GENERAL Flashcards
Dual duct system
Hot air and cold air supplied by separate ducts to be mixed at ea controlled space to provide the desired supply air temp. Consumes a lot of energy.
Surge arrester
Device installed in a water line to minimize the effects of water hammer caused by quick closing valves.
Plenum
Space bt clg and structure above, used as a slow moving duct
Occupancy group
Designation for a group of occupancies with comparable fire safety considerations.
Inch of water
Unit of pressure equal to the pressure of a column of water one inch high. One inch of water = 0.03609 psi
Variable are volume (VAV)
AC system accommodating thermal load changes by varying flow of supply air instead of temperature
Alternation
Reversal of an alternating current wave, 2 of which create a complete cycle
Hub
End of a pipe enlarged to receive the end of another pipe so as to form a joint. Also called a bell.
Flat plate system
Device used to collect solar energy, usually consisting of a glazed cover, transfer medium (water or air), absorber plate and insulation
Thermosiphon
Circulating air with natural convection from heating. I.e. Ventilating a bldg by sending warmed air out the top and siphoning cooler air at the bottom
Branch vent
Connects one or more individual vents to a stack vent
Reversible-acting valve
Opens when pressure is applied and closes when pressure is released
Power factor
Ratio of real power in watts to the product of voltage and current
Register
Grille and damper to control amount of air passing thru
Differential thermostat
Responds to temperatures at 2 different locations…. It’s used to activate a solar heating system when he collector is water the the storage medium
Sabin
Unit of sound absorption equal to absorption of one square foot of open window
Impedance… And what do you measure it in?
Resistance in an AC circuit consisting of resistance, reactance or both. Measured in ohms.
Damper
Decide inserted in an air stream to modulate restrict or divert flow of air
Expansion valve
Valve which controls the flow and reduces pressure of the refrigerant, allowing it to evaporate and absorb heat
Standard air
Air at a standard temperature and pressure
OSHA
Occupational safety and health administration regulating working conditions
Friction factor
Factor used to calculate loss of pressure of a gas or liquid fluid through ducts or pipes
Therm
Unit equal to 100,000 BTUs
Flame spread classes
Rate at which flame will spread over a surface. Class I has least flame spread, class III the most
Heat of fusion
Heat given off by a liquid in changing to a solid or heat absorbed by a solid melting to a liquid… Without change in temp.
Ball check valve
Spring-operated check valve in a piping system in which pressure against a movable ball allows fluid to flow in one direction. When it flows in the other it closes ball against a seat and interrupts flow.
Star connection
Method of connecting the windings on a 3-phase transformer in which one end of all three windings is connected to a common neutral center point, forming a Y shape. Also known as a wye connection.
Interceptor
Device traps grease sand hand string etc. installed in certain drains.
Globe thermometer measures….
Mean radiant temp
Building authorization
Control by automatic equip of a number of bldg functions, usually including HVAC
Neutral
Wire or conductor equidistant on voltage from the phase conductors of the systems… Not the same as ground
U factor or U value
Overall rate of heat flow of a particular wall section, expressed on BTUs per hour per degree F per square foot
Concentrating collector
Device to collect solar energy, usually
Parabolic in shape, for concentration isolation to achieve high temperatures
Coefficient of performance COP
Ratio of heat delivered by a heat pump to the amount of energy supplied. (Or amount of energy removed by a refrigeration machine to the energy expended in removal). Similar to
Efficiency but sometimes
Exceeding 100% so it is expressed
As a number.
Typical COP for a heat pump
2.7
Ballast
Electrical device providing starting voltage and regulating current flow in fluorescent and other lamps
Underwriters loop
Plumbing arrangement on steam boilers to avoid rapid loss of water in the boiler due to a break in the condensate return line. Also. Hartford loop.
Fixture unit
Unit of liquid flow used in sizing supply and drainage pipes. Equal to
1 cubic foot per minute or 7.5 gallons per minute
Manometer
U-shaped tube partially filled with a liquid, used for measuring the pressure of a fluid
Aspect ratio – what 2 things does it relate to?
Ratio of the longer to shorter dimension of a duct which affects duct friction or of a room which relates to light reflection
Balancing damper
Damper provided to regulate flow when system is being balanced or tuned to design requirements
dBA
Decibel measured in the A scale, weighted to account for the special sensitivities of the human ear.
Cooling tower
Structure to evaporatively cool a liquid by contact with air.
Fusible sprinkler head
Sprinkler head normally closed by a plug I f low melting point alloy which melts at a predetermined temp
Pitch… Is and depends on what factors
Tone of sound dependent primarily on frequency and somewhat on sound pressure and waveform
Two pipe system
Hot or chilled water system having only one supply and one return line. It can supply heated or chilled water to a zone but not both at the same time.
Grain
Unit of weight, where 7000 grains = one pound; used primarily as a measure of the weight of moisture in air.
Emissivity
Rate at which a surface material at given temp radiates/emits energy. Varies from 0.0 to 1.0, where 1.0 is the theoretical emissivity of a perfect black box
Capacitance … Measured in
Measure of the ability of two or more closely spaced plates to store
Electricity. Measured in farads
Three phase
Describing a form of alternating current produced by a generator having three rotating coils positioned 120 degrees apart
Efficacy
Ratio of lumens emitted by a lamp to the electrical power consumed by the lamp
Mass Law
Theoretical law stating that for ea doubling of mass in a wall there is a 6dB drop in the amount of sound transmitted… In actuality it’s closer to 5
Another word for a downspout
A leader
Sound level meter
Measures sound pressure on dB and gives a reading
Sone
Subjective system of measuring loudness based on the reference point of one some equal to a sounds pressure level of 40 dB
Photometry
Measurement of light distribution, illumination, and intensity, usually with a photometer.
Inductance
The property of an electrical current by which a change in current induces an electromotive force. The unit of
Inductance on the Henry.
Total heat… Also known as…
Total sensible and latent stored in the air… Also known as
Enthalpy
cfm
Cubic feet per minute, flow rate of air in a mech duct
Psychrometer in chart involves
Wet bulb, dry bulb, dew point temp, relative and absolute humidities, enthalpy, and sensible heat ratio
What does sound energy turn onto
When it is absorbed ?
Usually heat
