Week 8: Chapter 4- Mechanical Systems

Chapter 4

Mechanical Systems  

In Chapter 4 we learned to, Identify renewable fuel sources, Compare heating systems and cooling systems and methods of heating and cooling, Specify the importance of commissioning of systems with which they are involved, Identify issues of human comfort with regard to HVAC, Show how to apply LEED energy-efficiency credits to a project.

Both mechanical and electrical systems require a fuel source in order to operate. The fuels used to generate power come from several sources, some of which are sustainable, and many of which ultimately are not. The US Department of Energy (DOE) acknowledges the following energy sources: bioenergy, coal, electric power, fossil fuels, fusion, geothermal, hydrogen, hydropower, natural gas, nuclear, oil, renewables, solar, and wind. These sources can be subdivided into those that fall under the Renewable Energy/Biomass program and those that do not.

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 biodiesel from corn has led to higher prices and concerns over the sustainability of growing corn itself because of intense reliance on petroleum-based fertilizers.

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  Fossil fuels provide over 85 percent 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 Energy Information Administration (EIA) in 2020, petroleum and natural gas account for 68.8 percent of current energy use in the United States. Coal is used for 11.3 percent, nuclear energy for 8.5 percent, and renewables account for only 11.5 percent. The transportation sector used 37 percent, industrial 35 percent, residential 16 percent and commercial 12 percent of all energy.

• 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 

• 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.

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  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 percent 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 photocells. Some people also object to the appearance of solar panel arrays.

• Photovoltaic (PV) arrays consist of a grouping of PV panels. A PV panel is a group of PV modules, each of which is composed of several PV cells. The PV array can either be a stand-alone power system with batteries for power storage or can be connected into the power grid, allowing it to “sell back” surplus power as well as to draw power when needed.
  

• Geothermal heat is an expensive though truly renewable resource. Strategies for geothermal heat range from deep penetration to molten rock through shallow groundwater solutions. Geothermal systems rely on the natural heat and cooling of the earth to provide energy. The advantages of geothermal systems include the elimination of boiler and heat rejector installation, operation, and maintenance, the elimination of all outdoor equipment, the elimination of water loop temperature controls, reduced mechanical room size, and increased energy efficiency. 1 There are several types of geothermal systems including closed-loop and open-loop systems. Within these two basic types, there are also several variations. For example, a closed-loop system can be horizontal or vertical or based under a body of water, while an open-loop system most commonly involves deep underground vertical cores.
  

• Electric power can be made in many different ways. According to the US Department of Energy, 11.3 percent of the nation's electricity was produced from coal in 2020. The fastest-growing fuel source for electricity generation is natural gas. Similar to coal, natural gas is a fossil fuel and is, therefore, ultimately in limited supply. Renewable energy sources accounted for only 11.5 percent of all electricity produced in the US in 2020. Fusion-produced energy is a current area of research, as is plasma research. The DOE is exploring both as possible energy sources for the future.

Fuel Considerations

• The choice of fuels must be tempered by a variety of concerns including cost, availability, and environmental impact. The majority of scientists agree that greenhouse gas emissions as the result of burning various fossil fuel sources have led to global warming. Many scientists also submit that we have reached the point where our consumption of oil is outpacing our ability to extract it from the earth, otherwise known as “peak oil.” According to these scientists, the availability of oil will continue to decline from this point forward. Coupled with this is the fact that many major sources of oil production are located in the Middle East, a politically unstable area for the United States.
• Nuclear fuel poses its own set of issues related to the disposal and containment of nuclear waste that is radioactive for millions of years. Communities across the world oppose the use of nuclear power and/or the disposal of nuclear waste.

Greenhouse Gases and Carbon Dioxide Emissions

• According to the DOE, the primary sources of carbon dioxide emissions by the US in 2012 include petroleum (43%), coal (31%), and natural gas (26%). Electricity generation (39%) and transportation-related (34%) greenhouse gases account for the majority of these emissions, followed by buildings (27%). Of the total greenhouse gas emissions, 92 percent consisted of carbon dioxide. The US was responsible for 17 percent of the total greenhouse gas emissions around the world in the most recent year for which data is available, 2011. Greenhouse gases trap heat in the form of radiation into the atmosphere, thus warming the surface of the planet. Major fossil fuels (coal, petroleum, and natural gas) account for 87 percent of the total energy used in the US during the past ten years.

Mechanical Systems

• Power produced from the different fuel sources can be used to power various types of mechanical systems. The common term for interior heating and air systems is HVAC (heating, ventilation, and air conditioning). The goal of HVAC systems is to provide for human comfort, and several different systems exist.

Human Comfort

• Human comfort varies from culture to culture as well as person to person. In the United States, most have come to expect interior spaces that have a fairly consistent interior temperature. How comfort is experienced is the result of a couple of factors including temperature and relative humidity: most can tolerate higher temperatures if the relative humidity is lower. 
• Creating these comfortable interior conditions in many areas of the world requires mechanical treatment of the air. These mechanical treatments are divided into heating and cooling and rely on the following methods of heat transfer: evaporation, radiation, convection, and conduction. Evaporation occurs when air moves across a wet surface, causing moisture to turn to vapor.
• An example of this would be standing in front of a fan after jogging a mile and sweating. When a warm body gives off heat this is called radiation. The car engine that has been driven recently radiates heat. Convection involves the movement of molecules. An example of this is the tendency of hot air to rise. Conduction occurs when two bodies are in direct contact. When stepping onto a cold tiled floor in the middle of winter, heat is conducted from the foot to the cold tile, making the feet become cold.

Heating Systems

• Heat comes in three forms: latent, sensible, and radiant. 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. As the first law of thermodynamics states: energy cannot be destroyed, it can only change state.
• There are several types of heating systems, and all of them rely on the previously mentioned methods of heat transfer. In general, heating systems can be divided into those that use water (hydronic systems) and those that use air.
  

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 relies on heating the surfaces of a space--walls, floor, or 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 these two sources. Similarly, radiant floor 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 baseboards or wall-mounted units.

Wood Systems

• Wood stoves/fireplaces have traditionally been used as a source of heating for historic buildings (prior to coal and electricity) as well as for off-the-grid buildings. Today, it is possible to purchase high-efficiency wood-burning stoves that include catalytic converters that burn the combustible gases, thus reducing the resultant air pollution. Masonry stoves provide thermal mass, thus adding to the indoor heat that is then radiated into the space. Thermal mass is the capacity of a body to store heat. Inserts can also be purchased to retrofit existing fireplaces.
• Wood pellets are compacted biofuel made from wood waste such as sawdust and provide a consistent heat source. They are compact to store because of their small size. Pellet stoves use wood pellets as fuel and are traditionally more efficient than other wood-burning systems. These can also be either freestanding or in the form of a fireplace insert. As with other wood systems, a chimney is required.
  

Geothermal Systems

• Ground Loop Heat-Pump Systems- These systems use either water or antifreeze that circulates through a closed loop. The pipe loop works as a heat exchanger and can be located either horizontally or vertically. Commercial systems often use vertical placement because of lot size restrictions. A horizontal placement is located three to six feet below ground, whereas the vertical loop might go as deep as 300 feet.
• Surface-Water Heat-Pump Systems- In the surface-water system, the heat-exchanger loop is located a minimum of ten feet beneath a body of water and is considered to be the most cost-effective system. When run beneath a pond, a closed-loop system can be used. By contrast, an open-loop system uses surface water as the heat exchange fluid and is circulated through the geothermal pump. This option is viable only where there is a plentiful supply of clean water.
• Groundwater Heat-Pump Systems- Water pumped from a well is used for the groundwater system. These are divided into three types: open systems, closed-loop systems, and standing-column systems. These systems can be very cost-effective.
• Hybrid Geothermal Systems- The hybrid system combines geothermal with another type of system. This hybrid approach is both highly efficient and cost-effective.

Cooling Systems

• Cooling can be provided to a space in three basic ways: by avoiding heat gain, by passive cooling strategies, and by mechanical cooling. A heat avoidance strategy involves siting the building to take advantage of prevailing winds, avoid direct sunlight, and allow for breezes. Several strategies have been adopted in different parts of the world to take advantage of passive cooling. Examples of passive cooling measures include front porches, wrap-around porches, deep overhanging eaves, towers for ventilation of hot air, central stair halls that are vented at the top, and the use of jalousie, hopper, or casement windows to direct breezes.

Types of Mechanical Cooling Systems

• There are several types of cooling systems, including central station systems, split systems, packaged units, and through-wall systems. Large buildings commonly use a central station system. The unit itself can be placed in the basement, on the roof, or split between these two locations.
• A split system is more commonly used in smaller buildings, including some residential applications. In this type of application, the compressor and condenser coil are located outside in a unit, whereas the evaporator coil and air handler are indoors.
• A packaged unit is generally placed on the roof with one unit for each zone. Air is provided to interior spaces through a series of ducts.
• A through-wall unit has the evaporator coil and fan on the inside, and a condenser coil, fan and compressor on the outside. These are frequently found in residential and hotel applications and tend to service a single room.
• Many interior spaces require air treatment in the form of either humidifying or dehumidifying to meet the comfort zone on a psychrometric chart. In humid parts of the country, dehumidification will reduce the perceived temperature during the summer months. Similarly, more humidity might be introduced during the winter for temperature increase and to reduce static electricity that is generated by really dry air conditions.

Blogging Assignment

Solar Power

Advantages:

• Reduced electricity bills: Solar panels can reduce your monthly electricity bills by up to 50% or more. 
• Increased property value: Installing solar panels can increase your property's value. 
• Energy independence: Solar panels allow you to generate your own electricity and store it for later use. 
• Environmental benefits: Solar panels are non-polluting and don't emit greenhouse gases, which are a leading cause of climate change. 
• Low maintenance: Solar panels have few or no moving parts, so they require minimal upkeep and are less likely to need repairs or replacements. 
• Tax breaks: You may be eligible for tax breaks when you use solar power. 
• Climate versatility: Solar systems work well in a variety of climates. 
• Renewable energy: Solar energy is a renewable energy source that's available every day and can be harnessed in all areas of the world. 
• Grid independence: Solar panels allow you to keep your lights on during grid outages. 
• Water conservation: Solar panels can help reduce water usage. 

Disadvantages:

• Solar installation is expensive- Purchasing, and then installing, a solar energy system is expensive.
• Solar panels are inefficient- According to the second law of thermodynamics, no machine will ever reach 100% efficiency. 
• The roof is not suitable for solar- If your roof doesn't face the sun, you won't be able to capture enough solar energy. 
• Energy storage challenges- To address the intermittent nature of solar power, energy storage solutions like batteries are often needed
• Solar energy depends on weather- A solar system totally relies on sunlight to produce electricity, making it vulnerable to weather variations.

Sources:

https://convert-solar.com/the-advantages-and-disadvantages-of-solar-energy/

https://www.poweredbydaylight.com/blog/what-are-the-main-disadvantages-of-solar-energy/

https://bkvenergy.com/learning-center/solar-energy-pros-and-cons/

https://www.bluettipower.com/blogs/news/top-7-advantages-and-disadvantages-of-solar-energy

https://www.photonbrothers.com/blog/how-much-will-my-electric-bill-be-with-solar-panels#:~:text=One%20of%20the%20main%20benefits%20of%20solar,amount%20you%20spend%20to%20install%20the%20panels.