COP of an industrial chiller? Help!

[Anon13]

Hello,

I am a novice in refrigeration. It is something I have studied quite less, only the most basic of starting concepts. My course doesn't go into deep until late this year. But I am currently doing my summer industrial training and my project includes calculating the COP of the chiller unit functional there.

My basic doubt is that which of the following two approaches should I adopt to find the COP-

1. I know the discharge and suction pressures. So should I make a p-h graph for these pressures and write the steady state flow equations and calculate Q/W?

OR

2. Should I measure the heat removed from water through specifications of the PHE package and also measure the work input of compressors in KW and divide the two quantities?

I request you all to PLEASE help me out, I will be very grateful. And forgive me any stupid questions I might have unknowingly asked or would ask.

[Tradewinds]

Go for 1. Plot it on a pH graph.

COPr = Refrigeration Effect / Work Done by compressor

[Peter_1]

2. is the good answer.

[Tesla]

Yes Peter is correct 2. is the only answer for chiller COP.
1. would only give the compressor COP. Then there is the system COP - which measures the whole system including all fans and pumps. Your answers will vary under different loads and with different types of compressors eg. the Turbocor chiller performs very well under low ambient conditions where most other compressors with oil require an elevated condensing temp for oil return.

[Tradewinds]

Hi Anon,
I found these on the net and thought you might find it helpful for your project

http://emt-india.com/BEE-Exam/GuideBooks/4Ch9.pdf - Have a look at chapter 9.5 onwards. Also, if you go to http://emt-india.com/BEE-Exam/GuideBooks (http://emt-india.com/BEE-Exam/GuideBooks/4Ch9.pdf) you can download all the chapters

http://www.mcquay.com/mcquaybiz/literature/lit_systems/AppGuide/AG_31-003-1.pdf?bcsi_scan_106ABDFCE01E65E8=0&bcsi_scan_filename=AG_31-003-1.pdf

Hi Peter/Tesla,
I thought it was meant to be based on compressor power and then pumps and fans etc were included as total system COP. Looks like I have some reading to do.
Thanks.

[mad fridgie]

If you want to know the "actual" COP, then you have to measure "actual" mass flows and temperatures/pressures. Just using design data, is just that design data. Even if equipment was tested, it would have been completed under ideal conditions with the system being in an ideal condition. Over time, equipment may deteriate. If this equipment is large you should consider measuring electrical KVA, not just Kw input.

Tradewinds, Heat of rejection, includes electrical input and is not directly related to "Net Refrigeration"

[Anon13]

Thank you so much Tradewinds, Peter, Tesla and Mad fridgie.

[Anon13]

If you want to know the "actual" COP, then you have to measure "actual" mass flows and temperatures/pressures. Just using design data, is just that design data. Even if equipment was tested, it would have been completed under ideal conditions with the system being in an ideal condition. Over time, equipment may deteriate. If this equipment is large you should consider measuring electrical KVA, not just Kw input.

Could you please elaborate on why I need the KVA values and not the KW? Plus I do not have in-line flow meter on the evaporator line, so is there anyway I can measure the flow rates without disturbing plant operation?

[mad fridgie]

If this is a large system, your client maybe paying for KVA, not Kw,
Use an non invassive flow meter on your water circuit.

[Magoo]

as per Mad Fridge's comment, power factor correction on system will save large amount of costs as well.

[Anon13]

Could you please also tell me how do I proceed to calculate the net power consumption of a 3 cylinder reciprocating compressor which is driven through a motor via a belt, the motor rated for operation at 75KW?

And apart from the compressor and the primary/secondary pumps used for circulating water through cold and hot wells, what else should be taken into consideration while calculating plant power consumption?

Once again, thanks for the help!