Water Chiller Preferential Loading

Preferential loading is desirable for systems that use heat recovery or free cooling to allow the equipment used in these schemes to remain more fully loaded. In a heat recovery system, a more heavily loaded heat recovery chiller produces more heat that can be recovered for the desired process.

Similarly, if the condenser free cooling method is preferentially loaded in the side stream arrangement discussed below, it receives the warmest return water temperature and thus continues to operate as load and/or condenser water temperature increases.

Preferential loading may also be beneficial for use with either a high efficiency chiller that should be fully loaded whenever possible, or a chiller using a fuel other than electricity, such as an absorption chiller using waste steam from a cogeneration plant, or a chiller coupled with an engine that generates electricity. When used with the latter, the system is able to preferentially load the alternate fuel chiller when the cost of electricity is high.

Preferential loading: parallel arrangement

If a chiller in a decoupled system is moved to the distribution side of the bypass line in a primary-secondary system, due to system hydraulics and temperatures, the chiller is preferentially loaded when it is turned on. As shown in Figure 44, Chiller 1 always receives the warmest system water and is preferentially loaded. As previously discussed, water chillers on the production side of the bypass line (Chillers 2 and 3) are loaded to equal percentages. The parallel preferential arrangement works best if Chiller 1 is capable of creating the desired system supply water temperature, as it will be sending chilled water directly to the distribution system.

Water chiller preferential loading

One caveat when applying this arrangement is that chillers on the production side of the bypass line will run more often at low part-load conditions. Older chillers or newer chillers with a high cycle point may not have this capability.

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