How to Reduce Chiller Power Consumption

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How to Reduce Chiller Power Consumption
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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. Its 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 systems energy
  use without jeopardizing plant operation or
  occupant comfort.

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Here are 3 things to think about

1. Consider variable speed retrofits
2. More means less. Running several parallel devices
   can maximize savings.
3. Increase the temperature of the supply

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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 theres 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 dont 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.

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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.

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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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