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High technology or low technology for buildings envelopes in residential buildings in Egypt
Alexandria Engineering Journal (2018) 57, 3779–3792
H O S T E D BY
Alexandria University
Alexandria Engineering Journal www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
High technology or low technology for buildings envelopes in residential buildings in Egypt Ayah-Allah Khalil a,*, Mohamed Fikry b, Waled Abdeaal b a b
Architecture Department at the Higher Institute of Engineering and Technology, Kafrelshikh, Egypt Architecture Department, Faculty of Engineering, Alexandria University, Egypt
Received 4 June 2018; revised 20 September 2018; accepted 1 November 2018 Available online 28 November 2018
KEYWORDS High tech; Low tech; Passive design; Active design; Intelligent fac¸ade; Sustainability; Energy efficiency; Thermal comfort; Natural ventilation; Simulation energy model; Economic benefits
Abstract Modern technology has greatly affected buildings’ envelope, which has a significant impact on the environmental considerations, users comfort and energy consumption. The paper addresses the subject of buildings’ envelopes and the external skin configurations, due to its importance as the first element facing the external environment. The contemporary studies of the environmental sustainability have made such a topic quite significant, especially in the context addressed in the research: residential buildings in Alexandria, Egypt. Such a domain has recently generated a broad debate and drawn increased attention among those involved in the design and management processes, owing to the problem of the increasing energy consumption, especially in the residential buildings, which is accompanied by a noticeable lack of awareness among both the designers and householders about the most suitable technology for building envelopes. The aim of this paper is to test some variables of design and construction, so as to determine the appropriate technology for the environmentally-efficient envelopes of the residential buildings. The presented ideas could be of some significance in formulating useful and applied guidelines in the field of architectural design and re-design of residential buildings/projects. The research introduces a comparative discourse of a literature review covering the different definitions and notions of ‘‘Low Technology” and ‘‘High Technology”, followed by a direct application on a case-specific context. Based on a systematic analysis using an Energy Plus simulation tool, the study concludes a set of statements and guidelines for designers. Ó 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Egypt has recently been suffering from increasing climate changes caused by the global warming, which has disturbed * Corresponding author. E-mail address: [email protected] (A.-A. Khalil). Peer review under responsibility of Faculty of Engineering, Alexandria University.
the thermal comfort and gradually increased energy consumption, especially in the cooling and heating aspects. The current economic crisis has aggravated the situation. Residential buildings in Egypt are considered as the major sector that consumes more than 50% of the total energy consumption. Electricity consumption for the residential purposes has been increasing at over 7–10% a year. Such a rate is expected to increase in the next years by about 35%, whereas more than 20% of the Egyptian residents live below the poverty line. Buildings’
https://doi.org/10.1016/j.aej.2018.11.001 1110-0168 Ó 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
3780 envelopes can account for 15% to 40% of the total cost of the building, and it can be more than 40% with building services; like the heating and cooling systems. High-performance envelopes could be achieved through using modern technologies in buildings envelops which protect the buildings from the outdoor conditions, provide the occupants with thermal comfort, reduce energy consumption, increase dependence on natural ventilation without HVACs and provide occupants with natural daylight without glare. The word technology generally integrates all the materials, systems and construction methods, and it can be performed either in low or high-level. Nowadays, there have been several mutations in buildings envelopes technologies that designers have adopted without sufficient awareness to achieve the principles of sustainability (the preservation of the environment, society, and economy), such technologies have had a negative effect on the environment and energy consumption. Using the appropriate technologies in buildings’ envelopes can reduce energy consumption up to 50%. Buildings may also produce sufficient energy for all the residential units through the renewable energy that can be produced either locally and nationally. All the current residential buildings in Egypt are built of bricks and concrete, which produce massive pollution when manufactured and make the buildings consume great energy in cooling, heating, and lighting over the lifespan of the building, in addition to wasting a lot of materials when demolished. This paper puts forward proposals on a residential building in Alexandria, Egypt to be used as a guide to reach the proper level of technology for the residential buildings in Egypt. This paper is organized into six sections. The first section identifies the research problem position in the Egyptian context and explores the research methodology. The second section uses a literature review to highlight the meaning of high technology and low technology. The third section reports and analyzes the reference case and its location. The forth section suggests a methodology for the experimental stage and analyzes the three cases (base case, low tech case, and high tech case) by using a simulation program for comparing the performance characteristics. The final two sections discuss the results and derive conclusions and recommendations to be used as guidelines for designers, researchers, governmental entities, students and householders. 2. Literature review Buildings’ envelopes can be built with two main levels of Technology; low tech or high tech. Based on the previous studies, the following definition identifies the meaning of each level. 2.1. Low technology Researchers view Low technology as the opposite of high technology. Low tech means using a simple technology, often of a traditional or non-mechanical kind [8]. Low tech can commonly be created with the least capital investment by the individuals or small groups. It increases dependence on the local natural resources and passive strategies to provide a stable comfortable environment, while using simple construction methods. Some other definitions have revealed that low tech allows the use of advanced technologies such as; PV’s and air conditioning units; however it operates through a low
A.-A. Khalil et al. energy lifestyle. It does not provide high comfort levels or high construction quality [14]. There is a critical analysis of the demands of low tech that can be summarized in the conservation of natural resources by using reusable or recycled construction products, minimizing energy consumption, longterm use of building parts, besides short transport distances during construction. Egypt has a lot of ancient ’Low Tech’ examples which highlight a lot of architectural concepts such as; minimizing the demand for energy used to cool the buildings in hot climates, decreasing heat gain, reducing solar heating, in addition to providing warmth in the winter [3]. 2.2. High technology High technology uses all the available modern potentials, while making the best use of the latest science, knowledge, materials, and machinery. High tech uses traditional building materials like stone, wood, and mud; but usually tends to the utilization of the manufactured materials like; metals, fiberglass and plastics, through the implementation of advanced procedures like; the intelligent facades, and High Tech construction methods such as; the advanced concept of assembled and disassembled buildings. High tech can also be used to reduce the mass of materials and land use [8]. High-tech has been assumed to mean, new cutting edge and usually complicated technologies that rely heavily on contemporary material science and credible product development [14]. High tech symbolizes the use of advanced technologies to provide maximum comfort style associated with energy standards. 3. Case study (Sidi-Gaber, Alexandria, Egypt) In this part of research, the case of Sidi-Gaber district, Alexandria will be identified, where it is important to study the climate of the site, as well as the current status of the reference case study. 3.1. Alexandria climate Generally, Egypt is divided into three climate zones: hot humid, hot mild and hot dry as shown in Fig. 1; Alexandria is located in the first zone. The Ko¨ppen’s climate classification also sorts the climate in Alexandria to be hot humid, zone (2A). The seasons in Alexandria can be divided into two main periods, summer and winter. Summer season lasts from May to October; it is hot but not so hot as Cairo. The air temperature in summer can reach 30°C/86°F, or even 32°C/90°F. The winter period starts in November and ends in April. Fig. 2 shows the air temperature of Alexandria all over the year. 3.2. Local case study The reference project for the experimental phase of this research, located in the Sidi-Gaber district, Alexandria, Egypt (31.2_N, 29.95_E) as shown in Fig. 3, is selected for some reasons – It is a prototypal project, so the developed design proposals give a wide impact.
High technology or low technology for buildings envelopes
3781 rooms starting from 15:00. The study has also revealed that all surveyed buildings had poor thermal performance and indoor air quality. Moreover, the study has showed that the envelopes of most investigated buildings are not airtight, with single glazed openings and non-insulated walls, and without shading treatments, as what will be detailed in the next part. 4. Methodology This section aims to determine the methodology adopted in the experimental stage of this research. Moreover, such a methodology takes several stages and the study was conducted in a stepped parametric analysis. 4.1. Simulation structure
Fig. 1 The three climate zones of Egypt, (1) hot humid, (2) hot mild and (3) hot dry [3].
– There are a lot of buildings under construction that can apply the new building regulations based on this study. – There is a previous study that has examined and surveyed the behavior of occupants, the times of occupancy, the rate of energy consumption and described the real conditions of the building in order to get more realistic results. The previous research for Attia, Evrard, & Gratia has studied the current situation of the buildings and found out that the average apartment occupancy in the residential building in Alexandria is about (4–5) people per unit, and the average power intensity of plug loads is about 6 W/m2. It has also presented the monthly occupancy, lighting schedules, and the total energy consumption as shown in Figs. 4–6 respectively. The total energy consumption for this typology of buildings is about 22 kWh/m2. Most of these apartment typologies are divided into three zones; bedrooms, living room and service zones (kitchen, corridors, and bathroom). According to the previous study, the Egyptian residential units in, during the summer season, turn on air-conditioners in living rooms between 17:00 and 23:00, and those serving bedrooms commonly operate between 23:00 and 5:00. Moreover, the airconditioners during Ramadan run for longer periods in living
Fig. 2
The study has investigated the effects of several suitable low and high technologies on the envelopes, applying the principles of sustainability; such as using local - reused or recycled- materials, which contributes to reduce a maintenance operation, has a low toxic gas and helps to rationalize the consumption of resources. In addition, systems used in building envelopes should help to apply the economic benefits over life cycle, allow light transmission without heat, and reduce energy consumption for cooling, heating and lighting. Such systems should also consider the international standards of indoor air quality, health, comfort, moisture control, noise control, securing indoor environment from foreign pollutants and employ the renewable energy resources. Moreover, construction methods in building envelopes should have a capacity to resist earthquakes, bear high workloads, be flexible enough and use components which are easy to assemble and disassemble in order to save money and efforts. This study has also considered the climatic analysis of the location. In this study, the reference case will be examined and modified to come out with the two applied proposals. Each technological level was investigated in a sequential process, as shown in Diagram 1. The evaluation of the whole process has been conducted through the achieved reduction in energy consumption and the increase in thermal comfort hours. Moreover, a comparison between the base case and the final improved proposals in the two levels of technology will show the effectiveness and applicability of each proposal. Design-Builder has illustrated advanced modeling tools in an easy to use interface for the most widely used energy simulation engine Energy-Plus. So, it is chosen as a simulation software for the energy simulation. It provides results of energy consumption, thermal comfort, daylight, cost and other parameters commitment for any building selected for analysis. With Design-Builder, all proposals can be examined [10].
Outdoor air temperature in Alexandria (design builder).
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Fig. 3
A reference case study model for a residential unit in Sidi-Gaber, Alexandria [4].
4.2. Base case performance The reference building has some Restrictions; it takes a north, south, east and west directions. There is no opening in the east and west faces as shown in Fig. 7; it is usually associated with
Fig. 4
the requirements of the region. Table 1 shows the input parameters for the base case, as Attia, Evrard, & Gratia research. All input parameters are initially fed into the basic case to examine its performance, and then the proposals for each level of technology are applied.
Occupancy schedules of the surveyed apartments [4].
High technology or low technology for buildings envelopes
Fig. 5
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Lighting schedules of the surveyed apartments [4].
Fig. 6
Monthly electricity consumption [4].
The base case was examined twice; firstly the simulation was performed with a cooling and heating system, and then without it. The results showed that the base case in residential homes didn’t reach the best thermal comfort, even with HVACs. Base case with HVACs had convenient indoor air temperature conditions, as shown in Chart 1. The discomfort hours in the base case with HVACs was 3271.85 per year, while it was 4147.09 per year without HVACs as shown in Chart 2. The base case with cooling and heating system consumed about 22.4 kWh/m2; as mentioned in the previous study for [4]. 4.3. Applied strategies This stage has been designed to examine the previous structure for the proposals mentioned in the methodology of this study. It is important to reduce the dependence on using the mechanical devices and equipment in achieving the buildings’ envelopes resistance to the external conditions; therefore the cooling and heating system is turned off in the application stage to depend only on the natural ventilation. 4.3.1. Low technology strategies Several studies on countries with low economic conditions have revealed that they use the low technology for achieving thermal comfort, since it has a good impact on saving the energy consumption. Through low technology, controlling the solar radiation and ventilation is done manually in all com-
Fig. 7
The base case model (design builder).
ponents of the building envelopes, specially the shading elements. Low technology uses passive systems for solar gain or loss. Shading elements, thermal mass, insulation, and natural ventilation should be carefully designed to achieve low tech goals. It is expected to have a significant impact in hot humid climates; therefore applying a suitable low tech in Alexandria’s buildings may be highly effective and reduce energy consumption. In the low tech proposal, water wall system is used as the simplest, smallest, and most economical method for providing a good thermal mass. Water walls store heat in summer and allow heat transfer in winter to provide the best thermal comfort. Water wall system has some characteristics: It uses the heat of sun and climate resources to provide heating and cool-
3784 Table 1
A.-A. Khalil et al. Input parameters for base case [4].
The components of the base case building envelope
External Walls
Ground Floor Slab
Roof Slab
Typical Floor Slab
Glass
6 mm Single Clear Glass
Window Frames
Building description: Shape No. floors and height
Rectangular (25 m–11 m) 6 and 2.8 m height per floor
Apartment description: Volume External wall area Roof area Floor area Windows area Glazing U-Value
366 m3 110 m2 122 m2 122 m2 60 m2 6.25
Chart 1
aluminum
Aspect ratio Exterior wall U Value Roof U-value Floor U-value Single clear glazing SHGC
2.3/1 2.5 W/m2 1.39 W/m2K 1.58 W/m2K Tv = 0.88 0.75
Indoor air temperature in base case with HVACs and without HVACs.
ing. It doesn’t rely on supplementary energy sources to function. It works as a collector and storage, has a long lifetime and needs little maintenance. Moreover, it can be built and installed by regular construction trades, without special equipment. Water is much better than concrete and stone in providing thermal mass with low cost, since it is more dynamic and can gain heat in winter or prevent it in summer faster. This
case also makes glazing control simple, reliable, effective, and convenient to use [5]. 4.3.1.1. Low tech insulation. Roofs and walls are the most important components of the buildings’ envelopes that are exposed to the direct solar gain; however the current roofs and walls construction is not insulated. The improvement in
High technology or low technology for buildings envelopes
Chart 2
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Discomfort hours in base case with HVACs and without HVACs.
the U-value of roofs and walls contributes to enhance the overall thermal performance of buildings. Therefore, the roof and walls of the building were modified to contain 10- cm insulation, the U- value for roof and walls became 0.4 w/m2K after adding the straw bale, as an insulating material [11]. Straw bale is used as an insulator because it is a natural and local material suitable for low tech and specified in the material directory of Design-Builder. Table 2 illustrates the new roof and walls components. On the other hand, the water wall system was used in the south facade for the previous reasons. The best thermal comfort results took place when the water walls were filled in summer and emptied in winter. When the water wall was filled, the U-value reached 1.653 w/m2K.
and south fac¸ade, its Solar Heat Gain Coefficient (SHGC) is 0.72, direct solar transmission 0.68, light transmission 0.811 and U value is 3.779.
4.3.1.2. Low tech glazing system. Glazing is responsible for about one third of energy loads of buildings, and it has a large impact on the thermal comfort. In this low tech proposal, single clear glass with low emission (6 mm) was used in the north
4.3.1.4. Low tech heat distribution stage. Natural ventilation is essential for the indoor thermal comfort, and changing windows operation to prevent the hot air can cause a considerable reduction in the mean radiant temperature of the space. There-
Table 2
4.3.1.3. Low tech shading. The previous research has revealed the fact that the effect of shading on reducing the heat gain becomes larger in hot climates. Several trials to achieve the optimum balance between daylight and thermal performance have shown that the best result for windows shading happened by using an internal shade with high reflection slats and low transmission. A shading surface for roof has been used to overcome solar radiation, improve the thermal performance and give the opportunity to use the roof as an outdoor space.
Low technology proposal input parameters.
The components of low tech case proposal
External Walls
South Wall (water wall system)
Roof
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Fig. 8
A.-A. Khalil et al.
Low technology proposal model (design builder).
fore, night ventilation was investigated during summer in this proposal. Windows in the reference case were set to open for about 5% of the day hours with 20% of the windows area, while the improved alternative opened 100% of the day hours with 100% of the area. During winter, heat generated from electrical equipment, artificial lighting, besides closing the windows helped to improve the thermal comfort [6]. Wind catchers, a passive technique used in residential buildings as a distribution method, were also used in this proposal. The section of each wind catchers is 1 m * 1.3 m and built from burned brick as shown in Fig. 8. The openings in the wind catchers are directed to wind direction; their level is usually set higher than the surrounding buildings. These openings use the same window operating schedule that was applied previously. 4.3.2. High tech strategies High tech proposal used an intelligent fac¸ade with smart and active materials and systems [13]. The intelligent skins can be changed so dynamically that the fabric of the building may not be inert, in order to reduce the energy requirements of the building and improve the indoor environment. As Walter Kroner has said, ‘‘intelligent design means striving to have outbuildings in harmony with nature, to protect its qualities, and to recognize its dynamic (and unpredictable) qualities, whether assets or liabilities” [15]. In this proposal, a double skin fac¸ade is used as a type of intelligent skin. It is a system involving an addition of a second glazed envelope which can create opportunities for maximizing daylight and improving energy performance. In the summer, the double fac¸ade reduces solar gains. A natural stack effect
Fig. 9
helps air to move and decreases heat. In addition, the structure of DSF with the glass and blinds re-radiate the solar emissions. In the winter, the double fac¸ade acts as a buffer zone between the building and the outer environment, minimizing heat loss, and improving U-values. It also works as a heat absorber. There are three clear categories of DSF; box window, corridor type and multi-story as shown in Fig. 9 [12]. The previous study [2] found out that window boxes type provides the best thermal comfort and has the least energy consumption at climate zone (2A); therefore this proposal uses the box window for the south wall. The box window in this proposal had 1 m depth and 1.47 m length; its height was the same as the height of each floor as shown in Table 3. Fig. 10 shows the north and south facades with the location of vents in high tech proposal. For the north fac¸ade, the DSF was used with 0.5 m depth and provided with vents. 4.3.2.1. High tech. insulation. High technology proposal used polyurethane foam for walls and roof insulation. Polyurethane foam is a high tech manufactured material from the material directory of Design-Builder. The new walls and roof slabs have the same U value used in the low technology proposal, although they are less thick and lighter (0.5 cm) as illustrated in Table 3. It is quite evident that the high technology uses thinner and lighter insulating materials than low tech. 4.3.2.2. High tech glazing system. High technology enhances the thermal performance of the glazing systems by inserting a transparent insulator such as; krypton, air, argon, or vacuum between the two layers of glass to reduce thermal conductance. The large gap between panes provides more insulating property such as; a double glass system and triple glass which are also used in the noise polluted environment to provide a good acoustic performance. High technology glazing uses smart window; whether active dynamic or passive. Active windows use electricity to align the electrolytic cell so that the window can become clear, or misalign. In this proposal, the glazing system used in south fac¸ade is Double glazing, clear with no shading for the internal layer. For the external south glass layer, the double Blue glass with 6 mm/13 mm argon was used, its Solar Heat Gain Coefficient (SHGC) is 0.494, direct solar transmission is 0.373, light transmission is 0.5 and U-value is 2.5. For north fac¸ade, a single clear glass used for the eternal layer, while the external one is Double Blue glass with 6 mm/13 mm Argon from the design- builder library.
Double skin facade (DSF) types.
High technology or low technology for buildings envelopes Table 3
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High technology proposal input parameters.
The components of high tech case proposal
External Wall
Roof
Vents Double glass
South and North facade (DSF)
South facade section
Fig. 10
North facade
South facade
High technology proposal model, south fac¸ade at left and north facade at right (design builder).
4.3.2.3. High tech shading. In this case, the simulation has been done twice; the first shading used a blind with high reflectivity slats for the external glass layer of south fac¸ade. The second
Fig. 11
one used more high tech shading, such as an electrochromic glass. In both cases the shade worked dynamically from 8:00 to 18:00 to provide the best thermal comfort.
Daylight simulation in different cases.
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Chart 3
Comparative analysis for indoor air temperature in all cases.
Chart 4
Chart 5
Comparative analysis for humidity ratio in all cases.
Comparative analysis for discomfort (hrs.) in all cases.
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Chart 6 Total discomfort hours annually (1) base case without heating or cooling (2) base case with cooling and heating (3) low tech proposal (4) high tech with blind proposal (5) high tech with electro-chromic proposal.
Chart 7 Total energy consumption (kWh/m2 per year), (1) base case with HVACs (2) base case without HVACs (3) low tech proposal (4) high tech with blind proposal (5) high tech with electro-chromic proposal.
4.3.2.4. High tech heat distribution stage. The double skin facade in this proposal is made up of two glazing layers with an intermediate cavity (1 m in the south and 0.5 m in the north); the natural ventilation was chosen for the cavity space. The inlet and outlet vents were closed at night in winter to keep the spaces worm. In summer, all vents kept open all the day to extract the heated air and reduce humidity. This method reduces the need for HVACs and depends only on the natural ventilation.
5. Simulation results The results of what has been studied and tested are discussed in four significant aspects. First, thermal comfort indices are compared, second energy consumption is indicated and finally both daylight and economic benefits are discussed.
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Chart 8
Comparative analysis between the three cases shows the initial cost and LCC (90 years).
5.1. Thermal comfort
5.3. Daylight
According to ASHRAE Standard 55-2010, there are some specific parameters that must be taken into account to examine the thermal comfort in any building; such as the environmental parameters, air temperature, mean radiant temperature, relative humidity, in addition to the personal parameters; like activity levels and clothing insulation [1], the results of simulation have shown that the air temperature and humidity ratio have been improved at all the modified proposals. Charts 3 and 4 show the internal air temperature and humidity ratio in the base case and the final modified proposals for summer and winter months. Using the electrochromic glass in high tech system provides the best thermal comfort in comparison with the other cases as shown in the Charts 5 and 6. High tech proposals have recorded the least discomfort hours per year, followed by low tech proposal. These proposals increased the comfort hours in the base case, even with heating and cooling systems. The use of Mechanical fans can help to increase natural ventilation, decrease humidity, and provide more thermal comfort in summer.
Good lighting is one of the main factors of indoor comfort that positively influences health and productivity [7]. The increased daylighting of the completely glazed fac¸ade introduces excessive glare and heat at certain times of the day, which requires further measures in design to reduce their negative effects. In both proposals, appropriate measures have been taken; double skin fac¸ade with double glass and Solar shading devices in high tech proposal is designed with airspace to decrease solar heat gain through the glazing and reduce the amount of glare caused by the increased access to daylighting. On the other hand, water wall system with high reflective blind shading provided daylight without glare and decreased the heat gain Fig. 11.
5.2. Energy consumption The total energy consumption of each proposal is presented in Chart 7. Energy-efficient practices were proposed in this study through low-tech and high-tech strategies for building envelopes, which greatly improved the energy efficiency of the studied residential building. In general, the results of the simulation revealed the great potentials of utilizing energy-efficient practices in residential buildings in Alexandria, Egypt. The results have shown that the total energy consumption for the building decreased by 46% for low technology proposal and about 50% for high technology proposal, as shown below. To conclude, the achieved energy-saving provides an example of the possible energy reductions that will be accomplished in the future built environments with two levels of technology.
5.4. Economic benefits This study shows that the base case has the lowest initial cost in comparison with the other proposals. Low tech case has a relatively low initial cost, while High tech case needs more investment during the construction period, since it has a relatively high initial cost. Both low and high tech cases almost have the same operating cost. Life cycle cost for low technology will be the lowest after 90 years (The lifespan of residential buildings), about 50% of the life cycle cost of the base case. The below equation is used to calculate the LCC after a known period of time [9]. The payback in low tech proposal will start after 5–7 years, while high tech proposal payback will start after 12–17 years as shown in the Chart 8. n P ð1þLÞ 1 ð1þrÞn LCC ¼ CI þ Lr CI: initial cost, p: annual operating cost, L: Increase rate in the price of electricity assumed 16%, r: Bank interest rate assumed 12%, n: lifetime
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Base case (Default construction, materials and systems) Low technology Natural, local materials – passive simple systems (water wall system)
High technology High technology materials intelligent facades systems (DSF).
Windows
Shading Roof shading
Windows shading (Blind with high reflectivity slats) manually controlled
Heat distribution stage
Heat modulation stage
Final proposal for high tech, the added envelope materials easy to disassemble
Insulaon Using Indirect gain/ loss, thermal mass walls that has a low heat gain in summer and allow heat transfer in winter (water wall)
Using low technology materials for glass (single clear or coloured)
Using a natural ventilation, Stack driven and using operating windows schedule ventilation.
Reducing air leaks
Using insulation in Roofs and walls (straw bale)
Wind catcher The opening in north-west
Heat modulation stage
Final proposal for low tech, the added envelope materials easy to disassemble
Intelligent façade
Insulaon
Windows
Shading
(Double skin façade- box window type), (dynamic windows)
Using high technology insulation materials for Roofs and walls (polyurethane foam)
High tech material for glass (Using double glass)
Using smart dynamic shading (dynamic Blind with high reflectivity slatselectro-chromic)
Manage windows opening
Fully integrated control
Diagram 1
Actuated window vents (only natural vent)
Heat distribution stage
Parametric simulation structure.
6. Conclusions Referring to the aim of this research about the importance of adopting the proper technology for building envelopes in the residential buildings in Egypt, the results have revealed that the appropriate technology can provide the best thermal comfort without HVACs, save energy consumption, in addition to providing natural daylight and considerate economic conditions. The experimentation process used a water wall system, single glass and Straw, a local, natural material in Egypt, as insulation material for the low tech system proposal, while High tech proposal used an intelligent fac¸ade (double skin fac¸ade) with high tech material for insulation, high tech glaz-
ing system, smart dynamic shaded, and a smart system for heat distribution. The experiences in this paper have revealed some results with guidelines that can be summarized as follows: The building envelopes have proved to be the most important element that can contribute to reduce the energy consumption and provide comfort of users. The word technology Integrates materials, systems and construction methods. Low technology provides the maximum use of natural, local resources, passive strategies and simple construction methods which have a low economic impact, whereas the high technology uses all available technologies that provide the best results in thermal comfort and energy saving.
3792 Water wall system proved that it is the best passive system, referring to low tech with low cost, and water is the best thermal mass, which can prevent heat in summer and allow heat in winter after the water gets emptied from the water walls. The awareness of using the proper technology, whether high or low, in building envelopes gives more comfort hours and saves more energy consumption than the current situation that uses HVACs. In buildings’ envelops, high tech gives more thermal comfort and saves more energy consumption than Low tech. Low tech has a low initial cost and saves about 46% of energy consumption, while high tech saved about 50% with high initial cost. The two cases almost have the same operating cost, which leads us to use the low tech in building envelopes because it is more convenient for Egypt economy; but the role of high tech in providing more thermal comfort should not be neglected. Increasing insulation, reducing air leaks, increasing winter solar energy, increasing glazing, introducing roof lights, introducing stacks/internal air flows, improving shading, exterior walls with high-mass material and controlling windows opening are essential in both high and low tech in order to remove the need for cooling, decrease heating energy and limit the need for artificial light. As a conclusion, the research will introduce some recommendations: – All designers are invited to use this methodology in order to achieve the best results: first, specify the building and climate zone; second, specify the criteria for performance; third, specify parameters depending on the level of technology (low or high); fourth, simulate the related parameters and finally, evaluate the design alternatives and make a decision. – It is highly recommended that researchers examine more low and high strategies or more parameters of the studied strategy. – The integration between high or low technology design and renewable energy production such using Photo-Voltaic systems or wind turbines certainly achieve the minimum energy consumption rates. Nowadays, all the researchers are aware that the building fac¸ade can generate electricity. – Both designers and householders need to study the costbenefit analysis, which provides developers and users with a clear view of opportunities and risks of investing in high or low tech in residential buildings. – It is important to take into account the other factors; such as the orientation of buildings and the openings ratio and so on, in new buildings – National codes should be highly considered in relation with the different building roles and practices in order to achieve the target of energy-efficient buildings in Egypt.
A.-A. Khalil et al. These results will be helpful for architects, managers, and designers to have a proper viewpoint in the design of fac¸ade elements and their positions. They play an important role in saving energy, which sounds very attractive to building owners who are interested in maximum profits through low construction standards and costs coupled with maximum utilities. Therefore, the awareness of building envelopes technology should be widely developed in order to highlight the importance of adopting these strategies and the economic benefits that will gained. References [1] AHSRAE, ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy, ANSI, USA, 2010. [2] A. Aksamija, Energy Performance of Different Types of Double Skin Facades in Various Climates, Department of Architecture, University of Massachusetts Amherst, Amherst, Massachusetts, USA, 2017. [3] S. Attia, A Tool for Design Decision Making: Zero Energy Residential Buildings in Hot Humid Climates, Presses universitaires de Louvain, Belgium, 2012. [4] S. Attia, A. Evrard, E. Gratia, Development of Benchmark Models for the Egyptian Residential Buildings Sector, Elsevier, 2012, p. 16. [5] D.A. Bainbridge, A Water Wall Solar Design Manual For environmentally responsive buildings that increase comfort, save money, and protect the environment, 2005. [6] N.V. Baker, Passive and Low Energy Building Design For Tropical Island Climates, Commonwealth Secretariat, London, 1987. [7] C. Gallo, M. Sala, A.A.M. Sayigh, Architecture: Comfort and Energy, Elsevier, UK, 1998. [8] B. Cody, The Role of Technology in Sustainable Architecture, 2014. [9] S. Fuller, S. Petersen, Life-Cycle Costing Manual for the Federal Energy Management Program, Department of Commerce, USA, 1996. [10] T. Maile, M. Fischer, V. Bazjanac, Building Energy Performance Simulation Tools – A Life-Cycle and Interoperable Perspective, Center for Integrated Facility Engineering, California, 2007. [11] A. Nails, H. Farm, Todmorden, 8RJ, O. Information Guide to Straw Bale Building, 2001.. Retrieved from . [12] H. Poirazis, Double Skin Fac¸ades, IEA SHC Task 34 ECBCS Annex 43, Sweden, 2006. [13] J. Wang, L.O. Beltra´n, J. Kim, From Static to Kinetic: A Review of Acclimated Kinetic Building Envelopes, Jonghoon Kim, 2012. Retrieved from . [14] N. Wienand, J. Zunde, Materials, Specification and Detailing: Foundations of Building Design. 2 Park Square, Taylor & Francis, Milton Park, Abingdon, OX14 4RN, 2007. [15] M. Wigginton, J. Harris, Intelligent Skins, Gray Publishing, Italy, 2002.
H O S T E D BY
Alexandria University
Alexandria Engineering Journal www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
High technology or low technology for buildings envelopes in residential buildings in Egypt Ayah-Allah Khalil a,*, Mohamed Fikry b, Waled Abdeaal b a b
Architecture Department at the Higher Institute of Engineering and Technology, Kafrelshikh, Egypt Architecture Department, Faculty of Engineering, Alexandria University, Egypt
Received 4 June 2018; revised 20 September 2018; accepted 1 November 2018 Available online 28 November 2018
KEYWORDS High tech; Low tech; Passive design; Active design; Intelligent fac¸ade; Sustainability; Energy efficiency; Thermal comfort; Natural ventilation; Simulation energy model; Economic benefits
Abstract Modern technology has greatly affected buildings’ envelope, which has a significant impact on the environmental considerations, users comfort and energy consumption. The paper addresses the subject of buildings’ envelopes and the external skin configurations, due to its importance as the first element facing the external environment. The contemporary studies of the environmental sustainability have made such a topic quite significant, especially in the context addressed in the research: residential buildings in Alexandria, Egypt. Such a domain has recently generated a broad debate and drawn increased attention among those involved in the design and management processes, owing to the problem of the increasing energy consumption, especially in the residential buildings, which is accompanied by a noticeable lack of awareness among both the designers and householders about the most suitable technology for building envelopes. The aim of this paper is to test some variables of design and construction, so as to determine the appropriate technology for the environmentally-efficient envelopes of the residential buildings. The presented ideas could be of some significance in formulating useful and applied guidelines in the field of architectural design and re-design of residential buildings/projects. The research introduces a comparative discourse of a literature review covering the different definitions and notions of ‘‘Low Technology” and ‘‘High Technology”, followed by a direct application on a case-specific context. Based on a systematic analysis using an Energy Plus simulation tool, the study concludes a set of statements and guidelines for designers. Ó 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Egypt has recently been suffering from increasing climate changes caused by the global warming, which has disturbed * Corresponding author. E-mail address: [email protected] (A.-A. Khalil). Peer review under responsibility of Faculty of Engineering, Alexandria University.
the thermal comfort and gradually increased energy consumption, especially in the cooling and heating aspects. The current economic crisis has aggravated the situation. Residential buildings in Egypt are considered as the major sector that consumes more than 50% of the total energy consumption. Electricity consumption for the residential purposes has been increasing at over 7–10% a year. Such a rate is expected to increase in the next years by about 35%, whereas more than 20% of the Egyptian residents live below the poverty line. Buildings’
https://doi.org/10.1016/j.aej.2018.11.001 1110-0168 Ó 2018 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
3780 envelopes can account for 15% to 40% of the total cost of the building, and it can be more than 40% with building services; like the heating and cooling systems. High-performance envelopes could be achieved through using modern technologies in buildings envelops which protect the buildings from the outdoor conditions, provide the occupants with thermal comfort, reduce energy consumption, increase dependence on natural ventilation without HVACs and provide occupants with natural daylight without glare. The word technology generally integrates all the materials, systems and construction methods, and it can be performed either in low or high-level. Nowadays, there have been several mutations in buildings envelopes technologies that designers have adopted without sufficient awareness to achieve the principles of sustainability (the preservation of the environment, society, and economy), such technologies have had a negative effect on the environment and energy consumption. Using the appropriate technologies in buildings’ envelopes can reduce energy consumption up to 50%. Buildings may also produce sufficient energy for all the residential units through the renewable energy that can be produced either locally and nationally. All the current residential buildings in Egypt are built of bricks and concrete, which produce massive pollution when manufactured and make the buildings consume great energy in cooling, heating, and lighting over the lifespan of the building, in addition to wasting a lot of materials when demolished. This paper puts forward proposals on a residential building in Alexandria, Egypt to be used as a guide to reach the proper level of technology for the residential buildings in Egypt. This paper is organized into six sections. The first section identifies the research problem position in the Egyptian context and explores the research methodology. The second section uses a literature review to highlight the meaning of high technology and low technology. The third section reports and analyzes the reference case and its location. The forth section suggests a methodology for the experimental stage and analyzes the three cases (base case, low tech case, and high tech case) by using a simulation program for comparing the performance characteristics. The final two sections discuss the results and derive conclusions and recommendations to be used as guidelines for designers, researchers, governmental entities, students and householders. 2. Literature review Buildings’ envelopes can be built with two main levels of Technology; low tech or high tech. Based on the previous studies, the following definition identifies the meaning of each level. 2.1. Low technology Researchers view Low technology as the opposite of high technology. Low tech means using a simple technology, often of a traditional or non-mechanical kind [8]. Low tech can commonly be created with the least capital investment by the individuals or small groups. It increases dependence on the local natural resources and passive strategies to provide a stable comfortable environment, while using simple construction methods. Some other definitions have revealed that low tech allows the use of advanced technologies such as; PV’s and air conditioning units; however it operates through a low
A.-A. Khalil et al. energy lifestyle. It does not provide high comfort levels or high construction quality [14]. There is a critical analysis of the demands of low tech that can be summarized in the conservation of natural resources by using reusable or recycled construction products, minimizing energy consumption, longterm use of building parts, besides short transport distances during construction. Egypt has a lot of ancient ’Low Tech’ examples which highlight a lot of architectural concepts such as; minimizing the demand for energy used to cool the buildings in hot climates, decreasing heat gain, reducing solar heating, in addition to providing warmth in the winter [3]. 2.2. High technology High technology uses all the available modern potentials, while making the best use of the latest science, knowledge, materials, and machinery. High tech uses traditional building materials like stone, wood, and mud; but usually tends to the utilization of the manufactured materials like; metals, fiberglass and plastics, through the implementation of advanced procedures like; the intelligent facades, and High Tech construction methods such as; the advanced concept of assembled and disassembled buildings. High tech can also be used to reduce the mass of materials and land use [8]. High-tech has been assumed to mean, new cutting edge and usually complicated technologies that rely heavily on contemporary material science and credible product development [14]. High tech symbolizes the use of advanced technologies to provide maximum comfort style associated with energy standards. 3. Case study (Sidi-Gaber, Alexandria, Egypt) In this part of research, the case of Sidi-Gaber district, Alexandria will be identified, where it is important to study the climate of the site, as well as the current status of the reference case study. 3.1. Alexandria climate Generally, Egypt is divided into three climate zones: hot humid, hot mild and hot dry as shown in Fig. 1; Alexandria is located in the first zone. The Ko¨ppen’s climate classification also sorts the climate in Alexandria to be hot humid, zone (2A). The seasons in Alexandria can be divided into two main periods, summer and winter. Summer season lasts from May to October; it is hot but not so hot as Cairo. The air temperature in summer can reach 30°C/86°F, or even 32°C/90°F. The winter period starts in November and ends in April. Fig. 2 shows the air temperature of Alexandria all over the year. 3.2. Local case study The reference project for the experimental phase of this research, located in the Sidi-Gaber district, Alexandria, Egypt (31.2_N, 29.95_E) as shown in Fig. 3, is selected for some reasons – It is a prototypal project, so the developed design proposals give a wide impact.
High technology or low technology for buildings envelopes
3781 rooms starting from 15:00. The study has also revealed that all surveyed buildings had poor thermal performance and indoor air quality. Moreover, the study has showed that the envelopes of most investigated buildings are not airtight, with single glazed openings and non-insulated walls, and without shading treatments, as what will be detailed in the next part. 4. Methodology This section aims to determine the methodology adopted in the experimental stage of this research. Moreover, such a methodology takes several stages and the study was conducted in a stepped parametric analysis. 4.1. Simulation structure
Fig. 1 The three climate zones of Egypt, (1) hot humid, (2) hot mild and (3) hot dry [3].
– There are a lot of buildings under construction that can apply the new building regulations based on this study. – There is a previous study that has examined and surveyed the behavior of occupants, the times of occupancy, the rate of energy consumption and described the real conditions of the building in order to get more realistic results. The previous research for Attia, Evrard, & Gratia has studied the current situation of the buildings and found out that the average apartment occupancy in the residential building in Alexandria is about (4–5) people per unit, and the average power intensity of plug loads is about 6 W/m2. It has also presented the monthly occupancy, lighting schedules, and the total energy consumption as shown in Figs. 4–6 respectively. The total energy consumption for this typology of buildings is about 22 kWh/m2. Most of these apartment typologies are divided into three zones; bedrooms, living room and service zones (kitchen, corridors, and bathroom). According to the previous study, the Egyptian residential units in, during the summer season, turn on air-conditioners in living rooms between 17:00 and 23:00, and those serving bedrooms commonly operate between 23:00 and 5:00. Moreover, the airconditioners during Ramadan run for longer periods in living
Fig. 2
The study has investigated the effects of several suitable low and high technologies on the envelopes, applying the principles of sustainability; such as using local - reused or recycled- materials, which contributes to reduce a maintenance operation, has a low toxic gas and helps to rationalize the consumption of resources. In addition, systems used in building envelopes should help to apply the economic benefits over life cycle, allow light transmission without heat, and reduce energy consumption for cooling, heating and lighting. Such systems should also consider the international standards of indoor air quality, health, comfort, moisture control, noise control, securing indoor environment from foreign pollutants and employ the renewable energy resources. Moreover, construction methods in building envelopes should have a capacity to resist earthquakes, bear high workloads, be flexible enough and use components which are easy to assemble and disassemble in order to save money and efforts. This study has also considered the climatic analysis of the location. In this study, the reference case will be examined and modified to come out with the two applied proposals. Each technological level was investigated in a sequential process, as shown in Diagram 1. The evaluation of the whole process has been conducted through the achieved reduction in energy consumption and the increase in thermal comfort hours. Moreover, a comparison between the base case and the final improved proposals in the two levels of technology will show the effectiveness and applicability of each proposal. Design-Builder has illustrated advanced modeling tools in an easy to use interface for the most widely used energy simulation engine Energy-Plus. So, it is chosen as a simulation software for the energy simulation. It provides results of energy consumption, thermal comfort, daylight, cost and other parameters commitment for any building selected for analysis. With Design-Builder, all proposals can be examined [10].
Outdoor air temperature in Alexandria (design builder).
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Fig. 3
A reference case study model for a residential unit in Sidi-Gaber, Alexandria [4].
4.2. Base case performance The reference building has some Restrictions; it takes a north, south, east and west directions. There is no opening in the east and west faces as shown in Fig. 7; it is usually associated with
Fig. 4
the requirements of the region. Table 1 shows the input parameters for the base case, as Attia, Evrard, & Gratia research. All input parameters are initially fed into the basic case to examine its performance, and then the proposals for each level of technology are applied.
Occupancy schedules of the surveyed apartments [4].
High technology or low technology for buildings envelopes
Fig. 5
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Lighting schedules of the surveyed apartments [4].
Fig. 6
Monthly electricity consumption [4].
The base case was examined twice; firstly the simulation was performed with a cooling and heating system, and then without it. The results showed that the base case in residential homes didn’t reach the best thermal comfort, even with HVACs. Base case with HVACs had convenient indoor air temperature conditions, as shown in Chart 1. The discomfort hours in the base case with HVACs was 3271.85 per year, while it was 4147.09 per year without HVACs as shown in Chart 2. The base case with cooling and heating system consumed about 22.4 kWh/m2; as mentioned in the previous study for [4]. 4.3. Applied strategies This stage has been designed to examine the previous structure for the proposals mentioned in the methodology of this study. It is important to reduce the dependence on using the mechanical devices and equipment in achieving the buildings’ envelopes resistance to the external conditions; therefore the cooling and heating system is turned off in the application stage to depend only on the natural ventilation. 4.3.1. Low technology strategies Several studies on countries with low economic conditions have revealed that they use the low technology for achieving thermal comfort, since it has a good impact on saving the energy consumption. Through low technology, controlling the solar radiation and ventilation is done manually in all com-
Fig. 7
The base case model (design builder).
ponents of the building envelopes, specially the shading elements. Low technology uses passive systems for solar gain or loss. Shading elements, thermal mass, insulation, and natural ventilation should be carefully designed to achieve low tech goals. It is expected to have a significant impact in hot humid climates; therefore applying a suitable low tech in Alexandria’s buildings may be highly effective and reduce energy consumption. In the low tech proposal, water wall system is used as the simplest, smallest, and most economical method for providing a good thermal mass. Water walls store heat in summer and allow heat transfer in winter to provide the best thermal comfort. Water wall system has some characteristics: It uses the heat of sun and climate resources to provide heating and cool-
3784 Table 1
A.-A. Khalil et al. Input parameters for base case [4].
The components of the base case building envelope
External Walls
Ground Floor Slab
Roof Slab
Typical Floor Slab
Glass
6 mm Single Clear Glass
Window Frames
Building description: Shape No. floors and height
Rectangular (25 m–11 m) 6 and 2.8 m height per floor
Apartment description: Volume External wall area Roof area Floor area Windows area Glazing U-Value
366 m3 110 m2 122 m2 122 m2 60 m2 6.25
Chart 1
aluminum
Aspect ratio Exterior wall U Value Roof U-value Floor U-value Single clear glazing SHGC
2.3/1 2.5 W/m2 1.39 W/m2K 1.58 W/m2K Tv = 0.88 0.75
Indoor air temperature in base case with HVACs and without HVACs.
ing. It doesn’t rely on supplementary energy sources to function. It works as a collector and storage, has a long lifetime and needs little maintenance. Moreover, it can be built and installed by regular construction trades, without special equipment. Water is much better than concrete and stone in providing thermal mass with low cost, since it is more dynamic and can gain heat in winter or prevent it in summer faster. This
case also makes glazing control simple, reliable, effective, and convenient to use [5]. 4.3.1.1. Low tech insulation. Roofs and walls are the most important components of the buildings’ envelopes that are exposed to the direct solar gain; however the current roofs and walls construction is not insulated. The improvement in
High technology or low technology for buildings envelopes
Chart 2
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Discomfort hours in base case with HVACs and without HVACs.
the U-value of roofs and walls contributes to enhance the overall thermal performance of buildings. Therefore, the roof and walls of the building were modified to contain 10- cm insulation, the U- value for roof and walls became 0.4 w/m2K after adding the straw bale, as an insulating material [11]. Straw bale is used as an insulator because it is a natural and local material suitable for low tech and specified in the material directory of Design-Builder. Table 2 illustrates the new roof and walls components. On the other hand, the water wall system was used in the south facade for the previous reasons. The best thermal comfort results took place when the water walls were filled in summer and emptied in winter. When the water wall was filled, the U-value reached 1.653 w/m2K.
and south fac¸ade, its Solar Heat Gain Coefficient (SHGC) is 0.72, direct solar transmission 0.68, light transmission 0.811 and U value is 3.779.
4.3.1.2. Low tech glazing system. Glazing is responsible for about one third of energy loads of buildings, and it has a large impact on the thermal comfort. In this low tech proposal, single clear glass with low emission (6 mm) was used in the north
4.3.1.4. Low tech heat distribution stage. Natural ventilation is essential for the indoor thermal comfort, and changing windows operation to prevent the hot air can cause a considerable reduction in the mean radiant temperature of the space. There-
Table 2
4.3.1.3. Low tech shading. The previous research has revealed the fact that the effect of shading on reducing the heat gain becomes larger in hot climates. Several trials to achieve the optimum balance between daylight and thermal performance have shown that the best result for windows shading happened by using an internal shade with high reflection slats and low transmission. A shading surface for roof has been used to overcome solar radiation, improve the thermal performance and give the opportunity to use the roof as an outdoor space.
Low technology proposal input parameters.
The components of low tech case proposal
External Walls
South Wall (water wall system)
Roof
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Fig. 8
A.-A. Khalil et al.
Low technology proposal model (design builder).
fore, night ventilation was investigated during summer in this proposal. Windows in the reference case were set to open for about 5% of the day hours with 20% of the windows area, while the improved alternative opened 100% of the day hours with 100% of the area. During winter, heat generated from electrical equipment, artificial lighting, besides closing the windows helped to improve the thermal comfort [6]. Wind catchers, a passive technique used in residential buildings as a distribution method, were also used in this proposal. The section of each wind catchers is 1 m * 1.3 m and built from burned brick as shown in Fig. 8. The openings in the wind catchers are directed to wind direction; their level is usually set higher than the surrounding buildings. These openings use the same window operating schedule that was applied previously. 4.3.2. High tech strategies High tech proposal used an intelligent fac¸ade with smart and active materials and systems [13]. The intelligent skins can be changed so dynamically that the fabric of the building may not be inert, in order to reduce the energy requirements of the building and improve the indoor environment. As Walter Kroner has said, ‘‘intelligent design means striving to have outbuildings in harmony with nature, to protect its qualities, and to recognize its dynamic (and unpredictable) qualities, whether assets or liabilities” [15]. In this proposal, a double skin fac¸ade is used as a type of intelligent skin. It is a system involving an addition of a second glazed envelope which can create opportunities for maximizing daylight and improving energy performance. In the summer, the double fac¸ade reduces solar gains. A natural stack effect
Fig. 9
helps air to move and decreases heat. In addition, the structure of DSF with the glass and blinds re-radiate the solar emissions. In the winter, the double fac¸ade acts as a buffer zone between the building and the outer environment, minimizing heat loss, and improving U-values. It also works as a heat absorber. There are three clear categories of DSF; box window, corridor type and multi-story as shown in Fig. 9 [12]. The previous study [2] found out that window boxes type provides the best thermal comfort and has the least energy consumption at climate zone (2A); therefore this proposal uses the box window for the south wall. The box window in this proposal had 1 m depth and 1.47 m length; its height was the same as the height of each floor as shown in Table 3. Fig. 10 shows the north and south facades with the location of vents in high tech proposal. For the north fac¸ade, the DSF was used with 0.5 m depth and provided with vents. 4.3.2.1. High tech. insulation. High technology proposal used polyurethane foam for walls and roof insulation. Polyurethane foam is a high tech manufactured material from the material directory of Design-Builder. The new walls and roof slabs have the same U value used in the low technology proposal, although they are less thick and lighter (0.5 cm) as illustrated in Table 3. It is quite evident that the high technology uses thinner and lighter insulating materials than low tech. 4.3.2.2. High tech glazing system. High technology enhances the thermal performance of the glazing systems by inserting a transparent insulator such as; krypton, air, argon, or vacuum between the two layers of glass to reduce thermal conductance. The large gap between panes provides more insulating property such as; a double glass system and triple glass which are also used in the noise polluted environment to provide a good acoustic performance. High technology glazing uses smart window; whether active dynamic or passive. Active windows use electricity to align the electrolytic cell so that the window can become clear, or misalign. In this proposal, the glazing system used in south fac¸ade is Double glazing, clear with no shading for the internal layer. For the external south glass layer, the double Blue glass with 6 mm/13 mm argon was used, its Solar Heat Gain Coefficient (SHGC) is 0.494, direct solar transmission is 0.373, light transmission is 0.5 and U-value is 2.5. For north fac¸ade, a single clear glass used for the eternal layer, while the external one is Double Blue glass with 6 mm/13 mm Argon from the design- builder library.
Double skin facade (DSF) types.
High technology or low technology for buildings envelopes Table 3
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High technology proposal input parameters.
The components of high tech case proposal
External Wall
Roof
Vents Double glass
South and North facade (DSF)
South facade section
Fig. 10
North facade
South facade
High technology proposal model, south fac¸ade at left and north facade at right (design builder).
4.3.2.3. High tech shading. In this case, the simulation has been done twice; the first shading used a blind with high reflectivity slats for the external glass layer of south fac¸ade. The second
Fig. 11
one used more high tech shading, such as an electrochromic glass. In both cases the shade worked dynamically from 8:00 to 18:00 to provide the best thermal comfort.
Daylight simulation in different cases.
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Chart 3
Comparative analysis for indoor air temperature in all cases.
Chart 4
Chart 5
Comparative analysis for humidity ratio in all cases.
Comparative analysis for discomfort (hrs.) in all cases.
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Chart 6 Total discomfort hours annually (1) base case without heating or cooling (2) base case with cooling and heating (3) low tech proposal (4) high tech with blind proposal (5) high tech with electro-chromic proposal.
Chart 7 Total energy consumption (kWh/m2 per year), (1) base case with HVACs (2) base case without HVACs (3) low tech proposal (4) high tech with blind proposal (5) high tech with electro-chromic proposal.
4.3.2.4. High tech heat distribution stage. The double skin facade in this proposal is made up of two glazing layers with an intermediate cavity (1 m in the south and 0.5 m in the north); the natural ventilation was chosen for the cavity space. The inlet and outlet vents were closed at night in winter to keep the spaces worm. In summer, all vents kept open all the day to extract the heated air and reduce humidity. This method reduces the need for HVACs and depends only on the natural ventilation.
5. Simulation results The results of what has been studied and tested are discussed in four significant aspects. First, thermal comfort indices are compared, second energy consumption is indicated and finally both daylight and economic benefits are discussed.
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Chart 8
Comparative analysis between the three cases shows the initial cost and LCC (90 years).
5.1. Thermal comfort
5.3. Daylight
According to ASHRAE Standard 55-2010, there are some specific parameters that must be taken into account to examine the thermal comfort in any building; such as the environmental parameters, air temperature, mean radiant temperature, relative humidity, in addition to the personal parameters; like activity levels and clothing insulation [1], the results of simulation have shown that the air temperature and humidity ratio have been improved at all the modified proposals. Charts 3 and 4 show the internal air temperature and humidity ratio in the base case and the final modified proposals for summer and winter months. Using the electrochromic glass in high tech system provides the best thermal comfort in comparison with the other cases as shown in the Charts 5 and 6. High tech proposals have recorded the least discomfort hours per year, followed by low tech proposal. These proposals increased the comfort hours in the base case, even with heating and cooling systems. The use of Mechanical fans can help to increase natural ventilation, decrease humidity, and provide more thermal comfort in summer.
Good lighting is one of the main factors of indoor comfort that positively influences health and productivity [7]. The increased daylighting of the completely glazed fac¸ade introduces excessive glare and heat at certain times of the day, which requires further measures in design to reduce their negative effects. In both proposals, appropriate measures have been taken; double skin fac¸ade with double glass and Solar shading devices in high tech proposal is designed with airspace to decrease solar heat gain through the glazing and reduce the amount of glare caused by the increased access to daylighting. On the other hand, water wall system with high reflective blind shading provided daylight without glare and decreased the heat gain Fig. 11.
5.2. Energy consumption The total energy consumption of each proposal is presented in Chart 7. Energy-efficient practices were proposed in this study through low-tech and high-tech strategies for building envelopes, which greatly improved the energy efficiency of the studied residential building. In general, the results of the simulation revealed the great potentials of utilizing energy-efficient practices in residential buildings in Alexandria, Egypt. The results have shown that the total energy consumption for the building decreased by 46% for low technology proposal and about 50% for high technology proposal, as shown below. To conclude, the achieved energy-saving provides an example of the possible energy reductions that will be accomplished in the future built environments with two levels of technology.
5.4. Economic benefits This study shows that the base case has the lowest initial cost in comparison with the other proposals. Low tech case has a relatively low initial cost, while High tech case needs more investment during the construction period, since it has a relatively high initial cost. Both low and high tech cases almost have the same operating cost. Life cycle cost for low technology will be the lowest after 90 years (The lifespan of residential buildings), about 50% of the life cycle cost of the base case. The below equation is used to calculate the LCC after a known period of time [9]. The payback in low tech proposal will start after 5–7 years, while high tech proposal payback will start after 12–17 years as shown in the Chart 8. n P ð1þLÞ 1 ð1þrÞn LCC ¼ CI þ Lr CI: initial cost, p: annual operating cost, L: Increase rate in the price of electricity assumed 16%, r: Bank interest rate assumed 12%, n: lifetime
High technology or low technology for buildings envelopes
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Base case (Default construction, materials and systems) Low technology Natural, local materials – passive simple systems (water wall system)
High technology High technology materials intelligent facades systems (DSF).
Windows
Shading Roof shading
Windows shading (Blind with high reflectivity slats) manually controlled
Heat distribution stage
Heat modulation stage
Final proposal for high tech, the added envelope materials easy to disassemble
Insulaon Using Indirect gain/ loss, thermal mass walls that has a low heat gain in summer and allow heat transfer in winter (water wall)
Using low technology materials for glass (single clear or coloured)
Using a natural ventilation, Stack driven and using operating windows schedule ventilation.
Reducing air leaks
Using insulation in Roofs and walls (straw bale)
Wind catcher The opening in north-west
Heat modulation stage
Final proposal for low tech, the added envelope materials easy to disassemble
Intelligent façade
Insulaon
Windows
Shading
(Double skin façade- box window type), (dynamic windows)
Using high technology insulation materials for Roofs and walls (polyurethane foam)
High tech material for glass (Using double glass)
Using smart dynamic shading (dynamic Blind with high reflectivity slatselectro-chromic)
Manage windows opening
Fully integrated control
Diagram 1
Actuated window vents (only natural vent)
Heat distribution stage
Parametric simulation structure.
6. Conclusions Referring to the aim of this research about the importance of adopting the proper technology for building envelopes in the residential buildings in Egypt, the results have revealed that the appropriate technology can provide the best thermal comfort without HVACs, save energy consumption, in addition to providing natural daylight and considerate economic conditions. The experimentation process used a water wall system, single glass and Straw, a local, natural material in Egypt, as insulation material for the low tech system proposal, while High tech proposal used an intelligent fac¸ade (double skin fac¸ade) with high tech material for insulation, high tech glaz-
ing system, smart dynamic shaded, and a smart system for heat distribution. The experiences in this paper have revealed some results with guidelines that can be summarized as follows: The building envelopes have proved to be the most important element that can contribute to reduce the energy consumption and provide comfort of users. The word technology Integrates materials, systems and construction methods. Low technology provides the maximum use of natural, local resources, passive strategies and simple construction methods which have a low economic impact, whereas the high technology uses all available technologies that provide the best results in thermal comfort and energy saving.
3792 Water wall system proved that it is the best passive system, referring to low tech with low cost, and water is the best thermal mass, which can prevent heat in summer and allow heat in winter after the water gets emptied from the water walls. The awareness of using the proper technology, whether high or low, in building envelopes gives more comfort hours and saves more energy consumption than the current situation that uses HVACs. In buildings’ envelops, high tech gives more thermal comfort and saves more energy consumption than Low tech. Low tech has a low initial cost and saves about 46% of energy consumption, while high tech saved about 50% with high initial cost. The two cases almost have the same operating cost, which leads us to use the low tech in building envelopes because it is more convenient for Egypt economy; but the role of high tech in providing more thermal comfort should not be neglected. Increasing insulation, reducing air leaks, increasing winter solar energy, increasing glazing, introducing roof lights, introducing stacks/internal air flows, improving shading, exterior walls with high-mass material and controlling windows opening are essential in both high and low tech in order to remove the need for cooling, decrease heating energy and limit the need for artificial light. As a conclusion, the research will introduce some recommendations: – All designers are invited to use this methodology in order to achieve the best results: first, specify the building and climate zone; second, specify the criteria for performance; third, specify parameters depending on the level of technology (low or high); fourth, simulate the related parameters and finally, evaluate the design alternatives and make a decision. – It is highly recommended that researchers examine more low and high strategies or more parameters of the studied strategy. – The integration between high or low technology design and renewable energy production such using Photo-Voltaic systems or wind turbines certainly achieve the minimum energy consumption rates. Nowadays, all the researchers are aware that the building fac¸ade can generate electricity. – Both designers and householders need to study the costbenefit analysis, which provides developers and users with a clear view of opportunities and risks of investing in high or low tech in residential buildings. – It is important to take into account the other factors; such as the orientation of buildings and the openings ratio and so on, in new buildings – National codes should be highly considered in relation with the different building roles and practices in order to achieve the target of energy-efficient buildings in Egypt.
A.-A. Khalil et al. These results will be helpful for architects, managers, and designers to have a proper viewpoint in the design of fac¸ade elements and their positions. They play an important role in saving energy, which sounds very attractive to building owners who are interested in maximum profits through low construction standards and costs coupled with maximum utilities. Therefore, the awareness of building envelopes technology should be widely developed in order to highlight the importance of adopting these strategies and the economic benefits that will gained. References [1] AHSRAE, ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy, ANSI, USA, 2010. [2] A. Aksamija, Energy Performance of Different Types of Double Skin Facades in Various Climates, Department of Architecture, University of Massachusetts Amherst, Amherst, Massachusetts, USA, 2017. [3] S. Attia, A Tool for Design Decision Making: Zero Energy Residential Buildings in Hot Humid Climates, Presses universitaires de Louvain, Belgium, 2012. [4] S. Attia, A. Evrard, E. Gratia, Development of Benchmark Models for the Egyptian Residential Buildings Sector, Elsevier, 2012, p. 16. [5] D.A. Bainbridge, A Water Wall Solar Design Manual For environmentally responsive buildings that increase comfort, save money, and protect the environment, 2005. [6] N.V. Baker, Passive and Low Energy Building Design For Tropical Island Climates, Commonwealth Secretariat, London, 1987. [7] C. Gallo, M. Sala, A.A.M. Sayigh, Architecture: Comfort and Energy, Elsevier, UK, 1998. [8] B. Cody, The Role of Technology in Sustainable Architecture, 2014. [9] S. Fuller, S. Petersen, Life-Cycle Costing Manual for the Federal Energy Management Program, Department of Commerce, USA, 1996. [10] T. Maile, M. Fischer, V. Bazjanac, Building Energy Performance Simulation Tools – A Life-Cycle and Interoperable Perspective, Center for Integrated Facility Engineering, California, 2007. [11] A. Nails, H. Farm, Todmorden, 8RJ, O. Information Guide to Straw Bale Building, 2001.