Building's Envelope: Surface-to-volume ratio as an energy saving tool in Jordanian homes Stampa E-mail

abstract in italiano

by Samer Abu-Ghazalah*  -  Abdulsalam A. Alshboul**
Nabil Abu Dayyed***  -  Ali Abu Ghanimeh****
* B. Arch., M.Phil., (Uk), Hon. Dip. Arch. (Uk) A.B.I. (Usa), Associate Professor,
Department of Architecture, University of Jordan
** B. Sc.,M. Sc., M. Sc. (Jordan), Ph. D. (Italy), Assiatant Professor, Department of Architecture, University of Jordan
*** B. Sc. Ph. D (Usa), Associate Professor, University of Jordan. Head of Department of Architecture Engineering

**** B. Sc. Ph. D (Italy), Associate Professor, University of Jordan. Department of Architecture Engineering

The need for knowledge of energy in buildings is increasing in the entire world and especially in Jordan in the last two years. Jordan is a non-oil producing country where the total energy bill is increasing rapidly due to elevating oil prices over the last 12 months. The 2005 budget of Jordan estimated the oil price around US$ 42. The current prices of oil exceeded US$ 60 per barrel by July 2005. A deficit of approximately US$ 40 million for each one US$ increase of price is occurring. Currently the deficit accounts for more than US$ 720 million. The total oil bill for the year 2005 will exceed US$ 1.6 billion or more than 50% of the total budget [1]. Figure one shows the increase of fuel prices during the last four years in Jordan.
Concern about energy consumption has been growing lately in residential buildings, as well as other sectors. In the residential sector of Jordan, it accounts for 18% of the total energy consumption [2]. The energy consumed in residential buildings includes kerosene, diesel, fuel, electricity, and natural gas that cover heating, cooling and lighting [3]. Energy consumption is rapidly increasing over the last two years in Jordan due to two main reasons: first, the natural population growth accounts for 2.8%[4], and second is the growing number of Iraqis living in Jordan due to the present situation in Iraq. The actual number is not determined, but it accounts for more than one million inhabitants [5].

A typical jordanian home

Most of the building regulations and design procedures in Jordan address the insulation of walls values ("U"), and the orientation of the building but only partially address the form and climate. No previous study to the ratio of surface of buildings to their volume has been tried in Jordan. The regular design parameters of a building envelope, which addressed by Jordanian building regulations that includes its section properties, fenestration details and dimension, are not the only parameters that affect energy consumption in buildings. The surface area which involves the calculation of the area of all walls plus the ceiling and compare it to the volume of the building is seen as a prime indicator that should be incorporated in building regulations in Jordan, as it is incorporated in other neighborhood countries. The former proposed surface to volume ratio does affect energy consumption, as this paper will attempt to prove. The designer should begin with desirable energy parameters, then go to the design of the building shape as Bhatnager et. al., 1997 emphasized in their paper [6]. He explained that only by trial and error, we could reach a considerable framework, which is time consuming, and its result is uncertain. This paper is trying to set a ratio that can be applied to adjust the design of the form of the buildings to reach a comfortable and well balanced energy formula.
Several international studies of surface-to-volume ratio or shape coefficient have been carried out throughout the world. Lam and others (2002) investigated the electricity consumption throughout the year to office buildings in Hong Kong. They investigated 20 office buildings and calculated the required amount of electricity needed throughout the whole year. They concluded “The consumption patterns showed distinct seasonal variations, indicating peak electrical demands during the hot, humid summer months from June to September, due to significant air-conditioning requirements” [7]. This study investigated the relationship between energy use and external weather conditions in terms of ambient temperature and cooling degree hours for each building separately. There are three major components facing the building professionals worldwide the environment, energy and the building [8]. Several other studies conducted on the commercial buildings using the shape coefficient such as Yik and others (2001). They concluded the importance of building envelope on the heat and cooling of commercial building [9]. In Jordan, as mentioned before, this is the first study to test this parameter.

Jordan consists of three main climate regions according to the elevation from the sea level.

  • The mountain region: Its elevation varies from 900 to 1700 meters above sea level. The Mediterranean climate prevails in this region where the climate is moderate and dry during summer and the monthly average temperatures are 29 °C. During winter it is cold and rainy and the monthly average temperatures are 8 °C. The rainfall annual average is 425 mm.
  • The desert region: Its elevation varies from 500 to 900 meters above sea level. It consists of about 80% of the total area of Jordan. The climate is very hot, dry, and dusty during summer, and cold and dry during winter. The monthly average temperatures are 10 °C during winter and 36 °C during summer. The rainfall annual average does not exceed 50 mm.
  • The valley region: Its elevation reaches 400 meters below sea level. It has the lowest point on Earth at the Dead Sea. The climate is hot and dry in summer and the monthly average temperature is 3 °C, and warm during winter with a monthly average temperature of 13 °C. The rainfall annual average does not exceed 10 mm [10].

In order to determine the appropriate ratio of S/V needed in design parameters for building regulations in Jordan, 20 case studies were tested in three different climatic conditions in Jordan. For the mountain region Ajlun City is suggested. The eastern section of Amman City is chosen for the desert region, as Amman City varies in height from 500 meter in the eastern section to 1000 meter in the western part. And for the valley region, the Zara Town at the Dead Sea is suggested. A quantification of the relationship between S/V ratio and the annual heating fuel demand is tried as a step towards reaching a specific S/V range. The different house configurations are chosen depending on the most used shapes and areas in cities in Jordan. There are 20 case study categories that will be discussed in detail in the Data Set section.
As discussed before, the variation of climate and temperatures at different regions in Jordan give different design parameters. During winter the average temperature varies from 13 ˚C in the valley region to 8 ˚C in the mountain area. There is no specific S/V ratio stated in the building regulations in Jordan. This research is trying to determine a new range ratio for S/V specific to each climate zone in Jordan to be incorporated in future building regulation amendments. Existing building regulations in Jordan consider the whole of Jordan as one region, which is not the case, as this paper trying to point out. Each region has its characteristics that should be reflected in the building regulations. It is suggested by this research to set and implement different categories in terms of building materials for each region that can comply with its climatic conditions.
This research hypothesizes that different building shapes affect energy efficiency according to the climatic conditions. Jordan which has three different climate zones has different inputs and outputs in terms of calculations. The surface to volume ratio, or the building's shape affect the energy demands. This paper is studying 20 case studies that have different shapes and areas, in three different locations in Jordan in order to obtain the best ratio of surface to volume.

A set of assumptions is suggested in order to obtain S/V ratio for different climatic regions in Jordan. It is divided into three main sections:

Section 1
Plan configuration: It is related to the shape and geometry of the house. A single-family house based on the most common area built in housing sector in Jordan of 90, 180, 270 and 360 square meters is selected. Five case studies were chosen that have different shapes. The first case study is a square building plan. The second case study is a rectangle plan with a ratio of its width to length, of 1:2. The third case study is a two-floor building of a square plan. The fourth case study is a two floor building of a rectangle plan with the same ratio as in case study two. The fifth case study is a courtyard, one-floor, square plan house and the internal courtyard. These five case studies represent the most common single-family housing building existing in Jordan and are applied four times depending on the selected area. The same floor plan with the same interior area is maintained in the selected five case studies, where only the shape and geometry were changed to achieve different S/V ratios. A total selected area of 10, 15, 20 and 30 square meters of a single glazing window for the 90,180, 270 and 360 square meter house respectively is assumed on the external house envelope with no shading devices according to the previous areas mentioned. A normal transparent glass of 6-millimeter thickness with aluminum framing is assumed. All 20 case studies are assumed to be parallel to the east west axis, as shown in tables 1, 2, 3, 4.

Section 2
Physical properties and building material: A typical wall section is selected in all 20 case studies, which is constructed from 10 centimeters stone facing, 20 centimeters reinforced concrete, 2.5 centimeters insulation material and 10 centimeters cement block followed by plastering of 2.5 centimeters. This is the most common section used in nearly all types of buildings in Jordan. The same materials of floors and roofs are used. The roof is constructed from a one way ribbed slab of 25 centimeters thick. “U” value is the heat in watts that will be transferred through one square meter of a construction where there is a difference of one degree centigrade between the temperature of the air on opposite sides. The “U” value or thermal transmission of a material is the inverse of its insulating value resistance U= 1/R. The higher the “U” value, the lower the insulation of a material [11]. The “U” value is determined according to Jordanian building codes [12], which is base on the American Society of Heating, Refrigerating and Air conditioning Engineers, (ASHRAE) (see the table above).

Section 3
Annual fuel consumption: The number of days in the year that have a mean temperature less than 20 ˚C is calculated from the Jordanian Meteorological center to determine N value. They are calculated for Ajlun City to be 900 hours, for Amman City 540 hours, and for Zara Town 180 hours [13]. Other factors such as the variation of wind velocity during the winter, the moisture, actual solar gain through glass, the tightness of construction and the effectiveness of weather stripping in minimizing infiltration are not considered in this investigation (fig. 2).

Section 4
The average indoor temperature (t) maintained during the heating period is assumed at 20 ˚C, according to the National Jordanian Regulations. The average outdoor temperature (ta) is obtained from the climatic data of the Jordanian Meteorological Department. Indoor design temperature (td) is set at 20 ˚C [14]. The internal heat gains are not taken into consideration in the Jordanian regulations. Outdoor design temperature (to) is taken as 3 ˚C for Ajlun and Amman Cities and 10 ˚C for Zara Town. The heating period (N) is determined by a survey for 100 house during 92 days where the temperature drops below 20°C, the winter days in Jordan, in each city which is presented in this table. The result is 6 operating hours per day for Amman City, eight operating hours for Ajlun City, and three operating hours for Zara Town. The efficiency of utilization of fuel (E) over the heated period is set to be 70%, while a heating value of one unit fuel (C) is set to be 41.34 kW/liter [15].

The calculation of S/V for the 20case studies has been carried over. The ratios range from 0.76 to 0.91 for the 90 square meter house. The lowest ratio was for the third case, which is one storey square plan. The highest ratio was for the fifth case, the courtyard one-floor house. The fuel demand varies from 662 liters for the third case to 891 liters for the fifth case for the City of Amman. For Ajlun City the same result occurs where 1,528 liters is required for the third case and 2,057 liters for the fifth case. For Zara town a sum of 185 liters is required for the third case to reach 249 liters for the fifth case. For the 180 square meters house the ratio varies from 0.58 to 0.76. The lowest ratio was for the third case study, which is a two-floor rectangle plan house. The required fuel was 1,200 liters for Amman City, 2,772 liters for Ajlun City and 335 liters for Zara Town. All the above mentioned numbers have a 0.58 S/V ratio. The highest ratio of S/V, 0.76, is for the fifth case study. It requires 1,668 liters in Amman City, 3,850 liters in Ajlun City and 465 liters in Zara Town, much higher than the third case study.
For the 270 square meters house we obtain the same results, where the highest S/V ratio, 0.67, is for the fifth case and the lowest ratio, 0.51, is for the third case. The fuel demand varies from 1,715 liters for the third case to 2,415 liters for the fifth case for the City of Amman. For Ajlun City the same result occurs where 3958 liters is required for the third case and 5,573 liters for the fifth case. For Zara town a sum of 479 liters is required for the third case to reach 674 liters for the fifth case. The 360 square meter house achieved the same previous results, where the highest S/V ratio, 0.65, is for the fifth case and the lowest ratio, 0.46, is for the third case. The fuel demand varies from 2,319 liters for the third case to 3,276 liters for the fifth case for the City of Amman. For Ajlun City the same result occurs where 5,200 liters is required for the third case and 7,408 liters for the fifth case. For Zara town a sum of 619 liters is required for the third case to reach 886 liters for the fifth case.
One important remark should be mentioned here is the inverse relationship of the S/V ratio versus the area of the house. The higher the area of the house is the less S/V is obtained. For example the 360 square meter house third case has a ratio of S/V = 0.46, the lowest in our 20 case studies. The highest value for S/V ratio for the third case is 0.76 for the 90 square meter house. This is also implies for other cases such as case 1, 2, 4 and 5. The highest S/V ratio is at the fifth case of the 90 square meter house, 0.91. This means that individual small houses, even at Zara town near the Dead Sea are not recommended. Building housing complexes of large areas such as 360 square meters of more than one floor will definitely reduce the heating bill.
This implies that for Ajlun City and the mountain region in general the typical two floor square house is the most appropriate form that have a 0.58 S/V ratio. The fourth case study, which is a two-floor rectangle plan, can also be implemented in this region, which has an S/V ratio of 0.62, which is close to the third case study. The fuel bill for any Ajlun house will rise significantly if other forms are implemented in this region. The yearly fuel consumption for the 180 square meter for example varies from 2,772 liters for the third case study to 2,795 liters for the fourth case study. For the first and second, the figures are 3,701 liters and 3,728 liters respectively. For the fifth case study the number reaches 3,850 liters. For the desert region such as the eastern section of the city of Amman, the third and fourth case studies are the most appropriate forms for this region, but also the first and second case studies can be used. Tables 7, 8, 9, 10, 11 show all figures in liters and calculate the heat loss for each case. The fifth case study, of a courtyard one floor house plan is not recommended in this zone due to the large amount of fuel consumption. It is calculated for the 90 square meter to be 891 liters, which rise to as much as 3276 liters in the 360 square meter house.
For the Dead Sea region, any type of the five case studies can be used due to the close temperature difference between indoors and outdoors during winter. The Dead Sea zone has the lowest temperature difference in all the above mentioned climatic regions. As tables 7-10 show, the difference is 7 ˚C, but for the mountain region it is 12 ˚C.

The current building regulations in Jordan do not include any indicators to the surface to volume ratio. The energy demand is affected by the building shape or form as this study points out. The surface area, which involves the calculation of the area of all walls plus the ceiling, compared to the volume of the building, is seen as a prime indicator that should be incorporated in building regulations in Jordan. This research suggests adding a new parameter to the building regulations in Jordan that involves S/V ratio as well as determining a range figure for each region in Jordan.
For the mountain region, the ratio should be around 0.76 for the 90 square meter house, 0.58 for the 80 square meter house, 0.51 for the 270 square meter house and 0.46 for the 360 square meter house due to the large temperature differences between outside and inside the building. This difference is 12 ˚C, as indicated previously. For the desert region, such as the eastern part of the capital Amman, the S/V ratio might range between 0.76 to 0.78 for the 90 square meter house, 0.58 to 0.66 for the 180 square meter house, 0.51 to 0.59 for the 270 square meter house and 0.46 to 0.55 for the 360 square meter house. This is due mainly to less temperature difference between outside and indoor building of 10 ˚C. For the valley region, the S/V ratio might vary from 0.76 to 0.91, 0.58 to 0.76, 0.51 to 0.67 and 0.46 to 0.65 for the 90, 180, 270 and 360 square meter houses respectively due to only 7 ˚C difference between outdoors and inside buildings. New software that has various areas and the required S/V should be developed in Jordan for building regulations.

A typical jordanian home
Further researches might address the other types of houses, such as apartment buildings of more than two floors, multiple building apartments, and high rise residential buildings to obtain the most appropriate S/V ratio. Other building types such as commercial, hospitals, hotels and other uses might also follow the same procedures of this research to determine the required S/V ratio. The amendments of the building regulations in Jordan to incorporate S/V ratio should start soon, as the price of oil is rising each month and the budget deficit is increasing accordingly. There is an urgent need to address this research result on a national level.
This research is not intending to give recommendations concerning improvement of the wall materials that will help in the reduction of heat transfer. This can be achieved in all climatic regions in Jordan. The “U” value of the stone constructed and “R” value for the wall can be improved by increasing the thickness of insulation material. Many architects discussed the importance of using of insulation material in building external walls in the Middle East, among them, is Miles Danby. He emphasized the past usage of thick stone walls as a heavyweight material combined with small openings located at high levels only. This thick stone wall construction traditionally provided adequate insulation [16]. The legislation of the municipalities in Jordan and the Jordanian Engineering council should provide for regulations of heat transfer and thermal resistance figures that can be allowed in buildings in Jordan. At the present time, no such thing exists for the insulation values or materials used in the construction of buildings.

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