=Paper= {{Paper |id=Vol-1539/paper4 |storemode=property |title=Investigation of Using Fuzzy Logic to Model Occupant Satisfaction and Behavior in a Building |pdfUrl=https://ceur-ws.org/Vol-1539/paper4.pdf |volume=Vol-1539 |dblpUrl=https://dblp.org/rec/conf/ifip12/CalisGB15 }} ==Investigation of Using Fuzzy Logic to Model Occupant Satisfaction and Behavior in a Building== https://ceur-ws.org/Vol-1539/paper4.pdf
    Investigation of Using Fuzzy Logic to Model Occupant
            Satisfaction and Behavior in a Building

                    Gulben Calis1, A. Burak Goktepe1, Irem Bayram1
               1
               Department of Civil Engineering, Ege University, İzmir, Turkey
            {gulben.calis,burak.goktepe,irem.bayram}@ege.edu.tr




       Abstract.

       Occupant satisfaction with indoor environmental conditions are in close
       relation to energy consumption in buildings. Despite the increasing efforts
       to maintain thermal comfort conditions in buildings with control
       strategies, occupants are not usually satisfied, and, thus, change their
       behavior which generally interfere with building operation systems.
       Therefore, modeling and characterizing occupant satisfaction and
       behavior are important considerations in the building energy use.
       However, occupant satisfaction and behavior as well as indoor
       environmental conditions have serious amount of uncertainty, and, thus, it
       is difficult to simulate them via traditional techniques. In this study, a
       total of 8 tests were conducted to monitor indoor environmental
       conditions in an educational building. A questionnaire was distributed
       during the monitoring period in order to understand the satisfaction level
       of occupants as well as their behavior preference. The results are utilized
       to model occupant behavior where fuzzy logic is preferred to tackle the
       uncertainty in the model parameters. Results denote that there is a
       significant potential of utilizing fuzzy logic to model occupant behavior
       under uncertain conditions similar to the real life.

       Keywords: Indoor environmental conditions; occupant satisfaction;
       behavior; modeling; fuzzy logic.


1      Introduction

Energy efficiency in buildings has emerged as a vital concept in energy conservation
during the past few decades. As a sector, buildings consume approximately 40% of
total energy consumption and the gap between predicted and actual building energy
performance is indicated to be up to 100% [1]. Not being able to predict the building
energy performance not only affects energy policies but also increases the
expenditures in the operation stage, adversely affect thermal comfort conditions, and,
thus, user productivity. Thermal comfort is of crucial importance due to the fact that it
characterizes the response of users in order to increase their satisfaction with the
environment. It is therefore undoubtedly among one of the most influential factors
affecting building energy consumption within its operational phase. Although, it is
possible to control the operation of energy systems and to monitor the energy
consumption via Building Management Systems, these systems cannot include
occupant behavior in their operating systems due to the complexity of modelling
occupant behaviour. In addition, smart meter technology is one of the most important
advancements in helping reductions in energy consumption; however, Armel et.al.

                                            - 32 -
claim that the full potential of the new smart meter technology cannot be exploited if
human factors are not considered; that is, a complete exploitation of smart grid has to
consider human in the loop [2].

The influence of occupant behaviour is under-recognized due to the complexity and
the great district discrepancy of occupant behaviour, which are not always reasonable
and often spontaneous [3]. As most of the existing studies on occupant behaviour are
carried out mainly from the perspective of sociology, they lack in in-depth
quantitative analysis, which is crucial in terms of developing any model. On the other
hand, the traditional approaches consider human behavior almost in a deterministic
way; however, many parameters influencing indoor environmental conditions and
occupant behavior vary significantly and cannot be predicted. Fuzzy logic is a
technique which enables to tackle the uncertainty in the model parameters (i.e. indoor
environmental conditions and occupant behavior). In addition, fuzzy rule-base
systems (FRBS) has the ability to simulate nonlinear behaviors by means of fuzzy
logic as well as fuzzy rules. Therefore, fuzzy logic is a promising technique to model
occupant satisfaction and behavior, which are unpredictable and that are not linear.

In this study, a total of 8 tests were conducted to monitor indoor environmental
conditions in an educational building. A questionnaire was distributed during the
monitoring period in order to understand the satisfaction level of occupants as well as
their preference of behavior in terms of changing indoor environmental conditions.
The data obtained by setting up the measurement campaign along with questionnaires
given to and answered by the occupants are utilized to model occupant behavior.
Fuzzy logic is preferred to tackle the uncertainty in the model parameters including
indoor air temperature, relative humidity, air velocity, air pressure and CO2
concentration, as well as occupant satisfaction levels with indoor environmental
conditions and their preference of behavior (action). The following sections present
the literature review, describe test bed building and data collection, introduce the
application of the methodology and present findings and conclusion.

2      Literature Review
Modeling occupant behaviour with respect to energy consumption in buildings mainly
aims at revealing the interaction between human and energy use. There are several
models that can be used for occupant behaviour. Action based models define
  occupant behaviors as actions. These studies focus on either occupant presence,
which are typically kept at an aggregate level [4-9] (e.g. occupied/unoccupied) or
typical activities such as the control of window openings or sun-shading devices [10-
15]. Probability theory [16-18] and stochastic models [19-23] are also among the most
commonly used techniques to predict the occupant behavior. Deterministic models use
predefined typologies whereas probabilistic models define parameters and equations
to calculate the probability of an occurrence. Studies utilizing deterministic and
stochastic models generally focus on simulating lighting energy use patterns [19, 21]
and window openings. Zhou et. al. used stochastic modelling to simulate occupants’
lighting energy use patterns [19] whereas Li et. al. investigated window-opening
behavior of occupants by using probability [20]. Palacios-Garcia et. al. proposed a
model to simulate the lighting's electricity consumption in the residents [21]. Chen et.
al. modeled occupancy in commercial buildings by using markov chain [22] and
McKenna et. al. presented a four-state model domestic building occupancy model for
energy demand simulations by markov chain outputs [23]. Despite their potential in
modeling occupant behavior, deterministic and probabilistic models are based on
assumptions and data. Deterministic models reveal one outcome at a time for each
assumed type of behavior and thus various calculations have to be done to model each
behavior. Probabilistic models yield the probabilities of a behavior and the distribution
of behaviors. Recently agent based models are also considered as an alternative
methodology in which behaviors of occupants are mimicked based on rules and
memory. Although these methodologies are widely used to model occupant behavior,
other influencing factors (i.e. indoor environmental conditions), which contribute to



                                            - 33 -
the variation in building energy consumption, and, thus, occupant behavior, are mostly
ignored or assumed to be steady.

Fuzzy logic is a promising technique to model occupant satisfaction and behavior. It is
based on fuzzy sets instead of classical crisp sets which use crisp boundaries. Thus,
partially belongingness concept is considered in fuzzy sets by means of real
continuous interval [0, 1]. In fuzzy set theory, each point in the set belongs to the set
with a membership value, and closer values to 1 increase the strength of
belongingness. In this manner, fuzzy logic enables to reason not only by means of
discrete symbols and numbers but also using ambiguous information. Fuzzy logic is a
formal characterization of fuzzy set theory with logical expressions to make heuristic
inference possible by linguistic rules.                                                ’
complexity, which arises from the uncertainty in the form of ambiguity, is considered
by allowing intermediate values and outcomes are regions instead of a single point in
the universe. Consequently, fuzzy logic is a powerful tool to model human behavior
and enables human-like inferences in an environment with uncertainty, vagueness, and
data imprecision [24-26].

Fuzzy rule-base systems (FRBS) can be used the simulation of nonlinear behaviors by
means of fuzzy logic as well as fuzzy rules. There are different inference techniques
which are used in FRBSs, such as, Mamdani [27], Sugeno [28], Tsukamoto [29]
systems. Mamdani system is the first inference implemented fuzzy inference
methodology, in which the variables are used in fuzzy relational equations in the
canonical form. The linguistic rules are associated with logical connectives namely,
and, or, else. Since the outcome is an area (or a region) in the output space,
defuzzification process is usually carried out to calculate a single value as an output
[24, 28]

Fuzzy logic was applied for modelling human behavior in several studies. In order to
model pedestrian walking path and behavior, fuzzy system and its hybrid models were
implemented [30, 31]. Another study revealed that by using fuzzy systems, human
behavior could be modeled more accurately [32]. Moreover, fuzzy ontology was used
for identification of human behavior [33]. Fuzzy logic system was also used to
simulate the behavior of residential occupants in terms of electricity use and lights in
the houses [34]. In recent studies, fuzzy controllers were applied to smart buildings in
which HVAC systems are regulated. Marvuglia et. al. developed a combined neuro-
fuzzy model, which produces indoor temperature forecasts that are used to feed a
fuzzy logic control unit that simulates switching the heating, ventilation and air
conditioning (HVAC) system on and off according to the indoor temperature [35].
Nowadays, fuzzy logic based controllers were able to control the HVAC and A/C
systems [36-43]. These studies show that fuzzy logic has potential to be used in
modelling occupant behavior which are unpredictable and that are not linear.

3      Test Building Description and Data Collection
The study was carried out at the Department of Civil Engineering, Ege University
located in Izmir, which is at Turkey's western coastline characterized by long, hot and
dry summers. Subsequently, reducing energy consumption for cooling and ensuring
thermal comfort conditions constitute the main concerns in this climatic zone. A total
of 8 tests were carried out in two periods spanning 2 and 3 days in June and July, 2014
respectively. These days were selected as there was high attendance to classes.
Physical and subjective measurements were conducted to obtain quantitative data on
the prevailing actual conditions. Data collection methods included: (1) a physical
measurement of certain parameters that influence the occupant satisfaction and
behavior, (2) a questionnaire as the subjective measurement.

Test bed building was constructed in 2002 and has no insulation on the exterior walls.
Heating and cooling are maintained via a centralized system. The building has double
glazed windows with aluminum frames. Four different classrooms, which are located
on the south, were selected for the case studies. These classrooms were selected as (1)


                                            - 34 -
they are the most commonly used ones and (2) they are the most affected ones by the
sun due to their location. The floor plans and the selected classrooms are presented in
Figure 5.




                         (a)                                         (b)




                                                 (c)

                  Fig. 5. a) 1st Floor plan, b) 2nd Floor plan, c) 3rd Floor Plan

Field measurements were taken every minute at a height of 1.1 m from the ground
level as advised in the prescriptions of the ASHRAE Standard 55-2010 [44]. Indoor
air temperature (T), relative humidity (RH), air velocity (V), air pressure (P) and CO2
concentrations were measured via the TESTO Thermo-Anemometer Model 435-2.
The subjective study involved collecting data via questionnaires. The questionnaire
was developed to gauge how occupants are feeling in terms of thermal comfort and
what they would like to do to feel more comfortable. The options for the first question
varied from very comfortable to very uncomfortable, whereas the options for the latter
question were window opening/closing, door opening/closing, cloth adjustment,
curtain closing, using air conditioning and no change. Details of the test design and
number of participants are presented in Table 1.

Table 1. Test design of the case study

           Measurement             Time                                               Number of
Test No                                      Classroom       Floor          Area
               Date              interval                                             Participants
  Test 1    18.06.2014         14:25-15:20      D104       1st Floor       136.6 m2        50
  Test 2    19.06.2014         13:05-13:50      D104       1st Floor       136.6 m2        43
  Test 3    18.06.2014         08:50-10:20      D204       2nd Floor       136.6 m2        43
  Test 4    19.06.2014         13:50-14:20      D204       2nd Floor       136.6 m2        46
  Test 5    23.07.2014         13:20-14:15      D209       2nd Floor        70.4 m2        30
  Test 6    23.07.2014         14:35-15:15      D209       2nd Floor        70.4 m2        32
  Test 7    24.07.2014         13:00-13:55      D209       2nd Floor        70.4 m2        30
  Test 8    25.07.2014         13:35-14:40      D309       3rd Floor        70.4 m2        30

Table 2 presents the statistical summaries of indoor measurements. Indoor air
temperature values ranged between 30.3 and 25 0C with mean values of 30.15 and
26.86 0C and standard deviations (STD) of 0.10 and 0.55, which indicate that indoor
air temperatures were relatively stable during the tests. Relative humidity values
ranged between 55.4 39.1%, with mean values of 51.12 and 40.35% and STDs of
2.04 and 0.46. Air velocities ranged between 0.3 and 0.01 with mean values of 0.04
and 0.01 whereas the STDs ranged between 0.09 and 0.01. CO2 concentrations ranged
between 4130 and 646 ppm with mean values of 3108.55 and 1128.25 ppm whereas
the STDs ranged between 37.4 and 600.88, which indicate large deviations between
measurements.


                                                 - 35 -
Table 2. Descriptive statistics of indoor environmental conditions

              Test 1     Test 2      Test 3         Test 4      Test 5          Test 6     Test 7        Test 8
Indoor air temperature (0C)
Mean         30.15    28.37          28.93          28.76          27.87        26.86          25.97     29.36
Std. Dev.     0.16     0.51          0.34           0.32           0.55         0.10           0.34      0.49
Minimum       29.7    27.10          28.4           28.6           27.3         26.5            25       28.2
Maximum       30.3    28.80          29.4            30            29.1          27            26.3      29.9
Relative Humidity (%)
Mean         40.35    42.30          51.12          41.68          47.49         43.6          47.69     43.44
Std. Dev.     0.66     2.04          4.16           0.79           1.34          0.50          0.54      0.46
Minimum       39.1    40.20          42.2           40.3           43.2          42.9          45.7      42.7
Maximum       41.7    47.20          55.4           43.4           48.9          44.9          48.3      44.8
Air Velocity (m/sec)
Mean          0.02        0.05           0.03        0.01          0.18          0.12          0.12       0.04
Std. Dev.     0.02        0.07           0.02        0.01          0.07          0.09          0.07       0.03
Minimum       0.01        0.01           0.01        0.01          0.02          0.01          0.01       0.01
Maximum       0.1          0.3           0.1         0.04          0.27          0.28          0.25       0.16
Air Pressure (kPa)
Mean        100.95       100.45      101.05         100.41      100.16          100.16     100.29        100.16
Std. Dev.     0.02        0.03        0.03           0.01        0.01            0.00       0.00          0.00
Minimum 100.89           100.43      101.01         100.38      100.16          100.16     100.29        100.15
Maximum 100.97           100.51      101.1          100.43      100.19          100.18     100.31        100.17
CO2 Concentration (ppm)
Mean      1555.91 1426.44 1128.25 1136.37 1487.44 1406.63 1167.69 3108.55
Std. Dev.  149.93 177.84 187.85 132.42 541.07      37.4   148.96 600.88
Minimum     1221     1156   646     973     566    1358     877    2054
Maximum     1806     1766  1315    1383    2351    1528    1374    4130

The results of the questionnaires are shown in Table 3. A total of 304 responses were
received and all of them were valid. The gender ratio of respondent students was 16%
female and 84% male. Majority of the students were seniors in the age range of 20-27.
Approximately t
and 73% of these occupants indicated that they would prefer to use air conditioning to
feel comfortable whereas window opening was ranked the second. Occupants who
                                                                            almost the
same ratio of 24%. Majority of these respondents indicated that using air conditioning
would be their first choice to prevent an uncomfortable indoor environment. In


                                                                           , it was the least preferred
behaviour among respondents.

Table 3. Questionnaire results


                                  Thermal Satisfaction                             Percentage
Behavior Preferences                                                  TOTAL
                                                                                      (%)
                                                                                                       Rank Order
                          V.C*      C*      L.A*     A*       H.A*
Window-Opening              1        2          8     9        5           25            8.2               3
Window-Closing              1        0          2     2        0           5             1.6               7
Door-Opening                3        3          2     4        3           15            4.9               4
Door-Closing                1        2          3     2        1           9             3.0               5
Cloth Adjustment            1        4          2     1        0           8             2.6               6
Curtain-Closing             1        1          2     0        0           4             1.3               8


                                                     - 36 -
Using Air-conditioning          8        51      67        56       14    196   64.5   1
No change                      26        10      6         0        0     42    13.8   2
TOTAL                          42        73      92        74       23    304   100
Percentage (%)                13.8 24.0 30.3 24.3                   7.6   100
*V.C: very comfortable, C: comfortable, L.A: light annoyance, A: annoyance, H.A: heavy
annoyance.


4        Application of the Methodology
In this section, results of questionnaires, which were conducted to understand
occupant satisfaction and behavior during cooling season, are applied to fuzzy model.
The numerical example aims at showing the approximation ability of the fuzzy model
in terms of characterizing occupant satisfaction with the indoor environment. In
addition, assessing average occupant satisfaction level and estimating the occupant
behavior are targeted.

Firstly, indoor air temperature, relative humidity, air velocity, air pressure and CO2
concentration variables that are measured in the indoor environment are characterized
with fuzzy variables as well as triangular membership functions. It should be noted
that mapping of a fuzzy set to the universe is represented by the membership function
concept. Then, if the universe of discourse is represented by X, the fuzzy set A can be
given by the following expression (Equation 1) [28]:

  ­° P A ( x1 ) P A ( x2 )      ½°      ­° P A ( xi ) ½°
A ®                      ...¾        ®¦            ¾                                   (1)
                                              


   °̄ x1           x2            °¿      °̄ i   xi °
                                                       ¿

Triangular membership function (Fig.1) can be given with the expression below
(Eq.2):
        ­ 0       xda
        °x  a
        °°  a  ad xdb
P ( x) ® bc  x                                                            (2)
         °      bdxdc
         °c  b   cdx
         °¯ 0

Therefore, a fuzzy relation can be inferred by means of max-min composition rule for
a triangular fuzzy membership function as follows:

                  ª   § xa c x· º
P ( x; a, b)   max«min¨    ,    ¸,0»                                                       (3)
                  ¬   ©ba cb¹ ¼

                            μA (x)
                                    1                       A



                                                                          x
                                    0
                                           a           b              c
                    Fig. 1. Representation of a triangular membership function

In a fuzzy rule-based system, each logical proposition in the universe of discourse is
characterized by a fuzzy set and the outcome of a rule is obtained by an implication
technique, which is referred to as an extension principle or approximate reasoning. In
                      ’                          applied and a fuzzy relation (R) is


                                                           - 37 -
(Eq.4):

                        ª                         º
P R ( x, y, ...) min«P A ( x), P B ( y),...»                                                                        (4)
                       «¬                      »¼

Obviously, fuzzy rule-based systems consist of several rules, which involve
antecedents, namely conjunctives (AND) and disjunctives (OR). The inference is
made by a decomposition method. Basically, decomposition can be made for
conjunctives as given by the following expression:

                 ª                                  º
P S ( y)      min« P A1 ( x), P 2 ( x),..., P L ( x)»                                                               (5)
  B                            A             A
                «¬                              »¼

Analogously, decomposition is done for disjunctive antecedents as follows:
                 ª                                  º
P S ( y)      max« P A1 ( x), P 2 ( x),..., P L ( x)»                                                               (6)
  B                            A             A
                «¬                              »¼

A graphical representation of a Mamdani fuzzy inference system is shown in Figure 2.
As can be derived from the figure that the outcome is a region; thus, it is required to
make a defuzzification in order to get single output value. There are several
defuzzification techniques in the literature; nevertheless, in this study, centeroid
method is preferred, and the formulation is as follows:

          ³ P A ( x) x dx
  x*          
                                                                                                                   (7)
          ³ P A ( x) dx
               
In which, A is fuzzy set, µA is membership function, x is input variable, and x* is
single output value.



                             ?(x 1 )                    ?(x 2 )                            ?(y)
                             A 11                      A12
 Rule 1                                    AND                     min                 B

                                                                           x2                         y1
                        input, x 1         input, x 2



                             ?(x 1 )                    ?(x 2 )                          ?(y)
                             A 11                  A12
Rule 2                                     AND                    min                  B              y2
                                                                                                           Implication
                                                                           x2
                                                                                                           Aggregation
                       input, x 1          input, x 2


Rule n                                                                                            n
                                                                                                              e
                                                   OR                                inference                xt
                                                                                     region


                  Fig. 2. Schematic representation of the fuzzy inference methodology




                                                                  - 38 -        e
                                                                                xt
Fig.3 shows the input fuzzy variables (indoor air temperature (T); relative humidity
(RH); air velocity (V); air pressure (P); CO2 concentrations(C)) and associated
triangular membership functions. As can be derived from the figures, fuzzy variables
have different partitioning from 3 to 5.




                                                                                 V
                                                                               (m/sec)




                                      P
                                    (kPa)




                 Fig. 3. Membership functions of the fuzzy input variables

Output variable of the model which characterizes the satisfaction of an occupant is
considered by Satisfaction Index (SI) variable. In Fig.4, membership function of SI
variable is shown. In order to quantify and model the occupant satisfaction, the results
of the questionnaires are graded per answers in the questionnaires. In other words,
each response of the occupants is quantified with a relative scale within [0,100],
which is a percentage indicating the satisfaction with the indoor environment.

           P(SI)
                    1



                                                                      SI
                                                                     (%)

                    0                                                  V (m/sec)
                        0    20      40       60      80       100

                Fig. 4. Membership function of the fuzzy output variable, SI




                                             - 39 -
In the next step, fuzzy rule-base is established using grid partitioning technique.
Namely, each rule is associated with each possible variation for considered fuzzy
input parameters; thus, totally 720 (5 x 3 x 3 x 3 x 4) different rules are included in the
fuzzy rule-base. It should be noted that the fuzzy partitioning of each variable is done
according to the range of the variable, and then the rules are developed while ensuring
enough precision in the inference. A sample rule from the rule base is given below.

IF CO2 is C2 AND T is T2 AND P is P2 RH is RH3 AND V is V3 THEN SI is SI3              (8)


5      Findings
Matlab and Fuzzy Logic Toolbox software packages are used to develop the presented
model. Next, the developed fuzzy model is employed with the test data that was
obtained from the measurement campaign which is explained in Section 3. In order to
observe the performance of the fuzzy model, the outcomes are compared with the
results of the questionnaires that were conducted in accordance with the
measurements. In this context, firstly, SIs are calculated over 100% per responses of
the occupants. After this, in order to calculate the combined satisfaction of all
occupants simultaneously; weighted averages, Performance Points (PP) are calculated
over 2 000. Then, establishing fuzzy inference according to performance points is
aimed. Fig. 6 shows a sample relationship among some model parameters and SI.




      PP




     V (m/sec)


                                                               CO2 (ppm)

                      Fig. 6. Relationships between model parameters



Inference mechanism during the calculation of the output of fuzzy model using rule-
base is presented in Fig. 7.




                                             - 40 -
                            Fig. 7. Fuzzy inference with rule-base



Finally, the results of the fuzzy model developed for occupant satisfaction are
compared to the actual questionnaire data. The closeness of the fuzzy model to the
actual data can be seen in the scatter plot given in Fig.8. It should be noted that the PP
value is a weighted average of the occupants of which maximum value is considered
as 2000 in this study. Any other formulation can be used to calculate such a value
analogously.

  2000

  1900
              R2 = 0.99
  1800

  1700

  1600

  1500
                                                        Line of equality
  1400

  1300

  1200
      1200      1300      1400     1500      1600       1700    1800      1900         2000

          Fig. 8. Scatter plot between fuzzy model outputs and questionnaire results


                                               - 41 -
As can be derived from Fig. 8, results of the developed fuzzy model are successful,
and easily capable of simulating the occupant satisfaction and behavior. The R2 value
is calculated as 0.99, which indicates an outstanding correlation between the model
and the questionnaire results. The R2 value also highlights the potential to tackle the
uncertainty with fuzzy logic.

6      Conclusion
This study aims at investigating the approximation ability of the fuzzy approach in
terms of characterizing occupant satisfaction with the indoor environment as well as
predicting occupant behavior. The results show that the developed fuzzy model is
capable of estimating the satisfaction levels of occupants when indoor environmental
conditions (i.e. indoor air temperature, relative humidity) are known. Considering the
fact that buildings are becoming more equipped with technologies that enable real
time monitoring, understanding and predicting occupant satisfaction and behaviors
will be achieved via the developed fuzzy model. In addition, the simulation of
occupant behavior provides a valuable chance to model the interaction with building
operation systems (i.e. HVAC). Consequently, the developed model enables to
develop energy efficient systems in the buildings with lower energy consumptions
considering the effect of human behavior as well as the uncertainty in the model
parameters.

Results indicate that there is a great potential to use fuzzy models for such behavioral
simulations and such a fuzzy system can be used to achieve successful occupant
behavior models for increasing occupant satisfaction as well as helping facility
managers to optimize operation strategies of the buildings. In further studies, existing
uncertainties and correlations should be evaluated with a larger database. Furthermore,
future studies could focus on incorporating such fuzzy inferences in the energy
efficiency problems directly. This study basically aims to show the potential of using
fuzzy logic to model occupant behaviors and related responses that can be utilized in
such efficiency optimization systems.




                                            - 42 -
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