Environmental Engineering Reference
In-Depth Information
TABLE 4.1
Estimated System and Component Efficiencies
Eficiency(%)
Component
Low
Target
High
Pumping
VFD pump drive
94
95
97
Power wires
96
98
99
Motor
94
96
97
Pump
60
70
75
Pipe friction
96
97
98
Total
49
61
68
Generating
Pipe friction
96
97
98
Turbine
70
80
85
Generator
93
95
96
Rectifier
95
97
98
Inverter
94
96
97
Total
56
69
76
Round-trip efficiency
27
42
52
sections, discrete component efficiencies are introduced. These values are
summarized in Table 4.1. The pump or turbine has the most impact on system
efficiency. Electrical system components including the motor generator have
relatively high efficiencies. One should note that the round trip efficiency
is not the figure of merit for an aquifer UPHES. Rather, the turbine opera-
tion efficiency should be emphasized because, during pumping, energy that
would otherwise be unused is used to pump water. Therefore, the pumping
cycle can be viewed as “free” and the generating cycle viewed as the effi-
ciency of merit for the system.
Aquifer Hydrogeology
The success of an aquifer UPHES installation depends on favorable hydro-
geologic conditions. Aquifer hydrogeology is briefly discussed in this section,
and typical values for important UPHES design parameters are introduced.
Aquifers fall into two major categories: unconfined and confined.
Unconfined aquifers are also called water table or phreatic aquifers because
their upper boundaries are the water tables. Usually, the most shallow
aquifer at a given location is unconfined, with confined aquifers below.
Unconfined and confined aquifers are separated by confining layers called
aquitards or aquicludes—geologic formations of very low hydraulic con-
ductivity. Unconfined aquifers generally receive recharge water from direct
