BOMI: AHU, Water Treatment, and Plumbing Exam Questions With Verified Answers.

BOMI: AHU, Water Treatment, and Plumbing Exam Questions With Verified Answers. What is the relationship between thermal comfort and metabolic heat? - answerThermal comfort exists when the temperature and relative humidity of a person's environment permit the person to lose, without conscious effort, metabolic heat at the same rate he or she produces it. Because temperature and humidity combine to make humans feel comfortable in their surroundings, these characteristics must be adjusted by the AC system in order to enhance human comfort. What occupant activity level is chosen when engineers design an air-conditioning system? - answerOffice building air-conditioning systems are typically designed to accommodate people engaged in sedentary activities, including tasks done while seated or standing. Sedentary activity is the most important condition because when people are sedentary, they think about their comfort or discomfort. What is the rate of exchange of fresh air for return air based on in an AC system? - answerThe rate of exchange of fresh air for returned air is based on the quantity of fresh air required for each building occupant over the course of time. Define heat - answerHeat is energy that flows from one object to another. Heat always travels from an object with more heat to an object with less heat until both bodies are the same temperature. What happens to the rate of heat transfer if the difference in temperature increases? - answerThe rate at which heat transfers increases as the difference in temperature between the two objects increases. What are the three methods of heat transfer? - answerConduction, Convection, and Radiation Define conduction - answerConduction is the direct transfer of heat from one body to another. The substances have to be in physical contact with each other, but there is no movement of the material itself. Define latent heat - answerLatent heat is the energy that is used or released during a change of state. Latent heat cannot be felt or measured with a thermometer because it is hidden within a substance. Define relative humidity - answerRH (relative humidity) describes the amount of water vapor held in the air. Does moist air have more or less density than dry air? - answerMoist air has less mass than dry air and is less dense than dry air. What is the atmospheric pressure of air at sea level? - answerAt sea level, atmospheric pressure exerts an average force of 14.7 pounds on each square inch of surface (14.7 psi). Explain Charles' Law. - answerCharles' law explains why gases expand when heated and contract when cooled. Given a certain quantity of gas, as temperature increases, volume increases. This is because the molecules have the opportunity to move more and spread out. As pressure increases and the volume decreases, the temperature will increase because compressing the gas causes the molecules to vibrate faster and collide into each other more frequently, causing friction heat. Explain Boyle's Law. - answerBoyle's law states that at a constant temperature, as the volume increases, the pressure decreases. If the pressure on a certain amount of gas is doubled, the volume of space it requires will be cut in half. As pressure goes up, volume goes down. How does the human body regulate its temperature? - answerThe body dissipates heat by sending blood from internal organs to the skin where the heat is thrown off into the surroundings by radiant heat loss, convective heat loss, or evaporation. Perspiring and losing the heat through evaporation is an evaporative cooling process and is used in air-conditioning systems as well as human bodies. What system produces the most heat in a building? - answerBuilding lights are the most significant internal heat source. The heat given off by lights depends mainly on the wattage rating of the lighting elements. Lighting systems produce heat loads of up to four watts per square foot. The heat gain from one watt of electrical energy is equivalent to 3.4 Btu per hour. How have office building AC systems been designed to compensate for heat gain from office equipment? - answerTo compensate for this heat gain from office equipment in modern office buildings, air-conditioning systems have been designed to offset one to three watts per square foot. What is pull-down load? - answerHeat left over from the day before must be removed the following morning when the air-conditioning system is restarted. The leftover heat is called the pull-down load and must be added to the instantaneous solar heat gain during the morning hours to determine the cooling load for the air-conditioning system.