Comfort Considerations in Net ZEBs: Theory and Design - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 125

are in the form of time series values; hence, they allow for visualizing the
dynamic performance of a building with respect to set-point comfort
conditions, but they do not provide an overall picture of its comfort
performance.
A number of metrics for assessing human thermal response to climatic
conditions or thermal stress have been proposed in the literature over the
pastdecades.Severalresearchershaveusedtermssuchas discomfortindex ,
stress index , or heat index to identify the (expected or actual) human
thermal perception of the thermal environment to which an individual or
a group of individuals is exposed. More recently, a new type of discomfort
index has been proposed in scientific literature, standards, and guidelines.
The new type allows for describing the long-term thermal discomfort in a
building and for predicting uncomfortable phenomena in a concise way;
in particular summer overheating. Most of these new indices summarize
the thermal performance of a building in a single value. They are called
long-term thermal discomfort indices and their ranking capability was
evaluated by Carlucci (2013).
3.2.3.1 Background
The Chartered Institution of Building Services Engineers (CIBSE)
introduced some overheating criteria based on the dry-resultant
temperature (CIBSE, 2002) that, for low air velocity, can be approximated
with the arithmetic mean of air and mean radiant temperatures of a given
thermal zone. In 2005, ISO 7730 proposed five methods developed upon
the Fanger comfort model. More recently, in 2007, EN 15251 reproposed
three of the ISO 7730 indices and extended their use also to the adaptive
comfortmodel,ifcompatible.Nicol etal. (2009)introducedan Overheating
risk index, which is derived from the statistical analysis of the measured
data collected in free-running buildings during the SCATs Project (Nicol
and McCartney, 2001). Robinson and Haldi (2008) also proposed an
Overheating risk index based on the analogy between human thermal
comfort perception and an electric capacitor. Often degree-hours are also
used to estimate heating or cooling loads, but with different base
temperatures. More recently, Borgeson and Brager (2011) used a particular
weighted degree-hour index, called Exceedance M , which weighs discomfort
hoursbyhourlyaverageoccupancyinaspecifiedzoneofabuilding.Carlucci
and Pagliano (2012) reviewed 16 long-term discomfort indices. Carlucci
(2013) deemed that none of these fully satisfied the needs for assessing