For a long time, architecture has been based on logic, and therefore substantiated in climate criteria [1
]. Traditional solutions make use of locally available resources which offer thermal inertia to the buildings thanks to the mass of cladding and partitions [2
]. The use of thick ceramic, stone or soil walls give rise to magnificent results characterized by a thermal stability and a decrease energy dependence. However, this solution limits the energy accumulation capacity, because the materials could never go below the minimum temperature at night or above the maximum temperature during the day [3
]. Furthermore, the heating or cooling of solids concentrates their energy only in the outer layers. Another drawback is that the energy load and unload takes place at a variable temperature. Hence they will never work at constant comfort conditions. Moreover, current construction methods have a tendency towards the lightness of the materials to cheap the structure and obtain a larger living area, which increase the looses on thermal inertia systems.
On the other hand, the bioclimatic architecture [1
] represents the use of materials and constructive elements under sustainability criteria. It represents the optimum-energy generation concept by means of the active or passive accumulation [6
], distribution of renewable energies [7
] and the integration of ecological building elements [8
]. The bioclimatic architecture comes back to the common sense criteria, making use of technological elements, which give rise to results similar to the traditional ones, without loosing the benefits of the current constructive methods. Typical accumulation systems are substituted by others based on the heat exploitation stored in Phase Change Materials (PCMs) [9
]. PCMs obtain energy from the outside and store it in form of energy represented as their liquid or solid state. As is known, the PCMs always obtain/release heat at the same temperature (e.g. 0 °C for the water). Therefore, by making use of chemical components to tune the changing temperature, new building designs may include PCMs to make use of their thermal capabilities. However, in real domestic implementations, the use of control systems becomes necessary to manage the air flows which allow the PCMs to change phase.
Because of new advances in home automation [10
], there is an important field which is created when connecting bioclimatic and automation principles. At present, the smart house systems or domotics
face a social change. Until very recently, domotics was described as a facility technical management. It was exclusively for the control of single devices in the residential or industrial sector, basically referring to isolated appliances, sensors or actuators. The new advances in technology, particularly in terms of information and communication technologies, has brought about a change in the approach in which the term domotics
moves towards new concepts of digital habitat or connected environment [13
]. Moreover, it evolves to concepts such as ubiquitous computing or ambient intelligence [14
], which puts mankind in an environment which adapts to the needs and preferences of the user, at the same time it satisfies external conditions. Furthermore, it would be desirable that the low cost and energetic consumption sensor, actuator and control devices introduced by the user, were able to create a network which takes individual and collective decisions.
If we focus on specific details, the two more important elements are those related with the Personal Area Networks (PAN) and the control of sensors and actuators. Moreover, these elements must be integrated into the bioclimatic architecture and the renewable energy concept. Therefore, the XXI century home should be a digital habitat; a connected residence, but at the same time it should be involved in sustainability and the environment. The location of new technologies in the house, and its acceptance by the user, requires, among other actions, a significant diffusion and activity to be undertaken.
Following these lines of research, we pursue the implementation of a distributed sensor network for the control of bioclimatic and sustainable houses. In this work, we create and adapt a distributed network based on an industrial bus which confers the possibility of sensing environment variables and actuating different non-standard elements for the conditioning of the home. The present work focuses on specific aspects of the house design and the control system bus developed for the different parameters, variables, sensors and actuators systems that coexist within. The paper is organized as follows: The rest of Section 1 describes the house and offers a brief overview of bioclimatic and non-standard elements in it. In Section 2 the control bus and the nodes in the network are described. Section 3 sets out the user interface. This interface manages the orders given by the user to the house and monitors the status of the system thanks to its graphical interface. Experimental results are presented in Section 4. Finally, Section 5 concludes the paper and suggests future developments.
1.2. The Bioclimatic House
Nowadays, different research projects in Spain focus on the convergence of construction, bioclimatic and domotics systems [17
]. However, for significant results, these studies should be carried out in environments with similar conditions to those in standard houses. Therefore, the system presented in this work has been installed in a solar bioclimatic house previously used for the Solar Decathlon 2005
], organized by the Department of Energy of the United States of America. In this workshop, universities compete to design, build, and operate the most effective and energy-efficient solar-powered house. The project of the Universidad Politécnica de Madrid raised these aspects (i.e., technology, sustainability and diffusion) in a proposal for the creation of a prototype of a potential house for the XXI century. The aspects related with the technology and diffusion are reflected in the later application of the first prototype, which after having been in the Solar Decathlon
, become a real laboratory and technology demonstrator in Spain.
The house (see Figure 1
) integrates sustainability elements based on the use of renewable energies, self-sufficiency energetic methods and recycled construction materials. The self-sufficiency is based on the correct use of the energy from a suitable control system, and the use of a bioclimatic design which reduces the energy needs for the achievement of adequate comfort levels inside the house.
The house has been designed to allow the air to circulate passively and create a comfortable environment without the need for complex elements. As previously mentioned, the classic storing procedures, used by the bioclimatic architecture, are those which accumulate heat or cold in the structure of the building. However, because of the dimensional limitations of the house, we have not used heavy elements in its construction. Hence, we have decided to use energy storage systems in the form of latent temperature; that is, to promote the phase change of a chemical substance storing the heat or cold in it.
The accumulation system used (i.e., Phase Sift Gel (PSG)) is made up of hermetic capsules of about 3 kg. each and of 28 × 48 × 3 cm3
. These capsules are located under the floor on top of a thermal insulator which is supported by the house structure. There are four PSG layers, three of them in the form of capsules and the fourth one inside the ceramic pavement (see Figure 2a
). Together with the PSGs we have included different active elements such as fans, peltiers and floodgates which, automatically controlled, create the conditions to modify the environmental variables in accordance with to the user needs. The system includes the following elements (see Figure 2b
12 fans: The fans are located in the false floor together with the PSGs. They allow the air movement which stores or obtains energy from the PSGs.
18 servomotors: These are used for the grid and floodgate control. They modify the ventilation apertures in the house, redirecting it to the outside or the inside part of the house depending on the user needs.
6 peltiers: The peltiers are used for the humidity control. When the humidity is higher than expected, the peltiers are activated and create a voltage potential which allows the air, when passing through them, to be dehumidificated.
150 PSG capsules: These capsules include the already mentioned PSG which stores energy in terms of latent temperature.
The 12 fans, six in the east wing and six in the west wing, are located between the capsules and are in charge of the wind stream from which the energy is extracted. Each fan moves a flow of 160m3/h. Therefore, for the entire house a 1,920 m3/h air flow is achieved. Because the house has approximately 180 m3 volume, if all the fans are working for one hour, the system achieves 10.5 air renewals per hour. However, the number of active fans will change according to the air flow needs.
The environmental conditioning inside the house makes use of the PSGs, peltiers and grids. In winter, the energy used to acclimatize the house is solar radiation. It heats the PSG elements during the day, while they regulate the heat use during the night. On the other hand, in summer, the freshness during the night must be stored in the PSGs, and must be used to cool the house during the day. In any situation, the system must be able to share the energy stored to acclimatize the house for the whole day.
An important element of the system are the grid and floodgates. These elements are located in the ceiling and false floor of the north and south facades to modify the air flows from the indoors to the outdoors. For its correct working, the grids and floodgates must be positioned according to the needs of the house. For example, on a summer night (see Figure 3a
), the north grids must be opened. Hence, the PSGs will obtain the freshness of the night while the rest of the house is aerated by opening the greenhouse and the north ceiling grids. When the day comes, the grids and greenhouse are closed outdoors (see Figure 3b
). Therefore, the house must recirculate the temperature stored during the night, keeping the house fresh.
Furthermore, the humidity control is associated with the air streams generated by the existing fans. This air flow, when passing across the false floor, enters the dehumidification system (i.e., peltiers). The different peltiers are activated depending on the humidity and user needs.