chiller performance

[tpodany88]

Carrier model 19dk61126AF

When conducting a performance evaluation should I have the heat recovery pump running regardless of outdoor conditions?

Should the condenser tonnage equal the Evap. tonnage plus the energy required to power the motor converted to BTU?

Notice in the picture of the design specs it does not list the condenser rated tonnage, why is that?

[Trehak01]

Man that looks like a nice clean environment to work in not like the tight dirty attics I work in! look at all the pretty colors haha.

[ryan1088]

That is amazing. Sorry can't help with your question, but that mech room is awesome!!!

[KnewYork]

Having worked for a factory for most of my life I will tell you what I was told by the factory people. Conducting a field performance test is as close to impossible as you can get. Producing a constant load...nearly impossible. Having calibrated and accurate thermometers placed in the exact places...nearly impossible. Maintaining precise flows...nearly impossible. When a factory does performance verification and testing they do so under almost laboratory conditions. Conditions that are almost impossible to replicate in the field. But go ahead and knock yourself out...you may get close but it won't be exact by any stretch. Are the tubes absolutely "as new". A 19DK is no spring chicken, so any fouling of even minimal amounts is going to skewed the results.

[manny238]

Good looking mech room.

[ga1279]

Your cooling tonnage is 171 tons, condenser tonnage is 212 tons, motor cooling figures to be 31 tons. Your high temp condenser (heat recovery) is not figure in the overall heat balance unless the condenser flow is restricted to compensate for the heat removed from the aux. condenser which is 125 tons. All these are design data you need to get your pretty machines to operate at full load or existing operating conditions and take all the pressure drops and temperatures entering and leaving the vessels, compute your actual GPMs to Delta "T"s and do your heat balance to create your performance. You will need your existing power factor and input KW. GEO

[KnewYork]

Your cooling tonnage is 171 tons, condenser tonnage is 212 tons, motor cooling figures to be 31 tons.

Your figures aren't accurate. Condenser tonnage is (GPM X Delta T)/30. Evaporator tonnage is (GPM X Delta T)/24. The condenser tonnage has to match the evaporator tonnage. The reason the flow rates through the condenser are greater and the formula for determining tonnage is different is due to heat of compression, not motor cooling. The flow rates or formulas don't change for chillers that are open drive. True some loss is associated with motor cooling, but certainly not 18% of full load capacity.

[ga1279]

Motor cooling is an additional load, as is the oil cooler in this case. Carrier actually spec 29 to compensate for adiabatic heat of compression + motor cooling in one constant number. Just as 24 is the constant for evap tons, it can be used as a constant for condenser tonnage as long as you add in .2844 X mtr KW. This you will find in the Trane service manuals as the formula for heat balance Evaporator tons + Motor cooling = Condenser tonnage +/- 2%. Provided all your measurements are accurate. This has been the formula professional engineers have used since day one. Remember these are used at full load. In the application in question the KW will have a slight increase due to heat recovery bundle. -GEO

[KnewYork]

Carrier actually spec 29 to compensate for adiabatic heat of compression + motor cooling in one constant number.

From this statement it appears that you are saying that motor cooling isn't 31 tons at full load. That's what I was getting at. Interestingly enough, at ARI standard 550/590-98 chilled water flow is calculated at 2.4 GPM/ton and condenser water is calculated at 3.0 GPM/ton. The reason is that the calculated load of the heat of compression is 25%. There is no provision in the ARI standard for motor cooling since some manufacturers employ an open design. The motor cooling part of the equation will affect the kW of the system, but I disagree that it's part of the heat transfer equation between the condenser and the evaporator. If that was true then could York use a different equation because they primarily use open drive motors? I agree motor cooling is an additional load to the overall system, but it isn't a factor in the standard by which all centrifugal chillers are rated.

[ga1279]

While I will agree with your statements, an open drive will still use a higher constant for the condenser as we would still have the additional heat load caused by compression. All I can say is you know what works for you.-GEO

[jayguy]

the tonnage calculation is: (DeltaT x GPM x Specific Heat x Specific Gravity) / 24 = Tons

this is for evaporator AND condenser water flows. the tonnage calculation doesn't care whether it is evaporator or condenser and it doesn't know the difference anyway.

using a different constant is a shortcut way of ASSUMING all of the other heat loads (heat of compressor, oil cooler, motor cooling, lazy technician leaning against the barrel, etc). and we all know that these heat loads change from day to day and hour to hour so using a shortcut, in my opinion, is inaccurate. on units where the motor (or starter) is cooled by the condenser (refrigerant or water), these other tonnage constants assume what those motor kW and efficiency values are.

the evaporator tonnage is listed on this OP's chiller as 170.83 tons and the condenser is listed as 212.50 tons...this also assumes that the fluid is water. if the fluid isn't water, then to accurately calculate the tonnage would require the fluids specific gravity and specific heat.

the fluid is listed as 'FW' which i am unaware what that means. a listed fouling factor of 0.0005 seems rather high to me. this might indicate a glycol of some kind. poor heat transfer in the tubes requires a higher lift which would indicate why the difference between the evaporator and condenser tonnage is so high. this is also an excellent reason why the constant factor in the tonnage equation should also always be 24.

[ga1279]

Well jayguy, if we are assuming as you suggest then I would have to say FW is Carrier speak for fresh water. Also if you don't mind please quit taking pictures of me holding down a centrifugal chiller by sitting on the evaporator, no one is supposed to know about that.-GEO

[jayguy]

...Also if you don't mind please quit taking pictures of me holding down a centrifugal chiller by sitting on the evaporator, no one is supposed to know about that.-GEO

all incriminating photos are available for purchase...the negatives are priced a bit higher!

[KnewYork]

this is for evaporator AND condenser water flows. the tonnage calculation doesn't care whether it is evaporator or condenser and it doesn't know the difference anyway.

Perhaps what we have here is a matter of semantics. When a performance test is done at the factory the paperwork doesn't show that the condenser was producing more tonnage than the evaporator. You work for JCI. If you have attended one of their centrifugal classes the two formulas are presented. When one is on a job trying to diagnose a problem the two different divisors (24 for evaporator and 30 for condenser) are used. How else is one to determine if the condenser and evaporator are doing the same amount of work? Using 24 as the constant for both sides will only lead to confusion. We know the condenser has to do more "work" to overcome the heat of compression. If one uses the same constant for both, then they are going to have to do the math to determine if the condenser is rejecting the same heat as the evaporator, hence the reason for the constant of "30" for the condenser. The math is already done.

Every reference I have found talks about the two different constants. Here's oneand another. ARI standard 550/590-98 says the same. But I guess in the end, we're all going to believe what we want to believe.

[jayguy]

...When one is on a job trying to diagnose a problem the two different divisors (24 for evaporator and 30 for condenser) are used. How else is one to determine if the condenser and evaporator are doing the same amount of work?...

the condenser and the evaporator NEVER do the same amount of work. the condenser always has to do more work. if it isn't doing more work than the evaporator, then there is a major problem and heat is being transferred in the wrong direction or heat is building up in another area.

...We know the condenser has to do more "work" to overcome the heat of compression. If one uses the same constant for both, then they are going to have to do the math to determine if the condenser is rejecting the same heat as the evaporator, hence the reason for the constant of "30" for the condenser. The math is already done...

i think the math is pretty easy to do....condenser work minus evaporator work = 'other heat loads' and when you use the proper formulas (that i presented) you can use them at all possible loads and under every condition...not just brand new and not just at full load and not just chillers. the formulas that i presented are energy loads that the water gained or lost no matter where they came from.

and the math is NOT already done using those constants because you are assuming way more than you are probably measuring including ambient heat gain (or loss), fouling, etc.

[spinning wheel]

Carrier model 19dk61126AF

1.When conducting a performance evaluation should I have the heat recovery pump running regardless of outdoor conditions?

ans.According to the design sheet, your condenser is rated at 212 tons. I would run both as this is what the unit was designed for and add both of the rejected heats to come up with total heat rejected.

2.Should the condenser tonnage equal the Evap. tonnage plus the energy required to power the motor converted to BTU?

ans.Who cares where the heat comes from, it is a combination of all the factors stated above. Who cares about 25 or 30. Just worry about that it exists unless you are an engineer.

3.Notice in the picture of the design specs it does not list the condenser rated tonnage, why is that?

ans.Carrier is lazy! You just need to do some math and it is there. BTUH = GPM x T x 500 (for water)

Good luck,

[HVAC_MY]

Interesting thread.

I agree with using (GPM X Delta T)/24 for both condenser and chilled water side (for DT design of 10 Deg F). Fully hermetic chiller will mean all electrical input has to be computed into the heat load as the kW is converted into rotational energy which is transferred to the refrigerant. Semi hermetic - some assumption on how much motor heat and inefficiency is thrown out to the surroundings and how much is into the system. External drive type will mean 90% of energy (assuming the motor eff is 90%) into the motor is into the system.

The use of condenser tons calculation using (GPM X Delta T)/30 is a shortcut which I feel has not been explained clearly to people operating chillers. I had the same argument just last week, (discussion) where the techs working in a semiconductor factory insisted I was wrong until I showed them that technically they are same but not accurate.

As for the test, it is a called a heat balancing test - but heat balancing test at site is used to check if measurement are accurate or not - i.e. is your flowmeter and temperature sensors accurate - if there is a small variation (+-5%) between condenser and chilled water load, it means measurements are accurate enough. If there is a large difference, something is not right in the measurements or some other heat load rejection has been missed - i.e. heat recovery chillers where you need to add both the cooling tower heat rejection and the heat captured for recycling into the equation.
I have seen some "smart" designs that assumed all heat rejected can be recycled, thus during low cooling loads, the system becomes imbalanced.

Chiller performance check will now depend on:

Power consumed by the chiller for cooling energy generated (kW/ton) with flow as per design values and Condenser water temperature into the chiller. Here you will have to get performance curves from the manufacturer for different Condenser In temp and different loading as the design specs will assume a fix CW in temperature when in reality your CW in can vary. You have to monitor the chiller performance of a period of time using flowmeters and accurate thermistors (constantly checking heat balance) and plot the data against the curves for different CW in temperature - a 3 D charting tool will be an excellent way to do. Or else take out data for a range of CW in temperature within the design range and plot it against the design value.

With the above you will know your chiller performance.