Effects of door opening pattern of an enclosed refrigerated display case on product temperature and energy consumption

Authors: DE FRIAS, ATILIO - University Of Maryland; Luo, Yaguang - Sunny; Zhou, Bin; ZHANG, BOCE - University Of Massachusetts; INGRAM, DAVID - Food And Drug Administration(FDA); VORST, KEITH - Iowa State University; BRECHT, JEFFREY - University Of Florida; Stommel, John

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2019
Publication Date: 12/7/2019
Citation: De Frias, A., Luo, Y., Zhou, B., Zhang, B., Ingram, D., Vorst, K., Brecht, J., Stommel, J.R. 2019. Effects of door opening pattern of an enclosed refrigerated display case on product temperature and energy consumption. Food Control. https://doi.org/10.1016/j.foodcont.2019.107044.
DOI: https://doi.org/10.1016/j.foodcont.2019.107044

Interpretive Summary: Enclosing open refrigerated display cases with glass doors improves temperature uniformity, enabling better maintenance of 5 °C or below cold temperature required by the US Food Code for fresh-cut leafy greens. However, the uncertainty surrounding the effect of door opening frequency and duration on temperature profiles and energy consumption hinders the adoption of this technology. USDA scientists demonstrated that door opening scenarios usually found in supermarkets did not significantly impact temperature uniformity, and operational energy consumption was reduced by 66% with doors even with this typical door opening regime. These findings will help the retail industry to continue embracing the display of highly perishable foods behind glass doors to support compliance with US Food Code with significant energy savings.

Technical Abstract: Retail display of highly perishable foods behind glass doors ensures uniform product temperatures, enabling better maintenance of cold temperature required for food quality and safety while reducing operational energy consumption. However, the associated effects of repeated door openings on product temperatures and the energy savings are unclear. In this study, we evaluated the effects of two frequencies (doors opened every 5 or 15 min) and four durations (doors held ajar for 5, 15, 30 or 60 s) on product simulator temperatures in a display case installed in our research supermarket. At ambient conditions (19.6 to 20.9 ºC, 60 to 70% RH), with a case thermostat setting of 0.6 ºC and a daily 30-min defrost cycle, the only statistically significant fluctuation in product simulator temperatures was found for the most aggressive opening schedule where the door was opened every 5 min for 60 s at each opening. Pairwise comparisons demonstrated that this treatment resulted in product simulator temperatures (< 6.6 ºC) that were significantly higher (p<0.001) or somewhat significantly higher (p<0.03) compared to product exposed to all other combinations. Product exposed to all other treatment combination resulted in temperatures that either never exceeded 5 ºC or briefly exceeded it only during the single 30-min defrost cycle. As a result, we selected an average opening sequence (every 10 min for 12 s) from the previous treatments to perform an energy consumption assessment of the case. Energy consumption was determined to be 66% lower than that compared to an open-retail display case (same model, make, size, operating schedule and thermostat setting). Even with the most extreme schedule where three of the six doors remained open continuously, there was still a measured 45% reduction in energy consumption as compared to that of the open-retail display case.