Environmental Engineering Reference
In-Depth Information
evolving and servers are becoming more energy efficient. However, it is expected that by 2050
the emissions resulting from data processing will surpass those from the airline industry
(Thomas, 2009).
Transportation
Transportation creates local and regional impacts as a result of burning fossil fuels,
including emissions of carbon monoxide, sulfur dioxide, volatile organic compounds,
NOx, and particle matter; and global impacts in the form of carbon dioxide and chloro-
fluorocarbons (CFCs) and hydrofluorocarbons (HFCs) from refrigeration and air-condi-
tioning systems. Other indirect emissions come from the use of consumable items
including motor oil and tires.
Transportation from food processors or packers to distribution centers is done by heavy-
duty semi-trucks (e.g., eighteen-wheelers, or Class 8 truck in the United States) or by train. In
some cases, one or more legs of the trip use planes or vessels followed by at least one leg by
truck. However, invariably transportation from the distribution center to the customer (e.g.,
retail, wholesaler, or consumer) happens by truck, which can be heavy- or medium-duty.
Heavy-duty trucks have better fuel efficiencies than medium-duty in terms of tonne of cargo
per kilometer and liters of diesel (tons per mile per gallon).
Furthermore, the incoming traffic of trucks to distribution centers takes place on
interstate highways without frequents stops and turns. Quite the opposite, trucks leaving
distribution centers en route to customers are subjected to city traffic with frequent stops,
waits, and turns, which reduces the fuel efficiency even more. See more details on this topic
in Chapter 13.
The refrigerated supply chain
Refrigerated supply chains are designed to handle food products that need chilling or freezing
temperatures. These are complex systems that contain uninterrupted links capable of
maintaining particular temperatures for each group of food products.
In the case of produce that need chilling, the refrigerated chain starts immediately after
harvesting when the produce is precooled to remove the “field heat” and then transported
in refrigerated trucks to grading facilities where they are classified, graded, and packed.
From there, products are stored in refrigerated warehouses and transported with refriger-
ated trucks to refrigerated distribution centers and grocers. Fruits and vegetables have
different sensitivities to temperature, so they need to be chilled to the adequate temperature
according to how tolerant to low temperatures they are. Some fruits and vegetables can be
frozen (Fig. 3.8).
Animal protein is chilled at processing plants after slaughter and then kept chilled, further
processed, or frozen. Similarly, ready-to-eat foods are distributed chilled or frozen.
With the exception of vacuum cooling, used to precool produce in the field, and cryogenic
fluids, used to freeze food products, low temperatures in refrigerated supply chains are attained
with equipment working according to the vapor compression cycle. The main environmental
impact of this type equipment is energy consumption and furtive emissions of refrigerants.
Some of these refrigerants destroy stratospheric ozone and others have a high global warming
potential. Chapter 8 includes a discussion on the emission of refrigerants from refrigeration
equipment and Chapter 11 discusses their energy consumption.
