Journal of Energy Engineering

Variable-speed pumps are becoming increasingly commonplace in the water distribution industry, replacing conventional fixed-speed pumps. While the principal benefit is reduced energy consumption and power costs, there are other significant advantages, including reduced leakage. This paper focuses on some of the economic and hydraulic benefits of using variable-speed pumps to improve the operation of water distribution systems, by presenting several examples that are intended to emphasize calculated results illustrating these benefits. In particular, a direct calculation of pump speeds to meet desired operating conditions exactly, a determination of optimal pump speeds for the most energy-efficient operation of water distribution systems, and an illustration of controlling potentially damaging transients are presented. These examples make use of a state-of-the-art optimization method based on genetic algorithms, along with the recent advances in hydraulic modeling technology.

This article provides a general picture of the state of technical developments with respect to wet/dry cooling towers. More stringent environmental protection requirements led to the introduction of the hybrid cooling tower, which effectively suppresses detrimental plume formation at an efficiency level comparable to that of the wet cooling tower. It is explained that the attainable exhaust air state, in conjunction with the ambient air state, is the only possible basis for a decision in order to obtain both a low-priced design and proper functioning. The cell-type construction, including material selection and automatic operation of the recooling system, is described in detail. In the last section, the fluid cooling tower, designed for a closed circuit, is presented as a combination of the essential elements of wet and dry cooling technology. When the ambient temperature is low, the fluid cooling tower can also be operated as a dry cooling tower, i.e., without water consumption or plume production. Both hybrid and fluid cooling towers of the cell type conform particularly well to the more stringent environmental protection requirements and to the standard of operational reliability set for recooling systems. It is therefore to be expected that use of these types will become more widespread.