New York City in the early 20th century was gripped with fear over a disease then known as “infant paralysis”: polio. An outbreak that began in 1916 affected 9,000 people and paralyzed 1,000 children before it was brought under control. At the time, there was not much parents and their children could do but live with the worry of contagion and manage the consequences of infection. Public warnings showing children in leg braces became a common sight in towns and cities. The threat of polio led U.S. President Franklin Roosevelt, himself afflicted by the disease, to launch the National Foundation for Infantile Paralysis (now the March of Dimes) in 1938 to fund polio research. Then in 1955, everything changed. Jonas Salk developed the first vaccine against the disease. Six years later, Albert Sabin developed an oral vaccine. Polio was officially eliminated from the U.S. by 1979.

Today, polio has been eliminated from all but three countries worldwide, thanks largely to the Global Polio Eradication Initiative, which started in 1988. Through the program, more than 2.5 billion children in 200 countries have been immunized. The effort has relied on more than $11 billion in funding and 20 million volunteers. And something else: refrigerators.

From the laboratory where vaccines are made to the final locations where they are administered, vaccines must be kept at constant, cold temperatures. (The optimal range is between two and eight degrees Celsius, according to the U.S. Centers for Disease Control and Prevention.) If they are not, they lose their potency and eventually expire altogether. The polio vaccine, for instance, loses around 10 percent of its potency at 25 degrees Celsius, and more than 25 percent when temperatures exceed 37 degrees—average spring and summer outside temperatures in India’s northern state of Uttar Pradesh, which was responsible for two-thirds of the global cases of polio in the early 2000s.

With the exception of safe water, no other modality to immunizations—not even antibiotics—has had such a major effect on mortality reduction.

The process of maintaining optimal cooling conditions for vaccines between transport, storage and administration is known as “the cold chain.” But maintaining the cold chain is a challenging proposition in many parts of the world. Nearly 50 percent of health centers providing vaccines around the world are either cut off from the electricity grid or lack access to a reliable flow of electricity; those that are grid-connected often operate in places that deal with power outages for 18 or 19 hours a day. Most health centers operating in those conditions rely on refrigeration systems that run on costly fuel-powered generators or batteries, or crude, unreliable cooling alternatives like ice. A 2014 study by the WHO and UNICEF found that only two percent of health facilities in low- and middle-income countries had adequate vaccine storage equipment; 20 percent had none at all. In many countries, more than 50 percent of immunization supplies are lost each year.

And yet, as the polio example indicates, vaccines play a crucial role in global health. “With the exception of safe water, no other modality, not even antibiotics, has had such a major effect on mortality reduction,” a 2009 report from the WHO, UNICEF and the World Bank declared.

Preventing vaccine spoilage to and within the many off-grid health centers around the world requires creative solutions, particularly amid intensifying efforts to end infectious disease epidemics by 2030 under the U.N. Sustainable Development Goals and independent directives from leading philanthropic voices like the Bill and Melinda Gates Foundation, which wants to eliminate malaria by 2025. These concerted efforts to increase the volume of administered vaccines will only intensify the need for a dependable cold chain. That is a challenge Julia Römer has been tackling since 2014.

Evaporative cooling

Römer is the lead engineer behind a new social enterprise called Coolar. Coolar was launched in 2014 to develop and commercialize an electricity-independent medical refrigeration system that can function without continuous power. Its product has yet to undergo a full field pilot and is not yet certified, but the technology underpinning it is simple and time-tested. Whereas typical refrigeration systems use a compressor to activate cooling, Coolar harnesses the natural cooling effect of evaporation through a physical-chemical reaction know as adsorption.


The cooling process starts with water being fed into a low-pressure evaporation chamber. As the water evaporates, the system’s internal temperature drops, cooling the storage compartment. Cooling continues until the evaporator fills with water vapor, at which point evaporation, and cooling, will stop.

To achieve greater cooling, an adsorbent is added to the process, to soak up the water vapor and create more space in the evaporator. The adsorbent Coolar uses is silica gel—the same agent that handbag and shoe manufacturers stash in little packs to prevent humidity and dampness from damaging their products. With the silica gel, Römer explains, “More water can evaporate, and the holding chamber will get colder and colder, like a normal fridge.”

Once the silica gel is full of vapor, hot water (60 to 70 degrees Celsius) is cycled through a heat exchanger, which heats and dries the adsorbent. The vapor in the silica gel condenses and then flows back into the evaporator, and the whole process starts again.

“Adsorption refrigeration has been known since the 1930s, but due to rapid electrification in the West it didn't take off,” explains Christoph Göller, who heads Coolar’s business development. Over the past decade, there has been renewed interest in the technology, however, particularly in Germany, whose ambitious near-term carbon emission reduction targets have spurred demand and investment in clean technologies of all kinds. “Advances in material science have enabled a small resurgence of adsorption refrigeration for industrial applications, mainly [to optimize] energy efficiency as we try to consume less due to our limited carbon budget,” Göller adds.

In fact, when Römer first began working on an electricity-independent refrigerator design as an industrial engineering student at Technische Universität Berlin, her focus was harnessing adsorption refrigeration on a small-scale for local household use, rather than solving medical cold chain issues in far-flung markets. But once Coolar was formed and market research got underway, the team realized there was not much demand among German consumers.

“We then looked at what are the most important items that need to be cooled in off-grid locations where our system has a natural reliability advantage, it turned out to be vaccines and medicines,” Göller says. The team discovered that major global health organizations and philanthropies are pouring money into new medical cooling technologies. The Global Alliance for Vaccines and Immunizations (GAVI) has alone allotted $650 million dollars for the cause, Römer says.

The cooling power of heat

Coolar’s technology has a unique advantage in many off-grid areas: because its cooling system runs on heat, it is potentially well suited for markets where natural sources of thermal energy are plentiful, and where small-scale solar technologies and alternative fuel innovations are gaining traction. “Storing heat is so much easier than storing electricity because we can just add a [storage] tank, so it [makes] sense to have a refrigerator that just runs on heat,” Römer explains. Being battery-independent also helps keep costs down.

Coolar has been testing its refrigerator with solar heat, using generic thermal panels. It stores the heat in an insulated tank for periods when there is no or low sunlight. “You don’t need really strong sun [because the system is] just using the warmth of the sun,” Römer notes, adding that even in locations that get little sun exposure, the system can be modified to work. Using concave mirrors to concentrate sunlight is one option, but any heat source—even a simple fire—that can warm water for the heat exchanger will work, Römer says.

There are limitations to Coolar’s technology, however, that the company is trying to contend with in its design. Scale is one. Coolar’s prototype capacities range between 180 and 200 liters, which will hold about 5,000 vaccine units. The size is on par with European household refrigerators but larger than other off-grid medical refrigerators on the market. The key reason is that adsorption refrigeration is better suited for larger systems.

“Smaller means more difficult with adsorption refrigeration devices because the cooling capacity is proportional to the amount of adsorbent—silica gel in our case—that can be put in the machine,” explains Göller. Building a small machine with a powerful and controllable cooling effect is a careful balancing act. “Then remove electricity from your toolbox and you have quite the engineering challenge on your hands,” he adds.

Other off-grid refrigeration manufacturers have had success with more standard designs, powered by solar-generated electricity. U.S.-based company Sundanzer manufactures small-format systems with 15 to 55-liter capacities powered by solar photovoltaic panels. The panel arrangement, consisting of two east-facing modules and two west-facing modules, can be installed onto a rooftop or pole or even on the ground if solar exposure is adequate. Sundanzer’s systems can self-regulate to the appropriate temperature for storing medical supplies using the power generated from the panels. What’s more, Sundanzer’s models also require no batteries, charge converters, or inverters.

“The fridges have a 100-hour holdover period,” says Krista Miller, general manager of Sundanzer’s office in Tuscon, Ariz. This means the refrigerators can stay cool for more than four days without a power supply.

Small format adsorption refrigeration is difficult because the cooling capacity is proportional to the amount of adsorbent in the device.

“To store medical vaccines, refrigerators need to be independently tested by an approved company via the WHO,” Miller adds. Sundanzer’s products are WHO certified medical products—a designation Coolar’s product is still too early-stage to attain, but one which reputable international health organizations require of the medical refrigerators they use.

“Certification only makes sense for finished products,” Göller explains. “We are still in the development-pilot stage, which means we are still making changes.” Coolar’s machines have been undergoing testing at an independent research institution in Potsdam, Germany, and the company has demonstrated one of its units at five remote health centers in Northwest Kenya. The team will wait for the results from the Potsdam tests before sending more units abroad, however.

Environmental “ifs”

The locations where Coolar conducts field tests will likely impact its final product. That is because refrigeration is highly climate-sensitive. While evaporative cooling is an effective way of lowering temperature—it is how humans and other animals that sweat keep from overheating—the process is most efficient in dry environments. Humidity poses a challenge.

“Any refrigerator is easier to run in dry [rather] than humid climates,” explains Göller. "The problem with humid air and temperature control are effects like condensation in the refrigerator that make cooling more difficult."

Developing refrigeration technology that will work in humid climates is an issue Ian Tansley is intimately familiar with. Tansley is the chief technology officer of Sure Chill, a U.K.-based off-grid refrigerator manufacturer. He has spent a lot of time working with refrigerators in West Africa, where he says an evaporative cooling system would be difficult to use. “It’s just too humid.” Tansely is quick to add that not every technology will be suitable to every climate, however.

The cooling technique Sure Chill uses in its systems is rooted in a simple fact of nature: that water is heaviest at four degrees Celsius. “You put ice in a glass of water, for instance, and after a couple of minutes, the water [just] beneath the ice will fall to the bottom of the glass,” Tansley explains. That is because the water that cools to four degrees Celsius first becomes heavier than warmer water. “Anything warmer will go upwards,” he adds. The result is a constant cycle of cooling, sinking, warming, rising water just below a frozen surface.

“When I first conceived it, to be honest with you, I thought we’d never be able to patent this, because every freshwater lake, every glass sold with ice at the top is essentially this system, but no one had patented this for refrigeration,” Tansley says. But the four-degree mark is significant in the immunization world, because it falls right in the optimal two- to eight-degree range.

Sure Chill was sponsored by the Gates Foundation to deliver what is essentially a passive device in which ice is placed and can then maintain an internal temperature of four degrees. The system has since made the list of WHO-approved medical refrigerators. Sure Chill’s products do require an energy input to ensure that the surface layer of water remains frozen, but Tansely says the system is source agnostic. “Because this system essentially relies on this density of water phenomenon, the source of the energy, the quality of the energy, the temperature you deliver that cooling to the system—it will translate anything to a perfect four degrees centigrade,” he explains.

Most off-grid refrigerators’ internal temperatures are not capable of such specificity, because they do not rely on a constant power source. Instead, they aim for a range. Coolar, whose device has two chambers, unlike typical household refrigerators, aims for an average of four to six degrees in the cooling chamber. Because it is a simple system that lacks control mechanisms, Römer explains the Coolar prototype is able to maintain this temperature range through constant active cooling. Household refrigerators, by contrast, do not run continuously; they have active cooling phases and inactive phases, when their cooling systems are off.

“When you have two chambers, one can be regenerating so that you have an [active] cooling system all the time,” Römer says.

She adds that vaccine storage procedures also help ensure that the storage chamber stays adequately insulated. “Normally people won’t open a [medical] fridge 10 or 30 times an hour. There are [strict] protocols they have to fulfill,” she says.

From lab to field

Coolar will determine how well its design functions under the often rugged conditions of remote, low-resource healthcare facilities once it starts distributing more of its devices for overseas field testing. Kenya has been the team’s main focus for piloting this year, because of a partner that is offering them access to a number of its remote health centers, Göller says. The European Institute of Innovation and Technology’s Climate-Knowledge and Innovation Communities (Climate-KIC) is helping Coolar explore potential pilots in Ethiopia and the Philippines, in addition to providing ongoing financial and business development support and mentorship. Coolar’s Climate KIC’s representative Timo Bandele Lassak does not deny the challenges ahead of the team.

“It’s quite difficult for them because health facilities in emerging markets usually don’t have a big budget,” he says.

“Of course, [Coolar] already has plans about the market size and who they would approach when it comes to a commercialization strategy,” Lassak adds. “But this is not what I’m focusing on, because we’re talking about two or three years down the road. My goal is to bring them out to rural areas and to have them successfully implement the pilot.”

Lassak, who has a background in development finance, has been working with former colleagues at German development agencies to identify pilot sites for Coolar’s device. A clinic in Ethiopia holds particular promise, Römer says. “They have all the same protocols that we have to fulfill, so they can test our refrigerator next to their normal ones” even if they do not immediately test with live vaccine samples, she adds.

“The financing part is really crucial. But most funding organizations working in the field are not able to fund product development.”

Coolar’s team has also been in discussions with potential pilot partners in India and Latin America, as well as with humanitarian aid organization Médecins sans Frontiers (MSF), which has health projects around the world.

Finding funding to support the pilots and post-pilot product revisions is the big challenge for Coolar at the moment. The team has made it this far with its product development and testing with €125,000 from Climate-KIC and awards from innovation and start-up competitions, like the Chivas Regal “Venture” challenge. But hardware innovation is cost-intensive, Römer says. The team will need additional backers if they are to succeed in eventually delivering Coolar to market. “The financing part is really crucial,” she explains. “You need to make sure you get the development right, and that you have the money for the material and the people.”

But, Römer adds, that kind of financial support is hard for early-stage businesses like Coolar to find. “Most of the organizations that are working in the field are not able to fund risky [product] developments, or [product] development as a whole.”

An eventual market

Coolar is hoping, however, that some of the small health organizations that test its product in the field will eventually become customers. The team is also eying large international NGOs like MSF and UNICEF, with whom Sure Chill and Sundanzer both partner. These large organizations are invaluable to building a more reliable immunization cold chain in low- and middle-income countries.

“[UNICEF] works with the ministries of health in various countries to help them procure on a larger scale—100 to 1,000 units,” Sundanzer’s Miller says. “They help get [refrigerators] into countries and get them installed.”

Miller’s company targets sales to these organizations, rather than working with individual clinics or small, local healthcare providers. Sure Chill does as well, but also works with governments health systems. For example, if a ministry of health in a particular country indicates a need to improve immunization delivery and is looking to purchase medical fridges, they will look to the major players for options. Often government health ministries buy medical refrigerators through international procurement organizations, like UNICEF, Tansley explains. “But the countries also buy directly.”

Sure Chill has about 10,000 refrigeration units disbursed across 38 countries, according to Tansley. The company’s unit capacities average between 30 and 50 liters—20 to 25 percent of Coolar’s current model. But on a recent trip to Nigeria, Tansley was told that one of Sure Chill’s units served about 30,000 people. “The volume can be misleading, because you can hold a lot of vaccine in quite a small space,” he explains. “[A population of] 20,000 or 30,000 can be served by a refrigerator with 100-liter capacity.”

That one product can contribute so much to global health underscores why Coolar is pushing to get its technology into the field and test the potential of evaporative cooling in the medical cold chain. “This is a really big problem,” Römer says. “We want to help in any way.”