Page 241 - Materials Chemistry, Second Edition

228 LIFE CYCLE ASSESSMENT HANDBOOK

(Wackernagel & Rees, 1996). Traditional design alternatives aim to alleviate
environmental strain by modifying the technological side of the problem and
treating ecosystems as outside the boundary for improvement. However,
reducing the ecological footprint can also be accomplished by modifying the
ecosystem side of the problem. For example, the most common ecosystems
present in residential areas are lawn and tree systems, both of which are effec-
tive in sequestering carbon (Singh, 2007), (Nowak, Crane, & Stevens, 2006).
Trees are also capable of removing pollutants such as particulate matter and
NO x (Nowak, Crane, & Stevens, 2006). In this context, planting a tree on the
lawn of the house can be thought of as being similar to replacing inefficient
light bulbs, as they are both solutions to decreasing the environmental footprint
of a residential home. Because of these issues, the residential system is worth
consideration. This design problem considers various technological, ecologi-
cal, and behavioral variables for a generic suburban home in Columbus, Ohio,
USA, as summarized in the following Figure 9.6.
The objective functions considered in this problem are to maximize total
profit, carbon saved, and water saved relative to a base case, which has a base
set of design variables. The resulting problem is a multi-objective mixed-
integer optimization program. A unique and challenging characteristic of this
problem is that it has no explicit objective functions in the form of f(X), where
X is the set of design variables; rather, the house portion of the design prob-
lem is simulated under a specific combination of design variables using the
building design program EnergyPlus (U.S. Department of Energy). Dynamic

Technological variables
HVAC and appliance efficiency, photovoltaics, roof color,
hot water system type (solar or conventional), insulation
grades, plumbing fixture flowrates

Objective functions
Minimize:
Cost
Water demand
Carbon emissions

Ecological variables Behavioral variables
Fraction of land used for grass/corn, Thermostat setpoint, seasonal window
on-site water generation, trees for shading control, building orientation to
shading and carbon sequestration true north

Figure 9.6 Residential system design problem considers various associated variables and
objectives (Landers, Urban & Bakshi, upublished). [Original work].