The need for energy conservation deserves everyone’s attention. Many institutional buildings in East African countries do not incorporate energy efficiency at the design, construction, and utilization stages. Energy efficiency in the built environment can make significant contributions to a sustainable energy economy. In order to achieve this, greater public awareness of the importance of energy efficiency is required.
Institutions of higher learning are in a position to champion such initiatives. The main objective of this paper is to present the findings of a comparative study carried out to analyze the energy performance of green building envelopes and conventional ones and, then, to recommend models of building designs that can lead to reduced energy use in the construction, use and maintenance stages.
In the short term, energy issues include demand side management such as consumers’ behavioural change, new efficient appliances, building technologies, legislation quantifying building plant performance and improved building regulations. With the building construction industry continuing to grow at a very fast rate, as evidenced by the 2005-2009 35.3% increase in cement consumption, it is imperative to consider energy efficiency from the design and construction of buildings to their utilization.
Building design
A Management Science Building (Nairobi)
Strathmore University’s Management Science Building’s (MSB) layout and foundations utilized well-shaped stone with no exterior finish. The curtain walling has twelve mm clear glass. The windows are aluminium framed fitted with 6 mm clear glass. The entire floor is ceramic tile while the interior has a cement and plaster finish. The calculated thermal transmittance, U-value through the wall combination, is approximately 6.1Wm2K-1 providing good thermal storage. The window glass U-value is 6.25X10-3 Wm2K-1 while glass curtain walls’ is 0.0125 Wm2K-1.
The MSB covers an area of approximately 734.546 square meters over four floors. The main building mass has a north-south orientation, presenting minimal direct solar radiation to the façade. The windows are made of aluminium frame and 6 mm clear glass. They are also inset and, thus, have shade from the building design and roof overhang. The building design has a maximum integration of day lighting. A nearby building shades the western façade while the eastern side has roof overhangs and inset windows, permitting minimal solar radiation. As a result, the students never suffer from glare.
Other key designs features are the extensive use of natural ventilation and a slab structure roof with polythene and tar coating.
Computer and Information Technology Building (Kampala)
Makerere University’s Computer and Information Technology (CIT) building consists of 200 x 400 x 200 mm concrete blocks with 25 x 150 x 75 mm clay face bricks finishing. Tinted and clear glassare incorporated in the curtain walling the interior of which has cement-plaster finishing. The lecture room floor is PVC tiles while the corridors are with of terrazzo flooring. The calculated thermal transmittance, U-value, through the wall combination is approximately 1.7 Wm2K-1, which ensures that minimal heat gets to the building interior. The window glass U-value is 3.125X10-3 Wm2K-1 while the tinted glass curtain walls is 2.125X10-3 Wm2K-1.
The CIT is a vast building with six floors. The building has a north-south orientation with the entrance canopy facing south. Clay-brick finish and glass make up the façade. The building mass is in square form with no void opening the result of which is uncomfortable lecture rooms. The building uses extensive air conditioning for the computer laboratories and server rooms. Most of the glass on the façade is blue tinted leading to extensive use of artificial lighting. Students complain of excessive heat from noon till evening, because the glass eastern and western facades transmit a lot of heat. Also, natural ventilation is limited to the window openings, thus the building interior has limited air circulation. The CIT roof is a pitched structure made of clay tiles that have excellent thermal properties.
Energy sources & consumption
The MSB’s main energy source is electricity from the national grid and a back-up generator. The MSB’s peak load during the research-recording period was about 8.5kW as is depicted in the MSB load profile graph for a typical weekday. This is because of the integration of extensive day lighting. The major loads are the server and computers which are in each lecture room. The estimated annual energy cost is at 85MWh.
The CIT faculty operates almost 24 hours daily 7 days a week and the biggest loads are lighting and computer. Lights in all computer laboratories, corridors and most lecture rooms operate for 24 hours. The CIT load profile graph shows a typical load profile for the building on a typical weekday. The estimated annual energy consumption is 880MWhrs.
Building management system (BMS)
The CIT building does not have any BMS integrated into it, therefore, all resource utilization is manual and user controlled. This has led to wastage of resources due to, for example, having the corridor lights on even when not necessary. On the other hand, BMS is integrated into the MSB to control the resource utilization. The BMS used bases on SNAP PAC System Architecture with OPTO-SNAP controllers. User defined control programming defines the functioning of the various components such as motion detectors, power cards and lighting control.
Discussion
Importantly, the CIT building has more floors and covers a much bigger area than the MSB. Nonetheless, even if they were to have the same design features, the CIT building would still consume much more power than the MSB. However, the CIT’s lack of some key energy efficient envelope design features aggravates its energy problem.
The MSB utilizes 4ft-25W electronic ballast fluorescent tube lighting and saves approximately 80% lighting energy due to daylight integration into the design and the use of electronic lighting controls such as motion detectors and power cards linked to the BMS. The CIT utilizes 32W magnetic ballast fluorescent tube fixtures that run almost 24 hours a day, consuming a lot of energy.
The MSB has mechanisms for rainwater harvesting and pumping to various water taps which meeting all of the water needs. As a way of enhancing proper waste management, an incinerator burns the non-recyclable waste and provides heat energy when required. On the other hand, CIT has water storage tanks at its top which don’t utilize rainwater.
Artificial ventilation should be at the top of CIT to produce a stack effect to improve air circulation and enhance student thermal comfort. Daylight features should also be included in spaces close to corridors to reduce the use of artificial lighting.
Recommended codes of practice
Considerations for building orientation include sun exposure, wind speed and direction, noise, pollution and the building’s shape. In East Africa, building orientation can greatly impact lighting and cooling costs. Depending on the building orientation, the three main aspects are daylight, solar gains, and shading. Computer modeling techniques such as ECOTECT allow tracing the sun’s path through the sky for each day of the year.
Proper orientation of buildings will reduce solar heat gain in the interior. Orientation towards wind breezes will enhance natural and cross ventilation. However, there is a risk of increased infiltration.
The building construction and materials used must have acceptable U values. These U-values could be achieved through insulation optimization where need arises. Heat and moisture movement within the building fabric is localized. The building must be airtight and thermally mass effective to reduce need for heating during cold months. Glazing area and glass performance should be optimum. Low E glass use avoids buildings behaving like greenhouses. Shading should also be implemented for solar control performance and windows should be large enough and located in positions where there is no direct solar radiation.
Buildings in East Africa rarely require any heating. Therefore, attention should be paid to the air conditioning systems. Building design features should ensure that little heat gets into the building to avoid big cooling loads. Extensive use of cross-ventilation and use of Perspex roofing with vents that can create a stack effect to maximise air circulation will greatly reduce the cooling load. An analysis must be made to design a cooling system for the hottest day scenario. Use of other techniques such as evaporative cooling in less humid areas can cost less than using vast air conditioners. Infiltration within the building should also be avoided for more efficient air conditioning utilization where they are used.
Daylight, for psychological reasons and especially in educational buildings, is very important. During the design of institutional buildings, natural daylight should meet the lighting requirements for daytime. As a standard, for a maximum depth of about 6 m from the façade in rooms, daylight should suffice, provided the façade is glazed for about 50% of its wall area.
Conclusion
Energy efficient building design is the result of applying one or more isolated technologies and an integrated whole-building process which requires the design team’s and top management’s advocacy and action throughout the entire project development process. The whole-building approach is easily worth the time and effort as it can save over 30% in energy costs over a conventional building.
Integrating energy efficiency, renewable energy, and sustainable green design features into all new and existing institutional buildings should become a top priority for management and government. This will make buildings that require less resource utilization more environmentally friendly and comfortable. East Africa member countries need energy conservation laws and building codes of practice to achieve this. Further research will serve to develop a complete overall guide for the design of energy efficient institutional buildings in East Africa.
References
[1] Building Research Board; “Building Diagnostics”: A Conceptual Framework by the National Research Council, U.S National Academy Press, Washington, D.C. 1985.
[2] PewCenter on Climate Change: “ClimateTech Book.”
[3] Taylor B.J., Imbabi M.S.: “The Building Envelope as an Air Filter”, Building and Environment.
[4] UBOS, “Uganda Bureau of Statistics”, National Statistical Abstract Report, 2010.
[5] TAREB: “Architectural Integration into buildings”, European Commission DG Tren Altener programme. Project no: 4.1030/C/02-101/2002.
[6] Peter Burberry: “Environment and Services” Eigth Edition, September 1981.
Principal author: Dr. Izael Da Silva holds a Ph.D. in Power Systems Engineering from the University of Sao Paulo,and is the director of CREEC (Centre for Research in Energy and Energy Conservation) in Uganda. He is also the coordinator of the MSc Renewable Energy Program which is supported by the Norwegian government and hosted at Makerere University.
Co-author: Edward Baleke Ssekulima holds a BSc in Electrical Engineering from Makerere University. He is completing his MSc in Renewable Energy and specializing in energy efficiency in the built environment, and he works as an Energy Officer at Uganda’s Ministry of Energy and Mineral Development.
