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129 Cards in this Set
- Front
- Back
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What is the set point for water leaving the chiller? |
40-45F
Evaporator water entering : 55F Evaporator water leaving: 45F Condenser water entering: 75F Condenser water leaving: 85F Refrigerant: 35F SST, 95F SDT.Back (Definition) |
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What type of displacement is a centrifugal compressor? |
Non-positive They are the only non-positive displacement conpressor |
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Why is the expansion tank located before the pump on the chilled water loop? |
This is the point of no pressure change so the pump will not see low pressure and cavitate |
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What is the purpose of an eliminator in a tube in barrel heat exchanger? What is the purpose of the target baffle in the condenser? |
To ensure that the saturated gas leaving the barrel does not contain liquid. No carry over will occur. This will ensure no liquid enters the compressor. CARRY OVER!! Target baffle deflects refrigerant and other objects away from the tubes where the refrigerant first enters the barrel. |
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A centrifugal pump will increase what type of pressure and decrease what type of pressure? |
It will increase static pressure and decrease velocity pressure |
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Does total pressure change in a centrifugal pump? |
No, (technically yes because of the heat of compression) |
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Why are staged centrifugal chillers used? |
The flashed gasses from the economizer are used to de-superheat the gas between stage one and stage two The NRE will increase, each pound of refrigerant will hold more heat, and you will need to move less refrigerant. (Mass flow drops). |
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What position is the inlet guide vanes on start up? |
They are closed. The centrifugal pump will be running at 40% capacity. Unloaded.
Inlet guide vanes are for capacity control |
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What is the primary and secondary purpose of a economizer in a centrifugal chiller? |
(1) De-Superheat the gasses leaving the first stage and entering the second stage (2) to ensure a solid column of liquid to the fixed metering device. |
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What is the media called in a cooling tower? |
Fill, Who is this “fill” guy and why are we always waiting for him |
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What is a common “low pressure” chiller refrigerant? (Bonus: water is R-718?) |
R-123 R-11 Below 15 psi (Yep) |
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What are some common high pressure refrigerants for centrifugal chillers? |
R-134a, R404a, and R-410a |
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Hermetic chillers use refrigerant to cool their motor. In what state does the refrigerant enter the motor |
Suction gas in and liquid out |
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Does an economizer increase the NRE? |
Back (Definition) |
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What is the 10-10-10 rule?
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Evaporator water entering : 55F Evaporator water leaving: 45F Condenser water entering: 75F Condenser water leaving: 85F Refrigerant : 35F SST, 95F SDT |
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Compressor lift? |
Compressor Lift: sct-sst
95F-35F 60 Fahrenheit degrees Note it is Fahrenheit degrees and not the other way around. |
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Cooling tower approach? |
=Tower water out- wet bulb outdoor You want a low number. Lower number means more efficient. So you want the water out to be as near as possible to wetbulb. |
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What is chiller temp rise/ drop? What is evap or cond approach temperature? What is the change in water pressure across the the vessel? |
10-10-10
Evaporator approach is a measurement of efficiency. You want a low number. Evap approach= 10 (water temp out(45) - SST (35)) You want the water to be as close the SST. |
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What is the cooling tower range? |
The water temp entering the cooling tower- the water temp leaving the cooling tower |
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Calculate water flow rate? |
Q(btu/hr) = (m)(c)(delta t)
m=500 for water always Evap pump 1 ton of cooling Q(btu/hr) = (500)(2.4 gpm) (10 F degrees)
Q(btu/hr) = 12,000 btu/hr |
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Is charge important for high side float systems? |
Yes because there is almost no superheat |
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What safeties are on a chiller control loop?
Which ones are MMR |
Back (Definition) |
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Dont meg what? |
Starter, solid state starter, vfd, compressor on vaccum |
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What is the temperature of the water entering and leaving the condenser? |
Evaporator water entering : 55F Evaporator water leaving: 45F Condenser water entering: 75F Condenser water leaving: 85F Refrigerant: 35F SST, 95F SDT |
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What temperature is the oil heated up to in the crankcase on the off cycle? |
Compressor oil temp: 140F Evaporator water entering : 55F Evaporator water leaving: 45F Condenser water entering: 75F Condenser water leaving: 85F Refrigerant: 35F SST, 95F SDT |
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Where is the oil filter? Before or after the oil pump? |
After the pump. Filter strainer is before the pump. |
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What type of material is the main bearing made from? |
Babbitt. |
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What is run-out |
Run out can be measured by the amount the center of the shaft is out of alignment with the center of rotation. Runout=bent shaft |
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What is the equation for tons of cooling?
This will only work with water and the supply water pump |
Tons= ((GPM)(delta t)) / (24) Tons = 1 =((2.4 GPM)(10 F degrees)) / (24) = 1 ton |
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What is the SST of a chiller? SDT? |
Compressor oil temp: 140F Evaporator water entering : 55F Evaporator water leaving: 45F Condenser water entering: 75F Condenser water leaving: 85F Refrigerant: 35F SST, 95F SDT |
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When there is a test question that asks “what does it take for the chiller to turn on?” Dont assume it has a water tower or that it is a centrifugal chiller. |
If it has a tower then it would have a condenser water pump flow switch. If it is a centrifugal chiller then the start up is pumps (CHWP and CWP), then oil pressure, then start up. |
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What is the difference between centrifugal and centripetal? |
Centrifugal is the force given to the refrigerant as it is pushed out of the pump vane.
Centripetal is apparently the wrong answer on the test. |
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What type of pump is the oil pump on a centrifugal chiller? |
Positive displacement Rotating vane |
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How low of a vacum should you pull? |
250 microns rising to 500 microns after 15 minutes.
Brand new pump can pull down to 25 microns. |
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When you pull 250 microns on a system and then you blank it off and the pressure rises what is causing that? |
Water at 250 microns vacuum would be ice so when you blank it off it will sublimate and instantly turn into a vapor in the system. This is what causes the pressure to rise. |
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Why do we change the vaccum pump oil after EVERY USE? (Bonus: what type of irregular running shows up as black on main bearing?) |
The moisture in the system ends up in the oil. (Main bearings that are black have high oil temps, main bearings covered in copper have acid build up. Surging shows up as scoring on the main bearing.) |
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The carrier centrifugal chillers are oil cooled but the oil is cooled with water? |
The oil temperature used to be controlled by a temperature sensor that controls a water regulating valve. The valve would throttle the water into the oil cooler. The water used for this used to be domestic city water but it was banned. So they used condenser water (clogging issues). Now they use suction gas so False. |
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Which way does the oil run across the oil filter? Outside to the inside? Or inside to the outside? |
Once the oil leaves the pump it goes into the oil filter from the outside of the filter to the inside because the outside has more surface area. |
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What causes bearings to turn black? What causes them to be be copper plated? What kind of damage does surging cause? |
Black is caused by high oil temperatures Copper plating is usually caused by acid build up in the system. The copper usually finds its way back to the compressor windings. Surging cause scoring and wear. |
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With interference parts what temperature do you have to heat up the parts to? |
200F (water boils at 193F in calgary) |
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Is most of the centrifugal compressor oil inside the oil sump or inside the motor housing? |
Inside the motor housing |
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For a chiller auto purge, What is the difference between adaptive mode and auto mode, and on? |
-On is on. -Auto mode will make the auto purge turn on with the chiller on start up. When the chiller stops the auto purge stops. -Adaptive mode will turn on the auto purge upon chiller start up and will continue to run until it doesn’t see any pump out. (The auto purge will turn on with the chiller for every start up. Then it will turn on and off periodically. However, It will then run less frequent based on the previous time it ran. Possibly more if it is continuing to perform pump outs. If it continues to see non-condensibles then there is a leak on the low side. Because the high side is 15 PSI so air can only enter through a low side leak). |
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How will the autopurge help you diagnose the leak location on a low pressure chiller? |
If there continues to be condensibles as the chiller runs without any shut downs then there is a leak on the low side. However, if there is a large amount of condensibles at start up (and not continously as the chiller is running)….then we can assume that when the chiller shuts down condensibles get into the system through the high side because the system has equalized. |
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What is the purpose of an auto-purge? |
An auto purge removes non-condensibles from the condenser thereby increasing its efficiency. It can also remove other contaminants and extend the machinery lifespan |
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What is the purpose of an auto-purge? |
An auto purge removed non-condensibles from the condenser thereby increasing its efficiency. It can also remove other contaminants and extend the machinery lifespan |
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T/F: If the auto purge is continuing to run pump outs while the machine is running the leak will be on the low side? |
True |
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(WARNING: This slide is one the teacher told us to remember but isn’t on the first test.) Some common misunderstandings with a MUA for the TQ? Profile plate Evap coil is after the fan section. What intiates a call for cooling on a MUA unit? |
High pressure is outside of the MUA Low pressure is inside after burner Evap coil is after the fan section. What intiates a call for cooling on a MUA unit? Outdoor air temperature. —————-
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What are the two things that influence the pressure on the outlet of the centrifugal? |
Size of impeller RPM of impeller |
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What is the high side pressure of a Low pressure chiller application? |
15 psi or below |
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Why does Shell and tube condeser has reverse flow? |
To achieve subcooling |
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TQ: Low side surge is the most common? |
True (according to the test) |
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What is a high voltage start? |
Over 2000V |
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What is a high voltage start? |
Over 2000V |
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Off loading the machine would remove the high side surging? |
True. |
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Surging is hard on the trust bearing? |
True |
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What is the difference between high side surge and low side surge on a centrifugal chiller? |
In a centrifugal chiller, high side surge refers to a condition where excessive pressure occurs on the discharge side of the compressor. This can happen if the load on the chiller suddenly decreases, causing an over-supply of refrigerant. On the other hand, low side surge occurs on the suction side and is associated with low refrigerant flow into the compressor, often due to low evaporator load. Both surges can be damaging and need to be carefully controlled to ensure efficient and safe chiller operation. (Teacher showed a video with surge on start up. He mentions the operator could have stopped the surging by decreasing the demand limit. This would have helped diagnose the surging issue.) |
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When you are pulling vapour what should you insure? |
Pump is running or there is no water in the evaporator barrel |
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How do you remove refrigerant from a chiller? |
(1) keep evap pumps running (2) use push pull method till no more liquid (3) use vapour recovery afterwards —————- (4) charge with vapour |
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What do we check on a maintenance? |
List
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What pressure is water 45C? |
0.300 inHG absolute (Not 3 or 0.03 or 0.3!!!!) 0.3 0.3 |
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What is R-718? |
very best thing ...... 970 BTU/Lb! Water |
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What is the most effective salt? |
Lithium bromide |
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What type of evaporator is used on an absorption chiller? |
Falling film evaporator Can have approaches of 4-5F |
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How do they test the tubes? |
Eddy current tube testing |
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Name the 4 components of a 2 pressure absorber? |
Evaporator (low) Absorber (low) Generator (high) Condenser (high) |
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Why do we need a dilution cycle and when do we use a dilution cycle? |
The dilution cycle is used when shutting the machine down and it is used to prevent crystallization.
Crystallization line is at the bottom of the graph |
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What is a good heat exchanger efficiency? |
70-75%
Below 70% is a possible leak Above 75% blockage is heat exchanger or in the absorber spray nozzles. |
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In an absorber where is there a pressure drop between? Generator, condenser, evaporator, and absorber |
Its between the condenser and the evaporator. The water in the pressure drop is below 1% salt |
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What refrigerant is in a 2 pressure absorber? |
R-718 (Water) 700 series are inorganic |
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The cooling tower water will pass through ________ then it will pass through the _________.
Generator, evaporator, condenser, absorber |
Absorber then condenser |
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How does the adsorber work? |
(1) liquid water in evaporator cools down chilled water and boils off 7mmHG abs. (2) steam travels over to absorber 6mmHG abs. It passes an eliminator. Steam is 55F (3) intermediate solution is pumped over falling film exchanger in the absorber. This allows the exchanger to remove the heat of condensing (and dilution, and evaporation) into water tower loop. The lithium brine is now able to decrease in concentration by absorbing more steam (weakening the solution). (4) the weak solution pulled from the bottom of the absorber via pump and moved through an economizer, gaining heat from the strong solution traveling in the opposite direction, and into the generator. (5) the generator uses heated steam to boil the water out of the brine solution. The steam goes to the condenser and the brine (now strong solution) is sent back into the absorber (first passing the economizer where it looses heat) and into the inductor and then pumped directly over the falling film heat exchanger as intermediate strength solution. (6) the steam leaving the generator and passing ton the condenser…. Will now get cooled and condensed with tower water and is now less than 1% concentration. The water is pulled from the bottom of the condenser and passes through a pressure drop. The water then enters the evaporator. |
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What does a hydrometer measure? |
Specific gravity. The specific gravity of water is 1. Stronger solution has a higher specific gravity. |
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How do you remove crystallization from an absorber? |
Use a tiger torch on the heat exchanger Usually in the heat exchanger. The closer you are to crystalization the more efficient you are running. So they used to run them inefficiently to limit downtime. |
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If there is nitrogen in the absorbed what will happen to your approach? |
It will increase |
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How do you have capacity control on an absorber? |
You turn down the prime mover ( steam entering the generator) from the steam source. Or you hold back the steam leaving the generator into the condenser. |
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What do we use for corrosion inhibitor in an absorber? |
Used to use Chromates but now Nitrates.
Octyl alcohol is a water wetter. (Increases efficiency by removing surface tension.) |
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What is the temperature of water at 0.300” Hg abs or 0.248” Hg abs? |
0.300” Hg abs (45F) 0.248” Hg abs (40F) |
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What is 0.300” Hg abs or 0.248” Hg abs in millimeters? |
0.300"= 7.62mm Hg abs (45°) 0.248"= 6.299mm Hg abs (40°) |
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How will you determine if there is premature wear inside of the absorbtion chiller vessels without opening up the system? |
By taking samples of the brine you can get an analysis of the brine and determine what trace elements are in the sample and know which parts of the system may be experiencing wear. |
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What is the setting for a low temp cut out on an absorber? |
34F |
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How much heat sent to the cooling tower is taken from the absorber vessel? |
2/3 (1/3 is from the condenser) Heat of Dilution Heat of absorption Heat of condensation |
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What type of valves are the service valves on an absorber? |
Diaphragm saddle valves |
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If it talks like an inductor, walks like an inductor then what is it? |
An inductor ( the pump mixes and transfers cool high concentrate with low concentrate solution to make intermediate concentrate solution and be sent towards the “falling film exchanger”.) Inductor kind works like Venturi effect. |
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On the York Max E, what type of coupler is used to connect the open drive to the centrifuge? |
Lovejoy coupler (Oil leaks out and goes into a plastic bottle) |
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On the York Max E, what type of coupler is used to connect the open drive to the centrifuge? |
Lovejoy coupler (Oil leaks out and goes into a plastic bottle) |
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What is the benefit of a single pass heat exchanger? |
Higher volume but it has a higher approach (aka the water leaving is not cooled as much ad a double pass) |
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If you are going to change the oil filter on a low pressure centrigal chiller? |
You must isolate and pull down a vacuum before opening up the filter section. |
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What is the purpose of a coupon rack on the condesing water that is used by the cooling tower? What ph? Less conductive means bad? |
It has a few different metal plugs that can be inspected to see if your chemical solution is not correct.
This along with a conductivity sensor. Less conductive means more sediment in system. Ph of around 7. |
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Add 1 biocide not 2 because you will get… How does the coductivity sensor activate and replace the cooling tower water if it detects bad Ph? |
Foam. Once the conductivity sensor senses that the water is not correct it will activate a dump water and makeup water. The contact head maker will count the revolutions on the makeupnwater pump and add the appropriate amount of inhibitor and biocide.
The make up water |
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Do high pressure chillers have relief valves that need to be replaced every 5 years? |
Yep |
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Tonnage of a scroll/recip chiller? |
10-200 tons |
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What can cause a high side surge?
What can cause a low side surge? |
A compressor operating in a Surge Condition will have refrigerant moving backwards from the condenser through the compressor to the evaporator A surge condition may be created by having too high of condensing refrigerant pressure. What can cause condensing pressure to rise? •Low condensing water flow = high condensing pressure Fouled condenser tubes = high condensing pressure •Non Condensables in the system Water bypassing through the divider plate on the condenser water head A surge condition may be created by having too low of an evaporator refrigerant pressure What could cause SSP to drop? • Low chilled water flow (Low Load) • Low chilled water return temperature (Low Load) • Fouled evaporator tubes (Low Load) • Low Refrigerant Charge |
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What is the difference between high side surge and low side? |
• A high side surge is a large, noisy and damaging to the compressor. It is the result of having a large reservoir of high pressure in the condenser that is trying to get back to the evaporator by going backwards through the compressor This type of surge can be very damaging to the thrust bearing ———————- Alow side surge is shorter in duration and not as loud • This is a result of having a relatively small amount of refrigerant vapor from the high side enter the evaporator via the compressor. This will increase evaporator pressure and reduce the lift, stopping the surge |
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Calculating compression ratio units? Psia or psi? |
PSIA SCP (abs) / SSP (abs) |
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What is the efficiency of a centrifugal chiller? |
Reciprocating Chiller • 1 - 1.23 kW /ton • Scroll Chiller • 1.1 - 1.23 kW /ton • Screw (Rotary) Chiller • .58 - .64 kW /ton • Centrifugal Chiller • .47 - .56 kW /ton |
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What is the efficiency of q recip compressor? |
Reciprocating Chiller • 1 - 1.23 kW /ton • Scroll Chiller • 1.1 - 1.23 kW /ton • Screw (Rotary) Chiller • .58 - .64 kW /ton • Centrifugal Chiller • .47 - .56 kW /ton |
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What is the efficiency of a scroll chiller? |
Reciprocating Chiller • 1 - 1.23 kW /ton • Scroll Chiller • 1.1 - 1.23 kW /ton • Screw (Rotary) Chiller • .58 - .64 kW /ton • Centrifugal Chiller • .47 - .56 kW /ton |
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What is the efficiency of a scroll chiller? |
Reciprocating Chiller • 1 - 1.23 kW /ton • Scroll Chiller • 1.1 - 1.23 kW /ton • Screw (Rotary) Chiller • .58 - .64 kW /ton • Centrifugal Chiller • .47 - .56 kW /ton |
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What is the efficiency of a screw compressor? |
Reciprocating Chiller • 1 - 1.23 kW /ton • Scroll Chiller • 1.1 - 1.23 kW /ton • Screw (Rotary) Chiller • .58 - .64 kW /ton • Centrifugal Chiller • .47 - .56 kW /ton |
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How do you convert inches of vacuum to psia? |
• What is a perfect vacuum in inches? 29.92" hg vac is a gauge pressure (0 inhg = atmosphere, 29.92 inhg = vacuum) • What is a perfect vacuum in PSIA? 0 #A • What is atmospheric pressure in Absolute? 14.7 #A • 29.92" hg / 14.7 # = 2.04 inches/PSI This is a conversion factor • A reference point is required to convert "hg to PSIA What is the reference point? • Atmospheric pressure! 14.7 #A • To convert "hg to PSIA the pressure is lower than atmospheric and that has to be considered • PSIA = 14.7 - (inches hg/2.04 " / # ) • From our example, PSIA = 14.7 - (19.5" /2.04) • PSIA = 5.14 -12°C Q Search ※ L |
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What is the conversion factor for inhg to psia? |
2.04
From our example, PSIA = 14.7 - (19.5" /2.04) • PSIA = 5.14 |
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What 2 solution samples will you need to evaluate the system performance of an absorption chiller? |
Strong solution and intermediate solution
(specific gravity and temperature) |
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What is the temperature of absorber? |
(1)Take the intermediate fluid temperature and specific gravity. (2) Use the specific gravity chart vs temperature chart to find the concentration. 1.7 s.g @ 113F => chart =>61% (3) use the concentration chart vs temperature. Use intermediate temp @ intermediate concentration to find REFRIGERANT TEMP AND PRESSURE!!! 113F @ 61% => chart => 6mmHg @ 40F
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What measurements do you use to find the temperature and pressure of the refrigerant in the condenser? |
The specific gravity of the generator and the temperature of the generator. (Usually they get the specific gravity of the strong solution after the heat exchanger because it is 132F and not 205F. |
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What two functions does the weak solution pump perform? |
(1) moves weak solution to the generator (2) mixed weak with strong solution (eductor) and to the absorber nozzles. |
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What is the purpose of the stabilizer valve? (In the absorber) |
To weaken the strong solution before it can crystalize |
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What is the purpose of the stabilizer valve? (In the absorber) |
To weaken the strong solution before it can crystalize |
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What is the unloader valve used for? |
It is used during low condenser temperature operation and start up |
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What is annual maintenance for the absorber? |
The cooling tower water tubes need to be brushed! |
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What is the compression ratio of a centrifugal chiller? |
3:1 to 5:1 |
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TQ:What is the most common cause of bearing failure (fan motor)? |
Over lubrication… aka buddy with the grease gun |
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How many tons is a centrifugal chiller able to handle? |
70-6000 tons |
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What is the difference between a mixing valve and a diverting valve? |
Mixing is 2 in and one out Diverting is 1 in and 2 out |
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Test: Memorize economizer mode for a chiller, the 10-10-10 rule, approaches and range, absorber cycle, sensors analog and digital, aux contact on pump for flow switch, dilution cycle, 140F,
Not on test: bearings temperature, |
Blah |
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What are the three forms of capacity control for a centrifugal chiller? |
Hot gas bypass Inlet guide vane VED |
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What is the low temperature cut out for a chiller? |
33F |
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What is the low temperature cut out for a chiller? |
33F |
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What is the difference between a stall and a surge? |
First it stalls then it surges |
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This has cards in the walk through at sait |
Yup |
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What is the benefit of a single pass chiller vs a double pass chiller? |
You can run higher volumes through the single pass chiller |
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What is the benefit of a marine header? |
You can remove the lines and service the tubes |
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For the water tower the conductivity sensor more conductivity means…. |
More pollutants. Once the sensor reads a higher than desired conductivity it will flush cooling tower water out and add 1 biocide (not 2) and 1 inhibitor. It will measure in the correct amount by using a contact head meter to calculate the amount of makeup water. |
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Because the shaft seal on the York is a weeping shaft seal that will loose oil at a predictable rate we will have to add oil back into the York chiller. How do you do that? |
You will pull a vaccuum down on the canister before opening the canister. |
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Who will work on the 4160V connections on a chiller? Connect the chiller, turn it on and off? |
An electrician |
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What is the vaccum pump under the adsorption chiller used for? |
Removing non-condensibles |
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When are absorption chillers most efficient? |
When they are nearest the line of crystallization. |
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When are absorption chillers most efficient? |
When they are nearest the line of crystallization. |
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There are two types of heads: marine and nozzle. Which one is easier to work on? |
Marine style |
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What type of pump is in your vacuum? (Bonus: what is a good vacuum?) |
rotary vane
250 microns, no higher than 500 for 10 minutes. |
