Chillers Flashcards
What is condenser approach
The difference between the temperature of the liquid refrigerant at the liquid line and the temperature of the LEAVING condenser water
What is evaporator approach
The difference between the temperature of the evaporating refrigerant in the evaporator and the temperature of the leaving chilled water
What is the generator
The component in an absorber that provides the heat required to separate the refrigerant from the absorber
Two types of centrifugal compressors
Open drive or refrigerant cooled
Difference between centrifugal and centripetal
centrifugal directs the refrigerant outward away from the shaft whereas centripetal pulls towards the center.
Centrifugal chillers are a ___ displacement device
non-positive
In a flooded system (chiller) ___ flows on the outside of the chiller barrel tubes and ___ flows through the tubes
refrigerant flows on the outside and water flows inside the tubes
in a Direct Expansion (chiller) system, _____ flows on the outside of the chiller barrrel tubes and ____ flows through the inside of the tubes
water flows on the outside and refrigerant flows on the inside
6 metering devices used on a chiller system
high side float low side float hand expansion valve orifice thermostatic expansion valve electronic expansion valve
two types of condensors
air cooled and water cooled
An unloaded compressor runs and capacity no lower than ___%
40%
what must run before and after centrifugal chiller operation?
oil pump
Define surge conditions
When a system is operating outside the design lift parameters
Define High side surge?
high condensing pressure pushing the refrigerant back to the evaporator
According to some guy (TQ), what is the most common surge type?
low side surge (but not really)
Name 4 common compressors used in Chillers
- Centrifugal
- reciprocating
- screw
- scroll
3 methods of capacity control on Centrifugal Compressors
*Inlet Guide Vanes
Variable Frequency Drives (VFD’S)
Hot Gas Bypass
2 primary reasons for Counter Flow
Increase subcooling and reduce flashing
A rule of thumb is that ___GPM/ton of refrigeration is required with ___ F ° drop in water temp
2.4GPM with 10F°
What is the 10/10/10 Rule
10° drop in water Evap, 10° rise in condensor and 10Delta in psi
Formula for Lift
in F° Saturated Condensing Temp - Saturated Suction Temp
Formula for Cooling tower Approach
Leaving Water Temp - Entering air wet bulb (smaller approach means more efficiency)
Formula to find BTU/H of a system
Qbtu/h=500xGPMusxΔT
500 for Us gallon
600 for imperial
Formula to find tonnage on a cooling system
Qton=(gpmxΔT)/24 to find tonnage of cooling on a system (us gal)
Qton=(gpmxΔT)/20 to find tonnage of cooling on a system (imperial)
Why do you never starve the inlet of a pump
this will cause it to Cavitate
What temperature is the Oil Sump kept at even when not in operation and why
140°F, this reduces the amount of refrigerant that the oil can contain
What is the difference between aBsorption and aDsorption
absorption is absorbent refrigerant in a liquid state.
adsorption is absorbent refrigerant in a solid state.
Define affinity
a molecule’s attraction to another molecule. (once bonded heat is required to separate them
Purpose of absorber
Remove heat with chilled water and allow refrigerant to bond
Purpose of generator
Add Steam heat to separate refrigerant bond
What 2 additives are used in a Lithium Bromine solution
Octyl Alcohol and Inhibitors
What are the 2 main functions of Octyl Alcohol
To be used as a wetting agent and as a surface tension breaker (allows for better heat exchange)
What are the main functions of an Inhibitor
Prevents rusting and corrosion of internal parts and piping
What are the 2 types of pump loops in use today
Primary Secondary, and Direct Primary
On a screw compressor, which rotor is the driving force?
Male Rotor (Take it bitch!)
What test is conducted to check the chiller tube integrity?
Eddy Current Test
TXV’s on most chillers will try to maintain what Super Heat
8-12°F
list 4 factors for Zone Valve Sizing
Pipe size
Flow Rate in GPM
Density of Water or Glycol
Pressure drop through the fan coil
list 4 types of valves used in a chiller system
hand isolation and feed valves
zone control valves
three way capacity control valves
check valves
Is a centrifugal chiller good with high or low compression ratios?
Low
Do compressors start fully loaded or unloaded?
unloaded
What do target baffles do?
Discharges refrigerant equally onto condenser tubes, protects condenser tubes from erosion or corrosion
