Trane TRG-TRC011-EN manual Capacity Control

period three

Capacity Control

notes

operate over a wide cooling-water temperature range, allowing the cooling- water temperature to vary with the load and ambient conditions without the risk of crystallization. For optimum control of leaving-chilled-water temperature, however, it is still generally recommended to design the system to minimize the rate at which the cooling-water temperature varies.

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Figure 49

During normal shutdown, an absorption chiller goes through a dilution cycle to reduce the concentration of the solution throughout the chiller. At this reduced concentration, the chiller may cool off due to lower temperatures of the space surrounding the chiller, but it will not be in danger of crystallizing.

In the event of a power failure, the chiller is not able to go through the normal dilution cycle. As the chiller cools down, those sections of the chiller that contain highly concentrated solution may crystallize. This is most likely to happen if the chiller is operating at or near full load prior to the power failure. Additionally, the probability of crystallization becomes greater the longer the chiller is without power and the cooler the temperature is in the equipment room.

Today, chiller manufacturers use a variety of methods to ensure that the solution is diluted in case of an electric power failure. One method uses a combination of normally-open valves that allow refrigerant to flow, by gravity, and mix with the concentrated solution.

In summary, the high-quality construction, smart microelectronic controls, and automatic purge systems of most modern absorption chillers have improved the monitoring and control of the cycle, to the point where crystallization is not the serious problem that it once was with absorption chillers.

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