2014 IIAR Technical Papers
Nashville, TN
36th Annual Meeting

Historically, most ammonia refrigeration machinery rooms exhaust directly to atmosphere. While this practice is fine during normal operations, it can leave emergeny responders in a predictment during and following a large liquid ammonia release. This paper presents treatment options and considerations to reduce the ammonia concentration exhaust air before it discharges to atmosphere.

Pressure relief device performance is affected by pressure drop in its inlet and outlet piping system. Recognized and generally accepted good engineering practice and National Regulations, Codes, Standards and Guidelines applicable to ammonia refrigeration systems require evaluation of these pressure drops and documented confirmation that they are within acceptable limits.
This paper presents a method that identifies the necessary documentation and uses a specialized software application that can evaluate any ammonia refrigeration pressure relief vent piping system, including those with common headers. The method is inexpensive, comprehensive, meets regulatory requirements and follows recognized and generally accepted good engineering practice.

Ammonia is the ideal industrial refrigerant, with high efficiency and broad utilization in industry, as well as attractive environmental properties. Use of air cooled ammonia systems is uncommon, though, with almost all ammonia systems employing evaporative condensers, based on past practice and assumptions concerning efficiency and system performance. The efficient use of air cooled condensing could allow the benefits of ammonia to be realized more widely. This paper studies efficiency and utility cost of a refrigerated warehouse using an ammonia refrigeration system in six U.S. cities, comparing evaporative and air cooled condensing.

The objective of this project was to determine the effectiveness of different methods of mitigating ammonia releases through a pressure relief device in an ammonia refrigeration system. A literature review was conducted and among the methods discovered, five were selected for further study and include: discharge into a tank containing standing water, discharge into the atmosphere, discharge into a flare, discharge into a wet scrubber, and an emergency pressure control system. All the methods were compared applying quantitative risk analysis where failure rates of each system were combined with ammonia dispersion modeling and with the monetized health effects of a system’s failure to contain an ammonia release.
​It was determined that the ammonia release height had the greatest influence on the downwind cost impact relative to the other variables, including weather conditions and release from multiple sources. While the discharge into a tank containing standing water was determined to have the lowest failure rate, the other discharge methods can be designed to have comparable failure rates and comparable release consequent cost. The emergency pressure control system, now required by codes, used in conjunction with the other ammonia release mitigation systems, was determined to be very effective.

The purpose of this paper is to describe the use of Layers of Protection Analyses (LOPAs) to analyze specific scenarios in two ammonia refrigeration systems. The LOPAs were able to formally analyze the reliability of these systems and, to a certain extent, produce results which can provide guidance throughout the industry.

The original limitations placed on using Level B chemical vapor protective clothing for emergencies involving ammonia vapor were created by an OSHA Interpretation letter written by an OSHA regional director in 1991. The original criteria established a 5,000 PPM limit on Level B chemical protective equipment. The Ammonia Safety and Training Institute (ASTI) has evaluated current chemical vapor protective equipment through live ammonia testing and recommends that the original 5,000 PPM limit be increased to 15,000 PPM for Level B chemical vapor protective clothing that meets degradation, penetration, and permeation standards described within this Technical Paper.

Sophisticated software is available commercially to model outdoor dispersion of pure gases such as ammonia from pressure relief valves, or ammonia-air mixtures from machinery room ventilation systems. A previous paper presented in 2013 provided a case study of using this software to model ammonia releases from inside an ammonia machinery room, or from piping or vessel leak points outdoors near ground level [1]. In this paper, the author applies the same analysis techniques to outdoor pressure relief discharges from single relief valves, discharge headers, and water diffusion tank vents. The analysis examines the impact of decisions such as release orientation (up or horizontal), discharge velocity, discharge elevation, etc.

This paper presents an overview of the reasons for charge reduction in air conditioning and refrigeration systems and discusses strategies for charge reduction: in compressors (oil), vessels, pipes, and heat exchangers. The focus is on heat exchangers, and microchannel heat exchangers in particular. In addition to a trivial reduction of internal volume as a strategy for charge reduction, the effect of mass flux on void fraction and needed manipulation of circuiting is presented. A framework and example of comparison between refrigerants based on their potential for low condenser charge is provided.

2014 Programa en español

Diseñar los sistemas de refrigeración por amoníaco con la carga de refrigerante más baja posible tiene muchos beneficios potenciales. Las normas de seguridad locales y nacionales por lo general llegan a ser menos restrictivas a medida que disminuye la carga de amoníaco. Los riesgos asociados con la exposición de las personas y los productos al amoníaco también se reducen con la disminución de la carga de amoníaco.
Tradicionalmente los Sistemas de Refrigeración Industrial han utilizado alimentación por líquido recirculado o inundado para distribuir el refrigerante en los evaporadores. Este tipo de sistema ofrece un sin número de beneficios operacionales y utiliza al máximo posible la carga del sistema, en un rango de 25 Lbs/ TR /3.0 kg/kW). Usando expansión directa (DX) en lugar de recirculación por bombas, se puede reducir la carga de amoníaco en los evaporadores hasta 50 veces y reducir la carga del sistema hasta una cantidad tan baja como 5.5 lbs/TR (0.7 kg/kW). Otros beneficios son:

• Controles simplificados
• Línea de succión seca energéticamente eficiente
• Evacuación de refrigerante más rápida y ciclo de desescarche más corto
• Reducción en el diámetro de las tuberías 
• Eliminación de las bombas de recirculación

A pesar de los beneficios potenciales asociados con el uso de amoníaco DX, no ha sido ampliamente aplicado debido al bajo rendimiento del evaporador y la dificultad para controlar el flujo de líquido. La identificación de las causas del bajo rendimiento del evaporador y el retorno de líquido así como la aplicación de nuevos diseños que abordan estas dificultades son el tema de este artículo.