HVAC 145 Questions with 100% Correct Answers | Updated 2024 | Guaranteed A+

HVAC Air Changes per Hour (ACH or ac/hr) - ✔ ✔ the hourly ventilation rate divi ded by the volume of a space. for perfectly mixed air or laminar flow spaces, this is equal to the number of times that the volume the space is exchanged by mechanical and natural ventaliation Air Conditioner - ✔ ✔ an appliance, system, or mechanism desig ned to dehumidify and extract heat from an area. usually this term is reserved for smaller self contained units such as a residential system Air Handling Unit (AHU) - ✔ ✔ a central unit consisting of a blower, heating and cooling elements, filter racks or chamber, dampers, humidifier, and other central equipment in direct contact with the airflow. this does not include duct work through the building British Thermal Unit (BTU) - ✔ ✔ any of several units of energy (heat) in the HVAC industry, each slightly more than 1 kJ. one BTU is the energy required to raise one pound of water one degree Fahrenheit, but the many different types of BTU are based on different interpretations of this "definition." in the United States the power of HVAC systems (the rate of c ooling and dehumidifying or heating) is sometimes expressed in BTU/hour instead of watts Centrifugal Fan - ✔ ✔ a mechanical device for moving air or other gases Chiller - ✔ ✔ a device that removes heat from a liquid via a vapor -compression or absorption refrigeration cycle. this cooled liquid flows through pipes in a building and passes through coils in air handlers, fan -coil units, or other systems, cooling and u sually dehumidifying the air in the building. chillers are of two types; air -cooled or water -cooled. Air -cooled chillers are usually outside and consist of condenser coils cooled by fan -driven air. water -cooled chillers are usually inside a building, and h eat from these chillers is carried by recirculating water to a heat sink such as an outdoor cooling tower Coil - ✔ ✔ equipment that performs heat transfer to air when mounted inside an air handling unit or ductwork. it is heated or cooled by electrical me ans or by circulating liquid or steam within it Condenser - ✔ ✔ a component in the basic refrigeration cycle that ejects or removes heat from the system. the condenser is the hot side of an air conditioner or heat pump. Condensers are heat exchangers, and can transfer heat to air or to an intermediate fluid (such as water or an aqueous solution of ethylene glycol) to carry heat to a distant sink, such as ground (earth sink), a body of water, or air (as with cooling towers) Constant Air Volume (CAV) - ✔ ✔ a system designed to provide a constant air flow. this term is applied to HVAC systems that have variable supply -air temperature but constant air flow rates. most residential forced -air systems are small CAV systems with on/off control Controller - ✔ ✔ a device that controls the operation of part or all of a system. it may simply turn a device on and off, or it may more subtly modulate the set point of components. most controllers are automatic but have user input such as temperature set points, e.g. a the rmostat. controls may be analog or digital Damper - ✔ ✔ a plate or gate placed in a duct to control air flow by increasing friction in the duct Deep Lake Water Cooling - ✔ ✔ the heat is rejected to deep lake regions to cool homes and offices, reducing th e energy costs Delta T (temperature change) - ✔ ✔ it is used to describe the difference in temperature of a heating or cooling medium as it enters and as it leaves a system Duct - ✔ ✔ specialized housing for the air flow Dehumidifier - ✔ ✔ a dehumidifie r is the equipment that extracts and removes humidity from the air. it works by cooling air to the point where water turns to liquid from vapor form and then the liquid is removed Diffuser - ✔ ✔ a diffuser is placed over ductwork, and it separates air wit h vanes going in differing directions. it evenly distributes air flow in the desired directions Dry Bulb Temperature - ✔ ✔ dry bulb temperature is the temperature of air measured by a thermometer which is freely exposed to the air while it is shielded fro m radiation and moisture. it is usually thought of as air temperature, and it is the true thermodynamic temperature. it is a measurement of heat intensity independently of humidity and a dry bulb thermometer is used to measure it Dry Bulb Thermometer - ✔ ✔ a dry bulb thermometer is a device that measures air temperature independently of humidity. it is freely exposed to the air it is measuring and is protected from the radiation and moisture Economizer - ✔ ✔ an HVAC component that uses outside air, under suitable climate conditions, to reduce required mechanical cooling. when the outside air's enthalpy is less than the required supply air during a call for cooling, an economizer allows a building's mechanical ventilation system to use up to the maximum amo unt of outside air Enthalpy - ✔ ✔ for a given sample of air, a measure of the total heat content (the sum of the heat energy of the dry air and heat energy of the water vapor within it). it is typically used to determine the amount of fresh outside air that can be added to r ecirculated air for the lowest cooling cost Evaporator - ✔ ✔ a component in the basic refrigeration cycle that absorbs or adds heat to the system. evaporators can be used to absorb heat from air or from a liquid. the evaporator is the cold side of an air conditioner or heat pump Fan Coil Unit (FCU) - ✔ ✔ a small terminal unit that is often composed of only a blower and a heating and/or cooling coil, as is often used in hotels, condominiums, or apartments Flow - ✔ ✔ a transfer of fluid volume per unit tim e Fresh Air Fraction (faf) - ✔ ✔ fresh air fraction quantifies action of the economizer, and is defined by (Mass flow rate of fresh -air / Total air flow rate)