Proceedings of 9th Windsor Conference: Making Comfort Relevant
Cumberland Lodge, Windsor, UK, 7-10 April 2016.
Network for Comfort and Energy Use in Buildings, http://nceub.org.uk
Occupant feedback in air conditioned and mixed-mode office buildings in
India
Sanyogita Manu1, Chinmay Patel1, Rajan Rawal1, Gail Brager2
1
Centre for Advanced Research in Building Science and Energy, CEPT University, Ahmedabad,
India
2
Centre for the Built Environment, UC Berkeley
Abstract
India has a largely cooling dominated climate where space cooling accounts for approximately 31% of the energy
consumed by commercial buildings. Deeper market penetration of air conditioning systems, higher income
levels driving higher comfort expectations, and growing floor space have led to a steep rise in associated carbon
emissions. India needs to adopt an energy efficient regime in which governments, businesses and individuals
transform the way buildings are designed, built and operated, while still maintaining high levels of occupant
satisfaction.
Two diverse approaches are practiced in India to achieve energy efficiency. The first relies on passive design
strategies based on traditional wisdom. The second relies on high-performance HVAC building conditioning
systems. Most Indian climate zones offer opportunities to design and operate buildings as naturally ventilated
or mixed-mode. But such design practices need to be promoted on the basis of scientific studies related to
occupant behavior, comfort and associated energy consumption.
This paper evaluates occupant satisfaction in a mix of consciously-designed air conditioned and mixed-mode
buildings based on online surveys, and limited physical measurements. The survey includes questions about
thermal comfort, indoor air quality, air movement, acoustics and adaptive controls such as windows and fans.
The paper offers an understanding about the perception and behavior of occupants in mixed-mode buildings in
various climate zones of India to help identify strategies to promote efficient mixed-mode buildings in both India
and other regions.
Keywords: Occupant satisfaction, Post-occupancy evaluation, Mixed-mode buildings, Thermal
comfort, Indian offices
1 Introduction
India boasts a rich tradition of naturally ventilated buildings with context-specific passive
design strategies. Until 10-15 years back, naturally ventilated buildings were the norm for
most building types. With better penetration of air conditioning systems in the market, higher
incomes resulting in higher comfort expectations and the rapid increase in built-up floor space,
air conditioned buildings increased in numbers. Today, many people perceive air conditioning
as a requirement, rather than a luxury. Most of the new buildings have air conditioning and
many of the old ones are being retrofitted with conditioning systems. This has resulted in a
wide array of mixed mode buildings that operate in naturally ventilated mode when the
outdoor conditions are favourable and switch over to air conditioning during the extreme
conditions. They usually have operable windows and ceiling fans.
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Since India has a predominantly warm to hot weather, air conditioning generally refers to
cooling and mechanical ventilation. During the mild winter season, the cooling is turned off
and the windows are either inoperable or kept shut. Buildings with inoperable windows
generally have better air-tightness. That is why new air conditioned buildings with sealed
envelopes tend to be more energy-efficient than old buildings that are retrofitted, since the
latter are originally designed to operate in naturally ventilated mode.
In India, electricity demand already exceeds supply. The largest and most significant end use
of electricity in commercial buildings is air conditioning. The rapid growth in new floor space
combined with an increase in thermal comfort expectations and aspirations, will lead to a
surge in demand for air conditioning. If permitted unchecked, the growth in building air
conditioning will add immense pressure on electricity infrastructure and exacerbate the
already extreme peak-demand problem in the country.
In order to prevent an increase in energy use associated with space cooling, the deployment
of low energy adaptive strategies in building operation is critical. To this end, an India specific
adaptive thermal comfort model (IMAC) was recently published based on extensive field
study of Indian offices in five climate zones and three seasons (Manu, Shukla, Rawal, Thomas,
& de Dear, 2016). The results from this study prove that the neutralities predicted by the
IMAC models for naturally ventilated buildings followed the outdoor temperatures more
closely than the existing international adaptive models for free-running buildings. However,
the most significant contribution of the IMAC study was to propose a single, valid and robust
adaptive model for mixed-mode buildings where the neutral temperatures ride (not
surprisingly) lower than the ASHRAE and EN15251 free running models. For mixed-mode
buildings, the IMAC study also shows evidence of neutral temperatures of up to 28.4˚C when
outdoor conditions ride at 38-40˚C (Manu et al., 2016).
In addition to implementing an India-specific adaptive comfort model, it is important to
understand the performance and operation of mixed-mode buildings in more detail from an
occupant’s perspective since a majority of the building stock is increasingly becoming mixedmode. Occupant surveys are important tools to measure the performance of buildings.
A paper analysing over 34,000 survey responses to air quality and thermal comfort questions
in 215 buildings across US, Canada and Finland (C Huizenga, Abbaszadeh, Zagreus, & Arens,
2006), clearly indicated that only 11% of buildings had 80% or more satisfied occupants. Only
26% of buildings met the (then current) ASHRAE Standard 62.1-2004 standards for acceptable
air quality.
In a study of web-based survey responses from 351 US office buildings, the researchers
concluded that satisfaction with the amount of space, noise level and visual privacy were the
most important parameters for overall workspace satisfaction (Frontczak et al., 2012).
Another study based on the same database used Kano’s model of satisfaction and identified
‘temperature’ and ‘noise level’ as basic IEQ factors (Kim & de Dear, 2011). This means that a
building’s poor performance in terms of thermal and acoustic performance has a significant
negative impact on overall satisfaction levels. Air quality and lighting were assigned to the
group of proportional factors exerting negative or positive impacts of comparable intensity
on overall occupant satisfaction.
In another study that analysed over 43,000 individual responses to the CBE web-based survey,
mixed-mode buildings were found to be performing much better than the overall building
stock with regard to thermal comfort and air quality (Brager & Baker, 2009). A post-occupancy
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evaluation of a building in Australia highlighted the importance of increased fresh air, daylight,
glare control, access to views, noise management, low VOC finishes towards improving user
experience of indoor environmental quality (Thomas, 2009). A survey on workplace occupant
satisfaction in 16 office buildings in Germany revealed that the occupants’ control of the
indoor climate, and the perceived effect of those interventions, strongly influenced their
satisfaction with thermal indoor conditions (Wagner, Gossauer, Moosmann, Gropp, &
Leonhart, 2007).
The design and operation of HVAC systems aims for an optimum ‘steady-state’ temperature
setting based on Fanger’s PMV-PPD model (Fanger, 1970) to provide acceptable thermal
comfort (Drake, de Dear, Alessi, & Deuble, 2010). The studies cited here indicate that this
‘static’ approach to thermal comfort in air-conditioned buildings may be detrimental to
occupant satisfaction and that a ‘person-centred’ approach to provide variability across time
and space is important (Brager & de Dear, 1998). Therefore, it is important to design mixedmode buildings to operate effectively in both naturally ventilated and air conditioned modes
without compromising occupant thermal comfort and indoor air quality. It is also important
to operate these buildings to take advantage of their ‘dual’ character in an optimal way. In
order to do this, one must understand the performance of a range of MM buildings in terms
of occupant satisfaction and gain an insight into how occupants use these buildings.
2 Methods
2.1 CBE survey
The CBE web-based survey tool (Charlie Huizenga, Laeser, & Arens, 2002) is an efficient way
of remotely getting occupant feedback on indoor environmental quality (IEQ) and various
other aspects of the building. The survey consists of a core module with eight IEQ categories
and additional modules such as window and fan usage. The phrasing of the questions and
options were tailored to suit the local culture and parlance to use the surveys effectively in
Indian offices. The survey asked occupants to rate their satisfaction with these different
aspects on a 7-point scale that ranged from -3 (Very dissatisfied) to 0 (Neutral) to +3 (Very
satisfied). The tool also has a unique feature that is helpful for diagnostic purposes; when an
occupant votes to be dissatisfied in any category, the tool automatically follows up with
branching questions that ask about the reasons for dissatisfaction. Details about the building
features such as floor area, number of occupants, LEED compliance and type of HVAC system,
envelope and glazing are filled out by the building manager separately. More details about
the CBE survey tool can be found in (Zagreus, Huizenga, Arens, & Lehrer, 2004). A list of the
most relevant survey questions for this study is illustrated in Table 1.
Table 1 Important categories from the CBE survey analysed in this paper
Category
Thermal comfort
Indoor air quality
Air movement
Window usage
Questions asked
Satisfaction with temperature, ability to control temperature,
thermal comfort during summer
Satisfaction with air quality (i.e. stuffy/stale, cleanliness, odors)
Satisfaction with amount of air movement, ability to control amount
of air movement
Satisfaction with operable windows (summer and winter and
monsoon)
Importance of having an operable window to the user
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Category
Questions asked
Times adjusted (daily, weekly, monthly)
Time of adjustment
Reasons to ‘open’ or ‘close’ a window
Satisfaction with ceiling fans, Times adjusted during summer (daily,
weekly, monthly), Time of adjustment, Reasons to turn ‘on’ or ‘off ’ a
fan
Fan usage
2.2 Building selection
The survey was administered in 9 buildings across three climate zones of India – hot and dry
(H&D), warm and humid (W&H) and composite (CT). Table 1 lists the buildings with their
locations and availability of operable ceiling fans and windows. The buildings were classified
into three categories:
1. Spatial mixed-mode (SMM) where certain zones of the building are air conditioned
and others operate in natural ventilation mode across the year. Such buildings have
provisions for operable windows and ceilings fans.
2. Temporal mixed-mode (TMM) where the entire building is air conditioned and
switched over between AC and NV modes based on the outdoor conditions. Such
buildings have provisions for operable windows and ceilings fans.
3. Air conditioned mode (AC) where the buildings are air conditioned for most part of
the year. When outdoor conditions are sufficiently favourable for the MAC to be
turned off, mechanical ventilation may be used). There is no provision for natural
ventilation (or operable windows) in these buildings.
Table 2 Details of the case study buildings
Building
Type
Spatial
mixedmode
Temporal
mixedmode
Air
Conditioned
Building City
code
SMM-1 Ahmedabad
Climate
H&D
SMM-2 Delhi
TMM-1 Ahmedabad
CT
H&D
Operable Ceiling
windows
fans Survey period
Y
Y
Mar, 2014
Y
Y
N
N
Mar-May, 2015
No. of
responses
48
16
31
Mar, 2014
TMM-2
TMM-3
TMM-4
AC-1
Ahmedabad
Ahmedabad
Delhi
Baroda
H&D
H&D
CT
H&D
Y
Y
Y
N
Y
Y
N
N
Mar, 2014
Mar-Apr, 2014
May-May, 2015
27
40
13
131
Apr-May, 2015
AC-2
AC-3
Pune
Pune
W&H
W&H
N
N
N
N
Sep-Oct, 2015
Sep-Oct, 2015
54
45
SMM-1 is the office of an architecture firm. It relies on passive design strategies to maintain
thermal comfort inside. It was designed to primarily operate in fully naturally ventilated mode,
but was later retrofitted with air conditioners, where occupants turn off the air conditioner
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and open the windows when the outdoor conditions are suitable for natural ventilation. The
building has a high vaulted roof structure over the studios that facilities better ventilation.
Both the operable windows and pedestal fans are operated by the occupants. It has low
openings on the south to reduce direct radiation. At other places, glass brick is sometimes
used to provide diffused daylight. The building mass is compact, and the building is partially
underground, further reducing the impact of direct radiation. Glazing is approximately 25%
of the wall area. The vaulted roofs have an air cavity filled with ceramic fuses (9” long conical
pieces mixed with concrete) to provide thermal insulation, and the entire roof is covered with
high SRI tiles. The immediate surrounding is heavily landscaped with dense trees and water
bodies, generating its own microclimate. The total floor area is spread across four levels,
including the mezzanine level.
SMM-2 is located on the outskirts of Delhi in the industrial sector of Greater Noida. The
building comprises of several conferences rooms, open plan work spaces and personal cabins.
It houses a laboratory for material testing of the products manufactured in the premises. The
building has 26-50% of wall area covered with high performance glass and self-operational
windows mostly facing north to utilise natural diffused light. Occupancy sensors and efficient
indoor lighting balances its lighting requirements. It has individual air conditioning units.
TMM-1 is a building design and consulting firm located on the seventh floor of an 11-story
building that is LEED Platinum rated. Other than installing double-glazed windows, TMM-1 did
not attempt to optimize the envelope, but instead reduced their energy consumption by
addressing the active systems. They have a very efficient HVAC system, demand controlled
ventilation, energy-efficient lighting and lighting controls, and occupancy sensors. TMM-1 has
operable windows, but they are not often used by the occupants as the air conditioning is
used for most part the year. The envelope is heavily glazed (51-75% of the wall area). In spite
of the high WWR and lighting controls, the building seems to rely more on artificial lighting
than daylighting. The materials used in TMM-1 conform to LEED 2.1 specifications such as low
VOC paints, coatings, adhesive, sealants and fabrics, green label carpets and cleaning
materials. It has an open-plan layout with individual or shared cabins on the east and west
periphery of the building.
TMM-2 is an office of a computer software developer firm in a heavily urbanized area, located
on eighth floor of an 11-story building (similar to TMM-1 being on an intermediary floor of a
taller building). It is representative of the most energy intensive building with a business-asusual envelope and air conditioning system and operation. The office has a variable air volume
(VAV) type central air conditioning unit that is on throughout the year. The walls are heavily
glazed, with the WWR almost identical to that in TMM-1 (51-75% of the wall area). The
windows are operable and have a reflective glazing. The building also has interior blinds and
exterior shading.
TMM-3 is an office of a building construction and MEP consulting firm in a less dense and
more vegetated area, located on ground and first floor of an 8-story building. It has a variable
refrigerant flow (VRF) type central air conditioning unit, operable windows and ceiling fans.
The glazing area is in between the other examples (30-50% of the wall area). The windows
have a clear glass, compared to the reflective glazing of TMM-2. While the air-conditioning in
TMM-2 operates almost continuously throughout the year, in TMM-3 occupants have a
choice to operate it when indoor becomes uncomfortable.
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TMM-4 is a LEED Platinum rated building located in the same complex as SMM-2. The building
which sits like a cube consisting of three floors; the top floor is surrounded by a balcony. The
roof has solar panels with transparent underneath to allow daylight penetration inside the
space along with occupancy sensors for lighting controls. 33% of wall area consists of high
performance glass. Each window unit has motorized louvers sandwiched between two glazing
panes. Some of these units are operable but are rarely used for natural ventilation. The facade
is made of rigid Polyisocyanurate (PIR) foam to insulate against heat and moisture. The
building uses primary and secondary chilled water pumping systems, active chilled beams,
primary AHU, cooling towers with variable frequency drive (VFD).
AC-1 is a single 9 storey block of a building complex on the outskirts of Baroda and a LEED
Gold rated building. Each floor has large open plan office spaces with over 100 people working
on each floor. It uses a VAV air distribution system controlled with a BMS operating system
running almost throughout the year. 40% of wall surface has high performance glazing
complimented by internal blinds.
AC-2 is part of a building complex spread over 10.5 acres. It is a LEED Platinum and a GRIHA
5-star rated building. With 92% of its energy produced on site, it is a ‘near’ zero-energy
building. 76-100% of its wall surface has high performance glazing with external louvers. It
doesn’t have the provision of operable windows or ceiling fans. VRF and radiant panels are
used for cooling. AC-3 in located in the same complex as AC-2 and has the same building
characteristics.
3 Results and analysis
Figure 1 shows the percentile ranking compared to the overall CBE dataset, and Figure 2
shows the mean percentage satisfied per survey category in each building (occupants voting
+1 and above were counted as satisfied). In both, green colors designate better performance
and yellow designates low performance.
Acoustic Quality
95
100
82
53
78
95
99
84
92
Air Quality
83
98
36
66
76
96
100
98
99
Lighting
85
100
78
30
85
61
98
98
99
Office Layout
56
99
23
5
77
80
84
92
98
Thermal Comfort
90
88
90
70
96
77
98
97
97
General Building
satisfaction
94
92
57
42
77
84
96
99
99
Workspace
satisfaction
77
99
43
43
82
97
98
98
98
AC-2
AC-3
SMM-1 SMM-2 TMM-1 TMM-2 TMM-3 TMM-4 AC-1
Figure 1 Percentile ranking of case study buildings compared to CBE database
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Acoustic Quality
78
78
61
39
55
76
80
58
56
Air Quality
78
93
54
57
76
73
96
82
87
Cleanliness/
Maintainance
85
100
79
59
89
100
95
89
99
Lighting
83
100
79
69
83
77
92
89
87
Office Furnishings
77
100
84
58
74
96
85
88
93
Office Layout
69
91
62
43
77
83
83
81
86
Thermal Comfort
75
76
71
53
74
51
81
76
74
Air Movement
69
100
52
69
70
82
88
79
77
General Building
satisfaction
98
100
82
69
86
90
94
98
93
Workspace
satisfaction
82
100
70
77
93
100
94
87
89
AC-2
AC-3
SMM-1 SMM-2 TMM-1 TMM-2 TMM-3 TMM-4 AC-1
Figure 2 Percentage of occupants satisfied in each case study building
Starting first with the comparison to the CBE database (Figure 1), AC-3 and SMM-2 stand out
as the best performers of the nine buildings followed closely by AC-2. TMM-1 and TMM-2 are
the lowest performers of the nine buildings across most categories but TMM-1 ranked
relatively well in thermal comfort, acoustic quality and lighting. These rankings, however, may
not reflect the performance of these buildings in the context that they operate since they are
being compared with the CBE database comprising buildings primarily from the US. The
cultural, social and economic contexts are different and are likely to affect occupant
expectations and how they use buildings. For the rest of this paper, comparisons are made
between the Indian case study buildings.
In terms of occupant satisfaction (Figure 2), SMM-2 ranks the highest, with more than 90%
satisfaction in all categories except thermal comfort (76% satisfaction) and acoustics (78%).
These are also the two categories which typically receive the lowest levels of satisfaction in
the overall CBE database (this is why buildings might have low levels of satisfaction in Figure
2, but still rank high in the CBE database in Figure 1).
The three AC buildings had high levels of satisfaction in all categories except acoustic quality
where AC-2 and AC-3 had less than 60% of the occupants satisfied.
Looking now at the temporal mixed-mode buildings, thermal comfort satisfaction ranged
from 51-74% (which was associated with 70-96th percentile in the CBE database, again a result
of thermal issues being a pervasive problem in buildings). In TMM-1, of the IEQ categories,
occupants were most satisfied with lighting, but the highest satisfaction ratings had nothing
to do with IEQ (i.e., office furnishings, general building satisfaction, and
cleanliness/maintenance). The satisfaction percentage in TMM-1 was lowest with acoustics,
air quality, office layout and air movement. Lack of sound privacy was the main reason for
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acoustic dissatisfaction while lack of visual privacy was the basis for dissatisfaction with office
layout. The open plan layout may have contributed to this dissatisfaction. A few occupants
from TMM-1 opined that the air was stuffy/stale, not clean and had a bad odor; the source
for bad odor was mainly from the toilets. However, the complaints were limited to one
particular zone. With regards to air movement satisfaction, occupants were mainly
dissatisfied with amount of air movement (saying they preferred to have more air movement)
and the ability to control the amount of air movement. This is not surprising given that this
building does not have fans, and that occupants rarely use the operable windows.
TMM-2 consistently had the lowest levels of satisfaction of all the buildings studied here, with
less than 70% satisfied occupants in all the categories except for workspace satisfaction,
where it was 77%. This higher satisfaction may, in part, be due to this office having relatively
low occupant density (10 sq.m. per person, compared to a more typical 6.5 sq.m. per person
for India). Amongst the dissatisfied categories, acoustic quality, office layout and thermal
comfort received the lowest satisfaction ratings (39%, 43%, and 53%, respectively). Lack of
sound and visual privacy were the main reasons for dissatisfaction with acoustics and office
layout respectively. Overall thermal comfort satisfaction was very low in TMM-2 compared to
the other buildings. Those who were dissatisfied cited multiple reasons of discomfort such as
incoming sun, air movement being too low and the heating/cooling system not responding
quickly to the thermostat.
In TMM-3, acoustic quality was the source of dissatisfaction for 45% of the occupants. In
TMM-4, 70% or more occupants were satisfied in all categories, except in thermal comfort,
where thermal satisfaction was lowest of all the buildings, at only 51%.
3.1 Thermal comfort
Occupants were asked about their opinion on thermal comfort in the building through
multiple questions asking about satisfaction with temperature, ability to control temperature,
and thermal comfort specifically during the summer. For each question, they answered on a
discrete 7-point scale from +3 (very satisfied) to -3 (very dissatisfied). The responses were
pooled into three groups of ‘satisfied’ (+1 to +3), ‘dissatisfied’ (-1 to -3) and ‘neutral’ (0). Figure
3 plots the percentage of occupants in each of these groups, for the three thermal comfort
questions.
ASHRAE Standard 55-2010 (ASHRAE, 2010) suggests that an acceptable thermal environment
is one in which no more than 20% of the occupants are dissatisfied with the temperature.
Although one can (and probably should) argue that we should strive for even high levels of
acceptability, this is how the standard is currently framed. Using this number, Figure 3a
suggests that 7 of the 9 buildings were below this threshold (redline in the graphs), but SMM2 just barely met it with 20% of the occupants dissatisfied with the temperature in their
workspace, and TMM-3 did not meet the threshold, with 22% dissatisfied.
The occupants who express dissatisfaction on the survey are given follow-up questions about
the reasons why. In TMM-3, which is located in the hot and dry climate zone, 38% of the
dissatisfied occupants reported feeling ‘often too hot’ and 63% were ‘often too cold’ in
summer, suggesting that the air conditioning was over-cooling more than necessary. This is
surprising since in TMM-3 occupants have a choice to operate the air conditioning or not
when the indoor becomes uncomfortable. In TMM-3 in winter, 13% were ‘often too hot’ and
38% were ‘often too cold’. 25% cited low air movement as the source of thermal discomfort.
25% felt their workplace was located in a zone that was colder than other areas in the
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building. 50% of the occupants reported the thermostat being adjusted by other people as
the source of discomfort, which could be strongly related to the overcooling problem in
summer.
In SMM-2 60% of the dissatisfied occupants reported feeling often too cold and 33% were
often too hot in summer. 40% cited high humidity or dampness as the source of thermal
discomfort.
16% of the occupants reported dissatisfaction with the temperature in their workspace in
TMM-1, TMM-2 and AC-3. These occupants tended to feel too warm in summer and too cold
in winter, suggesting that conditioning wasn’t adequate. The main reason for discomfort were
low air movement and hot/cold pockets. In TMM-1, physical measurements showed that the
temperature variation across the zones was more than 16˚C, which is significant. In TMM-2
and AC-3, occupants also complained about the thermostat being controlled by others as a
source of discomfort.
In TMM-4, 33% of the occupants expressed dissatisfaction with the thermal comfort in their
workspace in summer (Figure 3b). The primary reasons seem to be poor air distribution since
36% of the occupants reported feeling often too hot and 36% reported feeling often too cold
in summer. Dissatisfaction was also high in TMM-2 (28%), SMM-2 (19%) and TMM-3 (16%).
These responses align with the dissatisfaction percentages in Figure 3a.
When asked to report their satisfaction with their ability to control temperature in their
workspace (Figure 3c), 38% of the respondents in TMM-2 and 25% in TMM-1, TMM-4
expressed dissatisfaction. At least 10% of the occupants across all case studies were
dissatisfied with the degree of control they had over the temperature. This number was
higher in mixed-mode buildings compared to air conditioned buildings.
(b)
(a)
(c)
Figure 3 Occupant satisfaction with thermal comfort
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3.2 Air quality
In response to the question related to satisfaction with the air quality (Figure 4), 36% of the
occupants in TMM-1 expressed dissatisfaction with the air quality at their workspace (Figure
4a) while 44% were dissatisfied with their ability to control the air quality (Figure 4b). 86% felt
that the air being stuffy/stale was big problem and 83% reported air not being clean as a
problem. 67% of the occupants felt bad odors from toilets, cafeteria, garbage bins and carpets
were a major problem.
20% of the occupants in TMM-2 reported dissatisfaction with the air quality in their
workspace (Figure 4a). The reasons for this dissatisfaction are not clear since the follow-up
questions were not answered but one of the comments reported air conditioners working at
a high temperature setpoint and recirculation of indoor air as a source of odor.
13% of the respondents in TMM-3 reported dissatisfaction with air quality (Figure 4a) as well
as their ability to control it in their workspace (Figure 4b). The reasons for dissatisfaction have
not been stated but may be related to dissatisfaction with thermal comfort due to low air
movement as reported in section 3.1. Most of the occupants in air conditioned buildings
expressed satisfaction with the air quality. However, at least 7% of the occupants were
dissatisfied with their ability to control air quality in their workspace across all nine buildings.
(a)
(b)
Figure 4 Occupant satisfaction with air quality
3.3 Air movement
Occupants in SMM-2 reported 100% satisfaction with the amount of air movement in their
workspace (Figure 5a). This may be explained on the basis of the responses to the window
usage questions where a majority of the occupants reported satisfaction with the operable
windows and their ability to open or close them (section 3.5).
Dissatisfaction was highest (30%) in TMM-1 where 40% of the occupants also reported
dissatisfaction with their ability to control air movement (Figure 5b). Occupants in this
building were also dissatisfied with the ceiling fans and windows which may have contributed
to their dissatisfaction with the air movement. More than 20% of the occupants were
dissatisfied with the amount of air movement and their ability to control it in their workspace
in SMM-1.
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Figure 5 Occupant satisfaction with air movement
3.4 Use of windows and fans
Ceiling fans and windows are the most widely used and cost-effective way of increasing air
movement and are widely used as an adaptive measure to alleviate thermal discomfort when
the indoor temperatures ride high (Manu et al., 2014). Operable windows were available as a
provision in all the mixed-mode buildings. However, in most cases the occupants did not
operate the windows for multiple reasons that have been highlighted below. As such, one
might characterize them as mixed-mode in design, but not in practice.
TMM-4 stands out as one of the mixed-mode buildings where the operable windows are being
used, yet the building got the lowest scores in terms of thermal comfort satisfaction. More
than 90% of the occupants reported satisfaction with the operable windows in their
workplace in summer (Figure 6a). All the occupants found it easy to operate the windows
(Figure 6c) and found them effective in helping them to stay comfortable in summer (Figure
6b).
TMM-1, which is the LEED Platinum building where the focus was on efficient active systems,
performed poorly with 48% of the occupants dissatisfied with the operable windows in
summer. 44% found it difficult to open or close the windows and 33% said that opening the
windows was ineffective in maintaining comfort in summer. The difficulty in operating the
windows may have to do with accessibility – 95% of the occupants shared control of the
windows with others and 64% never adjusted their windows in summer. Windows were either
inaccessible (25%) or were kept closed due to noise, glare and odors (33%). 30% of the
occupants reported that the management discouraged the use of operable windows.
In SMM-1, 16% of the occupants reported dissatisfaction with the operable windows and
found the windows ineffective in maintaining comfort in summer. 13% found it difficult to
open or close the windows in their workspace. 15% of the occupants did not adjust the
windows because of complaints from co-workers and 31% said the windows were inaccessible.
This was surprising since SMM-1 is the building that paid particular attention to using passive,
architectural strategies to achieve low energy use. 9% of the occupants in SMM-1 shared the
control of the windows with others in their workspace.
The most frequently cited reasons for opening a window in all the six buildings were, ‘to feel
cooler’, ‘to increase air movement’ and ‘to let in fresh air’. Interestingly, the prevailing reasons
to close a window were ‘to feel cooler’, ‘outdoor temperature getting warmer than indoors’
(both of these related to having air conditioning on during a hot day), and ‘to reduce outdoor
noise.’ These reasons show that window interaction is driven predominantly by outdoor
temperature, air quality and noise levels.
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(a)
(b)
(c)
(d)
Figure 6 Occupant satisfaction with the use of windows
More than 70% of the occupants reported satisfaction with the ceiling fans in their workplace
in the three buildings that had them – SMM-1, TMM-2, TMM-3 (Figure 7). The most cited
reasons to turn on a fan in these three buildings were ‘to feel cooler’ and to ‘increase air
movement’ while the reason to turn off a fan was to ‘reduce air movement’ and because ‘a
co-worker requested it.’ These are all as one might expect, and the majority of the occupants
in these buildings said they were very sure of having the desired effect when they interacted
with fans. In TMM-2, 73% of the occupants adjusted the fans daily in summer.
Figure 7 Occupant satisfaction with the use of fans
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4 Discussion
The surveys revealed SMM-2 as the only building that had more than 70% satisfaction rate
across all categories. All AC buildings scored well in all categories except in the case of AC-2
and AC-3 where a satisfaction percentage of less than 70% was reported in acoustic quality.
Overall, occupants seemed to be most dissatisfied with acoustic quality, air movement and
office layout.
Lack of adequate air movement was repeatedly cited as a source of thermal discomfort.
Occupants were also dissatisfied with the ability to control air movement and opined that
they needed more of it. Poor air movement may have resulted in hot/cold air pockets in the
building – occupants also reported feeling often too hot or cold in summer.
The most cited reasons to turn on a fan were ‘to feel cooler’ and to ‘increase air movement’.
Moreover, when asked about the confidence of having the desired effect on turning on a fan,
the majority of the occupants voted that they were confident about this effect. This shows
that occupants perceive fans as fast-acting and they rely on it for achieving comfort in a short
span of time. However, even in buildings that had ceiling fans, occupants refrained from using
them because of complaints from co-workers. It is important to provide ceiling fans to ensure
occupants have more control over the air movement but it is equally important to design the
space plan and controls to ensure occupants are able to use them.
Windows were opened for fresh air, to feel cooler and increase air movement, and closed
when the outdoor got warmer than indoors, and to reduce outdoor noise. The key take-away
from this result is that the occupants preferred to have air movement and when there was a
combination of windows and fans in use, they worked well in providing it. But, similar to the
barriers in using ceiling fans, in most mixed-mode buildings operable windows were provided
but since the management did not encourage their use, occupants kept them close. They
remain closed for long periods of time without regular maintenance making it difficult to
operate them in the rare cases where occupants tried to open them. Noise, glare and odor
were also cited as reasons for keeping the windows closed. More interesting, complaints from
other occupants also affected window operation indicating conflicts between occupants’
preferences.
A result worth noting here is that, for the case studies in this paper the air conditioned
buildings provided higher levels of thermal comfort than in the mixed-mode buildings (the
only exception was SMM-2). This goes against what might have been expected based on
adaptive comfort theory, which suggests that having access to operable windows might
produce higher levels of control and satisfaction. This may be explained by two observations
– first is that with an exception of SMM-2, all other mixed-mode buildings were not being
actively operated in mixed-mode. SMM-1 was designed as a passive building which was later
retrofitted with air conditioning. TMM-1 and TMM-2 are located on individual floors of
buildings that are typical office buildings with high window-to-wall ratio, designed to be air
conditioned throughout the year. On the other hand, all air conditioned case studies are high
performance, LEED-rated buildings with optimized envelopes and efficient air conditioning
systems. They are better than the ‘business-as-usual’ air conditioned office buildings in India.
TMM-4 is also a high performance, zero- emissions building. It is difficult to explain the low
satisfaction in the thermal comfort category since the occupants did not respond to the
follow-up questions but lack of controls was cited as a source of discomfort.
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