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adrian116
22-04-2009, 01:11 PM
Dear all

I am doing a project to optimize the power consumption of a water cooled chiller . But my consultant told me that i can first make a model to estimate the power consumption of a chiller base on the change of (1) chilled water flow, (2) chilled water supply temper, (3) chilled water return temperature, (4) condenser water temperature(entering chiller), (5) Condenser flow.

What is the benefits in estimating power consumption of the chiller?

Once i know the power consumption under some conditions, what i can do to lower the chiller power consumption?

Thank You

Segei
22-04-2009, 05:41 PM
Dear all

I am doing a project to optimize the power consumption of a water cooled chiller . But my consultant told me that i can first make a model to estimate the power consumption of a chiller base on the change of (1) chilled water flow, (2) chilled water supply temper, (3) chilled water return temperature, (4) condenser water temperature(entering chiller), (5) Condenser flow.

What is the benefits in estimating power consumption of the chiller?

Once i know the power consumption under some conditions, what i can do to lower the chiller power consumption?

Thank You
You have to determine an efficiency of the chiller. Efficiency is power use per unit of refrigeration. Better efficiency will save energy. Probably, a chiller has two major variables. Refrigeration load and ambient conditions. Ref. load influence on water flow and tem. in and out. Ambient con. influence on cond. water flow and cond. water temperature. Choose the best efficiencies(changing flows and temperatures) at certain ref.load and amb. cond.

adrian116
23-04-2009, 06:07 AM
Thanks for replying.

Do you mean to find the highest efficiency with the power estimated by the model by changing the variables? But how this result compare to the real one?

I am confusing why estimation is needed instead of investigate the real chiller directly?

adrian116
23-04-2009, 07:49 AM
Can i say that the estimation is used to simulate the chiller in order to find the highest efficiency? Is it reasonable?

I have found many paper about power optimization of chiller and conclude following points:
(1) lower the condenser water temperature. This can be modify by replacing the cooling tower with a lower energy and larger fan. VSD is also preferred.

(2) Increase the flow of condenser water. But why?

(3) chiller sequencing. To find the efficiency of chillers in a plant system and setup the most power saving sequencing.

(4) keep the chilled water supply temperature as high as possible. But why?

(5) operating chillers in the max-cap range. Is this mean a chiller is more efficient at full load than part load? Why?

Segei
23-04-2009, 04:03 PM
Thanks for replying.

Do you mean to find the highest efficiency with the power estimated by the model by changing the variables? But how this result compare to the real one?

I am confusing why estimation is needed instead of investigate the real chiller directly?
If you have a good model of the plant, you can calculate power use by changing the value of variables and choose the most efficient values. You need millions tests on real plant to explore all combinations of variables.

Segei
23-04-2009, 04:19 PM
Can i say that the estimation is used to simulate the chiller in order to find the highest efficiency? Is it reasonable?

I have found many paper about power optimization of chiller and conclude following points:
(1) lower the condenser water temperature. This can be modify by replacing the cooling tower with a lower energy and larger fan. VSD is also preferred.

(2) Increase the flow of condenser water. But why?

(3) chiller sequencing. To find the efficiency of chillers in a plant system and setup the most power saving sequencing.

(4) keep the chilled water supply temperature as high as possible. But why?

(5) operating chillers in the max-cap range. Is this mean a chiller is more efficient at full load than part load? Why?
1. It should be balance. Larger tower require more capitals and more fan power. Sometimes additional fan power exceed compressor energy savings at lower condensing pressure.
2. Water flow should be balanced as well. Additional flow can lower cond. pressure, but require additional pump energy. Total power(compressors+fans+pumps) should be minimum.
3. Sequence should be chosen to avoid part-load operation.
4. The higher water temperature, the higher suction pressure can be and compressor efficiency will improve.
5. Screw compressors have poor part load performance especially at capacity lower than 50%. Very often pump don't have VFDs and their power use unchanged at different loads. At part load, total plant efficiency will be lower.

adrian116
24-04-2009, 04:28 AM
1. It should be balance. Larger tower require more capitals and more fan power. Sometimes additional fan power exceed compressor energy savings at lower condensing pressure.
2. Water flow should be balanced as well. Additional flow can lower cond. pressure, but require additional pump energy. Total power(compressors+fans+pumps) should be minimum.
3. Sequence should be chosen to avoid part-load operation.
4. The higher water temperature, the higher suction pressure can be and compressor efficiency will improve.
5. Screw compressors have poor part load performance especially at capacity lower than 50%. Very often pump don't have VFDs and their power use unchanged at different loads. At part load, total plant efficiency will be lower.

Thank for replying.

for (4) why higher water temperature will result highter suction pressure?

for (5) Why part-load is inefficienct compare with full load for a single chiller?

Besides those five points. Do you have any suggestion in improving a chiller plant system to have significant savings?

Thank you

Segei
24-04-2009, 05:05 PM
Thank for replying.

for (4) why higher water temperature will result highter suction pressure?

for (5) Why part-load is inefficienct compare with full load for a single chiller?

Besides those five points. Do you have any suggestion in improving a chiller plant system to have significant savings?

Thank you
Assume that water flow is constant. Compressor is designed for certain ref. load or certain temp. difference. For example. Design temp. difference is 5degC. If water 2degC, suction temp. will be 7degC. If water is 5degC, suction temp. will be 10degC.
About part-load.
Full load. Compressor 100TR(ton refrigeration) and 200HP(horse power). Water pump 10HP, condenser fan 20HP. Total power use 230HP. Efficiency 230/100=2.3HP/TR
50% load. Compressor 50TR, 120HP. Pump 10HP, fan 10HP. Total power 140HP. Efficiency 140/50=2.8HP/TR
Full load is more efficient than 50% load.