192 / 248
BEAM P
LUS FOR
N
EW
B
UILDINGS
I
NDOOR
E
NVIRONMENTAL
Q
UALITY
(I
EQ
)
V
ERSION
1.2
I
EQ
14 T
HERMAL
C
OMFORT IN
N
ATURALLY
V
ENTILATED
P
REMISES
Copyright © 2012 BEAM Society Limited. All rights reserved.
Page 171
temperatures. This range extends beyond the comfort zones established
for air-conditioned buildings, and may more closely reflect the local
patterns of outdoor climate.
Analysis of the available data has established that behavioural
adaptations, such as changes in clothing insulation or indoor air speeds,
could account for only half the observed variance in thermal preferences
of people when in naturally ventilated buildings. Given that physiological
adaptation is unlikely to play much of a role; it is suggested that the rest of
the variance is attributable to psychological factors
[4]. Relaxation of
thermal expectations may be due to a combination of higher levels of
perceived control and a greater diversity of thermal experiences in a
naturally ventilated building.
For the purposes of ASHRAE 55-2004, occupant-controlled naturally
conditioned spaces are those spaces where the thermal conditions of the
space are regulated primarily by the occupants through opening and
closing of windows. The ‘Optional Method for Determining Acceptable
Thermal Conditions in Naturally Conditioned Spaces’ is intended for such
spaces. In order for this optional method to apply, the space in question
must be equipped with operable windows that open to the outdoors and
that can be readily opened and adjusted by the occupants of the space.
Mechanical cooling for the space should not be available, although
mechanical ventilation with unconditioned air may be utilised. The method
applies only to spaces where the occupants are engaged in near
sedentary physical activities, with metabolic rates ranging from 1.0 met to
1.3 met, and may freely adapt their clothing to the indoor and/or outdoor
thermal conditions.
Allowable indoor operative temperatures for spaces that meet these
criteria may be determined from Figure 5.3 in ASHRAE 55-2004. The 80%
acceptability limits are for typical applications and shall be used when
other information is not available.
The allowable operative temperature limits in Figure 5.3 may not be
extrapolated to outdoor temperatures above and below the end points of
the curves in this figure. If the mean monthly outdoor temperature is less
than 10°C or greater than 33.5°C, this option may not be used, and no
specific guidance for naturally conditioned spaces is included in this
standard. Consequently, for the BEAM assessment, months for which the
mean monthly outdoor temperatures are outside these limits can be
discounted.
It is most likely that some of the premises within a building development
will be subject to higher than average external heat gains, with consequent
higher internal temperatures during summer months. Those premises at
more exposed facades will suffer from adverse winter conditions. It is
appropriate to examine the detailed thermal performance of the most
susceptible premises, and based on detailed analysis employ mitigation
measures, such as changes in fabric design and other solar control
strategies.
When air-conditioning is likely to be installed the type, rating and
installation of units should be such as to provide for control over thermal
comfort conditions over the range of thermal loads that are likely to arise.
The Predicted Mean Vote (PMV) refers to a thermal scale that runs from
Cold (-3) to Hot (+3), originally developed by Fanger and later adopted as
an ISO standard. The original data was collected by subjecting a large
number of people (reputedly many thousands of Isreali soldiers) to
different conditions within a climate chamber and having them select a
position on the scale the best described their comfort sensation. A
mathematical model of the relationship between all the environmental and