Chapter 4 Mechanical Systems

 Sources of Fuel

Bioenergy is produced from organic matter such as corn, municipal waste, and wood. In theory, these resources are renewable, but additional energy is required for their production. Furthermore, the recent emphasis on bio-diesel from corn has led to higher prices and concerns over the sustainability of growing corn itself because of intense reliance on petroleum-based fertilizers.

Fossil fuels provide over 85% of the fuel for electricity in the United States.

Fossil fuels include petroleum, coal, and natural gas. All fossil fuels are finite in quantity, in that they take millions of years to accumulate and are associated with greenhouse gases.

Coal is a naturally occurring fuel that can be obtained either through underground mining operations or strip mining. Although coal is abundant in some parts of the world, it takes millions of years to form. After this resource has been tapped, it will take millennia to reconstitute. Coal has long been associated with pollution (mercury, nitrogen, and sulfur) and greenhouse gases. New programs are being created to capture these gases as well as to make mining a safer occupation for miners. According to some researchers, this technology will not be resolved until 2030, and by this time, it will be too late with regard to greenhouse gas emissions and global warming.

Oil, like natural gas and coal, is a fossil fuel and is largely dependent on foreign sources, particularly those located in the Middle East. According to the DOE in 2007, oil was used in 99% of vehicles and represented 40% of current energy use in the United States.

Natural gas is a fossil fuel used for some alternative-fuel vehicles and is touted as clean burning. The use of natural gas as a fuel source has increased substantially in the last few decades. Fracking (short for hydraulic fracturing) is a much-debated way to obtain natural gas and oil from the earth by injecting high-pressure fluids into rock to fracture it, thus releasing the natural gas contained within. The fracking process uses water and sand combined with chemicals (some of which are known toxins). The process results in toxic waste that can endanger local water supplies.

Hydrogen is a commonly occurring element. Developers of hydrogen technologies seek to reduce US dependence on foreign oil. Hydrogen can be made from fossil fuels and renewable sources such as wind, geothermal, and solar. No emissions result from hydrogen-fueled vehicles.

Nuclear energy has long been the subject of debate in the United States.

The primary reason is that radioactive material is produced which must then be stored for millions of years. The DOE is currently working to make nuclear energy a viable, competitive, and environmentally sound choice. A major concern associated with nuclear energy is the possibility of a reactor meltdown and leakage of radioactive materials into the surrounding area.

Renewables are energy sources that are not limited, and are constantly refreshed. These include solar power, wind power, hydropower, and geothermal sources.

Wind turbines are placed on the landscape to capture the prevailing winds and convert them to energy in the form of electricity. Although these are now commonly used in some parts of the country, they raise concerns among environmental advocates over danger to birds and bats. Others object to the appearance of windmill farms on the landscape or to the noise they produce. Recent efforts to locate wind farms off the coast have also met with resistance.

Hydropower (also called hydroelectric power) is generated by water and is, therefore, a renewable energy source. According to the DOE, researchers are looking for ways to reduce the environmental impact of this power source that has the current capacity to produce the equivalent energy to 500 barrels of oil. The US currently uses approximately 18.89 million barrels of oil per day; of this, less than one half of 1% is biofuel, according to the DOE. The environmental impact associated with hydropower includes the damming of large bodies of water and the subsequent destruction of adjacent land through flooding, as well as the potential for dam breaks and downstream flooding.

Solar energy comes from the sun. Methods for capturing this energy include photovoltaic cells and solar panels. Solar energy can be stored in batteries and used to generate electricity and heat water for buildings. The primary drawbacks of solar energy include the high cost of collection cells, the use of batteries, and the use of cadmium in photo cells. Some people also object to the appearance of solar panel arrays.

Heating Systems

Sensible heat is measured using a thermometer. Latent heat marks a state change such as solid to liquid or liquid to gas. Radiant heat is a form of electromagnetic radiation.

Hydronic Systems 

Boilers are used to heat water to provide either hot water or steam for heat.

The hot water or steam is pumped and then piped through a building and delivered to various room units. This system is commonly used in large buildings and multi-building complexes. Boilers require expansion tanks for the water to expand as it heats, piping to and from unit radiators, a pump to move the water or steam, and radiators. The hot water may also be used for other applications in the building.

Radiators can be divided into two types: steam and hot water. Steam radiators are primarily found within historic buildings and have been largely replaced with hot-water radiators. According to the DOE, hot-water radiator systems are the next most common system after the heat pump in new residential constructions in the United States.

Electric Systems 

Radiant heating relics on heating the surfaces of a space wall, Root. ot ceiling. The two primary types of radiant systems include radiant panels and radiant floors. In both systems, heat can be provided using either electricity or hot water. Radiant panels consist of aluminum that is heated using one of their tro sources Similarly, radiant for systems incorporate either electric cables, or water piping through which heat is distributed to the floor.

Forced air is the most common system installed within new residential and commercial constructions. Using outside air, the heat pump moves warm air through the interior in the winter months and reverses to push in cool air during the summer months. Air-source pumps are the most common, although other types of systems exist, such as the ground-source heat pump.

The ground-source heat pump is much more efficient, but it is expensive to

install.

Furnaces are used to heat air that is then distributed through the building using ductwork. If fossil fuels are used to heat the air, a chimney flue is required to vent the gases to the outside. These contain a pilot light for continuous operation. Depending on the specifics of the system, these can either be inefficient or highly efficient.

Electric resistance is a type of system that uses electricity to produce heat.

The electricity itself can be produced from a variety of fuels. Because of the inefficiency of this process, electric heat is expensive. Delivery methods for this form of heat include both forced-air systems and individual room baseboard or wall-mounted units.