THERMAL BARRIER FOR VENTILATED ROOFS

Abstract

A system and a method are described for the passive conditioning of internal environments having ventilated roofs as coverings; the method involves absorbing 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 transferring the absorbed heat back to the external environment during the night, the absorption being implemented through Phase Change Materials, PCM, in which the heat exchange between PCMs and the external environment is favored by an air current that is generated spontaneously due to the effect of natural thermal gradients.

Claims

1. A system for a passive conditioning of internal environments having ventilated roofs for covering, of a type comprising one or more ventilation chambers placed under a waterproof roofing mantle, the one or more ventilation chambers having the function of dissipating part of heat entering the environment to be conditioned, the system further comprises a plurality of containers containing Phase Change Materials, PCM, positioned inside the one or more ventilation chambers, the containers of PCMs being in a heat exchange relationship with air present inside the one or more ventilation chambers; wherein: the containers are installed in a center of a ventilation channel suspended between tiles and an underlying support layer, so that a ventilation air flow completely envelops the containers; the system further comprises perforated metal profiles to which supports are fixed on which the PCM containers lean; and the supports comprise a bar fixed, one third of its length, to an element on which there are anchors which, made to pass through holes in the metal profile and inserted in an opposing element, prevent its movement.

2. The system of claim 1, wherein the containers are plates made of plastic material.

3. The system of claim 2, wherein the plates comprise a plurality of PCM macro-containers, independent of each other, so that they can be trimmed for any dimensional issues during installation.

4. The system of claim 3, wherein the PCM macro-containers are provided with a stiffening frame.

5. The system of claim 3, wherein each of the macro-containers has longitudinal welds, designed to divide each of the macro-containers into at least two parts, so as to reduce the risk of segregation of the PCM.

6. The system of claim 1, wherein the containers have overall dimensions of 0.90.30.01 m.sup.3.

7. Method for a passive conditioning of internal environments with ventilated roofs, of a type which uses a system according to claim 1 and involves absorbing at least part of heat coming from an external environment during hottest hours of a day, so as to reduce heat entering the environment to be conditioned and to transfer the absorbed heat back to the external environment during nights, the absorption being implemented through Phase Change Materials, PCMs, wherein the heat exchange between PCMs and external environment is favored by an air current that is generated spontaneously due to an effect of natural thermal gradients.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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: [0026] FIG. 1 schematically represents the effect of the application of PCM in the building envelope; [0027] FIGS. 2 (a, b) show containers able to receive the PCMs inside them; [0028] 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; [0029] FIG. 4 shows a portion of the roof where the PCM containers are installed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] 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.

[0031] 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.

[0032] The experimental activity, conducted following preliminary numerical investigations, made it possible to detect a reduction of 1215% of the incoming thermal energy through a discontinuous roof placed in the Po Valley, with a consequent decrease in energy demand.

[0033] FIG. 1 schematically represents the effect of the application of PCM in the building envelope.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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).

[0039] 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).

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] 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.

[0045] According to a preferred embodiment, the containers (1) have overall dimensions of 0.90.30.01 m.sup.3.

[0046] FIGS. 3 (a, b) and 4 show the installation of the containers (1).

[0047] 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.

[0048] 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.

[0049] 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).

[0050] 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.

[0051] 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).