Net ZEB Design Processes and Tools - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 157

simple models with a limited number of inputs and outputs are sufficient
during the concept design phase, more complex tools with a larger number
of outputs at a finer time step are necessary during the design development
phase. Consider, for example, the design of thermal energy storage. In the
concept design phase, monthly annual energy balances may be sufficient
because only the general effect of the thermal mass on the overall building
monthly or annual energy performance is required, in order to estimate
the order of magnitude for renewable energy system capacity. In the design
development phase, however, the designer may want to understand the
effectofthethermalmassoncomfortandindoortemperatureduringtypical
days of the year. This type of study requires building simulations that can
be performed at a sub-hourly time step. Appropriate model resolution is
discussed at length in Section 4.3.
Another reason that multiple tools are required during the different design
stages is that since each tool was developed for a specific purpose and in
a certain context (e.g., for code compliance or a specific type of building
or climate), each has its own assumptions, capabilities, strengths, and
constraints that limit its range of applications and make it appropriate
to obtain only certain information. These limitations are a concern when
modelingconventionalbuildings,buttheypresentanevengreaterchallenge
for low- or net-zero energy buildings because of the particular features
of these buildings. Net ZEBs will typically include some passive design
features, energy efficiency, and conservation measures, as well as on-site
RETs generating thermal and electrical energy. As shown during a
benchmarking exercise (Athienitis et al. , 2010) produced by the IEA SHC
Task 40 - EBC Annex 52, these particularities are not necessarily part of
conventional buildings and as a result, are not always fully implemented or
supported in all commercial design tools. Thus, it is common that multiple
tools are required to encapsulate the interactions between different building
components and obtain necessary feedback to complete a design.
A review of building performance simulation tools shows that up to now,
most developed tools are not design tools but rather tools to evaluate
performance of a design. Even complex and very advanced tools can rarely
be used at all stages of design simply because they require a set of inputs
often unavailable at the early design phases of the building. Complex tools
canbeusedtojudgeadesign,butmostofthemcannotprovideguidelines to
achieve a high-performance building. Conversely, simple tools that require
a limited set of inputs are not suited for a precise evaluation when dealing