An excellent opportunity for the wide use of ammonia arose with the advance in microchannel heat exchanger technology, with its low refrigerant charge and high heat transfer coefficients for condensation. Ammonia is widely accepted as an environmentally compatible refrigerant with a GWP value of zero and adequate efficiency. However, it is a toxic compound, and this constrains its use in populated areas. Smaller size, lower weight, and lower cost are also influential assets for air conditioning and refrigeration applications. Besides this, microchannel heat exchangers are made from fully and easily recyclable aluminum.
As liquid subcooling is a major contributor to the charge of ammonia, it is advantageous to optimize the heat exchanger’s operation with reduced subcooling – not only for improved heat transfer but to reduce ammonia charge.
Special attention should be given to the anti-corrosive properties of heat exchangers to avoid leakages of ammonia. Thicker tube walls and protective treatments and coatings contribute to corrosion protection and are indispensable to ensuring ammonia systems’ safe operation, especially in harsh environmental conditions and chemically polluted corrosive atmospheres.