Good insulated package performance is incumbent upon our ability to regulate the absorption of heat. The methods we employ and trickery to which we resort in our feeble attempts to outsmart the natural laws of thermodynamics and prolong the inevitable rests not on our ingenuity, but on the adoption of cleverness that has been perfected by the insect world over millions of years.

Just before dawn, a lone darkling Beetle (Stenocara gracilipes) emerges from his burrow and scurries up the side of a towering sand dune in one of the most arid habitats on Earth, the Namib Desert along Africa’s southwest Skeleton Coast. Here, the cool ocean breezes generated by the cold Benguela current running up from Antarctica collides with a wall of barren desert sand that stretches for hundreds of miles, stifling rainfall, but creating a brief and dense morning fog. Once the beetle has staggered to the summit of the sand dune in the dim morning light, he turns into the wind and performs a slow-motion, acrobatic headstand with only his forelegs to support him. Remaining perfectly still, the approaching veil of fog drapes over him, quickly forming droplets of water on the hydrophilic bumps of his wing cases (the elytra). The water droplets settle in the hydrophobic channels between the bumps, and once large enough, roll up the beetle’s back towards his head and into his awaiting, inverted mouth.  Imbibing a few drops is all that is needed for him to race home, insulate himself by burrowing deep in the desert sand, and rely on the fog-harvested water to help regulate his body temperature and survive yet another desert day.

Recently, this model of fog-banking has gone high-tech. Students at the University of Engineering and Technology in Lima, Peru, have constructed a billboard with a hydrophilic surface, similar to that of the Darkling Beetle. They have elegantly engineered a method for capturing, condensing, funneling, purifying, storing, and dispensing up to 96 liters of fresh water a day from a single billboard. It requires no electricity to operate, little maintenance, and each costs less than $1,800 to install. The advent of this technology and design has made a positive impact on the people in this region of South America. The desert city of Lima and the nearby coastal villages receive less than one half inch of rainfall per year. Yet the atmospheric humidity is nearly constant at 98%. Since the billboards were installed, villagers and communities are now able to lessen their over-reliance on dirty and contaminated community well water, reducing their risk of contracting waterborne diseases and illnesses.

Additionally, the water is capable of aiding in the distribution of vaccines to the desert villages without depriving residents of precious drinking water. Just-Add-Water gel packs (JAW packs) containing a few grams of polyacrylate gel powder are able to absorb 400 times their weight in water. When frozen at area healthcare facilities, they provide longer refrigerant capabilities than frozen water alone and are used in portable carriers for vaccine transport to populations in remote locations. A few frozen JAW packs filled with spent fog-harvested water are all that is needed to insulate and protect the vaccines and survive yet another desert day.

No other creature on Earth can claim the prize for improving the quality of life for mankind more than the industrious honeybee (Apis mellifera). Since ancient times, humans have observed and treasured their complex societies and tireless efforts. In addition to the nutritional, medicinal and culinary benefits of honey that we enjoy — it is the only food made by insects that is consumed by man, never spoils and contains hydrogen peroxide, a natural antibiotic — and the nearly limitless uses for beeswax — everything from blacksmithing to surgical implants — honeybees offer us another great gift: insight into HVAC. That’s right. Modern air-conditioning and all that we know about rapid evaporation technology (used in some passive packaging systems), we owe directly to the honeybee’s profound architectural knowledge and behavior.

The honeybee’s ability to regulate temperature and humidity levels within the hive is essential for maintaining the protective and nutritional quality of the honey — the colony’s life source — and for ensuring proper development of the young pupa in the nursery during the summer months. If humidity levels are not held in check, the honey will spoil and the colony will die. Also, the temperature must be kept at a constant 34.5° C ± 2.5° C from late winter to early autumn, when the hive is active.

Here’s how they do it. In a typical hive (40,000–60,000 bees), honeycomb cells are built near the bottom of the structure along with the brood cells where the queen will lay as many as 1,500 eggs a day. These contain nectar collected from flowering plants and are comprised of about 80% water. The honey (the worker bees’ only food) is stored in a separate comb above the brood.

Walkways of exactly 3/8“ are maintained between sections of comb for passage and air circulation. As the outside temperature rises, bees within the hive (known as heater bees) line up in one direction and begin fanning their wings, increasing airflow circulation throughout the hive. This intentional and progressively accelerating draft keeps temperatures down and causes the water in the cells containing nectar and honey to evaporate, cooling the hive. When water concentration of the honey is reduced to exactly 18%, the bees know to seal-off the cells by secreting wax. The mass of stored honey provides a thick layer of insulation for the community busy at work below. Should the weather become excessively hot (as high as 43° C), some of the bees will forage for water, return to the hive, and place these drops of water in empty cells surrounding the brood and spread them in thin sheets across the empty comb. The bee’s fan-current evaporates the water, lowering the temperature even further. This is the same heat absorption physics behind some cutting-edge passive packaging systems commercially available today, where the evaporating blocks of nanoporous material are placed in a compartment above, cooling the product below.

In winter, honeybees don’t become dormant like many other insects, but create a warm microclimate inside the hive and subsist on the stored honey. They warm themselves and the nest as a whole by vibrating their flight wing muscles — like revving the engine in neutral. They retain this precious heat by allowing only small openings in the nest, secreting propolis (plant resins and gums), to seal holes and cracks, and by rallying around their queen in a clustering mass. By so doing, they can keep the core of the hive at 30° C, even if the outside temperature reaches minus 40° C. To maintain their heat-generating calorie burn, the colony consumes more than two pounds of honey a week throughout the winter, hence the strenuous collection of nectar during the warmer months.
In broader terms, the honeybee has educated us on how to protect vaccines from the ravages of heat and freezing during transport, a critical component for maintaining the quality of our version of the honey — vaccines — ensuring the protection of our young and elevating the quality of life in our communities.

The behavioral mechanism by which butterflies (Papilio, et.al.) regulate heat gain and loss is by body orientation angle and wing angle relative to the sun. Unlike moths, which generate heat through muscle movement, a butterfly’s ability to survive is dictated by the amount of direct solar radiation. This heat balance is essential for flight, eating, mating and migration. This also helps to explain why butterflies take to the wing only during the day, and moths at night. The ability of butterflies to absorb heat is precipitated on wing surface color, shape and patterns. The heat absorbing top-side of a butterfly’s wings are always darker in color than the underside, and act as giant solar collectors comprised of thousands of tiny hexagonal scales that serve the same purpose as radiator fins, to regulate the rate of absorption. The veins in a butterfly’s thin, membrane-like wings are nearly non-existent near the edges and become thicker and more abundant closer to its body, designed to help dissipate heat near the edges and concentrate the heat conductivity at the thorax. Hairs near the base of the wings and on its body provide additional heat dissipation to avoid overheating.

Solar radiation can play a significant role in the performance of packages designed to transport temperature-sensitive drugs. That is why most passive insulated shippers are made of white foam or are shrouded in white corrugate boxes or contain heat reflective liners and thermal pallet covers which can reduce the rate of radiant heat absorption by as much as 70%. Of course, size and geometry are also important and orientation to the sun plays a significant part, too. The temperature of a non-insulated aluminum air cargo container (called a ULD) sitting on an airport tarmac on a 20° C sunny day, can rise to an internal temperature of 76° C within 30 minutes. In fact, insulated packages of all types are most vulnerable to heat damage plane-side.

What will the next generation of thermal packaging design be? If the lessons we have learned in the past are any indication, we have only to look to nature for the answers. 

Reference

1. Nørgaard, T., and Dacke, M., Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetles. Department of Biology. University of Lund. Sölvegatan 35, S-22362 Lund, Sweden.

---

Kevin O’Donnell is senior partner at Exelsius Cold Chain Management – U.S. He is the former chair for the International Air Transport Association (IATA) Time & Temperature Task Force, a member of the USP Expert Committee on Packaging, Storage and Distribution, and a temporary advisor to the World Health Organization (WHO). He blogs at www.clutchcargo.us. He can be reached at kevin.odonnell@exelsius.us.