How to Reduce Chiller Power Consumption

1. How to Reduce Chiller Power Consumption

2. 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.

3. Consider variable speed retrofits • More means less. Running several parallel devices can maximize savings. • Increase the temperature of the supply Here are 3 things to think about

4. 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.

5. 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.

6. 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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