2010 IIAR Technical Papers
 San Diego, CA
32nd Annual Meeting

Effective Water Treatment for Evaporative Condensers
Author: Allan Browning, Mike Sanders, and Dan Weimar

Evaporative condensers are widely used for industrial refrigeration because they are more energy efficient than air cooled systems. However, to achieve these benefits, effective water treatment is required to maintain maximum heat transfer efficiency, minimize water usage, and protect the system from water related problems. Variations in water quality and the design of evaporative condenser systems present unique water treatment challenges that must be addressed on a plant-by-plant basis. On-site maintenance practices also influence the success of water treatment programs. In many facilities, the water treatment program and on-site maintenance practices can be improved to provide better protection and reduce operating costs.
Optimization of Refrigeration Plant Operation Engineering Approach
Author: Sergei Khoudiachov

For years, many professional engineers focused on the design of energy efficient refrigeration plants. Although a well-designed refrigeration plant is the foundation of energy savings, the efficient operation of a refrigeration plant is the ultimate goal of the energy saving process in industrial refrigeration. Through efficient operation, up to 70–80% of total energy savings can be achieved. Ideally a refrigeration plant control should have: • Software to determine optimum set points and optimum operating strategies. • A PLC to implement these set points and operating strategies. There are several PLCs on the market which can properly implement certain set points and operating strategies. But software that is capable of determining optimum set points and optimum operating strategies does not exist because it is very complicated to create this type of software. Who should determine these set points and operating strategies? Typically this job is given to system operators. They have often done their best to optimize the operation of the refrigeration plants but several typical mistakes are often made during the optimizations. To maximize efficiency of the refrigeration plants, optimization should be focused on major energy saving measures. The best way to save energy is to operate refrigeration plants at condensing pressures as close as possible to the optimum pressures. Other energy saving measures that can be accomplished are: optimization of suction pressure, optimization of defrost settings, use of VFDs, optimization of compressor sequencing, and remote tuning. The nuances of each of these ideas is discussed including the misconceptions, hesitance to implement, and solutions to common missteps in the process.
Evaporator Arrangements for Large Scale Cool and Cold Storage Applications
Author: Stefan S. Jensen, B.Sc.Eng. MIEAust, CPEng, NPER

The evaporator arrangements in large refrigerated warehouse facilities need to satisfy a range of objectives, some of which may be conflicting. Focusing on the facility owner, these objectives generally relate to facility utilization, energy efficiency, workplace health and safety issues, operability, temperature uniformity, temperature flexibility, consistency of air movement, capital costs and operating costs including maintenance. In modern large scale cool and cold storage facilities being constructed in Australia, the use of ceiling-mounted induced draught finned air coolers is generally limited to smaller areas, some batch blast freezers and loading docks. Ceiling-mounted induced draught evaporator arrangements will therefore not be discussed. For the main cool and cold storage areas, a variety of penthouse unit and alcove unit evaporator designs have evolved over the last two to three decades. This paper will describe the evolution of a range of such evaporator arrangements. It will attempt to detail the practical experiences associated with each design and focus on the type of design improvements that were made each step of the way, how successful these improvements were in practice and what other improvements can be made in the future. Due to the climatic conditions in most parts of Australia and due to a desire to conserve energy, there has been a general trend away from hot gas defrost and towards automatic ambient air defrost in the evaporator arrangements described in this paper. The ambient air defrost concept employs several automatically operated doors and shutters to direct warmer ambient air over the cooling coil to effect the frost removal while at the same time separating the cooling coil from the refrigerated space. Electric defrost is practically no longer used in large scale refrigerated warehouses in Australia with volumes greater than approximately 15,000 m³ (500,000 ft³) except in some CO2 applications. This is mainly due to energy efficiency and reliability issues and electric defrost will therefore not be discussed. Although the evaporator arrangements discussed in this paper are suitable for most refrigerants including synthetic substances and secondary refrigerants, the applications shown mainly employ natural refrigerants, i.e., NH3 and CO2.
Ammonia Refrigeration Design for LEED Certification
Author: Tom Dosch, PE and Doug Scott

This paper describes how a refrigerated warehouse with an efficient refrigeration design using ammonia can achieve LEED® certification. Development of a sustainable “green” facility with LEED certification includes site considerations, indoor air quality, water efficiency as well as methods and materials of construction used in the building. The largest single category, Energy and Atmosphere, provides an excellent opportunity to utilize advantages of ammonia refrigeration. A facility being built in San Diego employed early and extensive analysis with assistance from utility programs to determine the cost effectiveness for design alternatives and efficiency investments including R-22 versus ammonia, high-rise building and material handling, LED lights, rainwater recovery, water-saving measures and solar (PV) generation. Controls and mechanical equipment were designed to make the entire system “variable capacity.” These design features helped the facility owner achieve LEED Gold certification while holding four times as much product as their existing facility and using half the energy.
Consider Two-Stage Systems to Save Power
Author: Richard A. Corbett, P.E.

In recent years, many low-temperature ammonia refrigeration systems using screw compressors have used single-stage compression to satisfy refrigeration loads in lieu of traditional two-stage systems. This paper compares performance data for both types of systems and estimated operating costs based on total brake horsepower (BHP) requirements for each type of system. The performance data shows that two-stage systems provide significant power savings without significantly increasing system complexity. The data also provides guidance for when to specify two-stage systems over single-stage systems. Performance charts are presented for low-temperature saturated evaporating temperatures ranging. from –20°F to –45°F. The charts show total system BHP requirements and estimated costs for the required total BHP at each low-temperature. Total BHP includes compressor BHP, condenser BHP, and recirculation pump BHP. The typical system used for the comparison is based on 300 tons of low-temperature refrigeration load and 200 tons of high-temperature refrigeration load. The system used for comparison is comprised of one low-temperature re-circulator operating at various low temperatures, one high temperature re-circulator operating at +25°F saturated evaporating temperature, rotary screw refrigeration compressors with thermosyphon oil cooling, and evaporative condensers operating at 95°F saturated condensing temperature. The system loads and operating temperatures are typical of many refrigeration systems.
The Vertical Pipe Sizing Program (VPS 2010): When “Less is More”
Author: David J. Ross and Lawrence F. (Tex) Hildebrand

In the world of ammonia refrigeration, it can sometimes seem that our intuitive sense of how things should work differs from the realities of the internal workings of the ammonia universe. One such example is when dealing with system performance and flow restrictions. As mechanical designer(s) we intuitively think bigger is better or that reduced flow restriction should allow improved performance. As some of our industry's experts have tried to help us understand, this is not always the case. When the real world verifies their counter-intuitive theories it can be a meaningful learning experience for everyone involved. This was the case in a recent low temperature spiral freezer application with a flooded evaporator and surge drum accumulator. According to today's standard safety practices, the surge drum was mounted on the roof with a significant vertical lift required in the suction return line. This same vertical difference provided what proved to be an excessive down force on the liquid supply leg. The application of theoretical liquid return line sizing and liquid feed rate control per Mr. David Ross's spreadsheet program proved the truth that sometimes "Less really is More."
How the PSM Mass and Energy Balance Relates to Your Plant’s Energy Usage
Author: Marcos Braz

OSHA and EPA regulations require that a mass and energy balance be performed and documented on systems that exceed a charge of at least 10,000 lbs. of ammonia. These documents are useful for the safety reasons that are intended by the agencies, but they also help personnel and consultants analyze and easily understand complex systems. Use of the MEB can help to determine if there are shortcomings in facility operations or in the refrigeration system itself. The MEB can also be used to help determine the extent of work required for an addition or retrofit of an existing refrigeration system. This paper explains the development of the MEB documents and how they can be used to help save energy and capital improvement costs and improve operations.
Thermodynamic Effects of Water in Ammonia on Evaporator Performance
Author: Bruce I. Nelson, P.E.

There is increasing interest in operating ammonia evaporators at reduced liquid overfeed rates (less than n=2), down to and including dry expansion (DX). Benefits include: reduced or eliminated liquid pumping power, dry or near dry suction lines, reduced liquid and suction line sizes, greatly reduced charge inventory of ammonia evaporators (as much as 30X reduction for dry expansion compared to pumped ammonia), reduced first cost, etc. A small amount of water (typically 2–6% by weight) is found in most industrial ammonia systems. This water is always concentrated in the low pressure side of the system and has the negative thermodynamic effect of increasing the bubble point of the ammonia liquid along the length of the evaporator circuits. This shift in the bubble point is normally neglected by evaporator manufacturers and designers since the shift is small (only 1–2°F) for pumped ammonia systems. However, as the liquid overfeed rate is reduced below n=2, and particularly in the case of dry expansion, this shift in the bubble point toward the end of the evaporator circuits may easily exceed the initial temperature difference (Entering Air Temperature – Evaporating Temperature), severely reducing evaporator thermal performance. Additionally, the shift in bubble point can “confuse” dry expansion control valves, further reducing performance. These thermodynamic effects of water in ammonia have not been fully recognized or well understood in the past and are the subject of this paper. The author also reviews and recommends methods for managing and removal of water from these systems.

2010 Programa en español

Rutinas de cálculo de potencias frigoríficas mejor adaptadas para la previsión de estrategias de ahorro de energía 
Author: Juan Carlos Lage Soto

Necesitamos que nuestros cálculos rutinarios de potencia frigorífica (mal llamada carga) se hagan con variantes que provean datos más oportunos y completos en el sentido de obtener mejores opciones de impacto en la previsión de ahorro de energía. Todo esto tiene que ver con la visión de los factores estocásticos que intervienen en el análisis de las secuencias e incidencias de las variaciones de las cargas térmicas en el comportamiento real y específico de los espacios sujetos a acondicionamiento de aire o al almacenaje de productos perecederos ya sea en refrigeración como en congelación. La base de lo anterior radica en la reflexión de que a carga evidentemente variable no podemos referir una fuente fija de suministro de potencia, asociada generalmente a arranques muy frecuentes de los equipos provocando con ello una alta demanda de energía, a menos que hagamos a esta más proporcional a la demanda real. La consideración de lo anterior conduce a mejorar los controles de los motores con frecuencia regulada y al uso de compresores múltiples, o, en instalaciones más complejas que sugieren asociación paralela de las demandas de frío; pero todo ello puede y debe ser seleccionado mejor si disponemos de un buen cálculo de la distribución de dicha demanda de potencia frigorífica. Por supuesto, nuestra selección final tendrá efecto no solo en el tamaño, número y cualidades eléctricas y de control en nuestros compresores, sino en obtener una mejor constancia en la temperatura y lograr un mejor control de la humedad relativa.
Doble etapa de compresión contra entapa sencilla de compresión con economizador tipo tanque flash en compresores de tornillo
Author: Víctor de la Fuente García

En sistemas de refrigeración cuando se requieren alcanzar temperaturas de trabajo para congelación de productos (–40°C) o de conservación de productos (–18°C) la tendencia común es utilizar sistemas de compresión en doble etapa. Esto tiene como origen el uso de compresores tipo reciprocantes que tienen relaciones de compresión máximas de 8:1 en amoníaco. Debido a las altas relaciones de compresión que manejan los compresores de tornillo, se puede realizar este trabajo con una sola etapa de compresión. En sistemas actuales se ha visto la tendencia de utilizar un compresor de tornillo de primera etapa o booster y otro de segunda esta o alta etapa, pudiéndose simplificar el sistema con un solo compresor pero con la ventaja de utilizar el puerto lateral o economizador del equipo, logrando consumos eléctricos iguales o menores que los de los sistemas con doble etapa de compresión. Este trabajo analizará desde el punto de vista energético, costos iniciales y de operación un sistema de compresión de doble contra etapa sencilla con economizador, tipo tanque flash.
Revision de criterios en el diseño de aplicaciones de economizadores en compresores de tornillo 
Author: Oscar Gomez

El diseño de Sistemas de Refrigeración Industrial tiene como principal objetivo ofrecer el mejor desempeño de los equipos así como la mejor eficiencia en la operación al menor costo. Una de las aplicaciones más conocidas ha sido el uso del puerto de succión lateral de los compresores tipo tornillo para una carga adicional y la mayoría de las veces esta carga ha sido utilizada para el subenfriamiento de refrigerante) para sistemas de refrigeración industrial, sin embargo, existen restricciones en la operación de los mismos que hace necesario realizar una revisión sobre los criterios de diseño para la aplicación así como las ventajas y desventajas de su uso. El objetivo principal de este trabajo técnico es abordar los diferentes tipos de diseño de economizadores, sus aplicaciones más comunes así como un comparativo de las eficiencias para cada uno de los casos, finalmente, se revisan los criterios para sus aplicaciones y las restricciones que existen para las diferentes aplicaciones en compresores de tornillo.
Dimensionamiento de dos sistema de refrigeración desde el punto de vista Técnico Económico en una aplicación de baja temperatura, con las alternativas de un sistema en cascada y un sistema en doble etapa
Author: Juan Manuel Quintanar Quintanar

En el ramo de la refrigeración industrial, en la actualidad el uso de los sistemas en cascada CO2- Amoníaco ha ido en aumento e importancia como una opción viable para las aplicaciones de baja temperatura, sin embargo, el uso de sistemas convencionales utilizando Amoniaco solo como refrigerante para esta aplicaciones de baja temperatura es más común actualmente. Este trabajo tiene como objetivo presenta los tipos de sistemas comúnmente ocupados en estas aplicaciones y presentar sus ventajas y desventajas tanto en costo de instalación, operación y mantenimiento y poder dar las herramientas para seleccionar uno específico en una aplicación de baja temperatura.
¿Compresor de tornillo o de pistones para aplicaciones de CO2?
Author: Mauricio Quiroga

El uso del CO2 como refrigerante ahora está siendo una posibilidad más común al mirar en nuevos sistemas de refrigeración. Las Compañías están produciendo los productos para refrigeración, los clientes con aplicaciones de Refrigeración Comercial, Industrial, e inclusive Aire Acondicionado están consientes de esta tendencia y algunos proveedores de componentes están desarrollando productos para satisfacer esta demanda. Las restricciones y la consecuente prohibición de utilizar refrigerantes CFC’s y HCFC’s están llegando a ser evidentes a nivel global e incluso el uso de HFC ahora es estudiado en Europa y en USA. También el uso de HFC ahora se está considerando un problema del Salud para los seres humanos y LA EPA (agencia de protección de la energía) en los E.E.U.U. ahora está tomando medidas de cómo ocuparse de este problema en un futuro próximo. Por ejemplo, Dinamarca tiene ya por varios años que prohibió todos los refrigerantes de HFC en sistemas con una carga refrigerante de más de 10 kilogramos. Sera necesario preguntarse, en un futuro al considerar el uso solamente de los refrigerantes naturales como: NH3–amoníaco, CO2– bióxido de carbono, HC – Hidro-Carbonos, H2O-Agua etc. si se prefieren Compresores de Tornillo o Compresores de Pistón (reciprocantes) para alguna Aplicación. Este Escrito describe además de esto, la importancia de incluir las pérdidas de la presión de la planta al comparar sistemas en operación en área sub-critica o inclusive para los sistemas operando en área trans-critica. Ofrece ejemplos del uso de compresores de pistón o de tornillo en plantas del CO2 instaladas como también en área sub-critica como trans-critica. Evalúa por experiencia y desde un punto de vista técnico qué oportunidades están disponibles con CO2, comparado principalmente con el NH3 (y R-22) pero al mismo tiempo observa que tendencias demuestra el mercado cuando es “limitado” para utilizar los refrigerantes naturales No tóxicos, en este caso CO2. La mayoría de la gente tiende juzgar mal las ventajas del CO2 como refrigerante puesto que no observan el sistema completo. Sería muy cerrado el indicar que los sistemas sub-críticos de CO2/NH3