Comfort Considerations in Net ZEBs: Theory and Design - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 114

velocity. Being the value at which heat flows entering and leaving the body
are balanced, or “neutralized”, it is also called neutrality temperature and
the thermal sensation corresponding is called neutral sensation or
neutrality.

Fanger's Predicted Mean Vote and Predicted Percentage Dissatisfied
The thermal comfort equation allows us to calculate the sets of the values
of the aforementioned variables for which the thermal load L of the body
will be equal to zero. For conditions in which the thermal load L of the body
is different from zero, Fanger proposes two indices to assess the degree of
departure from the comfort situation: the Predicted mean vote (PMV) and
the Predicted percentage of dissatisfied (PPD). PMV is an analytical index
derived from the thermal comfort equation and tuned using approximately
1300 surveys:

(3.15)

which allows us to estimate the mean value of the thermal sensation votes
of a large group of people expressed according to the ASHRAE seven-point
scale of thermal sensation ( Table 3.1 ).

Table 3.1 ASHRAE seven-point scale of thermal sensation

Question How do you feel
at this time?
Descriptor Cold Cool Slightly

cool

Neutral Slightly
warm

Warm Hot

Value −3 −2 −1 0 +1 +2 +3

Although PMV is derived for steady-state conditions, it can also be applied
with an acceptable approximation if PMV is within the range [−2, +2] and
the aforementioned variables describe small fluctuations within the
following intervals (ISO, 2005):

- Metabolic activity: M ∈ [0.8, 4.0] met