Chiller Comparisons: Ammonia Vs. R-134a
In this age of HFCs such as R-134a, the ammonia industry is taking a more aggressive stance.
One question posed here at the 25th annual conference of the International Institute of Ammonia Refrigeration (IIAR): “Is it possible for ammonia to be used in areas where conventional wisdom says R-134a is the best choice?”
According to two presenters at separate technical sessions, the answer is yes.
Comparing Chillers
Holger Tychsen of York Refrigeration/Frick offered a technical paper comparing R-134a chillers to packaged ammonia chillers for air conditioning applications. (His company makes both types of systems.) He said ammonia chillers can be a design choice rather than 134a — if some technological twists are added to the conventional ammonia system.“There are a lot of opportunities here,” he said. “We know that ammonia systems are highly energy efficient, but not competitive on a first-cost basis. But are they so efficient that the extra cost can be recovered over the lifetime of the equipment?”
His study focused on the two approaches for a unit with about 300 tons of refrigeration (TR) capacity. A key factor of the study was the ability of each concept to operate at part load. “To make the comparison as fair as possible, the Integrated Part Load Value (IPLV) method described in ARI Standard 550/590 was used,” he said.
He described R-134a as “a low-pressure refrigerant which produces a relatively large volume of gas which must be moved by the compressors to provide each unit of refrigeration — about 35 percent more than for R-22 and ammonia.” He also focused on the need for 134a to be used with POE oils, “which tend to absorb a lot of moisture.” He noted that as an HFC, R-134a is a refrigerant with a global warming potential that is causing some concern in parts of Europe.
Ammonia, he said, has no ozone depletion potential (ODP) or global warming potential. It is corrosive and flammable, although difficult to ignite, and it can’t work with copper, so steel piping and components must be used. This adds to costs.
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He described the 134a unit as a “simple system” with semi-hermetic, suction-gas-cooled compressor motors, shell-and-tube flooded evaporators with enhanced copper tubes, no service valves if they’re not wanted, an electronic control center, and a low overall height.
A typical ammonia water chiller unit, he said, has standard open twin-screw compressors with variable-volume ratio regulation and capacity regulation down to 10 percent; standard flanged, high-efficiency, low-noise motor; standard, semi-welded, plate-and-frame condenser; liberal use of service valves; and uses a polyalphaolefin oil (PAO).
His findings: “Today’s ammonia chillers operating at standard IPLV operating conditions can compete with an R-134a chiller. Considering that some countries have placed a tax on equivalent emissions (partly based on global warming issues) and that we can expect more countries to follow, ammonia’s pure cost competitiveness will continue to grow.
“On the other hand, R-134a chiller units can also deliver high efficiency. In many cases, because of safety regulations or less available investment capital, these units will be the right choice.”
Other aspects of his comparison:
“If manufacturers use the new designs, they can tap into a very large market that already is moving toward natural refrigerants,” noted Tychsen. “The environmental benefits are less compelling now in the U.S. than in Europe.
“When environmental concerns become more important in the U.S., packaged ammonia units can be ready in design, efficiency, safety, and costs.”
Operating Costs
Costs also drew attention from Robert Port of Hixson Inc., Cincinnati, who said, “The defining differences favoring the choice of ammonia over R-134a are going to be lower overall operating costs of ammonia systems, the flexibility in meeting complex and multiple refrigeration needs, and for many applications, lower first costs.”He also maintained that “The codes and standards that govern the two refrigerants are not as different as one might think. For example, the machinery rooms for all systems over 100 hp must meet requirements for industrial occupancy, regardless which refrigerant is used.”
He reported on a number of projects. An East Coast food processing plant, for example, had two 28-year-old R-11 systems, each with 230 TR. That plant also relied on a two-stage ammonia system for coolers, process area HVAC units, jacketed tanks, glycol chillers, and proprietary food processing equipment.
“The proposed project was promising, and would kill three birds with one stone,” Port said, “eliminating dependence of CFC refrigerant, retiring aged plant equipment, and increasing the available refrigeration capacity.”
After looking at several options, it was decided “to connect the chilled-water-loop refrigeration load to the existing central ammonia refrigeration system.” The project involved installing a flooded plate-and-frame chiller and screw compressor and creating a third temperature service to minimize energy consumption.
“The theoretical calculations gave R-134a a slight kW/TR advantage over ammonia. However, the actual compressor testing data show that the ammonia screw compressor has the advantage over the R-134a screw compressor. This is because the increased mass flow requirements for the R-134a translate into increased refrigerant flow, which increases the frictional losses in the compressor.”
A second project involved a master plan to eliminate some CFC and HCFC rooftop units and packaged water chillers at an Upper Midwest powdered beverage manufacturing facility. The plan was to “transfer their refrigeration loads to a central ammonia refrigeration system.”
Two choices were considered. The installation of a packaged
R-134a centrifugal chillers, condenser water pumps, and closed-loop fluid controls would have a lower first cost. The other choice — flooded ammonia plate-and-frame heat exchangers, screw compressors, and evaporative condensers — was said to have better overall system operating costs.
The scale tipped toward the second option.
Port said, “After examining the facts when comparing ammonia to R-134a for use as a refrigerant in a food processing facility, the following factors make ammonia a superior choice:
Informal Talk
Refrigerant 134a was also part of an informal panel session in which members could offer comments on ways IIAR could better market itself. Several attendees at the session encouraged the association to advocate the use of ammonia in areas where it could be competitive with 134a.One comment was, “Ammonia has found a place in the industry. With our growth, we are looking at new opportunities.”
Another focus was on working closer with the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) to promote the “R” in its name. Attendees who also were ASHRAE members encouraged IIAR members to work through ASHRAE’s technical committees to consider more refrigeration topics.
Part of the session had an international focus. Attendees from overseas noted that in some European countries, ammonia faces similar regulatory constraints as in the United States. Designers have been specifying HFCs, often on a cost basis. Ironically, it was noted, the future of HFCs is uncertain in Europe.
Attendees urged IIAR to work more closely with environmental groups to promote ammonia. An IIAR staff member noted that representatives of Greenpeace are invited to association conferences.
Publication date: 06/23/2003
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