Impact of condensing temperature in refrigeration system

Chiller performance depends on the various factors like condenser temperature, evaporation temperature, compressor loading, refrigerant quantity etc.

One of the major factors which impact the chiller performance is condenser saturation temperature.

Condenser saturation temperature depends on various factors like

  1. Variation in cooling water temperature. cooling water temperature depends upon performance of cooling tower and atmospheric condition. Performance of cooling tower can be analyzed by observing approach in the cooling tower while atmospheric condition cannot be controlled.
  2. Performance of condenser.Typically cooling water leaving temp and condensation temp should have not more than 3 Deg C of difference. ( normally known as condenser approach). if it gets increased due to either fouling or scaling it should be cleaned and brought down to original levels
  3. Quantity of refrigerant.Caused by loss of refrigerant, leakage to be identified and refrigerant top up to be planned.
  4. Compressor performance.Refer O&M manual of supplier for fixing compressor performance.

Let us analyse relation of specific power consumption wrt to condenser saturation temperature.

For analysis we have selected HSO2028 compressor of JE & Hall, considered RPM as 2900, suction temp as 2 deg C. Analysis is performed by varying condensing temperature of various refrigerant like R22, R134q and Ammonia.

Graph of Condensing temperature vs BKW/TR is plotted at graph ‘G-1’. Graph shows Specifc power consumption of R22 and R134a are almost similar across various temperature ranges, while for ammonia refrigerant specific power consumption is lower. This suggest that ammonia refrigerants are more efficient while operation than both R22 and R134a.

Comparing rise in specific power consumption from 31 to 45 deg C of condensing pressure. We can easily observe that SPC gets deteriorated from 0.53 BKW/TR at 31 Deg C to 0.86 BKW/TR  at 45 Deg C for R22 Refrigerant. Rise in specific power consumption is almost similar for the entire three refrigerants selected.

 Graph G1 also shows there is approx 3.5% rise in compressor power with each deg C rise in condensing temperature.

Second Graph’G2’ shows percentage of increase in power consumption across temperature range considering 31 deg C condensing temperature as base temperature. Graph shows specific power gets increase to 63%, 67% and 64% for R22, R134a and Ammonia refrigerant only.

Conclusion and learning :

Each deg C of rise in condensing temperature adds 3.5% increase in specific power consumption of refrigeration system, Hence Condensing temperature to be maintained as lowest possible limit.

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