Mechanical Sciences HVAC
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An enclosed conduit through which air is moved from one place to another
A tube in heat exchanger (condenser or evaporator) used to transfer heat into or out of the refrigerant in an air conditioning unit, usually finned to increase heat transfer surface area.
A system that conditions all the air in a central apparatus and distributes it to conditioned spaces through two parallel mains or ducts. One duct carries cold air and the other duct carries warm air. The supply fan runs at a higher pressure than a low velocity system and each zone requires a mixing box with sound attenuation
Dual duct high velocity system
A system that conditions all the air in a central apparatus and distributes it to conditioned spaces through two parallel mains or ducts. One duct carries cold air and the other duct carries warm air.
Dual duct low velocity system
A combination hot water heating and chilled water cooling system that circulates hot and/or chilled water to provide heating or cooling using common piping and terminal heat transfer apparatus.
Dual-temperature water system
A unit heater without a fan that is installed in a duct or a plenum
A mechanical device used to create a current of air by movement of a broad surface or a number of such surfaces within a sealed plenum
The cleaning of previously conditioned air while maintaining desired temperature and humidity
A mechanical refrigeration system arranged and controlled to utilize condenser heat for some useful purpose
An all-water system is one in which hot or chilled water is used to convey heat to or from a conditioned space or process through piping connecting a boiler, water heater or chiller with suitable terminal heat transfer units located at
the space or process
One-millionth of a meter
HVAC system that serves a relatively small number of zones from a single central air handling unit.
A unit heater or duct heater used for preheating outside air.
Outside air heater
A unit heater that has no fans and uses radiant heating
Radiant unit heater
Ratio of how much water vapor is in the air to how much the air can hold at a specific temperature.
A continuous run of pipe or tube from supply connection to return connection.
An air system that supplies air to multiple locations through a common duct. Temperature control is obtained by adjusting the volume of the supply air furnished.
Single zone air system
Equipment installed in or contiguous with the area served.
Terminal heating equipment
An air system that provides warm and cool air in separate ducts. Individual room or area temperature control is obtained by adjusting the amount or ratio of warm and cool air being mixed and introduced to the environment.
Variable air volume systems
STATE the three main environmental characteristics that are controlled in an HVAC system
- Controlling the temperature
- Relative humidity
- Cleaning air
EXPLAIN how terminal heating equipment heating is controlled.
The local control thermostats call for heat as the cooling load in the space drops below maximum.
DESCRIBE the various HVAC filter types
- Fibrous media filters are composed of a coarse fiber material such as fiberglass, metal mesh, or
- vegetable fibers
Electric air cleaners uses static electricity to charge and attract the dust to metal sheets that can then be cleaned
- The high efficiency particulate air (HEPA) filter is the most efficient air
- cleaning system available.
Activated Carbon Filters remove gases and vapors from recirculated air.
STATE the purpose of filters in an HVAC system.
Filtration allows previously conditioned air to be cleaned while maintaining desired temperature and humidity.
LIST the ways a hydronic system may be classified
All water systems may be classified by temperature, generation of flow, pressurization, piping arrangement, and pumping arrangement.
LIST the heat sources that are used in an HVAC system
- Fuel-fired boilers
- Waste heat furnaces and boilers
- Solar energy collectors
- Heat pumps
- Direct-fired radiant heaters
EXPLAIN the basic principle of how a heat pump operates
The key to the operation is the reversing valve. A heat pump is a mechanical refrigeration system arranged and controlled to utilize the condenser heat for some useful purpose, typically space heating.
Given a diagram, EXPLAIN the basic cycle of the
following cooling systems:
a. Compressed gas
b. Steam jet
c. Heat sink
- A special gas called a refrigerant is compressed, turning it into a superheated
- The steam jet refrigeration system may be used if an abundant supply of high
- pressure steam is available.
- The heat sink method of providing air conditioning requires a large body of cool
- water, usually subterranean or drawn from deep lakes.
STATE the purpose of a cooling tower
A cooling tower is a device for cooling water by utilizing the evaporative cooling effect of the water.
IDENTIFY the three types of fan control
- damper control,
- variable speed control,
- inlet vane control.
1. EXPLAIN the purpose of the following equipment used in a cooling system:
c. Pump configuration
- Piping systems are the means by which thermal energy fluids are transported from one
- place to another.
- In general, in-line pumps are used in small systems or secondary systems, such as freeze-prevention loops. Base-mounted pumps are used for most applications. Double-suction pumps are
- preferred for larger water volumes, such as cooling towers, over 300 to 400 gpm, because the purpose of the double-suction design is to minimize the axial thrust from water entering the impeller.
- A fan is a device used to cause a current of air by movement of a broad surface
- or a number of such surfaces within a sealed plenum
Chemically bonds to exterior of charcoal
Permeates the charcoal
Used to reduce sound in the high velocity HVAC system
Hydronic Systems, 30 psig <250 Degrees F
Hydronic Systems, 150 psig 250 to 350 Degrees F
Hydronic Systems, 300 psig 350 to 450 Degrees F
Static Pressure is proportional to
Brake Horse Power is proportional to
- Bhpi = (RPMi)3
- Bhpf (RPMf)3
As outdoor temperature _________, efficiency of a heat pump _________ .
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