Rescuing the Ozone
A recent survey conducted by the Air Conditioning and Refrigeration Institute (ARI) suggests that about half of the 80,000 chlorofluorocarbon (CFC) chillers that were in service in the early 1990s have been converted or replaced with non-CFC refrigerant units. In this month’s M/E Roundtable, engineers discuss progress that has been made—and a prognosis for the future.
CONSULTING-SPECIFYING ENGINEER (CSE): To what extent has converting systems to non-CFC refrigerants been a part of your business? Describe some examples of these types of projects.
LEADER: Very little of our business has involved refrigerant retrofit for “second generation” refrigerant alternatives. For A/E firms, involvement is generally limited and comes mostly in the life-cycle-cost analysis phase. Often, the chiller manufacturer takes over from there. We haven’t seen many viable [refrigerant] retrofit opportunities, usually due to issues with tube-bundle life and the efficiency compromises made with refrigerant retrofits. A high-efficiency replacement chiller usually makes more sense so long as the problems with removal of the old and installation of the new don’t involve major structural and architectural building work.
BROWN: Retrofit of non-CFC refrigerants is roughly 5 to 10 percent of our business. In the Houston area, we see contractors doing most of the repair and maintenance of existing CFC equipment. Therefore, it is not really an engineered item.
CSE: What are the best alternative refrigerants to CFCs? What types of refrigerants are you specifying?
BROWN: We are specifying R-134a and R-718 as alternative, non-chlorine refrigerants. Depending on the project scope, occasionally R-123 and R-22 are incorporated into the design, sometimes based on owner preference and ease of maintenance. Occasionally, we see a strange refrigerant such as ammonia.
SCHLUENDER: When possible, on large systems we have been installing ammonia. However, on small systems we install R-134a. In low-temperature situations, we specify 404a.
Generations of refrigerants
LEADER: The “second-generation” refrigerant alternative to CFC-11 is [hydrochlorofluorocarbon] HCFC-123. The alternative to CFC-12 is [hydrofluorocarbon] HFC-134a and the second-generation alternative to HCFC-22 is still HCFC-22.
Third-generation alternatives, which may never show up in the U.S. market, are HFC-245ca to replace HCFC-123, and HFC-152a to replace HFC-134a. The extreme flammability of third-generation refrigerants may doom their use in the United States. Another, HFC-245fa, shows promise for replacing HCFC-123 in large tonnage applications, but the economics of [American Society of Mechanical Engineers] ASME pressure-vessel construction will affect this. It has zero [ozone-depletion potential] ODP compared with 0.014 for HCFC-123; however, its [global warming potential] GWP is over six times higher, so I don’t see much future for this, either.
The 407C and 410A [refrigerants] are the next alternatives for HCFC-22. Since they are blends of several other HFCs, they have evaporation properties that occur over a range of temperatures. This makes them difficult to deal with in the design of the evaporator and control of condensing pressure. They are on the market now and are seen in small unitary equipment for residential and commercial applications. The 410A will likely be the choice for new equipment, and 407A for replacement applications. The 410A operates at about a 50-percent higher pressure than HCFC-22 and needs an appropriate design, whereas 407A is a close clone of HCFC-22 and is compatible with traditional seals and gaskets.
We are specifying 123, 143a and 22 on our projects unless a client has a corporate policy permitting only the use of a specific refrigerant. Life-cycle economics dictate that the refrigerant is balanced with other factors such as ODP, GWP—direct and indirect—reliability and refrigerant safety. Chillers are built so “tight” today that leaks have become a secondary issue and long-term refrigerant availability is not a concern.
CSE: There is renewed interest in ammonia and carbon dioxide [CO 2 ]—some of the earliest substances to be used as refrigerants—as replacements for chlorine-based synthetic refrigerants. Has your firm specified systems that use these refrigerants?
BROWN: We like ammonia and CO 2 refrigerants, but one must be well aware of the toxicity and malodorous qualities. However, the use of these types of refrigerants is very limited for commercial projects.
LEADER: Ammonia, without a doubt, is one of the best refrigerant options available, provided the mechanical codes allow it for the application. A recent project application is a low-temperature (-40°F) environmental wind tunnel for an automotive client.
SCHLUENDER: I believe that ammonia is the best alternative; however, with the bad publicity that it has gotten over the years, it is sometimes difficult to sell to an owner. More research and development needs to be devoted to ammonia for use in small systems, such as what is being called “critically charged systems.” I have not used carbon dioxide; however, in the correct application, such as an industrial application, I would not have a problem using it. But unless carbon dioxide has an odorant added, it could be very dangerous. Ammonia is a self-alarming refrigerant [at levels] as low a 5 ppm [parts per million].
CSE: Does equipment that you specify usually include sophisticated programmable-logic controllers [PLCs] and sensors for detecting refrigerants?
SCHLUENDER: Yes, and if it does not come with the equipment, we engineer a control system.
LEADER: When the requirements of ASHRAE [American Society of Heating, Refrigerating and Air-Conditioning Engineers] Standard 15 are imposed by the mechanical codes, refrigerant monitors are used to sound an alarm, start emergency-ventilation systems and lock out open-flame appliances—such as boilers—if they are in the same equipment room as the chillers. I’m not sure that the monitors are PLCs necessarily, but most likely, microprocessor-based programmable controllers.
BROWN: Generally, [controllers and sensors] are part of a packaged piece of equipment from the manufacturer that is set at the factory. However, in renovation or retrofit jobs, one has to be careful that the proper sensor is being utilized for the various types of refrigerants that may be present.
Carbon dioxide and global warming
CSE: Do recent decisions by the Bush administration with respect to carbon-dioxide emissions have any effect on the specifications of heating, ventilating, air-conditioning and refrigerating engineers?
SCHLUENDER: At this point, I don’t believe so.
LEADER: If you’re referring to the move by Congress to ban funding of any measures designed to implement the Kyoto Protocol because it would hurt the U.S. economy, I don’t think so.
A recent trend in A/E firms’ specifications requires chillers to focus on performance and efficiency at both full load and part load, probably based on an estimated building-load profile and energy-rate structure. From my experience following the days of the oil embargo of the 1970s, until there are more economic incentives—such as rebates, credits or offsets for reductions in emissions, etc.— to get owners out of the first-cost mindset and pay a premium for high-efficiency equipment, things won’t change. In many cases, as in many residential applications, high efficiency doesn’t pay for the first-cost premium. There has been a lot of press lately in the trade magazines about the poor payback of high EER [energy-efficiency ratio] equipment (13-14) vs. 9 EER in residential applications and how it’s being oversold.
BROWN: We are mandated by building code and will respond as required. We are aware of ongoing proposed changes, but no drastic decisions by the administration have significantly affected specifications. Something that we need to be aware of are periodic protocol meetings and decisions, and keeping up with changing technology.
CSE: What are some of the determining factors in types of refrigerants to use for an application? In other words, do different types of projects call for different refrigerants?
BROWN: We are primarily using commercial applications comparing initial costs vs. operating efficiencies. Smaller projects tend to use packaged equipment in which R-22 is still the prevalent refrigerant. Larger tonnage projects open up the option to various refrigerant types, each with its own characteristics of efficiency, costs, toxicity and flammability.
LEADER: [There is] no doubt that the evaporator and condenser operating temperature and pressure have a big influence on the initial list of suitable refrigerants. Additional considerations include the overall tonnage of the system as well as thermodynamic and physical properties of the refrigerant that affect heat-exchanger and compressor sizing, compressor type, equipment first cost and operating and maintenance costs. All these factors must be balanced with environmental issues, such as ODP and GWP, and maybe long-term refrigerant availability and pricing.
SCHLUENDER: The selection of refrigerants is normally quite simple. There are several factors that I look at: size of system, application, location of the facility and code restrictions. For example, the ideal use of ammonia would be a large process cooling job in a rural area. In an urban area, local codes and safety of a large population must be considered and there would be a high probability that ammonia would not be used.
CSE: What standards and code issues have an impact?
BROWN: ASHRAE Standard 15 Safety Code for Mechanical Refrigeration (including ventilation of machine rooms), ASHRAE 62-99 Ventilation Requirements, ASHRAE 34 Safety Classification of Refrigerants and local building codes.
SCHLUENDER: [Dealing with] emergency discharge of refrigerant, explosion hazard of some refrigerants such as ammonia and whether the refrigerant can be used directly in a personnel space.
LEADER: ASHRAE Standards have a very big impact whether or not they’re adopted as code, because they represent the standard of care in our industry, and to ignore them can get you in trouble in the courts. They have a big impact on the life-cycle economics of the design of an HVAC system for a building.
CSE: Have you had any particularly challenging or innovative projects using CFC-replacement technology?
BROWN: The challenge we have with replacing refrigerant is that, technically, there is no such thing as a “drop-in” refrigerant. Some come close, but there is always a compromise. When the refrigerant is changed or altered, the equipment does not operate at the same original efficiency, therefore, design changes or alterations must be done to account for the change in capacity. These design changes can be challenging on specific facilities because a re-creation of load capacity needs to be determined.
SCHLUENDER: If ammonia is used, it must be a fully engineered system—with respect to the valves, receiver, suction accumulator, etc.—whereas we normally rely on the manufacturer of equipment to engineer these for us.
CSE: The Montreal Protocol has essentially eliminated halon fire-extinguishing systems. What has replaced halons for fire suppression in data and telecommunications facilities? Has carbon dioxide successfully replaced halon systems?
LEADER: We have successfully used CO 2 , in both low pressure and high-pressure applications, to replace Halon 1301. We’ve also used some of the chemicals on the market (FM-200, Inergen) to a lesser extent. Most of our specialty fire-protection system work is with industrial and automotive applications, such as paint-mixing and -storage rooms, and the sheer volume of those applications has always favored CO 2 due to cost of the extinguishing agent.
In projects with communications and data centers, we will specify water-based systems unless specifically instructed otherwise by the owner’s personnel or insurance underwriters. FM-200 seems to be the “agent of choice.” It works just like Halon 1301—except it requires a greater quantity. It doesn’t mix or disperse well and costs more. Inergen-type systems use a much higher percentage of floor space for the equipment protection and there is not always a willingness to accept this sacrifice of net floor area.
BROWN: FM200 replaces Halon, and we have had satisfactory results using this. We have not used CO 2 or dry-powder extinguishing systems.
SCHLUENDER: We have not used replacements to a great extent. We have been installing double-interlocked dry-pipe systems in lieu of chemical systems, almost exclusively.
CSE: What is the biggest issue in refrigerants today?
LEADER: Knowing the issues to consider in making an informed choice for a refrigerant for a particular application. It’s a decision that should be made with an open mind and a balanced approach to weighing the factors that include first cost, refrigerant cost, operating cost, maintenance cost, availability of local technical support, environmental factors [ODP, direct and indirect GWP], safety factors, refrigerant charge, operating pressure and return on investment.
It’s best made using a life-cycle-cost analysis first to identify and prioritize the economic issues and then deal with the environmental and human side of the equation.
BROWN: The biggest issue I see is the research and development of azeotropes, zeotropes and blends that will supercede the HCFC refrigerants at a high efficiency level.
The entire market is waiting for a “drop-in” replacement that is non-global warming and non-ozone depleting, with maximum efficiency.
M/E Roundtable Participants
Ronald W. Brown, P.E., vice president, Day Brown Rice Inc., Houston
Mark Schluender, P.E., senior mechanical engineer, The Austin Co., Kansas City, Mo.
Philip Leader, P.E., technical director, mechanical engineering, Albert Kahn Associates, Detroit, Mich.
Scott Siddens, moderator
Life of a Chiller: When to Retrofit
If a chiller is 10 years old or less, it’s probably a good candidate for retrofit because of its efficiency and remaining service life. If it is done at the time of a major overhaul, it can be cost effective.
If a chiller is between 10 and 20 years old, it becomes a choice between the more efficient, more expensive replacement option and the less expensive, less efficient retrofit project.
A retrofit usually costs 20 to 40 percent of the total installed cost of a replacement chiller. However, the efficiency difference can pay back that first-cost difference in a very short time. A life-cycle-cost analysis is the best tool to use to make this decision.
If a chiller is over 20 years old, it’s so inefficient that it would be better to replace it. Usually simple payback periods are on the order of three years, even in an office building application with limited hours of operation.
The focus today is on efficiency. CFC-11 is one of the most efficient refrigerants produced, but its ozone-depletion potential (ODP) has severely impacted its use. HCFC-123 is a close second in efficiency, but concerns about its safety have scared a lot of people off. Clearly, HCFC-123 is one of the best overall solutions, especially in light of the advancements made in chiller leak tightness.
It was stated at a May 1999 convention in Petten, The Netherlands, that if responses to global warming had been taken prior to measures for ozone protection, R-123 might not have been scheduled for phaseout under the Montreal Protocol. The argument is that R-123 phaseout will increase the net global warming from chillers by 14 to 20 percent while their use would have less than a 0.001 percent increase in ozone depletion. R-123 is used in more than half of all new chillers sold, or more than all competing refrigerants combined.
All three refrigerants have their place and are acceptable solutions. The U.S. Environmental Protection Agency in its technology brief titled “Choosing an Optimal Chiller in the Face of a CFC Phaseout” actively supports this position. The choice should not be based on one criterion, but a combination of ingredients that produces the highest return on investment.
Back to Basics: Ammonia and Carbon Dioxide
Ammonia was first introduced as a refrigerant in 1860. It contains only nitrogen and hydrogen, has a zero ozone-depletion potential and virtually zero global-warming potential relative to CO 2 . Health and safety aspects preclude its use in “comfort” HVAC applications.
Likewise, CO 2 (R-744) was first used in 1866 and is the yardstick all other refrigerants are measured against for GWP. Propane (R-290) also has a long application history, is very efficient and is showing up in refrigerators in Europe today.
It is likely that the day will come when we see one or some of these products in the consumer marketplace. Ammonia and propane have excellent performance characteristics compared to R-123 (COP of about 10.72 to 11.17 vs. 11.38 for R-123). CO 2 isn’t as suitable at standard chiller rating conditions since the condensing temperature exceeds the critical temperature for CO 2 and, even under ideal conditions, it’s coefficient of performance is about half that of the others.