2.2.1. Conveying the Advantages of Climate Adaptive Design
One of the key aspects of the second preparatory activity was to communicate and discuss the current building practice with local stakeholders involved in preparing the case study buildings. Within several workshops undertaken with the planning and development team of the case study, the following aspects were highlighted in order to present advantages of climate adaptive design.
The aspects and advantages of climate adaptive design have been widely covered in literature. One of the key aspects in this respect is to assess and learn from the vernacular architecture as described in great detail in [19
] and more recently in [20
]. The outer building shell, with its direct interaction with the climate, is especially of particular focus, as reviewed in depth in [21
]. Schelbach further describes in [22
] how the fundamental principles of climate adaptive architecture can be applied to modern buildings. The function of buildings is first and foremost to provide shelter, from external threats as well as climatic conditions. A thermally comfortable indoor environment is therefore a prerequisite in any design, however the term ‘comfortable’ depends on a series of external factors: personal conditions (e.g., young, old, healthy, ill), activities (e.g., sleeping, working, running), and clothing (e.g., light or heavy clothes). Influencing parameters on thermal comfort are usually temperature (room temperature, surface temperature, temperature differences), air quality (humidity, CO2
levels, oxygen levels, air velocity), and radiation (from systems, materials, or solar radiation).
The external climatic conditions obviously heavily influence the internal thermal conditions of a building; however, Heating, Ventilation and Air Conditioning (HVAC) systems can provide a defined indoor environment regardless of the building’s architecture. Providing a stable 21 °C indoor temperature even when the external air temperature is 35 °C does not just result in exceptionally high cooling energy demands, but also provides unhealthy environments, where people step from a hot outdoor climate into a heavily cooled building. The more external factors such as climate, site, and use of the building, are therefore taken into account during planning, resulting in a climate adaptive building, the less (externally provided) energy the building will need in order to provide a comfortable indoor environment. The use and time of use of the building play in this context a significant role in the overall design: residential buildings are most heavily occupied during mornings, evenings, and nights, with usually less usage during daytime. Non-residential buildings, such as office buildings, are mostly used during daytime and are in addition characterized by heavier internal gains by people, machinery, and lighting. Solar gains must therefore be even more rigorously reduced in non-residential buildings to keep the cooling loads to a logical minimum.
Climate-adaptive design takes advantage of the site without causing additional investment cost, for example by reducing the impact on energy demand for cooling by appropriate orientation, layout, and making use of natural ventilation. However, building orientation and also building layout are certainly influenced by urban planning. While climate adaptive architecture clearly relies on corresponding zoning plans regarding possible orientation, layout, height, and the like, standard designs, which disregard local conditions, do not consider the characteristics of the place influencing indoor air conditions, but use building service technologies and thus energy to deliver the requested comfort. Climate adaptive architecture is thus based on a detailed assessment of the overall climate as well as the local weather conditions such as daily and annual temperature, humidity curves, and radiation.
2.2.2. Climatic Zones in Nigeria and Design Strategies
In Nigeria, there is no data on official climate classification from a Nigerian institution as the agency responsible for this information. According to the Köppen-Geiger climate classification, Nigerian is divided into five zones, namely the tropical savanna climate (Aw), the hot semi-arid climate (BSh), the tropical monsoon climate (Am), the hot desert climate (BWh) and the tropical rainforest climate (Af) [23
Similarly, Nigeria is located wholly within the tropical zone but shows significant climatic variations in different regions of the country. Two principal wind currents affect Nigeria. The Harmattan, from the northeast, is hot and dry and carries a reddish dust from the desert. The southwest wind brings cloudy and rainy weather. These conditions result in four climate types distinguishable as one moves from south to north. The climate is predominantly hot and dry in the north, with higher temperature and humidity swings, and it is hot and humid in the South, with fairly constant temperature and humidity levels. For the hot and humid climate, the seasons are not sharply defined, with constant temperatures throughout the year. Temperatures rarely exceed 32 °C, but humidity is very high and nights are hot. The hot and dry climate exerts enormous influence on the country and has a very distinguishable rainy season and a dry season [24
With a specific view on Abuja, the savannah climate predominant in the Abuja region is characterized by dry and wet seasons, constant high temperatures, low to moderate humidity levels, and limited temperature differences between day and night. Based on these characteristic conditions, one can deduct general architectural principles focusing particularly on cooling for these climatic regions. Shading and high performance glazing are important to reduce solar gains. External envelopes with low thermal transmittance can reduce heat losses, thus reducing the overall cooling load. Temperature regulative building materials and high thermal mass, which can store and release heat, ensure that heat generated during the daytime can be slowly discharged during cooler night times, even when temperature differences are not too high. Buildings, which are partly buried in the ground, can use the stable temperatures of the earth to balance peaks and variations in temperature. Wind towers or earth ducts can be applied to pre-cool buildings, however consideration must be given to the local micro-climate when using pre-cooling systems, as the effectiveness will strongly depend on local temperature and humidity ranges.
The design principles should follow the approach in first exploiting passive design measures, secondly in providing energy-efficient systems, and thirdly in applying renewable energy technology (see Figure 2
). This logical approach will ensure that the architecture will play a significant role in the overall energy efficiency of the building, as it follows the requirement of the climate, site, and building use. To support the exploitation of the thermal characteristics of the building structure together with adequate use of building services and renewable energy systems, advanced thermal dynamic simulation models can be used to provide detailed design scenarios.
The mass residential and utility buildings can particularly profit from intelligent and economical building design, which uses resources wisely, economically, and in a local context, as the principles of climate adaptive architecture can and should be applied to any building in order to provide adequate indoor thermal comfort in a highly efficient way under these challenging climatic conditions.
2.2.3. Objectives and Procedure of the Case Study
Discussions with Nigerian stakeholders made it clear that climate adaptive design is the key to reducing electricity consumption for cooling in a cost-efficient way. However, apart from studies about vernacular and historical architecture and model building simulations, there was insufficient information available on how to introduce climate adaptive design into current design approaches and how specific measures would affect investment cost and energy savings [24
]. In order to learn more about the gap between current design practice and climate adaptive design, a demonstration project was carried out together with a local developer with the objective to improve standard designs by applying various measures [25
]. The building is located in Abuja Federal Capital Territory.
In order to demonstrate how climate adaptive design could be implemented in standard, local working procedures and design in Nigeria, a pilot project was set up for a typical multi-unit residential building. The goal of the project was to provide a showcase of energy-efficient design by delivering two almost identical buildings on one site to allow for a tangible and unique comparison in terms of design procedure, cost, and energy savings.
For this purpose on a site in the North of Abuja, two building blocks were planned for construction, one a ‘Business as usual building’ (BAU) representing the typical design and construction method, the other a ‘Green Building’ (GB) which would feature higher energy efficiency standards and include renewable energy systems. Both buildings were equal in terms of size and number of flats; they differed however in terms of the building specification, compactness, material properties, shading, and HVAC systems, as further described below.
The detailed objectives of the development of the pilot project have been summarized as follows:
Work closely with the local stakeholders to provide a knowledge base and sound methodology for energy-efficient design to those involved in planning and constructing the building.
Consider local climate, resources, and design procedures in order to allow for a high replication potential.
Define different scenarios for the energy-efficient design, which should vary in cost, complexity and reduction in energy demand. Compare the ‘Business as usual’ design with the developed scenarios.
Select the most appropriate energy-efficient design to be constructed together with the ‘Business as usual’ design.
The procedure was to first assess the ‘Business as usual’ (BAU) design provided by the local planners in order to quantify energy consumption and CO2
emissions. Based on the BAU design, four scenarios which varied in terms of energy efficiency, implementation of advanced building energy systems, and costs were developed in close collaboration with the local planning team to provide appropriate designs that were suitable for the local environment in terms of material and system availability, and local knowledge and skills, as well as local environmental and other framework conditions. The development of the scenarios followed the principal logic of sustainable design (see Figure 2
), which had been elaborated with the local planning team. Each scenario consisted of various sets of measures. The BAU, as well as the four developed scenarios were subsequently analyzed in a detailed energy and cost assessment. After the finalization of the scenario development and analysis, one final design of the ‘energy-efficient’ building block (the ‘Green Building’ or GB as referred to below) was selected for construction.
The building site was located in the northern part of Abuja, Nigeria, in a (at the time of planning) still mostly undeveloped area. There was no significant shading by vegetation and there were only minor topographical changes within the site, meaning that the area where the buildings were to be erected was relatively flat. For the assessment, the following location data was used: Longitude: 9.07°/Latitude: 7.39°/Elevation above sea level: 476 m. Local weather data for the project site was derived using the ClimateTool software [27
]. The area around Abuja falls into tropical savannah climate with monthly mean temperatures ranging above 18 °C, and distinct dry and wet seasons. The temperature in Abuja ranges from low 20 °C up to 40 °C over 80% of the daytime, and 50% of the night-time temperatures range on or above 25 °C. Night cooling can be exploited if temperature differences between day and night are greater than 10 K and absolute humidity at the minimum night temperature is below 12 g/kg. For the selected location there would be a constant need for night cooling as temperatures during the day generally exceed 21 °C, but the relatively small difference between night and day temperatures and relatively high humidity levels during the night mostly prevented night cooling. Yearly total irradiation (horizontal) is with 1800 kWh/m2
a relatively high, thus solar potential could be used for the application of renewable energy systems.
As described above, two building blocks were planned for construction on the selected site. Both buildings consisted of three flats over two floors featuring the same size as well as number of flats and rooms. Layout and sizes of units within the two buildings were (apart from some minor details) the same. Each flat was approximately 140 m2
and consists of a living or dining room and kitchen on the ground floor, as well as two bedrooms with walk-in closets and bathrooms on the first floor. The BAU design was defined as a building that represented commonly built practice by the local planning team. The built-up form of the external envelope as well as the building system reflected standard specifications as applied throughout numerous projects carried out by the involved participants. The set-point temperature for heating was defined as 20 °C and for cooling as 25 °C. The domestic hot water (DHW) demand was calculated as 30 L/person/day. The main building properties have been summarized in Table 1
In the first stage, a detailed energy and cost assessment was undertaken on the BAU design. The energy analysis was carried out using the software package PHPP Version 9 [28
]. The package was chosen as it provides low cost and is an easy to learn alternative compared to more complex and/or more expensive simulation tools such as EnergyPlus [29
] or TRNSYS [30
]. The requirement was that the chosen simulation tool could be applied in the training sessions with local planners and stakeholders, and would allow the tool to be used with relatively limited amounts of training and simulation knowledge. The tool is based on Excel and SketchUp [31
], which have been considered to be most widely available and known by the local planners. The analysis provided by the tool included heating and cooling demands [kWh/(m2
a)], maximum heating and cooling loads [W/m2
], frequency of overheating [%], and primary energy demand. The tool allows variations in the building design as well as the building energy system. By choosing this simplified method, it was accepted that the results could not be as detailed as compared to simulations carried out with a thermal dynamic simulation tool. Nevertheless the results should provide meaningful comparative answers to the different measures applied in the scenarios.
The cost assessments were carried out based on cost data delivered by the local quantity surveyor and architects. Electricity costs were calculated with 20 NGN/kWh. Since the BAU design did not consider orientation, compactness of the building shape, or shading, the calculated cooling load was excessively high, as it was generally accepted practice that the air conditioning system would provide a comfortable indoor environment regardless of the buildings’ architecture.
In the second stage, various scenarios were developed together with the local planning team. The objective was to provide variations ranging from no-cost scenarios with reasonable improvements, up to high-cost scenarios and very complex systems. The latter might have not been considered for this pilot project, but was considered important to serve as examples for future projects. The results are discussed in the following Section 3