UPDATE: Colmac Coil publishes DX Ammonia Piping Handbook 2^nd Edition

Colmac Coil Manufacturing Inc.’s tested and patented technology allows for low charge industrial ammonia refrigeration designs using direct expansion (DX). The Low Temperature DX Ammonia system address the main issues associated with ammonia as a refrigerant, that have previously prevented its use at low suction temperatures. Colmac Coil’s newly published DX Ammonia Piping Handbook 2^nd Edition provides engineers and designers with the guidelines needed for the successful design of low charge DX ammonia refrigeration systems from +10°C to -45.5°C (+50°F to -50°F).

Addressing the problems of low temperature NH₃ systems

DX ammonia has been applied with some success in medium and high temperature systems with suction temperatures about -6.6°C (+20°F); however, to date, it has not been used successfully at freezer temperatures. When the suction temperature is below approx. -6.6°C (+20°F), certain characteristics of ammonia result in the very poor performance of evaporators. In the newly published DX Ammonia Piping Handbook, Colmac Coil outlines how its new technology has addressed and mitigated these following issues:

1. Separation of liquid and vapor phases

When temperatures are below -6.6°C (+20°F), direct expansion with ammonia results in stratified/wavy two-phase flow patterns. Colmac Coil has developed a new technique which, when applied to the inside of evaporator tubes, causes the liquid NH₃ to coat the entire inside surface of the tubes by capillary action. This enhanced tube technology allows for low temperature DX ammonia to perform as good or better than bottom feed pumped ammonia circuiting.

2. Refrigerant distributor technology

Colmac Coil has also developed (patent pending) a new refrigerant distributor technology, the Colmac Tank Distributor, which has the following characteristics:

• Refrigerant pressure drop across the tank distributor during operation is very low, only 2-4 psi.
• Any oil or debris entering the tank distributor is captured in a drop leg (which is an integral part to the design) before it can enter the coil and foul tube surfaces.
• Performance of the tank distributor is completely insensitive to liquid temperature (subcooling)
• Graduated orifices in each distributor tube allow for equal distribution of refrigerant to all circuits over an extremely wide operating range of 0% to 700% of rated capacity.
• Graduated orifices and large diameter distributor tubes allow full flow (minimal restriction) of hot gas during hot gas defrost.
• The number of parallel evaporator circuits possible in a single tank distributor can be as high as 48.

3. Removal of water from ammonia

DX ammonia evaporator performance can be significantly reduced by even a small amount of water (1-3%) in the system. Especially in freezing systems, which operate at suction pressures below one atmosphere (in a vacuum), water must be effectively removed during operation. Colmac Coil has developed an effective ammonia distillation vessel design and installation strategy, both of which are described in the DX Ammonia Piping Handbook.

Key Benefits of DX Ammonia

• Reduced ammonia charge
• Simplified controls
• Energy efficient dry suction line
• Reduced line sizes
• Fast, energy efficient defrost
• Elimination of ammonia re-circulator pumps

Interview with Bruce Nelson, President of Colmac Coil Manufacturing



View Colmac Coil's DX Ammonia Piping Handbook 2^nd Edition

Colmac Coil to present low charge DX ammonia at Eurammon Symposium 2013

About Colmac Coil Manufacturing Inc.

Founded in 1971, the company has grown to become one of the world’s leading manufacturers of refrigeration evaporators and liquid air coolers, dry coolers, air-cooled condensers, and heat pipe air-to-air heat exchangers for the commercial and industrial heat transfer markets. Located in Colville, Washington, USA, with manufacturing facilities in Colville and Paxton Illinois, Colmac is set up for flexible manufacturing, allowing for the production of customised orders to fit specific customer needs and requirements.