Refrigeration systems continue to evolve toward natural refrigerants
The food retail, foodservice and industrial cooling industries are in the midst of a momentous transition in their refrigeration system architectures. In an era driven by historic regulatory activity and the necessity to deploy sustainable systems, the number of refrigeration options available to these operators seems to be growing exponentially — and with that, an equal amount of confusion about what is the best future-proof system alternative. To get to what many call the “end game” of achieving compliance and meeting corporate sustainability objectives, more businesses are looking at systems based on natural refrigerants to help them achieve these goals.
The term “natural refrigerant” refers to substances that naturally occur in the environment. Unlike the synthetic refrigerants that have commonly been used in refrigeration applications — including hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs) — ammonia (NH3 or refrigerant name R-717), propane (refrigerant name R-290) and carbon dioxide (CO2 or refrigerant name R-744) are three naturally occurring refrigerants that pose very little threat to the environment.
The emergence of natural refrigerants must be looked at from a historical perspective, because in many ways it is a re-emergence.
In the 1980s, scientists discovered that CFC usage was causing a hole in the ozone layer. An international treaty was quickly formed called the Montreal Protocol, which aimed to phase out the use of these substances. However, in recent years, the HFCs that succeeded CFCs were found to be a significant source of global warming.
As a result, the environmental impacts of refrigerants are measured by two key factors: global warming potential (GWP) and ozone depletion potential (ODP).
While new synthetic refrigerants are being developed that offer lower GWP and no threat to the ozone layer, many of these are either largely untested or yet to be deemed as acceptable substitutes by global environmental regulations, such as those set forth by the U.S. Environmental Protection Agency (EPA).
Know Your Naturals
Ammonia was among the first refrigerants used in refrigeration applications. While its superior thermodynamic properties made it a logical first choice for early refrigeration systems, its toxicity requires the careful adherence to safe application procedures to ensure operator and customer well-being. With the advent of CFC refrigerants in the mid-twentieth century, the refrigeration industry moved away from R-717 in favor of lower-risk synthetic alternatives that offered comparable performance characteristics. Even so, ammonia’s suitability in low-temperature applications has made it a mainstay in industrial, process cooling, cold storage and ice rink applications.
Propane is a hydrocarbon that was also identified in the early days of refrigeration as an effective refrigerant. Its high-capacity, energy-efficient performance and very low GWP are offset by its classification as an A3 (highly flammable) substance. But as synthetic refrigerants became available for many refrigeration
applications, R-290 was largely abandoned in lieu of its CFC-based counterparts.
Since the 2000s, R-290 has been regaining global popularity as a lower-GWP,
effective alternative to HFCs like
R-404A and HFC-134a — especially
in a wide range of low-charge,
CO2 is non-toxic and has proved to be a very effective alternative to HFCs in both low- and medium-temperature applications. CO2-based refrigeration
systems have been successfully deployed in commercial and industrial applications in Europe for nearly two decades. Because of its low critical point and high operating pressure (around 1,500 psig or 103 bar), CO2 refrigeration strategies — such as cascade, secondary and transcritical booster—must be designed to account for its unique characteristics. In light of current environmental regulations, the popularity of these systems has
increased significantly in North America in recent years.
When reviewing the brief application history of these refrigerants and their synthetic counterparts, it’s apparent that the search for the perfect refrigerant is an ongoing quest. It’s important to keep this in mind when evaluating natural refrigerants. Yes, efforts are needed to mitigate their associated risks and ensure their safe use, but natural refrigerants represent true sustainable alternatives without sacrificing performance.
Natural refrigerants pose very little risk to the environment. Each delivers high energy efficiency and excellent thermodynamic properties. But, it’s important to understand their unique design and application considerations.
In contrast, natural refrigerants are not only the benchmark for ultra-low GWP and ODP, they’re also acceptable for use in most refrigeration applications (subject to use conditions).
Necessity is the mother of invention
Today, the use of natural refrigerants is on the rise. Companies are taking a fresh look at them to achieve their sustainability objectives, whether that’s complying with environmental regulations or aligning with their customers’ green sensibilities. As technology continues to improve, equipment manufacturers are working closely with these forward-thinking companies to develop innovative solutions. This has resulted in several creative natural refrigeration applications that belie their traditional uses — like ammonia being used in supermarket systems and CO2 playing a larger role in industrial process cooling.
Ammonia trials in food retail
In September 2015, the Piggly Wiggly supermarket company opened a new 36,000-square-foot store in Columbus, Ga., that utilizes an NH3/CO2 cascade system manufactured by Heatcraft Worldwide Refrigeration. The all-natural refrigerant system uses an ultra-low charge of ammonia (53 pounds) located on the facility’s roof. The
ammonia condenses the CO2 and is circulated to the store’s low-temperature cases via direct expansion; the medium-temperature circuit is cooled by a CO2 liquid pump overfeed. Since the total refrigerant charge of the system has a GWP under 150, this store is one of 10 supermarkets in the U.S. to receive the highest certification level (platinum) from the EPA’s GreenChill Partnership. It’s also the fourth supermarket in the U.S. to use this NH3/CO2 cascade architecture.
In its first six full months of operation, this store consumed 28.5 percent less energy than a conventional outlet, translating into reduced energy costs of $33,170. The use of natural refrigerants also offsets the rising costs of traditional synthetic HFCs, which will only continue to rise as supplies dwindle. While the system does come in at a higher initial cost than a conventional system, the energy savings combined with the lower refrigerant costs for the lifecycle will likely result in a lower total cost of ownership. And with the growing number of utility incentives available for green technology, there will also be opportunities to mitigate these first costs.
From a safety perspective, it’s important to point out that this ultra-low charge of ammonia never comes into proximity with staff or customers in the store’s occupied space. A safety study performed by Heatcraft confirmed that there was no identified risk in the event of a catastrophic leak of the small 53 pounds of charge.
CO2 adoption in industrial cooling
In cold storage applications, where ammonia has been the preferred refrigerant for decades, companies are also seeking to lower ammonia charges. As older ammonia
systems near replacement, many operators are evaluating the best option to expand their facility’s low-temperature capabilities. They’re accomplishing this by adopting NH3/CO2 cascade systems that not only utilize very low charges of ammonia, but also keep the R-717 circuit out of occupied spaces. There’s also a regulatory driver behind this trend.
To ensure the safety of systems that require more than 10,000 pounds of ammonia, the Occupational Safety and Health Association (OSHA) created the Process Safety Management of Highly Hazardous Chemicals (29 CFR 1910.119) standard. In recent years, these systems have been subject to rigorous inspections enforced by OSHA’s National Emphasis Program (NEP) on process safety management regulated industries. For owners and operators of these large ammonia systems, this means the added responsibility — and expense — of continuous record keeping in preparation for NEP inspections.
Propane in food retail
When major retailers like Target publically announce their intentions to use only propane in their self-contained units, it’s an indication that the perceptions about the mainstream viability of R-290 are shifting.
The smaller charge limits make R-290 a logical fit for Target’s smaller, stand-alone refrigerated display cases and coolers. All of this is part of the retailer’s pledge to become a sustainability leader in the food retail space.
In making this shift, Target has also asked contractors who might be working on propane-based equipment to seek the necessary training. Over the next six months, Target plans on opening a few stores that will use only stand-alone propane systems.
New article series to explore the potential of natural refrigerants
Sustainability objectives, first costs, energy efficiency, safety, maintenance requirements and regulatory compliance: there are myriad factors to consider when choosing a modern refrigeration system — often eliciting conflicting opinions among decision makers within an organization. Whether you’re selecting 1,000 tons of refrigeration, or specifying a few walk-in coolers for a restaurant or convenience store, the number of system sizes and options can be daunting to evaluate.
To help your organization wade through the confusion and make these difficult decisions, I’ll be authoring an article series over the next several months that will look at the potential of natural refrigerants in modern refrigeration equipment. This informative series will start next month by focusing on R-290, taking a closer look at its applications in small, stand-alone systems and other emerging architectures. Then, we’ll work our way to increasing larger retail and industrial architectures — all the while keeping you updated on the latest regulatory changes and sustainability drivers shaping this dynamic refrigeration landscape.
Energy Saver has updated web site, blog, and social media presence. Aimed at helping you save money and energy, Energy Saver has been offering ideas on ways to fuel economy practices, renewable power options, and ways to prepare your home for the winter months. Some of the information is practical advice, while others are about the why behind this whole effort.
Why are we doing this?
- It’s something everyone needs to know. People cannot make lifestyle changes and informed, energy efficient choices if its importance is not explained. Understanding why choices matter encourages and enables people to make good choices.
- Technology advancement and adoption needs public support. Things like solar panels for homes, wind farms, and electric vehicles need a market. Markets don’t just happen—they need to be developed by helping buyers understand the benefits of energy efficiency and renewable energy.
- It sounds like hard work but it’s just a series of steps. Much like trying to improve one’s health, becoming more energy efficient is about lifestyle adjustments. Getting used to turning off lights and lowering the thermostat isn’t glamorous or exciting, but small changes add up—and getting into the habit of being energy efficient is more than half the battle.
- Saving energy is not about sacrifice or doing without. It is about being able to do more, with more – more savings and more comfort
- You can do it! That’s the most important thing.
Go ahead and make those small changes. You’ll see that you don’t have to go on an energy “diet;” you just have to adjust your lifestyle a little here and there. You’ll be glad you did.
Your air ducts are one of the most important systems in your home, and if the ducts are poorly sealed or insulated they are likely contributing to higher energy bills.
Your home’s duct system is a branching network of tubes in the walls, floors, and ceilings; it carries the air from your home’s furnace and central air conditioner to each room. Ducts are made of sheet metal, fiberglass, or other materials.
Ducts that leak heated air into unheated spaces can add hundreds of dollars a year to your heating and cooling bills, but you can reduce that loss by sealing and insulating your ducts. Insulating ducts in unconditioned spaces is usually very cost-effective. Existing ducts may also be blocked or may require simple upgrades.
Designing and Installing New Duct Systems
In new home construction or in retrofits, proper duct system design is critical. In recent years, energy-saving designs have sought to include ducts and heating systems in the conditioned space.
Efficient and well-designed duct systems distribute air properly throughout your home without leaking to keep all rooms at a comfortable temperature. The system should provide balanced supply and return flow to maintain a neutral pressure within the house.
Even well sealed and insulated ducts will leak and lose some heat, so many new energy-efficient homes place the duct system within the conditioned space of the home. The simplest way to accomplish this is to hide the ducts in dropped ceilings and in corners of rooms. Ducts can also be located in a sealed and insulated chase extending into the attic or built into raised floors. In both of these latter cases, care must be taken during construction to prevent contractors from using the duct chases for wiring or other utilities.
In either case, actual ducts must be used — chases and floor cavities should not be used as ducts. Regardless of where they are installed, ducts should be well sealed. Although ducts can be configured in a number of ways, the “trunk and branch” and “radial” supply duct configurations are most suitable for ducts located in conditioned spaces.
Air return duct systems can be configured in two ways: each room can have a return duct that sends air back to the heating and cooling equipment, or return grills can be located in central locations on each floor. For the latter case, either grills must be installed to allow air to pass out of closed rooms, or short “jumper ducts” can be installed to connect the vent in one room with the next, allowing air to flow back to the central return grilles. Door undercuts help, but they are usually not sufficient for return airflow.
You can perform a simple check for adequate return air capacity by doing the following:
- Close all exterior doors and windows
- Close all interior room doors
- Turn on the central air handler
- “Crack” interior doors one by one and observe if the door closes or further opens “on its own.” (Whether it closes or opens will depend on the direction of the air handler-driven air flow.) Rooms served by air-moved doors have restricted return air flow and need pressure relief as described above.
Maintaining and Upgrading Existing Duct Systems
Sealing your ducts to prevent leaks is even more important if the ducts are located in an unconditioned area such as an attic or vented crawlspace. If the supply ducts are leaking, heated or cooled air can be forced out of unsealed joints and lost. In addition, unconditioned air can be drawn into return ducts through unsealed joints.
Although minor duct repairs are easy to make, qualified professionals should seal and insulate ducts in unconditioned spaces to ensure the use of appropriate sealing materials.
Aside from sealing your ducts, the simplest and most effective means of maintaining your air distribution system is to ensure that furniture and other objects are not blocking the airflow through your registers, and to vacuum the registers to remove any dust buildup.
Existing duct systems often suffer from design deficiencies in the return air system, and modifications by the homeowner (or just a tendency to keep doors closed) may contribute to these problems. Any rooms with a lack of sufficient return airflow may benefit from relatively simple upgrades, such as the installation of new return-air grilles, undercutting doors for return air, or installing a jumper duct.
Some rooms may also be hard to heat and cool because of inadequate supply ducts or grilles. If this is the case, you should first examine whether the problem is the room itself: fix any problems with insulation, air leakage, or inefficient windows first. If the problem persists, you may be able to increase the size of the supply duct or add an additional duct to provide the needed airflow to the room.
Minor Duct Repair Tips
- Check your ducts for air leaks. First, look for sections that should be joined but have separated and then look for obvious holes.
- Duct mastic is the preferred material for sealing ductwork seams and joints. It is more durable than any available tape and generally easier for a do-it-yourself installation. Its only drawback is that it will not bridge gaps over ¼ inch. Such gaps must be first bridged with web-type drywall tape or a good quality heat approved tape.
- If you use tape to seal your ducts, avoid cloth-backed, rubber adhesive duct tape — it tends to fail quickly. Instead, use mastic, butyl tape, foil tape, or other heat-approved tapes. Look for tape with the Underwriters Laboratories (UL) logo.
- Remember that insulating ducts in the basement will make the basement colder. If both the ducts and the basement walls are not insulated, consider insulating both. Water pipes and drains in unconditioned spaces could freeze and burst if the heat ducts are fully insulated be-cause there would be no heat source to prevent the space from freezing in cold weather. However, using an electric heating tape wrap on the pipes can prevent this. Check with a professional contractor.
- Hire a professional to install both supply and return registers in the basement rooms after converting your basement to a living area.
- Be sure a well-sealed vapor barrier exists on the outside of the insulation on cooling ducts to prevent moisture condensation.
- If you have a fuel-burning furnace, stove, or other appliance or an attached garage, install a carbon monoxide (CO) monitor to alert you to harmful CO levels.
- Be sure to get professional help when doing ductwork. A qualified professional should always perform changes and repairs to a duct system.
Carbon Monoxide Detectors
Carbon monoxide (CO) detectors are required in new buildings in many states. They are highly recommended in homes with fuel-burning appliances such as natural gas furnaces, stoves, ovens, water heaters, and space heaters. An alarm signals if CO reaches potentially dangerous levels.