Achieving the nearly zero energy building concept - A study based on practical experience

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1 Achieving the nearly zero energy building concept - A study based on practical experience SIMON PESCARI, VALERIU STOIAN, DANIEL DAN, DAN STOIAN Department of Civil Engineering and Equipment, Faculty of Civil Engineering University Politehnica Timisoara 2 nd Traian Lalescu Street, Timisoara, ROMANIA simon.pescari@student.upt.ro Abstract: - The current paper deals with the impact of the European Directive on energy efficiency in buildings sector. The European Directive on buildings sector has two target in order to reduce the energy consumption. First target regards existing buildings, where efficient solutions must be found for thermal rehabilitation and the second target is for new buildings for which it must be established in the design phase some minimal criteria in order to reduce the energy consumption. This request imposed for the new buildings has led to the energy efficient buildings. The first energy efficient building is the passive house. This building represent a solution for reducing the necessary energy for heating and cooling. The nearly zero energy building represents an improvement of the passive house by supplying the necessary energy with renewable energy. In Timisoara was built a duplex passive house, and the north-east part of the duplex was improved to achieve the nearly zero energy building request. The current study presents the improvements that were made to the passive house and the results of this improvements. Key-Words: - Energy, energy efficient building, passive house, nearly zero energy building, thermal insulation. 1 Introduction The reduction of the primary energy represents the most important care of humanity and because of this; the main concern of the biggest government all over the world is to reduce the energy consumption. As a first action to solve this goal, the European Union adopted the Directive, a directive which has the target to reduce 20 percent the greenhouse gas emissions, a 20 percent cut of primary energy consumption by improving the energy efficiency and also to increase the renewable energy consumption with 20 percent. All those requirements from Directive have to be achieved until For The European Union to reach its target, the Directive sets mandatory requirements for each member states by introducing new laws and new national norms or improving the existing norms [1]. The EU Directive addresses to all areas of energy consumers, but the building sector represents a priority because 40 percent from total energy consumption in EU is used by this sector. Romania as an EU member has to achieve the target of European Directive, so for that, between 2010 and 2014 the Romanian Government introduced new laws and news additional request for existing laws. Also in 2013 was introduced law 159 for amending and supplementing law no. 372/2005, the energy performance building law, in 2014 was introduced the law 23 to approve the Government Emergency Ordinance no. 57/2013 amending law 220/2008 for promote energy production from renewable energy sources [2]. The Romanian Standard on thermo-technical calculation of structural components of buildings, was modified in 2011 by increasing the minimum thermal resistances required and decreasing the heating demand for new buildings. Nevertheless, Romania do not have a code for energy efficient buildings. The Romanian standard do not satisfy the minimal criteria for a passive house and for nearly zero energy building. A residential dwelling designed and built according to Romanian standard has a heating demand between 100 and 150 kwh/m 2 /year, which leads to the impossibility of being unable to satisfy the European Directive requirements. ISBN:

2 Therefore, in order to achieve the goal imposed, in Romania it began building energy efficient buildings according to the European codes and standard. One of the known standard for efficient energy building is The Passive Standard elaborated by Passive House Institute from Darmstadt, Germany. Near Timisoara was built a passive house according to Passive House standard. The house is duplex, and the south-western part of the duplex is designed like a passive house and the north-eastern part of the duplex was improved to achieve the nearly zero energy building request. 2 Energy efficient buildings concept The energy efficient buildings concept emerged as a response of the necessity to reducing the energy demand. The buildings are responsible of 40% from total energy consumption and the energy efficient buildings represents the best solution to improve the buildings sector in regards to energy consumption. According to the issues at which it refers, are known several concepts of energy efficient buildings: - The passive houses concept, which is supposed to increase the energy performance and reducing the energy demands by improving the thermal resistance of envelope elements and using high performing equipment for heating, cooling, domestic hot water and lighting; - The nearly zero energy buildings concept, which in addition to passive houses concept is supposed to use renewable energy for supplying the energy produced by conventional sources. - The active houses concept, in addition to nearly zero energy buildings concept is supposed to use only renewable energy for the all necessary energy. The passive house concept and the nearly zero energy buildings concept are frequently used in Europa. 2.1 The passive house concept Passive House is defined as a building that provides a high indoor comfort throughout the year with maximum 15 kwh/m 2 /year for heating and cooling and 120 kwh/m 2 /year total energy [3]. This concept was developed by Wolfgang Feist and Bo Adamson in 1988 and improved after 1996 by Passive House Institute. In order to achieve the passive house concept a building have to satisfy the following minimal criteria: the building must have a compact configuration for free thermal bridges, airtight envelope, an advantageous orientation for solar gains and a ventilation system with heat recovery of 75% or more; the energy demands for heating and cooling must be 15 kwh/m 2 /year or less and total energy demands should not exceed 120 kwh/m 2 /year; the envelope elements of the building must have a high level insulation and as a recommendation, the heat transfer coefficient for exterior walls can be 0.15 W/m²K or less and for horizontal envelope elements 0.10 W/m²K or less and the window frames must be well insulated and it must be used low-e glazing to prevent the heat transfer. According to Passive House Standard, a passive house does not need to be heated actively. The heating of the indoor air is realized using the ventilation system with heat recovery and heat pump. This minimal criteria for passive house is the same all over the world but some criteria details can be modify or adopted according to exterior climate data. For a passive house the good planning and the technology used for thermal insulation are crucial. It is very important to correlate the thermal residence of the envelope with building services. For realizing this correlation and for a proper designing it must be used a design tools especially created for designing and verifying a passive house. This design tool is Passive House Planning Package (PHPP) and is the only tools accepted to design a passive house and to verify the minimal criteria for a passive house [3]. 2.2 The nearly zero energy building concept This concept of energy efficient buildings is known in various form. So, Zero-Energy Building (Zeb), Net-Zero Energy Building (NZEB) and Near Zero- Energy Building (nzeb) are terms used to describe the Nearly Zero Energy Building Concept [4]. Zeb and NZEB terms are similar and both of them define buildings with zero energy and also zero carbon emissions. NZEB term defines a building whose energy consumption is almost zero or consume a little more energy than they produce. This "almost" is a very subjective value, may depend on economic, social and environmental conditions. Since the residential buildings are responsible for about 40% of total energy consumption from fossil fuels, this concept is regarded as one of the main ways to reduce the carbon emissions and dependence on fossil fuels. Nearly zero energy building can be independent of the national electricity grid by producing renewable ISBN:

3 energy on site and reducing consumption through appropriate design of the building and using a highly efficient building service. A nearly zero energy building also can be defined as: -Net Zero Site Energy which means that the annual consumption of the building must be covered by the energy generated from renewable sources of energy. This energy must be produce on-site; -Net Zero Source Energy which means that the building produces enough energy in one year to cover the annual energy consumption of the building; -Net Zero Energy Cost which means that the cost for exported energy from the building to the national electricity grid must be equal or greater than the cost for imported energy from the electricity grid to the building; -Net Zero Energy Emissions: which means that the building produces energy from renewable resources equal or more than the energy produced from fossil fuels. According to the definitions above the main characteristic of Nearly Zero Energy Building is the reduced energy consumption. The easiest possibility to realize a nearly zero energy building is to adopt the minimal criteria for a passive house and improve the services and the sources of energy [4]. A passive house has an energy demands of 15 kwh/m 2 /year for heating or cooling and 120 kwh/m 2 /year total energy which must be covered by renewable energy in order to achieve a nearly zero energy building. In addition it is necessary to use efficient equipment, ventilation system with heat recovery, heat pumps, and renewable energy for heating the domestic hot water and economic light elements as LED technology. season is -15 o C and the exterior temperature for hot season is 30 o C [5]. This temperature difference between cold and hot seasons represents a challenge when the passive house minimal criteria was adopted. 3.1 General information about studied building The building was designed using PHPP. In order to achieve the passive house minimal criteria, for this house it was applied the Passive House technology step by step [6]. Fig.1 The studied passive house, near Timisoara. The house is a duplex house with two storeys. It has a compact form and the main dimension are: m length, 6.67 m width and 7.76 m high (figure1) [7].The 1 st floor is larger than ground floor. The usable area of the building is 182 m 2. The infrastructure of the building is made from isolated foundation of precast concreted block. 3 Case study- Nearly zero energy building Even thought, the energy efficient building concept appeared in 1988, the first passive house was built in 1990 and the number of the passive houses all over the world is estimated to be In Romania this concept is new. In Romania are less than 10 buildings known to be built it according to passive house minimal criteria. In 2011 a passive house was built near Timisoara. The building was adapted to the exterior climate data of Timisoara. Timisoara is located in the west Romania and has temperate climate. According to Romanian code, the exterior temperature for cold Fig.2 The thermal insulation between the foundation and the wall under the ground. ISBN:

4 This concrete block was connected by foundation beams and it was choose this foundation type to eliminate the thermal bridges from the floor on ground. For the foundation and for the ground under the house it was adopted two particular solution in order to achieve the passive house standard. First solution is that, it was introduced a thermal insulation layer between the foundation and wall under the ground (figure 2) and the second solution refers to fact that the foundation and the walls under the ground was thermal insulated (figure 3). Fig.3 The thermal insulation on the foundation and on the walls under the ground. The vertical structure is made using vertical hollow ceramic block with a thickness of 250 mm. The floor above ground floor is a wood concrete composite slab. The roof is a terrace roof with a slop of 2%. The compact form of the building, the foundation type and the terrace roof, had the propose to optimize the energy demands and more immortally to eliminate the thermal bridges. 3.2 Thermal characteristic for the studied building According to the passive house minimal criteria, for each envelope elements it can be establish a maximum heat transfer coefficient value right from the design phase. For this, it was recommended the value of 0.15 W/m²K for the heat transfer coefficient for exterior walls, and for horizontal envelope elements a value of 0.10 W/m²K or less. The verification of the passive house criteria and energy demands for heating or cooling and total energy demands was realized using PHPP. This verification was made in the design phase and after the building was finished. In order to satisfy all the passive house minimal criteria and after the verification with PHPP, it was proposed and adopted the following thermal insulation and heat transfer coefficient: -The exterior walls was thermal insulated with 300mm of polystyrene and it was established a heat transfer coefficient value of W/m²K. According to the criteria that for passive house aren t accepted thermal bridges, the anchors used for fixed the insulation board, were buried in polystyrene and insulated with polystyrene lids. The thermal insulation of the wall starts under the ground as it can see in figure 3. -The floor over the ground was thermal insulated with 400 mm of polystyrene. The heat transfer coefficient for the floor over ground is W/m²K and the component layers are presented in figure 4. Finishing - 15mm Adeziv - mortar 5mm Hidroinsulation - 2mm Cement mortar 50mm Concrete slab - 100mm Bituminous membrane Thermal insulation (Polystyrene expanded 250mm) Thermal insulation (Polystyrene expanded 150mm) Ballast - Ø mm Compacted soil 400mm Foundation soil Fig 4 The floor over ground stratification. For the floor over the ground, the thermal bridges were eliminated by introducing a thermal insulation layer between the foundation and wall under the ground (figure 2) and by insulated the foundation and the walls under the ground (figure 3). -Terrace roof was thermal insulated with 425 mm of polystyrene, in two layers. Initially, according to the first phase, it was established a number of two layers of thermal insulation, one layer of 320 mm thickness above the wood beams (structural elements of the floor) and one layer of 80 mm thickness under the wood beams (figure. 5). The heat transfer coefficient for the floor over ground is W/m²K and the rest of the layers components of the terrace roof are presented in figure 5. Ballast 50mm Geotextile Bituminous membrane 5mm Sand Cement mortar, slope 2% min. 50mm Polyethilen foil Thermal insulation (Polystyrene expanded) 320mm Vapour barrier Wooden floor 50mm Mineral wool 100mm, between timber beams 150x250mm Steel profiles 60mm Gypsum plaster board 10mm Interior finishing Fig.5 The terrace roof stratification. ISBN:

5 -The floor over air was thermal insulated with 300mm of polystyrene and it was established a heat transfer coefficient value of W/m²K. -Windows have the heat transfer coefficient of W/m²K and the exterior door of 1.1 W/m²K. Following the manner of achieving the insulation thickness for each envelope elements, it can be said that the house is wrapped in insulation, thing that can be seen in figure 6. Fig 6 The cross section through the building. 3.3 Energy demands for the studied building The passive house built near Timisoara is a duplex house and for this reason it we chose that, the south-western part of the house to be used as a passive house and north-eastern part to be improved the other part to achieve the nearly zero energy building request(figure 7). Fig 7 The presentation of two parts in which was divided the building. In order to finish all the detail for the passive house, the south-western part, which remains only a passive house, it was equipped with a high performance HVAC system with energy recovery. For heating, it was installed an air-water heat pump. According to the results obtained from the PHPP, in the design phase, the energy demands for the heating or cooling was 15 kwh/m 2 /year and total energy demands was 100 kwh/m 2 /year for the entire building. The energy demands presented above are only a simulation of the energy consumption, used to establish all the details for the envelope elements and for the facilities. Another simulation of energy demands was performed for the passive house (south-western part of the building) after the building was finished, all the HVAC system was installed and all the passive house minimal criteria were met. According to the results of the simulation, the energy demands for heating or cooling is 15 kwh/m 2 /year and the total energy demands is 66 kwh/m 2 /year. This last simulation confirm that all the requests from the design phase were fulfilled and according to passive house minimal criteria, this part of building can be certified as a passive house. The actual passive house is one of the first passive houses in Romania, and in Romania the energy efficient buildings represents a new concept, leading to the necessity to verify the energy consumption for a few years. Therefore, it was implemented a monitoring system to establish the real consumption for heating and cooling, the total consumption of the building, the interior temperature and the other interior comfort parameters [8]. According to the monitoring results the energy consumed for heating was kwh/m 2 /year and the total energy consumed is kwh/m 2 /year. The monitoring values are between May 2013 and April The difference between theoretical consumption obtained using PHPP and the real consumption obtained from monitoring data may be due to the exterior climate data, the use of ventilation system and occupants number. The energy balance was performing for an interior temperature of 20 o C and for 4 occupants. The interior temperature recorded by monitoring system is higher than 20 o C and number of occupants is only 2. These two facts can be the reason of the difference of consumptions obtained. The north-eastern part of the building was improved to achieve the nearly zero energy building requests. This part is a passive house too; all the envelope elements are the same with south-western part. In order to improve, it was performed an energy balance to establish the energy demands for this part taking into account that, this part of the house is located in north-east, and it does not have windows facing south. The results of this energy balance were almost the same with the results of the passive ISBN:

6 house part. The energy demands for heating are less than 15 kwh/m 2 /year and total energy demands 66 kwh/m 2 /year. The improvements for this house are: -chancing the heat pump from air-water heat pump to water-ground heat pump; -installing the solar photovoltaic panels which generate 5.2 kw for supplying the energy necessary. The annual estimated energy produced by the solar photovoltaic panels is 4700 kw. This energy can cover 34 kwh/m 2 /year from the total energy consumption of the building. More than half of total energy demands can be covered by the energy produced by the solar photovoltaic panels if the energy consumption is according to PHPP simulation. If the energy consumption is according to monitoring data from the passive house, the energy produced by the solar photovoltaic panels cover 75% from the total energy demands. In this case the building needs only 12 kwh/m 2 /year from the electricity grid or energy produced from fossil fuels. Thus, the building meets the early zero energy building request. 4 Conclusion The paper presented a building which was built it according to passive house minimal criteria. The building is a duplex house and it was separated as follows, a part of the building is a passive house and the other part is a nearly zero energy building. The passive house concept and nearly zero building are something new in Romania. Currently, there are maximum ten passive houses build in the whole country. The local climate condition and all the passive house criteria determine a high cost to build a passive house. In order to convince people that the passive house represents a solution to reduce energy consumption and after few years the passive house can be an economical building, for the studied building was monitored the energy consumption, the interior humidity and the interior temperature. The separation between the two types of building concept was realized only when the passive house was finished. The improvements for achieving the nearly zero energy building were the groundwater heat pump and the solar photovoltaic panels. The groundwater heat pump is more suitable for the exterior climate conditions of Timisoara and it can reduce the energy demand for heating. The photovoltaic panels have the purpose to ensure as much as they can the total energy demand for the building. According to the monitored value and to the annual estimated energy produced by the photovoltaic panels for the studied building, only 12 kwh/m 2 /year of energy must be cover from the electricity grid or from the energy produced using fossil fuels. The total energy demand which is provided from conventional sources is nearly zero. Therefore, the analyzed building meet the early zero energy building request. The conclusion is that the nearly zero energy building concept can be achieved by fitting a renewable energy sources and it is very hard or impossible to realize a nearly zero energy building without designing the house according to the passive house criteria. Acknowledgements This work was partially supported by a grant of the Romanian National Authority for Scientific Research, CNDI UEFISCDI; project number PN- II-PT-PCCA Contract 74/2012. This paper is supported by the Sectorial Operational Programme Human Resources Development POSDRU/159/1.5/S/ financed from the European Social Fund and by the Romanian Government. References: [1] European Parliament, Directive 2010/31/of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (recast), Bruxelles. [2] gia-de-calcul-al-performantei-energetice-acladirilor [3] Feist, W et. al Passive house Planning Package 2007, Technical information. PHI-2007/1, Darmstadt: Passivehouse Institut. [4] Principles For nearly Zero-energy Buildings, Buildings Performance Institute Europe (BPIE), [5] C107/2005-Normativ privind calculul termotehnic al elementelor de construcţie ale clădirilor. Ministry of Regional Development and Tourism (in Romanian). [6] D. Stoian, et. al. Life Cycle Assessment of a Passive house and a Traditional house - Comparative Study Based on Practical Experiences, Life-Cycle and Sustainability of Civil Infrastructure Systems, International Association for Life-Cycle Engineering, [7] assivehouse. [8] ISBN: