Environmental Engineering Reference
In-Depth Information
Many sources of energy possess some risks to human health from direct exposure,
external contact, inhalation, or ingestion. Fossil fuels, especially coal, are known for their
emission of particle matter, mercury, aliphatic hydrocarbons, and aromatic hydrocarbons.
Continuous exposure to these compounds can cause respiratory illnesses, cancer, and
death. However, not only do fossil fuels have noxious emissions, but combustion of
ethanol also generates many aromatic compounds similar to those emitted by the
combustion of gasoline (Jacobson, 2007), and biodiesel produces particle matter similar
to regular diesel.
Similar to electricity, a calorie of mechanical energy has more value than a calorie of heat
and as a result a higher quality. Mechanical energy can be used to drive mechanical devices or
can be easily transformed to other forms of energy, such as electricity, that can be easily trans-
ported and converted back to mechanical, heat, or radiant energy. Also, 100 percent mechani-
cal energy can be transformed into heat, whereas heat (contained as chemical energy in fuels)
can be transformed into mechanical energy with an efficiency upto 50 percent. The other 50
percent is released to the atmosphere as a loss.
Furthermore, a high-temperature calorie has more value than a low-temperature calorie
because it can be converted into mechanical energy more efficiently (Bessette, 2003). In
contrast, low-temperature calories, also called “low-quality heat” or “waste heat,” do not have
enough energy to be converted into mechanical energy by traditional technologies. Efforts
are in place to develop equipment to harvest that low quality heat and put it to work to produce
electricity, mechanical energy, or in absorption refrigeration units.
Embodied energy
Embodied energy is the cumulative energy used in the production of manufactured goods
throughout its entire life cycle. Goods can be any product, such as a building, an automobile,
a pound of aluminum, a can of soup, or a kilogrem of beef.
For a generic product, the energy accumulated during its life cycle includes production of
raw material, transportation, manufacturing, distribution, installation, use of energy during
useful life, and disposal/decommission. More specifically for food products, the embodied
energy during production of raw materials includes expenditures in the production of fertiliz-
ers and pesticides, field machinery, irrigation, harvesting, and crop drying. Transportation
includes the energy spent to transport the raw materials from the farm to the processor and
once processed, from the processor to distribution centers, and from there to retailers.
Depending on the food product, the transportation, method, and the assumptions made, energy
use during transportation can vary between 3 and 12 percent.
Energy spent during processing varies proportionally to the degree of processing. Food
products that are low-processed foods accumulate a relatively small amount of energy during
processing. However, with exception of fruits and vegetables that can be eaten raw,
low-processed food need further preparation at home with the consequential consumption of
energy. Canning is the processing technique that has the lowest consumption of energy when
compared to other techniques. Food products that undergo phase changes during processing
(e.g., evaporation and freezing) have the highest energy consumptions and embodied energies
(Table 11.2).
To be protected and contained, processed food needs packaging, which contains its own
amount of embedded energy that ultimately becomes part of the embodied energy of the con-
tained food product. For instance, in a can of corn, approximately 27 percent of the embodied
energy belongs to the can (Brown and Batty, 1976).
