Civil Engineering Reference
In-Depth Information
Table 1 Design-phase uncertainties
Design uncertainties
Classification
Characteristics
Forecasting weather conditions
Internal
NZEB performance is estimated using historical weather data, which might change or fluctuate
significantly during building operation, resulting in a change in the actual energy use profile and the
required energy balance from renewables (Robert and Kummert
2012
)
Predicting energy savings
Energy use and savings are typically estimated using building simulation models where several
assumptions about existing building conditions and future use are made (Verbruggen et al.
2011
;
Hirsch et al.
2009
; Wang et al.
2009
; and De Wit and Augenbroe
2002
). However, these assumptions
often result in significant differences between predicted and actual energy use in the building
(Yudelson
2010
; Dell'lsola and Kirk
2003
; Soebarto and Williamson
2001
). For example, the design
engineer might estimate that a commercial building will be operated 60 h per week, but that might
increase or decrease depending on the tenants of the building and their energy use behavior. In
addition, several studies indicate that buildings use more energy afterhours that during regular
operation time (Sanchez et al.
2007
; Webber et al.
2007
), making the assumption of ideal schedule for
building operation a major source of uncertainty when calculating energy savings
Predicting equipment
performance and costs
The building equipment installed in the NZER could be unreliable in its operation (Stadler et al.
2009
). In
addition, facilities managers often lack time, necessary skills, and experience required to ensure that
equipment is running as designed. Another important aspect is that technology innovations might make
the expensive equipment installed today in the building outdated in a few years. This might reduce the
resale value of NZER, making the initial investment less desirable (Brown
2008
)
Offsite generation prices of
renewable energy
External
The price of offsite-generated renewable energy could be as uncertain as fossil fuel prices due to the
unreliability in their efficiency and operation (Mavrotas et al.
2003
)
Predicting occupancy energy use
characteristics
A substantial amount of a building performance is related to occupants' behavior and how they use energy.
Considerable differences in energy use are associated with the high uncertainty of occupant behavior
(Azar and Menassa
2012a
)
Fluctuating energy costs
High uncertainties associated with the fluctuating energy costs have a strong influence on the expected
economic benefits from energy savings in NZER. In addition, the use of expensive offsite renewable
energy sources might not make economical sense when traditional energy costs are low (Marszal et al.
2012
and Elkinton et al.
2009
)
(continued)
