A new decade for social changes

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A new decade

for social changes

9 772668 779000 ISSN 2668-7798

www.techniumscience.com

Vol. 36, 2022

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Assessment of building design and overheating on occupants’

thermal comfort and energy performance considering self- build houses in a hot arid urban environment

Sara Ouanes¹, Leila Sriti¹, Mohamed Amine Khadraoui²

1 Laboratory of design and modeling of architectural ambiances and urban forms (LACOMOFA), Department of Architecture, Mohamed Khider University of Biskra, BP 145 RP, Biskra, 07000, Algeria, ² Department of Architecture, University of Bejaia, Algeria

[email protected], [email protected], mohamedamine.khadraoui@univ- bejaia.dz

Abstract. In recent years, energy conservation issues, environmental problems and their consequences on public health have increased interest in climatic responsive design to achieve better thermal comfort conditions inside the building without enhancing energy consumption. As people spend most of their time in interior spaces, indoor thermal conditions significantly impact their health and wellbeing. Extended exposure to extreme temperatures might cause heat-related illnesses, respiratory and cardiovascular diseases, or death. This paper evaluates the indoor thermal environment generated by the residential buildings’ fabric under overheating conditions.

The study was conducted during the summer in a typical residential district in Biskra (Algeria).

To assess the thermal response of the buildings’ fabric by taking into account the natural and social context of Biskra, as well as, the energy consumption behaviour of householders, a dynamic simulation study was performed over 115 self-build houses. The results showed that indoor thermal conditions in the analysed building were far from the optimum comfort air temperature except when using air conditioners. The most unfavourable conditions were reported in July and August when the air conditioners have to run full time to mitigate the effect of overheating. This implies that houses are poorly designed and failed to deal with overheating.

To address with this issue, the residents are constrained to use air-conditioning most of the time to achieve thermal comfort which leads to increase in energy usage. Finally, despite the government reduced the cost of electricity and gas bills by 65% in southern provinces as a financial support for householders, serious problems of discomfort remain in the prevailing housing stock. Legislation and measures must be taken and enforced at provincial and local level regarding housing which should include energy efficiency and thermal comfort.

Keywords: Thermal comfort, energy efficiency, building design, occupants’ behaviour, urban housing, hot arid climate.

1. Introduction

In the last decades, environmental problems and energy conservation issues have increased interest in climate responsive design strategies to achieve better thermal comfort conditions inside buildings without enhancing energy consumption for heating and cooling needs. Environmental performance of buildings is related to various factors including climate,

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Technium Social Sciences Journal Vol. 36, 725-734, October, 2022 ISSN: 2668-7798 www.techniumscience.com

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location, construction features, material specifications, design strategies, the efficiency of the installed HVAC (Heating, ventilation, and air condition) system,… etc. However, recent studies with occupant-based focus have shown that human behaviour significantly impacts energy consumption, even more than building design [1] .

In this regard, creating suitable living spaces is greatly influenced by the physical structure of the built environment in different levels of design including climate characteristics, site integration, urban planning and envelope features. In return, occupant’s interaction with the building should not be underestimated. Therefore, energy usage of household does not only depend on the performance of the building HVAC systems but also on the life style of the occupants. A building must be energy-efficient and provide comfortable indoor environment to the occupants. If suitable indoor conditions are not provided, the occupants take alternative measures to achieve the desired environment. Such measures include heating or cooling the space by using heaters, air conditioners and ventilation systems. In all cases, these adjustment measures increase the energy consumption and the cost of electricity and gas bills for households. While discussing thermal comfort, it is remarkable to notice the amount of literature devoted to this subject, on the other hand, the energy consumption behaviour of the residents to achieve satisfactory levels of comfort remains a relatively under-studied topic.

In general, thermal comfort is difficult to measure since it is very subjective and may change from a person to another and involves a contextual response. Nevertheless, indoor thermal environments that form the thermal conditions suitable to the majority of the occupants are categorized and called the thermal environmental conditions for human occupancy developed by the American Society of Heating, Refrigerating (ASHRAE) and HVAC Engineers [2] . The ISO and ASHRAE Standards deal with comfort matters in a similar way to provide comfort standards. There are two main thermal comfort models used by ISO and ASHRAE standards: 1) the predicted mean vote (PMV) and the predicted percentage dissatisfied (PPD) models; 2) Adaptive thermal comfort models. The first one was introduced by Fanger based on climate chamber experiment. It is also called PMV/PPD model of thermal comfort. The PMV model consists 7-point thermal sensation scale ranges from (+3) Hot to (-3) Cold. The model was later adopted as ISO standard. The second model is adaptive comfort model. It consists three categories, physiological adaptation, behavioural adaptation and psychological adaptation. In this model the occupants adapt the surrounding environment to suite their expectations by changing their metabolic rate (activity), clothing (rate of heat loss) or using control systems (windows, fans, blinds, doors) [3] .

According to the thermal comfort models, the occupant’s thermal comfort can be evaluated by means of thermal metrics including the air temperature range [4] . The effects of exposure to low and high temperatures on health have been the focus of many studies [5] . Discomfort can lead to dysfunction of the body’s heat regulating mechanism and can affect the physical health of a person. In general, the optimal range where the human body’s thermal regulation can adjust the climatic conditions extends from 15°C to 25°C [6] . Numerous studies reviewed the correlation between thermal indoor conditions and the health situation of the occupants, particularly as it relates to the health of those most sensitive to temperatures outside the range [7] –[9] . One study [10] reported that pupils experienced symptoms in free-running classrooms in hot weather included nosebleeds, sweating, tiredness and lack of concentration.

Keeping indoor temperatures within the limits of 18.4°C and 24.3°C with a relative humidity of 55% promoted and maintained the perceived health and wellbeing of the occupants –mostly older people-. Nevertheless, energy cost concerns often inhibited the implementation of cooling/heating devices even when temperatures were perceived to be uncomfortable (over 28°C/ below 15°C) [11] . Moreover, due to uncertainties in thermal comfort perception in

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homes, the WHO guidance for air temperatures range from 18°C and 24°C is directed to protecting health [9] .

As people spend most of their time in interior spaces, indoor thermal conditions significantly impact their health and wellbeing. The problem is even more complex in regions with hot and dry weather conditions where extended exposure to extreme temperatures might cause heat-related illnesses, respiratory and cardiovascular diseases, or death. Algeria is the largest countries in the African continent. It comprises more than two million square kilometers of land, more than four-fifths of which is desert. Considering the harsh climate of Algeria, air conditioning, ventilation and electric lighting, account for up to 40% of building energy and national electricity consumption [12] . In southern Algeria where a desert climate prevails, cooling energy demand accounts for the highest share of energy consumption in buildings.

Furthermore, there is no policy or measures relating to energy efficiency and thermal comfort and most of the houses are not designed by professionals. As a consequence, the existing housing stock does not provide optimal indoor thermal comfort. This situation is further exacerbated by the poor thermal performance of exterior building envelope; in particular, solar radiations and heat gain through windows, exterior walls and roofs represent a significant component of the cooling load and consequently a major contributor to energy consumption in hot climates [14] . As a result, domestic energy efficiency improvements are commonly encouraged to mitigate their contribution to climate change, lower their energy costs, and improve the comfort and health for the residents [9] . Passive design strategies at urban and building scales have been largely adapted for building thermal and energy efficiency in various climatic conditions because the indoor environment is affected by surroundings and building design.

In recent years, the quality of housing programs in Algeria has been improved significantly. However, most of the existing houses have been constructed without any concern for passive design strategies that could have fitted these buildings to such sensitive climate conditions. To deal with this issue and to choose the best design strategies for the residential buildings, it is very important to know the actual situation of the indoor environment in terms of thermal comfort and energy consumption. Accordingly, the goal of this research is to analyse the indoor environment of typical residential buildings in Southern Algeria, in order to evaluate their thermal comfort conditions and to determine the influence of building design on comfort and energy demand. The study also attempts to understand how the energy consumption behaviour of the residents impacts energy demand with regard to acceptable indoor comfort levels. It, also, aims to develop possible renovation strategies for existing buildings as a solution to reduce operation of air-conditioning systems and to achieve savings in the total energy consumption of buildings.

2.Methodology

2.1.Location and climatic characteristics of the study area

The study was conducted in the city of Biskra. It is located in the southeast of Algeria at 34°5' North latitudes and 5°43' East longitudes (Figure 1). According to Köppen climate classification Biskra falls in hot desert climate (BWh, in the Köppen climate classification).

Typically, the climate of Biskra is extremely dry and arid; with hot summers and cold winters.

Biskra has substantial variations between winter and summer. The extreme minimum temperatures can go as below as 3°C in the cold season; in return, the maximum temperatures can exceed 45°C in July (Figure 2); annual mean temperature is about 22.8°C, relative humidity does not exceed 40%, while rainfall is irregular, rare and does not exceed 125mml/year. These

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climate variables are based on the long-term weather patterns between 2000 and 2009 from the Meteonorm database [14] .

Figure 2.Daily temperatures over a year in Biskra [10]

2.2.Description of the case study

This research focuses on the thermal behaviour of 115 buildings in a residential district during the hot season. The investigation area was 200 x 200 m² urban grid that comprised 115 self-build double row houses distributed over 9 street blocks (Figure 3). The emergence of

“new” social paractices in the construction of these houses that are completly different from the traditional practices poses serious problems of discomfort in the prevailing housing stock. Self- build owners usually make custom layouts and façades after receiving their building permits.

The building blocks are created by the city council and follow an orthogonal grid where streets intersect at right angles to each other. The walls use one layer of thermal mass (mostly 15 centimeters thick hollow brick: lightweight material), plasterd from the inside, while can either have an exterior finish or be bare (Figure 3). Nonetheless, old buildings, an example of climate responsive architecture, had irregular urban layout and were built from local materials. In addition, they used different construction techniqes as well as thick massive walls that varied between 0.6 to 1 meters.

2.3.Simulation model

The dynamic simulation model CitySim was selected to calculate cooling loads due to the thermal exchanges between the outdoor and indoor environments and to evaluate the indoor air temperatures. The inputs for the simulation model are: building model, and hourly weather

Figure 1. Location of Biskra and the residential case studies

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data. The indoor air temperatures and the energy consumption required for the operating of cooling loads are calculated on an hourly basis. The weather data used a Typical Meteorological Year (TMY) climate dataset from Meteonorm to initiate the simulation for 4416 hours between 15 April and 15 October.

The simplified geometry of the buildings was modelled in SketchUP from the official 2D district layout (Figure 3). Site investigation was undertaken to characterize the physical aspects of buildings (construction materials, surface colours and textures, and heights). The shortwave reflectance of each dwelling was given by the color of its exterior finish. Details of construction materials were caclulated in reference to the Algerian Technical Regulation Document [16] and are listed in table 1. Each building was considered single thermal zone and did not account for internal heat loads. Due to uncertanties in thermal comfort perception in homes, the WHO guidance have focused on the air temperature and set safe bounds to protect the health of occupants [6] . For the calculation of the air temperatures and the cooling load, we followed the WHO guidance instead of the guidelines for energy efficiency purposes of the technical regulation document that sets indoor temperatures between 21°C and 27°C.

B005

B001 B056

B052

B021

B014 B041

B029 B015 B066

B023

B008

B007 B035

B030 B036 B088

-LOT1- -LOT8-

-LOT7-

-LOT6-

-LOT5-

-LOT4-

-LOT3-

-LOT2-

B060

B061 B104

B111

B067

B042 B082

B087 B096

B075

B078 B072

B113 B110

B049

B054

Figure 3. Up: photos of some houses; bottom : 3D view of the simplified district model in SketchUP

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Table 1. Thermal transmittance of building components [12] .

Envelope Element Material Thickness

(m)

Thermal transmittance (W/m².K) External wall Cement plaster

Hollow brick Plaster

0.020 0.150

0.020 1.81

External roof Granite tile Cement plaster Rib and brick slab Plaster

0.025 0.020 0.200 0.020

2.36

Ground floor Granite tile Cement plaster Floating slab Backfill

0.025 0.020 0.150 0.200

2.05

Windows Single

glazing

0.004

5.8 3.Results and Discussion

This study presents the thermal conditions generated within 115 self-build residential units in an urban district in Biskra, Algeria. The number of hours the indoor air temperatures rose above the comfort range (given as 18°C to 24°C) was calculated from mid–April until mid- October (4416 hours total). Considering the overheating period in Biskra is spread over 7 months from April to October, the cooling demand represents the major energy consumption.

We will not discuss instances where temperatures went below 18°C. This comfort range for air temperatures is directed by the WHO to protecting and improving the health and wellbeing of occupants. Figure 4 shows, for each building, the percentage of hours air temperatures did not meet the requirements for comfort and health. All buildings presented significant portion of time when indoor air temperatures were above 24°C normally considered not to ensure good health. The highest was recorded in building (B088) for 97.4% of the time while the lowest was recorded in building (B005) for 82.1% of the time. Additionnally, all dwelings were thermally discomfortable for 100% of the time from July through August.

It is mandatory to operate these households by cooling at the condition that they can afford sufficient energy and costs for air conditioning. In our field visits, we observed that all houses were equipped with air conditioners which indicates that householders could afford air conditioning systems, but we couldn’t determine their operation time and their electricity bill.

Regardless, widening the gap between air temperature and the comfort temperature (24°C) increases the cooling demand and energy use. We found that air temperatures rose far from the comfort range. For instance, temperatures above 30°C occured 48% to 80% of the time. The majority of existing homes were built without any consideration for passive design techniques that may have adapted these buildings to such sensitive climate conditions.Therefore, the thermal behaviour of the envelope should be enhanced to save energy because it does not respond to the particularities of the hot climate.

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Figure 4. Percentage of discomfort hours i.e. temperatures above 24°C

Figure 5 shows that the cooling energy demand of buildings differed and varied between 81.2KWh/m² to 306.7KWh/m². Buildings with one storey showed higher cooling demand than those with two or three stories. High energy usage for cooling can prevent or restrain householder from living in thermal environments that are good for health. In this regard, among the strategies to protect health and assist the population on economic and social issues, the

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Algerian government initiated and signed an executive order that manages the reduction of the electricity bill by 65% for residents of the south who suffer from hot weather conditions as long as their energy consumption does not exceed 12000KWh/year, yet serious problems of discomfort remain in the prevailing housing stock. Unfortunately, there are no mandatory policies or obligations relating to energy efficiency of dwellings.

Financial factors were among the main reasons householders did not complete the plasterworks on the exterior walls of their self-build houses [17] . We found a strong negative correlation (R²=-0.9777) between the mean indoor air temperature and the solar reflactance of the envelope (Figure 6). Increasing the solar reflectance resulted in more comfortable indoors.

Buildings with light color exterior plaster finishes (shortwave reflectance>0.5) showed better thermal conditions than buildings with cement or without exterior finishes (shortwave reflectance =0.15). As a result, the reasons behind these “new” social practices –rooted in self- build homes all over Algeria- is yet to be investigated and linked to their implications on the indoor thermal comfort.

Figure 6.Linear correlation between shortwave reflectance and mean air temperature

0.1 26.4 52.9 79.4 105.9

KWh/m³

Figure 5. Annual cooling demand of buildings -Output of CitySim-

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4. Conclusion

The study provides valuable insights about the thermal response of self-build housing’s fabric. The indoor temperature is usually dependant on outdoor temperature and follows the similar trends of increase and decrease in temperature. Living spaces are unable to passively create comfortable indoor environment at least for longer period of time. In particular, the health and wellbeing of occupants are put at risk if no or inefficient cooling system is operated during high temperature peaks.

It is doubtless that for creating the best possible thermal indoor environments, the provision of cooling in summer is mandatory in hot climates. However, this necessity does not have to be at costs of increasing the contribution to climate change posed by increased energy use in buildings that are not adapted to their environments. Interventions and solutions, by passive design at both the building and urban scales, should be directed to ensure energy savings, healthy indoors at affordable costs.

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