Authored by Maatouk Khoukhi*
Abstract
A zero-energy building, also known as a zero net energy (ZNE) building, net-zero energy building (NZEB), net-zero building or zero-carbon building is a building with zero net energy consumption, meaning the total amount of energy used by the building on an annual basis is roughly equal to the amount of renewable energy created on the site. With up to 80 per cent of UAE’s electricity consumed by buildings for essentials such as air conditioning in a hot desert climate, moving to what are called “Nearly Zero Energy Buildings (nZEBs)” to save energy and cut consumption is an important step into the future. The promotion and the awareness to develop Nearly Zero Energy Buildings (nZEBs) in the UAE is also aligned with the Paris Agreement in 2016, Dubai Plan 2021, and Abu Dhabi Plan 2030. As a first step towards achieving nZEBs in UAE, a very simple approach to reduce the energy consumption of a typical office building located in Abu Dhabi is presented in this paper. This is achieved by comparing different alternatives of walls, roofs, and daylighting by selecting the best window to wall ratio to allow sufficient daylight and natural ventilation, type of glazing, building orientation, and HVAC systems. To simulate the building energy consumption, the office building is designed on Revit and with the help of Sefaira plug-in; the energy consumption has been analyzed by applying different strategies. The result shows that the best design configuration would lead to 55% energy saving compared with the base case.
Keywords: Zero energy building; Low energy building; Case study
Introduction
Typically, low-energy buildings will encompass a high level of insulation, very energy efficient windows, a high level of airtightness and natural/ mechanical ventilation with very efficient heat recovery to reduce heating/cooling needs. Passive solar building design may boost their energy performance to very high levels by enabling the building to collect solar heat in winter and reject solar heat in summer and/or by integrating active solar technologies (such as solar collectors for domestic hot water and space heating or PV-panels for electricity generation). In addition, other energy/resource saving measures may also be utilized, e.g. on-site windmills to produce electricity or rainwater collecting systems [1]. As buildings around the world are among the main energy consumers, reducing the energy consumed by the buildings is presently the most significant confront in the construction sector. The Greenhouse Gas (GHG) releases from the sector of a building have been gathered between 1970 and 2010 and have presently reached the value around 10 GtCo2eq/y. Heating, ventilating and air-conditioning (HVAC) accounts for the greatest proportion of energy used in buildings. In harsh climate conditions where industrial activities are not extensive, buildings consume more than 70% of the total energy requirements, mainly due to the HVAC system use. COP21 Paris agreement requires immediate actions aimed at reducing building energy consumption. The UAE pledge of combating global warming at COP 21 in 2015 by their strategy for the development of nZEBs [2]. Therefore, high-energy performance of buildings has become a requirement for any new construction in many countries including the UAE since 2009. Unfortunately, these regulations are not applied to existing buildings that have been built prior to the release of Estidama codes. Estidama, which means ‘sustainability’ in Arabic, is the initiative, which will transform Abu Dhabi into a model of sustainable urbanization. Its aim is to create more sustainable communities, cities and global enterprises and to balance the four pillars of Estidama: environmental, economic, cultural and social [3]. Buildings are huge consumers of energy and they consequently are the substantial contributor to climate change as they emit one-third of the global greenhouse gas. Consequently, several high performing building concepts have emerged that include low energy buildings zero energy buildings, nearly zero energy buildings and passive buildings [2]. In Europe, new regulation targeting to all new buildings to be nearly zero energy consumers by 2020 [4]. The US also set a target to achieve net zero energy buildings for all the new residential and commercial buildings by 2020 and 2030, respectively [5].
Excessive energy consumption has become a serious issue to solve in the 21st century while buildings consume more than 40% of the worldwide energy [6] while it reaches 80% in UAE [7]. This has encouraged the country to take an action by releasing Estidama code in 2009 [8], highlighting different sustainability concerns about site selection, systems, water, energy, materials, and indoor environmental quality with different weight [9]. More than 25% of the buildings in Dubai were identified as inefficient and have a high energy saving potential [10]. Recent research has concluded that the saving potential can reach up to 30.8% in UAE public houses [11]. The concept of ZEB before was reviewed to consider in priority reducing the energy demand and installing energy efficient equipment has been interpreted as an off grid building with an autonomous energy supply [12]. A quite important number of papers have been published in the last decades exploring the potential towards achieving net-zero energy status and/or low energy consumption. Some papers (e.g. Refs [13-16]) dealt with this topic in conceptual and holistic manner. Some others are more focused on selected types of buildings (e.g. Refs [17,18]). An extensive work dealing with a common and cross-national understanding on principles of sustainable, realistic nearly Zero-Energy Buildings, both new and existing [1]. A simplified methodology for evaluating the impact of point thermal bridges on the high-energy performance of a passive house has been detailed by one team and concluded that substantial increase in heat transfer could occur and this result will improve the accuracy of the heat transfer prediction [19]. Another analysis, which focused on predicted occupant comfort with a concentration on heat transfer through windows in hot humid climates [20]. Researchers using a combination of simulation techniques and future climate predictions examined the extension of a passive house approaches to the hot climates in the Arabian Gulf region [21]. The result suggested that Schneider comfort charts could be used as an analysis technique in such a climate to demonstrate benefits and passive house would result in lower energy cooling. Surveys of a modest sample of passive house buildings were carried out in-situ and concluded that the Passive House standard was robust and gave predictable savings [22].
The building’s total energy consumption can be significantly reduced by considering different strategies including the building’s design and construction alternatives during the early stages of design. Some important factors are suggested to be studied. Glazing types are important to be considered such as Solar Heat Gain Coefficient (SHGC) which represents the solar radiation that is transmitted through glazing or absorbed and reemitted inward [23] in addition to U-value which expresses the heat rate that is transferred by a material or a composite [24]. U-Value has to be studied as well for other buildings envelop components such as roof and walls. The balance of introducing the appropriate natural light and the heat transmission through openings has to be reviewed to specify the window to wall ratio, which is recommended to be between 20% and 30% [25] considering the opening’s orientation. Estidama requires a maximum U-Value of 0.3, 0.2, and 1.9 W/m2K for walls, roof, and glazing, respectively while SHGC is required to have a minimum of 0.3 [26]. Heating, Ventilation and Air Conditioning (HVAC) system selection is critical in buildings energy consumption. Recommended HVAC systems for offices buildings are Constant Air Volume (CAV), Variable Air Volume (VAV), Passive Chilled Beams (PCB) and Active Chilled Beams (ACB). CAV, which is a low-cost system that simply supplies a constant airflow rate while the air temperature varies according to users’ preference [27]. VAV, which supplies variable airflow at a constant temperature, which enhances the temperature control, dehumidification the air passively and decreases the energy consumption [28]. PCB, which consists of a heat exchanger in a casing, suspended from the ceiling; when chilled water passes in the pipes, it increases the surrounding air density by cooling it, which allow it to replace the air at the bottom of the space creating air motion cooling the space. ACB, which works by the same concept of PCB but with an integration of air supply [29]. As a first step undertaken in this investigation, towards achieving nZEBs in UAE, is to present a very simple approach to reduce the energy consumption of a typical office building located in Abu Dhabi. This is achieved by comparing different alternatives of walls, roofs, and daylighting by selecting the best window to wall ratio to allow sufficient daylight and natural ventilation, type of glazing, building orientation, and HVAC systems. To simulate the building energy consumption, the office building is designed on Revit and with the help of Sefaira plug-in; the energy consumption has been analyzed by applying different strategies.
Case Study and Climate Data
In this study, the initiative is to find different strategies that are suitable to the climate to improve the energy performance of an office building located in Abu Dhabi, which is characterized, by a hot-humid climate with long and very hot summers and mild winters. The climate was further analyzed using a weather data software, Climate Consultant. The building has a rectangular shape of four floors with three or four offices, one bathroom, and storage room on every floor. The total area of the building is 1,700 m2. The building energy consumption without any strategy of reducing the energy consumption is found to be 402,682 kWh/year, which is relatively high compared to what it could be reached by applying different strategies. According to the Wind Wheel from Climate Consultant, the maximum wind seems to be coming from the southwest direction. This is useful when considering the openings in the building for natural ventilation. The Climate Consultant that allowed us to look closely at various weather data that could give us the full quantitative image of our site has been also used. The chart simply shows the dry bulb temperature ranges surrounding the recorded high and low temperatures. The design high and low temperatures, average high and low temperatures, and the mean or average temperature. These values are calculated for each month and for the full year by Climate Consultant. Dew Point Temperature (DPT) is the temperature at which air becomes completely saturated, a temperature where water vapor starts to condense out of the air. The Dry Bulb Temperature (DBT) indicates the ambient air temperature. It is also called “Dry Bulb”. It is named that for the sole purpose a thermometer could indicate that air temperature and is not affected by the moisture of the air. Above this temperature, the moisture stays in the air. If the dew point temperature is close to the wet bulb temperature, the relative humidity is high. If the dew point temperature is close to the dry air temperature, the relative humidity is low. The DPT and DBT are shown in Figure 1 (Figure 1).
Building Description
Building design
The building that is being studied is an office building, as shown in Figure 2, located in Abu Dhabi, UAE. The office building has four floors each with an area of 450 m2. The building’s external dimensions are 13.0 x 35.2 m with 16.4 m height. There are nine offices, two washrooms, two staircases, and a common room on each floor (Figure 2).
Base case design concept
To design a low energy building, a concept base case for the building is created where the U-values of the construction components are selected based on what was used prior to the release of Estidama codes. We should mention here that the base case building is the existing one. The building is oriented towards the South with a window-wall ratio (WWR) as shown in Table 1. The building uses a constant air volume (CAV) – Return Air Central AHU. We should mention here that there is no heat transfer through the floor slab of the building (Table 1).
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