THERMAL BARRIER FOR VENTILATED ROOFS

Description

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention refers to a method, and to a system for implementing such method, for the passive conditioning of internal environments having ventilated roofs as a covering.

2) Background Art

The building sector is responsible for more than a third of the global energy demand and related CO2 emissions and a large part of this energy is used for heating and cooling indoor environments covered by ventilated roofs. European Parliament Directive 2010/31/EU on the energy performance of buildings, at point 25, highlights an increase in air conditioning systems in European countries which causes considerable problems during periods of peak demand and at the same time leads to an increase in the cost of electric energy. For this reason, the need to prioritize those strategies that make it possible to improve the summer energy performance of buildings is underlined: “we should focus on measures that avoid overheating, such as shading and a sufficient thermal capacity of the building work, as well as on further development and application of passive cooling techniques, especially those that help improve indoor climatic conditions and the microclimate around buildings.

There are numerous research and development works that tend to overcome, as far as possible, the described problem.

Patents have been selected which provide for the application of Phase Change Materials, PCM, on the roof, with the aim of improving performance, some of which exploit ventilation as a technique to facilitate the dissolution and solidification process of the PCM. The selected patents are as follows.

US-A1-2005178524 (Building conditioning technique using phase change materials in the roof structure) provides for the application of two PCMs in two different positions within the roof package. A first layer of PCM is positioned above the insulating layer, below the structure which supports the tile cladding, while the second is positioned below the insulating layer, above the plasterboard false ceiling.

US-A1-2021062510 (Retrofit roof with a phase change material modulated climate space) describes the application of PCM on roofs for the redevelopment of existing buildings. More specifically, a PCM-containing compound is placed over the existing cover, over which a second cover is then built. The new roof is fixed to the existing one but, through the use of joists, it remains raised by about 10 cm allowing the passage of air.

CN-A-111578361 (Interlayer ventilation type phase change heat storage structure and pavement method thereof) provides for the construction of a sandwich structure in which air channels are used to increase the thermal flow to the PCM, accelerating the accumulation and release of energy with the aim of increasing the insulating capacity of the casing. This application provides for the possibility of installation both in walls and in floors.

CN-A-109403556 (Shape-stabilized phase-change and embedded tubular ventilation roof) describes the creation of a layer of PCM within the roof package, more specifically between a leveling layer and the waterproofing membrane. An air gap is created below the roofing package, in which air can move both naturally and due to a fan connected to an electric valve.

Researches have not revealed any patents involving the creation of a layer of PCM suspended inside the air gap of a ventilated roof, as defined in the architectural technology sector.

US-B2-10 487 496 describes a system according to the preamble of Claim 1.

SUMMARY OF THE INVENTION

Object of the present invention is improving the performances obtained with current technologies, through a system and a method using such system, respectively in accordance with claims 1 and 2.

The method for passive conditioning of internal environments having ventilated roofs for covering involves the absorption of at least part of the heat coming from the external environment during the hottest hours of the day, so as to reduce the heat entering the environment to be conditioned, and to transfer the absorbed heat back to the external environment during the night, this absorption being implemented through Phase Change Materials, PCMs, wherein the heat exchange between PCMs and external environment is favored by an air current generated by the wind (forced convection) or by effect of natural thermal gradients (natural convection).

The system for the passive conditioning of internal environments having ventilated roofs for coverage is of the type comprising one or more ventilation chambers placed under a waterproof roofing mantle, the ventilation chambers having the function of dissipating part of the heat entering the environment to be conditioned. The system further comprises a plurality of elements, comprising PCMs, positioned inside the one or more ventilation chambers, the elements comprising PCMs being in a heat exchange relationship with the air present in the interior of the one or more ventilation chambers.

In practice, the invention consists in the coupling of two consolidated technologies which have always been studied and developed independently of each other.

The first of these technologies is the ventilated roof, a system that allows the creation of one or more ventilation chambers under the waterproof roofing, whose main objective in summer is to dissipate part of the heat entering through the casing in order to reduce energy costs for cooling. In winter, the function is to evacuate the water vapor generated indoors, without significantly affecting the heat exchange, because it is placed on the insulating system of the building envelope. The single cavity that is usually formed is 4÷10 centimeters, and can be created, for example, by means of a wooden substructure made up of uprights and crosspieces, or by variously perforated metal profiles.

The second technology consists in the use of Phase Change Materials, PCMs, which are incorporated in the building envelope as a passive cooling technique, i.e. as a system which allows improving the energy performance of the building during the summer season, without further burdening the air conditioning system.

Ultimately, the proposed invention provides for the application of PCMs inside the air gap of ventilated roofs. It is not a simple application of two different technologies, whose effects are merely the sum of the effects of the two technologies applied individually. In fact, the positioning of the elements containing PCM in a stream of air significantly improves the heat exchange with the PCM itself and increases its efficiency. In other words, the ventilated roof technology improves the efficiency of the PCM as the increased heat exchange makes it possible to increase the amount of PCM that changes phase and the very speed of the phenomenon.

There are several hundred known and studied PCMs and they can be classified according to the phase change performed (solid-solid, solid-liquid, gas-liquid, solid-gas); in case of applications on the building envelope, those which carry out the solid-liquid transformation for aspects related to the specific volume are generally used. Among these, two macro-categories are identified on the basis of their composition: organic and inorganic. The former are characterized by good chemical and physical stability, reliable thermal behavior and are non-corrosive, but at the same time they usually have low density and low thermal conductivity. The latter, on the other hand, have greater thermal conductivity and latent heat, but are corrosive and, if installed incorrectly, the solid phase risks segregating with respect to the liquid, drastically reducing complete regeneration. They are often characterized by the phenomenon of undercooling.

In case of the technology proposed here, the PCMs used are of the inorganic type, which, given the small quantity envisaged, have a higher latent thermal capacity than organic PCMs. Fundamental for the selection of the PCM to be used, in addition to the thermal capacity, are thermal conductivity and phase change temperature. In case of the latter, considering the application outside the building, the choice mainly depends on the climatic conditions of the place of installation. This technology is mainly aimed at roofs with high irradiation and prolonged summer season, such as the Mediterranean area for example: therefore, it can be roughly estimated that the phase change temperatures of the PCMs that can be used are in the range of 35÷50° C.

Preferred embodiments and non-trivial variants of the present invention are the subject matter of the dependent claims.

The technology described here falls within the passive cooling techniques and is aimed in particular at pitched roofs characterized by both a discontinuous covering (tiles), such as Portuguese or Marseilles tiles, and a continuous covering, such as metal roofs. It can be considered an upgrade of the well-known technology of ventilated roofs and, given that the construction does not involve upheavals of consolidated techniques but only an integration of the same, it can be easily implemented both in case of new constructions and in case of renovations of existing buildings.

Pitched roofs make up a large share of the built heritage in the Mediterranean area and, at the same time, represent a stylistic custom of many new buildings. The technology presented here therefore lends itself to large-scale applications in climatic areas subject to significant summer air conditioning, such as the whole area of the Mediterranean basin, and fully responds to the need to improve the energy performance of buildings during their cooling.

It is understood that all attached claims form an integral part of the present description.

It will be immediately obvious that innumerable variations and modifications can be made to what is described (for example relating to shape, dimensions, arrangements and parts with equivalent functionality) without departing from the scope of the invention, as appears from the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better described by some preferred embodiments, provided by way of non-limiting example, with reference to the attached drawings, in which:

• • FIG. 1 schematically represents the effect of the application of PCM in the building envelope;
  • FIGS. 2 (a, b) show containers able to receive the PCMs inside them;
  • FIGS. 3 (a, b) show the ventilated cavity under the waterproof covering and a possible solution to support the suspension of the containers within the ventilation channel;
  • FIG. 4 shows a portion of the roof where the PCM containers are installed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention consists in the installation of containers (1) filled with Phase Change Material, PCM, in ventilated roof coverings in order to improve their summer energy performance, reducing the solar gain through the envelope and therefore the energy expenditure for cooling.

The containers (1), similar to thin rectangular plates, have inside a material (PCM) which, subject to certain thermal shocks, is able to change phase, passing from liquid to solid form and vice versa. When PCM melts, it is able to accumulate large amounts of energy, while, when it solidifies, it releases the energy accumulated during melting. When the PCM accumulates or releases energy, it is charged or discharged respectively, and its temperature during phase changes remains almost unchanged.

The experimental activity, conducted following preliminary numerical investigations, made it possible to detect a reduction of 12÷15% of the incoming thermal energy through a discontinuous roof placed in the Po Valley, with a consequent decrease in energy demand.

FIG. 1 schematically represents the effect of the application of PCM in the building envelope.

The curve called “external temperature” shows the variation of the external ambient temperature over 24 hours, with a maximum in the central hours of the day and a minimum at night.

The curves called “internal temperature without PCM” and “internal temperature with PCM” respectively show the consequent variation of the internal temperature in case of absence and presence of PCMs in the ventilated attic.

As it becomes clear from the comparison of these last two curves, in case of use of PCM, there is an attenuation of the internal temperature, shown by the hatched area between the two curves. A phase shift between the maxima of the curves can also be noted.

Finally, the broken line, present in the lower part of the diagram, shows the changes in state of the PCM. The changes of state both occur at the same temperature, which remains constant during the change of state itself.

The application of this type of material in the roofing package, more specifically inside the air gap of ventilated roofs, makes it possible to limit the amount of heat entering the building during the day, as part of the energy is accumulated by the PCM during the dissolution. This phase is represented by the left side of the broken line, in which the PCM absorbs heat (sensible, latent, sensible).

At night, thanks to the ventilation in the cavity with air at cooler temperatures, the accumulated thermal energy is released causing the solidification of the PCM and, consequently, its regeneration. This phase is represented by the right side of the broken line, in which the PCM gives off heat (sensible, latent, sensible).

FIG. 2a shows containers (1), able to receive the PCM inside them. The containers (1) have a large surface area compared to the volume. In particular, the thickness is kept as low as possible, in order to optimize the heat exchange and therefore the ability of the material to melt and solidify on a daily basis. Even if the heat exchange is improved by ventilation, it is still advisable to use all means to increase the exchange itself.

The containers (1) are plates made of plastic material. Each plate consists of three PCM macro-containers (1a, 1b, 1c), and equipped with a stiffening frame (2), independent of each other and which therefore can be cut out for any dimensional problems during installation. Each of these macro-containers (1a, 1b, 1c) also has two longitudinal welds (3), which divide each of the three macro-containers (1a, 1b, 1c) into three parts.

The macro-container (1a) is divided into three parts (11a, 12a, 13a), the macro-container (1b) is divided into three parts (11b, 12b, 13b), finally the macro-container (1c) is divided into three parts (11c, 12c, 13c).

This partitioning is done with the aim of reducing the risk of segregation of the PCM, which would lead to a separation of the PCM components and prevent it from completely solidifying once dissolved.

FIG. 2b shows in detail the shape of the stiffening frame (2) and one of the macro-containers (1a) and the welds (3a) with which the containers (1) are assembled.

According to a preferred embodiment, the containers (1) have overall dimensions of 0.9×0.3×0.01 m³.

FIGS. 3 (a, b) and 4 show the installation of the containers (1).

The containers (1) are installed on average in the center of the ventilation channel under the roofing mantle, suspended between the tiles (20), or another element designed to waterproof the roofing mantle such as a simple metal sheet or a sandwich metal panel, and the underlying support layer (30), so that the ventilation air flow completely envelops the containers (1) themselves.

According to the invention, as shown in FIG. 3, the ventilated cavity under the waterproof covering is made using perforated metal profiles (10), which allow the anchoring of the elements of the discontinuous covering made up of roof tiles or pantiles (20) and, at the same time, guarantee the passage of air. Supports (11) are fixed to the same perforated metal profiles (10) on which the PCM containers (1) are placed.

According to the invention, the supports (11), which can be made both of metal and of plastic, comprise a bar (12) fixed, one third of the length, to a disk (13) on which there are four anchors (15) which, passed through the holes in the metal profile (10), prevent its movement by inserting itself into an opposing element (14).

The PCM containers (1) are installed by placing the containers (1) themselves on the supports (11), which are hooked to the under-tile perforated profiles (10) as shown in FIG. 3. Each support (11) allows the support of two containers (1), one on each end, and allows a free installation by adapting to under-tile profiles (10) of different heights and variable lengths of containers (1). The graphic indication of four supports (11) for each row of three PCM pockets (11, 12, 13 of columns a, b, c) must be considered as minimum and possibly increased as the slope of the pitch decreases.

FIG. 4 shows a portion of the roof which shows the installation of the PCM containers (1) between one metal profile (10) and another, supported by supports (12).