Drawing final lessons from the SDG framework for future engineering priorities.

The UN Sustainable Development Goals (SDG) that have not yet been addressed in this short series are: decent work and economic growth; responsible consumption and production; peace, justice and strong institutions; and partnerships for the goals (goals 8, 12, 16 and 17). However this month’s column is not just a catch-all, sweeping up the left-overs. These goals have a lot in common in the refrigeration context.

The thread that ties them together is energy efficiency.

I have been fascinated for several years—some of my colleagues might even say fixated—by the remarkable range in energy performance of cold storage buildings in the logistics sector. I find it difficult to understand how the average store in a pan-European survey could use ten times more energy on an annual basis than the best-in-class. This discrepancy is between the best and the average; by definition half must be worse than average.

In studying this phenomenon I have come to some surprising conclusions. The one that gets most resistance from the refrigeration community is that the best practice metric I use is not dependent on the design ambient for the site. I have studied warehouses in northern Europe, with a relatively cool climate, and in northern Australia, well into the tropics, and found if best practice design principles are applied, the annual energy use per cubic foot for the stores will not be significantly different.

This needs a little explanation. If the store is well insulated, well maintained and well run—all features of a “best practice” facility—the heat load imposed on the building by the ambient will not be significant. If the refrigeration system is well designed and well operated, over the course of a year the peak ambient operating condition becomes relatively unimportant. The key to best practice in this regard is to allow the compressor discharge pressure to float down as low as possible. In this way the efficiency overnight and in cooler months will dominate total consumption figures, and the relatively few times it has to run flat out won’t have a massive effect on overall performance. This idea can be extended to encourage operation during lower ambients by adjusting the setpoint automatically a few degrees.

Soccer commentators sometimes talk about “a game of two halves,” and the visual representation of the average daily changes in ambient dry-bulb temperature in the U.S. shown in this map paints a similar picture. On the right, where daily variation is on average less than 14°F (7.8°C) in July, the load shifting strategy is less necessary, but on the left, where daily variation can be as high as 45°F (25°C), a lot can be gained by floating heads and shifting loads.

My analysis of the SDGs reinforces that this is a great time to be an engineer. There is plenty of interesting and useful “decent work” around and great scope for economic growth in refrigeration. We need to take our responsibilities in consumption and production more seriously than in the past, and we need strong institutions, like ASHRAE, emphasizing the need for good engineering and encouraging a greater understanding of these odd quirks of system operation. Finally, we need to recognize that no segment of the industry can achieve these goals alone; it requires a higher degree of interdisciplinary collaborative work than ever before. This extends beyond our comfort zone of refrigeration engineering and needs to encompass finance, risk management, education, mentoring and, above all, communication skills.

Daily variation—a game of two halves.

SOURCE: PRISM CLIMATE GROUP, OREGON STATE UNIVERSITY; MAP FROM U.S. CENSUS BUREAU