Department of Civil Engineering, College of Technological Studies, Shuwaikh 70654, Kuwait
In this paper, a building model representative of a typical Kuwaiti dwelling has been implemented and encoded within the TRNSYS-
Keywords: energy efficient building, sensitivity analysis, TRNSYS simulation program, energy conservation code
Economical and industrial development in countries, which have a dry desert climate, has led to an increasing demand for electricity, much of which is consumed by air conditioning system, which are used extensively to overcome the indoor thermal discomfort during the harsh summer season. Kuwait has a long harsh summer season extending from April to October, and the ambient temperature during this is very high. Daily average temperature often goes beyond 45oC with strong solar radiation, which strikes each part of the building in turn as the sun moves around a clear sky. The solar intensities on horizontal surfaces are the greatest at mid-
Each of these factors could influence the cooling load of the building. The degree of influence of each factor will vary from one building to another depending on the variation in architectural design, function of the building and materials used in the construction. In Kuwait, the Ministry of Electricity and Water (MEW) issued an energy conservation code in 1983, Ministry of Electricity. This code represents a set of regulations that guides the construction of new buildings. All buildings that had received authorisation to be built prior to the code do not include any energy conservation measures. The National Housing Authority (NHA) undertakes to use new building materials that were not considered in the MEW code but are reliant on the information received from the Kuwait Institute for Science and Research (KISR). However, Kuwaiti-
Therefore, the aim of this paper is to arrive at a building design that is both energy-
In this study, the sensitivity analysis technique is used to achieve building energy efficiency through proper selection of variables conditions and building design and materials. The latter technique with the assessment of computer simulation program i.e. TRNSYS-
2.1 Techniques of sensitivity analysis for building
Sensitivity analysis for building is a technique developed for optimizing a number of system parameters. Sensitivity analysis techniques are used in building energy efficiency to minimize building energy consumption and to achieve the best load and energy characteristic with respect to building input parameters and deployment of computer simulation programs (Lomas and Eppdl, 1992; Cordon, 1992).
2.2 Computer simulation program
Building case studies were modelled using the computer simulation program TRNSYS (Solar Energy Laboratory, 1996) with required specific building input parameters, which have been supplied to the simulation program. The sensitivity analysis is designed to have a building cases that are the same in terms of building input parameters in the whole of the simulation input, except for the input parameter under concern (Joseph et al., 1996). As a result, the difference in simulation results can be interpreted as having only been caused by the change in the input parameter, are shown in table 3 (Spitler et al., 1989).
Descriptions of the thermophysical building materials, required building input parameters, and building cases are presented in Table 1, Table 2 and Table 3, respectively. Buildings were modelled using the TRNSYS-
2.3 Building case details
The building materials of the building cases were selected as most representative of construction materials, fairly similar to a government dwelling type NHA (National Housing Authority). The dimensions of the building (single storey building) are 15m x 8m, giving a living area space of 120m2 with height of 3m (Ministry of Planning, 2004). The building floor plan is shown in Figure 2, whilst the thermophysical building materials of required input data for simulation and building model for all cases are shown in Table 1, Table 2 and Table 3 respectively. The openings to the outdoors were represented by two windows, each with an area of 1.4m2 and a wooden door of area of 2.2 m2. Furthermore, thermal properties of windows and door are illustrated in section 3.4. Building cases were modelled, simulated and encoded using TRNSYS-
3. Building construction components
The construction components of the building cases consist of building envelopes; namely exterior walls and roof. The prevailing exterior walls in Kuwaiti buildings are generally of two types; 'AAC' wall (Autoclaved Aerated Concrete) and concrete block wall (which may be called 'classical wall'). NHA (National Housing Authority) buildings are limited to these two types of wall construction. However, none of these walls have been investigated in terms of their energy conservation measures. Thus, building envelopes using wall building construction materials of Classical and AAC as well as the prevailing type of roof (i.e. flat roof) were considered in this study. Further details about construction components used in Kuwaiti building are described next.
3.1 Classical wall
The classical wall was introduced into the construction field in the early 1940s after the discovery of oil in Kuwait. Its initial form consisted of a concrete block and cement mortar. The elements of this wall developed gradually until the late 1970s, when thermal insulation was added. Detailed cross-
3.2 AAC Wall
'AAC' (Autoclaved Aerated Concrete) is a cementitious matrix made by introducing air or gaps into the prepared slurry. The air is usually entrapped in a closed cell form (ACICO, 1996). Since the early 1980s, the AAC Block has become popular in Kuwait's construction market. The technology of the AAC was brought from Germany through a local company called National Industries Company (NIC). However, NIC recently installed a plant that produces aerated concrete blocks (called the 'Azel' block) or the AAC block in Kuwait itself. The AAC blocks are made usually with bulk densities in the ranges 400-
o The AAC block works as two construction components in one element, namely; block and thermal insulation.
o The AAC block is light; therefore, it requires thickness for it to be used in exterior walls. It should be at least 20-
o The cost of the AAC block is close to the cost of the classical wall if thermal insulation is added. However, costs could be a lot higher if a layer of wire mesh (chicken mesh) was to be installed over the AAC block to strengthen and bond the cement plastering with AAC block.
o There are only two construction factories that produce the AAC block locally in Kuwait.
o It is not strong enough to tolerate holes in the wall to hang pictures or any other aesthetic items.
Despite the advantages and disadvantages of the two walls, the AAC block has been used by the National Housing Authority (NHA), the private sector and government buildings, irrespective of energy consumption issues. Detailed wall cross-
The traditional flat roof is almost universal in Kuwait. The roofs of dwellings were extensively used for sleeping areas before mechanical cooling was known and were also used as storage. However, the main reason why flat roofs continue to be largely used is due to the fact that Kuwaiti family members are increasing in number and size and they prefer to live together rather than move to another place. Therefore, more building space is required and can be obtained by extending either horizontally or vertically. Therefore, the flat roof is a more flexible and cheaper way for this type of building construction to be extended than any other roof. In view of this, the flat roof is very popular and is used by most Kuwaiti people. It is also specified by the Kuwaiti Government through the NHA housing program as well as by most of the private buildings in Kuwait. Thus, the building case of this study will have a flat type of roof. The thermophysical properties of the roof are shown in Table 1 and its detailed cross-
Windows and doors in Kuwaiti buildings are varied in their thermal performance and material properties. In the following section, the windows and door are investigated, to promote a guideline strategy that may address future energy conservation codes.
Most windows in Kuwaiti buildings nowadays consist of a double pane of 6mm or 8mm-
When the sun's energy impacts on a building's envelope, heat will enter either directly through the transparent areas or it will be absorbed and the heat will enter the building by conduction through opaque elements. Inappropriate sizes of window openings could result in a large area of glass, which in the case of Kuwait's buildings could be a major source of heat gain. Inappropriate choice of glass may transmit up to 85% of the heat gain from incident sunlight (Al-
Researchers have suggested that a glass area of 1/16 of the floor area of a room should be satisfactory for lighting purposes in a hot dry climate (Saini, 1980). The issues are accounted for in the selection of building design cases for further simulation, see case 3, case 6 and case 7 (Table 3).
One door of 1 metre wide and 2.2 metres height is used in this study. It consists of plywood on two sides with a 35mm air gap in between. This is a typical construction material for a door in Kuwait buildings. The door pervading thermal resistivity is 0.606 m2 C W-
4. Simulation results
4.1 Building parametrical study for energy consumption analysis
Simulations were conducted on the building case using material properties shown in Table 1 and Table 2. In order to arrive at an energy-
4.2 Energy consumption for the building cases
The seven building cases, shown in Table 3, were simulated using TRNSYS-
5. Design guidance for Buildings in Kuwait
The results of the energy consumption analysis using TRNSYS-
1. Use of the classical wall (case2) gives a reduction in annual energy consumption equal to 0.2% compared to the use of the AAC wall (case 1), which equals to 1.2 %, in comparison with building case 3, see Table 4.
2. It was found that the infiltration component of the building case was the major contributor to the building's energy consumption (cases 3, 4 and 5). Thus, any effort to reduce energy consumption should be aimed towards decreasing the amount of uncontrolled air leakage. In building case 5, it was found that the infiltration value of 1AC/h is a main contributor to energy consumption in Kuwaiti buildings. The annual energy consumption of building case 4 with an infiltration value of 0.6 AC/h shows an increase of 3.2%, while building case 5 with an infiltration value of 1AC/h shows an increase of 8.9%, respectively, in comparison with building case 3.
3. The window area plays an important role in building energy consumption in the Kuwaiti environment. When the area of the window glazing was increased as in building case 6 and case 7, energy consumption increased to 3.8% and 7.1 %, respectively, with respect to case 3. Therefore, using large areas of glass in buildings in Kuwait is a major source of solar heat gains. There are certain treatments to the glazing that may reduce heat gains. For example, using double glazed windows can reduce heat gains by at least 10%, and also the placement of windows will have a considerable effect. Windows in the direction of north-
4. Case 3 presented in Table 3, Table 4 and Table 5 emerges as the best case from those simulated, as its annual energy consumption was found to be the minimum with a value of 14.68 MWh. Case 3 corresponds to the use of the classical wall construction, orientating windows in a North-
6. Summary and conclusions
Parametric studies were conducted on exemplar building cases, where the materials were chosen as shown in Table 1. Seven cases were considered, which represented the designs typical of Kuwaiti domestic buildings. The effect of building envelope, window types, size and direction, infiltration and ventilation were investigated. The classical wall is shown to be more energy-
Furthermore, it should be emphasised that the data in the building cases shown in Table 3 does not cover all the building code's necessary data. This is simply an attempt to fulfil the need for updated information on energy implications of building materials and design for Kuwait. This will contribute to the establishment of an enhanced building code of practice for Kuwait, though a comprehensive treatment of this issue is beyond the scope of this study.
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