senate on the 11th of November 2011, refrigeration plant users in Australia explored ways of minimizing the impact of this new legislation. Not only does the legislation assign a price on carbon pollution thereby increasing electricity costs. It also includes a special levy on hydrofluorocarbon (HFC) refrigerants. The latter has increased the retail price of HFC’s by 300 to 500% as of July 2012. There are several pathways available to Australian refrigeration and air conditioning plant users of avoiding the impact of the levy on HFC refrigerants. It has been a common misconception that these pathways are generally characterized by a capital cost penalty and lack of acceptable benefit(s) in terms of return on additional investment. By way of practical, real life comparisons, this paper details the end-user business benefits associated with giving ammonia a chance in those medium size applications, which prior to the advent of the Carbon Tax Bill were reserved for HFC refrigerants. These real life comparisons are based on four dual stage ammonia refrigeration systems in different geographical locations in Australia ranging from temperate to subtropical environments. The plant designs are characterized by the application of a range of relatively innovative design concepts including automatic ambient air defrost in frozen storage facilities, automatic oil return and oil distribution to the compressors, office air conditioning by means of ammonia refrigerant, variable speed drive semi-industrial and industrial reciprocating compressors, employment of secondary refrigerant in chilled storage rooms, automatic venting of ammonia vapours from frozen storage rooms in the event of leaks, floating evaporating and condensing pressures and so on. The facilities described would traditionally have been reserved for HFC based refrigeration systems. This is commercial reality based on plant capital costs, plant simplicity, the cost of electrical energy and the cost of maintenance. The paper describes the decision process on the part of the four end users that led to a departure from traditional thinking and what the practical and commercial consequences have been of a decision in favour of natural refrigerants and high energy efficiency plant design. In the case of one particular end user, the paper will compare the annual energy consumption of two facilities that are almost identical in terms of floor area and refrigerated volume, but where the two facilities are serviced by two different types of refrigeration systems. One plant is serviced by a traditional HFC based refrigeration system, the other by a new generation ammonia based refrigeration system.
Design Methodology and Impact of Cross-flow Heat Exchangers in Refrigeration and Air Conditioning Systems
Author:  Dr. S Zahid H. Rizvi, PhD, C. Eng.

This paper discusses the design of heat exchangers’ for refrigeration and air conditioning systems and also the use of extended surface heat transfer for these heat exchangers. Cross-flow heat exchangers are extensively used in refrigeration and air conditioning applications. The basic design includes a heat exchanger coil-block located in an airstream for cooling and heating purposes. Several construction options are available, including: (1) various spaced fin coils; (2) electric, hot gas or water defrosting; (3) fan(s). Also heat exchangers can be designed for low air velocity, standard velocity and as sloped unit evaporators.

The size and cost of the heat exchanger is dependent upon the heat duty, the allowable pressure drop and the geometry of the heat transfer area. Often one heat transfer resistance within the overall heat transfer dominates and this determines the amount of surface area required for the duty. The dominance of this resistance is often broken by the use of extended surface (fins), which will result in a lower surface and hence smaller heat exchanger. The extended surface performance can be predicted by a number of indicators: fin effectiveness, fin efficiency, enhancement and augmentation. This paper will also consider which, if any, of the above performance indicators are the best and the design methodology for the heat exchangers.
Leveraging Energy-Efficient Lighting Technologies to Reduce Waste Heat and Operating Costs
Author: Aaron Raftery and Kelsey Cummings

In food processing facilities operating continuously, the lights are always on—making lighting related energy costs a significant operating expense, and efficiency upgrades a source for substantial savings. Inefficient lighting also contributes unnecessary waste heat to a facility, taxing the cooling system and further adding energy costs. A properly designed energy-efficient lighting project in a typical food processing facility with refrigerated spaces can reduce lighting related energy costs by up to 90%, with an additional 30-40% savings from reduced waste heat.

In order to achieve this level of savings, it is crucial to match appropriate lighting technologies to the various applications that exist within a processing facility. In refrigerated and freezer warehouse spaces, LED lighting far outperforms HID and fluorescent technologies. In open areas with ambient temperatures above 35°F (2°C), such as processing spaces and refrigerated truck docks, an LED lighting system’s benefits over high efficiency fluorescents tend to diminish—in these cases high efficiency fluorescents are generally the most cost-effective option.

This paper outlines the current state-of-the-art lighting technologies and design recommendations for food processing facilities, while detailing costs, typical ROI and benefits posed by each in the different applications.
Ice Rink Case Study: Comparing a Transcritical CO2 Direct System Against an Ammonia Heat Recovery System.
 Author: Dave Malinauskas

The re-emergence of Carbon Dioxide as a refrigerant provides another alternative for ice rink refrigeration systems. This is a natural extension of Transcritical supermarkets which are gaining popularity in Europe. When operated transcritically, carbon dioxide can take advantage of the waste heat in the refrigeration process as it has very high discharge temperatures. This heat can offset the energy required for building heating applications. This technical paper will present the results of a case study which compares the energy consumption of three types of refrigeration systems; a basic ammonia refrigeration system with no heat recovery, an Ammonia heat-recovery system, and a Carbon Dioxide Transcritical heat recovery system. In each case, the operation of the refrigeration system will be optimized based on ambient conditions. The analysis will calculate the energy required to refrigerate the ice sheet, and will calculate the energy required to heat the building after the waste heat from the refrigeration process is recovered. And finally, this comparison will be done for multiple cities in North America, which represent a diverse cross section of annual ambient conditions.
Case Study: Use of Dispersion Modeling Software in Ammonia
Author:  Martin L. Timm, P.E.

Sophisticated software is available commercially to model outdoor dispersion of pure and mixed gases such as ammonia from pressure relief valves, or ammonia-air mixtures from machinery room ventilation systems. The software is available from multiple vendors and is widely used in the chemical process industry, but is less commonly used in the refrigeration industry. This software can provide important information to building designers and owners as input to the decision-making process. It can show how decisions regarding the location, orientation, elevation, and velocity of ventilation discharges to atmosphere can influence the dispersion of leaking ammonia and the downwind concentration at points of interest. It can also be used to evaluate possible benefits to locating ammonia equipment inside of a properly ventilated machinery room vs. locating the equipment outdoors. This paper documents a case study of a hypothetical machinery room along with atmospheric dispersion model results for various design options. The design options include indoor vs. outdoor location of a vessel, horizontal vs. vertical discharge of machinery room exhaust, and low-velocity vs. high-velocity machinery room exhaust. It also shows the potential reduced impact to downwind areas as a result of recent standard changes that have increased dilution by increasing the emergency ventilation rate for machinery rooms from 12 to 30 air changes per hour.
Heat Transfer Rates & Refrigeration System Performance
Author: Leo A. Daly

Heat transfer rates are a fundamental factor in determining the performance of the refrigeration system. Applying basic refrigeration principles to heat transfer rates, we can accurately predict the effect on the remaining elements, system efficiency, and the refrigeration components. This paper provides a simple method, using tables and graphs, to assist in selecting set-points and equipment with the ideal heat transfer rates for enhancing the performance of a system. The topics of frost and flow regime are introduced, as they relate to the heat transfer characteristics of any fluid. To illustrate the effects of heat transfer rates, multiple examples have been provided in the Appendix.
Proper Application and Sizing of Metering Devices for Ammonia Refrigeration
Author: John Yencho

This paper will cover four main subjects: 1) the origin of valve sizing equations, 2) the manner in which these equations are applied to industrial refrigeration valves, 3) how proper application of these equations can be utilized to improve performance of the valves, the safety and efficiency of the system, and 4) general guidelines on pipe sizing, with particular attention to applications in ammonia refrigeration. This paper is intended to provide guidance and a general resource refrigeration system design.

2013 Programa en español

Movimiento y manejo de amoníaco líquido y aceite dentro de sistemas de refrigeración
Author:  Silvio Toro

Este trabajo explica la transferencia de amoníaco líquido y aceite desde y hacia evaporadores recirculados inundados o de expansión directa; así mismo, plantea diferentes esquemas para drenaje de líquido y aceite desde separadores de líquido o recipientes de presión constante a recibidores de alta. También se plantean los diferentes métodos y diagramas de flujo para transferencia de amoníaco líquido para sistemas recirculados en los lados de alta y baja presión, con utilización de sistemas sin bomba y por medio de impulsión por bomba. Con el contenido de esta conferencia se plantean diferentes esquemas de conexión para resolver problemas de acumulación y drenaje de líquido desde acumuladores de succión, separadores de líquido hacia recipientes de presión constante, así como retorno de aceite a los compresores en las instalaciones de amoníaco.
Estudio de un caso real de golpe hidráulico en tuberías de refrigeración con amoníaco
Author:  David Sanchez Rojas

El correcto diseño de tuberías y arreglos de válvulas para evaporadores alimentados por líquido recirculado de baja temperatura es fundamental para evitar los fenómenos de flujo conocidos como golpes hidráulicos. Estos pueden clasificarse en tres tipos: golpe de líquido por desaceleración súbita, golpe inducido por condensación, y golpe de líquido impulsado por vapor. Todos ellos tienen el potencial de ocasionar fuertes ruidos, movimientos en las tuberías e incluso fracturas debidas a las ondas de presión generadas. Actualmente, en una planta procesadora de vegetales, se están presentando una serie de golpes hidráulicos en un cabezal general de retorno al cual se encuentran interconectados dos enfriadores de placas y que se ha dejado preparado para la adición de un tercero. La intención de este trabajo es identificar los aspectos que pueden evitar la ocurrencia de este incidente, así como presentar recomendaciones para que instalaciones futuras operen de manera más segura y, en los casos donde el diseño lo permita, de forma más eficiente.
Conceptos básicos de psicrometría para aplicarse en proyectos de refrigeración industrial
Author:  Jorge Hernandez

El propósito del trabajo será ofrecer un resumen de los conceptos básicos de psicrometría con el propósito de crear un interés en el tópico en el mundo de la refrigeración industrial. La aplicación de conceptos básicos de psicrometría pueden ser beneficiosos cuando se están diseñando y/o analizando ciertos procesos de refrigeración industrial (nuevos y/o existentes). El trabajo incluirá la descripción de varias tablas psicométricas usadas por diferentes entidades y fabricantes incluyendo la de ASHRAE, con la salvedad de que aunque diferentes en su forma arquitectónica, todas proveen la misma información básica (y los mismos valores) necesaria(os) para analizar cualquier proceso psicométrico.
Ineficiencias térmicas y termodinámicas sobre aspectos energéticos en una planta productora de hielo
Author:  Juana Gutierrez Bautista, Job Castro Montesinos, and Karen Morlin Trejo

El conocer el aprovechamiento energético en los sistemas de refrigeración es uno de los temas de mayor interés, debido a los costos de operación y mantenimiento involucrados en las instalaciones. Teóricamente, se puede reducir entre un 20 y 40% de las ineficiencias de un sistema de refrigeración que abarcan desde cuestiones de un mal diseño a la utilización o manipulación inapropiada de los medios, equipos o accesorios disponibles. El objetivo del trabajo es analizar y cuantificar el consumo de energía desde el punto de vista térmico y eléctrico, determinando el flujo de calor o energía calorífica y trabajo de los diferentes elementos mecánicos para la producción de hielo en bloques y hielo en tubos, para terminar haciendo un par de sugerencias al respecto.
Comparando la construcción de evaporadores de amoníaco ¿Cuál es el major?
Author: Bruce I. Nelson, P.E.

Los fabricantes de evaporadores industriales de amoníaco ofrecen varios tipos de construcción entre los que están: acero galvanizado, tubos de acero inoxidable con aletas de aluminio, tubos de acero inoxidable con aletas de acero inoxidable y tubos de aluminio con aletas de aluminio, así también, un variado número de protecciones contra corrosión. Tratando de decidir cuál es mejor para cierta instalación y/o proceso puede ser confuso y aparece esta pregunta: “¿Cuál es el mejor para mi aplicación?”. Los metales utilizados en cada tipo de construcción mencionado tienen propiedades únicas que afectan al evaporador en términos de rendimiento térmico, el peso, la energía de descongelación, resistencia a la corrosión y el costo. El buen desempeño y la eficiencia energética tienen un efecto directo positivo sobre la rentabilidad de la inversión para la instalación. El peso de los evaporadores puede afectar a la estructura del techo del edificio en el caso de unidades montadas sobre el mismo, especialmente en las zonas de alta sismicidad. En las plantas de procesamiento de alimentos donde los productos químicos de limpieza agresivos están siendo cada vez más utilizados en los evaporadores, el comportamiento apropiado a la resistencia a la corrosión es crítico. El artículo analiza los diferentes tipos de construcción y sus características y hace recomendaciones sobre qué tipo de construcción mejor se adapta a las aplicaciones específicas y entornos operativos.