A Comparison of Energy Efficiency of Stainless Steel, Aluminum, and Enameled Cast Iron Pot
Induction cookers use the process of electromagnetic induction to produce heat more efficiently and with fewer polluting side effects compared to fuel burning methods. Ecuador has been implementing plans to make residential consumption of energy more efficient. The process of replacing liquefied petroleum gas (LPG) based cookers with induction cookers was started in 2014 . This change in household cookers is expected to be followed by increased manufacturing of suitable cookware. Villacís and colleagues  conducted a study to compare the energy efficiency of stainless steel, enameled cast iron and aluminum pots with similar dimensions. Their goal was to assess what type of cookware would be best for reducing household energy use.
Methods of the Study
The researchers evaluated the physical properties and performance of pots using several tests. In order to assess energy efficiency, they first looked at how well the pots could retain their heat at differing distances between the bottom of the pot and the induction zone. Next they measured the concavity/convexity of the pots, and exposed the pots to thermal impact situations to evaluate structural changes of the pots with heating. The study followed ASTM F 1521-03 and NTE 2851 standard testing procedures.
Outcomes of the Study
The first test assessed how well the pots could retain heat with increasing distance from the induction zone. The distance was increased by using fittings made of the same material as the pot being tested. The generated data revealed a dramatic plummet in the energy efficiency of the aluminum pot, which worked to a maximum height of 7.1mm. Beyond this point it did not retain enough heat. Meanwhile stainless steel and cast iron pots performed relatively similarly. They reached a maximum height of 15mm and their energy efficiencies declined at comparable rates.
The second test assessed the relationship between pot bottom concavity/convexity and energy efficiency. Pot bottom concavity is a slight inward bump at base of the pot which allows it to make more contact with the induction zone. The evaluation of concavity/convexity to energy efficiency was done using 6 stainless steel pots with different diameters. These tests showed that energy efficiency increased with increasing pot bottom concavity, until the concavity reached a maximum value of 0.9mm. The energy efficiency was approximately 94% at this point.
The next test judged which pot would maintain its efficiency and structural integrity with use. All three materials responded differently to heat. The stainless steel pot had a concave shape and it became convex, the aluminum pot had a convex shape and it became concave, and the enameled iron pot which was already concave increased its concavity. The researchers mentioned that the structural changes could pose problems to maintaining energy efficiency, mainly due to reduced contact between the induction zone and the pot. A convex base poses an additional problem of increased instability during use.
This part of the study also evaluated whether each pot sustained its initial energy efficiency after the expected structural changes due to heating had occurred. Interestingly the energy efficiency of the aluminum pot increased by 1.70% while the efficiency of the stainless steel pot and the enameled iron pot decreased by 3.28% and 6.9%, respectively. The increase in the efficiency of the aluminum pot was related to the earlier finding that increasing concavity also increases energy efficiency, until a certain point.
Although these results suggest that stainless steel may be the better option when manufacturing pots, it was actually the cast iron pot that performed the best throughout the testing procedure. Initially the efficiency of the cast iron pot was 91.35%, the efficiency of the stainless steel pot was 86.62%, and the efficiency of the aluminum pot was 82.10%. Even though the enameled iron showed the greatest loss in efficiency with continuous use, it actually outperformed the other two materials. The cast iron pot remained relatively similar to its initial structure and its energy efficiency value was approximately 85% after the test. Meanwhile the aluminum and stainless steel pots showed less structural stability due to the changes in their shapes and their efficiency values were approximately 83% after the test. The researchers also noted that after 40 tests all three pots still met the Ecuadorian energy efficiency standard of 80% .
This study assessed the energy efficiency of pots made from stainless steel, aluminum, and enameled cast iron. The materials all responded differently to regular heating but cast iron maintained the greatest structural integrity. This allowed the researchers to conclude that cast iron is the most sustainable option . This study was undertaken in response to the sustainability initiatives introduced by Ecuador in 2007, which aim to improve residential energy use . International Partnership on Mitigation and MRV, “Promoting Induction Cooking in Ecuador Promoting Induction Cooking in Ecuador,” 2015. [Online].  S. Villacís, J. Martínez, A. J. Riofrío, D. F. Carrión, M. A. Orozco, and D. Vaca, “Energy Efficiency Analysis of Different Materials for Cookware Commonly Used in Induction Cookers,” Energy Procedia, vol. 75, pp. 925–930, 2015.