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Building M is located on Reunion Island on the outskirts of the town of Le Tampon at a high altitude (Figure 1)and benefits from a tropical climate. From 1972 to 1991, Building M housed an army school. In 1994, the South Campus of the University of Reunion Island was created and the army buildings were converted into classrooms for the future students.
Contents
- Passive design systems
- Building performance and simulation software
- On site production
- Monitoring
- Conclusion
- References
In order to meet the local needs in terms of energy self-sufficiency and building performance, the University of Reunion Island has opened a new department at ESIROI its Graduate Engineering School, called The Department of Construction & Energy, to which Building M was assigned.
Like the other timeworn buildings, Building M does not respect the basic bioclimatic principles, such as natural cross ventilation and daylighting. Reunion Island has to face several issues. Indeed, the first major issue is that Reunion has one of the more polluting energies of the world with 820g of CO2 emitted for 1 kWh produced.
Given the increase in demographic trends, the island is already facing a growing demand for energy (Figure 3) according to a recent study. In addition, the energy consumption of the building sector represents a huge share of the overall energy production.
In this context, the existing Building M will be retrofitted and will be a flagship building in terms of green design. The aim is to design a net zero energy building, that is to say a Net ZEB, which will produce more energy than it consumes.
Called BIBAS (réhaBiliation et Innovation pour des BAtiments à énergie positive avec Stockage de l'énergie dans les DOM), the project consists in retrofitting 1,400 square meters of net floor area. The total cost of the operation that includes the study and the renovation will cost in the region of €3.5 Million. Work is due to commence in June 2014.
The project is promoted by the University of Reunion Island in collaboration with professionals, as shown in Table 1 below:
The project is expected to reach three main objectives. First and foremost, the energy consumption of the entire building will be cut down and will not exceed 13 kWh/m²Net Floor Area/year.
The second objective is to design innovative solutions in terms of acoustic and thermal comfort, as well as natural daylighting systems. In order to be self-sufficient, a new energy storage system is required. Indeed, a system of compressed air energy storage has been chosen for the building. This Compressed Air Energy Storage system (CAES) has already been tested on a wide scale but needs to be tested at the scale of an individual building.
However, even if this system is not the most effective, it is by far the most adapted for such a project. To achieve this goal, satisfactory coordination between these three steps must be ensured:
Passive design systems
A huge range of innovative systems will be set up in Building M, especially in terms of thermal comfort and natural daylighting. Firstly, this retrofit will be based on the local climate taking the surroundings into account and creating a harmonious relationship between the building and its immediate environment. As a result, it is essential to collect data concerning the local weather (Figure 5).
As shown in Figure 5, two seasons can be observed: the summer period with outdoor temperatures that range from 13 °C to 30 °C and the winter with temperatures that vary from 8 °C to 22 °C.
Secondly, the purpose is to find a solution so as to warm the building in winter and protect it from the sun in summer, using passive solar systems that are incorporated into the building, as well as taking environmental resources such as wind, sun and vegetation into consideration.
To cope with summer temperatures, interior and exterior light shelves associated with solar protection will be set up in the building. These systems will be sized using engineering tools such as the sun path diagram of Reunion Island as well as different software tools which will establish the design and evaluation of the most satisfactory option. According to the results obtained, the most appropriate solution consists in creating a specific system on each side of the building. Thanks to this design, natural daylighting will be provided with the exterior light shelves in summer, whereas in winter, when the solar height is lower, the interior light shelves will play this key role.
In addition, a patio will be designed so as to provide natural cross ventilation. A chimney principle has been chosen to create the ventilation phenomenon. In order to minimize the solar heat gain, an external wooden cladding consisting of 6 cm of insulation material, will be installed.
Moreover, large openable windows with exterior and interior louvres will optimize natural cross ventilation as illustrated in Figure 6.
In the wintertime, the solar protection will let the sun stream through the windows and heat the classroom by increasing the ambient temperature. Furthermore, with an adequate insulation system applied in particular on the roof and the walls, a temperature included in the comfort zone of the occupants should be reached.
It must be pinpointed that this thermal comfort depends on six parameters: clothing, metabolism (linked to the level of activity), the wall temperature, the air temperature, the relative humidity and the wind speed. In tropical regions, the Givoni comfort diagram is a suitable tool for the assessment of thermal comfort. The Givoni comfort chart is based on the expected indoor temperature rather than outdoor conditions. Using Givoni’s comfort diagram on a psychometric chart, it is possible to predict the different operational periods for natural ventilation and ceiling fans. Three comfort zones can be defined according to the wind speed (Figure 7).
Thanks to passive technologies such as the skylights, the light shelves and the patio, visual and thermal comfort objectives should be attained.
Due to the rugged relief of the island, the region of “Le Tampon” is relatively well protected from strong winds. Therefore, the building does not require specific protection from this factor. In addition, the main facades of the building are positioned towards the north-east and the south-west. Consequently, the orientation of the building is quite adequate to benefit from thermal breezes.
One of the greatest challenges of the retrofit was to find a new approach in order to provide natural daylighting without significant costs. The solution chosen by the designer is to create skylights with two specific functions. Indeed, they will let the light come through to the classrooms as well as creating an upper ventilation system.
Building performance and simulation software
Simulation tools are used in order to evaluate and optimize different architectural and engineering options. This stage plays a pivotal role in the overall design process insofar as it ensures high-energy performance and a high level of occupant comfort inside the building. Energy, thermal and visual comfort, as well as acoustics, are simulated and optimized.
In the first place, a 3D model of the building is carried out, using the Google Sketchup software for instance, or a model is imported from CAD (Computer-Aided Design) tools.
Besides, the energy performance of the retrofitted building is evaluated using the EnergyPlus software. Thermal simulations are conducted in the same way. As a result, air temperature, surface temperature or operative temperature can be measured.
In addition, daylighting tools, such as Daysim or 3DS Max Design, are used in order to examine daylight strategies and evaluate the occupant’s visual comfort. The aim is to improve the daylight autonomy of the different rooms and ensure that daylight objectives are achieved. It also leads to the design of efficient solar control systems such as the light shelves.
Finally, aeraulic simulations will help to assess the efficiency of the systems set up in order to maximize the natural cross ventilation phenomenon.
A weather file of “Le Tampon” is used so as to define the position and the weather conditions around the building throughout all these stages. These data are collected from the on-site weather station set up by students of the Graduate School of Engineering ESIROI, just outside the existing building.
On-site production
In terms of performance, one of the main objectives of the retrofit is to make Building M as autonomous as possible with regard to the power grid.
To meet this challenge, an innovative system consisting of a photovoltaic production unit coupled with a storage unit will be tested and implemented.
The production unit will be composed of 160 m² of photovoltaic panels and the electricity production is estimated at 22,000 kWh/year.
With regard to the system of storage, the solution chosen by the designers is a Compressed Air Energy Storage system. It must be highlighted that this will be a world first because no other Net ZEB currently uses this technology. Compared to batteries, the most widespread storage system at present, the Compressed Air Energy Storage system is a clean form of technology.
The operating principle of the system is straightforward in relation to the building energy demands:
Should the case arise that the photovoltaic production is not sufficient to meet the building’s energy demands, the CAES system restores the stored energy.
However, up to now, the principle of the CAES system has been set up for high levels of power as for instance the compression of air in large underground cavities using wind energy (Toledo 2010). Therefore, one of the main issues of the BIBAS project is to develop and adapt this technology to the level of an individual building.
Moreover, another main issue related to this solution concerns the management of the different phases: production, storage and consumption. There is no doubt that this is a kernel issue for the success of the project.
This is the reason why several surveys have been conducted and a prototype of the CAES system will be built. The goal is to evaluate the behaviour of the system restricted by climate constraints (e.g. fluctuation of solar radiation) as well as the overall energy demand of the building that is directly related to its occupancy rate.
Monitoring
Monitoring is one of the main strategies generally used to reduce the overall energy use of a build¬ing significantly. When the retrofit will be completed, the building’s per¬formance will be monitored and analyzed in order to verify the achievement of the design goals and better target efforts to reduce the building energy use.
Thus, electric submetering systems will be implemented to monitor loads and collect data on the energy consumption of Building M.
Monitoring will allow one to quantify and to follow the energy consumption by type of end-uses (lighting, plug loads or air-conditioning). The data collected will be useful in order to implement a building management system which will efficiently control the air-conditioning systems (operating period, setpoint temperature) and schedule exterior lighting.
Conclusion
Building M will be the second Net ZEB on Reunion Island after ENERPOS and also one of the few educational Net ZEBs existing in a tropical climate. The innovative aspect of this project is that it aims to transform an existing university building into a Net ZEB with innovative energy storage.
Supported by the French Agency for Environment and Demand Side Management (ADEME), one of the main objectives of the BIBAS project is to find innovative solutions in order to reduce the energy consumption of existing buildings significantly. The retrofit sector is one of the major energy issues in Reunion Island. Indeed, most non-residential buildings which are more than 15 years do not respect the basic bioclimatic principles (cross natural ventilation, sun shading). Consequently, cooling systems have become the only means to reach thermal comfort.
Therefore, if the BIBAS project is a success, the solutions found will be used for future retrofitting projects on Reunion Island.
Moreover, from an educational perspective, this future Building M will be a practical working tool for the future students of the Department of Construction & Energy. Indeed, the building’s performance will be analysed in real time as part of the research project.
By way of conclusion, the BIBAS project will promote the know-how of Reunion Island in the field of sustainable construction.