REDUCE THE COOLING DEMAND IN YEMENI OFFICE BUILDING BY USING NIGHT VENTILATION IN ADEN AND HODEIDAH CITIES 能源世界 - 中国建筑节能网

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1 REDUCE THE COOLING DEMAND IN YEMENI OFFICE BUILDING BY USING NIGHT VENTILATION IN ADEN AND HODEIDAH CITIES Aymen Aklan, Panyu Zhu, Marlon Leão, Érika Borges Leão, Volker Huckemann (IGS - Institut für Gebäude- und Solartechnik, Univ.-Prof. Dr.-Ing. M. Norbert Fisch, School of Architecture at the Technical University of Braunschweig, Germany) Abstract :Nowadays the need to apply some strategies to reduce the cooling demand in Yemeni office building becomes an essential issue especially in hot climate such as in Aden and Hodeidah cities. Yemen has four main different types of climates, coastal plains, west and central highlands, East plateau and similarities desert and there are needs to utilize the climate properties in order to achieve low energy consumption in office building. This paper discuss the actual situation of cooling demand in both cities Aden and Hodeidah by using simulation program (DesignBuilder- Energy plus). The thermal simulation model was built in the (DesignBuilder) and applies night ventilation strategy in order to reduce the cooling demand. The strategy of night ventilation will be improved in the simulation model by controlling the night ventilation depends on the air temperature difference between outdoor and indoor. The result shows the amount of energy saving which could be achieved by night ventilation and avoid overheat which could be caused when outdoor temperature higher than indoor temperature. The simulation result shows that energy saving could be achieved in Yemeni office building by using night ventilation with air temperature restriction. Keywords: Night ventilation, Office building, Cooling demand, Air temperature differences 1.0 Introduction In Yemeni office building there are essential steps have to be done to develop some strategies concept in order to reduce the significant amount of energy consumed and improve the thermal comfort for the building occupants. In order to achieve energy efficiency in Yemeni office building so there are needs to give more attention and analysis for the different climate types of the country. Climate of Yemen and particularly in Aden and Hodeidah cities shows high temperature during summer. Due to high outdoor temperature and the fact that no bioclimatic design strategy is considered for Yemeni office buildings, so a considerable amount of energy is being used for cooling through air condition equipment to maintain thermal comfort for the employers in office buildings. Solutions have to be made to decrease the energy consumption by using advanced design strategies. Ventilation plays an important role to decrease the cooling demand and its serves to provide fresh air and remove the heat absorbed by building construction through day time in summer season. Night ventilation helps to prevent overheating during the 1

2 day and reduce the cooling power required to remove the heat inside the building and provide Fresh air to improve the thermal comfort. Night ventilation will be effective when outdoor temperature lower than indoor temperature in order to provide cold air from outdoor to indoor of the building and avoid overheat will be occur in case of outdoor temperature higher than indoor temperature. 2.0 Characteristics of the climate and office building in Hodeidah city 2.1 Climate of Hodeidah The climate of Hodeidah city is very hot with high percentage of humidity in the summer time and mild in the winter time. Hodeidah city is located in the west of Yemen in coastal plain climate. The temperature in summer day time is extremely high with high Solar radiation during summer time. In summer the temperature reach to 41 C and at night time it reaches to 30 C as shown from simulation weather data result in figure (1). In winter time as shown in figure (2) the highest temperature is 30 C and the lowest temperature 22 C. In both summer and winter season the reference day shown in both figures is 21 July in summer and 21 December in winter. The monsoon rains coming from the Indian Ocean in summer season plays a role to moderate the high temperature of summer. 2.2 Office building and climate Hodeidah city plays an important role in Yemeni economy during the last century as main sea port to export and import all kind of goods till the union of both parts of Yemen in 1990 and after the union of Yemen it becomes the second main seaport after Aden city. Many office building located in Hodeidah city in extremely hot climate. The effect of high direct solar radiation which penetrates the building façade will increase the cooling demand in office building in Hodeidah city. The problem will be clear with absence of proper design in term of energy saving and energy efficiency in building sector without standard in Yemen to regulate the energy consumption in office building. In this type of extremely hot climate the cooling demand and power will be the essential point and the most energy will consumed by air condition devices. The absence of proper design and passive strategy to reduce the energy consumption such as natural ventilation and shading or improve the façade performance to protect the building from 2

3 the high direct solar radiation is found in most of the building. The concept to use night ventilation to reduce the cooling demand will improve the energy efficiency of the office building in Hodeidah city. The simulation model was built in design builder program and result will be shown in this paper to examine the actual energy consumption and the strategy to reduce the cooling demand in office building in the climate of Hodeidah city. Air temperature C Air temperature C Day hours Day hours Figure (1) Outdoor Temperature summer day 21 July Figure (2) Outdoor Temperature winter day 21 December 3.0 Characteristics of the office building in Aden 3.1 Climate of Aden Aden city is located in south of Yemen and the climate of Aden city is extremely hot climate through summer time and also moderate in winter. The average temperature in most of the year in Aden city is between 22 C and 38 C. The outdoor temperature is more than 30 C from March to November which means that the average temperature is very high. During summer time in June, July and August the maximum outdoor temperature can reach to 40 C but through the night time the temperature decreases. The figure (3) shows this difference between maximum and minimum which will be useful to utilize this temperature difference in term of energy efficiency for office building in Aden city. The temperature difference can reach to 12 C in some cases this happened during summer and winter time figures (4). The temperature difference between day and night time will be essential factor to remove the heat absorbed in the building structure. Encouraging night ventilation from out door will remove the heat absorbed in the building structure when the office is unoccupied. If the outdoor temperature is lower than indoor temperature through the night so there will be possibility to reduce the indoor temperature. 3

4 Air temperature C Air temperature C Day hours Figure (3) Outdoor Temperature summer day 21 July Day hours Figure (4) Outdoor Temperature winter day 21 December The climate of Aden city has little rain fall or precipitation during all the year which represent the desert climate. The average of precipitation is from 2-5 mm which is small amount especially in summer time. The sunshine hours reach to 300 hours per month during summer time and the minimum sunshine hours could be found in February which about 200 hour per month. Aden has high percentage of humidity which reaches to 75% almost of the year. 3.2 Office building and climate In hot climate it s very important to avoid overheat when using natural ventilation which could happen in case the outdoor temperature is higher than indoor temperature. In order to achieve the energy efficiency by using night ventilation so simulation model will examine in this paper. The need to use cooling in office building is required in almost of the year in the climate of Aden and Hodeidah cities due to high outdoor temperature. 4

5 Figure (5) Office building-aden city Figure (6) Aden government office building-aden city The pictures above show some types of office building which is build recently in Aden city using glass façade without considering the energy consumption. The designer of office building doesn t give attention to design building with energy efficiency in Aden city. 4.0 Model Description Figure (7) Office model in DesignBuilder The model office room was built in Design builder program as shown in the figure (7) and simulated in the program with weather data for both cities Aden and Hodeidah. Both models are typically the same dimension and they are simulated separately with the weather data for every city to analyze the thermal behavior. The model room is oriented to the four main directions in order to see the thermal effect of every office model with different orientation. The result of design builder is shown in hourly, monthly and yearly. The design builder program is using energy plus calculation formulation which approved in ASHRAE 140. The thermal model was simulated during all the time of the year in order to understand the thermal behavior of office model during all the time of year summer and winter, day and night. The simulated model 5

6 represents the actual office building in both cities and the thermal office model is simulated as adiabatic office which means that the office model zone is surrounded by many different zones which have the same thermal behavior of the simulated office model. All walls and roof of the model office is used as adiabatic walls and roofs. The reason to use the adiabatic model because the time to run simulation with whole real building will take too long time just to check one parameter due too many calculations should be done and in the same time the adiabatic model will give result as simulating whole building The floor plan dimension of the office model is 4 meter length and 3 meter width with total area 12 m2. There are two models used in simulation program, one model oriented in direction (north south) and the other model oriented (east west). The table below shows all office model details and description for the standard case. Area of the model office = 12 m2 Height of the zone = 3 meter U value of external walls = 1.6 w/m2.k U value of internal walls = 2.0 w/m2.k Location Aden and Hodeidah cities- Yemen Volume of the zone = 36 m3 Working hours = 8 18 h Thickness of wall = 0.3 m Thickness of wall = 0.2 m U value of external glass = 2.0 w/m2.k (solar protection glass) Table (1) Model office description This thermal model represents the prototype of the office building in both cities of Aden and Hodeidah. The External and internal walls are typically which is used for office building in both cities. In the simulation model every city is simulated according to its own materials which are used to build the office building. The details of the internal gain are shown in the table below. Person in each zone = 2 Computer in each zone = 2 Lighting Density = 13 w/m2 Internal gain and ventilation Person gain = 150 W Computer gain = 140 W Cooling temperature set point = 26 C Air change rate occupied = 1/h Air change rate unoccupied = 0.3 /h 6

7 Infiltration rate = 0.3 /h Night ventilation = 22 4 h Table (2) Model office internal gains 4.1 Methodology of simulation process The both climates of Aden and Hodeidah cities were simulated in the thermal model in Design Builder program. The thermal model of office building in both climates was simulated firstly without air temperature restriction, after that it s simulated with improvement of air temperature restriction which is applied to the thermal model in order to calculate the amount of energy saving in cooling demand. 5.0 Result of Simulation 5.1 Cooling demand The simulation result shows that the cooling demand is very high in summer time due to high outdoor temperature. The monthly cooling demand result from simulation model in figures (8, 9) shows the cooling demand very high in summer time and more than 15 kwh/ m 2 per month during months May, June, July, August, September and October. The annually cooling demand reaches to 200 kwh/ m 2.a in figures (10, 11). The simulation result shows that there is cooling demand in winter time. The annually cooling demand is shown in both figures with different orientation. kwh/ m 2 kwh/ m 2 7

8 Months Months Figure (8) Monthly cooling demand in Hodeidah city Figure (9) Monthly cooling demand in Aden city kwh/ m 2.a kwh/ m 2.a Orientation Orientation Figure (10) Annual cooling demand in Hodeidah city Figure (11) Annual cooling demand in Aden city 5.2 Night Ventilation with restriction- Aden and Hodeidah cities In order to avoid the overheated through night ventilation, the design builder program which used to simulate the office model has the advantages to control the night ventilation by the different between outdoor and indoor temperature. The simulation program DB used natural ventilation which allow the ventilation only when the outdoor temperature lower than the indoor temperature. This control for ventilation allowed to prevent overheated could be caused when outdoor temperature higher than indoor temperature. The program used values to control the ventilation as shown below in the table. Value of natural ventilation in DesignBuilder Ventilation progress 0 Outdoor temperature< indoor temperature -50 No restriction 2 Outdoor temperature + 2< indoor temperature 8

9 Table (3) Ventilation Progress The table above shows that the possibility to have different ventilation situation to control the night ventilation, the first case when the outdoor more than indoor temperature and its referred by value (0) the second case when there is no restriction which means the ventilation will be allowed without any restriction for different temperature between outside and inside and in this case the ventilation depend on the scheduled time and its referred by value (-50). The third case allows ventilation when the outdoor temperature +2 more than indoor temperature and it s referred by value (2). There are potential to have overheated during some time when outdoor more than indoor temperature in second case. The first and third case will be simulated in office building model and will be compared with second case in order to examine the effect of control the night ventilation depend on air temperature different on the cooling demand of office building. The simulation office model will oriented to different orientation in order to calculate the reducing in cooling demand in every orientation Aden City kwh/m2.a 9

10 Orientation Figure (12) Annual cooling demand in Aden city with and without air temperature restriction Hodeidah City kwh/m2.a Orientation Figure (13) Annual cooling demand in Hodeidah city with and without air temperature restriction. The Result in figure (12, 13) shows significant reduce in cooling demand when using T (temperature) restriction and only allow night ventilation when outdoor temperature + 2 more 10

11 than indoor temperature. The using of 2 C degree different in third case of ventilation show more effect on reduces cooling demand than use only no restriction likes the second case or the first case. The graph above shows only reduce in cooling demand with different orientation are due to T restriction without any effect for any other parameter. 7.0 Conclusion After simulation done for both cities it is proved that natural night ventilation plays an important role in decreasing the energy efficiency in Yemeni office building and improvement of the night ventilation by air temperature restriction will reduce the cooling demand for both cities Aden and Hodeidah. The amount of energy saving in cooling demand could be reach to 10% of the total cooling demand required. The proper design for building façade will help to encourage and increase the natural ventilation. 通过夜间通风降低也门 Aden 和 Hodeidah 城办公建筑制冷能耗 Aymen Aklan, Panyu Zhu, Marlon Leão, Érika Borges Leão, Volker Huckemann (IGS - Institut für Gebäude- und Solartechnik, Univ.-Prof. Dr.-Ing. M. Norbert Fisch, School of Architecture at the Technical University of Braunschweig, Germany) 摘要 : 如今通过设计手段降低办公建筑制冷能耗已经成为一个重要课题 在 Aden 和 Hodeidah 等气候炎热的地区显得尤为迫切 也门的气候类型可分为沿海平原气候, 中西部高原气候和东部高原及类沙漠气候 应当认清不同气候类型特征以实现办公建筑制冷低能耗 本文利用模拟软件 DesignBuilder- Energy plus 讨论了 Aden 和 Hodeidah 两个城市制冷能耗的实际情况 在 DesignBuilder 中建立热环境模拟模型, 并对该模型采取夜间自然通风以降低制冷能耗 模拟中根据室内外温差调节夜间通风, 对模型进行优化 结果显示了通过夜间通风可以节约的能耗, 以及室外温度高于室内温度时可能产生的过热情况 模拟结果表明了也门办公建筑可以实现的能效水平 关键词 : 夜间通风 References 办公建筑制冷能耗空气温度 - AboulNaga M. M., Abdrabboh S.N., Improving night ventilation into low rise building in hot arid climates exploring a combined wall roof solar chimney, 1999, United Arab Emirates. 11

12 -AL-ajmi F.F., Simulation of energy consumption for Kuwaiti domestic buildings, 2007, UK. -Al-shibami F.H., Thermal comfort and energy efficiency in Yemeni houses, PhD Thesis, 2004, University of Sheffield, Sheffield. - DesignBuilder Manual, 2008, - Ezzeldin S., Rees, Cook, Performance of mixed mode cooling strategies for office buildings in arid climates, 2009, UK. - Haase M., Amato A., Ventilated façade design in hot and humid climate, 2006, China. - Ossen D.R., Optimum overhang Geometry for building energy saving in tropical climates, 2005, Malaysia. - Prelgauskas E., Enhanced natural ventilation in hot arid lands, 2002, Australia - Vollebregt R., Boonstra C., Natural ventilation and cooling strategies in new office designs, 1998, University of Athens, Greek. - Ward H.A. Overheating Analysis of a naturally ventilated office building in temperate climate, 2008, Chech Republic. 12