Active thermal insulation system utilizing phase change material and a cool air source

[0001] The embodiments of the present invention relate to a system of enhancing the efficiency of a thermal insulation system utilizing phase change material and a cool air source.

[0002] Insulation has been utilized for decades to control the flow of tempered air. For example, insulation substantially prevents heat from flowing from a high temperature zone to a cool temperature zone. For example, the cool zone may be an interior of a structure such that the insulation helps maintain the cool internal temperature. Likewise, the interior temperature may be heated so that the insulation helps maintain the heated internal temperature. In other words, the insulation slows the rate of heat transfer.

[0003] Unfortunately, a change in either the inside or outside temperature is instantly reflected in the change in the rate of heat flow. Therefore, in order to maintain the desired internal temperature, the heating and cooling equipment must be able to respond quickly to changes in the temperature difference. Such is not always easy since the equipment must overcome a large volume of air or a large mass in the internal zone, both of which resist rapid temperature changes. Accordingly, during rapid external temperature fluctuations, the internal temperature is often either higher or lower than desired.

[0004] There lacks a method of maintaining a relatively constant rate of heat flow so as to maximize the efficiency of conventional heating and cooling equipment and to improve the correlation between the desired internal temperature and the actual internal temperature. Such a method would minimize the temperature variations and the energy output required to maintain a desired internal temperature.

[0005] Conventional forms of insulation comprise fiberglass rolls, batts, blankets and loose fill. Other types of insulation include cellulose, mineral wool and spray foam.

[0006] Materials known as phase change materials (“PCMs”) have also gained recognition as materials which alone, or in combination with traditional insulation, reduce home heating or cooling loads, thereby producing energy savings for consumer.

[0007] PCMs are solid at room temperature but as the temperature increases the PCMs liquefy and absorb and store heat, thus potentially cooling an internal portion of a structure. Conversely, when the temperature decreases, the PCMs solidify and emit heat, thus potentially warming the internal portion of the structure. Systems using PCMs with traditional insulation materials allow the PCMs to absorb higher exterior temperatures during the day and dissipate the heat to the internal portion of the structure at night when it tends to be cooler.

[0008] Known PCMs include perlite, paraffin compounds (linear crystalline alkyl hydrocarbons), sodium sulfate, fatty acids, salt hydrates and calcium chloride hexahydrate. While this list is not exhaustive, it is representative of the materials which exhibit properties common to PCMs.

[0009] In most current systems, both conventional insulation and PCMs are used in one or more known configurations. For example, U.S. Pat. No. 5,875,835 to Shramo and assigned to Phase Change Technologies, Inc. and incorporated herein by this reference, discloses packaged PCM placed between two layers of conventional insulation. U.S. patent application Ser. No. 11/061,199 to Brower and also assigned to Phase Change Technologies, Inc., and incorporated herein by this reference, discloses packaged PCMs used in combination with a single layer of conventional insulation. Regardless of the configuration, in high temperature environments, PCMs may remain liquefied for long periods of time such they are ineffective until such time that the ambient temperature drops below the PCM's transition temperature. Unfortunately, in warm climates, like desert locations in the Southwest United States, the temperatures may not drop below the PCM's transition temperatures for days or longer.

[0010] Consequently, there is a need for a controllable system and/or method that is able to return a liquefied PCM to its solid state in response to, for example, ambient temperatures exceeding the PCM's transition temperature. Such a controllable system and/or method is energy efficient and reduces or eliminates peak energy loads of those utilities providing the electricity or gas to a service area incorporating such systems and/or methods.

[0011] Accordingly, a first system embodiment of the present invention comprises: a phase change material; a cool air source operable to cool air below a transition temperature of the phase change material; and means for controlling the cool air source such that cool air can be directed from the cool air source to an area proximate the phase change material.

[0012] A first method embodiment of the present invention comprises: providing phase change material in a subject structure; providing a cool air source; and when needed, activating the cool air source to provide cool air proximate the phase change material, said cool air being below a transition temperature of the phase change material.

[0013] In one embodiment, cool air is provided to an attic space causing PCM placed in the attic to solidify. In other embodiments, cool air is channeled past adjacent PCM via ducts, plenums or other air passageways. In yet other embodiments, conventional insulation is used in combination with the PCM.

[0014] Other advantages, objects, variations and embodiments of the present invention will be readily apparent from the following drawings, detailed description, abstract and claims.

[0026] For the purposes of promoting an understanding of the principles in accordance with the embodiments of the present invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention claimed.

[0027] Reference is now made to the figures wherein like parts are referred to by like numerals throughout. FIG. 1 shows a cross-sectional view of a resistance-capacitance-resistance (RCR) model generally referred to as reference numeral 100. The cross-section comprises an interior drywall 110, first insulation layer 120, PCM 130, second insulation layer 140 and exterior wall portion 150.

[0028] FIG. 2 shows a cross-sectional view of a resistance-capacitance (RC) model 200 of the present invention. The cross-section comprises an interior drywall 210, PCM 220, insulation layer 230 and exterior wall portion 240. Similar to FIG. 1, there is shown a space 245 between the exterior wall portion 240 and the insulation layer 230. This arrangement mimics a typical attic. However, with other walls, the space 245 may be reduced or eliminated.

[0029] FIG. 3 shows a sheet of packaged PCM 250 comprising a plurality of vacuum cells or pockets 260 suitable for containing the PCM. While a square configuration is shown, those skilled in the art will recognize that other shapes (e.g., rectangular) are possible.

[0030] While PCMs have proven reliable alone, or in combination with conventional insulation, to facilitate the heating and cooling of interior spaces, they are not without limitations. PCMs struggle in warm weather climates, like those experienced in the Southwest United States, where ambient temperatures may exceed the PCM's transition temperature for extended periods of time. Consequently, in such environments, the PCM may remain in a liquid state for extended periods of time thereby reducing the PCM's usefulness. That is, PCMs are useful as long as they change phase (liquid to solid and vice versa) routinely since they store and emit heat as a result. For example, when the PCM remains in a liquid state it is unable to store any additional heat such that it provides no further benefit until the PCM begins changing phase back to a solid.

[0031] The embodiments of the present invention provide a system for lowering the temperature of a PCM when ambient temperatures are, or are predicated to remain, above the PCM's transition temperature (e.g., 80° F.) for brief or extended periods of time.

[0032] FIGS. 4 through 9 show various system configurations which facilitate the embodiments of the present invention and which are suitable for residential, commercial and industrial structures.

[0033] FIG. 4 shows a first system configuration 300, positioned below a roof deck 305, comprising a first conventional insulation layer 310, PCM layer 320 and a second conventional insulation layer 330. The roof deck 305 is positioned above the first conventional insulation layer 310 while deck joists 315 support both conventional insulation layers 310, 330 and the PCM layer 320. As shown, the second conventional insulation layer 330 includes multiple channels 340 on an upper surface thereof. The channels 340 provide a location for placement of packaged PCM 325. Moreover, the channels 340 are able to receive and direct cool air 350 provided by a cool air source (not shown), such as one or more air conditioning units. The channels 340 allow the cool air 350 to directly contact the packaged PCM 325.

[0034] The cool air source may be manually and/or automatically operated. In a manual mode, a user determines when, and for how long, to run the cool air source. In an automatic mode, system sensors in communication with a controller (not shown) determine when, and for how long, to run the cool air source. In either mode, the objective is to run the cool air source as need (e.g., until the PCM 325 is changed from a substantially liquid phase to a substantially solid phase). The ambient temperature, expected ambient temperatures over time, time of day and type of PCM 325 may collectively play a role in determining when, and for how long, to run the cool air source. The controller is programmed to utilize all or some of the aforementioned information in determining when, and for how long, to run the cool air source. In a manual mode, a user having sufficient understanding of the aforementioned information is able to adequately control the cool air source.

[0035] In one exemplary automatic system, a local system is controlled in response to temperature and the time of day. Accordingly, when sensors 326 (see FIG. 7) provide feedback to the controller indicating that a temperature proximate the PCM 325 is above the PCM's transition temperature and the time of day is within an acceptable pre-established range of times of day, the cool air source is activated. The cool air source may be run for a fixed amount of time (e.g., 30 minutes) or additional system sensors may provide feedback indicating that the PCM 325 has returned to a substantially solid phase thereby triggering the controller to deactivate the cool air source. Acceptable times of day are ideally during off-peak hours of a subject energy-producing utility providing electricity and/or gas to the area wherein the active PCM system is located.

[0036] It is also conceivable that the subject energy-producing utility may control a plurality of residential and/or commercial cool air sources. In such an embodiment, one or more central controllers maintained and/or managed by the utility are responsible for a plurality of cool air sources installed at homes and businesses within the utility's service area. In this manner, the utility is better able to control its energy load thus ensuring that demand remains level within a suitable range and does not spike or peak dramatically.

[0037] FIG. 5 shows a second system configuration 400, positioned above a roof deck 405, comprising a first conventional insulation layer 410, PCM layer 420 and second conventional insulation layer 430. A membrane 435 positioned above the first conventional insulation layer 410 protects the first conventional insulation layer 410 from direct sunlight and energy. The membrane 440 may be any suitable material and may be reflective to repel thermal energy from the sun. In this configuration 400, channels 440 are provided on a lower surface of the first insulation layer 410. Again, the channels 440 provide space for the packaged PCM 425 and the flow of cool air 450 past the packaged PCM 425.

[0038] FIG. 6 shoes an overhead view of one possible air flow pattern 470 suitable for the system configurations 300, 400 shown in FIGS. 4 and 5. Moreover, the air flow pattern 470 may be used in any of the embodiments shown herein or covered by the claims hereof. The air flow 350, 450 is channeled through a manifold or duct 480 positioned between insulation layers 310, 330 and 410, 430. The manifold or duct 480 includes a series of opening (not shown) along its length to allow the cool air flow 350, 450 to exit therethrough. As the air flow 350, 450 exits the manifold or duct 480 is travels along the channels 340, 440 in the corresponding insulation layer 330, 410. In this arrangement, the air flow 350, 450 can be efficiently forced through the duct 480 and dispersed evenly through the channels 340, 440. In other arrangements, the air flow 350, 450 can be forced directly into the channels 340, 440.

[0039] FIG. 7 shows a cross-sectional view of a third system configuration 500, positioned below a roof joist or rafter 505, comprising a conventional insulation layer 510 and PCM layer 520. The conventional insulation layer 510 and PCM layer 520 are secured within a container 530 by a support member 540. The container may be made of any suitable material including plastic or metal. A space 550 defined below the support member 540 receives and directs cool air as needed. The support member 540 is ideally fabricated of a mesh, wire or any material or configured material that allows the cool air to act on the PCM layer 520. Ideally, the cool air is able to interact directly with the packaged PCM 525 thereby causing the fastest transition possible. The container 530 may be attached to, or integrated with, the rafter 505 using any well-known means. A single structure may require installation of multiple containers 530 to cover a subject roof area. Alternatively, the container 530 may be large enough to cover a subject roof area and maintain a corresponding conventional insulation layer 510 and PCM layer 520.

[0040] FIG. 8 shows a cross-sectional view of a fourth system configuration 600 comprising a first conventional insulation layer 610, a first PCM layer 620, a second PCM layer 630 and a second conventional insulation layer 640. In this configuration, the two PCM layers 620, 630 are positioned on opposite sides of an air duct, plenum or passageway 650. As with the previous configurations, cool air is provided to the passageway 650 thereby causing a substantially liquid PCM to return to a substantially solid PCM. Again, the materials or configuration of materials forming the duct, plenum and passageway 650 permit the cool air to act on packaged PCM 625.

[0041] FIG. 9 shows a cross-sectional view of a fifth system configuration 700, positioned below a roof joist or rafter 705 and within an attic area, comprising a conventional insulation layer 710 and PCM layer 720. A container 730, with one or more meshed or open surfaces 735, maintains the conventional insulation layer 710 and PCM layer 720 near an underside surface of a roof. In this configuration, cool air is directed into the entire attic space to facilitate a phase change of the packaged PCM 725. In another configuration, the conventional insulation layer 710 and PCM layer 720 are positioned between rafters directly above a subject structure's ceiling.

[0042] Although not shown, each of the systems described herein may also incorporate an outlet for exhausting heat emitted by the PCM during the liquid phase to solid phase transition. The emitted heat integrates with the cool air and is exhausted accordingly. The outlet may lead to the atmosphere or any desired location.

[0043] It will be understood by those skilled in the art that countless other system configurations are conceivable and for the sake of brevity are not disclosed herein but are intended to be covered by the claims below.

[0044] FIG. 10 shows a graphical representation (load v time) of a none-PCM system 750 and a PCM system 760 at a residence or commercial facility. Both graphs depict the none-PCM and PCM system 750, 760 in relation to a standard load (L1) related to electric usage without activated air conditioning and a second load (L2) including an activated air conditioning component. Both graphs 750, 760 clearly depict that the use of air conditioning increases the energy load. However, with the none-PCM system 750, the time component of each air conditioning activation is greater than a corresponding time component for the PCM system 760. Thus, the air conditioning cools the subject area in the same manner but the air conditioning is run for shorter periods of time with the PCM system 760 thereby saving energy. FIG. 11 shows a smooth graph depicting a collective load over time representation.

[0045] FIG. 11 shows a graphical comparison (load v. time) between an active PCM system, like that described herein, and a non-active or passive PCM system. The graph 800 representing a non-active PCM system clearly depicts a peak load 810, exceeding a undesired load 815, while the graph representing the active PCM system depicts a level load over time without any obvious peak load or spike above the undesired load 815. In other words, with the active PCM system, the load of an energy provider is manageable such that peak loads can be controlled, reduced and/or eliminated.

[0046] Although the invention has been described in detail with reference to several embodiments, additional variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.