Building conditioning technique using phase change materials

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BUILDING CONDITIONING TECHNIQUE fans can make the room feel colder and leSS comfortable to USING PHASE CHANGE MATERLALS the room's occupants.

Some industrial plants have installed cooling Systems in

RELATED APPLICATIONS AND TECHNOLOGY the ceiling area of manufacturing facilities where excessive The present application claims priority from U.S. Provi heat is generated during manufacturing or processing. Such sional Patent Application Ser. No. 60/041,379 entitled cooling Systems typically remove heat generated in manu BUILDING CONDITIONING TECHNIOUE USING facturing or production processes So that manufacturing or PHASE CHANGE MATERIALS, filed Mar. 26, 1997, production processes do not have to be intermittently shut down to allow the room to cool.

which is incorporated in its entirety herein by reference. The present application also relates to the technology disclosed Phase change materials Such as Salt hydrates, metals, in U.S. Pat. No. 5,532,039 for THERMAL BARRIERS FOR alloys, poly-alcohols, eutectics and paraffins have been BUILDINGS, APPLIANCES AND TEXTILES, which is proposed as materials useful for controlling temperature assigned to the assignee of the present application and is also changes. Generally Speaking, phase change materials pos incorporated in its entirety herein by reference. 15 sess an ability to change their physical State (e.g., from a

Solid to a liquid and Vice-versa) in a given temperature range

FIELD OF THE INVENTION when either absorbing or emitting heat. During a period of rising temperature, heat is absorbed by phase change mate

The present invention relates to building materials having rials until the melt temperature is reached. During a period enhanced thermal properties. More particularly, the present of decreasing temperature, heat Stored in a liquid phase invention relates to construction techniques utilizing mate change material is released when the Solidification tempera rials containing phase change materials. ture of the phase change material is reached. BACKGROUND OF THE INVENTION There are significant differences between the latent heat of absorption during the phase change temperature range and

It is generally known that a comfortable room climate in the Sensible heat absorption which occurs outside the phase residential and industrial buildings is attained when (i) the 25 change range. For example, Water, a common phase change average room temperature is constant over time; and (ii) the material, releases a latent heat of approximately 335 kilo temperature distribution in the room is constant, i.e., there joules per kilogram (kJ/kg) when it freezes and becomes ice. are no drafts. The comfort Sensation is especially dependent Conversely, when ice melts, it absorbs heat at a rate of upon the temperature gradient between floor and ceiling. approximately 335 kJ/kg. When water or ice is not at a phase The greater the temperature gradient between floor and change temperature, its Sensible heat absorption or emission ceiling, the less comfortable the room feels. In winter, for is 4kJ/kg. It can be seen that the latent heat absorption during example, a temperature gradient in a room of 5 C. or more a phase change is nearly 100 times higher than the Sensible may exist. Such a floor-to-ceiling temperature gradient leads heat absorption outside a phase change temperature. to a cold Sensation in an occupant's lower body and a warm 35 Another quality of phase change chemistry is that the Sensation in the occupant's upper body and head, resulting temperature of the phase change material during latent heat in a generally uncomfortable feeling. absorption remains constant. In contrast, the temperature of To achieve a comfortable room, it is important to reduce a material during Sensible heat variations changes. Thus, the floor-to-ceiling temperature gradient to about 3 C., or when Sensible heat is absorbed by a phase change material, leSS. Studies have shown that when a floor-to-ceiling tem 40 the temperature of the phase change material rises. When perature gradient is greater than 3 C., the comfort range of Sensible heat is emitted by a phase change material, the the room (i.e., the room temperature range which is per temperature of the phase change material falls. ceived as comfortable to the occupants) is lower than with Phase change materials have been Suggested for use in a lower floor-to-ceiling temperature gradient. When occu building construction. For example, U.S. Pat. Nos. 4,587, pants perceive a room as comfortable, it has been shown that 45 279 and 4,617,332 teach the direct addition of phase change they will voluntarily lower the thermostat setting of the materials into the wet mix Stage of concrete. However, this room, thereby maintaining the room at a lower average technique can reduce the compressive and other Strength temperature with a commensurate decrease in energy con properties of the resulting concrete.

Sumption and costs. Phase change materials. Such as glass containers, have The temperature gradient in a room is normally estab 50 been used in interior and exterior walls. Because, however, lished as a result of warmer air in the room having a lower convective heat flow in a room typically travels up the wall density than colder air in the room. The lower density Surface (i.e., parallel to the wall), and does not directly Strike warmer air migrates to and remain at the top of the room. the wall Surface, the phase change material in the walls is not This leaves the coldest air at the bottom of the room, and Significantly engaged. In addition, phase change contain establishes a gradient of air temperatures between the 55 ment Structures designed for walls have not been widely warmer air near the ceiling and the colder air at the floor. adapted to other Surfaces due to the different mechanical Conventional techniques usually involve the heating of air requirements of walls as compared to floors and ceilings. near the floor, using, for example, baseboard hot water or hot air radiators located on or adjacent the interSection of floor SUMMARY OF THE INVENTION and walls. Newer techniqueS Such as in-floor heating ducts 60 The technique of the present invention for minimizing the or wires also heat the colder air at the floor. However, Such floor-to-ceiling temperature gradient of a room containing a conventional techniques typically neglect the effect an ceiling, a floor, walls, at least one door and at least one excessively high ceiling temperature has on a room's floor window, includes the utilization of a first phase change to-ceiling temperature gradient. material adjacent the ceiling Surface and a Second phase Of course ceiling fans are Sometimes installed in homes 65 change material adjacent the floor Surface. In order to and public buildings in an attempt to redistribute the warmer effectively minimize the floor-to-ceiling temperature gradi air near the ceiling. However the drafts created by ceiling ent of the room, the first and Second phase change materials

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may be either different or the same, with the melting envelopes. The containment envelopes are preferably 10 temperature of the first phase change material adjacent the mm thick. The width of the cells defined by adjacent lattices ceiling higher than the crystallization temperature of the is preferably approximately 12-14 mm. The cover is a rigid Second phase change material adjacent the floor. In one member which, when used for flooring applications, pro embodiment of the technique of the present invention, a vides mechanical Support for the people and the furnishings principal portion of the first phase change material posi in the room. The cover can also serve as a fire retardant to tioned adjacent the ceiling Surface is heptadecane, and a prevent fire from Spreading to the panels. principal portion of the phase change material adjacent the In alternative embodiments of flooring materials of the floor Surface is octadecane. In a preferred embodiment of the present invention, phase change materials may be incorpo technique of the present invention, the melting temperature rated into carpet backing, foam or other liners upon which of the first phase change material is 25 C. plus or minus 1 a carpet in installed, or even in carpet fibers. In alternative C. and the crystallization temperature of the Second phase embodiments of ceiling materials of the present invention, change material is 22 C. plus or minus 1 C. the phase change materials may be incorporated into ceiling tiles. Details of these embodiments are further discussed

BRIEF DESCRIPTION OF THE DRAWINGS 15 below.

FIG. 1 is a schematic of a vertical section of a room in To test the effectiveness of the present invention, a test which the floor/ceiling temperature gradient of the room is protocol was developed utilizing two 2"x2"x2" boxes fabri minimized and the comfort range lowered by incorporating cated using acrylic panels. The /s" acrylic panels of the first the building construction technique of the present invention. “control’ box were empty. The acrylic panels employed in FIG. 2 is a differential Scanning calorimetry heat absorp the second box totaled the same thickness but were filled tion diagram for a phase change material blend useful in the with phase change material.

building construction technique of the present invention. The heat Source for each of the control and PCM boxes FIG.3 is a differential Scanning calorimetry heat emission was a 100 watt light bulb suspended centrally in each box. diagram for a phase change material blend different than that 25 The light bulbs were controlled by separate thermostats illustrated in FIG. 2, but also useful in the building con placed in each box. Because the thermostats could not be precisely Set at Specific temperatures, the “on/off tempera

Struction technique of the present invention.

FIG. 4 is a plan View of a ceiling tile containing phase tures may have varied slightly.

change material useful in the building construction tech Probes were affixed in each box, with one taped probe nique of the present invention. facing the floor and one taped probe facing ceiling Surface. FIG. 5 is a plan view of a floor tile containing phase An additional probe was mounted to the center of one of the vertical walls of the PCM box. All probes and thermostats change material useful in the building construction tech were shielded from direct heat radiation. nique of the present invention.

To conduct the tests, the control and PCM boxes were

DETAILED DESCRIPTION 35 placed in a climate control room having an ambient tem

Applicant has discovered that incorporation of tempera perature of from 56.5° F to 59.0° F. The boxes were sealed to eliminate air flow. Each box was wrapped with two layers ture Stabilizing phase change materials in both the ceiling of air bubblepack insulation having an R value of 5.6 per material and the floor covering can minimize the tempera layer. Each test was run for a minimum of six hours. Data ture gradient typically present in rooms from floor-to 40 from a continuous two hour period which represented the ceiling, and also further minimize convection of air and most consistent data was Selected as representative. Test formation of drafts in rooms. The temperature gradient, results are Summarized in Table 1.

convection of air and formation of drafts are minimized by the phase change materials in the ceiling absorbing heat TABLE 1. prior to melting, thereby effectively delaying an increase in 45 room temperature near the ceiling above the melting point, PCM PCM PCM

FLOOR FLOOR CELING

and the phase change materials in the floor materials effec CONTROL & CELING ONLY ONLY tively delay the cooling of floor materials below the freezing temperatures of phase change material. range A range A range A range A The preferred temperature gradient thereby established 50 FLOOR 67.1- 23 69.O- 2.0 69.7- 13 67.2- 1.1 from floor-to-ceiling is 3 C. or less, most preferably less 69.4 71.0 71.0 68.3 than 3 C. In an interior room, the phase change materials CELING 70.3- 3.4 71.0- 1.9 70.3- 2.5 69.0- 2.0 are preferably encapsulated and present in a thickness of 73.7 72.9 72.8 71.O

from 3 to 10 mm in the ceiling and also in the floor material. 71.0 71.0 70.4 It is most preferable when employing the present invention 55 FLOOR- 67.7- 6.O 69.O- 3.1 69.7- 3.1 67.2- 3.8 in an interior room, that is, a room without windows or with CELING 73.7 72.9 72.8 71.O minimal window exposure to the outside, that phase change RANGE

CYCLES 4 2.5 3.0 3.0 materials be incorporated only into the ceiling and floor of PER HR the interior room.

Most preferably, the phase change materials are incorpo 60 rated in a panel System in which the phase change materials To reduce the floor-to-ceiling temperature gradient, it is are restricted within flexible containment envelopes, which, now recognized that the preferred arrangement of tempera in turn, are overlaid with lattice. Metal lattice are preferred, ture Stabilizing phase change materials are vertical to the with aluminum and aluminum alloys the preferred lattice temperature gradient. At a minimum, the ceiling temperature material. The lattice defines a plurality of side-by-side 65 differential should be minimized. Most preferably, the ceil Spaced apart holes which can accommodate expected expan ing and floor temperature differentials should be minimized. Sion of the phase change material within the containment A preferred thermoregulating effect is achieved when tem

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S 6 perature Stabilizing phase change materials would be on the The four phase change materials listed in Table 2 are surface of the floor and the ceiling of the room. Preferably nontoxic, noncorrosive, nonhydroscopic, Stable to ther the complete Surfaces of the floor and the ceiling are covered mocycling and Show no Supercooling effect. These proper with the temperature Stabilizing phase change materials in ties makes them especially Suitable for building applica certain quantities. If only parts of the floor and ceiling are tions. Problems associated with low resistance to ignition covered with the temperature Stabilizing phase change can be overcome by adding fire retardants Such as haloge material, the phase change material quantity has to be nated hydrocarbons (chlorinated, brominated or fluorinated enhanced to obtain the same thermoregulating effect which hydrocarbons). The flame retardant should be preferably is received under a complete covering. incorporated into the phase change material in a quantity of It is noted that a reduction in the temperature gradient is approximately 10% of the total weight to provide a self also obtained if only the floor or the ceiling is covered with extinguished effect. It has been determined that the incor temperature Stabilizing phase change material. That means poration of flame retardant additives do not cause a change that an arrangement of temperature Stabilizing phase change in the melting and crystallization temperatures. material only in a floor covering or only in a ceiling covering Other phase change materials. Such as polyethylene is also appropriate. The arrangement of the preferred 15 glycol, mixtures of different acids or Salt hydrates Seems also arrangement of the temperature Stabilizing Phase Change to be appropriate for an application in this building condi Material is shown in FIG. 1. tioning technique because of the temperature range where The minimum temperature at the floor should be 19 C. their phase change takes place and their latent heat capacity. and the maximum temperature at the floor should be 25 C., The application of the Suggested phase change material with a preferred temperature of 22 C. ASSuming the pre where the latent heat absorption/emission during Solid ferred floor temperature of 22 C. and a preferred tempera liquid transitions is used to establish a thermoregulating ture gradient of not more than 3 C., the appropriate ceiling effect makes its enclosure in containment Structures neces temperature should be 25 C. Preferably one or two phase Sary. Such containment Structures are either microcapsules change materials should be Selected in which their phase with diameters between 1 and 10 microns, or special con changes takes place in a temperature range between 21 C. 25 Structed container Systems.

and 26 C. Most preferably, the phase change material in the Microencapsulated phase change material can, for floor should be selected to release heat if the floor tempera example, be applied to the ceiling tiles in form of a coating. ture drops under 22 C., and thus, its crystallization point The thickness of this coating layer should be approximately should be about 22 C. The phase change material selected 3 mm. A coated phase change material layer of 3 mm to absorb Surplus heat on the top of the room has a preferred thickness causes a weight increase of the ceiling tile of 1 m melting point or temperature of about 25 C. It will be by about 2 kg.

understood by those skilled in the art to which the present For a floor application the microencapsulated phase invention pertains, that temperatures given here are not exact Change material can be filled into the air Spaces of a temperatures, but rather approximate temperatures. Espe

cially in the case of phase change material mixtures, the Soaking process. The 35 lattice-like fabric or a foam material by a melting and crystallization points or temperatures are likely fabric or the foam shouldthickness be of the three-dimensional approximately 5 mm to include to cover a range, rather than a single degree.

Phase change materials having phase changes in the fabric or the foam can then be either laminated to thelattice enough phase change material. The three-dimensional back preferred temperature ranges of the present invention Side of the carpet or can be used to create Separate floor tiles. include linear crystalline alkyl hydrocarbons (paraffins) 40 The floor tiles should have a fabric coverage on both sides listed in Table 2, and mixtures thereof. to avoid a loSS or damage of microencapsulated phase

TABLE 2

change material during the use. Another possibility for a floor application is to make the carpet from Acrylic fibers

PHASE Melting Crystallization Latent Heat Latent Heat 45 with incorporated microencapsulated phase change material CHANGE Point Point of Absorption of Emission or to coat the back Side of the carpet with microencapsulated MATERIAL o C. o C. J/g J/g phase change material.

Hexadecane 21.1 12.2 235.2 236.6 These applications are Suitable to reduce the temperature Heptadecane 25.0 16.5 176.4 1826 gradient in Small interior rooms especially of residential 50 buildings. In larger rooms a higher quantity of temperature

Stabilizing phase change material may be necessary to get desired effects.

In View of the temperature requirements discussed above, For this purpose container-like ceiling tiles should be used octadecane is a preferred phase change material for incor which include a larger quantity of temperature Stabilizing poration in or on a floor (these positions collectively refer 55 phase change material. This container Should be directly enced to herein as “adjacent the floor or floor Surface), due attached to the ceiling. The phase change material layer in to octadecane's crystallization point of 22.0 C. the liquid stage should be about 10 mm thick. Such a Heptadecane, with 250 C. melting point, is a preferred container with a size of 0.5 m by 1 m would include a phase phase change material for incorporation in or on a ceiling change material quantity of approximately 3.5 kg. The Surface. 60 container bottom should be made of a material with a high Ablend of the four phase change materials listed in Table thermal conductivity and a Smooth Surface to ensure a good 2 is suitable for both floor and ceiling placement. FIGS. 2 heat transfer to the phase change layer So that the phase and 3 illustrate differential Scanning calorimetry diagrams change material can properly absorb the Surplus heat. A plan showing both heat absorption and emission of Such a blend. view of Such a tile is shown in FIG. 4. This blend possesses a melting point of about 25 C. and a 65 Otherwise, to enhance the quantity of the temperature crystallization point of about 22 C. Its latent heat capacity Stabilizing phase change material in the floor, container-like is about 150 J/g. structures should be used which are located between the

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insulation layer and composition flooring, with a thickneSS 5. The method of minimizing a floor-to-ceiling tempera of the composition flooring not exceeding 20 mm. A ture gradient of a room according to claim 1, wherein the honeycomb-like Structure is preferably used to contain the Step of incorporating a first phase change material further phase change material. The cells should have a Size of comprises the Step of approximately 10 mmx10 mmx10 mm. installing ceiling tiles containing Said first phase change Because phase change materials react on any temperature material on the ceiling Surface. change in the environment by absorbing or emitting heat, overnight temperature changes can be used to recharge ture6. gradient The method of minimizing a floor-to-ceiling tempera of a room according to claim 1, wherein the phase change materials. A floor application of a phase Step of incorporating a first phase change material further change material can also be beneficially employed in com bination with a floor heating System. Peak energy demands comprises the Step of.

over the daytime can then be shifted to off peak hours applying a coating containing Said first phase change overnight by using the floor heating overnight to recharge material to the ceiling Surface. the phase change material. The Stored latent heat inside the 7. The method of minimizing a floor-to-ceiling tempera phase change material can then be used to fulfill the heating 15 ture gradient of a room according to claim 2, wherein the requirements over the day. This technique should Substan Step of incorporating a first phase change material further tially reduce utility costs. comprises the Step of

In buildings where large amounts of heat are generated installing ceiling tiles containing Said first phase change over the day, for instance by machinery, equipment or Solar material on the ceiling Surface. radiant incidence from outside, it would be appropriate to 8. The method of minimizing a floor-to-ceiling tempera use ceiling tiles containing phase change material in com ture gradient of a room according to claim 2, wherein the bination with a cooling System. The cooling System can be Step of incorporating a first phase change material further used to take out the heat absorbed by the phase change comprises the Step of material to get it recharged. This can also be done in off peak hours overnight So that also in this case the energy demand applying a coating containing Said first phase change for cooling purposes can be shifted to off peak hours which 25 material to the ceiling Surface. also leads to a Substantial utility cost reduction. 9. The method of minimizing a floor-to-ceiling tempera Furthermore, using an air conditioning System in a ture gradient of a room according to claim 1, wherein the building, the operation time and therefore the heating and Step of incorporating a Second phase change material further cooling requirements can be Substantially reduced. Estima comprises the Step of tions based on experimental data have shown that by cov installing floor tiles containing Said Second phase change ering floor and ceiling of a room (30m) with a phase change material on the floor Surface. layer of about 3 mm, which includes a phase change material 10. The method of minimizing a floor-to-ceiling tempera quantity of about 70 kg, the use of the air conditioning ture gradient of a room according to claim 1, wherein the system could be reduced by about 40% which is another Step of incorporating a Second phase change material further important benefit of the thermoregulating effect created by 35 comprises the Step of the phase change material. laying a carpet containing Said Second phase change Presently preferred embodiments of the present invention material on the floor Surface. and many of its improvements have been described with a 11. The method of minimizing a floor-to-ceiling tempera degree of particularity. It should be understood that this ture gradient of a room according to claim 2, wherein the description has been made by way of preferred examples, 40 Step of incorporating a Second phase change material further and that the invention is defined by the scope of the comprises the Step of following claims. installing floor tiles containing Said Second phase change What is claimed is:

1. A method of minimizing a floor-to-ceiling temperature material on the floor Surface. gradient of a room containing at least a ceiling Surface, a 45 12. The method of minimizing a floor-to-ceiling tempera floor Surface, and walls, comprising: ture gradient of a room according to claim 2, wherein the incorporating a first phase change material adjacent the Step of incorporating a Second phase change material further comprises the Step of ceiling Surface, Said first phase change material having laying a carpet containing Said Second phase change a melting temperature, and material on the floor Surface. incorporating a Second phase change material adjacent the 50 13. A building room containing at least a ceiling Surface, floor Surface, Said Second phase change material having a floor Surface, and walls, further comprising: a crystallization temperature:

wherein Said melting temperature of Said first phase a first phase change material having a melting temperature change material is greater than Said crystallization and fixedly positioned adjacent the Surface of the temperature of Said Second phase change material. 55 ceiling; and 2. The method of minimizing a floor-to-ceiling tempera a Second phase change material having a crystallization ture gradient of a room according to claim 1, wherein Said temperature and fixedly positioned adjacent the floor melting temperature of Said first phase change material is Surface;

25 C. plus or minus 1 C. and said crystallization tempera wherein Said melting temperature of Said first phase ture of Said Second phase change material is 22 C. plus or 60 change material is higher than Said crystallization tem minus 1 C. perature of Said Second phase change material, with 3. The method of minimizing a floor-to-ceiling tempera Said first and Second phase change materials adapted to ture gradient of a room according to claim 2, wherein the minimize a floor-to-ceiling temperature gradient estab walls are free of phase change materials. lished in the room.

4. The method of minimizing a floor-to-ceiling tempera 65 14. The building room according to claim 13, wherein ture gradient of a room according to claim 1, wherein the Said melting temperature of Said first phase change material walls are free of phase change materials. is 25 C. plus or minus 1 C. and said crystallization

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temperature of Said second phase change material is 22 C. principle portion of the first phase change material is plus or minus 1 C. heptaecane, and a principle portion of the Second phase 15. The building room according to claim 13, wherein the change material is octadecane.

walls are free of all phase change material. 22. The building room according to claim 13, wherein a 16. The building room according to claim 14, wherein the principle portion of the first phase change material is walls are free of all phase change material.

17. The building room according to claim 13, further heptaecane, and a principle portion of the Second phase comprising: change material is octadecane.

ceiling tiles containing Said first phase change material 23. A method of minimizing a floor-to-ceiling temperature positioned adjacent the ceiling Surface. gradient of a room in accordance with claim 1 including the 18. The building room according to claim 14, further Step of:

comprising: incorporation a flame retardant into at least one of the first ceiling tiles containing Said first phase change material and Second phase change materials. positioned adjacent the ceiling Surface; and 15 24. A method of minimizing a floor-to-ceiling temperature floor tiles containing Said Second phase change material gradient of a room in accordance with claim 23 wherein the adjacent the floor Surface positioned adjacent the floor flame retardant comprises approximately 10 percent of the Surface. total weight of the fire retardant and the at least one of the 19. The building room according to claim 13, further first and Second phase change materials.

comprising: 25. The building room according to claim 13 including a floor tiles containing Said Second phase change material flame retardant incorporated into at least one of the first and positioned adjacent the floor Surface. Second phase change materials.

20. The building room according to claim 14, further 26. The building room according to claim 25 wherein the comprising: flame retardant comprises approximately 10 percent of the a carpet containing Said Second phase change material 25 total weight of the fire retardant and the at least one of the positioned adjacent the floor Surface. first and Second phase change materials. 21. A method of minimizing a floor-to-ceiling temperature gradient of a room in accordance with claim 1, wherein a k k k k k