Chapter 25 Flashcards
(33 cards)
How is subcooling accomplished on some low temp systems
The liquid line is refrigerated using the liquid in the same unit
Two compressors connected at the motor end are called
Tandem
Two or more compressors piped together are called
Parallel rack system
What must be used if equipment is used in low ambient
Some kind of head pressure control or a way to maintain minimum head pressure
What happens if head pressure gets too low
The refrigerant control will starve the evaporator
What are the four methods of maintaining head pressure
Partially fill condenser with liquid refrigerant
Stop or slow condenser fans
Partially or completely close ambient air Oliver’s on the condenser
Heat the condenser or receiver
In hot weather what will be closed/open on headmaster valve
B or D will be closed
C and R will be open
As the ambient temperature goes down head pressure goes down, what opens and closes on headmaster valve
B or D starts to open
C starts closing
R is open
Large compressors sometimes have electric or hydraulic unloaders which control what
Number of cylinders that are pumping
What are the three types of water cooled condensers
Shell in tube
Shell in coil
Tube in tube
What is on the inside tube of a tube within a tube condenser
Water on the inside, refrigerant on the outside
What is the counter flow design principle
Water enters condenser where refrigerant leaves. Coldest water by coldest refrigerant, maximum delta t
What is the purpose of a cooling tower
It is for make up water lost due to evaporation
What is the purpose of the bleed in a tower
It bleeds water off the tower to help keep mineral deposits from building up in the sump of the tower
What is one danger if a water tower
Legionaries disease which will breed in water towers
How much water do towers use
Two gallons per ton per hour
What is the normal water temperature drop through a tower
Entering and leaving should be around 10 degrees
What is an evaporative condenser
The condenser is located inside the tower
What are the three most popular styles of defrost
Off cycle
Electric defrost
Hot gas defrost
On which type defrost system is a pump down control system important
Electric Defrost:
Pumps out evaporator when there is no refrigerant left in the coil
Speeds up defrost cycle
Get oil return back every time you pump down
Compressor will start under low loads
Describe the pump down control sequence
Thermostat satisfies and opens which deenergizes liquid line solenoid coil
Compressor continues to run and removes refrigerant from the low side and liquid line
The unit will cycle off on the low pressure switch
What are the three advantages of a heat exchanger in the liquid and suction line
Increases sub cooling
Increases efficiency
Lessons chance of liquid reaching the compressor
What are the two types of motor control for controlling temperatures
Thermostatic
Pressure
What are the three components of a basic oil control system
Oil separator
Oil reservoir
Oil level regulator
