Unit 22 Quiz Flashcards
Coil of tubing packed into a shell and then closed and welded.
Shell and coil
Water in the inner tube removes heat from the refrigerant in the outer tube.
Tube-within-a-tube coil
System where water is used over and over such as chilled water or cooling tower system.
Recirculated water system
A water cooling tower that has a fan on the side of the tower that pushes air through the tower as opposed to an induced draft tower.
Forced draft tower
Rejects heat absorbed into the system from the evaporator.
Condenser
Water used once and then wasted down the drain.
Waste water system
Turns a condenser fan on and off to maintain a correct pressure within the system.
Fan cycling
Most expensive condenser but can be cleaned mechanically with brushes. Straight copper tubes fastened into an end sheet within a steel shell.
Shell and tube
Located at the inlet or outlet to condenser. Used to control head pressure.
Air damper
Removing heat from the superheated hot refrigerant gas down to the condensing temperature.
Desuperheating
One half used for winter operation and both halves used for summer operation.
Condenser splitting
What state is the refrigerant in when it leaves the condenser?
High pressure high temp liquid
Where is the evaporative condenser located?
Inside the cooling tower
What is the purpose of condenser flooding?
To keep pressure up inside the condenser
so that the correct amount of refrigerant
Reaches the metering device.
What are five ways to control head pressure?
- Dampers
- Condenser flooding
- VFD
4.Condenser splitting - Fan cycling controls
A high efficiency condenser coil operating with an ambient temperature of 95 F will condense refrigerant at what temperature?
95F + 15F = 110F
A cooling tower can be constructed with different types of fill material used to help cool the water. What are three types of fill material that can be used?
Redwood, Fiberglass, Plastic
Condensers can be air cooled or water cooled. What are three condenser configurations for a water cooled condenser?
Shell in tube, shell in coil, tube in tube
A water pressure regulating valve for a water-cooled condenser works like a thermal expansion valve (TXV). As head pressure increases, the water valve will ______ water flow through the condenser to keep the head pressure correct.
Increase
How is mineral buildup in the evaporative condenser controlled without using chemicals?
Blow down
Water boxes refer to _______.
The end caps of the shell and tube condenser
Water used to cool condensers can either be _______ or __________.
Wasted, recycled
Where is the ORI valve placed in the system and what does it do?
- Outlet of condenser/inlet of receiver
- Regulates pressures in the condenser
- Opens to relieve pressure when the set point is exceeded
The outdoor condensing unit that uses R-410A refrigerant should have a subcooling value of 10 degrees. The high side manifold gauge reads 317 psig. You place a thermocouple at the exit of the condenser to measure the temperature. What temperature would indicate the unit is properly charged with the correct amount of refrigerant?
100F -10F =90F
True or false: The ORD valve can be adjusted.
False
True or false: As the ORI valve throttles down, the ORD valve will open to keep the receiver at the proper pressure to supply liquid refrigerant to the metering device.
True
True or false: A condensing unit that measures low subcooling has too much refrigerant.
False
True or false: A low subcooling number could also mean the condenser is dirty.
True
True or false: When measuring condenser subcooling for commercial and industrial applications, the pressure must be read close to the condenser outlet, not at the compressor service valve.
True
True or false: For an air-cooled condenser, the refrigerant inside the condenser coil will begin to condense at a temperature 30 degrees higher than the air passing over the coil (also known as ambient air).
True
True or false: Ambient air temp moving across a regular fin and tube condenser coil is 95F for a unit using R-22 refrigerant. The pressure inside the condenser that the refrigerant is starting to condense at is 278 psig.
True
True or false: Charging a unit that has a dirty condenser coil will not affect subcooling.
False
True or false: Hot gas enters the condenser from the bottom of the condenser.
False
True or false: The shell-and-coil and tube-in-tube condensers can only remove mineral buildup by using chemicals.
True
True or false: Natural draft cooling towers can be negatively affected if prevailing winds cannot blow through it.
True
True or false: The Low Ambient Control (LAC) valve is a combination of the ORI and ORD valve.
True
True or false: Shell type condensers (shell-and-tube & shell-and-coil) are also used as a receiver to hold the entire refrigerant charge of the system.
True
As the ____ valve is throttling closed, the _____ valve is opening to allow pressure in the receiver to maintain proper receiver pressure, regardless of the outside ambient conditions.
ORI, ORD
What would be the result if an air-cooled condenser had two fans and one stopped running?
Over heating and high head pressures will occur
What methods are used to prevent the water in the cooling tower from freezing during the winter?
Anti-freeze chemical solution can be placed in the water, adding a heater, bubble acrotor
As voltage frequency _____ in a variable frequency drive fan motor, the motor speed ______.
Increases, Increases
Explain three ways water can be lost in a cooling tower.
Leaking valves
evaporation
high winds
Where is the ORD valve installed and what does it do?
Hot gas line & Inlet of Receiver.
Provides proper pressure for the receiver
in order to supply liquid refrigerant
to the metering device
when ORI valve is closed off
Use the diagram to draw in the location of the ORI and ORD valves.
If the spring pressure of a water regulating valve is increased, the system head pressure will _________.
Increase
In a tube-within-a-tube condenser, the refrigerant flows in the ______ tube and the water flows in the ______ tube.
Outer, Inner
What is the condenser saturation temperature if there is 20F of subcooling and the outlet temperature of the condenser is 90F?
90F + 20F = 110F
In order for a flooded condenser type head pressure control system to operate, what device/component holds the extra refrigerant in warmer weather when the condenser doesn’t need to be flooded.
Receiver
A normally operating water cooled condenser is operating with a 10 degrees differential between water in and water out. If scale forms on the water tubes and the entering water is 85F, which of the following is possible?
Both a & b are correct
A. The outlet water temperature will be lower than expected.
B. The system head pressure will rise
How does the inverter on a VFD drive know when to speed up or slow down the condenser fan on a cooling tower?
The Sensors send signals in regards to temperature to the VFD drive to either slow down or speed up the condenser fan
Name four tasks that need to be checked when performing preventive maintenance on cooling towers.
Water pressure
Water meter
Water regulating valve
Float valve
Where does refrigerant vapor condense in a typical condenser?
Middle
What happens in the switching section of a variable speed motor drive controller?
Changes DC to AC
To measure the coil resistance on a current relay, what terminals would you put your test probes on?
L & M
There are four shapes used to increase the amount of warp for a bimetal device. What are tow shapes that can be used?
Helix & Hairpin
