Net ZEB Design Processes and Tools - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 213

highlyinfluenced bytheoccupantproperties (e.g.,activity levelandclothing
level) and the indoor environmental conditions (air temperature, relative
humidity, surface temperatures, and air speed). Most detailed BPS tools
calculate the environmental conditions (e.g., air and surface temperatures)
and allow them to be readily used to predict comfort levels, based on
assumed occupant properties. Several tools, including EnergyPlus, provide
higher-level thermal comfort metrics, such as PMV and predicted
percentage of people dissatisfied (PPD) (Fanger, 1970). In environments
where occupants have a greater ability to adapt (e.g., operable windows
and change clothing level and activity level), static assumptions neglect
occupants'abilitytoimprovetheircomfortlevel(deDearandBrager,1998).
Instead, an adaptive comfort model should be considered (e.g., ASHRAE
Standard 55 (ASHRAE, 2010c)). Adaptive comfort models, which are valid
for naturally ventilated buildings, suggest that occupants are tolerant to
wider operative temperature ranges.
There are a number of additional thermal comfort conditions that must be
considered during design. These include drafts (localized elevated airspeeds
from cold windows, cracks, or diffusers), which may require CFD to
accurately determine; asymmetrical radiant temperatures (e.g., a
particularlyhotorcoldsurfaceinonedirection);warmorcoldfloorsurfaces
(which can affect occupants via conduction); rapid changes in temperature
over time; and high vertical temperature gradients (ASHRAE, 2004).
Though many of these cannot be quantified with BPS without using CFD,
building material and geometry and HVAC system (e.g., radiant floor
heating) selection can be guided by these considerations. For instance,
ASHRAE Standard 55 (ASHRAE, 2010c) provides limitations on the
comfortable floor temperature range. Floor temperature output is available
from many BPS tools (e.g., EnergyPlus and ESP-r).
Modeling thermal comfort accurately should be a major priority in Net ZEB
design as soon as sufficient detail is available to apply the aforementioned
models. Knowledge of typical occupant activities, clothing level (e.g., dress
codes), personalized controls, and corporate culture (in commercial
buildings) are all important inputs to modeling efforts. The ASHRAE
Thermal Comfort Tool (ASHRAE, 2010b) can be used to predict comfort
based on several different comfort models if the main environmental and
occupant conditions are known.