Residential Energy Audit - Chapter 1

Relative humidity measures how saturated the air is with a percentage of water vapor. It is a measurement of the amount of moisture in the air compared to the maximum amount of moisture the air can hold at a given temperature. A higher relative humidity indicates that the air is holding more moisture, while a lower relative humidity indicates that the air is drier. This measurement is important in understanding weather patterns, as well as for various applications such as agriculture, HVAC systems, and human comfort.

Temperature is a measure of how fast molecules in a substance are moving or vibrating. It is a physical quantity that indicates the degree of hotness or coldness of an object or environment. The correct spelling of the word is "temperature," and the other two options, "temperture" and "tempereture," are misspellings of the word.

Metalized coatings are used on glass to reduce its solar transmittance by reflecting some solar radiation. This helps to control the amount of heat and light that passes through the glass, making it more energy-efficient and reducing the need for cooling systems. By reflecting solar radiation, the metalized coating also helps to protect the interior of buildings from harmful UV rays, which can cause fading and damage to furniture and other objects. Additionally, the metalized coating can enhance the appearance of the glass by giving it a reflective or tinted finish.

Heating engineers use a unit of measurement called a heating degree day (HDD) to describe how long the temperature is below 65 degrees Fahrenheit during each day, month, or year. The HDD is a useful metric for determining the heating requirements of a building or a region, as it quantifies the severity and duration of cold weather conditions. By calculating the HDD, heating engineers can accurately estimate energy consumption and determine the appropriate heating system size and capacity needed to maintain a comfortable indoor temperature.

Relative humidity refers to the amount of moisture present in the air compared to the maximum amount it can hold at a given temperature. The level of relative humidity can greatly affect how comfortable individuals feel in a particular environment. High relative humidity can make the air feel heavy and sticky, while low relative humidity can result in dryness and discomfort. Therefore, relative humidity is often more important than the outdoor air temperature in determining comfort as it directly impacts how the air feels and affects the body's ability to regulate temperature through sweat evaporation.

A BTU (British Thermal Unit) is a unit of measurement used to quantify heat. Specifically, it represents the amount of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit.

To find cooling degree days, you need to calculate the total number of degree-days by adding up the daily degree-day values. The degree-day values are determined by subtracting the cooling balance point, which is a specific temperature (in this case, 78 degrees F), from the average temperature. This calculation helps estimate the amount of cooling needed to maintain a comfortable indoor temperature.

Latent heat refers to the heat that is released or absorbed during a phase change, such as when a substance changes from a solid to a liquid or from a liquid to a gas. This heat is not available for use because it is involved in the process of changing the state of matter rather than raising the temperature.

Water boils at 212 degrees Fahrenheit or 100 degrees Celsius. This is the temperature at which water changes from a liquid to a gas and forms bubbles. The boiling point of water is influenced by factors such as atmospheric pressure, altitude, and impurities in the water. In the Fahrenheit scale, 212 degrees is the boiling point, while in the Celsius scale, 100 degrees is the boiling point of water.

This statement is based on the law of conservation of energy, which states that energy cannot be created or destroyed, only converted from one form to another. This means that the total amount of energy in a closed system remains constant. Therefore, the statement is true.

When warm air comes into contact with cool objects, the temperature difference causes the warm air to cool down. As the air cools, it loses its ability to hold moisture, resulting in the formation of tiny beads of water on the surface of the cool objects. This process is known as condensation. It is responsible for the formation of dew on grass in the morning or frost on a freezing cold surface.

During the refrigeration cycle, the refrigerant evaporates in the evaporator and absorbs heat from the metal tubes, fins, and passing air. The compressor then compresses the refrigerant, preparing it to condense within the condenser. In the condenser, the refrigerant's latent heat is transferred to the condenser's tubes, fins, and the passing air. This process allows for the removal of heat from the refrigerated space, making the statement true.

Glass is known for its transparency and ability to allow light to pass through it. This property also applies to solar radiation, which is a form of light. Therefore, it is true that glass can transmit around 80% to 90% of incident solar radiation.

Heat is trapped within a greenhouse due to the combination of glass' solar transmittance and infrared absorbency. Glass allows solar radiation to enter the greenhouse, which warms up the interior. However, the glass also absorbs and re-emits the infrared radiation that is emitted by the warm objects inside the greenhouse. This trapped infrared radiation cannot easily escape, leading to an increase in temperature within the greenhouse. The lack of ventilation further prevents the escape of heat, contributing to the greenhouse effect.

Completely saturated air means that it is holding the maximum amount of water vapor it can hold at a given temperature. When air is saturated, its relative humidity (rh) is 100%. This means that the air is holding all the moisture it can hold and any additional moisture will result in condensation or precipitation.

Relative humidity is a measure of the amount of moisture present in the air compared to the maximum amount the air could hold at that temperature. When relative humidity is high, the air is already saturated with moisture, making it difficult for sweat to evaporate from the skin. This is because evaporation is the process by which sweat cools the body, and if the air is already saturated, the sweat cannot evaporate effectively. Therefore, a high relative humidity reduces the effectiveness of sweat evaporation, leading to discomfort and potentially heat-related illnesses.

The statement is false because there is efficiency loss the further the heat travels through the air duct distribution system away from the heat exchanger. As the heat travels through the ducts, it encounters friction with the walls of the ducts, which leads to heat loss. Additionally, there may be leaks in the ducts, further contributing to heat loss. Therefore, the efficiency of heat transfer decreases as the heat travels further away from the heat exchanger.

Cooling degree days are less reliable as a predictor of summer cooling costs than heating degree days are for winter heating costs. This is because the amount of shade and relative humidity play a significant role in determining comfort during the summer, in addition to the outdoor air temperature. Therefore, relying solely on cooling degree days may not accurately estimate cooling costs.

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed in an isolated system. It can only be transferred or converted from one form to another. This principle is based on the understanding that energy is a fundamental quantity that remains constant in any physical process. Therefore, the correct answer is "Energy can not be created or destroyed."

This statement is true because wind is caused by the movement of air from areas of high pressure to areas of low pressure. The air moves in order to equalize the pressure difference between these regions. This movement of air creates wind, which can be felt as a breeze or a strong gust depending on the pressure difference.

Darker colors actually absorb a higher percentage of incoming solar energy. Dark colors tend to absorb more light and heat, while lighter colors reflect more light and heat. This is why wearing lighter colored clothing in hot weather can help keep you cooler, as it reflects more sunlight away from your body.

Incandescent light bulbs work by passing an electric current through a filament, which heats up and produces light. However, a significant amount of energy is lost in the form of heat. This is because the process of converting electrical energy into light is not very efficient in incandescent bulbs. Only about 10% of the electricity is actually converted into visible light, while the remaining 90% is released as heat. Therefore, the statement that only 10% of the electricity is converted into light in incandescent light bulbs is true.

Conduction is the transfer of heat through direct contact between particles of a substance. In this case, the correct answer states that heat conducts through solid objects. This means that when there is a temperature difference between two objects in contact, heat energy will flow from the warmer object to the cooler one through the solid material. This process occurs due to the vibration and collision of the particles within the solid, allowing the transfer of thermal energy.

Metalized glass coatings are commonly known as low-e glass. Low-e glass, or low emissivity glass, is a type of glass that has a thin metallic coating applied to its surface. This coating helps to reflect heat and reduce the amount of ultraviolet and infrared light that can pass through the glass. This improves the energy efficiency of the glass, making it a popular choice for windows and other applications where thermal insulation is important. The term "metal glass" and "carbon glass" are not commonly used to refer to metalized glass coatings.

The correct answer is "The heat content is directly related to the mass of the water." This means that the amount of heat energy stored in a given amount of water is directly proportional to the mass of the water. In other words, the more water there is, the more heat energy it can hold. This is because heat energy is transferred and stored in the water molecules, and the more molecules there are, the more heat energy can be absorbed.

The sun's rays are more intense when directly overhead because they travel through less of the Earth's atmosphere. When the sun is directly overhead, the rays have to pass through a shorter distance of the atmosphere, resulting in less scattering and absorption of the sunlight. This allows more of the sun's energy to reach the surface, leading to higher intensity.

The second law of thermodynamics states that heat naturally flows from regions of high temperature to regions of low temperature, without the need for any additional energy from an external source. This principle is known as the law of heat transfer or the law of entropy. It explains why hot coffee cools down in a cold room and why ice melts when left at room temperature. The law also implies that it is impossible to have a completely efficient heat engine, as some energy will always be lost as waste heat.

Radiation is the transfer of heat through electromagnetic waves, such as infrared radiation, without the need for a medium to conduct it. Unlike conduction (heat transfer through solid objects) and convection (heat transfer through a moving liquid), radiation can occur in a vacuum or through empty space. Therefore, the correct answer is "heat flies through space from one object to another."

Convection occurs when heat is transferred by a moving liquid such as air. In this process, the heated particles in the liquid become less dense and rise, while the cooler particles sink. This creates a continuous circulation of the liquid, allowing the heat to be transferred from one area to another. This phenomenon is commonly observed in everyday life, such as when hot air rises and cool air sinks, creating air currents and breezes.

Temperature, relative humidity, solar radiation, precipitation, and wind effect all affect the comfort of people outside. Temperature refers to the level of heat or coldness in the environment, which can impact how comfortable individuals feel. Relative humidity is the amount of moisture present in the air, and excessive humidity can make it feel hotter and more uncomfortable. Solar radiation refers to the energy from the sun, which can cause discomfort if it is too intense. Precipitation, such as rain or snow, can also affect comfort levels. Finally, wind effect can make it feel cooler or warmer depending on its intensity.

Glass is a better absorber of infrared radiation compared to many plastic glazings. Plastic glazings tend to transmit a significant amount of this radiation instead of absorbing it. This leads to higher heat loss from greenhouses that are glazed with plastic, as the absorbed radiation helps in retaining heat. Therefore, the statement that glass absorbs earthly infrared radiation better than plastic glazings, resulting in greater heat loss from plastic-glazed greenhouses, is true.

Bright white and polished metal objects have a high reflectivity, meaning they reflect a large percentage of incoming solar energy. The answer, 80% to 98%, indicates that these objects reflect a significant amount of the solar energy that reaches them, helping to reduce the amount of heat absorbed and keeping them cooler.

Indoor humidity is influenced by the temperature and humidity of outdoor air. The outdoor air conditions can directly affect the moisture levels inside a building. If the outdoor air is warm and humid, it can increase the indoor humidity. Similarly, if the outdoor air is cold and dry, it can lower the indoor humidity. Therefore, the temperature and humidity of outdoor air play a significant role in determining the indoor humidity levels.

For the best indoor comfort during the summer, the relative humidity (rh) should be less than 60%. High humidity levels can make the air feel hotter and more uncomfortable, as the moisture in the air hampers the evaporation of sweat from our bodies. Lower humidity levels help to facilitate sweat evaporation, making us feel cooler. Additionally, high humidity can promote the growth of mold and mildew, leading to potential health issues and damage to the indoor environment. Therefore, maintaining a relative humidity below 60% is ideal for optimal indoor comfort during the summer.

The given answer lists three measures of energy: BTU (British Thermal Unit), Foot-pounds, and Kilowatt-hours. These are commonly used units to quantify energy. BTU is a measure of heat energy, often used in heating and cooling systems. Foot-pounds is a measure of work or mechanical energy, representing the amount of energy needed to move one pound one foot. Kilowatt-hours is a unit of electrical energy, commonly used to measure electricity consumption. These three measures cover different aspects of energy and are widely used in various fields.

Glass is known to be transparent, allowing most of the incident solar radiation to pass through it. Only a small portion of the solar radiation is reflected or absorbed by the glass. This is why glass is commonly used in windows and other applications where we want natural light to enter a space. Therefore, it is true that glass reflects or absorbs only 10% to 20% of the incident solar radiation.

Warmer air can actually hold more moisture than cooler air. As the temperature increases, the air molecules move faster, creating more space between them. This increased space allows for more water vapor to be present in the air. Conversely, cooler air has slower-moving molecules and less space, resulting in a lower capacity for moisture. Therefore, the statement that warmer air cannot hold more moisture than cooler air is false.

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One BTU (British Thermal Unit) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. 778 foot-pounds is equal to the amount of work done when a force of one pound is applied over a distance of 778 feet. Since one BTU is equivalent to the work done by one pound over one foot, 778 foot-pounds is equal to 1 BTU.

When air cools down, its capacity to hold moisture decreases. If the outside air cools down to 70 deg F, it will reach its dew point temperature, which means the air is saturated with moisture. At this point, the relative humidity is at 100% because the air cannot hold any more moisture. Therefore, the relative humidity value may change to 100% rh.

The factors that determine indoor comfort are air temperature, moving air, relative humidity, and radiant temperature. Air temperature refers to the level of heat or coldness in the air, which can affect how comfortable people feel. Moving air, such as from fans or ventilation systems, can also impact comfort by providing a cooling effect. Relative humidity is the amount of moisture in the air, and maintaining an optimal level can help prevent dryness or excessive humidity. Radiant temperature refers to the temperature of objects or surfaces in the room, which can influence how warm or cool a person feels.

The outdoor conditions that affect the space-conditioning needs of a home include temperature, relative humidity, solar radiation, precipitation, and wind effect. Temperature plays a crucial role in determining the heating or cooling requirements of a space. Relative humidity affects the comfort level and can impact the efficiency of cooling systems. Solar radiation determines the amount of heat gain from the sun, which can increase the cooling load. Precipitation can affect the moisture levels in the air and the potential for water damage. Wind effect can impact the heat transfer through convection and increase the cooling or heating load.

Moving air increases bodily heat losses through convection. Convection is the transfer of heat by the movement of a fluid, in this case, air. When air is in motion, it carries away heat from our bodies, resulting in a cooling effect. This is why a breeze or a fan can make us feel more comfortable in hot weather. Conduction, on the other hand, is the transfer of heat through direct contact, and radiation is the transfer of heat through electromagnetic waves. While both conduction and radiation play a role in heat transfer, it is the movement of air (convection) that is specifically mentioned in the question.

The transfer of chemical energy into heat at the flame is usually more than 99% efficient. This means that a very small amount of energy is lost as waste and the majority of the chemical energy is converted into heat. This high level of efficiency is desirable as it allows for maximum utilization of the energy source and minimizes energy wastage.

Heating energy flowing through pipes and ducts can be lost through different mechanisms. One of these mechanisms is conduction, which occurs when heat is transferred through direct contact between the heated pipes/ducts and their surroundings. Another mechanism is radiation, which involves the emission of heat energy in the form of electromagnetic waves from the surfaces of the pipes/ducts. Lastly, convection is another way in which heat can be lost, as it involves the transfer of heat through the movement of air or fluid around the pipes/ducts.

Combustion is a chemical reaction that occurs when a fuel combines with oxygen to produce heat and light. Oxygen is necessary for combustion as it acts as the oxidizer, allowing the fuel to burn. Carbon and hydrogen are commonly found in fuels and are essential components for combustion. The flame is the visible result of the combustion process, as it is produced when the fuel reacts with oxygen and releases energy in the form of heat and light.

Glass does not reflect or absorb 50% to 100% of the incident solar energy. Instead, glass allows a significant amount of solar energy to pass through it, making it transparent to sunlight. Some portion of the solar energy may be absorbed or reflected by the glass, but it is typically a small percentage. Therefore, the statement is false.

Condensation formation on a window is undesirable because it creates a moist environment, which is favorable for the growth of insects and microbes. Insects such as mosquitoes and flies are attracted to the water droplets and can become a nuisance indoors. Additionally, microbes such as mold and mildew thrive in damp conditions and can cause health issues and damage to the window frame and surrounding areas. Therefore, it is important to prevent condensation on windows to avoid the growth of insects and microbes.

During the refrigeration cycle, the refrigerant evaporates in the evaporator. This process involves the absorption of heat from three sources: the metal tubes, the fins, and the passing air. The metal tubes provide a pathway for the refrigerant to flow through, allowing it to absorb heat from the surrounding environment. The fins increase the surface area of the evaporator, enhancing heat transfer between the refrigerant and the passing air. Finally, the passing air carries away the heat absorbed by the refrigerant, completing the heat exchange process.