Insulation Performance of Building Components and Effect on the Cooling Load of Homes in Saudi Arabia

Abstract

A common practice in the construction of residential and commercial buildings in Saudi Arabia is to insulate the outer walls and windows only. Other building components such as the roof, columns and slabs, and doors are usually neglected. Moreover, vital components such as the roof and windows are especially neglected in commercially built residential and commercial buildings. The aim of this study is to put this common impression and practice to the test by quantifying the contribution of every building component to the overall air-conditioning load of the building. The hypothesis evaluated in this paper is that despite the common practices, there could be an optimum selection of insulators for the building components that yields the lowest energy consumption and maximum savings not only in energy costs but also installation costs. The required air-conditioning load is determined using manual calculations and the HAP software package for 1022 possible configurations. The findings of the analysis point to the importance of the roof, as it is the major contributor to the thermal load, followed closely by columns and slabs, with 44.2% of the overall cooling load. It is found that a single wall consisting of 2 cm of cement plaster, 20 cm of cement–polyurethane brick, and 2 cm of cement plaster is less expensive and has higher thermal resistance than any of the more expensive double walls. The study found one scenario of possible configurations with the optimized selection of building materials and their insulation materials that provides the most effective insulation at the lowest cost.

1. Introduction

The first usual targets for insulation are those building components with the largest exposed outside surface areas: the walls. With time, the use of clay bricks and other options such as aerated bricks gained popularity in the construction of residential buildings as a better substitute for cement bricks due to their higher resistance. Investigations were conducted to characterize the thermal performance of superior brick materials and specify the advantages they provide over ordinary cement bricks [1,2,3]. With time, other options for wall insulators and wall insulation procedures were introduced, such as double walls of normal bricks sandwiching an insulating material such as polystyrene or polyurethane, and more economic single (cement or clay) bricks with an inserted insulation layer.

By altering the insulation material, concrete grade, steel reinforcement size, and sample size combinations, Thangarasu and Henderson [4] studied the thermal insulation performance of several sandwich concrete panels (SCP). The study included both the experimental testing and finite element analysis of two different combinations of insulating materials and concluded that one of their suggested combinations provided better thermal insulation. According to Bolattürk’s research [5] on the insulation thickness in concrete composite panels employing polystyrene as an insulation agent, the ideal range for insulation material thickness is between 20 and 170 mm. By altering the thickness from 50 mm to 150 mm, Kim and Allard [6] examined the thermal sensitivity of precast sandwich concrete walls. Similar to this, Ucar and Balo [7] investigated insulating materials including foam board and polystyrene and found that for the greatest performance, the insulation material thickness should be between 10.6 and 76.4 mm.

Many studies were conducted to present the economic advantage of increasing a wall’s thermal insulation performance [8,9]. Said and Racz’s work [10] is a sample of an attempt to specify economically optimum insulation thickness. Other advanced studies, such as that by Mujahid and Zedan [11], evaluated the performance of different insulation wall systems available in the construction market in Saudi Arabia and identified insulators with the best insulation-to-cost performance. Tewfik [12] dedicated his Ph.D. thesis to a comprehensive study of the common wall systems used in residential buildings in Riyadh and emphasized the importance of deficiencies in design and construction on the performance of wall thermal insulation.

On the application side, interest was placed on some building components such as windows where energy providers try to increase awareness by publishing recommendations for reflective and double-glass windows [13]. Samen et al. [14] conducted a feasibility study on the use of discarded cotton fibers in the construction of lightweight, low-thermal-conductivity laterite–cement composites for structural purposes. With a 29% inherent energy reduction versus traditional materials, the samples they created look to be a promising eco-friendly composite with good thermal comfort, a small embodied energy, and low environmental impact owing to a sustainable approach. Alaoui et al. [15] used the following two strategies: (i) an experimental investigation with the goal of identifying the thermal characteristics of the regional building materials often utilized in the southeast of Morocco, and (ii) TRNSYS simulations were performed to forecast and improve the thermal performance of two different building types in this area. According to the findings, a building made of clay and other traditional building materials offers greater thermal comfort than a brick building.

The literature review reveals noticeable improvement in the efficiency and the performance of the insulation envelope, but most of the published research does not include the contribution of all other components of the total exposed surface area of the building (especially the roof and column/slab) and the importance and the practices of insulating these components. It is also evident from the literature review that the locally available insulating materials in Saudi Arabia and their combinations have not yet been investigated in detail. This work is concerned with bridging this research gap with the analysis of the total exposed surface area of residential buildings in order to quantify the contribution of each and every component of the surface area to the overall thermal load of the building. Comparing the contributions of all components determines whether the common practices in Saudi Arabia are justified.

With regard to technical objectives, the first one is to classify, quantify, and document the different building components of residential buildings in Saudi Arabia, along with representative samples of different common thermal insulations for every component, and the thermal properties of building components and their insulators. Next, the contribution of every building component to the overall air-conditioning load of the building is determined. The aim is to determine which components should be taken into consideration (thermally effective components) and which can be neglected.

One of the main objectives of this study is to concentrate on how to select the best insulator combinations of all of the thermally effective components to yield the maximum savings in energy consumption and in construction costs as well. Finally, based on the knowledge of the thermally effective building components used in this study, and based on the optimum selection procedure of insulation suggested by this study, modifications and/or additions to the current construction standards in Saudi Arabia are suggested to help lower the national consumption of energy and to lower the insulation cost burden for all citizens.

2. Materials and Methods

Figure 1 shows the methodology adopted in this study. First of all, the building components and materials were surveyed and classified. The data were procured from various manufacturers and suppliers of those materials in Saudi Arabia.

Table 1. Physical and thermal properties of materials and insulation of walls and roofs commonly used in Saudi Arabia.

Building Material or Insulation Material		Conductivity (W/mK)	Thickness (mm)	Density (kg/m3)	Specific Heat (J/kgK)	R (m2K/W)	Rt (m2K/W)
Cement plaster		0.72	20	1860	840	0.028
		0.8	20	1682	840	0.025
Heavy-weight hollow cement brick HWHCB (200 mm)		1.04	200	1105	840	0.192
HWHCB (150 mm)		0.96	150	1362	840	0.156
HWHCB (100 mm)		0.81	100	1618	840	0.123
Cement brick, hollow block slab (Hordi)		1.092	250	1083	840	0.229
Hollow clay brick (300 × 200 × 200)		0.595	200	833	880	0.336
Hollow clay brick (300 × 200 × 150)		0.497	150	778	880	0.302
Hollow clay brick (300 × 200 × 100)		0.44	100	834	880	0.227
Hollow clay brick Hordi (450 × 200 × 200)		0.603	200	722	880	0.332
Polystyrene-insulated cement brick	Solid cement brick (80 mm)	1.42	80	2400	840 *	0.056	2.279
	Extruded polystyrene (70 mm)	0.032	70	28	1280 *	2.188
	Solid cement brick (50 mm)	1.42	50	2400	840 *	0.035
Polyurethane-insulated cement brick	Solid cement brick (80 mm)	1.42	80	2400	840 *	0.056	3.008
	Polyurethane (70 mm)	0.024	70	28	1537 *	2.917
	Solid cement brick (50 mm)	1.42	50	2400	840 *	0.035
Polystyrene-insulated clay brick	Solid clay brick (80 mm)	0.636	80	2400	840 *	0.126	2.392
	Extruded polystyrene (70 mm)	0.032	70	28	1280 *	2.188
	Solid clay brick (50 mm)	0.636	50	2400	840	0.079
Reinforced concrete (75 mm)		1.726	75	2400	960	0.043
		1.75	75	2300	960	0.043
Reinforced concrete (100 mm)		1.726	100	2400	960	0.058
		1.75	100	2300	960	0.057
Reinforced concrete (200 mm)		1.726	200	2400	960	0.116
		1.75	200	2300	960	0.114
Reinforced concrete (250 mm)		1.726	250	2400	960	0.145
		1.75	250	2300	960	0.143
Reinforced concrete (300 mm)		1.726	300	2400	960	0.174
		1.75	300	2300	960	0.171
Precast concrete (75 mm)		1.5718	75	2500	960	0.048
Siporex brick		0.383	200	633	N/A	0.522
Sand		0.87	50	1500	880	0.057
Cement tile		1.06	30	1500	840	0.028
Extruded polystyrene		0.032	50	28	1280	1.563
Extruded polystyrene		0.032	75	28	1280	2.344
Extruded polystyrene—roof		0.027	75	33	1280	2.778
Polyurethane (board)		0.024	50	28	1537	2.083
Polyurethane (board)		0.024	75	28	1537	3.125
Polyurethane—roof		0.023	75	30	1537	3.261
Rockwool		0.042	50	50	840	1.190
Rockwool		0.042	75	50	840	1.786
Perlite (loose fill)		0.054	75	94	1090	1.389

* estimated.

provides the physical and thermal properties of the material and insulation of walls and roofs commonly used in Saudi Arabia. Thermal conductivity, density, specific heat, and thermal resistance were tabulated for each component. The data were taken from manufacturers’ specifications. The overall thermal resistance (R_t) of the combinations was calculated. Appendix A represents a tabulation of the building components’ combinations, i.e., the matching of building components and their available insulators. It also represents the detailed component combinations, collective physical and thermal properties, and collective costs. Collective costs include the cost of the different materials of a combination and their installation cost. It should be noted that the materials’ prices and manpower costs vary with time and place. Although the relative comparison of the materials and labor cost is more stable and remains mostly unchanged for longer economic cycles.

The analysis of this research was performed with and limited by the following assumptions and constraints:

• The model used for cooling load calculations is a one-dimensional steady-state heat transfer model, which was solved using HAP software.
• Construction deficiencies such as the breaking of insulation boards during installation were not taken into consideration.
• Building components’ uniformity was assumed, i.e., neglecting the interruption of any building component such as plastering between the bricks of single walls, the imperfect match between insulation boards of double walls, and the concrete between hollow block slabs (Hordi) in Hordi roofs.
• As the building was shifted from a single-wall to a double-wall system, the column width was kept fixed even though the thickness of the columns increased.
• Changes in insulation performance over time due to aging and other environmental factors were not considered.

Figure 2 shows the studied house, which is a common example from a real medium-sized villa in Riyadh, Saudi Arabia, with an area of 375 m² (12.5 × 30) and a total constructed area of 556 m². The dimensions and engineering details of the ground and first floor are shown in Figure 2b,c. This chosen house represents the major trend of current houses in Saudi Arabia. The outer surface of the building is divided into distinct components according to the material used. Some of these components are familiar to public insulation practices, such as the windows, walls, and roof. Other components include different parts of the outer surface of the building that are usually not included in the insulation process, such as doors, concrete slabs and columns, window frames, and brick and concrete frames that support windows and doors.

For this investigation, the Hourly Analysis Program (HAP) was employed. Carrier, a provider of cooling, heating, and refrigeration systems, created this computer program. The program’s objective is to help engineers create HVAC systems for commercial buildings. It offers two tools in one: a simulation of energy use and cost computation, as well as load estimation and system design. HAP system design features and HAP energy analysis features make up the two sections of the program [16].

The following are the steps for the calculation of cooling load by HAP:

(1) Selection of city. Riyadh was selected, as the meteorological data of Riyadh were already available in the HAP database. The design dry bulb temperature for Riyadh was 45 °C and comfort conditioning requirements were kept to 24 °C and 50% relative humidity.

(2) Space properties were selected for walls, ceilings, doors, windows, partitions, etc., along with the infiltration, equipment, lighting, and occupants. The areas and thickness of each component were specified in this step.

3. Results and Discussion

3.1. Analysis of Building Components and Their Insulation

In

Table 2. Contribution of components of the studied house to the total exposed area.

#	Component	Area (m2)	Total Cooling Load without Insulation (W)	Total Cooling Load with Common Practice Insulation * (W)
1	External Walls	366.9	18,190	2721
2	Roof	191.0	15,517	15,517
3	Windows	46.33	6184	4439
4	Columns and Slabs	85.87	8584	8584
5	Doors	9.9	148	148
Total		700	48,623	19,402

* Using a combination of CS1, D1, R6, W4, N3. Details are mentioned in Appendix A.

, the partial area of the outer shell components of the studied house with their relative penetrating thermal load is listed for two situations. The two thermal situations presented in the table are the plain building (the building without any insulation) and the conventional common practice, where the latter represents the building with usually insulated components (walls and windows). The total shell surface area is about 700 m². The total cooling load for the plain building is about 48.6 kW, and that for common-practice insulation is about 19.4 kW. So, a reduction in cooling load of about 60% is evident. Since the common practice only suggests the insulation of external walls and windows, the other dominant loads of the roof are not considered to be reduced.

Figure 3 shows the comparison of the areas of the studied house components. The external walls constitute the major component with more than half of the total area. The second major component is the roof with more than one-quarter of the total area. The remaining portion, which constitutes about one-fifth of the area, is shared between concrete columns and beams, windows, and doors. It seems that this area’s comparison is the real stimulant of the common practice of insulating only the walls and to some extent insulating the roof. The windows are commonly insulated because of the direct sunlight and its contribution to the thermal load.

The real significance of each one of these components can be made clear by comparing their individual thermal contribution to the overall thermal load. As shown in Table 2 and Figure 4, the significance of each component slightly changed from that of the area comparison. The walls decreased to slightly more than one-third of the total in terms of significance, while the roof increased to be closely competitive with walls, although its area is half of that of the walls. Windows and columns and slabs became much more significant. Doors, on the other hand, became much less significant than in the area comparison.

By now, it is clear that neglecting some of the building components in the insulation processes is justified, such as doors and less significant components. However, other components such as roofs and columns and slabs proved to be worthy to be taken into consideration.

This last thought is confirmed when a further comparison is made to show the thermal contribution of each building component after the common practice of only insulating walls and windows is put into place. Figure 5 shows the results of this comparison. Here, the roof became the major contributor to the thermal load, followed closely by columns and slabs, rising from 17.7% to 44.2% of the overall cooling load. This is very important, given the results reported in some surveys that the majority of homes in Riyadh are constructed without any form of roof insulation. Al-Juwair [17] reported that 95% of residential houses considered in his study were not using roof insulation. In other words, 95% of residential buildings lack the insulation of the components that contribute 93.6% of the cooling load.

These important comparative results point to the validation of the hypothesis of this research and encourage us to move forward with challenging the common practices of residential building insulation in Saudi Arabia. It is important to note that for the sake of controlling the limit to which this study goes, components with a relative area of less than one percent of the total exposed area were ignored. These include components such as window frames, door frames, and piping spaces. The decreasing significance of the bigger contributors, i.e., the doors, supports this action.

As for the other practice of insulating the building with the most expensive insulation materials and systems in order to obtain the highest reduction in thermal load and to raise the thermal comfort to its peak, a simple comparison of the walls listed in Appendix A and Figure 6 shows that combination W6, which is a single wall (consisting of 2 cm of cement plaster, 20 cm of cement–polyurethane brick, and 2 cm of cement plaster), is less expensive and has higher thermal resistance than any of the more expensive double walls. This is also represented in Figure 6, where a comparison of the contribution of every wall to the thermal load of the building is presented. The results shown in Figure 6 are compatible with the comparative study of Mujahid et al. [11]. A minimum cooling load of 2219 W is evident for W6, whereas the maximum is 18,190 W in the case of W1. So, a huge reduction in the cooling load (almost eight times with W1) is evident in the case of W6, which consists of layers of 2 cm of cement plaster, 20 cm of cement–polyurethane brick, and 2 cm of cement plaster.

Figure 7 shows a comparison of the cooling load of various combinations of roofs. It is clear that the combination R3 (which consists of 3 cm of cement and tiles, 5 cm of sand, 7.5 cm of polyurethane board, a water insulation layer, 7.5 cm of concrete, a 20 cm concrete slab, and 2 cm of cement plaster) gives the minimum cooling load of 1.76 kW, whereas R1 gives the maximum cooling load of 15.5 kW. So, again, a reduction of about nine times is evident when roof combination R3 is used instead of R1. Roofs using other types of insulation materials, which are R2 (polystyrene), R4 (perlite), and R5 (rockwool), also perform well compared to non-insulated roofs.

Figure 8 shows a comparison of the cooling load of various column and slab and window materials. It is clear that the column and slab combination CS2 (which consists of 2 cm of cement plaster, 30 cm of concrete, and 2 cm of cement plaster) gives the minimum cooling load of 7.3 kW. However, this reduction in cooling load (only a 17% reduction compared to CS1) is at the cost of an additional 10 cm concrete layer. Moreover, the window N4 (which consists of a clear reflective double-glazed window) gives the minimum cooling load of 3.6 kW.

3.2. Cooling Load Estimation of Different Combinations

In this concluding phase of the analysis, the task is to perform complete thermal load calculations of the chosen sample building to compare the overall thermal performance of the building when it is equipped with different combinations of building materials and insulators. Many previous studies reviewed in this paper compared the different combinations of a single component. For example, some works focused on walls, others on windows, and so on. Here, we compare the whole thermal envelope in different combinations of building materials as solved by HAP. Although the previous section proved our point of challenging the common practices, in this section, a thorough comparison of the whole building with different combinations of all of the building components matched together is performed. This aim is to first prove practically the flaws of the common practices and second to pave the road for a new practice and procedure to search for an optimum selection of building materials and thermal insulators. The cooling load estimation includes the following steps:

• The overall cooling load is calculated for the building in its plain form, i.e., without any form of thermal insulation.
• The overall cooling load is calculated for the building with common insulation, i.e., with only walls and windows insulated with the common form of insulation.
• The overall cooling load is calculated for the building heavily insulated with the most expensive insulation available in the local construction market.
• A wide range of cooling load calculations are performed by matching the various combinations of all building components in search of an optimized selection of building combinations (building materials and their insulators) and an optimum match of the combinations of the different components.

The results of these four steps single out an optimum scenario of building combinations that provide the maximum insulation effect with construction costs lower than the most expensive choice in step 3.

Table 3. Scenarios of combinations for each of the four steps of the final phase.

Step No.	Building Type	Scenario of Combinations
		Columns and Slabs	Doors	Roof	Walls	Windows
1	Plain building	CS1	D1	R1	W1	N1
2	Common practice of building insulation	CS1	D1	R6	W4	N3
3	Most expensive building insulation	CS2	D3	R7	W10	N4
4	All possible scenarios	1120 possibilities

shows the combination matching of each of the steps above. In step 4, a full optimization procedure was performed to find the optimum scenario of building combinations among 1120 practical matching possibilities. These practical possibilities were elected among 2464 matching options where impractical matches were removed. A good example of an impractical (rejected) scenario is matching walls and columns of different thicknesses.

Extensive calculations were performed to determine the cooling load of each scenario of building combination shown in Table 3 for 1120 possibilities. Figure 9 shows the consolidated results of these efforts.

Because the doors’ significance is low, and for the sake of simplicity, we focus in Figure 10 on one-quarter of the results (255 possibilities) by showing only the results of the scenarios that include door D3 only. The figure was also rearranged to show the scenarios as their construction costs become higher. This figure sums up what this research is all about. The rightmost point refers to the scenario of the building combinations that has the most expensive insulation. Its cost comes at the top of the construction costs line, and its corresponding cooling load is shown with the same point shape and color. The orange-colored line that passes through the point of the cooling load of this scenario differentiates between those scenarios that perform better than the most expensive choice (points below the orange line) and those that perform worse (above the line). It is clear that there are many choices other than the most expensive one that perform much better with lower construction costs. We can say that we have found one scenario with the optimized selection of building materials and their insulation materials that provide the most effective insulation and cost less. Although, the word optimized seems to have a broader range than we expected; for example, one can incur a much lower cost for just a small increase in the cooling load.

Figure 11 is the comparison of cooling load and cost of the plain, commonly insulated, optimized, and most-expensive insulated buildings. It is clear that the less-common practice of using the most expensive insulators available in the local construction market is not justified. An educated selection of building materials and insulators leads to a better-insulated building with lower construction costs.

4. Conclusions

Based on the theory considered in this study, there may be an ideal choice of insulators for building components that result in the lowest energy consumption and the greatest possible savings in installation costs in addition to energy expenditure. Different locally available building materials and insulators were surveyed and investigated in this research. Using the HAP software program, the required air-conditioning loads were calculated for 1022 different configurations. The following are the main conclusions:

The roof is the major contributor to the thermal load, followed closely by columns and slabs, rising from 17.7% to 44.2% of the overall cooling load. In total, 95% of the residential buildings in Saudi Arabia lack the insulation of the components that contribute 93.6% of the cooling load. Those components are the roof and columns and slabs. It was also found that combination W6, which is a single wall (consisting of 2 cm of cement plaster, 20 cm of cement–polyurethane brick, and 2 cm of cement plaster), is less expensive and has higher thermal resistance than any of the more expensive double walls. The study also revealed that there are many choices other than the most expensive one that perform much better with lower construction costs. One scenario was found in this study with the optimized selection of building materials and their insulation materials that provide the most effective insulation at the lowest cost.