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Electric centrifugal heat-recovery chiller

An electric centrifugal heat-recovery chiller, or water-to-water heat pump, as it sometimes is called, is capable of producing 42°F chilled water while also producing 155°F condenser water that can be recovered for space heating or reheat (Figure 9). Following the basic precepts of reverse Carnot-cycle efficiency, this machine requires significantly more electrical power than a standard high-efficiency chiller (1.370 kw per ton vs. 0.571 kw per ton).

Figure 10 shows the comparatively high emissions per ton-hour of cooling of an electric centrifugal heat-recovery chiller. If heat from the machine can be recovered for useful purposes, however, this can be a super-low-emissions option (Figure 11). Such a machine never should be operated in situations in which heat cannot be recovered; not only will the CO₂ emissions be the highest of any of the options discussed here, operating costs will be incredibly high.

Summary

Obviously, the next step is to develop annual numbers. However, on the basis of the full-load comparisons, several conclusions can be drawn:

• Based on stand-alone chiller technology, in St. Louis, the lowest CO₂ emissions are achieved with a high-efficiency centrifugal chiller.

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  Emissions comparisons are highly related to site location and the source of electrical generation.

• Cogeneration options promise lower CO₂ emissions, but with increased complexity and maintenance costs.

• For the right application, the heat-recovery-chiller concept can yield lower CO₂ emissions with less complexity and lower maintenance costs.