Applying Natural Refrigerants to New Applications

Is it feasible to apply lowcharge ammonia technology in an application that has traditionally been dominated by the use of HFCs and other synthetic refrigerants? That’s what a big-end user wanted to know when it approached Azane Inc., a package supplier based in California, to manufacture a lowcharge ammonia chiller that provides chilled water to a HVAC air conditioning system.

“When the industry thinks of HVAC, they don’t think ammonia because the HVAC world has been dominated by synthetic refrigerants in packaged systems,” said Caleb Nelson, vice-president at Azane, Inc. “We couldn’t use ammonia in an HVAC packaged air-handler system because you can’t risk leaking it into the airstream that is feeding the building. But this project is an example of how ammonia can be an ideal refrigerant when you’re providing air-conditioning with chilled water coming from a chiller.”

Historically, people have thought of using ammonia mainly as a refrigerant and not for comfort cooling, but there is a growing trend that began in Europe in which large companies in the United States are deciding to apply natural refrigerant systems in new and diverse applications. Several major food producers have publicly stated their desire to phase out or reduce HFCs to meet current and pending federal restrictions and regulatory requirements.

“What companies are realizing is the need to start finding different ways of applying this type of refrigeration,” said David Blackhurst, director at Star Technical Solutions, which owns Azane, Inc. “They are realizing that going straight to synthetics is not the smartest move. All of the big guys are looking for alternative ways [to create] refrigeration.”

By using a low-charge ammonia chiller for comfort cooling, the big-end user decided to invest in a system that promises to be financially beneficial, will fly under the radar of federal regulatory requirements and is considered safer to operate.

“It’s a natural system, so they won’t have to worry about replacing it in 10 years because it gets legislated out. You could call it future-proof,” Nelson said. “Although upfront costs are higher, the system will last 50 to 75 percent longer because it is more robust and built to a different standard than HFC systems. A total cost of ownership benefit can be realized when you consider the longer life and the fact that an ammonia system will be 20 to 25 percent more efficient than an HFC system starting on day one.

“From a safety standpoint, the only thing flowing to and from the package is chilled water. And in the event of a leak, as soon as it’s automatically detected at 25 ppm, the automatic, immediate response is to ramp the condenser fans to 100 percent speed to dispel and divert ammonia, pushing it 30 to 40 feet above the unit where it will dissipate and most likely go unnoticed,” Nelson said.

“Since the air-cooled condenser fans are integrated with the unit, if you do the math, we’ll realize about 10,000 fresh air changes per hour inside the unit in the event of a leak. This is over 300 times the code requirement for air changes when there’s a leak in a machinery room,” he added.

The decision to shift from synthetic refrigerant to ammonia in an HVAC application is also a significant step for the ammonia refrigeration industry due to the big-end user’s high profile. “They can be the leaders in paving the way for others to understand this technology,” Nelson said. “Decisions they make are more profound because they are helping to create a market for the new applications.”

The system Azane built provides 300 tons of cooling at a charge level of 1.65 lb/TR and utilizes a tube and fin condenser that also directly cools the compressor oil with ambient air. The package includes a flooded plate-andframe evaporator that provides a level of stability and increased efficiency because it can operate with no superheat that allows the suction pressure of the compressor to increase. This represents just one of the advantages of using an azeotropic refrigerant such as ammonia instead of a blended synthetic refrigerant where flooded operation would not be possible.

There is a healthy level of forgiveness and resiliency in the system as well, which is important for a lowcharge system. Minor refrigerant losses and overcharging of refrigerant will not negatively affect the performance of the system, due to the design of the surge vessel above the flooded evaporator. While this vessel is meant to be nearly dry during normal operation, there is enough refrigerant present and enough empty volume available to allow for some variance in charge. Even extreme levels of overcharging would not result in liquid floodback to the compressor due to the sizing of the surge vessel.

Air-cooled options are rare in packaged ammonia systems, but they are especially valuable in areas with high water costs or water shortages. “In most locations, we can show that an air-cooled solution can compete with the efficiency of an evaporative condensed system even in the hottest climates,” Nelson said. In the final analysis, the project is expected to show that ammonia in a low-charge system can perform superbly in an HVAC application.

“It’s not all hypothetical talk anymore,” Nelson says. “People are actually doing it.”