Energy Efficient Building Design Strategies For Hot Climates Construction Essay

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This research discusses energy efficient design strategies of traditional houses in Iraq (hot-arid climate), climatic design techniques and potentials for renewable energy systems that can be implemented in the contemporary residential design techniques in order to offset the absence of produced energy (due to current economic and political issues) and help decreasing demand for electricity, which is used extensively to overcome the indoor thermal discomfort during the harsh summer seasons. A comparison between traditional Baghdadi house (Hosh), which existed before the discovery of oil, and a contemporary house design option is to be made to evaluate the thermal performance of both options in this climatic zone in order to adapt more energy efficient design strategies; and also to integrate features for sustainable building design and potentials to implement renewable energy systems.

A simulation modeling is to be used to conduct analysis of energy efficient design strategies, namely relating to building envelope, size and direction, ventilation, shading elements, and using renewable energy systems in order to present recommendations that helps in consequential energy offset while preserving comfort.

Keywords:

Introduction

Examining the energy demand in such region, buildings, with particular reference to residential houses, are one of the most significant energy-sensitive entities (Al-ajmi & Hanby, 2008). It is stated that buildings consume over half of all electricity and one-third of natural gas (Yilmaz, 2007). Reduction of energy consumption in residential buildings is a major aim worldwide and is a particular challenge in this region for the reasons mentioned previously (Al-ajmi & Hanby, 2008). Therefore, sustainable design strategies are of great importance nowadays in order to reduce energy consumption in residential buildings.

One may say that sustainability was already a driving force in the past, showing its validity in those days in different forms and techniques. Therefore, problems and precautions in design and construction did not change fundamentally, although a lot of development was seen in materials and technology. Of course, these developments may have had some negative effects (Yilmaz, 2007).

Energy efficient design strategies for traditional houses in such climate are significantly different from each other as it can be easily seen in the traditional design (Yilmaz, 2007).

Description of Problem Area

Energy consumption is becoming more and more important in today's world because of a possible energy shortage in the future. Efficient use of energy has become a key issue for the most energy policies (Yilmaz, 2007).

In regions where hot-arid climatic zone is prevailed, practically in Iraq, present economic and political circumstances have become the main reasons that led to a significant energy shortage although Iraq has a spare operational capacity of oil supply in comparison with other countries around the world.

A significant need for new energy efficient design strategies and developed buildings construction standards in this area has become essential in order to offset the absence of produced energy and help decreasing demand for electricity, much of which is consumed in air conditioning systems, which is used extensively to overcome the indoor thermal discomfort during the harsh summer seasons (Al-ajmi & Hanby, 2008).

Conceptual Framework

Figure (1) provides a diagram of the conceptual framework that has devised for this research.

The proposed research study into traditional and contemporary building design systems will rely on an experimental research strategy in the positivist system of inquiry (developed design strategies). The research will attempt to establish a "comparison" (Groat and Wang, 2002, P. 254) between a treatment (independent variable) and an outcome (dependent variable) through the evaluation of measured results.

Figure (1) Conceptual diagram of the research variables (Groat & Wang, 2002)

Research Questions

Do traditional houses perform better than contemporary ones? Why?

Is it feasible to use traditional design strategies in contemporary houses?

How could we achieve a sustainable building design in such climatic zone?

Do we need new or developed strategies in order to achieve sustainable building design in such climatic region?

What if we integrate renewable energy systems into traditional house design?

Project Goals and Specific Objectives

The purpose of this research is to:

Make a comparison and evaluation of thermal performance of residential houses (traditional vs. contemporary) in Iraq (hot-arid climate) in order to adapt more developed and energy efficient design strategies.

Integrate new trends for sustainable design in residential houses in this area.

Potentials to implement renewable energy systems.

This research is achieved through the following:

Extensive overview of the antecedent literature in the area of energy efficiency and thermal building performance in such climatic zone.

Identify the most effective strategy from the literature that can be applied in order to develop more energy efficient design strategies.

Un-wrap issues of energy efficiency, building performance and sustainable design systems.

Use a simulation modeling as a tactical tool to make comparison between contemporary and traditional building design systems and energy performance in order to investigate the thermal characteristics and energy savings for both building designs using different strategies and also potentials to integrate sustainable features using renewable energy system.

Test outcome results and write a research report accordingly which combines my understanding of the relevant theory and previous research with the results of my empirical research.

Literature Review

The literature review is structured around the key concepts of significance of energy efficient design strategies, thermodynamics of hot-arid climates, Inventory of traditional design elements in hot-arid climate and energy simulation methods. These key concepts have led to the research questions and the proposed methodology for this research proposal. See figure1 for the map of literature reviewed.

Figure () Map of sources reviewed

Figure () Research Literature Review Diagrammatic (Groat & Wang, 2002)

Building Design Strategies

Climatic Building Strategies

Research by Ochoa & Capeluto (2008) states a quick review of design strategies for different climatic zones. This is necessary to examine when and how design strategies should be considered, particularly during design process. Climatic building strategies in hot climates differ from those of cold ones, For example, in cold climates heat collection and storage is essential, and ventilation must be limited for the same reasons. Short daytime and low radiation levels in winter make maximum penetration of natural light to be desired.

On the other hand, in hot climates heat must be excluded, the amount of relative humidity controlled, and the thermal mass cooled usually through natural ventilation during the night. Daylight penetration must be carefully managed using control devices (see figure 1) (as cited in Ochoa & Capeluto, 2008, Building and Environment, P.1830).

Figure (1) Building strategies for cold and hot climates (Ochoa & Capeluto, 2008).

Optimized Building Envelope

A building envelope is a skin that separates between the interior and the exterior of a building. It serves as the outer shell to protect the indoor environment as well as to facilitate its climate control (controlling heat transfer between building layers).

The study by Danny Harvey (2009) reviews the literature concerning energy efficiency that can be achieved through optimized building envelope.

According to Danny Harvey (2009), "The effectiveness of the thermal envelope depends on:

(1) The insulation levels in the walls, ceiling, and other building parts;

(2) The thermal properties of windows and doors; and

(3) The rate of uncontrolled exchange of inside and outside air which, in turn, depends in part on the air tightness of the envelope (infiltration/excitation)" (Energy Efficiency, P. 141).

Reducing the Cooling Load

Energy conservation and climatic design techniques that can be implemented in residential houses in this area (hot-arid climate) are useful for reducing cooling energy consumption (Al-Temeemi, 1995).

Danny Harvey's (2009) research found the following: Reducing the cooling load requires:

(1) Orienting a building to minimize the wall area facing directions that are most difficult to shade from the sun;

(2) Clustering buildings to provide some degree of self shading (as in many traditional communities in hot climates);

(3) Providing fixed or adjustable shading;

(4) Using highly reflective building materials;

(5) Increasing insulation;

(6) Using windows that transmit a relatively small fraction (as little at 25%) of the total (visible + invisible) incident solar energy while permitting a larger fraction of the visible radiation to enter for daylighting purposes;

(7) Utilizing thermal mass to minimize daytime interior temperature peaks;

(8) Utilizing night time ventilation to remove daytime heat; and

(9) Minimizing internal heat gains by using efficient lighting and appliances.

The combination of external insulation, thermal mass, and night ventilation is particularly effective in hot-arid climates, as placing the insulation on the outside exposes the thermal mass to cool night air while minimizing the inward penetration of daytime heat into the thermal mass (Energy Efficiency, P. 141).

Passive cooling techniques

By using the above measures to reduce the thermal load of the building, other techniques requires small inputs of mechanical energy to optimize passive cooling processes (Danny Harvey, 2009).

Danny Harvey's (2009) research discussed the following major passive cooling techniques:

Passive ventilation

Passive ventilation reduces the need for mechanical cooling by directly removing warm air when the incoming air is cooler than the outgoing air, reducing the perceived temperature due to the cooling effect of air motion and increasing the acceptable temperature through psychological adaptation when the occupants have control of operable windows.

Passive ventilation requires a driving force, and an adequate number of openings, to produce airflow. It can be induced through pressure differences arising from inside-outside temperature differences or from wind.

Design features, especially traditional, that create thermal driving forces and/or utilize wind effects include courtyards, atria, wind towers, solar chimneys, and operable windows. Passive ventilation not only reduces energy use, but can improve air quality and gives people what they generally want. In buildings with good thermal mass exposed to the interior air, passive ventilation can continue right through the night, sometimes more vigorously than during the day due to the greater temperature difference between the internal and external air. Night time ventilation, in turn, serves to reduce the cooling load by making use of cool ambient air to remove heat (as cited in Danny Harvey, 2009, Energy Efficiency, P.142).

Evaporative cooling

Danny Harvey's (2009) study further discussed the following in terms of producing evaporative cooling techniques:

Evaporation of water cools the remaining liquid water and air that comes into contact with it. The coldest temperature that can be achieved through evaporation is called the wet-bulb temperature and depends on the initial temperature and humidity (the higher the initial humidity, the less evaporation and cooling that can occur). There are two methods of evaporative cooling the air supplied to buildings. In a direct evaporative cooler, water evaporates directly into the air stream to be cooled. In an indirect evaporative cooler, water evaporates into and cools a secondary air stream, which cools the supply air through a heat exchanger without adding moisture. By appropriately combining direct and indirect systems, evaporative cooling can provide comfortable temperature-humidity combinations most of the time in most parts of the world. Evaporative cooling is most effective in dry regions, but water may be a limiting factor in such regions. However, arid regions tend to have a large diurnal temperature range, so thermal mass with external insulation and night ventilation can be used instead (Energy Efficiency, P.142).

Influence of Energy Efficient Design Strategies on Design Stages

The architectural design process is iterative and moves from the abstract (definition of massing, orientation, and image) to the specific (lighting control, mechanical ventilation type) (as cited in Ochoa & Capeluto, 2008, Building and Environment, P.1830).

At the design stage, key decisions taken by architects can significantly influence potentials to optimize building efficiency. These include decisions affecting the selection of building components.

According to Ochoa & Capeluto (2008), "As it advances and more specialists are called in to solve details, earlier decisions, which could have an enormous influence on the building performance, are expensive and harder if not impossible to change" (Building and Environment, P.1830).

Other influential factors unrelated to climatic strategies must be taken into account. For example, a certain orientation that is ''bad'' for energy consumption might define how well the building performs (Ochoa & Capeluto, 2008). However, it would require an Integrated Design Process (IDP), in which the design process optimizes the building performance by involving all members of design-making team from the beginning.

The importance of an Integrated Design Process (IDP) on building systems approach

Danny Harvey's (2009) study found the following:

The systems approach requires an Integrated Design Process (IDP), in which the building performance is optimized through an iterative process that involves all members of the design team from the beginning. However, the conventional process of designing a building is a largely linear process, in which the architect makes a number of design decisions with little or no consideration of their energy implications and then passes on the design to the engineers, who are supposed to make the building habitable through mechanical systems (Energy Efficiency, P. 140).

The steps in the most basic IDP are: & to consider building orientation, form, and thermal mass

& to specify a high-performance building envelope & to maximize passive heating, cooling, ventilation, and daylighting & to install efficient systems to meet remaining loads & to ensure that individual energy-using devices are as efficient as possible and properly sized & to ensure the systems and devices are properly commissioned By focusing on building form and a high-performance envelope, heating, and cooling loads are minimized, daylighting opportunities are maximized, and mechanical systems can be greatly downsized (Danny Harvey, 2009).

Thermodynamics of Hot-Arid Climates

Any consideration to energy efficiency applications or design strategies in any climatic zone requires examining of thermodynamics and human comfort.

In his Text "Natural Energy and Vernacular Architecture: Principles and Examples, With Reference to Hot Arid Climates", the author demonstrates properties of energy that must be considered in order to fully understand climatic phenomena. Heat, radiation, pressure, humidity, and wind, among other factors, interact mutually to establish microclimatic conditions appropriate to hot-arid climatic (Fathy, 1986).

According to Fathy (1986), the following are some of these basic concepts applied to hot-arid climates:

Thermal gain

Solar radiation is the principal source of heat in hot-arid zones, and this heat can be transmitted during the day to the building interior in a number of ways. The most important is by conduction of the absorbed solar radiation through the walls or roof at a rate determined by the thermal conductance (or thermal resistivity) of wall components. (The relationship involving the incoming and reflected solar radiation absorbed and re-emitted heat and heat gain is shown in figure 2 below for the case of a typical white painted surface).

Figure (2) (Fathy, 1986)

Heat gain can also be caused by ventilation. The rate of gain is dependent on the ventilation rate. Ventilation heat gain can be avoided by restricting the size of openings, especially during the heat of the day. The other sources of heat gain are the inhabitants of the building themselves and household equipment such as electric lights and appliances. These sources, unlike the solar radiation, can contribute heat even at night (see figure 3) (Fathy, 1986).

Figure (3) Modes of heat transfer (Fathy, 1986)

Thermal loss

Heat is lost by conduction through the walls, by exactly the same process that it is gained from the direct solar radiation once it has been absorbed by the surface or through the roof by a combination of convection and conduction. Ventilation is also another mode of heat loss. Evaporation from the surface of the building or from objects within the interior can produce a cooling effect on the building which acts as a source of heat loss. In hot arid climates, this can be a particularly effective cooling mechanism since the rate of evaporation in dry air is very high. Figure 3 also shows the modes of heat loss (Fathy, 1986).

Cooling by evaporation

Evaporative cooling is used for cooling in hot dry areas (such as in Iraq, where the people place against the windows panels of dried desert plants, which are kept moist by water dripping from perforated pipes positioned above them) (Fathy, 1986).

Dynamic thermal equilibrium

The heat gained by the building can be expected to be balanced by the heat lost and an internal temperature distribution thus established. These temperatures are dependent on the outside temperature and the ratio of the heat gained to the heat lost and can be adjusted by regulating the sources of heat gain and loss. Before examining the systems and devices that have been developed to do this in the hot arid zones, it is first necessary to have an idea of the heat-regulating mechanism of the human body and the microclimatic conditions for human comfort.

Table (1) Heat gain and loss processes for the human body (Fathy, 1986).

Mechanism

Gain Process

Loss Process

Metabolism

Basal heat production

 

 

Digestion

 

 

Activity

 

 

Muscle tensing and shivering in response to cold

 

Radiation

From solar radiation-direct and reflected

To surrounding air

 

From radiation by radiators

 

Conduction

From air above skin temperature (increased by air movement)

To air below skin temperature

 

From warmer bodies in contact

To cooler bodies in contact

Evaporation

 

From respiratory tract

 

 

From skin covered with perspiration or applied water

Conditions of human comfort

A convenient standard for thermal comfort is required. Analysis shows that a variety of factors can be involved in situations of discomfort. For example, temperature alone does not determine discomfort. In Athens, 32 °C is quite bearable, but it is generally intolerable in Bahrain. The difference is due entirely to the relative humidity of the atmosphere. In Bahrain the air is very humid and perspiration evaporates slowly, decreasing the body's ability to lose heat. In Athens, with its dry air, the evaporation rate is high and perspiration evaporates quickly lowering body temperature. The factors that have been identified as standard for thermal comfort within buildings are: air temperature, air humidity, rate of air movement, level of radiation, and rate of heat production by the bodies of people in the building [4].

Inventory of design elements for traditional housing design in hot-arid climates

Building materials

The materials surrounding the occupants of a building are of prime importance for protection against heat and cold. Considering an external wall exposed to a high outside air temperature and a lower inside air temperature (see figure 4), the rate of heat flow transmitted through the wall from the outside air to the inside air is proportional to the air temperature difference, area of the wall, and rate of global heat transmittance that can be determined from an analysis of the components of the total resistance to heat flow. The total resistance is composed of the resistance to heat flow through the material, the interfacial resistance at the external surface, and the interfacial resistance at the internal surfaces. Since the interfacial resistances are determined primarily by temperature conditions over which the builder has little control, his principal effect on the heat transmittance is on changing the resistance to heat flow through the wall material (Fathy, 1986).

Figure (4) (Fathy, 1986)

Table 2 lists the thicknesses of walls composed of various construction materials needed to achieve coefficients of approximately 1.1 kcal/hm²C°. The mud brick is most appropriate for achieving thermal comfort in addition to being widely available to all segments of the population (Fathy, 1986).

Table (2) Thicknesses of walls of different material (Fathy, 1986)

Wall Material

Wall Thickness

Thermal Transmittance

 

(in m)

(in in)

(in kcal/ hm²C°)

Hollow brick block

0.30

12

1.10

Double-wall brick with holes and 8-cm cavity

2 x 0.12

2 x 4.7

1.12

Brick wall with holes

0.38

15

1.03

Sand-lime brick

0.51

20

1.25

Hollow block sand-lime brick

0.51

20

1.16

Lime

0.51

20

1.10-1.35

Concrete

1.00

39

1.20

Orientation

In hot climates, the sun is the major source of heat. The position of the sun must be determined for all hours of the day at all seasons as well as the direction of the prevailing winds, especially during the hot season. In addition, for an ensemble of buildings forming a sector, there will be reflection from adjacent buildings and wind screening by clusters of buildings, which contribute to a specific microclimate for each location in the sector. Wind movement and humidity also are important and should be considered simultaneously with the direct and indirect effects of the sun. The main objective is to establish the optimum orientation with regard to the sun and the prevailing wind (Fathy, 1986).

Shading

Generally, a building with a facade opening to the west is the worst case encountered in hot-arid climate, owing to the heat gain of the surrounding environment during the day and the angle of altitude, which allows the sun's rays to penetrate into the interior.

Openings

Window openings normally serve three functions: to let in direct and indirect sunlight, to let in air, and to provide a view (Fathy, 1986).

The venetian blind

One device which can be added directly to the window is the venetian blind. This blind is made of small slats, about 4-5 cm wide, closely set in a wooden frame at an angle that will intercept the sun's rays. The slats are often movable so the angle can be changed. This feature of adjustability renders venetian blinds very useful in regulating solar radiation and wind flow into rooms. Using the venetian blind, the sun's rays can be blocked out without obstructing the breeze, which generally blows from the northwest in most hot arid areas like Iraq. As shown in figure 5a, changing the position of the blind alternatively by to block the direct sunlight, the wind is redirected uselessly over the heads of the occupants, as figure 5b illustrates. Also, if the slats are made of metal, they then absorb some incoming radiation and reradiate it into the room as heat (Fathy, 1986).

Figure (5) (Fathy, 1986)

The Shanshool or Mashrabiya

This was a cantilevered space with a lattice opening, where small water jars were placed to be cooled by the evaporation effect as air moved through the opening. The name is used for an opening with a wooden lattice screen composed of small wooden balusters that are circular in section and arranged at specific regular intervals. The shanshool has five functions. These functions involve: (1) controlling the passage of light, (2) controlling the air flow, (3) reducing the temperature of the air current, (4) increasing the humidity of the air current, and (5) ensuring privacy. Its cooling and humidifying functions are closely related. All organic fibers, such as the wood of a shanshool readily absorb, retain, and release considerable quantities of water. Wind passing through the interstices of the porous-wooden shanshool will give up some of its humidity to the wooden balusters if they are cool, as at night. When the shanshool is directly heated by sunlight, this humidity is released to any air that may be flowing through the interstices. This technique can be used to increase the humidity of dry air in the heat of the day, cooling and humidifying the air at a time when most needed. The balusters and interstices of the shanshool have optimal absolute and relative sizes that are based on the area of the surfaces exposed to the air and the rate at which the air passes through.

In addition to these physical effects, the shanshool serves an important social function: it ensures privacy from the outside for the inhabitants while at the same time allowing them to view the outside through the screen (Fathy, 1986).

Table (3) Summary of architectural elements of traditional building in Iraq (hot-arid climate), as they have been common from the 13th to the end of the 19th century. Retrieved from http://www.brainworker.ch/Irak/architecture.htm

 

Oda: the simple room

Tarma: open balcony with pillars

Ursi: most probably from russi, russian. The most important room of the house, as at the same time you may see, but not been seen as much as in a tarma, ivan or talar. Its separated from the tarma by a window-wall from colored glasses, without door. Those were the masterpieces of Baghdadi carpentry.

Talar, a usable open room behind the tarma. The difference to the iwan is, that it can't be entered directly from the rooms beside it. I's separated from the tarma by additional pillars.

Iwan(or Liwan), a room behind the tarma or adjacent tot the inner courtyard, that is on one side open.

Hosh, the central courtyard, often with a fountain in the middle.

sirdab, the cellar, that did not only serve as store, but  as cooling hall and for the provision of cool air through the badgir-sirdab-system.

neem, a cellar that is only half buried. Mostly with one window.

During the hot summer nights the roof was and is used in Baghdad for sleeping. The high value of privacy demanded, that no house was higher than the others, so that nobody was able to look down on his neighbors roof.

 

kabishkan: The Penthouse, from where one is able to control all the house. Often those rooms have been placed like eyries in all four corners of the inner courtyard. 

The roof

If the outdoor air temperature is higher than the indoor temperature, the outer surface of the roof exposed to the sun is heated as it absorbs radiation, and, being in contact with the outside hot air, also is heated by conduction. The roof then transmits this heat to the inner surface, where it raises the temperature of the air in contact with it by conduction. At the same time, it radiates heat that is absorbed by people and objects indoors, thereby affecting thermal comfort. In hot arid countries, since the air temperature drops considerably during the night, the inhabitants have arranged the roof architecturally into loggias or open galleries and lightweight roof covers. These loggias and roof covers have the double function of shading the roof during the day and providing physiologically comfortable living and sleeping spaces at night (Fathy, 1986).

Figure (6) Different types of roofing in hot-arid climates (Fathy, 1986)

The wind-escape

The technique of using the suction caused by low air-pressure zones to generate steady air movement indoors is used in the design of the wind-escape. The funnel and side tube used to illustrate the Bernoulli effect or Venturi action (see figure 7) are transposed into the structural elements of an architectural design in order to accelerate air movement and to create drafts in places with no exposure to the outside, such as basements in Iraq. This concept can be applied more advantageously in designs for use above ground. The wind-escape can accelerate effective ventilation and air circulation when used with other devices for air movement such as windows, doors, and the malqaf or wind-catch (Fathy, 1986).

Figure (7) Bernoulli Effect (Fathy, 1986)

The malgaf

In hot arid zones, a difficulty is found in combining the three functions of the ordinary window: light, ventilation, and view. Therefore, it is necessary to satisfy the three functions ascribed to the window separately. To satisfy the need for ventilation alone, the malqaf or wind-catch was invented. This device is a shaft rising high above the building with an opening facing the prevailing wind. It traps the wind from high above the building where it is cooler and stronger, and channels it down into the interior of the building. The malqaf thus dispenses with the need for ordinary windows to ensure ventilation and air movement. The malqaf is also useful in reducing the sand and dust so prevalent in the winds of hot arid regions. The wind it captures above the building contains less solid material than the wind at lower heights, and much of the sand which does enter is dumped at the bottom of the shaft. In the areas of An-Najf and Al-Kufa in Iraq, where air temperature is very high in summer, people live in basements ventilated by small holes in the ceiling and a malqaf with a very small inlet. Figure 8 shows plans and the section of a residence with a basement from this region. However, as the airflow is small and the air circulation is insufficient, this design is unhealthy and a possible cause of lung diseases. In some designs, the drafts from the malqaf outlet are cooled by passing over water in the basement.

Figure (8) The Malgaf (Fathy, 1986)

The Bãdgir-sirdab

In Iraq (hot-arid climate)and the countries of the Gulf, a specific type of malqaf called the bãdgir was developed. The system badgir-sirdab was a cheap, environmentally friendly and energy saving solution to create an acceptable climate inside houses. Not an easy endeavor with outside temperatures of over 50°C during summer. The badgirs caught the wind and led it through the cool cellar into the house.

Figure (9) The Bãdgir-sirdab (Fathy, 1986)

It has a shaft with the top opening on four sides (occasionally only two), and with two partitions placed diagonally across each other down the length of the shaft to catch breezes from any direction. This shaft extends down to a level that allows the breeze to reach a seated or sleeping person directly. A great advantage of the malqaf and the bãdgir is that they solve the problem of screening resulting from the blocking of buildings in an ordinary town plan. Several research centers have been working to develop the best configuration for the implantation of blocks of buildings, while avoiding screening of blocks by those upwind. When designing the malqaf and the bãdgir, it is important to determine the airflow pattern around the house, following the principles of aerodynamics, and to orient the inlet appropriately in the airflow. Generally, a building placed in the wind will create a zone of compression to the windward side and a low-pressure zone to the leeward side. This low-pressure zone continues a certain distance beyond the building, depending on the wind velocity, as illustrated in figure 10. The faster the wind velocity, the shorter the low-pressure zone extends, because of eddies created on the leeward side which disrupt the smooth airflow pattern. For normal wind velocities, the length of the low-pressure zone can be taken to be five times the height of the building (Fathy, 1986).

Figure (10) (Fathy, 1986)

The courtyard house

The relatively static cooling system used in a courtyard house can provide the basis for understanding modifications that can generate air movement by convection. In hot dry zones, air temperature drops considerably after sunset from re-radiation to the night sky. The air is relatively free of water vapor that would reflect the heat or infrared radiation back toward the ground. As evening advances, the warm air of the courtyard, which was heated directly by the sun and indirectly by the warm buildings, rises and is gradually replaced by the already cooled night air from above; this cool air accumulates in the courtyard in laminar layers and seeps into the surrounding rooms, cooling them. In the morning, the air of the courtyard, which is shaded by its four walls, and the surrounding rooms heat slowly and remain cool until late in the day when the sun shines directly into the courtyard. The warm wind passing above the house during the day does not enter the courtyard but merely creates eddies inside, unless baffles have been installed to deflect the airflow. In this way, the courtyard serves as a reservoir of coolness (Fathy, 1986).

Evaluation of building performance and energy consumption: energy simulation method

"Energy Simulation in Building Design" explains two distinct stages of predicting building energy consumption. The first stage is concerned with predicting the energy requirements to satisfy the demands of the building's activities; this is found by modifying the various heat gains and losses as a function of the distributed thermal capacities. In the second stage, these energy requirements are modified by the operating characteristics of the plant to give the energy actually consumed. The first stage is concerned with the design of the building to reduce the energy requirements, while the second stage is concerned with the design of the installed plant to best match these requirements and minimize consumption (Clarke, 2001). The first stage is significant in developing effective and detailed methodology which has to be used in supporting results of this research study (see figure 11).

Figure (11) building model - first stage (Clarke, 2001)

According to American Society of Heating, Refrigerating and Air-Conditioning Engineers (2009), the standard demonstrates the method for estimating energy use for building modeling design and associated design optimization (forward modeling) as follows (ASHRAE, 2009):

General modeling approach

A mathematical model is a description of the behavior of a system. It is made up of three components:

1. Input variables (statisticians call these regressor variables, whereas physicists call them forcing variables), which act on the system. There are two types: controllable by the experimenter and uncontrollable (e.g., climate).

2. System structure and parameters/properties, which provide the necessary physical description of the system (e.g., thermal mass or mechanical properties of the elements).

3. Output (response, or dependent) variables, which describe the reaction of the system to the input variables. Energy use is often a response variable.

The science of mathematical modeling as applied to physical systems involves determining the third component of a system when the other two components are given or specified. There are two broad but distinct approaches to modeling; which to use is dictated by the objective or purpose of the investigation (as cited in ASHRAE, 2009, P. 19.1).

Forward models

The objective is to predict the output variables of a specified model with known structure and known parameters when subject to specified input variables. This approach presumes detailed knowledge not only of the various natural phenomena affecting system behavior but also of the magnitude of various interactions (e.g., effective thermal mass, heat and mass transfer coefficients, etc.). The main advantage of this approach is that the system need not be physically built to predict its behavior (ASHRAE, 2009). Thus, this approach is ideal in the preliminary design and analysis stage and is most often used then. The primary benefits of this method are that it is based on sound engineering principles usually taught in colleges and universities, and consequently has gained widespread acceptance by the design and professional community (ASHRAE, 2009).

Major government-developed simulation codes, such as BLAST, DOE-2, and EnergyPlus, are based on forward simulation models (see figure 12) (ASHRAE, 2009).

Figure (12) Flow chart for building energy simulation program (ASHRAE, 2009)

Selecting an analysis method

The most important step in selecting an energy analysis method is matching method capabilities with project requirements. The method must be capable of evaluating all design options with sufficient accuracy to make correct choices. The following factors apply generally:

• Accuracy: The method should be sufficiently accurate to allow correct choices. Because of the many parameters involved in energy estimation, absolutely accurate energy prediction is not possible.

• Sensitivity: The method should be sensitive to the design options being considered. The difference in energy use between two choices should be adequately reflected.

• Versatility: The method should allow analysis of all options under consideration. When different methods must be used to consider different options, an accurate estimate of the differential energy use cannot be made.

• Speed and cost: The total time (gathering data, preparing input, calculations, and analysis of output) to make an analysis should be appropriate to the potential benefits gained.

• Reproducibility: The method should not allow so many vaguely defined choices that different analysts would get completely different results.

• Ease of use: This affects both the economics of analysis (speed) and the reproducibility of results (ASHRAE, 2009).

Building energy simulation

"Simulation research involves controlled replication of real-world contexts or events for the purpose of studying dynamic interactions within that setting" (Groat & Wang, 2002, P. 278). Building energy simulation is used as a tool in the design of buildings, for determining compliance to building standards and for the economic optimization of building components. It can be used on buildings of any size, from one zone residential houses to multi-zone large commercial buildings (ASHRAE, 2009).

There are different methods of building energy analysis which vary in complexity, but all have three common elements, the calculation of space heating and cooling loads, the load on secondary equipment, and the energy requirements of primary equipment. Secondary equipment is that equipment which distributes the heating, cooling or ventilating medium to the conditioned space, while primary equipment is central plant equipment that converts fuel or electricity to the heating or cooling effect. Generally, as a method becomes more complex it becomes more accurate. However, the improved accuracy usually comes with increased effort and time to perform a simulation (ASHRAE, 2009).

Methodology and Research Analysis Techniques:

Strategy and Tactic

The proposed methodology is an experimental research strategy conducted by a simulation modeling program as a tactical tool with required specific building input parameters (independent variables) integrated with the program software used for the purpose of this study.

A comparison between traditional Baghdadi house design (Hosh) and a proposed contemporary house design is to be made to evaluate the thermal building performance (thermal characteristics) and economic optimization of building components (dependent variables) in Iraq (hot-arid climate) in order to adapt more energy efficient design strategies; and also to integrate new sustainable features into buildings and potentials to implement renewable energy systems.

Table () Proposed Research TopStraTa (TopicStrategyTactic)

Research Method

Methodology

Strategies

Tactics

Experimental and simulation research method.

(Comparison of traditional and contemporary design and building thermal performance in hot-arid climatic zone)

Analysis techniques is presumed to be designed to have four different building cases, Case 1, 2, 3 and 4respectively

Building Model to be created using computer soft-wares, Ecotect, or EnergyPlus.

The input data for the analysis consist in the specific parameters.

Measurement of the outcome variables.

Analysis Techniques

As shown in table (4), analysis techniques is presumed to be designed to have four different building cases, Case 1, 2, 3 and 4 respectively, the same climatic data for a local weather condition (hot-arid zone) (uncontrollable input variables) are applied to all cases. All cases are presented with respect to the same following considerations: building location and orientation, building dimensions, indoor temperature, and number of occupants, lighting and building usage and air-conditioning system. Case 1 and 2 are the same with respect to contemporary building components but different in building design layouts (contemporary vs. traditional) in the whole of the simulation results, Case 3 represents the traditional building case with respect to building components and design layout (Al-ajmi & Hanby, 2008).

Case 4 is going to be the most optimized results with respect to building components and design layout from the previous cases integrated with a proposed renewable energy component and system upgrades.

Table (4) Building model cases for thermal analysis

Case No.

Building Cases

A

Building components (contemporary design option)

A-d

Building design strategy (contemporary design layout)

B

Building components (traditional design option)

B-d

Building design strategy (traditional design layout)

C

Renewable energy components and design upgrades

E

Considerations affecting energy output (e.g. climate)

1

â-

â-

â-

2

â-

â-

â-

3

â-

â-

â-

4

The most optimized results from cases 1, 2, or 3 respectively

â-

â-

Building Description

Building cases components which are proposed to be different in building materials (layers), thickness, and thermal properties are as follows: (1) Exterior Walls, (2) Floors. (3) Roofs.

These components are integrated into a particular building design layout (design strategies); the following are proposed input data (independent variables or treatments) for the building design cases associated with design layout alternatives:

Floor plan shape

Wall area

Roof area

Windows area

Building volume

Windows type

U-value of the window

Internal shading factor

Infiltration air change

Outcome Measures

The simulation model is to be conducted to investigate the "thermal characteristics and energy use" for both traditional and contemporary design layout using different design strategies and also potentials to integrate sustainable features for renewable energy system within these options (Al-ajmi & Hanby, 2008).

Figure (14) Building model cases Inputs data (Al-ajmi & Hanby, 2008)

Selecting appropriate energy analysis computer programs:

According to ASHARE (2009), "Selecting a building energy analysis program depends on its application, number of times it will be used, experience of the user, and hardware available to run it. The first criterion is the capability of the program to deal with the application. For example, if the effect of a shading device is to be analyzed on a building that is also shaded by other buildings part of the time, the ability to analyze detached shading is an absolute requirement, regardless of any other factors. Because almost all manual methods are now implemented on a computer, selection of an energy analysis method is the selection of a computer program" (ASHRAE, 2009).

Pilot Study

The pilot study is an experimental research to develop building model cases for the proposed treatments (building components and design layouts). The intention is to make a comparison between the proposed building cases 1, 2, 3 & 4 respectively, to get the most optimized results and integrate the outcome with proposed renewable energy component(s) in order to adapt a developed design strategies for sustainable building system, as described in the conceptual framework section of the research proposal. The pilot study is intended to have the following elements:

Energy Simulation Program software.

A computer building model for traditional design layout (see figure 13).

A modified computer building model for traditional design layout (this represents the contemporary design option by excluding design strategies that are employed in traditional design option.

Building components description for both traditional and contemporary building cases, as decried in the analysis techniques section.

Figure (13) Traditional Baghdadi house (Hosh) Retrieved from http://www.brainworker.ch/Irak/architecture.htm

Recommendations

Solar Radiation is the primary source of heat gain in this area during the long summer season with extreme high temperature. Therefore the summer period (cooling energy) will dominate any design strategy (Al-Temeemi, 1995).

Develop design guidelines for sustainable building approaches; this could be managed by employing appropriate traditional design features into sustainable building design to help creating a favorable microclimate.

Time Table

Method of procedures

Planned Start

Planned finish

Literature review on relevant theory which will lead to a summary report and a initial annotated bibliography till the final report submission

15 March

1 August

Examine strategies and tools that are need for the energy simulation

1 April

15April

Create the building simulation model

15 April

1 May

Collect and test data

3 May

22 May

Analysis of input data

1June

15 June

Development of the final report by measuring the outcome variables results from the simulation

15 June

1July

Final report and submission

1 July

1August

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