Perceived IEQ conditions: Why the actual percentage of dissatisfied
persons is higher than standards indicate?
Risto Kosonen*, Mervi Kajaala and Tarja Takki
Halton Oy, Finland
*
Corresponding email: risto.kosonen@halton.com
SUMMARY
The design criteria for indoor environmental quality are specified in several international
standards. Even though numeric physical measures define accurately the indoor
environmental conditions, only the perceived quality determines the total performance of the
building from user’s point of view. Thus, it is important to evaluate how well the set targets
are fulfilled. In this study, an occupant satisfaction survey was conducted to analyze the
perception for the actual indoor environmental quality in 29 office buildings. The results
depict that even if the average satisfaction shows high scores major problem areas exist in
some parts of the buildings. In several buildings, the actual percentage of dissatisfied persons
is higher than 30 %. In practice, commissioning and maintenance processes are often
neglected. Also, the required adjustments in the HVAC-systems are not executed after layout
changes of workplaces. That leads to problems in thermal comfort, indoor air quality and
acoustic privacy.
KEYWORDS
Perceived IEQ, occupant satisfaction, post occupancy evaluation, field study
INTRODUCTION
It is well known that the indoor environment is an important factor not only for occupants’
comfort as a whole, but also for their health and productivity. Indoor environment comprises
several factors (acoustics, lighting, thermal environment, air quality). The individual
performance is affected by the working environment. The latest studies have proved that the
investment on improved IEQ (thermal comfort, IAQ, acoustics and lighting) is very costeffective (Fisk and Seppänen 2007, Wargocki and Wyon 2006, Hongisto 2005 and Juslen
2007).
In offices all these factors have an impact on workers, but the most significant two are thermal
environment and air quality. According to a study of BOMA (BOMA 1999) 90 % or more of
the respondents give the following six features a rating of very important: comfortable
temperature, indoor air quality, quality of building maintenance work, building management’s
responsiveness, building management’s ability to meet the tenant’s needs and acoustics.
There are several international and local standards and guidelines that give recommendations
and propose design criteria for achieving good indoor environment (ISO 7730 2005, EN
15251 2007, ASHRAE 55 2004, CEN CR 1752 1998, etc.). Recommended values for the
mean air velocity, air temperature, relative humidity, vertical temperature gradient and mean
radiant temperature both for winter and summer conditions are listed in these documents.
Also the minimum outdoor air flow rates to be supplied into the space by the ventilation
system in order to assure good air quality for the occupants in the room are defined (EN
15251 2007). Outdoor air flow rate of 7-10 l/s per person is namely required in office
buildings.
The thermal sensation of the body as a whole (general thermal comfort) can be predicted by
calculating the predicted mean vote (PMV) index introduced in ISO 7730 2005. The predicted
percentage dissatisfied (PPD) index, obtained from the PMV index, provides information on
thermal discomfort (thermal dissatisfaction) by predicting the percentage of people likely to
feel too hot or too cool in the given thermal environment. The criteria for the excellent level
of PPD- index is 6 % (EN 15251 2007). Criteria for the good and basic levels are set to 10 %
and 15 %, respectively.
A model for local discomfort that predicts the percentage of dissatisfied due to draught was
introduced by Fanger et al. (1988). An index called draught rating (DR) index was derived as
a function of mean air velocity, air temperature and turbulence intensity. A draught rating
(DR) lower than 15 % is recommended in the standards. CEN CR 1752 (1998) specifies
different limits on DR for three categories of thermal environment in rooms. The set
categories for the predicted thermal state of the whole body (EN 15251 2007) and local
discomfort (CEN 1752 1998) are shown in Table 1.
Table 1. Recommended criteria and categories for the thermal environment.
Category
I
II
III
Thermal state of the body
as a whole
Predicted
Predicted mean
percentage of
vote
dissatisfied
PPD
PMV
[%]
<6
-0.2<PMV<+0.2
< 10
-0.5<PMV<+0.5
< 15
-0.7<PMV<+0.7
Local
discomfort
Percentage of
dissatisfied due
to draught
DR
[%]
< 15
< 20
< 25
Perceived air
quality
Percentage of
dissatisfied
PD
[%]
< 15
< 20
< 30
Required
ventilation
rate for
occupants*
[l/s/pers]
10
7
4
* Total ventilation rate for a room is calculated based on diluting emissions from people and the building emissions
(Category II: 0,35-1,4 l/s,m²).
The abovementioned overall thermal sensation levels are confirmed as guidelines in recently
approved standard EN 15251, which highlights the importance of maintenance of good
thermal conditions, when energy performance of building is designed to fulfil the Energy
Performance of Buildings Directive (EPBD).
During the design process, the desired thermal conditions for a space may be selected based
on the defined international or national indoor climate classifications (e.g. CEN CR 1752
(1998) and FISIAQ 2001). In the selected indoor climate class the target values are set for
both maximum percentage of dissatisfied for the body as a whole (PPD) and for the local
discomfort (DR). In addition, the relevant targets for indoor air quality, outdoor air flow rates
and acoustics conditions are set during the design process.
Even though numerical physical measures define accurately different factors of the indoor
environment, only the perceived quality determines the total performance of the building from
user’s point of view. The occupant IEQ survey is a tool that helps to assess how well a
building is performing from the viewpoint of its occupants (Zagreus et al. 2004). Further, a
holistic approach of IEQ development and maintenance is required for an effective process to
improve the perception of indoor climate conditions. A systematic method for the assessment
and improvement of IEQ has been proposed by Takki and Virta (Takki and Virta 2007).
In this paper, the results of the occupant satisfaction surveys are presented where the
perception of the actual indoor environment quality is analyzed in 29 office buildings.
METHODS
Historically, building occupants have been underutilized as a source of information on
building performance. In this study, an occupant satisfaction survey was conducted to analyze
the perception for the actual indoor environment quality in 29 office buildings. The questions
assess satisfaction with the following IEQ areas: office layout, office furnishing, thermal
comfort, indoor air quality, lighting, acoustics, safety and security, and building cleanliness
and maintenance. Basic demographics are also collected from respondents and information
about their workplace. The survey questions elicit whether the workspace is in the internal or
perimeter zone, near a window, and also the orientation and the layout type of the office are
linked with the collected information.
A web-based survey has been utilized as a diagnosis tool to identify specific problems and
their sources. Whatever a respondent indicates dissatisfaction with an aspect of building
performance, a branching page follows with more detailed questions about the nature of the
specific problem.
The approach of the Web- based survey gives two main benefits: 1) it can inexpensively be
administered to many buildings and 2) its interactive branching questions allow it to “ drill
down “ into areas that occupants rate poorly and thus in many cases diagnose the root of the
problems. The approximate time required to complete the survey is 5-12 minutes.
Upon starting the survey, participants click through a series of questions asking them to
evaluate their satisfaction with different aspects of their working environment (Fig.1).
Satisfaction is rated on a seven-point scale ranging from “very satisfied“ to “very
dissatisfied”, with a neutral midpoint.
Figure 1. A sample of the occupant IEQ survey page.
The respondents who indicate dissatisfaction (the lowest three points on the scale) are
branched to a follow-up screen probing them for more information about the nature of their
dissatisfaction. Respondents who indicate neutrality or satisfaction move directly to the next
survey topic.
As a rule of thumb is that a 50 % response rate is required to reduce non-response bias to an
acceptable rate (Hill et al. 1999). In the conducted surveys, the response rate have ranged
from 45 % to 97 %, with the majority of response rates between 50 % and 75 % and the mean
at just over 68 %.
RESULTS
The described survey has been used to evaluate the performance of 29 office buildings in
Finland. Survey clients include both government and private organizations locating in
Helsinki metropolis area. All buildings are mechanically ventilated and equipped (except one
building) with air-conditioning system. The studied buildings fulfil the requirements of either
indoor class excellent or good in Finnish classification (FISIAQ 2001). Thus, the buildings
represent the state-of-the art technology in Finland. The used mechanical systems are all-air
systems with centralized air-conditioning and active chilled beam systems with room or zone
based control.
Results of an individual building
Occupants were asked to vote on their overall perceptions of IEQ to see the most critical
factors for improvement. Fig.2 presents a survey result demonstration where satisfaction
ratings are tabulated for each point on the scale. This executive summary is particularly useful
to managers to see a top-level overview of the most critical environment factors. As in this
case, the lowest general satisfaction levels are rated on air quality, thermal comfort and
acoustics.
Average Scores by Category
General satisfaction
Building
General satisfaction
Workplace
Office Layout
1.71
1.64
1.83
Office Furnishing
1.41
0.88
Thermal Comfort
0.83
Air Quality
1.57
Lighting
0.85
Acoustics
1.18
Cleanliness
1.10
-3
-2
Very
Dissatisfied
-1
0
1
Maintenance
2
Gen
eral
Gen
eral
Offi
ce
Offi
ce
The
rma
Air
Qua
Ligh
ting
Aco
usti
Cle
anli
Mai
nte
-3
-2
-1
0
1
2
3
3
Very
Satisfied
Figure 2. An example of average occupant satisfaction survey results in a case-study building.
However, even if average satisfaction rating is quite often used to categorize buildings
(Zagreus et al. 2004, Euleb 2007), it cannot define the actual number of persons who are
dissatisfied with the conditions. It should be noted that the average satisfaction score could be
reasonably good but eventually there might be zones where the percentage of the dissatisfied
could be even 30-60 %.
An occupation perception map is a tool for analyzing more closely the location and actual
number of dissatisfied persons. In the map in question, the percentage of the dissatisfied with
environmental factors are exhibited in different zones. Afterwards this information can also
be exploited for focus field audits on the problem areas and workplaces. For example in a
case-study building, there are one problem area for air quality and four for thermal comfort
(Table 2). In this case, acoustic privacy is rated very low in all zones, respectively.
Table 2. An example of occupation perception map in a case-study building.
Analysis of building stock
Occupants’ overall perceptions on the studied 29 buildings are shown in Fig. 3. From the
point view of the occupants, thermal comfort, IAQ and acoustics (noise level and acoustic
privacy) have got the lowest average ratings. Almost in all buildings, those factors are the
main concern for improvements.
In this survey, there are buildings where the average ratings on thermal comfort, air quality
and acoustics are negative (average all dissatisfied). Still, in most of the cases average ratings
on survey categories are positive indicating at least partial satisfaction on the system
performance.
3
2
1
0
-1
-2
Techical
maintenance
Average of all buildings
Cleaning
Acoustics
Lighting
Indoor Air
Quality
Thermal
comfort
Office
furnishing
Office layout
Workspace
Building
-3
Figure 3. Benchmark comparison of average satisfaction ratings and their variations by survey
category (n=3796 persons in 29 buildings)
When the total numbers of the dissatisfied are computed (negative rates of –1, -2 and –3
together), the number of the dissatisfied persons is very high (Fig. 4). The percentage of
dissatisfied on thermal comfort and air quality is over 20 % in many buildings. To further
confirm that the level of dissatisfied is indeed anomalously high, only 6 buildings of 29 cover
ASHRAE´s (ASHRAE 55-2004) demand of less than 20 % dissatisfied on general thermal
comfort. The results are even worse in acoustics privacy: the percentage of dissatisfied is
typically 30-60 %. All this depicts that actual perception on IEQ is much lower than during
the design phase set requirement level. In practice, it seems that even the requirements of the
lowest indoor class (15-25 %) is difficult to be met when the metric is satisfaction rating on
IEQ.
100 %
90 %
80 %
Dissatisfied (%)
70 %
60 %
50 %
40 %
30 %
20 %
10 %
0%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Case buildings (29)
Thermal comfort
Indoor Air Quality
Acoustic Privacy
Figure 4. The percentage of the dissatisfied on thermal comfort, air quality and acoustic
privacy in 29 buildings. Case buildings are binned in the ascending order of dissatisfied on
thermal comfort.
DISCUSSION
Parameters to characterize ventilation may include ventilation rates, contaminant levels and
physical characterization of the indoor environment. These factors affect human responses
through each other but also independently. Outdoor air flow rate of 7-10 l/s per person is
namely requested in international standards. However, the latest studies have proved that the
air flow rate of 20-30 l/s per person is required to enhance perceived air quality (Fisk and
Seppänen 2007).
Criteria for an acceptable thermal climate can be specified as requirements for general (the
overall sensation of the body) or local thermal discomfort. Such requirements can be found in
existing standards and guidelines. Despite the excellent control over environmental conditions
in climate chambers, it has not been possible to assess how dissatisfaction due to multiple
sources is defined. For example, people may be dissatisfied due to general thermal comfort
and/or dissatisfied due to local discomfort parameters, but at the present there is no method
for combining the total number of people finding environment unacceptable.
In investigating perceived IEQ, it is essential to note that existing standards are based on
laboratory research on college-aged subjects and not people working in the office
environment. In field studies, the actual percentage of the dissatisfied is much higher than in
standards e.g. 12 % (Hwang and Cheng 2007), 12 % (Schiller 1990) and 48 % (Melikov et al.
2005). All this confirms that in practice, it is not easy to meet targets for occupant perceptions
on IEQ.
This study shows that the percentage of dissatisfied according to the surveys is much higher
than the set target values in the international standards. It is essential to note that subjects are
asked what the thermal conditions usually are like in the occupied building. In this kind of
retrospective approach, subjects may exaggerate how often and to which extent they are
dissatisfied on IEQ, in order to ensure that something will be done about it.
Another source of variation in surveys is that in the survey it is not possible to know how bad
the conditions have been in the past in all the places the subjects have been occupied. There
could be only limited time period that the occupants are referring to when they complain.
Regardless, the percentages of the dissatisfied on thermal comfort and air quality are
(separately or together) often over 30 %. To further confirm that the levels of dissatisfied are
indeed anomalously high, only 6 of the 29 buildings cover ASHRAE’s (ASHRAE 55-2004)
requirement of less than 20 % dissatisfied on general thermal comfort. The results are even
worse in acoustics privacy: the percentage of dissatisfied is typically 30-60 %.
In this occupation satisfaction survey, systematic physical field measurements were not
carried out to explain the difference. However, the executed audits demonstrated that different
technical problems might exist. Generally, the main reasons for the high number of the
dissatisfied persons are the faults in commissioning and maintenance process. Also nowadays,
the design process is mainly focusing on the peak load conditions and the performance of the
system is not sufficiently analyzed during mid-season. In addition, organizational changes are
continuous and require changes not only in the workplace layouts but also in the mechanical
systems. Without adjustments, layout changes might create e.g. draught, lighting and air
quality problems.
CONCLUSIONS
The results depict that even if the average satisfaction in IEQ survey shows high scores major
problem areas may exist in some parts of buildings. Also in many buildings, the actual
percentage of dissatisfied persons is higher than 30 % especially with thermal comfort, indoor
air quality and acoustics. In the building stock, commissioning and maintenance process are
often neglected. Also, the required system adjustments are not executed after layout changes
of workplaces. Using the perception map as a tool to find out the problems areas, it is possible
to focus improvements cost-effectively to critical workplaces and simultaneously improve
significantly perception on IEQ.
ACKNOWLEDGEMENT
The study is supported by Technology Agency of Finland (TEKES). The authors thank Prof.
David Wyon for insightful comments on analysis and Mr. Harri Itkonen for discussions of
this paper.
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