1
By definition, thermal comfort is subjective and involves a contextual response [23–25]. Studies 2
over the past two decades have shown that thermal comfort can mean an altogether different set of 3
parameters for people living in different climates. Several attempts have been made to develop a 4
systematic methodology by incorporating the design features required when building for varying 5
human thermal requirements and climatic conditions [26]. In addition, expectations about comfort for 6
occupants who use mechanical means to control the built environment differ from those ofthe 7
occupants who use building design parameters (windows, ventilators or shading) to modify the built 8
environment ('free running') [27,28]. Therefore, there is a need to better understand the interaction 9
between the occupant and the built environment by considering both the dynamic thermal 10
environment and the occupants' activities. The importance of thermal comfort studies is now well 11
established in building design. A large number of studies have been carried out to make thermal 12
comfort models more robust by incorporating regional and contextual parameters. Currently, heat 13
balance approach and adaptive thermal comfort models are both being adopted in thermal comfort 14
definitions [28–3133]. Each approach has its own advantages and limitations. People have an inherent 15
capability to adapt to the changing conditions of their indoor thermal environment; the adaptive 16
thermal comfort model duly addresses this phenomenon. The adaptive principle expresses the 17
fundamental assumption of the adaptive model: 'if a change occurs such as to produce discomfort, 18
people react in ways that tend to restore their comfort' [17, 18,19 20]. The basis for the adaptive 19
thermal comfort model is the findings of field surveys on thermal comfort. An occupant in a naturally 20
ventilated building responds actively to changes in the thermal environment and uses the available 21
adaptive opportunities to the fullest to restore comfort. The socio-cultural and traditional contexts also 22
govern adaptive opportunities [25]. 23
Adaptive thermal comfort studies use temperature alone as the parameter to accommodate the 24
regional and contextual variables (thermo-physical properties of building materials, climatic 25
parameters, the age of occupants and the activity level of occupants). EN-ISO 7730, EN 15251, 26
ASHRAE 55 and ASHRAE 62.1 are the existing standards in this domain. These are widely accepted 27
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8 and referred to in designing an indoor environment (thermal comfort, air quality, noise and light). The 1
European standard EN 15251 covers all aspects of comfort, such as thermal comfort, air quality, 2
acoustics and visual comfort [5, 8, 30, 31]. It also allows designers, engineers and architects to 3
perform energy calculations that have consequences for the environment. Table 1 shows the 4
acceptance temperature and predicted mean vote (PMV) ranges according to the EN 15251 standard 5
for mechanically cooled and naturally cooled buildings [6]. This standard is mostly applicable to new 6
and relatively new existing buildings but is not applicable to old residential buildings (constructed 7
before 1945) [6,7,30,31]. In particular, it has some important drawbacks: 8
It recommends broad criteria only and thus has to be modified at the national level. 9
It does not consider local discomforts (asymmetric radiant temperatures, day lighting, 10
vertical air-temperature differences and surface temperatures), which often occur in 11
historic buildings (typically, un-insulated buildings with heating systems). 12
It provides design parameters instead of design methods, which can be confusing for 13
designers. 14
It does not discuss the number of rooms to be monitored when estimating comfort in 15
multi-room buildings. 16
Table 1
17
It is clear that considering only the history of outdoor temperatures (e.g., dry bulb temperature, 18
running mean temperature and weighted running mean temperature) as a single variable to represent 19
comfort in buildings fails to explain experimental thermal comfort results [17]. These results support 20
an argument for increasing the complexity of the time scale that needs to be considered to account for 21
the variations. Moreover, various studies show that incorporating occupants' clothing level and 22
activity together with the temperature can cover a broad spectrum of contexts and both regional and 23
local variables, thereby increasing the accuracy of the estimation of comfort [17]. A number of 24
adaptive thermal comfort studies have demonstrated that clothing level (measured in 'clo') is strongly 25
correlated with the running mean indoor temperature rather than the mean outdoor temperature [17]. 26
This supports the proposition that the building itself should be considered, in addition to human 27
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9 thermal experience and comfort expectations, in contrast to a focus on outdoor temperatures [17,26]. 1
For the old buildings of Liège, it is found that the clothing level of occupants is weakly related to the 2
outdoor temperature but strongly related to indoor temperature variations. This interesting 3
phenomenon was observed during the comfort survey. Because people stay in these old houses for a 4
long time, it can be assumed that they have become accustomed to the built environment and have 5
altered the functionality of the rooms (i.e., by using different rooms and setting different preferred 6
temperatures at different times of the day and year) to optimize their thermal comfort according to the 7
affordability of energy and heating equipment. 8
4. Methodology
9
The characteristics of the residential buildings of Liège are discussed in Section 2. This is 10
important because it underlines the relevance of this study, which is carried out on pre-1945 11
residential buildings. The high percentage of functionally active buildings in this category demands 12
the investigation of occupants’ thermal comfort preferences and expectations, in contrast to the widely 13
discussed existing thermal comfort standards (mostly applicable to new buildings). To judge the 14
applicability of the existing standards for defining comfort in fully functional pre-1945 residential 15
buildings, long term thermal monitoring has been carried out in 20 residential buildings, followed by a 16
questionnaire-based thermal comfort survey in 85 houses. ASHRAE 55 protocols for field studies are 17
followed in the thermal comfort survey [10]. The long-term monitoring of the indoor environment is 18
carried out in two phases. The first phase involved 10 houses during winter (November 2011 to 19
February 2012), when the heating system is ON in most houses. The second phase involved another 20
10 houses during spring (March to May 2012), when the heating systems are mostly OFF. The 21
comfort surveys are carried out between 17:00 h and 20:00 h on weekdays and from 11:00 h to 20:00 22
h on weekends to enable the collection of sufficient information. The local temperature and relative 23
humidity are measured at body height (1.1 m from the ground) by using a handheld data acquisition 24
system (environmental meter, Omega instruments, UK). In each thermal comfort survey, occupants 25
were advised to sit ideal for 20 minutes before taking measurements and recording the preference. An 26
average of five measurements is taken for analysis to minimize the errors. Building design 27
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10 parameters, such as external façade characteristics, materials used for construction, built-up area, type 1
of heating system and renovations, are also recorded. Occupants are questioned about the various 2
strategies they followed to make themselves comfortable in their houses. The measured data, together 3
with information collected during the thermal comfort survey, are used to evaluate the actual thermal 4
comfort in accordance with the thermal performance of the houses [10]. The questionnaire for the 5
comfort survey is designed to address the objectives of the study, in addition to providing enough 6
specific and subjective information to draw meaningful conclusions. The data collected during the 7
comfort survey are analysed to evaluate the prevailing comfort status in those houses. This study 8
identifies the parameters that need to be considered to improve the energy efficiency of the occupied 9
historic houses. 10
Section 1 of the thermal comfort questionnaire covered the socio-economic status of the
11
occupants and their family composition. Section 2 covered the building's age and its type of
12
construction. Section 3 addressed any specific issues about the house and its functioning. Section 4
13
constituted the heart of questionnaire and collected information about the thermal comfort,
14
expectations and preferences of the occupants during both winter and spring. Section 5 recorded the
15
occupants' past, current and intended future activity level when expressing their comfort status.
16
Section 6 focussed on collecting supplementary information covering a broad range of indoor
17
environment characteristics that might be the cause of discomfort or indirectly influence the comfort
18
status of the occupant (e.g., indoor air quality and natural lighting level).
19
5. Results
20
5.1 Thermal performance monitoring of buildings 21
A thermal performance evaluation of buildings with respect to outdoor temperature variations 22
and prevailing indoor temperatures is an important aspect of judging the overall thermal performance 23
of residential buildings. In this study, 20 residential buildings constructed before 1945 in the city of 24
Liège are monitored in two phases. In the first phase, 10 houses are monitored during winter (from 25
December 2011 to February 2012). These house numbers have 'W' prefixes to denote 'winter'. During 26
11 this time, the heating systems in all houses were ON. In the second phase, another 10 houses are 1
monitored in the months of March to May 2012, with the house numbers having 'S' prefixes to denote 2
'spring'. During this period, the heating system in most houses was switched OFF. Table 2 presents 3
the details and important characteristics of all the 20 houses – namely, those that have an influence on 4
the indoor thermal environment. All the houses considered in this study are terraced (exposed to the 5
air on two sides). It is observed from Table 2 that most of the houses used natural gas for heating 6
despite having relatively old heating systems. The long term monitoring included recording the 7
temperature and, relative humidity profiles and the illumination level (inside and outside of each 8
house). Table 3 presents the significant parameters that define thermal comfort, such as family 9
configuration, temperature profile and comfort status for the monitored houses. All the parameters are 10
measured via data loggers (HOBO-U12 RH/Temp/Light/External Data Logger, USA). The data 11
loggers were installed in the living room, one bedroom and the outdoor area of each house because 12
the functionality of rooms may differ. Different rooms were occupied during different times of the 13
day and for different durations. This can influenceinfluences the patterns of dominant temperatures in 14
living rooms and bedrooms. The temperature sensor accuracy was ± 0.35°C, the humidity sensor 15
accuracy was ±2.5% RH and the light intensity measurement instrument accuracy was ±2 lumen/ft220 16
lux. All these parameters are recorded at intervals of 30 minutes. The houses are being used normally 17
throughout the monitoring period, without imposing any restrictions on the occupants, to assessmake 18
the monitoring results realistically. Occupants are also invited to behave normally. The collected data 19
are analysed to obtain the thermal profiles for the living rooms and bedrooms of the houses and the 20
dominant temperatures during different times of the day and seasons of the year. 21 Table 2 22 Table 3 23 Figure 1 24
Section 1 of the thermal comfort questionnaire covered the socio-economic status of the
25
occupants and their family composition. Section 2 covered the building's age and its type of
26
construction. Section 3 addressed any specific issues about the house and its functioning. Section 4
27
constituted the heart of questionnaire and collected information about the thermal comfort,
12
expectations and preferences of the occupants during both winter and spring. Section 5 recorded the
1
occupants' past, current and intended future activity level when expressing their comfort status.
2
Section 6 focussed on collecting supplementary information covering a broad range of indoor
3
environment characteristics that might be the cause of discomfort or indirectly influence the comfort
4
status of the occupant (e.g., indoor air quality and natural lighting level).
5
5. Results
6
Figure 2
7
5.21 Winter thermal performance analysis 8
5.1.1 Winter thermal characteristics of the monitored house 9
10
In the first phase of the monitoring exercise, the indoor thermal conditions for 10 pre-1945 11
residential buildings in Liège are monitored. Table 2 shows that most houses are over 100 years old 12
and also presents the 24-hour average temperature swing for living rooms and bedrooms at the start 13
and end of the monitoring period. Table 2 shows that the swing in living room temperature is always 14
higher than that in bedrooms. Only one house temperature profile is presented in this paper, as similar 15
temperature profiles are observed in all the 10 houses that are monitored during winter. Figure 1 16
presents the layout of house W_10, and S_3. Figure 2 shows the daily maximum and minimum 17
temperatures profiles of the living room and bedroom of the monitored houses with respect to outdoor 18
temperatures. FromThese house falls under typology Maison Moyenne (Average house) [10]. 19
External wall of the houses are massive and overall thickness of external wall is about 0.3m thick 20
including insulation (0.22 m +0.08 m) [10]. Insulation is applied from inside. Internal walls are 0.07m 21
to 0.12m thick. These types of houses are constructed at the end of the 19th century and in the 22
beginning of the 20th century. These houses are constructed in the urban area along the street and in 23
groups (have shared façade on two sides). These houses also have adjoining gable, width of the house 24
is 5 to 6 metres and room height ranging from 3.5 to 4 meters. These houses consist of 2 to 3 floors 25
with significant height. This type of houses has pitched roof with a provision to allow skylight to the 26
interiors. Front facade is made up of brick and decorated with decorative stone or projections or 27
13 coloured bricks [10]. It is observed from the temperature profiles in all monitored houses, it is 1
observed(winter) that the decay in the living room temperature is rapid compared with that in the 2
bedroom. For house numbers W_3 and W_4, low temperatures are observed in the living room, 3
caused by renovation work in the living room during the monitoring period (frequent opening of doors 4
and windows led to high infiltration by colder outside air). The temperature profiles of the monitored 5
houses revealreveals that the living room is functionally more active (occupied for more hours in a 6
day), with) and occupants preferring aprefer higher temperature there in winter compared with their 7
temperature preferences for the bedroom. It can be concluded from the temperature swing that living 8
rooms lose heat quickly in winter compared with bedrooms. The un-insulated walls and large glazing 9
areas on the façades of the monitored houses are responsible for the radiant temperature asymmetry. 10
This conclusion is supported by the relatively high indoor clothing level of occupants and the 11
temperatures corresponding to thermal sensation votes (TSVs). Relatively old heating systems in 12
combination with un-insulated walls raise questions about the efficient functioning and overall 13
efficiency of these buildings. This issue can be linked to the presence of large glazed areas on the 14
front and rear façades of the houses. Finally, it can be concluded that the glazing on an external façade 15
is an important reason for discomfort in winter (sensations of cold). 16
The layout of the house W_10 presented in Figure 1 shows that the front and rear façades and the 17
south wall of this house are exposed to the environment without any shading (by trees or other 18
buildings). This house is oriented on an East–West axis (front façade facing East) and has double- 19
glazed windows with internal movable blinds. It has a central heating system using natural gas with an 20
automatic thermostat. The heating system is less than five years old. In winter, the thermostat is set to 21
20°C. The orientation of the house is such that the front façade received sunlight only in the morning 22
and the rear facade received sunlight only in the afternoon. Therefore, overheating in summer, caused 23
by solar gain, is a possibility. The availability of more sunlight in the afternoon until the late evening 24
hours in summer could lead to discomfort (mainly for the rooms on the first and second floor) if the 25
movable blinds on windows are not used effectively. It is observed that, in winter, the maximum 26
temperatures of the living room and bedroom are 25°C and 22°C, respectively. (Figure 2a). These 27
14 temperatures are well within the range for a comfortable indoor environment with typical winter 1
clothing. 2
It is also important to analyse the daily minimum and maximum temperature fluctuations to 3
assess the thermal comfort of the building. For this house, an interesting pattern is observed, whereby 4
the maximum and minimum temperatures of the bedroom are always between the maximum and 5
minimum temperatures of the living room, suggesting that the temperature fluctuation in the bedroom 6
is less than that in the living room. For this house, the temperature in both the living room and 7
bedroom is well regulated over the full 24-hour period. This may be a preference related to the 8
presence of infants in the house. The 24-hour average temperature profile of this house suggests that 9
the swing in average temperature in the bedroom is maintained well within 0.5°C to 1°C but in the 10
living room it is 1.5°C to 2°C. (Figure 2a). The minimum temperatures of the living room and 11
bedroom fluctuated less than the maximum temperatures, with fluctuations ranging from 0.5°C to 1°C 12
over the 24-hour period for both rooms. (Figure 2a). It is important to study the minimum-temperature 13
behaviourprofile because it not only definesaffect the comfort level but also affects heating energy 14
consumption. This effect is also reflected in the average temperature profiles. There is a high level of 15
thermal regulation in this house. The energy consumption is reasonably high, being 4750 kWh (750 16
kWh for electricity and 4000 kWh equivalents for natural gas) during the monitoring period. As per 17
present guidelines, EPBD 2010, in residential buildings Belgium is trying to limit heating energy 18
consumption 130 kWh/m2/year for existing and new construction. Zero energy building guideline is 19
trying to limit heating energy consumption 15 kWh/m2/year [7]. 20
5.1.2 Winter temperature profile in the monitored house 21
The functionality of a house is related to the context and behaviour of its occupants. Indoor 22
temperature data collected during the thermal monitoring of the 10 houses in winter are analysed to 23
find the dominant temperatures and their durations (in hours) for the bedrooms and living rooms. 24
Figures 3 to 5 show the duration (in hours) for which different temperature ranges are observed in the 25
bedrooms and living rooms. in winter monitoring period. During the monitoring period, renovation 26
work was occurring in the living room for houses W_3 and W_4, leading to a living room temperature 27
15 of less than 15°C. For house W_2, relatively high temperatures are maintained in both the living room 1
and bedroom because the owner of the house was ill. 2 Figure 3a3 3 Figure 3b4 4 Figure 4a5 5 Figure 4b 6 Figure 5a 7 Figure 5b 8
The survey would be incomplete if it does not provide information about the time of day for 9
which particular ranges of temperature are preferred by the occupants of the houses. Therefore, the 10
24-hour day is divided into three periods: 11
a) 08:00 h to 17:00 h: This period is selected because the occupants of the house tended to be at 12
work (except on weekends). 13
b) 17:30 h to 22:00 h: In this period, the occupants tended to have returned from work and be 14
spending most of their time in the living room after dinner. It is assumed that, after 22:00 h, 15
most occupants has gone to bed. 16
c) 22:30 h to 07:30 h: This period is important for examining the patterns of heating before the 17
occupants leave for work. 18
Figures 3a and 3b show Figure 3 shows that, between 08:00 h to 17:00 h, there is a small 19
difference between bedroom and living room temperatures. In the bedroom, the dominant temperature 20
ranges are between 15.1°C and 18°C and <15°C. However, for the living room, the dominant