How to improve A/C efficiency



2.1 What is kW/ton


nkW/ton means electrical energy that total plant consumes to produce 1 cooling ton for 1 hour.


( 1 Cooling ton = 12,000 Btu)


What is kW/ton




Useful information about kW/ton



kW/ton of split-type A/C is ~ 1.4

kW/ton of package A/C is ~ 1.2

kW/ton of water chiller A/C is ~ 1.0

If we can improve kW/ton from 1.0 to 0.9, we will save money 10% in every ton cooling.


Where is kW from ?



nkW plant is total power consumption of chiller plant


  =   kW Chillers +

  kW Chilled water pumps  +

  kW Condenser water pumps +

  kW Cooling towers


Where is Ton from ?



nTon is total cooling production from chiller plant


  = (Tch return – Tch supply)x Flow /24 when

  T ch return is chiller water return temperature (F)

  T ch supply is chiller water supply temperature (F)

  Flow is chiller water flow rate (USGPM)


Nature of kW/ton




2.2 Variable Speed Drive




Affinity law




Why VSD can save energy ?



Sample: Traditional condenser pump plant




New condenser pump with VSD




Saving Energy from VSD




2.3 How to improve kW/ton


We have 2 ways to reduce kW/ton


  1. Increase Cooling ton output or..

  2. Decrease kW consume of the plant


1. Increase Ton



To increase cooling ton has limits.


Most of plant is fully capacity

Output capacity must depend on machine’s performance

Chiller has internal control to adjust output capacity automatic. To force them to work more than capacity is not possible.

It’s possible to increase “flow” in some situation to increase “ton” without start more chiller but you have to know a way.



Sample: Increase cooling capacity by vary   primary flow




2. Reduce kW by CPEM




kW/ton comparison



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