How to Reduce Chiller Power Consumption
                     HOW TO 
REDUCE 
CHILLER 
POWER 
CONSUMPTION
INTRODUCTION
 When looking for energy savings in an existing chiller plant or during plant renovation, look 
beyond the chiller. Despite having the highest peak load of any component, the chiller may not 
be the largest contributor to total annual energy consumption. It’s more important to consider 
how all of the components work together throughout the year to maximize savings. Paying 
attention to part-load efficiency is critical for maximizing savings.
 There are also simple and low- or no-cost operational changes that can be investigated to 
significantly reduce an existing system’s energy use without jeopardizing plant operation or 
occupant comfort.
1. Consider variable speed retrofits
HERE ARE 3 THINGS TO THINK ABOUT 2. More means less. Running several parallel devices can 
maximize savings.
3. Increase the temperature of the supply
CONSIDER VARIABLE SPEED RETROFITS
The majority of components in the Hitachi chiller cooling system and Hitachi chiller air conditioning system can get the benefit of 
VFDs that have variable speeds. In actuality, all modern energy codes require VFDs for these parts in new systems as well as 
major retrofits. VFD prices have also decreased drastically over the last few years.
As can be seen in the chiller variable and constant speed performance charts, which are on the page 38 there’s an immense benefit 
of using VFDs in chillers, however, only if condenser water temp relief can be used.
Cooling tower fans offer another way to reduce energy consumption by using VFDs. With the loading and outdoor wet-bulb 
temperature drop Variable speed fan motors don’t just conserve energy for fans because of fan law benefits (a fan operating at 
50 percent speeds draws 12.5 percentage of power used by the fan running at 100%) However, they also offer better 
temperature control.
More means less. Running several parallel devices can 
maximize savings.
The plant equipment of the chiller generally runs more efficiently with a load of part. Chillers 
for instance can operate at their maximum efficiency between 40 – 60% of their capacity. 
Fans and systems pumps for cooling connected in parallel could also benefit from a system 
of control which operates more pieces machinery at slower speeds opposed to a staging 
system that allows the operating equipment to expand up to maximum capacity before 
settling for the next unit. For chillers and cooling towers the more equipment you run, the 
greater the area of heat transfer across all points of operation that improves the efficiency 
of the equipment and also reduces pressure drop. Pumps, making the most of savings from 
the law of pumps and operating at optimal pump efficiency points is essential. (The pump 
law works comparable with the law of fan: if the speed of the pump decreases the energy 
consumption will be reduced by the cubic root of the decrease in speed.) But, any control 
system modification must take into account chiller and cooling tower minimum flow limits.
INCREASE THE TEMPERATURE OF THE SUPPLY
The majority of commercial systems are constructed with the temperature of chilled water that 
ranges from 40 F to 45 F. This usually allows the proper dehumidification process and an 
acceptable temperature of supply air for the occupants of spaces in peak hours. But, the 
peak conditions of weather and load are not often observed.
The implementation of a reset for the temperature of supply air control can reduce energy 
consumption in many ways. First, when cold supply air temperatures are not required 
(acceptable humidity levels and no zones at peak load), raising supply temperatures can 
help prevent over-dehumidification of spaces and unneeded latent cooling. In addition 
setting higher air supply setpoints will permit chilled water supply temperature to increase 
significantly, increasing the efficiency of chillers. Overall, chiller efficiency increase about 2 
percent per degree chilled water supply temperatures is increased.
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