Tyson class Flashcards by Tarek Bakir

Dry bulb temp

Temp of air

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Wet bulb temp

Temperature of the air measured with a glass bulb covered with a wet cloth

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Relative humidity

Actual amount of moisture in the air compared to the total or maximum moisture the air can hold

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Grains of moisture

Unit of measure used to determine the amount of moisture in the air

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Dew point temp

Temperature at which moisture condenses on a surface

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How many grains of moisture in 1 LB of water

7000

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Mass flow rate unit

LB/hr

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Enthalpy unit of measure

Btu/Lb

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BTU capacity formula

Mass Flow Rate X delta H (change in enthalpy)

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Mass flow rate formula

Cfm x Specific Density x 60

= lb/hr

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Q sensible formula

1.08 x cfm x delta T

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Air heat capacity formula

Mass Flow Rate x delta H
= BTU/H

4.5 x cfm x delta H

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Economizer open% formula

Return air - mixed air
—————
Return air - outside air

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Coil bypass factor formula

Leaving air - coil temp
____________
Entering air - coil temp

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Sensible heat factor formula

Sensible heat quantity
____________
Total heat quantity

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What is more dense, dry air or moist air

Dry air

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Where is the vapor barrier placed

On warmest wall

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Total pressure formula

Static + velocity

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Pitot tube ports give what measurements on the side and bottom

Side port is static

Bottom port is total

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Velocity (ft/min) formula

4005 x (square root of velocity pressure)

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Cross sectional area of round duct

3.14 x (radius squared)

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Total external static pressure formula (furnaces)

Supply static just before coil - return static right after filter

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CFM fan laws

RPM 2/RPM1 = CFM2/CFM1

Double RPM -= double CFM

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Static pressure fan laws

(RPM2/RPM1)squares = SP2/SP1

Double RPM = 4 x static

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HP fan laws

(RPM2/RPM1)cubed = HP2/HP1 | Double RPM = 8 x HP

Fan driver and sheave relationship

RPM driver x diameter of driver (motor) = RPM driven x diameter driven (fan)

2 main main fan classifications

Propeller and axial

3 main centrifugal fan types

1) Forward curve 2) Backward inclined 3) Radial or straight blade

Forward curve fan application

Furnace or small to medium RTU

Pros of forward curve fan (3)

Low speed Quiet Light inexpensive construction

Cons of forward curve fan

High HP requirements at near free delivery

Pros of Backward inclined fan

Non overloading when wide open

Backward inclined fan application

Industrial and commercial ventilation

Advantages of radial blade fan (2)

Ideal for high static pressure | Ideal for areas with high dust content

Disadvantages of radial blade fans (3)

Noisy Low volume means larger size to do the job Lower Efficiency

Most efficient fan?

Air foil (backward curved) 90%

What position does a non conventional reversing valve go to in a deenergized state

Fail to heat

pressure required to move slide valve on 4 way valve

75-100 psi

Define Heat Pump Balance Point

Lowest possible outdoor temperature at which the Heat Pump can satisfy the needs of the building. Below balance point requires auxiliary heating

Define unitary equipment

Any unit that comes completely assembled from the factory (RTU)

Where are the metering devices typically located on a ductless split system

Outdoors at the unit

What special precautions must be taken with the liquid line when installing ductless split systems

Must be insulated

What is the minimum SEER rating on residential split systems

Velocity required on AC system

400 cfm/ton

Low ambient control setting

55F

Unitary equipment | Ideal SST, SDT, system super heat and subcooling

SST = 40F SDT = 105F System superheat = 20-30 Sub cooling = 10F

Face velocity

400-500 ft/min

What does PTAC stand for, give 1 example

Packaged Terminal Air Conditioner Heat pumps

Give 3 forms of CAPACITY control

Condensor fan cycling Hot gas bypass Compressor unloading

Give 3 forms of HEAD PRESSURE control

Condensor fan cycling Condensor flooding Damper control

Unit clearances from edges

B-52 says 10 ft | B-149 cas code says 6 ft

Velocity required for heat

450 ft/min

Average delta T for cooling

20F

What is the difference between a direct and indirect cooling system

Direct system cools the medium (air) directly (residential ac) Indirect cools water and water cools the medium (chilled water system)

What is EER and how is it calculated

Energy Efficiency Ratio Output energy (BTU/hr) ————— Input electrical energy (watt/ hr)

What is ASHRAE ideal temp for comfort and efficiency

75F

What parts make up a headmaster and what is it used for

ORI (open on rise of inlet) and ORD (open on rise of differential) Used to maintain head pressure during low ambient conditions

What is a timed low pressure bypass timer, why is it used

Timed contacts that bypass the low pressure control for 3-5 min to allow head pressure to to rise to normal conditions without tripping during low ambient conditions

Economizer mixed air temperature setting

55F

2 types of dampers | Which is better for mixing

Parallel and opposed blade Opposed give better mixing but promote stratification (layers of different temperature air)

Why are VFDs often used with VAV boxes

When dampers close at VAV boxes, static pressure increases. VFDs reduce fan speed to keep static pressures low

Biggest advantage of RTU

Reduced cost of rental space

What is the pressure setting for a DPRV (discharge pressure regulating valve)

Pressure equivalent to 34F | eg. R-22 @ 34F = 60 psi

Heat pump defrost coil engages at what temp?

40-42F (to maintain a safety TD of 10)

What are the symptoms of faulty compressor valves

Higher than normal suction pressure, lower than normal discharge pressure, lower amp draw

Typical AC supply temp

50-60F

AHRI test condition temperatures for Return air and Ambient

80F return air | 95F ambient

What type of fan is used on a window AC

Slingular

What fan is used for high velocity with low static pressure

Propeller

Define radiation

Transfer of energy in the form of waves through space

Calgary summer and winter design temp

84F summer | -24F winter

Define thermal mass

Ability of an object to store heat

Define Thermal Lag

The time it takes for heat to pass through an object

Define flywheel effect

A building constructed with materials with a high thermal mass to provide inertia or resistance to temperature fluctuations

Describe thermal mass used for heating

Concrete exposed to sun to help heat in winter

Describe thermal mass used for limited summer time over heating

Mass shielded from solar gain but exposed to occupants. Heat is absorbed throughout the day and then released overnight to assist HVAC system

What is the air velocity of the draft produced when walking past someone

25 ft/min

Tyson class Flashcards

(77 cards)