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I. INTRODUCTION TO AMMONIA REFRIGERATION

Mechanical refrigeration was developed in the 19th century based on the principle of vapor compression.¹ The first practical refrigerating machine using vapor compression was developed in 1834 and by the late 1800s refrigeration systems were being used in breweries and cold storage warehouses.² The basic design of the vapor compressor refrigeration system, using one of many available refrigerants in a closed cycle of evaporation, compression, condensation, and expansion, has changed very little since the 1870s. Present day systems are more efficient, include engineered safety features, are available in smaller sizes, and require comparatively smaller capital outlays.

Early refrigerants included ammonia, sulfuric ether, carbon dioxide, sulfur dioxide, methyl chloride, and some hydrocarbons.³ Of these, only ammonia has secured a lasting role as a refrigerant.

Ammonia was first synthesized in 1823 by reacting air and hydrogen and the first commercial production of synthetic ammonia began in 1913.⁴ Presently, there are an estimated two billion metric tons of ammonia present in the world. Of this amount, approximately five percent is man-made. Approximately 18 million metric tons of ammonia are produced annually in North America alone, and of this amount, less than two percent is used for refrigeration.⁵ Since ammonia is a common, naturally occurring compound in the environment and can be naturally broken down into harmless hydrogen and nitrogen molecules (the atmosphere consists of nearly 80% nitrogen), it is often referred to as a "natural refrigerant".⁶

Ammonia was first used as a refrigerant in the 1850s in France and was applied in the United States in the 1860s for artificial ice production.⁷ The first patents for ammonia refrigeration machines were filed in the 1870s.⁸ By the 1900s, ammonia refrigeration machines were being commercially installed in block ice, food processing, and chemical production facilities.⁹ From 1875 onwards, ammonia refrigeration was being applied to ice rinks, first as a brine chiller and later as a direct refrigerant.¹⁰

During the 1930s, air conditioning markets began to develop, first for industrial applications and then for human comfort.¹¹ The use of smaller units for domestic refrigerators increased substantially between 1920 and 1930. By the 1930s, halocarbons such as chlorofluorocarbons (CFCs) had been developed to replace the use of poisonous refrigerants such as sulfur dioxide and methyl chloride. Halocarbons were believed to be the perfect refrigerants because they had no odor, were nontoxic, were comparable in power requirements and price with the other refrigerants, and were suitable for equipment available at that time.

Over the seven-decade period from the 1930s through the 1990s, nearly all state and local building codes, air conditioning equipment standards, design standards for air conditioning systems, and installation guidelines were developed for equipment and systems utilizing one of the many halocarbon refrigerants. In the United States, most engineering standards applicable to air conditioning systems and equipment were developed by the American Society of Heating, Refrigerating and Air conditioning Engineers. In addition, major equipment suppliers developed products to comply with these codes that permitted only halocarbon refrigerants. Architects, consulting engineers, and contractors applied these halocarbon systems in their air conditioning project designs and installations.

During the same seven decades, the amount of halocarbon refrigerants lost to the atmosphere through leaks due to system design and maintenance is estimated to have exceeded many times the amount actually required by refrigeration plants, thereby increasing the demand for halocarbons and securing the refrigerants' commercial success.¹² Consequently, halocarbons became the refrigerant of choice for residential and commercial air conditioning applications, while ammonia remained the refrigerant of choice for the industrial refrigeration industry. This growth in the use of halocarbons, promoted as safe refrigerants under trade names such as "Freon", took place before their damaging impact on the environment was known.

Today, ammonia refrigeration is used significantly in the food processing and preservation industries and to a certain extent in the chemical industries.¹³ Ammonia refrigeration is the backbone of the food industry for freezing and storage of both frozen and unfrozen foods.¹⁴ It is the workhorse for the post-harvest cooling of fruits and vegetables, the cooling of meat, poultry, and fish, refrigeration in the beverage industry, particularly for beer and wine, refrigeration of milk and cheese, and the freezing of ice cream.¹⁵ Practically all fruits, vegetables, produce and meats, as well as many beverages and juices, pass through at least one facility that uses an ammonia refrigeration system before reaching our homes.

More recently, air conditioning provided by ammonia refrigeration systems have found limited applications on college campuses and office parks, small scale buildings such as convenience stores, and larger office buildings.¹⁶ These applications have been achieved by using water chillers, ice thermal storage units, and district cooling systems. In Europe, where regulatory regimes have encouraged new applications, ammonia refrigeration systems have been used safely for air conditioning in hospitals, public buildings, airports, and hotels.¹⁷ Ammonia refrigeration has also been used to provide air conditioning for the International Space Station and Biosphere II.¹⁸ Installation at power generation facilities represents an emerging application of ammonia refrigeration. Unfortunately, a broader application of ammonia as a refrigerant is hampered by restrictive regulations at all levels in the U.S.