Numerical assessment of night ventilation impact on … · Numerical assessment of night ventilation impact on the thermal comfort of vernacular buildings ... Energy retrofitting

RESEARCH ARTICLE

Numerical assessment of night ventilation impact on the thermalcomfort of vernacular buildings

Parthena Exizidou1 • Elias Christoforou1 • Paris A. Fokaides2

Received: 17 August 2016 / Accepted: 15 December 2016 / Published online: 7 January 2017

� Springer International Publishing Switzerland 2017

Abstract Night ventilation, is one of the most effective

passive cooling techniques that may contribute to the

improvement of the occupants thermal comfort conditions.

Despite the justified effectiveness of night ventilation, few

studies quantified its influence on the thermal comfort of

vernacular buildings, especially under warm dominant

climates. The aim of this study is the investigation of the

impact of night ventilation on the thermal comfort of

vernacular buildings under summer dominant environ-

mental conditions. The subjects under investigation was

one traditional buildings in the city of Nicosia in Cyprus. In

terms of this study numerical analysis regarding the ther-

mal comfort of the investigated buildings was performed

by employing Energy Plus and the flow solver of Design

Builder. The indoor operative temperature distribution, the

indoor air velocity and a thermal comfort related index

were identified in selected thermal zones of the examined

building using night ventilation. The results of this study

quantified the potential temperature decrease that can result

on vernacular buildings due to the use of night ventilation

and revealed some restrictions with regard to the allowed

percentage of the opening sizes towards achieving optimal

thermal conditions in space. This study aspires to provide

useful insight regarding the importance of humans’

behavior in terms of enabling night ventilation to vernac-

ular buildings, as well as to con-tribute to the ongoing

scientific discussion on this subject.

Keywords Vernacular building � Night ventilation �Computational fluid dynamics (CFD)

List of symbols

Dexp Experimental temperature difference (�C)Dsim Simulated temperature difference (�C)fcl Clothing surface area factor (–)

hc Convective ehat transfer coefficient (W/m2K)

IC Inequality coefficient (–)

lcl Clothing insulation (m2K/W)

M Metabolic rate (W/m2)

Text Ambient temperature (�C)ta Air temperature (�C)tcl Clothing surface temperature (�C)tr Mean radiant temperature (�C)pa Water vapour partial pressure (pa)

Var Relative air velocity (m/s)

W Effective mechanical power (W/m2)

Abbreviations

3D Three dimensional

CFD Computational fluid

dynamics

FVM Finite volume method

Indexes

exp Experimental

sim Simulated

t Time

& Paris A. Fokaides

[email protected]

1 Frederick Research Center, 7, Filokyprou Str., 1036 Nicosia,

Cyprus

2 School of Engineering, Frederick University, 7, Frederickou

Str., 1036 Nicosia, Cyprus

123

J Build Rehabil (2017) 2:2

https://doi.org/10.1007/s41024-016-0021-6

1 Introduction

Energy retrofitting is an area of the construction industry

which has gained public awareness in the recent years.

More than a quarter of the existing European building stock

was constructed prior to the middle of the last century [1].

These buildings are certainly valued for their cultural and

architectural significance as they reflect the unique char-

acter and identity of European cities, but they were

appointed to address the needs of their original inhabitants.

The difference between original and contemporary occu-

pants’ lifestyle, clothing and activity as well as the thermal

comfort perception itself, is a parameter that needs to be

taken into consideration when assessing the thermal com-

fort of vernacular dwellings today. People’s perceptions of

comfort are influenced by cues from the built environment,

yet humans may adapt the indoor environment, to achieve a

different set of indoor conditions.

Vernacular buildings have evolved through time

acquiring their specific form and layout, through a process

of trial and error. This process implicates the consideration

of multiple environmental and anthropological variables.

The environmental and bioclimatic design elements of

vernacular architecture; amongst which are the considera-

tion of climatic conditions, topography, rational use of

local resources concerning employed materials and com-

plexity of construction was highlighted in previous studies

[2–4]. Passive heating and cooling strategies of vernacular

buildings presumed upon the proper use of materials as

well as buildings’ location and orientation. Other envi-

ronmental approaches though incorporated into the build-

ing design required the active involvement of the user.

Some examples include the shutters operation to control

the direct solar heat gains, the watering of plants to enable

evaporative cooling, and the windows opening to exploit

night ventilation Natural night ventilation is an interesting

passive cooling method in moderate climates. Driven by

wind and stack generated pressures, it cools down the

exposed building structure at night, in which the heat of the

previous day is accumulated [5]. Whilst, the prediction of

occupant behaviour may result to more accurate definitions

of the buildings’ energy requirements, few accounts men-

tion the role of the user in the establishment of thermal

comfort; even fewer studies approach the variant of occu-

pant behaviour when assessing vernacular buildings.

This study aims to provide useful insight regarding the

impact of natural night ventilation on the thermal comfort

of vernacular buildings under summer dominant climatic

conditions. In the following section, a comprehensive lit-

erature review is conducted regarding previous studies

examining the impact of night ventilation to energy con-

sumption of buildings, as well as numerical analysis

practices applied to vernacular buildings to investigate

their thermal comfort. In Sect. 3 the employed methodol-

ogy is presented and Sect. 4 presents and discusses the

results of this study.

2 Literature review

2.1 Night ventilation

Night ventilation, also referred as night cooling, is one of

the more efficient passive cooling techniques that may

contribute to the reduction of the cooling load of buildings

and to the improvement of occupants’ thermal comfort.

Night cooling is based on the circulation of the cool

ambient air in space which results to the decrease of both

the temperature of the building’s structure and of the

indoor air. The cooling potential is mainly based on the

relative difference between the outdoor and indoor tem-

peratures during the night period as well as the air flow

rate, the thermal capacity of the building and the appro-

priate coupling of the thermal mass and the air flow.

Various studies were implemented in the recent parts with

the aim to quantify the impact of night ventilation to build-

ings [6–9]. The majority of these studies regarded office

buildings. Pfafferott et al. [10] conducted experiments in two

offices in order to determine the efficiency of night ventila-

tion dependent on air change rate, solar and internal heat

gains. Corgnati and Kindinis [11] investigated in their study

the activation of building thermal mass by means of outdoor

air ventilation, exalting the effect of night ventilation. In the

study conducted by Geros et al. [12], the efficiency of night

cooling techniques was investigated in 10 different urban

canyons. A typical room under air-conditioned and free-

floating operation was investigated, considered as single-

sided or cross ventilated during the night period. Ramponi

et al. [13] analyzed the cooling effectiveness of night-ven-

tilation for office buildings placed in the center of urban areas

of increased density for three European locations. Night

ventilation rates and energy savings were calculated for the

buildings and compared to the energy demand of the

unventilated buildings. A typical office room was modelled

by Artmann et al. [14]. In his study, the effect of different

parameters (climate, thermal mass, heat gains, air change

rates and heat transfer coefficient) on the effectiveness of

night ventilation was evaluated. Climatic conditions and air

flow rate during night-time ventilation were found to have

the largest effect. Kubota et al. [15], the effectiveness of

night ventilation for residential buildings under warm and

humid climatic conditions was examined. The thermal

environment evaluation showed that night ventilation would

provide better thermal comfort for terraced houses occupants

2 Page 2 of 11 J Build Rehabil (2017) 2:2

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compared with the other ventilation strategies. Santamouris

et al. [16] calculated the absolute energy contribution of

night ventilation based on energy data from two hundred

fourteen air conditioned residential buildings using night

ventilation techniques. The results showed that the higher the

cooling demand of the building, the higher the potential

contribution of night ventilation under specific boundary

conditions. In Le Dreau et al. [17], heat transfer during 12 h

of discharge by nighttime ventilation in a full scale test room

was investigated. Different ventilation types, air change

rates, temperature differences between the inlet air and the

room, and floor emissivity were examined. Roach et al. [18]

examined the effect in cooling energy of commercial office

buildings from economiser cycles and night time ventilation

when used separately and combined. In the study ofGoethals

et al. [19], a global surrogate-based optimization procedure

was set up to find room/system design solutions which

induce a high convective heat flux during night cooling in a

generic open plan office.

Despite the fact that several studies were conducted

regarding the numerical investigation of night ventilation

impact on the energy consumption of buildings, few studies

were implemented to examine the impact of night venti-

lation to vernacular buildings by means of numerical

simulation.

2.2 Energy performance of vernacular buildings

The numerical investigation of the thermal performance of

vernacular buildings consists a subject that was widely

approached [20–22]. The energy and microclimatic per-

formance of Mediterranean vernacular buildings was

investigated by Cardinale et al. [23]. The study focused on

two types of buildings that are the examples of vernacular

architecture in Southern Italy, namely the Sassi of Matera

and the Trulli of Alberobello. Zhai and Previtali [24] per-

formed an extensive analysis and computer energy model-

ing for a number of representative vernacular architectural

techniques and features summarized for different climatic

regions. The simulation results of the energy models sug-

gested that considering traditions seen in ancient vernacular

architecture as an approach to improving building energy

performance is a worthwhile endeavor and a scientific

guidance can help enhance the performance. In the study

conducted by Nguyen et al. [25], six old houses in rural and

urban areas in Vietnam, were investigated to understand the

climatic design strategies employed and their effectiveness

in maintaining human comfort and health. The results of

this study indicated that vernacular housing in Vietnam is

creatively adapted to the local natural conditions and uses

various climate responsive strategies. Kristianto et al. [26]

investigated the thermal comfort conditions, particularly air

velocity, inside of Minahasa Traditional House, a wooden

raised floor house originated from Tomohon, North Sula-

wesi. Computational fluid dynamic (CFD) analysis was

applied in the study and the effectiveness in creating ther-

mal comfort several variations of openings and stilts height

were evaluated. Simulations results showed that higher

stilts height is higher air velocity inside the test house and

that houses with roof opening has higher internal air

velocity compared to houses with wall opening. The study

conducted by Presetyo et al. [27] aimed to describe Rumah

Lontiok, one of Malay traditional houses and to investigate

its thermal performance. The authors revealed that against

the existing notion, the investigated traditional house pre-

sented a poor thermal performance. The aim of the study

undertaken by Stephan et al. [28] was to evaluate the

thermal inertia in high porosity limestone old buildings in

summer and to determine the impact of a retrofitting solu-

tion on thermal behaviour of these stone buildings. The

analysis of data underlined the advantages of insulation for

thermal inertia on stone buildings. Orehounig and Mahdavi

[29] collected data for five hammans that were used for the

generation of building performance simulation models. The

study showed that the hygrothermal conditions in hammams

vary considerably over time and space and that fairly

stable thermal conditions were achieved. In [30], the

authors conducted a combination of field measurements and

simulations in order to determine the renovation require-

ments. The analysis showed that the improvement of

building service systems and the energy source holds the

largest energy saving potential. Dili et al. [31] compared

and analyzed the thermal performance of traditional and

modern buildings of Kerala, India. Analysis using Biocli-

matic charts revealed that the thermal comfort of traditional

buildings was comparable to contemporary ones.

3 Methodology

3.1 Thermal Comfort Index

In terms of this study, the thermal comfort was determined

according to the well-established ISO 7730:2005 [32]

standard and the PMV index. The PMV index predicts the

mean value of the votes of a large group of persons on the

7-point thermal sensation scale (see Table 1), based on the

Table 1 Seven-point thermal

sensation scale (PMV Index)

[32]

?3 Hot

?2 Warm

?1 Slightly Warm

0 Neutral

-1 Slightly Cool

-2 Cool

-3 Cold

J Build Rehabil (2017) 2:2 Page 3 of 11 2

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heat balance of the human body. PMV was calculated using

Eqs. 1–4.

PMV ¼ ½0:303� expð�0:036MÞþ 0:028�� fðM�WÞ� 3:05� 10�3�½5733� 6:99�ðM�WÞpa�� 0:42

� ½ðM�WÞ� 58:15� � 1:7� 10�5�M�ð5867� paÞ� 0:0014

�M�ð34� taÞ� 3:96� 10�8� fcl

�½ðtclþ 273Þ4�ðtr þ 273Þ4�� fcl� hc�ðtcl� taÞg

ð1Þ

tcl ¼ 35:7� 0:028� ðM �WÞ � Icl

� f3:96� 10�8 � fcl � ½ðtcl þ 273Þ4 � ðtr þ 273Þ4�þfcl � hc � ðtcl � taÞg

ð2Þ

hc¼2:38 � jtcl� taj0:25 for 2:38 � jtcl� taj0:25[12:1� ffiffiffiffiffiffi

varp

12:1� ffiffiffiffiffiffi

varp

for 2:38 � jtcl� taj0:25\12:1� ffiffiffiffiffiffi

varp

( )

ð3Þ

fcl ¼ 1:00þ 1:290� lcl for lcl\0:078 m2K/W

1:05þ 0:645� lcl for lcl [ 0:078 m2K/W

� �

ð4Þ

The calculation of PMV is based on the metabolic rate

of the occupant (M), the temperatures of the air, the human

surface and the space walls (ta, tcl, tr, respectively) which

are used to quantify heat losses due to conduction (lcl),

radiation (fcl) and convection (hc), the air velocity in space

(Var) and the evaporation (pa) and respiration heat losses.

The metabolic unit used (met) equals to 58.2 W/m2 and the

clothing unit (clo) to 0.155 m2 �C/W. The intervals in

which the PMV is applicable are given in Table 2.

3.2 Numerical analysis process

The calculation of the PMV index requires the definition of

the indoor conditions, including buildings air, radiative and

operative temperatures as well as the air velocity distri-

bution in space. To this end Energy Plus and the flow

solver of Design Builder were employed. Energy Plus is an

energy analysis simulation software tool performing

dynamic sub-hourly thermal load calculations. Basic

important capabilities of Energy Plus comprise.

• sub-hourly time-step simulations for the interaction

between the thermal zones and the environment;

• heat balance based solution technique for building

thermal loads that allows for simultaneous calculation

of radiant and convective effects at both in the interior

and exterior surface during each time step and;

• the use of Conduction Transfer Functions for the

calculation of Transient heat conduction through

building envelope.

Energy Plus is a stand-alone simulation program without

a ‘‘user-friendly’’ graphical interface. In this study Design

Builder was used as a graphical interface. Through Design

Builder and Energy Plus a very fine zoning was performed

and detailed calculation took place at each time step

(Fig. 1). Detailed information regarding geometry, mate-

rials, activity, internal gains, infiltration and natural venti-

lation was integrated into the thermal models for the

accurate representation of the energy performance of the

under-study buildings.

Design Builder also contains a computational fluid

dynamics (CFD) three dimensional (3D) flow solver which

was applied. Design Builder CFD uses finite volume

methods (FVM) to solve a set of partial differential equa-

tions that represent the conservation of mass, the conser-

vation of energy and the second law of Newton

(momentum equation). The equation set comprises the

three velocity component momentum equations, the

Navier–Stokes equations, the energy equation using the k-eturbulence model and equations for turbulence kinetic

energy and the dissipation rate of turbulence kinetic

energy. The simulation input of airtightness building per-

formance is given in Table 3.

The results of the internal CFD analysis were the pre-

diction of the airflow and temperature field. By using a

detailed weather file, the introduction of outside air to the

inside of the building through the position and the size of

the openings was studied and the benefits of natural ven-

tilation, cross ventilation and their effects to the internal

environment temperatures and thermal comfort of occu-

pants were examined.

4 Results and discussion

The subject of investigation was a vernacular building in

the city of Nicosia (Fig. 2). The building is located in the

traditional core of Kaimakli (35�11014.0800N,33�22036.3100E), and it is a typical two-storey courtyard

house with an ‘‘L’’ shape typology. The ground floor

building has a lounge-circulation zone (portico) in North–

South direction. The yard is located in the southern part of

Table 2 PMV parameter intervals in which PMV is applicable [32]

M 46–232 W/m2 (0.8–4 met)

lcl 0–0.31 m2K/W (0–2 clo)

ta 10–30 �Ctr 10–40 �CVar 0–1 m/s

pa 0–2700 Pa

2 Page 4 of 11 J Build Rehabil (2017) 2:2

123

the plot, allowing the exposure to solar heat gains of the

building. The external walls of the building are built with

adobe bricks of 50 cm thickness, and the sloped roof of the

building consists of tiles, MDF plywood, an insulation

layer and wooden beams. In this study, results for Zone 6, a

cross ventilated room next to the ground floor portico of the

building was simulated (Fig. 1). The simulation results

were validated using the inequality coefficient [23], based

Fig. 1 a Design Builder 3D

geometry simulation. b Design

Builder model top view

Table 3 Simulation input of

airtightness building

performance

Openings Walls Floors Roof

Windows Doors External Internal External

Flow coefficient (kg/s.m@1 Pa) 0.00014 0.0014 0.0001 0.003 0.0007 0.0001

Flow exponent 0.65 0.65 0.7 0.75 1 0.7

J Build Rehabil (2017) 2:2 Page 5 of 11 2

123

on measurements provided by the University of Cyprus

research group involved in Biovernacular project [33]

presenting a good agreement The inequality coefficient is

used to validate prediction models used in thermal per-

formance and describes the inequality in the magnitude

domain due to three sources: unequal tendency (mean),

unequal variation (variance) and imperfect co-variation

(co-variance). The resultant coefficient can range in value

between 0 and 1, with 0 indicating a perfect match and 1

denoting no match [34].

IC ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1n

Pnt¼0ðDsim;t � Dexp;tÞ2

q

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1n

Pnt¼0ðDsim;tÞ2

q

þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1n

Pnt¼0ðDexp;tÞ2

q ð5Þ

where Dsim;t ¼ ðTint;t � Text;tÞsim the recorded temperature

difference and Dexp;t ¼ ðTint;t � Text;tÞexp the simulated

temperature difference between the interior and the envi-

ronment. Since summer season has the most significant

impact on the total energy consumption of the buildings in

Cyprus, the validation focused on the cooling period. As

night ventilation has an impact on the thermal performance

of buildings during summer, simulations were performed

for the warmest summer months (July, August—see

Table 4). The inequality coefficient for this period was

found to be equal to 0.17.

4.1 Impact of night ventilation on operative

temperature

In Fig. 3 the impact of night ventilation on the operative

temperature of the investigated building is presented. The

windows were considered to be open from 7 pm to 7 am,

whenever the conditions were suitable for night ventilation.

The operative temperature is calculated as the average

value of the air and the radiant temperature. From the given

figure it can be retrieved that night ventilation results to an

average reduction of the operative temperature of 2.7 �C.The maxi-mum temperature reduction during night hours is

5.7 �C. This analysis also revealed the importance of night

ventilation during the night, as the temperature reduction

mainly occurs daily from 8 pm until early in the morning.

Another expected finding is the zeroing of time lag as the

operative temperature minimum in space is found to

overlap with the ambient temperature minimum; for closed

windows, an average time lag of 3 h is observed. The

Fig. 2 Investigated Building: a exterior facades, b interior view of

the ‘‘portico’’ [33]

Table 4 Climatic data for July–August for Nicosia

July August

Dry bulb temperature (�C)Maximum 34.8 34.7

Minimum 15.8 20.4

Daily average 24.6 27.3

Monthly statistics for wind speed (m/s)

Maximum 11.8 10.3

Minimum 0 0

Daily average 4 3.6

Table 5 Reduction of operational temperature for cross and single

ventilation

July August

30% 100% 30% 100%

Cross ventilation

Average 4.2 5.4 4.4 5.7

Max 6.5 7.9 6.5 8.1

Min 2.2 2.7 1.9 2.5

Single ventilation

Average 3.1 4.1 3.2 4.4

Max 5.4 5.9 5.0 6.4

Min 1.1 2.0 1.1 2.0

2 Page 6 of 11 J Build Rehabil (2017) 2:2

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impact of the night ventilation on theoperative temperature

is summarized in Table 5.

Figure 4 presents the three dimensional operative tem-

perature contour within space for the investigated thermal

zone (9 pm, 01/07). According to this figure, the temperature

gradient in space is much higher in the case of closed win-

dows, resulting to significant temperature differences within

the same space. This is not observed for the opened windows

simulation, where a more homogeneous temperature distri-

bution in space is observed. This finding results due to the

circulation of the cool ambient air in space; the temperature

differences given in Fig. 3 are also confirmed anew.

As it can be retrieved from Fig. 4, the main reason for

the higher temperature decrease is the fact that the inves-

tigated thermal zone is cross ventilated. As expected, cross

ventilation creates some further issues regarding the high

air velocities that will be observed in the building, which

are not in-line with the thermal comfort prerequisites

(Table 1). To this end, a discussion regarding the allowed

opening sizes towards achieving optimal thermal condi-

tions, presented in the following section, is required.

4.2 Indoor air velocity restrictions in night

ventilation

Figure 5 depicts the indoor air velocity contour for the

investigated thermal zone for closed and opened windows

respectively. In the case of the closed windows, the air

motion is attributed to natural convection and thus to the

temperature gradient in space, whereas in the case of open

windows, it is obvious that the air is in motion due to the

entrance of fresh air in the space. As it can be retrieved

from the presented results the air velocity in space, exceeds

1 m/s in the case of the cross ventilated thermal zone. The

maximum air velocities are found as expected near the

Fig. 3 Night ventilation impact

on operative temperature

Fig. 4 a Operative temperature—closed windows. b Operative temperature—open windows

J Build Rehabil (2017) 2:2 Page 7 of 11 2

123

windows. Regarding the closed windows cases, the air

velocity in space has an average velocity of less than

0.1 m/s.

It can be deduced from the calculated air velocities that

although natural night ventilation in cross ventilated rooms

enables the significant reduction of the operative temper-

ature, the indoor air velocities reached are much faster than

those considered within the thermal comfort range. The

maximum allowable indoor air velocities to meet the cor-

responding draught rating categories of the 7730:2005

Standard [32] do not exceed 0.8 m/s. To this end a further

analysis was conducted assuming partly open windows for

the cross ventilated zones. Based on an iterative process, it

was found that 30% windows opening ensured air veloci-

ties in cross ventilated spaces of less than 0.8 m/s. The

reduction of the windows opening area effects as expected

the temperature decrease due to night ventilation.

In Fig. 6 the indoor operative temperature is provided

for fully opened windows and for a 30% opening per-

centage for the case of the cross ventilated investigated

thermal zones. In this figure the actual limitations of night

ventilation with respect to the allowed indoor air velocities

are presented. According to this figure, the average tem-

perature decrease in the case of cross ventilated thermal

zones was 2.2, whereas the maximum temperature differ-

ence in the examined case was 4.7. Compared to the results

given in Sect. 4.1, it is deduced that limitations in indoor

air velocity may reduce the impact of night ventilation up

to 50%.

4.3 Impact of night ventilation on thermal comfort

Figure 7 presents the impact of night ventilation to the

thermal comfort of the investigated space, as calculated

Fig. 5 a Indoor air velocity—closed windows. b Indoor air velocity—open windows

Fig. 6 Night ventilation impact

on operative temperature—30%

windows opening

2 Page 8 of 11 J Build Rehabil (2017) 2:2

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using the PMV index (see Sect. 3.1). The calculations were

performed by assuming that the air conditioning system

was not in use in both cases. Also a 30% opening per-

centage was considered. The results prove the value of

night ventilation to vernacular buildings in terms of

improving the thermal comfort conditions, as the PMV

index presents a significant decrease. The average PMV

index was found to be 1.1 for the night ventilated thermal

zone, whereas the corresponding number for the non-ven-

tilated zone was 2.25. As it can be deduced from the

results, an average improvement of 51% was achieved in

the investigated thermal zone with the exploitation of night

ventilation.

Although the derived PMV indexes seem to be in the

range of slightly warm to warm in the seven-point thermal

sensation scale, it should be stated that two schools of

thought exist regarding the thermal comfort research area,

namely ‘‘static’’ and ‘‘adaptive’’. The static model meets

the ISO Standard 7730 based on Fanger’s predicted mean

vote (PMV/PPD) [32], as well as the ASHRAE’s Standard

55-Thermal Environmental Conditions for Human Occu-

pancy [35] and it was employed in this study. On the other

hand, the adaptive model, states that factors beyond fun-

damental physics and physiology play an important role in

building occupants’ expectations and thermal preferences.

The way people interact with the environment, their

behaviour changes can modify their thermal expectations

[36, 37].

Figure 8 presents the adaptive thermal comfort levels of

the master bedroom, according to EN 15251 (CYS EN

2007) [38]. For Class II buildings, which is the class tai-

lored for new buildings and renovations, the allowable

maximum difference between this comfort temperature and

the actual indoor operative temperature is ±3 �C. The

analysis of the results showed that the adaptive thermal

comfort levels are mostly satisfied, and only occasionally

Fig. 7 a PMV Index—closed windows. b PMV Index—OPEN WINDOWS

Fig. 8 Adaptive thermal

comfort levels according to EN

15251 (CYS EN 2007)

J Build Rehabil (2017) 2:2 Page 9 of 11 2

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the thermal conditions are out of the ±3 �C set by the

standard.

5 Conclusions

The aim of this study was the investigation of the impact of

night ventilation on the thermal comfort of vernacular

buildings under warm climatic conditions. To this end, the

thermal behaviour of a vernacular building in the city of

Nicosia was numerically investigated. Energy Plus and the

flow solver of Design Builder were employed. According

to the findings of this study, night ventilation may have a

significant impact on the temperature and on the thermal

comfort levels in vernacular buildings. Some restrictions

with regard to the opening percentage were revealed,

resulting from the al-lowed air velocities in space. The

temperature decrease due to natural ventilation was found

to reduce to a factor of 2, the air velocity being within

acceptable levels. Regarding the thermal comfort levels,

these were found to be improved on an average percentage

of 26% with the use of night ventilation. Although the

thermal comfort according to the PMV scale was consid-

ered to be in the slightly warm levels, the implementation

of an adaptive model, would have revealed a better per-

formance of night ventilated spaces.

Acknowledgments Authors are indebted to the research project

‘‘Innovative methods for protection and conservation of sustainable

design elements of vernacular architecture in the historic centre of

Nicosia—Biovernacular’’ for the financial support of this work.

Biovernacular was funded by the European Regional Development

Fund and the Republic of Cyprus through the Research Promotion

Foundation (Project Technological Development and Innovation

De9rlg 2009–2010, AMHQXPIRSIJER/AMHQX/0609/BIE).

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