Control measures to mitigate cross-contamination between cascade CO2-NH3 refrigeration systems, as well as the development of electrochemical ammonia compressors, are among the innovations that may boost uptake of ammonia for HVAC&R applications, heard participants in last week’s Gustav Lorentzen conference in Edinburgh.
"CO2-NH3 industrial refrigeration plants can be very reliable if designed correctly. But CO2 leakage into an ammonia circuit can be a problem," said Angus Gillis of UK-based Star Refrigeration.
With this in mind, he researched three options for mitigating the risk of cross-contamination. Option one is to install an ammonium carbonate detector and emergency isolation valves. Option two is to use a double-wall heat exchanger, and option three is to use twin ammonia circuits that allow continued operation should one of the ammonia circuits need repairing.
His paper concluded that option three is the way to go. "Twin ammonia circuits are a cost-effective and robust control measure that can be implemented without incurring a significant efficiency penalty," said Gillis.
He stressed the importance of using high-pressure components designed for natural refrigerant systems to ensure maximum reliability.
Meanwhile, researchers led by Yunho Hwang of the Center for Environmental Energy Engineering in the Department of Mechanical Engineering at University of Maryland found that using an electrochemical ammonia compressor improves the efficiency of the vapour compression cycle.
The electrochemical compressor, based on a proton exchange membrane fuel cell, utilises hydrogen as a carrier gas to transfer ammonia across the membrane. "Ammonia was selected as the working fluid because of its high latent heat and electrochemical interaction with hydrogen and the proton exchange membrane," state the researchers in their paper.
By using the natural refrigerant ammonia, they argue that their electrochemical compressor is an environmentally friendly option that can boost system efficiency.
"The ammonia electrochemical compressor consumes less power than mechanical compressors since its process approaches an isothermal gas compression process without using any moving parts or lubrication oil," the paper states.
The vapour compression system using the electrochemical compressor "has a much higher coefficient of performance than conventional mechanical compressors," it concludes.
The 12th IIR Gustav Lorentzen Natural Working Fluids Conference– held in Edinburgh on 21-24 August – brought together HVAC&R industry experts, academics, students and other interested parties to discuss the latest technological and policy developments driving wider uptake of natural refrigerants such as hydrocarbons, CO2 and ammonia worldwide.