Who is EFdeN?
We are a team of young professionals, working together aiming to educate the general public, change mentalities, transform the way of living and improve energy efficiency in Romanian buildings.
The EFdeN 4C House was the representative of Romania at the Solar Decathlon Europe competition in 2014 in Versailles. The challenge launched by Solar Decathlon involves designing and building an energy efficient and sustainable solar energy house, while pursuing increasing density and mobility in urban areas, reducing consumption, innovation in all areas, and the viability of the project on the national market.
EFdeN is an energy efficient solar house designed for the urban environment as a solution to the Bucharest’s issues of low density and mobility, an adaptable housing unit both to the environmental parameters and to the inhabitants’ necessities and desires. What is different about this dwelling in the Solar Decathlon Europe 2014 context is neither the flexible compartimentation nor the intelligent systems that activate its installations, not even its modularity or the sustainability of the materials used. What stands out in the EFdeN prototype is the steadfast step towards innovation in energy efficiency: the integration of a productive bioclimatic greenhouse. Dedicated to the “urban farming” concept, this component is the central architectural element of the house being both a source of a spectacle of light on the inside and a community generator on the outside.
Due to our desire to change something in the mentality of today’s society and due to the context in which we lived in we have the benefit of looking from a creative point of view at materials on the market thus introducing an innovative perspective by placing them in a new architectural and urban concept. In this regard, the first point we want to bring in discussion refers to creating a space with multiple valences within the home: a green space. As it can be seen further on the greenhouse has an important role in architecture, urban design and energy efficiency.
We try new languages in the formal use of materials, such as ceramic slabs size to coat the ventilation system of the facade. Yet another innovation as far as the constructive system is concerned, can be found in the structure of the house. This mixed system of wood and metal represents a new approach to Romania’s collective assemblies. Moreover, the mix of the two types of phase changing materials will have an important impact in energy efficiency and comfort conditions.
Owing to the fact that it has found a number of sustainable solutions to numerous problems, EFdeN 4C has become a Research Center for Indoor Environmental Quality.
Designed to meet the requirements of the comfort conditions contest of the Solar Decathlon competition, the comfort parameters are constantly monitored by sensors. The automation and HVAC systems work together to maintain optimum comfort conditions indoors.
The metal structure has been designed according to the latest seismic design standards, taking into account the appropriate wind and snow loads. The dimensioning of structural elements resulted from structural calculations and simulations using specialized software.
All house systems are integrated within a building management system. Basically, systems are self-adjusting according to preset automation scenarios. Lighting, air conditioning and ventilation can also be remotely controlled via a mobile application. Using the same application, all indoor comfort parameters can be monitored in real time.
EFdeN house uses 22 photovoltaic panels to produce more energy than it consumes annually. Some overproduction is stored in batteries and used during the night-time, while the surplus can be injected into the national electricity grid.
Achieving thermal comfort
The design process of systems and strategies intended to assure optimal thermal comfort parameters started with climate analysis for the permanent location of the house, Bucharest.
Bucharest has a continental climate, characterized by dry summers and cold. Due to the position of the Romanian Plain, powerful winds arise in Bucharest, despite urbanization.
Temperatures during winter are frequently below 0°C and seldom below -10°C. During summer, the median temperature is 23°C, despite temperatures reaching a maximum of 35-40°C in central urban areas. During transition seasons, media temperatures vary between 18-22°C.
IEQ parameters in the EFdeN House
Indoor temperature during summer 26°C
Indoor temperature during winter 20-22 °C
Relative humidity 40-55 %
CO, concentration max. 800 ppm (parts per million)
Formaldehyde concentration max. 30 Ug/m3
Sound level max. 25dB
Exterior design parameters
Exterior temperature during summer 35,3 °C
Relative humidity during summer 35%
Exterior temperature during winter -15°C
Relative humidity during winter 80%
Thermal comfort vs. Energy efficiency
Considering the climate conditions in Romania, the consumption associated with the thermal comfort assurance is the largest consumer of energy in a household. In order to reduce consumption without affecting comfort parameters, passive solutions have been implemented in EFdeN House. Passive solutions are those that don’t consume electrical energy and include house orientation, thermal insulation, the use of high performance glazing, the use of phase-changing materials, ventilated facade, the use of thermal mass and the use of the greenhouse for preheating fresh air for ventilation.
Passive strategies for achieving thermal comfort
Materials with high thermal mass have the ability to engulf a large amount of heat. In other words, they heat up and cool down slowly, providing the house with thermal inertia. The high thermal mass materials used in the EFdeN house work together with the greenhouse, absorbing the heat in the winter during the day, being irradiated by the sun and releasing it in the indoor environmental night.
Phase changing materials
There are materials that at a certain temperature threshold (23 or 26°C in EFdeN house), change their aggregate state, exchanging heat with the indoor environment.
In the EFdeN house they were implemented as wall-mounted panels. They also provide thermal inertia to the house, attenuating the maximum hot or cold loads.
It was designed to limit winter heat loses and summer heat gains. Thermal buffer rooms, such as the windfang and technical rooms are placed towards the northern facade, the most exposed to heat losses during winter. The greenhouse and glazed surfaces facing the south benefit from direct solar irradiation, thus providing the indoor space with heat gains. These are limited during summer by shading.
Fresh air preheating in the greenhouse
During winter and transition periods, the fresh air for ventilating the house is not extracted from the outside, but from the greenhouse. We thus use the greenhouse effect during winter; during the summer, the greenhouse is naturally ventilated in order to avoid its overheating.
Made of ceramic tiles, it limits heat gains during summer by providing a circulating layer of air; during winter the vents are closed and the air is trapped, forming an insulating layer which limits heat losses.
Thermal insulation and high-performance glazed surfaces
To limit unwanted heat transfer through the building envelope we used thermal insulation consisting of 35 cm of mineral wool in the outer walls. Glazed surfaces are triple-layer, and those exposed to the Sun are low-e.
Active strategies for achieving thermal comfort
Fitted into walls and ceilings, prefabricated radiant panels through which hot or cold water, depending on the season, is circulated, ensures the thermal parameters in the house. They provide a high thermal comfort because, in addition to heating or cooling the ambient air, they bring the surfaces with which the body changes heat by radiation in optimal parameters. In addition, thermal stratification is very close to the optimal comfort curve. Moreover, compared to radiators, heating / cooling is much more uniform.
Heat recovery unit
It is part of the house ventilation system. It makes the two air streams meet (the vitiated air that is exhausted and the fresh air introduced) and without mixing, they are exchanging heat. Basically, we recover the heat that we would otherwise give it out with the exhaust air. The rest of the heating / cooling load is covered by a heating / cooling coil, so the fresh air introduced into the house has the optimal temperature.
The heat pump is the equipment that prepares the hot or cold water required for thermal regulation of the indoor environment. It is essentially a refrigeration system, which consumes electricity to transport heat from cooler environments to warmer environments. Therefore, the pump can extract heat from outside air and carry it inside, even if the outside air is cooler. It has the advantage of providing the thermal agent with low parameters, suitable for operation with the radiant panels. It also works in the summer, basically reversing this cycle, transporting heat from the inside to the outside. Depending on the environment from which they extract heat, the heat pumps may be groundsourced (geothermal pumps), water-water or air-water pumps. Albeit being most efficient, geothermal pumps require drilling, which was forbidden in the Solar Decathlon competition.
Achieving Indoor Air Quality
It implies the refreshing of indoor air by natural means, so the air is only moved by natural pressure differences between different areas of the building, provided there are openings in the building envelope. This pressure difference may be due to the difference in air temperature or wind pressure. In the EFdeN house, natural ventilation is made when the outside air parameters are close to the comfort parameters by two methods. The first, cross-ventilation, involves opening the windows on the opposite facades of the building. The second, based on the naturally ascending flow effect, takes place in the greenhouse and has the role of preventing it from overheating during summer.
It is the exhaust of vitiated air from the inside and the introduction of fresh air from the outside, the air being forcefully moved with the use of fans. The vitiated air is extracted from the bathrooms, the kitchen and the lobby, and the fresh air is introduced into the house in the inhabited rooms: the living room and the bedrooms. Thus, the flow of air inside the house is from inhabited spaces towards rooms with humidity, heat, smell (baths and kitchens) and not vice versa. Although it consumes energy, mechanical ventilation has the advantage that we can control the airflow, thus limiting energy losses. In addition, we can treat this air by changing its parameters so it meets the requirements of indoor comfort before introducing it into the indoor environment.
Air quality monitoring
The carbon dioxide concentration, relative humidity and air temperature are constantly monitored in the inhabited rooms via sensors. Thus, based on the pre-set automation scenarios, the building management system controls the ventilation system according to these parameters, ensuring at all times that the indoor air is in the set parameters, without wasting energy.
Achieving Acoustic Comfort
Solar Decathlon contest requirements
In the Comfort Conditions contest, the acoustic quality of the house was assessed in two ways: measuring the sound emitted by the operation of the equipment in the house and the attenuation of sound coming from the outside through the building envelope. Thus, in the inhabited rooms, the sound pressure level should not exceed 25 dB, which is a low for a standard home, which prompted us to use various sound attenuation strategies.
It all began in the design stage when,taking into account the technical acoustic specifications of the equipment and the sound attenuation characteristics of the building materials and the sound insulation, acoustic simulations were performed in various equipment operating scenarios and various levels of the sound coming from the outside of the building.
Mineral wool was used as a sound insulating material, which has very good characteristics in this regard. Thus, in addition to the mineral wool in the exterior walls, which primarily acts as thermal insulation, mineral wool was added to both the interior walls and the floors to limit the propagation of the acoustic waves from the technical rooms to the inhabited spaces.
Integrated sound absorbing materials
Sound-absorbing materials have also been used in the interior design to improve the acoustics of large spaces, such as the living room. In this regard, the best performing soundproofing material currently available on the market, Basotect, has been integrated into the living room sofa. Acoustic simulations have shown that this strategy significantly reduces the reverberation time, a parameter that affects the intelligibility of speech and, implicitly, the acoustic quality.
Achieving Visual Comfort
The most important architectural element of the house, the greenhouse, has besides its roles as relaxation space, productive garden and contribution to energy efficiency, the role of ensuring natural daylight in all the rooms of the house. All living rooms have views towards the greenhouse, thus assuring, combined with traditional glazed surfaces, enough daylight during daytime. This provides visual comfort, given the benefits of natural light to the artificial light.
For areas where natural light is not sufficient, for activities that require more light, or for lighting at night, artificial lighting is used. For energy efficiency, there were used only LED light bulbs. Lighting is focused on work surfaces, such as the kitchen counter, instead of illuminating the entire kitchen surface, while ensuring the minimum necessary for artificial lighting. Also, for transition and traffic spaces such as the windfang and hallways, lighting is controlled by motion sensors. The choice and positioning of the luminaires was made after natural lighting simulations and using specialized computing programs, ensuring both the appropriate light intensity and other factors, such as avoiding the directlight glare.
It was based on the concepts of modularity, transformability and integration of nature and traditional Romanian elements. To enhance visual comfort and illumination efficiency, white furnishings and light-colored flooring were used to reflect light and provide diffuse indirect light.
The Research Center
Since being rebuilt in Romania in 2015, the EFdeN house has received a great deal of attention throughout the media, public events, academic research, etc. Due to the fact that the house is an example of best practices, multiple students from different domains have chosen EFdeN 4C as a research point for their projects and theses. Every week, there are tours dedicated to the general public, and since its opening, thousands of people have shown interest in this house.