1、Towards Net Zero Energy Buildings in Hot Climates : Part 1, New Tools and MethodsFranois GARDE, PhD, PE Mathieu David, PhD, PEMember ASHRAEAurlie Lenoir Eric Ottenwelter, PEStudent Member ASHRAEABSTRACTThe paper presents the results of a French National research project on Net zero energy design tha
2、t just ended in December 2009. The project named ENERPOS has focused on the development of new methods and tools for the design of Net Zero Energy Buildings in hot climates. Three French university research laboratories and two HVAC practices have been involved in the project. The initial objectives
3、 of the ENERPOS project were : - to develop new methods and tools for the design of net zero energy buildings in hot/tropical climates;- to point out that the factor 3 is easy to meet. The energy index must be below 55 kWhe/m.year (net floor area);- to gather the world of research and the profession
4、al sector for improving the use of new simulation tools;- to do a transfer of knowledge from research to the professional fields once the proposed method validated.The methods and tools have been applied to the design of the first zero energy building of the French overseas departments located in La
5、 Reunion. The design and the construction of the building has perfectly matched with the realization of the ENERPOS project. The completion was in October 2008, just one year before the end of the ENERPOS project.The ENERPOS building, named similarly as the project itself, is a very low energy build
6、ings. The main features are listed below : All rooms and spaces are cross naturally ventilated and equipped with high efficient ceiling fans. The tutorial classroom have no air-conditioning at all. solar shadings have been designed and optimized thanks to 3D simulations. The building meets the PEREN
7、E requirements (PERENE, acronym of Energy Performance of Buildings) is a local standard for labeling energy efficient buildings. 350 m of BIPV roofs (50 kWp) produce the renewable energy of the building.In terms of tools to use, the proposed method is innovative : the use of free softwares commonly
8、used either by the architect or the engineer was the key stone of the process. Then, once the building was modeled or imported from CAD tools, thermal or energy simulations have been conducted. Daylight simulations have also been done to improve the daylight autonomy. The method has been tested and
9、validated by professional partner IMAGEEN involved in the project. IMAGEEN now uses it for all its new buildings projects. This guarantee the reproducibility and efficiency of the method.Franois Garde is a Professor in the Department of Sustainable Design and Environment, ESIROI, University of La Re
10、union, LeTampon, La Reunion. He is also one of the Sub-Task leaders of the new International Energy Agency SHC Task40/ECBCS Annex 52“Towards net zero energy solar buildings”. Aurlie Lenoir is a PhD Student at the Laboratory of Physical and Mathematical Engineeringfor Energy and Environment, Le Tampo
11、n, La Reunion. Mathieu David is a lecturer in the Department of Sustainable Design Environment, ESIROI, University of La Reunion, Le Tampon, La Reunion. Eric Ottenwelter is the Director of Imageen, an energy consulting practice specializedin Green BuildingsLV-11-C055450 ASHRAE Transactions2011. Amer
12、ican Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAES prior wri
13、tten permission.INTRODUCTIONThe concept of Net/Near zero energy building (Net ZEB) is now often used and is most of the time included as a specific topic in all the renowned congresses involved in the energy efficiency of buildings (ASHRAE, Clima2010, Eurosun etc.). Despite this, the concept is stil
14、l generic and there is no harmonized understanding about what is really a Net Zero Energy Building. This is why an international work was started in 2008 within the framework of the International Energy Agency “Towards Net Zero Solar Energy Buildings” (Task40/Annex 52 2008). The objective of this wo
15、rk is to study current net-zero, near net-zero and very low energy buildings and to develop a common understanding, a harmonized international definitions framework (Sartori 2010a), new design tools, innovative solutions sets and industry guidelines. This includes new requirements on comfort and ene
16、rgy performances (Sartori 2010b), the management load matching and grid interaction (Voss 2010) and an exhaustive benchmarking about the existing Net ZEBs already built around the world. There are few Net ZEBs built around the world so far. Very little work is available about the design of Net ZEBs
17、in hot/tropical regions as well. This is why a 3 years programme has been launched in France about this specific topic under the name “EnerPos”, French acronym for POSitive ENERgy building. ENERGY CONTEXT IN THE FRENCH OVERSEAS DEPARTMENTSA standard non-residential building in the french tropical re
18、gions is often badly designed with no respect to the basic bio climatic principles. The active systems such as air-conditioning and artificial lighting are often over-sized and therefore are very energy consuming. The average energy index for an office building is 160 kWh/year/m (net floor area) in
19、terms of annual electricity consumed. The three main sources of energy usage are air-conditioning (50% of the power bill), artificial lighting (11%) and computers (25%) for a standard office building. The efforts for energy savings must focus on these end-uses, all the more than lighting and compute
20、rs are mainly responsible of the indoor thermal loads in the building to evacuate by air-conditioning. Turning to the energy background of the French overseas departments, the situation is extremely complicated because the energy demand is increasing regularly with an annual growing percentage of 4%
21、. The means of electricity production are restricted, mainly fuel powered and can not spread indefinitely. The electricity is dear and generates important greenhouse gas emissions. The kWh is extremely polluting with 820g of CO2 per kWh of the electricity produced. The proportion of renewable energy
22、 used for electricity production dropped from 100% in 1982 (thanks to hydro power) to 34% in 2009. The energy demand has increased by 2.5 during the same period. The demography remains important in these departments and will be stabilizing in 2010. The electricity shortages occur more and more often
23、 because the French public utility EDF can not face the energy demand in summer. More specifically to Reunion Island, the Regional Council encourage the construction of green buildings; indeed, the Regional Council has funded an energy plan for the entire island named PRERURE, the objective of which
24、 is to make Reunion energy self-sufficient by 2025. Therefore, because of the energy and environment weight of the building sector in the french overseas departments, the set-up of a research program around the low/zero energy building like EnerPos is of prime interest in these tropical regions. The
25、 results and the principles issued from this project could be applied to any country that endures a hot climate.AIMS AND SCOPE OF ENERPOSHow to reach the near/net zero energy target in hot/tropical climates ?First of all, the question is what is a Net ZEB? As there is still no harmonized definition,
26、 here is one that is applied at La Reunion. A Net Zero Energy Building is a very low energy building that balances its low energy consumption by the use of renewable energy on site and on a annual basis. As for the requirements in terms of energy consumption, it is asked that the energy index must b
27、e equal at least to 50% of the energy consumption of a building compliant to the local thermal regulation.Second, the main characteristics of buildings in hot climates are listed below: the main source of energy is electricity only; 2011 ASHRAE 451 in terms of energy consumption and for non-resident
28、ial buildings, the most important (by order of importance) end-uses are air-conditioning (50%), computers/plug loads (25%) and artificial lighting (11%). That implies that efforts must focus on the modeling of thermal and visual comfort in terms of simulation tools; in terms of passive design, there
29、 are two main principles in tropical climates : a good solar protection and an efficient cross natural ventilation to ensure a good level of comfort.Then, according to these principles, the design of a low energy building relies on several basic steps which are : A good knowledge of the local climat
30、e (for tropical climates, direction of thermal breezes, orientation of the sun, TMY files available); A good design of the surroundings (vegetation around the building to avoid overheating) -eg car parks not allowed in front of the main facades of the building, a 4m band of vegetation around the bui
31、lding must be planned; Priority must be given to the passive design (roof insulation, solar shadings for windows, cross natural ventilation, use of daylighing); Innovative or alternative solutions sets must be proposed; Energy efficiency of systems are mandatory (high SEER for chillers if necessary,
32、 Energy Efficient light bulbs etc.).Then, once these steps have been taken into account, the use of renewable energy can be considered as part of the building design process. This process is necessary to avoid getting a so-called Net ZEB with very bad energy index but with an important surface of PV
33、 panels to balance solely its high energy index.The main idea of all this is that the building itself must operate as long as possible with passive techniques -ie without any energy consumption. And this is a huge step to climb because this implies a dramatic change into the design methods that are
34、used by the design practices which mainly focus on the sizing of active systems (air-conditioning, artificial lighting) rather than focusing on how and how long can the building operate on the passive mode.Issues in the design process of Net ZEB in tropical climatesSo far the design process in Franc
35、e is not well adapted to the design of Net ZEB and does not allow the easy achievement of energy efficient buildings. A reorganization from the brief to the construction of the building itself is therefore necessary. Several issues must be sorted out to improve the design process of Net ZEB and are
36、briefly listed below :1. The lack of discussion between the people involved in the design process ie the architect and the engineers is an obvious weakness for optimizing the passive design of the envelope and the systems. In some cases, the design teams selected by public owners the Regional Counci
37、l, the University and the City Councils have most of the time an overall good level of knowledge but unfortunately the brief of the building is not accurate enough in terms of objectives and energy performance requirements to meet.2. Most of the time, the CAD tools used by the Architect cant communi
38、cate with the simulation tools used by the energy consultants. The building needs to be re-modeled either because the programs used does not read the dxf/dwg file format or the building file is too detailed. This is unfortunately a very time-consuming process.3. These tools are often used by the Arc
39、hitects under their maximum potential. They mainly focused on the presentation of their projects rather than use it to optimize the solar shadings devices for example.4. The working habits of the HVAC design practices and their knowledge in terms of top design tools have to be upgraded. As said befo
40、re, there is a gap between the Net Zero Energy goal and the tools used by the common engineers. The working habits focus more on the sizing of the systems (air-conditioning, artificial lighting) and not on the passive optimization of the building. This radical change into the building design process
41、 implies that new simulation tools must be used -eg the simulation programs must be capable of modeling the airflow transfers to take into account the effect of cross natural ventilation or the useful daylight index for daylight performances. As for lighting, only programs mostly developed by manufa
42、cturers are used to determine the number of luminairs required to reach the minimum luminance level. The requirements in terms of luminance are not adapted to tropical climates for certain buildings and lead to an over-sizing of the 452 ASHRAE Transactionslighting devices. Moreover, the level of day
43、light factor required are suitable for European country only and lead to wrong results under tropical climate where the diffuse radiation remains fierce even during cloudy conditions. The concept of sky classification must be adapted to these climates. 5. Lots of countries experiencing a tropical cl
44、imate are developing countries. That means that the basic HVAC practice cant afford expensives CAD or simulation tools. This implies that open source and efficient simulation tools must be suggested.So the question is “How to bridge the gap ?” Which design tools are suitable with which methodology ?
45、 That is one of the reason why the EnerPos project has been launched.The EnerPos programmeEnerPos is one of the 11 research projects that have been selected by the French National Research Agency_ANR after the 2006 PREBAT call for proposals. PREBAT is the ANR Branch dedicated for all that concern Bu
46、ilding Research in France. The aim of PREBAT is to reach the Factor 4 by 2025 for the building sector. Enerpos concerns the design of zero energy building in the French overseas departments ie DOM under hot and humid climates with a particular emphasizes on the transfer of knowledge from research to
47、 the professional practices. Enerpos is a 3 year running project that started in early 2007 and ended in December 2009. The team was composed with three French university research laboratories and two HVAC practices. The initial objectives of the ENERPOS project were : to develop new methods and too
48、ls for the design of net zero energy buildings in hot/tropical climates; to point out that the factor 3 is easy to meet. The energy index must be below 50 kWhe/m.year (kilowatthour of electricity per m of net floor area, all end-uses included); to gather the world of research and the professional se
49、ctor for improving the use of new simulation tools; to do a transfer of knowledge from research to the professional fields once the proposed method validated.To meet the above objectives, complementary skills coming from either professional engineers or academic researchers have been pooled together, so that everybody can share everyones experience. This is why private and public partners are involved in EnerPos. The EnerPos team has gathered two design practices; IMAGEEN and TRIBU. They are all specialized in Energy Management and Green Building design res
