Indoor Microclimate Conditions and the Impact of Transformations on Hygrothermal Comfort in the Old Ottoman Houses in Algiers

ABSTRACT This article focuses on the assessment of microclimatic conditions in the Ottoman residential buildings in the old city of Algiers. It aims to identify the nature of architectural transformations and to analyse their impact on hygrothermal comfort and the indoor microclimate so as to suggest ways to improve the current level of comfort within the traditional houses. The object of this article is to identify the nature of this transformation process, to find out, not only what triggers it but what fuels it, and to analyse its impact on the environment, or more specifically, on the hygrothermal comfort, within the building. It entails, primarily, an analysis of the colonial and post-colonial architectural transformations, followed by a verification of all the components of hygrothermal comfort through numerical simulation and modelling. The aim is to correct the interior comfort of the current houses in the Casbah. The results obtained will clarify the nature of these colonial and post-colonial changes, which were carried out to satisfy the needs of the inhabitants, and lead to an evaluation of environmental quality, assessed through the parameters that influence the indoor microclimate of houses in Algeria.


Introduction
Algeria possesses a rich heritage consisting of natural, cultural, material and immaterial elements.This heritage can be seen through a set of shared architectural, social, aesthetic, cultural, historical and economic values.The Casbah of Algiers 1 is part of this heritage and is a synthesis of much stratification.Representative of Mediterranean culture, it consists of traditional houses which have retained their authenticity and integrity through their aesthetic features and architectural elements, as well as through the materials used.The preservation of their original aspect and value has earned the Casbah a place on the World Heritage List since 1992.

Research aim
This work is part of a multidisciplinary research, focusing primarily on the environmental issue.Although the Casbah in Algiers has been the subject of numerous historical, urban, architectural or socio-economic studies (Abdessemed-Foufa 2011;Chergui 2011;Ebru Karabag and Fellahi 2017;Hadjri 1993;Icheboudene and Nacib 2003;Kacher 2013;Lesbet 1985;Ravéreau 1989;Zidelman and Belakehal 2016), the environment, sustainability and interior comfort of its residential heritage are rarely been addressed.Our approach is in line with this research and aims for innovative and practical results.
This research work will, first and foremost, lead us to an understanding of the ingenuity of architectural practices in Algiers, from which solutions and recommendations can be made to improve the current conditions of comfort inside the houses of the Casbah.Our objective is to address this rich residential heritage and analyse its degradation in terms of the interior microclimate.

The bioclimatic aspects of the Casbah in Algiers (comfort/discomfort)
The Casbah of Algiers, as illustrated in Figure 1, is the product of an intermingling of social and cultural elements steeped in history.It represents the complex superposition of several historical strata where cultures, either adopted or rehabilitated to fit a way of life, have been preserved.
Due to its central geographical location in the Maghreb, the medina has, historically, occupied a strategic position within greater Algiers (Pasquali 1951).Once bordered by remarkable fortifications, it is built on a hill and traversed by winding streets.Its urban planning is typical of the Arab-Berber period.According to Ravéreau (1989), it is this site which has created the city.Algiers, like any other Mediterranean city, has a climate characterised by hot, dry summers and mild, humid winters.However, the passive comfort inside these traditional houses seems to have been ensured without the need of sophisticated household appliances.In fact, the tiered structure of the buildings, which follow the slope of the land, as well as their southeastwardly orientation, allow them to enjoy the benefits of the morning sun until well into the afternoon.Their alignment in a direction opposite to the prevailing northwest wintry wind provides additional protection and contributes to winter comfort.(Lespes 1930).
Furthermore, the sloping relief of the land gives rise to two clearly differentiated paron one side, al-djabal, the upper part, overlooking the sea, and on the other, al-wata, the lower part, adjacent to the coast (Haedo 2004).In the upper area, where the buildings are dense and the streets winding, there are residential areas with local shops and oratories.In the lower part, on the other hand, where the roads are regular, following an orderly route, its proximity to the city gates favours the concentration of its economic, spiritual, political and administrative functions.Our study focuses on the residential area of the Upper Casbah.
According to a brief description by Glovin (1988), the traditional houses of the Casbah share certain fundamental characteristics.First of all, they are two storeys high and arranged around a central space (patio with arcades).They possess a skylight and Chebâk (shielded ventilation).All the rooms are disposed around a central space (arched patio) with an accessible terrace above and often, because of the slope of the land, a basement below.A menzah, supported by the upper part of the house, occupies the western part of the terrace.
These houses are composed of three important elements, as is represented in Figure 2: the Sqifa (an entrance space, a permanent feature in the houses of the medina, constituting a transition between public and private space); the wast-al-dar (centre of all the rooms in the house); and the biouts (rooms).Service spaces or basements occupy the spaces created by the slope of the land which reach up to the level of the ground floor by following the shape of the ground.The houses are attached to each other and can communicate with each other via the stah (terraces).In fact, the importance of terraces in houses facing the sea has been emphasised by Le Corbusier (1994).
The medina is a combination of factors dictated by nature and human know-how.Dr Shaw testifies (Shaw 1983) that, in Algiers, at the beginning of the eighteenth century, fairly solid square-shaped houses were generally built from traditional materials which could be found locally.These included solid clay brick (used for the construction of load-bearing walls, foundations and vaults), stone (used in the form of rubble to build ground floor walls and foundations, combined with brick) and slaked lime (mixed with sand and other elements such as wood and oil).The central courtyard, a feature of almost all the houses in the Casbah, is paved with marble.This is proportionate to the size of the house and is surrounded by galleries, supported by columns, where the apartments are located."Algerian cedar wood" is used for corbels and staircases, beams, consoles, doors, balustrades and shutters.
In general, the quest for comfort has been recognised as one of the first human driving forces behind man's need for shelter (Lucchi 2016).Consequently, comfort is defined as the relationship between the individual and his environment and as such, needs an interdisciplinary approach (Nicol and Humphreys 2002).Moreover, its concept has evolved over the passage of time, influencing architectural design (Pigliautile et al. 2018).During the Antiquity and the Middle Ages, comfort was related to space.Before the French Revolution, it was concerned with ornament while, in the middle of the twentieth century, it became associated with sanitary conditions and the desire to meet the needs of the user.Today, the idea of comfort is linked to environmental concerns (Moser 2009).Since hygrothermal comfort is recognised as the main objective of this approach, any effort to improve human living standards should not compromise the natural or living environment (Croiset 1968).
The quest for comfort was once a major concern for the population of the Casbah (Ravéreau 1989) and is represented in Figure 3.It influenced the choice of site and the position and size of the apertures.The aim was to create a place that not only benefited from the climate but limited its negative effects to provide a living space in perfect harmony with the environment.In fact, this approach to climate management remains the main objective of traditional architecture today (Di Turi S. et al. 2017).It is now recognised as a bioclimatic architectural design that considers the impact of environmental components, such as temperature, humidity and wind velocity, both on the environment and on hygrothermal comfort (Carmen Ma Muñoz-González et al. 2018).
Throughout the colonial and post-colonial periods, these authentic houses continued to undergo various transformations as the inhabitants strived to reach certain levels of modernity.The result is the superposition of two architectural models (local and colonial) which reflect two different ways of life (ancestral and contemporary).These architectural transformations, most often considered in a negative light, directly impacted their hygrothermal comfort and their environment.In the context of these particular environmental, political and social challenges, residential buildings in the old city of Algiers are facing significant deterioration which has had irrevocable consequences in terms of discomfort ((PPSMVSS, 2017)). 2 2 Permanent Plan for the Safeguarding and Enhancement of Secured Areas is presented as a tool for the management and protection of built and urban cultural heritage, with the aim of preserving historical values.The concept comes from Law 98.04 of June 15 1.3.The typologies and characteristics of houses in the Casbah of Algiers Various studies have been carried out on the typology of traditional Algerian houses in order to establish a typological classification.For the purpose of this study, it is necessary to mention two of the most influential.Firstly, the work carried out by the Atelier Casbah (1981), on the typologies of housing in the old city, helped us identify both the original and converted types (see Figure 4).Secondly, a more recent study (Missoum 2003) on a house in the medina of Algiers, defines the terminology of domestic architecture used in Ottoman archival documents, and focuses on three specific terms: dar (house); dwira (small house) and ulwi (attic).
1.3.1.House wast al-dâr (with patio) This is the most common typology and takes the form of an introverted dwelling.It is characterised by the organisation of spaces around a central patio with porticoes, divided by a gallery of arcades.The patio is geometrical in form and the surrounding rooms match the shape of the ground.The vertical distribution of the house is organised on two distinct levels which are connected by a staircase.

House with chebâk
This is a small house built on two levels, with a terrace and, sometimes, a basement.It is organized around a covered or semi-covered wast-al-dâr, with a chebâk, t through which both air and light enter the building.This is a rectangular opening in the ground, protected by bars, and is located on one side of the wast-al-dâr.Service spaces often occupy the ground floor and the basement is sometimes used as a shop or warehouse.

House with ulwî (attic)
This is a tall house without a patio which generally has no outside gate.Due to high urban concentration, it occupies a small parcel of land and is pierced with large openings to the street.This work addresses two case studies of the Chebâk typology and identifies the nature of the changes that both have undergone, one with positive results; the other with negative.The results obtained from dynamic thermal simulation and in situ measurements were compared to those of a previous work (Benchekroun et al. 2018), which addresses two case studies of the wast-al-dâr typology.Here, the results obtained, also through simulation and modelling, similarly show one case of positive change, and another of negative.This research gave us the chance to study a typology particularly well adapted to the Casbah of Algiers.

Transformation process and its impact on thermal comfort
French colonization greatly modified the site of Algiers and its medina.Major urban planning operations were carried out between 1830 and 1866 which saw the demolition of many of the Muslim city's buildings as well as the construction of new roads around its upper region.These changes not only affected the urban structure of the town but also impacted the buildings built along its axes (Lespes 1930;Oulebsir 2004).At the end of the nineteenth century, the French introduced the Haussmann style, resulting in irreversible changes within the traditional houses, both in those with a patio and those with a chebâk.
After Algeria's independence, most of the original families moved out of the Casbah to live in European apartments, leaving it vulnerable to the effects of a rural exodus which caused overpopulation and overcrowding.It became a place of transit and asylum for the poor (Dris 2002) as the original inhabitants were replaced by rural people whose aim was to leave the district as soon as possible.Some even deliberately degraded their homes to receive social housing.
The observations made by the Casbah Workshop in 1981 underline the state of degradation of the Casbah of Algiers.Highlighting the causes of its degradation, they link it to high densification, a phenomenon resulting from socio-economic change.Due to the increasing number of families sharing the same dwelling, its functions were modified, resulting in spatial transformations (Benchekroun and Chergui 2017).Some of these changes are illustrated in Figure 5 of this work and include the introduction of elements of minimal comfort and the use of new building techniques.These impacted on the spatial and aesthetic aspects of the spaces by transforming their function and modifying their architectural decoration.The first part of this study focuses on the redistribution of spaces, with all its consequences, and the disintegration of the architectural model.The result is a new type of housing with interior partitions and openings towards the outside (drilling or widening of openings in the façade).Terraces have been extended and extra storeys added, thus modifying the size of the house.Nevertheless, our research will show that by far the most important change came through the introduction of new modern comfort zones associated with new functions (bathroom, lounge, dining room).This meant the introduction of new materials (reinforced concrete, cement, beams and slabs, modern bricks, hydraulic mortars and cement lacquers) to replace or co-exist with traditional ones (earth, lime, cedar logs, old bricks and rubble), the use of new construction techniques (introduction of metal beams and brick arches to replace the original cedar wood) and the substitution of architectural elements (gallery railings or balustrades; doors; elements of joinery; old ceramic flooring) (PPSMVSS).
The remainder of this study is organised into three parts.Section 2 describes the methodology used to conduct our study.Section 3 presents our findings which are finally analysed in section 4 with the appropriate conclusions drawn.

Material and methods
Our research aims to address a two-fold problem: that of colonial and post-colonial architectural transformations to residential buildings, on the one hand, and hygrothermal indoor comfort, on the other, and how they affect man's relationship with his environment.To achieve our objective, and obtain convincing results, we adopted several appropriate, scientific methods and studied documents related to the subject.Our methodology consists of the following steps: • Case studies and surveys

Case studies and surveys
Our area of research corresponds to the Upper Casbah (see Figure 6a).This is the most well-preserved part of the medina with high-density housing.It contains the highest number of functional houses that have characteristics relevant to our study.These houses are representative of all the typologies of the Ottoman period, irrespective of the changes they have undergone.They belong either to a main category (authentic houses with original elements preserved) or a sub-category (houses that have undergone spatial transformations, adapted to new functions).This study focuses on the chebâk typology which is the most common typology in the Casbah, after that of the wast-al-dâr, the subject of a previous study (Benchekroun et al. 2018).
Our two case studies, one showing positive changes, the other negative, are both houses belonging to the same typology.They are both located in the same area of the same district and share the same topography.They both benefit from the same climatic conditions.In order to identify the changes each house has undergone, and to study their impact on interior comfort, we used the OGEBC3 archives.These allowed us, first of all, to identify the original state of the buildings under study.A preliminary on-site investigation was, then, carried out to assess the current state of the property and to identify those changes which date back to the colonial and post-colonial period.
For the purpose of this investigation, archival documents (plans) were updated, using a counter and a laser (a) The original state of case "A" range finder.These tools allowed us not only to take current readings, but to restore and update the old ones, thus identifying the architectural transformations.
This approach consisted of collecting field data from the selected houses, which was, then, analysed and classified according to both nature and category, by referring to a model technical sheet taken from examples of previously published brochures (Cherif-Seffadj N. et al. 2012;CORPUS EUROMED 2017).The data were organized in two ways: from typological recognition, dealing with physical and social information, on the one hand, to the identification of the altered components, on the other.bedroom, was extended after Independence to include a kitchen and an accessible terrace.
This house has undergone several transformations.At the level of the sqifa, for instance, a functional change has taken place, converting a former coffee production plant into a kitchen.A small bathroom with a toilet has been added and the floor covering has been changed.The position of the outside door has been modified and a window has been filled in.On the first floor, the old wooden ceiling has been replaced by a false one (a postcolonial constructive technique) in an attempt to combat wood moisture.It is a privately owned house and the occupants are the original owners.This explains the continued upkeep of the building (the walls are whitewashed every year).On the second floor, a false ceiling now takes the place of the traditional wooden one.A new window has been cut into the wall of one of the rooms and two water points (sinks) have been installed.In the menzah (a terrace overlooking the site and the sea), an extension has been added to include a kitchen with a floor, composed of metal joists fixed to a brick vault, in very good condition, dating from the colonial period.Other changes include the opening up of three new windows, the installation of a toilet and the addition of an elevated concrete floor (accessible terrace).New electronic devices or appliances have also been introduced and include 2 computers, 2 televisions, 2 refrigerators, 2 air conditioners and 2 stoves.and bathroom between the ground floor and the next level.This upper floor has a small chebâk and large rooms.The menzah has two rooms and an accessible terrace.
This house has undergone several transformations, as is shown in Figure 7. On the level of the sqifa, the changes have been functional.Two stores have been converted into two poorly lit and poorly ventilated rooms.A bathroom with a toilet has been built over a non-functional well, which has been blocked up, leaving the house vulnerable to rising humidity.On the level of the first floor, a new window has been added and the traditional wooden ceiling has been replaced by a false one.This is in a severe state of degradation due to water infiltration, which has caused damp and loss of material.The house is privately owned and has seen an increase in the number of occupants (4 families, 18 people) who are not the original owners.Thus, any alterations carried out at the property have been made without the advice of competent specialists.
Finally, at the level of the menzah, the chebâk has been covered over which has reduced the entry of both air and light.The subsequent space has been divided into two rooms, each one housing a family, with a new opening for each room.The floor dates back to the colonial period (corrosion of metal joists).The use of new materials in the form of cement and glycerophtalic paint does not allow the walls to breathe, which has resulted in a high level of humidity, with damp on the level of the floor (presence of mould).New electronic devices have been introduced: 1 refrigerator; 1 boiler; 1 washing machine, 1 stove, 2 computers, 2 air conditioners and a fan and 3 televisions.Due to a lack of maintenance, this house suffers from poor ventilation and lighting, which results in foul odours.

On-site measurements
These results, as shown in Figure 8, are based on the findings of a measurement campaign which was conducted during the summer and the winter of the period 2017-2018 (during the month of August and January).For each of the three typologies, two sample houses were studied (one in its original state; one converted), making a total of six houses in all.The choice of this measurement method was influenced by previous studies dealing with the same subject (La Gennusa et al.Fato, and Di Turi 2016).In order to measure the thermo-hygrometric parameters (temperature, relative humidity and air velocity) in relation to ISO 27726, this measurement campaign was carried out under the normal living conditions of the inhabitants and with the same number of people.All the original and converted living spaces were measured using three instruments, two automatic and one manual, as is represented in Figure 9: • Data logger and data acquisition system, Fluke Hydra 2635A Series II with six thermocouple connections, 4 K types and 2 T connections, illustrated in Figure 9a was placed in the spaces of the first and second floors (four rooms and two chebâk).
• Four internal temperature and humidity miniloggers of the Testo 174H, 2018 (see Figure 9b) were pre-programmed to start and stop at specific dates and times.For our case study, sample readings were taken every minute for every 24 h, in keeping with the UNI 10586 recommendations, so that thermo-hygrometric data could be continuously recorded.Once the recording was finished, the data were transferred to a computer and analysed.These devices were placed in the ground floor kitchen, first and second-floor bedrooms and the menzah kitchen.• A manually operated TMA5 anemometer (Figure 9c) was used in all the spaces.This is a compact pocket tool used for measuring indoor air temperature, humidity, ventilation and air condition.

Thermal dynamic simulation
Thermal dynamic simulations were carried out using the Design Builder v.4.8 software.This is the first complete user interface for the Energy Plus thermal simulation engine.In this study, dynamic thermal simulation was used to evaluate the performance of the two houses under study in terms of energy efficiency and comfort.
The objective was to compare the difference, not only between the two houses, but also between their original and converted state, to see if this has had an impact on interior comfort.Moreover, the volume of the two case studies was created to analyse the effects induced by temperature, humidity and ventilation as well as the PMV "Predicted mean vote" (ISO 7730).
Our work with Design Builder began with the construction of our models (the houses of the Casbah of Algiers).First, the site was selected from a predefinition of its location (geographical situation defined as "Algiers") and its climatic data (introduced by the meteorological file).Then, the geometric shapes of our models were developed by means of the 2D drawing by Autocad.The data of the models obtained were established as follows: • Activity data: We were able not only to define the function of each zone and the density of occupation [number of people present, hours of occupation, occupation period (typical/scheduled day)] but also introduced metabolism activity (total heat emission per person which includes convective gain, both radiant and talent) and selected the different clothing levels for both the summer and winter periods.We also included data for the current state of the house such as the input from computer equipment, kitchen appliances and air temperature control systems (heaters and air conditioners).• Construction data: In this step, we were able to define the contiguity of some of the walls by selecting those components that modelled heat conduction through walls, roofs, floors and all the opaque elements of the building shell and by adapting the thermal properties of traditional materials.
• The openings: In this software, these are treated as building exceptions and include windows (interior, exterior glazing and, for case A, in its original state, roof glazing), holes (for arches), doors and vents (often located above the windows or at the level of the stairs).We were able to model both their position and function.
• CVC data: loaded from the HVAC 4 Model.We selected natural ventilation for the house in its original state, and input for the house in its current state [auxiliary energy (Domestic hot water (DHW) is modelled in our models by  Heating, ventilation, and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort.Its goal is to provide thermal comfort and acceptable indoor air quality.HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer."HVAC".Merriam-Webster Dictionary.
a boiler that heats the building, heating (the type of heating is convective, the space is heated by an air system and controlled by a setpoint on the injected air temperature. The system is modelled using the Energy Plus ideal loads system) and air conditioning (the system selected for our models is a split air conditioner and the fan)].
Once all the input parameters were defined, summer and winter simulations were carried out for both "A" and "B" cases, in both their original and converted states.The aim was to examine thermal behaviour, energy consumption and environmental conditions for all the spaces selected and to analyse the effects of thermal and energy profiles on the converted cases.

Model validation
Readings were taken in August (summer) and January (winter).The results presented in Table 1 and in Figure 10 correspond to the average temperature and humidity recorded on a typical day.Model validation was an important step in our study in order to ensure convincing results.This was done by drawing up a table to include all the spaces where temperature, humidity and ventilation were measured.Furthermore, all the values collected over the 24 h of a typical day were added to give an average hourly reading, which was compared to the one simulated under the same conditions and for the same spaces.By using a specific mathematical equation (see [1]), we were able to calculate the error rate in accordance with the method developed by (Petrone et al. 2016;Shafqat and Oosthuizen 2012).
Error ¼ the measured value À the simulated value the measured value Â 100 (1) The results discussed in this section, and the onsite measurements appended in the index were added (as shown in Figure 10 and Table 1) to give a more detailed study.
Several studies have been carried out on model validation (Ferdyn-Grygierek 2014;Huijbregtsa et al. 2015;Masoumi, Nejati, and Alah Ahadi 2017;Shafqat and Oosthuizen 2012).For our study, we adopted a method that enabled us to compare the models to each other so that the given assumptions could be either confirmed or refuted.The results of the simulation were compared to those taken on site.For the purpose of this research, we focused on the validation of the model for indoor temperature and humidity because these are the two most important factors for indoor comfort in the two case studies.Figure 10 gives an example of a comparative reading between the in situ results and those simulated by Design Builder for all the strategic places throughout Case A, on a typical summer day, with regard to these two parameters.Other examples, using the same method, are included in the appendix.
The figures show that, for Case A, the summer temperatures remained constant, varying between 20°C and 28°C, with the Menzah as the hottest space.The humidity varied between 45% and 67% for the same period.According to JY Charbonneau and Fanny Provencal (Charbonneau and Provençal 2004), relatively low levels of humidity, temperature and air velocity help to make an optimal comfort situation.Table 1 shows the temperature and humidity variations and includes the rate of error between the two sets of results (in situ/simulated).For the model to be validated, the average rate of error for 85% of the cases should not exceed 5% (Shafqat and Oosthuizen 2012).In our research, based on the numerical calculations obtained, the error rate was relatively low: the simulation values were sufficiently close to those taken on site.The curves of the graph show a high degree of convergence.Thus, we were able to conclude that the model presented was accurate enough and could be used for the thermal calculations of the building.

Results and discussions
Indoor microclimatic conditions were analysed from graphs showing temperature fluctuation, ventilation, humidity and the PMV index for the two case houses in both their original and converted state.These simulate results represent microclimatic conditions for two typical days in each of the two seasons (summer from March 21 to October 22; winter from October 23 to March 21) and correspond to the measurements taken in situ in the same week and on the same day.
The Predicted Mean Vote Model (PMV) is considered to be the most recognised model in thermal comfort standards.The analysis of this model, in both naturally ventilated and air-conditioned buildings, reveals a percentage of either underestimation or overestimation.The PMV index predicts the average vote value for a large group of people, measured on a seven-point thermal sensation sca+ 3 very hot; + 2 hot; + 1 slightly warm; + 0 neither hot nor cold; -1 slightly cold; -2 cold; -3 very cold.To obtain a satisfactory thermal comfort situation, the PPD should be less than 10% which corresponds to a PMV of between -0.5 and +0.5 (Syed Ihtsham ul Haq Gilani et al, 2015).
For Case A, the difference in temperature fluctuations (presented in Figures 11 and 12), between the house in its original state and its current one, is minimal.The average maximum temperature in both cases is 30°C on account of thermal inertia, which reduces the fluctuations and acts as a temperature stabilizer.Thermal inertia is the ability of the house to absorb heat, store it and release it slowly.For humidity and ventilation, however, the disturbances are significant, which confirms the destabilisation of air circulation due to certain alterations that the house has undergone.In both the original and converted case, the humidity is estimated at between 40% and 60% which can be explained by the different thermal gradient associated with the thermal inertia of the building walls.In the former case, ventilation and air distribution are natural; in the latter, it is artificial and readings vary between 0 and 70 kWh coinciding with an increase or decrease in temperature.The PMV index, which represents the sensory comfort felt by the user, is, during the summer period, between 0 and -1 for the house in its original state, and between 0 and -2 for the house in its current state.In the winter period, it is between 0 and 1 for the original house and between 0 and 2 for the house in its current state.As the figures show, there is very little difference between the house in its original state and its transformed state.The thermal sensation is cool for the summer and warm for the winter: thus, creating a feeling of comfort in both seasons.
For Case B, as illustrated in Figures 13 and 14, the house in its original state shows a constant difference between the indoor and outdoor temperatures, confirming a balanced temperature transmission.In comparison, however, the house in its current state shows almost no difference between interior and exterior temperatures, indicating insufficient transmission created by the architectural changes it has undergone.With regard to humidity levels, significant differences between the two house states can clearly be seen, ranging from 60% to 65% for the house in its original condition, and from 60% to 80% for the house in its current state, during the summer season.During the winter period, the levels range from 60% to 65% for the former house and from 65% to 70% for the latter.For the former case, ventilation is natural and air transmission inside the house is constant, with no disturbance.For the latter, peaks of 180 KWh (summer period) and 160 KWh (winter period) can be observed.These figures can be explained by the phenomena of thermal inertia, humidity, air intake and outlets due to the presence of heating and cooling appliances (air conditioning) which affect the temperature.
During the summer period, the PMV index is between 0 and −2 for the house in its original state, and between −2 and 5 for the house in its current condition.During the winter period, it is between 0.5 and 2 for the original house, and between −1and − 3 for the current house.This can be explained by the level of humidity created by the heating system in winter and the cooling system in summer, relative to the volume of energy provided by them.
It is recommended that for optimal comfort, an air temperature of about 22°C should be maintained, with a relative humidity level of between 40% and 60%.The movement of air should be at a rate of 0.5 to 1 m/s allowing people with little activity to feel a comfortable freshness.In warmer places, to provide satisfactory relief, speeds of 1.25 to 2.5 m/s are needed (Schreiber 1985).

Conclusion
The building sector has always been subject to change, fuelled by the demands of function and performance.Until the post-modern period, change meant the construction of new buildings to the detriment of architectural masterpieces.However, in recent years, the trend has been towards the renovation of existing structures, taking into account current comfort conditions.This study takes a novel approach in assessing both the impact of the historical indoor climate on two traditional houses of the Casbah in Algiers and the risk of deterioration of their indoor comfort.The methodology developed combines modelling, hygrothermal simulation of the building (temperature, humidity, ventilation and PMV) and a historical approach (an examination of the layers of change these houses have undergone over the centuries).This method has shown that the reconstruction of the historic climate of a house is possible from which might arise optimal changes, that could meet the demands of current comfort.It is possible to reconstruct climatic conditions that can be tested on site.It was important in this study, therefore, to obtain a finite element model that could accurately describe the two cases.
This research work correlates two case studies of houses belonging to the same typology.The results obtained both by simulation and from in situ measurements, show that house B suffers from overheating: the internal temperature is higher than the external one.This is due to the different alterations that have been carried out by the residents without expert advice, including installation of toilets, the opening of new windows and the obstruction of others.The use of new materials (concrete, paint, plastic) has resulted in a remarkable difference in temperature which has influenced air circulation and created a destabilisation, causing a high level of humidity.It is, therefore, a case of negative transformation on the indoor climate of the house.House A, on the other hand, shows a positive transformation in terms of indoor climatic conditions.The minimal and well-established alterations have not affected the indoor comfort of the house.
The aim of this work is to recommend a series of renovation solutions, illustrated through Case "A", that fulfil the current comfort requirements of the occupants without the risk of condensation (deterioration of the framework) or other problems.In order to allow air to circulate and sunlight to enter the building, it is important not to cover the chebâk or close the roof, thus, avoiding humidity on the floors and walls.The natural ventilation of the house can be improved by avoiding the obstruction of apertures or the opening of new ones.The installation of modern ventilation devices should be undertaken in a calculated way (need, functionality, position).Traditional construction techniques should be adopted and local materials used in order to prevent decay and to improve the durability of the building.These should include earth bricks and lime, or water repellent products, such as "water repellent paint or waterproof coating" that allow the walls to breathe and reduce humidity levels.Toilets, bathroom and water points should be installed along the same axis as waste water evacuation.The installation of kitchen appliances, computers and air conditioning and heating equipment must be done, not only according to need but also in consideration of their strategic position so as to avoid overheating which inevitably leads to discomfort.
diagram of natural ventilation in the house of the Casbah (b) Cut on a house has patio at the Casbah of Algiers (c) Constructive detail of a wall at the Casbah

Figure 5 .
Figure 5. Transformations suffered by the Casbah of Algiers.(Source: (a): Atelier Casbah; (b): authors) (a) The original state of case "A" (b) The current state of case "A".

Figure 6 .
Figure 6.(a) and (b): Current house of case "A" and its transformations.(Source: authors) (a) The original state of case "B" (b) The current state of case "B".

Figure 8 .
Figure 8. measurements made during the month of August and January.

Figure 10 .
Figure 10.Example of comparison between the measured and simulated results of Case "A" during the summer period for temperature and humidity parameters on a typical summer day.(a) OLD CASE "A" IN SUMMER PERIOD.(b) CURRENT CASE "A" IN SUMMER PERIOD.

Figure 11 .
Figure 11.Results obtained by simulation of case "A" in its current and former state during the summer period.(a) OLD CASE "A" IN WINTER PERIOD.(b) CURRENT CASE "A" IN WINTER PERIOD.

Figure 12 .
Figure 12. Results obtained by simulation of the case "A" in its current and former state during the winter period.(a) OLD CASE "B" IN SUMMER PERIOD.(b) CURRENT CASE "B" IN SUMMER PERIOD.

Figure 13 .
Figure 13.Results obtained by simulation of the case "B" in its current and former state during summer period.(a) OLD CASE "B" IN WINTER PERIOD.(b) CURRENT CASE "B" IN WINTER PERIOD.

Figure 14 .
Figure14.Results obtained by simulation of the case "B" in its current and former state during the winter period.

Table 1 .
Comparison of measured and simulated values of temperature and humidity for the case "A" in summer (Source: authors).