CA1115264A - Method and system for the compact storage of heat and coolness by phase change materials - Google Patents
Method and system for the compact storage of heat and coolness by phase change materialsInfo
- Publication number
- CA1115264A CA1115264A CA299,798A CA299798A CA1115264A CA 1115264 A CA1115264 A CA 1115264A CA 299798 A CA299798 A CA 299798A CA 1115264 A CA1115264 A CA 1115264A
- Authority
- CA
- Canada
- Prior art keywords
- liquid
- phase change
- tank
- change material
- heat
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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- 238000001816 cooling Methods 0.000 claims abstract description 9
- 238000005057 refrigeration Methods 0.000 claims abstract description 8
- 239000007788 liquid Substances 0.000 claims description 89
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 56
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- 229920003023 plastic Polymers 0.000 claims description 28
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- 238000007710 freezing Methods 0.000 claims description 14
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- 229920002457 flexible plastic Polymers 0.000 claims description 10
- 239000007791 liquid phase Substances 0.000 claims description 9
- 238000009413 insulation Methods 0.000 claims description 8
- 238000005086 pumping Methods 0.000 claims description 8
- 238000005338 heat storage Methods 0.000 claims description 7
- 108010053481 Antifreeze Proteins Proteins 0.000 claims description 5
- 230000002528 anti-freeze Effects 0.000 claims description 5
- 230000008569 process Effects 0.000 claims description 5
- 230000006911 nucleation Effects 0.000 claims description 3
- 238000010899 nucleation Methods 0.000 claims description 3
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- 238000013517 stratification Methods 0.000 abstract description 4
- 230000005923 long-lasting effect Effects 0.000 abstract 1
- 238000004806 packaging method and process Methods 0.000 abstract 1
- 150000003839 salts Chemical class 0.000 description 11
- 230000007797 corrosion Effects 0.000 description 9
- 238000005260 corrosion Methods 0.000 description 9
- -1 salt hydrates Chemical class 0.000 description 8
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 5
- 230000008020 evaporation Effects 0.000 description 5
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- 150000002739 metals Chemical class 0.000 description 3
- PODWXQQNRWNDGD-UHFFFAOYSA-L sodium thiosulfate pentahydrate Chemical compound O.O.O.O.O.[Na+].[Na+].[O-]S([S-])(=O)=O PODWXQQNRWNDGD-UHFFFAOYSA-L 0.000 description 3
- 239000012815 thermoplastic material Substances 0.000 description 3
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- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
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- ASTWEMOBIXQPPV-UHFFFAOYSA-K trisodium;phosphate;dodecahydrate Chemical compound O.O.O.O.O.O.O.O.O.O.O.O.[Na+].[Na+].[Na+].[O-]P([O-])([O-])=O ASTWEMOBIXQPPV-UHFFFAOYSA-K 0.000 description 1
Landscapes
- Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
Abstract
METHOD AND SYSTEM FOR THE COMPACT STORAGE
OF HEAT AND COOLNESS BY PHASE CHANGE MATERIALS
ABSTRACT OF THE DISCLOSURE
While many materials and additives which will melt and freeze at various temperature levels for storing and releasing large amount of heat thereby per unit volume have been disclosed, the packaging of these materials with suitable non-corrodible long-lasting heat exchange structures has been cumbersome and expensive The present invention provides an inexpensive, high performance, non-corrodible thermal storage method and system adaptable to materials over a wide range of temperatures, including a heat exchanger which provides uniform phase change throughout the volume of the entire storage mass.
Problems of thermal expansion, stratification and subcooling are eliminated. Thermal storage methods and systems embodying the present system may advantageously be used for off-peak storage of electric refrigeration, cooling and heating as well as solar heating and other applications.
OF HEAT AND COOLNESS BY PHASE CHANGE MATERIALS
ABSTRACT OF THE DISCLOSURE
While many materials and additives which will melt and freeze at various temperature levels for storing and releasing large amount of heat thereby per unit volume have been disclosed, the packaging of these materials with suitable non-corrodible long-lasting heat exchange structures has been cumbersome and expensive The present invention provides an inexpensive, high performance, non-corrodible thermal storage method and system adaptable to materials over a wide range of temperatures, including a heat exchanger which provides uniform phase change throughout the volume of the entire storage mass.
Problems of thermal expansion, stratification and subcooling are eliminated. Thermal storage methods and systems embodying the present system may advantageously be used for off-peak storage of electric refrigeration, cooling and heating as well as solar heating and other applications.
Description
BACKGROUND OF THE INVENTION
.
The bulk storage of heat or coolness at certain temperature levels has many applica-tions such as solar heating of buildings at 85 to 120~F, solar Rankine engines or absorption refrigeration machines a-t 200 to 250`~F, off-peak hour opera-tion of air conditioners at 30 to 600F, off-peak hour operation of r-efrigeration plants at -20 to ~20~F, etc. The materials used, except in the case of water at 320F, must be carefully mixed in certain proportions with special equipment and techniques, and must be kept away from materials that will corrode. Such materials are bulky and heavy to transpor-t, and must be used in contact with large area hea-t exchange devices because of the poor thermal conductivity of these heat storage materials.
In order to minimize volume, weight, and cost~
heat of fusion materials with change of phase between solid and liquid have been proposed, tested and tried experimentally because 7,000 to 12,000 BTU's per cubic foot can be stored within the above narrow temperature ranges, whereas if only a liquid phase is used, such as water, capacity is limited to 2,000 to 3,000 BTU's per cu. ft. or so. These heat of fusion materials, usually inorganic salt hydrates, must have provisions to prevent stra-tification and subcooling.
Most prior designs have used air~ as the heat transfer medium. Such prior ar-t designs have been very bulky due to -the required volume of the air ducts and also have required multiple encapsulation because of the requisite multiple air passages of comparatively large cross sectional area. In certain instances the prior art has attempted to u-tilize liquid as the heat transfer medium; however such prior art arrangements have been largely limited to the freezing of water in metallic tanks, plates or tubes. However, such metallic devices suffer from corrosion and cause galvanic ac-tion which can cause rapid deter-ioration of various component parts. Moreover they are expensive and in~lexible, subject to damage due to expansion of the phase ~ ~ -~ y ~,y~, ~-hange material, and are heavy and difficult to transport.
O-~ner suggestions have involved multiple encapsulation with its consequent high cost.
SUMMARY OF l'HE INVENTION
There are eight primary problems that have here-tofore prevented the use of hea-t of fusion materials, or so-called phase change materials, from being used in the storing of thermal energy in a practical manner. They are cost of equipment, poor thermal conductivity of phase change materials (PCM's), corrosion, volume change during fusion, evaporation ` of water from sale hydrates, subcooling and stratification of such materials, and cost of shipping. The way that the present invention solves these eight problems is enumerated below.
1. Cost of equipment: The fi.rst advantage of the present invention is that it enables the use of plas-tic heat -transfer tubing whose relatively low thermal conduc-tivity can be compensated for by greatly increasing the heat transfer surfaces in accordance with the method and system of this invention -thereby providing a large saving in cos-t. ~ne or ;
only a few plastic tanks are used instead of multiple encap-sulation, thus also lowering cost.
~ 2. Poor thermal Conductivity: The limi-tation in ; heat transfer rates, moreover, is not in the liquid conduit material but in the body of -the phase change material. Thus the large amount of plastic heat transfer area is matched with characteristics of the PCM by a multiplicity of small plastic liquid transporting tubes distributed uniformly throughout the entire mass of the PCM. The heat flow path at any point is thus made very short.
3. Corrosion: Corrosion is of particular importance because inorganic salt hydrates provide the necessary medium for a battery if two dissimilar metals are present in any form ..
.. . ..
:.
w-;thin the salt. Severe corrosion of the metals can result quickly. Plastics alone, including tubing, headers and fitting, or with but one non-corrodible metal such as stainless steel anywhere within the salt can be satisfactory.
4. Volume Change: The problem of volume change during fusion is grea-tly lessoned by having a flexible plastic material for both the outer container for the PCM ând for the heat transfer surfaces all throughout the PCM. They will take up any thermal expansion forces both on a large scale and also locally in connection with a particular tube.
However, an element of this invention is that the plastic tubes within the PCM are arranged so that the average temperature between the liquid in any point in any tube throughout the PCM and that in the adjoining -tube is approximately the same.
This is accomplished by means of mul-tiple parallel circuits with U-bends at -the end of each circuit and every alterna-te tube connected to a supply header and -the adjoining -tubes to a re-turn header. See patent to C.D. MacCracken and Helmu-t Schmidt, #3,751,935 dated August 14, 1973 for a method of crea-ting an ice slab of uniform temperature for ice skating rinks which has since become the leading way to build an ice rink in the U.S.A.
referred to commercially as the Icemat* ri~k.
When water is frozen to ice, which is one of the many PCM's u-tilized in this invention, -the heat -transfer liquid enters -the supply header and small tubes -typically at about 240F and leaves the small tubes and return header at about 32F. With a small plastic tube a-t 24F adjoining one at 320F the average temperature is 280F and ice will form at a rate caused by that average temperature. Halfway to the U-bends in each parallel circuit the temperature in the supply tube will be 26F and the adjoining return tube? 30~F, giving the same average temperature of 28F. At the U-bends, where the supply and return small plastic tubes are joined, the temperature will be 28 F in both.
*a trademark - 4 -'' .
Therefore ice advantageously builds uniformly on allt~es entirely throughout the whole tank of water. The water level rises in the tank because of the increased specific volume of the ice formed but there is no sideward expansion forces as -the ice joins from one spiral layer to the other because the extra water volume has been sqeezed upwards previously. The rise in water level provides a measure of the ex-tent of the fusion process. The extra water on top is -the las-t to freeze.
Similarly in other PCM's the volume change is accom-odated without thermal forces. Generally, it is a fact that PCM's with a melting point above 32F shrink when they solidify and for 320F and below they expand. For the PCM's that shrink when they solidify, the tank is filled with liquid phase PCM
above the level of the tubes by the amount of the volume change -shrinkage.
5. Evaporation: Evaporation of wa-ter from salt hydrates changing their composi-tion and -thermal performance -take place even through scaled plastic walls because of the property of plastics called "water vapor transmission". This means that salt hydrates sealed into multiple small plastic containers will eventually change in performance with no way -to repair this ~ . .
except replacement. In the present invention only one or at most a few, relatively large con-tainers are used to hold the salt hydrates wi-th removable covers so that water may be poured in to refill the lost water evaporated up to a mark showing the proper level.
6. Subcooling: A major problem of salt hydrates is subcooling, dropping below the freezing point without crystal-lizing or ireezing taking place. This occurs because all the crystals are melted when the salt hydrate is heated above the melting(f~eezing) point and these crystals are not presen-t to seed or nucleate upon recooling. Additives have been discovered for many of the sale hydrates to promote nucleation (see patents to M. Telkes numbers 2,677,66~ and 2~936,7L~1). Ano-ther very .. .. . . . . .
- . , :,: . . . ': ' simple method is practical in -~hç case o~ the-presen~-invention where the salt hydrates wi-th mel-ting points above room temperature are held in a few large insulated tanks. A very small projection from the tank outside of the insulation keeps the salt hydrates in this projection, or finger, from melting when heat is applied. Thus the frozen crystals are present at all times and will nucleate crystallization when the salt hydrate is cooled below its freezing point. For example, the velocity of crystall-ization of sodium thiosulfate pentahydrate is about one inch per minute, so a 4 ft.diameter tank nucleates through-out in an hour or less when cooling is provided by the heat transfer liquid.
7. Stratificationo Another problem of salt hydrates which this invention overcomes is the stra-tifica-tion of s~lid c/rystals which, being heavier, in the case of mos-t salt hydrates, sink to the bottom. They often nucleate into different hydrate molecule combinations as they fall through warmer areas. Because of incongruent phase change in these different hydrate molecules the overall composition is changed and consequéntly the performance. Also a permanent precipitate forms at -the bottom. One solution to -this has' been to limit -the vertical dimension to an inch or so. In the present invention a straw~like mat of rubberized hair or other inert low density matting is used as a spacer between the -tubes. This effectively fills all the space in the tank with such small openings like a filter that there is no room for crystals to fall through. In addition since the dual tubing averages the temperature uniformly throughout, the crystal gr~owth will be also uniform through-out and there will be no temperature differences to cause large crystal build-ups in one area over another.
., ,. : .
~ 8. Shipping Cos-t: An average solar heated house is required to store one million BTU's, and at 100 BTU's per pound, five tons of PCM is needed and must be shipped.
The present invention provides for the PCM to be shipped in heated tank trucks and pumped through a hose in liquid form into the lightweight tanks and heat exchange tubing units which have been previously installed and -tested. It is well known that use of tank trucks is a much more economical method of transporting and delivering :Large volumes of liquid to many delivery points than by sealed containers.
THE DRAWINGS
The invention may be better understood by reference to the drawings.
Fig. 1 is an elevational view of the -thermal storage device showing a cylindrical, open--top -tank with spiral -tubing and spacer mats in cross-section.
Fig. 2 is an elevational view of the flexible tubing grid and spacer matting being rolled up into a heat exchanger assembly.
Fig. 3 is sectional plan view of the spiral tubing g*id and spacer matting rolled up and installed in the cylindrical tank.
Fig. 4 is an elevational sectional view similar -to Fig. 1 of the thermal storage apparatus showing a rectangular -tank with -tubing mats tensioned around spacer bars and running up and down vertically.
Fig. 5 shows a schematic arrangement of a thermal storage apparatus connected to pump, heat input and output devices and piping.
- Fig. 6 shows an enlarged partial sectional view of a portion of the apparatus of Fig. 1 showing tubing, spacer material and phase change material in a partially frozen condi-tion O
:
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Refering now -to the drawings in greater detail, Figure 1 illustrates a phase change thermal storage unit 2 which stores and releases a large amoun-t of heat and cool-ness per unit volume owing to heat capacity of the phase change materials. There are many materials and additives which when phase change takes place release a large amount of heat when it freezes and absorbs large amounts of heat when it melts. Examples of PCM's are indicated further below.
Thermal storage device 2 consists of a semi-flexible walled open-top tank or container 4 which preferably is made of thermoplastic material to provide flexibility and resis-tance to corrosion, an important factor. Most phase change ma-terials (PCM's) are corrosive to metals.
Prior to filling the tank wi-th PCM24 a preformed roll of flexible tubing mat 8 and rubberized hair 22 is placed in the tank. This roll of mat 8 and rubberized hair 22 fills the space in the tank so that no region within the entire tank is more than a short distance away from the mat tubing which carries the heat transfer fluid 26 for hea-ting (mel-ting) and/or cooling (freezing) of -the PCM. Heat transfer fluid 26 may be water, or if used below 32F (o C), an anti-freeze solution must be utilized such as e-thylene glycol with water. The flexible -tubing mat 8 is prefabricated in the factory using extrudel twin tubings of small diameter 1/4" approx.) usually made of synthetic plastic material which are kept clo'sely spaced and parallel to one another by means of a spacer s-trip assembly which consists of a rigid plastic strip 12 and a flexible plastic strip 14 attached together in such a way -that they form tight pockets for -twin tubing 10. A more popular methocl of pre-forming this grid of mat 8 is heat sealing. For uses involving :
.
Z~
temperatures too high for common plastics, synthetic rubber or elastomeric compounds may be used such as EPDM (ethylene propylene diene terpolymer). A number of -twin tubings 10 (number of tubings is dependent on the width of the mat grid, a popular width is 4ft. nominal which requires 32 twin -tubings spaced 1 1/2" center to center) are placed at a given spacing and parallel to one another. A rigid vinyl strip 12 is placed under the tubings 10 and a flexible vinyl strip 14 is placed over the tubings 10 in such a way that it is located right over the rigid strip 12. These two strips 12 and 14 are then heat sealed together between the dual tubes so that they form loops around individual tubings. These mats 8 may be fabricated to any desired I
length. At one end of the mat 8 two headers are installed;
one is supply header 16 and the other return header 18. On -the o-ther end of the mat 8 the 'U' bends 20 are ins-talled.
Referring -to Fig. 2 the flexible tubing mat 8 and rubberized hair matting 22 are rolled together by laying ... .
out on a long table a longer length of the horse hair matting 22 on top of the flat extended flexible tubing grid.
Then a roll is formed starting from the 'U' bend end of the mat keeping the starting circle as small as possible (about
.
The bulk storage of heat or coolness at certain temperature levels has many applica-tions such as solar heating of buildings at 85 to 120~F, solar Rankine engines or absorption refrigeration machines a-t 200 to 250`~F, off-peak hour opera-tion of air conditioners at 30 to 600F, off-peak hour operation of r-efrigeration plants at -20 to ~20~F, etc. The materials used, except in the case of water at 320F, must be carefully mixed in certain proportions with special equipment and techniques, and must be kept away from materials that will corrode. Such materials are bulky and heavy to transpor-t, and must be used in contact with large area hea-t exchange devices because of the poor thermal conductivity of these heat storage materials.
In order to minimize volume, weight, and cost~
heat of fusion materials with change of phase between solid and liquid have been proposed, tested and tried experimentally because 7,000 to 12,000 BTU's per cubic foot can be stored within the above narrow temperature ranges, whereas if only a liquid phase is used, such as water, capacity is limited to 2,000 to 3,000 BTU's per cu. ft. or so. These heat of fusion materials, usually inorganic salt hydrates, must have provisions to prevent stra-tification and subcooling.
Most prior designs have used air~ as the heat transfer medium. Such prior ar-t designs have been very bulky due to -the required volume of the air ducts and also have required multiple encapsulation because of the requisite multiple air passages of comparatively large cross sectional area. In certain instances the prior art has attempted to u-tilize liquid as the heat transfer medium; however such prior art arrangements have been largely limited to the freezing of water in metallic tanks, plates or tubes. However, such metallic devices suffer from corrosion and cause galvanic ac-tion which can cause rapid deter-ioration of various component parts. Moreover they are expensive and in~lexible, subject to damage due to expansion of the phase ~ ~ -~ y ~,y~, ~-hange material, and are heavy and difficult to transport.
O-~ner suggestions have involved multiple encapsulation with its consequent high cost.
SUMMARY OF l'HE INVENTION
There are eight primary problems that have here-tofore prevented the use of hea-t of fusion materials, or so-called phase change materials, from being used in the storing of thermal energy in a practical manner. They are cost of equipment, poor thermal conductivity of phase change materials (PCM's), corrosion, volume change during fusion, evaporation ` of water from sale hydrates, subcooling and stratification of such materials, and cost of shipping. The way that the present invention solves these eight problems is enumerated below.
1. Cost of equipment: The fi.rst advantage of the present invention is that it enables the use of plas-tic heat -transfer tubing whose relatively low thermal conduc-tivity can be compensated for by greatly increasing the heat transfer surfaces in accordance with the method and system of this invention -thereby providing a large saving in cos-t. ~ne or ;
only a few plastic tanks are used instead of multiple encap-sulation, thus also lowering cost.
~ 2. Poor thermal Conductivity: The limi-tation in ; heat transfer rates, moreover, is not in the liquid conduit material but in the body of -the phase change material. Thus the large amount of plastic heat transfer area is matched with characteristics of the PCM by a multiplicity of small plastic liquid transporting tubes distributed uniformly throughout the entire mass of the PCM. The heat flow path at any point is thus made very short.
3. Corrosion: Corrosion is of particular importance because inorganic salt hydrates provide the necessary medium for a battery if two dissimilar metals are present in any form ..
.. . ..
:.
w-;thin the salt. Severe corrosion of the metals can result quickly. Plastics alone, including tubing, headers and fitting, or with but one non-corrodible metal such as stainless steel anywhere within the salt can be satisfactory.
4. Volume Change: The problem of volume change during fusion is grea-tly lessoned by having a flexible plastic material for both the outer container for the PCM ând for the heat transfer surfaces all throughout the PCM. They will take up any thermal expansion forces both on a large scale and also locally in connection with a particular tube.
However, an element of this invention is that the plastic tubes within the PCM are arranged so that the average temperature between the liquid in any point in any tube throughout the PCM and that in the adjoining -tube is approximately the same.
This is accomplished by means of mul-tiple parallel circuits with U-bends at -the end of each circuit and every alterna-te tube connected to a supply header and -the adjoining -tubes to a re-turn header. See patent to C.D. MacCracken and Helmu-t Schmidt, #3,751,935 dated August 14, 1973 for a method of crea-ting an ice slab of uniform temperature for ice skating rinks which has since become the leading way to build an ice rink in the U.S.A.
referred to commercially as the Icemat* ri~k.
When water is frozen to ice, which is one of the many PCM's u-tilized in this invention, -the heat -transfer liquid enters -the supply header and small tubes -typically at about 240F and leaves the small tubes and return header at about 32F. With a small plastic tube a-t 24F adjoining one at 320F the average temperature is 280F and ice will form at a rate caused by that average temperature. Halfway to the U-bends in each parallel circuit the temperature in the supply tube will be 26F and the adjoining return tube? 30~F, giving the same average temperature of 28F. At the U-bends, where the supply and return small plastic tubes are joined, the temperature will be 28 F in both.
*a trademark - 4 -'' .
Therefore ice advantageously builds uniformly on allt~es entirely throughout the whole tank of water. The water level rises in the tank because of the increased specific volume of the ice formed but there is no sideward expansion forces as -the ice joins from one spiral layer to the other because the extra water volume has been sqeezed upwards previously. The rise in water level provides a measure of the ex-tent of the fusion process. The extra water on top is -the las-t to freeze.
Similarly in other PCM's the volume change is accom-odated without thermal forces. Generally, it is a fact that PCM's with a melting point above 32F shrink when they solidify and for 320F and below they expand. For the PCM's that shrink when they solidify, the tank is filled with liquid phase PCM
above the level of the tubes by the amount of the volume change -shrinkage.
5. Evaporation: Evaporation of wa-ter from salt hydrates changing their composi-tion and -thermal performance -take place even through scaled plastic walls because of the property of plastics called "water vapor transmission". This means that salt hydrates sealed into multiple small plastic containers will eventually change in performance with no way -to repair this ~ . .
except replacement. In the present invention only one or at most a few, relatively large con-tainers are used to hold the salt hydrates wi-th removable covers so that water may be poured in to refill the lost water evaporated up to a mark showing the proper level.
6. Subcooling: A major problem of salt hydrates is subcooling, dropping below the freezing point without crystal-lizing or ireezing taking place. This occurs because all the crystals are melted when the salt hydrate is heated above the melting(f~eezing) point and these crystals are not presen-t to seed or nucleate upon recooling. Additives have been discovered for many of the sale hydrates to promote nucleation (see patents to M. Telkes numbers 2,677,66~ and 2~936,7L~1). Ano-ther very .. .. . . . . .
- . , :,: . . . ': ' simple method is practical in -~hç case o~ the-presen~-invention where the salt hydrates wi-th mel-ting points above room temperature are held in a few large insulated tanks. A very small projection from the tank outside of the insulation keeps the salt hydrates in this projection, or finger, from melting when heat is applied. Thus the frozen crystals are present at all times and will nucleate crystallization when the salt hydrate is cooled below its freezing point. For example, the velocity of crystall-ization of sodium thiosulfate pentahydrate is about one inch per minute, so a 4 ft.diameter tank nucleates through-out in an hour or less when cooling is provided by the heat transfer liquid.
7. Stratificationo Another problem of salt hydrates which this invention overcomes is the stra-tifica-tion of s~lid c/rystals which, being heavier, in the case of mos-t salt hydrates, sink to the bottom. They often nucleate into different hydrate molecule combinations as they fall through warmer areas. Because of incongruent phase change in these different hydrate molecules the overall composition is changed and consequéntly the performance. Also a permanent precipitate forms at -the bottom. One solution to -this has' been to limit -the vertical dimension to an inch or so. In the present invention a straw~like mat of rubberized hair or other inert low density matting is used as a spacer between the -tubes. This effectively fills all the space in the tank with such small openings like a filter that there is no room for crystals to fall through. In addition since the dual tubing averages the temperature uniformly throughout, the crystal gr~owth will be also uniform through-out and there will be no temperature differences to cause large crystal build-ups in one area over another.
., ,. : .
~ 8. Shipping Cos-t: An average solar heated house is required to store one million BTU's, and at 100 BTU's per pound, five tons of PCM is needed and must be shipped.
The present invention provides for the PCM to be shipped in heated tank trucks and pumped through a hose in liquid form into the lightweight tanks and heat exchange tubing units which have been previously installed and -tested. It is well known that use of tank trucks is a much more economical method of transporting and delivering :Large volumes of liquid to many delivery points than by sealed containers.
THE DRAWINGS
The invention may be better understood by reference to the drawings.
Fig. 1 is an elevational view of the -thermal storage device showing a cylindrical, open--top -tank with spiral -tubing and spacer mats in cross-section.
Fig. 2 is an elevational view of the flexible tubing grid and spacer matting being rolled up into a heat exchanger assembly.
Fig. 3 is sectional plan view of the spiral tubing g*id and spacer matting rolled up and installed in the cylindrical tank.
Fig. 4 is an elevational sectional view similar -to Fig. 1 of the thermal storage apparatus showing a rectangular -tank with -tubing mats tensioned around spacer bars and running up and down vertically.
Fig. 5 shows a schematic arrangement of a thermal storage apparatus connected to pump, heat input and output devices and piping.
- Fig. 6 shows an enlarged partial sectional view of a portion of the apparatus of Fig. 1 showing tubing, spacer material and phase change material in a partially frozen condi-tion O
:
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Refering now -to the drawings in greater detail, Figure 1 illustrates a phase change thermal storage unit 2 which stores and releases a large amoun-t of heat and cool-ness per unit volume owing to heat capacity of the phase change materials. There are many materials and additives which when phase change takes place release a large amount of heat when it freezes and absorbs large amounts of heat when it melts. Examples of PCM's are indicated further below.
Thermal storage device 2 consists of a semi-flexible walled open-top tank or container 4 which preferably is made of thermoplastic material to provide flexibility and resis-tance to corrosion, an important factor. Most phase change ma-terials (PCM's) are corrosive to metals.
Prior to filling the tank wi-th PCM24 a preformed roll of flexible tubing mat 8 and rubberized hair 22 is placed in the tank. This roll of mat 8 and rubberized hair 22 fills the space in the tank so that no region within the entire tank is more than a short distance away from the mat tubing which carries the heat transfer fluid 26 for hea-ting (mel-ting) and/or cooling (freezing) of -the PCM. Heat transfer fluid 26 may be water, or if used below 32F (o C), an anti-freeze solution must be utilized such as e-thylene glycol with water. The flexible -tubing mat 8 is prefabricated in the factory using extrudel twin tubings of small diameter 1/4" approx.) usually made of synthetic plastic material which are kept clo'sely spaced and parallel to one another by means of a spacer s-trip assembly which consists of a rigid plastic strip 12 and a flexible plastic strip 14 attached together in such a way -that they form tight pockets for -twin tubing 10. A more popular methocl of pre-forming this grid of mat 8 is heat sealing. For uses involving :
.
Z~
temperatures too high for common plastics, synthetic rubber or elastomeric compounds may be used such as EPDM (ethylene propylene diene terpolymer). A number of -twin tubings 10 (number of tubings is dependent on the width of the mat grid, a popular width is 4ft. nominal which requires 32 twin -tubings spaced 1 1/2" center to center) are placed at a given spacing and parallel to one another. A rigid vinyl strip 12 is placed under the tubings 10 and a flexible vinyl strip 14 is placed over the tubings 10 in such a way that it is located right over the rigid strip 12. These two strips 12 and 14 are then heat sealed together between the dual tubes so that they form loops around individual tubings. These mats 8 may be fabricated to any desired I
length. At one end of the mat 8 two headers are installed;
one is supply header 16 and the other return header 18. On -the o-ther end of the mat 8 the 'U' bends 20 are ins-talled.
Referring -to Fig. 2 the flexible tubing mat 8 and rubberized hair matting 22 are rolled together by laying ... .
out on a long table a longer length of the horse hair matting 22 on top of the flat extended flexible tubing grid.
Then a roll is formed starting from the 'U' bend end of the mat keeping the starting circle as small as possible (about
2'-l~'' diameter). When one completes the rolling process, a roll is formed which has alternate layers o:F flexible -tubing 8 and a spacer medium in -the form of a flexible fibrous low density material having relatively large spaces be-tween fibers, for example, a rubberized hair 22 is used in pole vault and high jumping landing pi-ts. The supply header 16 and return header 18 are on the outside of the roll, but as can be seen in Figure 3 an extension of the layer of spacer matting separates the tubing and tank wall.
This roll is then installed in t he tank 4. Two ports are provided in the tank cover 6 for inlet connection _ g _ :
. .
' . ,' ~l$~
assembly 27 and outlet connection assembly 28 which are connected to -the supply header 16 and return header 18 and -to tubing nipples 17 by known plumbing methods. For large tanks more than one tubing mat 8 may be placed end to end in Figure 2 and rolled up in one roll so as to limit the pressure drop of fluid 26 in the -tubing.
The device 2 is filled with a suitable PCM 24 in accordance with the temperature requiremen-ts of -the application. The tank 4 is kept covered using a clamped plywood or plastic cover 6, fill plug 25, and gaske-t 9 held by clamps 37 as a prevention against dust accumulation, evaporation, leakage in shipment, and con-tamination of the PCM 24 and also to keep the lightweight buoyant heat exchanger from raising up ou-t of the often heavier density PCM when in the liquid s-tate. Insula-tion 32 is provided all around the tank 4 with insula-ted base 34. The tank 4 is also provided wi-th a nuclea-ting element in the form of a tubular conduit which protrudes ou-tside the insulation 32 and is exposed to ambient temperature. The purpose of nuclea-ting device 30 is to retain some frozen crystals of the PCM 24 while all the PCM 24 inside the tank 4 is in molten state. These trapped crystals in the nucleating device 30 are very helpful in initiating the crystallization of the PCM for avoiding subcooling. It is a -tendency of the liquified PCM when there are no crys-tals present within the material that it becomes subcooled which is undesirable ~'l because it delays the phase change and reduces its effect-iveness.
Fig. 3 shows a sectional plan view of Fig. 1 to show how the spacer matting is located with respect to the tubing grid. Depending upon the heat transfer cycle time for charging and discharging the PCM storage material, a - ~thinner or thicker matting may be selec-ted with consequent - 1 0 - , '.
`
change in length of tubing grid and matting. Details of this are discussed later. From the description of ~ig. 1 the detail elements may be understood.
Fig. 4 illustrates another -thermal storage device 2. The device includes a rectangular tank 5 which is preferably made of a thermoplastic material which there-by provides its quali-ty of beingsemi-~le~:ible and resistant to corrosion to various chemicals used as PCM's. However, the tank may be metallic~ particularly if the PCM is water, and a plastic liner or coating 3 is used over the metal.
The rectangular design of the tank 5 facilitates the use of flexible tubing mat 8 without -the use of spacer material throughout the length of the mat 8. The mat 8 is installed differently by festooning the mat up and down around the spacer rods 40 which are lnstalled in two rows, one near the top of the tank 5 and the other near the bottom. In each row spacer and support rods 40 are equally spaced for example at approximately 1 1~2" to 6" center-to-center distance and are arranged parallel to one another. Supply header 16 and return header 18 are located on the flange into the upper portion of the tank 5 where they are secured in place by header holding clips 38 which are shown a-ttached to the flange wall of the tank 5. The other end of -the ma-t 8 which has 'U' bends 20 is located on -the flange of the upper por-tion of the tank on the opposite side from the headers. The 'U' bends 20 are secured in place on the flanges by using an anchor strip 36 which has the same number of hooked fingers as the ? U' bends. After assembly the tank 5 is filled with .
the PCM 24. The tank 5 has a cover 7 to prevent evaporation and contamination by falling foreign matter but need not be the clamped cover of Fig 1 because the tubing assembly is anchored by spacer rods 40. The tank is located on an ' ~.
:
insulated surface 34 and is well insula-ted all around with insulation 32. A nucleating device 30 extends through the insulation 32 outside the tank. As described under Figure 1, this nucleating device 30 retains some crystals while all the other PCM 24 is in molten state inside -the tank 5.
Theæ trapped crystals in the nucleating device 30 help start the freezing cycle without undergoing subcooling.
Figure 5 shows a schematic diagram of a thermal s-torage system with a tank 50 containing a PCM for storing thermal energy by the latent heat of fusion, a pump 52 for pumping heat transfer liquid 26 through multiple small tubes 8 and 10 as shown in Figure 1, and a variety o~ heat inpu-t devices on the left side and heat output devices on the right side connected with piping 53 and valves 55, some of which are not shown because it is obvious to selec-t various piping circuits by valving. Fig. 5 depicts an illus-trative system only, For example starting at the top left and proceeding down are shown examples of heat input equipment solar col-lector 54, air coil 56, heat pump 58, electric resistance liquid heater 60, fossil fuel boiler 62, ice skating rink grid 64, and cold storage room 66.
Starting at top righ-t and proceeding down are shown examples of heat output equipment including agri-cultural or industrial process heater 70, water heater 72, heating coil in air duct 74, heat pump 76, radiant base-board heater 78, radiant floor heater 80, Rankine engine 82, absorption air conditioner 84, and air cool or cooling tower 86.
The various heat input devices shown 54-66 may all be used -to melt a PCM in tank 50 selected for -the appropriate temperature level of -that hea-t input device.
For example solar collector 54 may heat fluid-. 26 to 130F
: .
,.
z~
as it is being pumped t-hrough collector 54 on its way to tank 50. Pipe insultation 57 prevents substantial change in temperature of fluid 26. The reader will understand that insulation 57 should be distributed throughou-t the system but is omitted to simplify the drawing,. In tank 50 so~id PCM sodium thiosulfate pentahydrate, which melts at 118~F, will begin to melt by taking heat from fluid 26, dropping its temperature from 1300F or slightly less to perhaps 1250F
as it leaves tank 50 and is pumped back to collector 54.
After several hours, the length of time depending on the total area and spacing of small tubes 8 and 10, the PCM ~ ,~
will be totally melted except for what is in nucleating device tube 30 in Figure 1.
The hea-t stored in the above example in -tank 50 may be pumped via fluid 26 -to various heat outle-t devices on the right side when desired by suitable valve operation.
For example heating coil in air duct 74 may be selected and heating provided -to a structure, not shown, in the usual manner. Or water heater 72 may be heated by fluid 26.
Similarly agricul-tural process 70, such as grain drying, may be performed or room radiant heating 80.
If a higher temperature PCM were selected, such as trisodium phosphate dodecahydrate at 150F, or magnesium ,' chloride hexahydra-te at 243~F, solar collec-tor 54 could be utilized advantageously to supply heat to heat output devices such as baseboard radiation 78, Rankine engine 82, and absorp-tion air conditioner 84. Heat pump 76 could be best utilized with a PCM ,at 32 F or 55 F supplying heat to the evaporator.
In similar manner the other heat inputs may be advantageously connected through tank 50 to many of the heat outlet units. One example of each will be men-tioned.
: :' ::
Air coil 56 can be used to melt ice in -tank 50 created by operation of heat pump 76.
Heat pump 58 can be used during night off-peak hours to melt a 1180F PCM tank 50 which will in turn provide heat during the day to air coil in duct 74.
Electric heater 60 can supply heat to melt PC~
at 150F in tank 50 during off-peak hours to be used during the day in baseboard radiator 78.
Fossil fuel boiler 62 7 undersized for direc-t heating application in a church, can store heat ahead of time in tank 50 and release it into the church on Sunday morning through radiant heater 80.
Ice rink 6L~ can be kept frozen during peak daytiMe hours by coolness stored a-t 12F in a PCM such as 22% ethylene glycol and water the previous night by operation of heat pump 76.
Cold storage room 66 may si~milarly be kept cold by storing coolness from the heat pump during off-peak hours.
Cooling tower 86 can be operated at night to freeze a 55 F~PCM and supply air conditioning through air coil 56 in the day-time.
There are many other combinations for which thermal storage may be used. It will be understood that there may be multiple heat inlets and multiple outlets which may be interconnected in various cross-combinations. Fig.
5 illustratively shows ~only some of the possible heat input and heat output equipment that might be advantageously used.
Figure 6 is an enlarged cross-sectional view of a section of the thermal storage device 2. The section shows two layers of mat 8 spaced apart approxima-tely 1" by rubberized hair 22 which has an open wiry appearance.
~ ~ .
~ 14 -, ~ 2~ t Rubberized hair has very large air spaces within the matted structure and actually leaves most of the space for PCM
24 while also keeping the layers of mat 8 spaced properly.
The flexible tubing mat 8 is factory fabricated using small diameter -twin tubings 10 which are extended out of thermoplastic material suitable for a wide range of tem-perature and is corrosion resistant.
Area 24A of PCM denote the frozen crystals around the tubes during a discharging cycle when the PCM is giving up heat. Areas 24B between the tubes show the melted unfrozen part. During a charging cycle this would be reversed. Heat domain divider line 42 denotes the location equidistant between the tubes where heat flow divides between the domain of each tube. It should also be no-ted that whichever of -the -tubes 10 of each pair is connected to inlet header 16 will have more frozen PCM surrounding it during a discharge cycle because it is colder and will have more melted PCM surrounding it during a charging, , heating cycle. Fig. 6 is shown near the halfway point (close to the U-bends) so little difference in temperature is noted, and thus the frozen PCM 24A will be fairly symmetrical.
It is understood -that the charging or freezing ~eriod involves solid PCM being around the tubes and melted PCM being out halfway between the tubes, while the melting period involves melted PCM around the tubes and frozen PCM
a~ the halfway point. Since liquid can transfer heat by conduction and convection, that is, moving around within its melted space, while solid PCM can only transfer by conduction, the freezing up period will take longer.
', '' , EXAMPLE ~ 2~ ~
1. An electric utility company introduces an off-peak rate of $.060 per KWH for 10. A.M. -to 10 P.M.
and $.015 from 10 P.M. to 10 A.M. A small office building uses 20 tons of chilled water air conditioning at 44 F
from 9 A.M. to 6 P.M. during the summer season. The following will show the storage equipment as shown in the present invention which is required and how much operating cost is saved.
Ice at 32F provides 44 F water with a 12 differential. The amount of ice required is compu-ted as follows:
(a) 12 hours x 20 tons x 12,000 BTU's per hour per ton 144 BTU's per pound of ice 56 pounds ice per ( cubic foot requires 357 cubic feet of ice in -the PCM tanks 50 or 5OA. A 6 ft. diame-ter plas-tic -tank five feet high is a practical maximum size and this holds 120 cubic feet up to a 4 1/4 ft. level. Therefore three 6 ft. diameter tanks are required.
The spacing of the plastic tubes within the ice must be such that all the ice be melted in 9 hours and all the water refrozen in 12 hours because there is a time period described above when the rates are low. The spacing determines the total hea-t transfer area and thus the length of the spiral tublng mat to be installed in the tan~.
I have found that 14 BTU/hr/sq/ft./ F can be transferred from an ice slah on both sides of -the mat up to 1" thick.
Assuming an average temperature differential of 40F when freezing the ice, it would mean the chilled anti-freeze solution would enter at about 24F and leave at 32~F
with an average of 28~F. A refrigerant suction temperature . , ~;. .. . .
`:
.
- of about 180F produces this desirable temperature pattern.
The calculation, then, is as follows:
(b) 20 tons x 12,0~0 BTU/hr/ton 14 BTU/hr/ft i F x 4 F = 4,286 sq.f-t.
and with mats 4 ft. wide, this meant 4286/4 - 1072 running ft. of mat located in three 6 ft. diameter tah~s. Such -tanks have a combined cross-sectional area of 85 sq. ft. The spirally coiled mats take up substantially the whole space in the cylindrical tanks. Thus each coil path has a width of 85/1072 = .079 ft. or .95 in. Therefore 1072 running feet in the three tanks provide 357 running feet per tank.
I have found out that pressure drop consider-ations as a practical matter limit mats to about 90 ft. in length. Thus you install more -than one mat in each tank 3 4 mats per tank each 89 ft. long, or 12 89 ft. mats in all.
The spacer material would be ~95" less -the width of the mat which is .31", thus about 5/8". An alternative is to use 6 mats 60 ft. long which would raise the cost of more headers and U-bends but would reduce pressure drop, allow for more low, and provide faster response.
The present opera-ting cost of -the offlce building air conditioning equipment would be about (c) $.06/KWH x 12,000 BTU/hr/-ton 746 BTU/KWH x 3.0 C.O.P. $-32/ton-hr Assuming that this small office building is operating 25 weeks, 5 days per week at 50% of full load 9 hours per day. the calculation is as follows:
(d) 25 x 5 x 9 x .5 x 20 = 11,250 ton-hrs., or $3,600 cost.
Since the refrigeration suction temperature will be lower because of the freezing of the ice, about 18 F vs.
This roll is then installed in t he tank 4. Two ports are provided in the tank cover 6 for inlet connection _ g _ :
. .
' . ,' ~l$~
assembly 27 and outlet connection assembly 28 which are connected to -the supply header 16 and return header 18 and -to tubing nipples 17 by known plumbing methods. For large tanks more than one tubing mat 8 may be placed end to end in Figure 2 and rolled up in one roll so as to limit the pressure drop of fluid 26 in the -tubing.
The device 2 is filled with a suitable PCM 24 in accordance with the temperature requiremen-ts of -the application. The tank 4 is kept covered using a clamped plywood or plastic cover 6, fill plug 25, and gaske-t 9 held by clamps 37 as a prevention against dust accumulation, evaporation, leakage in shipment, and con-tamination of the PCM 24 and also to keep the lightweight buoyant heat exchanger from raising up ou-t of the often heavier density PCM when in the liquid s-tate. Insula-tion 32 is provided all around the tank 4 with insula-ted base 34. The tank 4 is also provided wi-th a nuclea-ting element in the form of a tubular conduit which protrudes ou-tside the insulation 32 and is exposed to ambient temperature. The purpose of nuclea-ting device 30 is to retain some frozen crystals of the PCM 24 while all the PCM 24 inside the tank 4 is in molten state. These trapped crystals in the nucleating device 30 are very helpful in initiating the crystallization of the PCM for avoiding subcooling. It is a -tendency of the liquified PCM when there are no crys-tals present within the material that it becomes subcooled which is undesirable ~'l because it delays the phase change and reduces its effect-iveness.
Fig. 3 shows a sectional plan view of Fig. 1 to show how the spacer matting is located with respect to the tubing grid. Depending upon the heat transfer cycle time for charging and discharging the PCM storage material, a - ~thinner or thicker matting may be selec-ted with consequent - 1 0 - , '.
`
change in length of tubing grid and matting. Details of this are discussed later. From the description of ~ig. 1 the detail elements may be understood.
Fig. 4 illustrates another -thermal storage device 2. The device includes a rectangular tank 5 which is preferably made of a thermoplastic material which there-by provides its quali-ty of beingsemi-~le~:ible and resistant to corrosion to various chemicals used as PCM's. However, the tank may be metallic~ particularly if the PCM is water, and a plastic liner or coating 3 is used over the metal.
The rectangular design of the tank 5 facilitates the use of flexible tubing mat 8 without -the use of spacer material throughout the length of the mat 8. The mat 8 is installed differently by festooning the mat up and down around the spacer rods 40 which are lnstalled in two rows, one near the top of the tank 5 and the other near the bottom. In each row spacer and support rods 40 are equally spaced for example at approximately 1 1~2" to 6" center-to-center distance and are arranged parallel to one another. Supply header 16 and return header 18 are located on the flange into the upper portion of the tank 5 where they are secured in place by header holding clips 38 which are shown a-ttached to the flange wall of the tank 5. The other end of -the ma-t 8 which has 'U' bends 20 is located on -the flange of the upper por-tion of the tank on the opposite side from the headers. The 'U' bends 20 are secured in place on the flanges by using an anchor strip 36 which has the same number of hooked fingers as the ? U' bends. After assembly the tank 5 is filled with .
the PCM 24. The tank 5 has a cover 7 to prevent evaporation and contamination by falling foreign matter but need not be the clamped cover of Fig 1 because the tubing assembly is anchored by spacer rods 40. The tank is located on an ' ~.
:
insulated surface 34 and is well insula-ted all around with insulation 32. A nucleating device 30 extends through the insulation 32 outside the tank. As described under Figure 1, this nucleating device 30 retains some crystals while all the other PCM 24 is in molten state inside -the tank 5.
Theæ trapped crystals in the nucleating device 30 help start the freezing cycle without undergoing subcooling.
Figure 5 shows a schematic diagram of a thermal s-torage system with a tank 50 containing a PCM for storing thermal energy by the latent heat of fusion, a pump 52 for pumping heat transfer liquid 26 through multiple small tubes 8 and 10 as shown in Figure 1, and a variety o~ heat inpu-t devices on the left side and heat output devices on the right side connected with piping 53 and valves 55, some of which are not shown because it is obvious to selec-t various piping circuits by valving. Fig. 5 depicts an illus-trative system only, For example starting at the top left and proceeding down are shown examples of heat input equipment solar col-lector 54, air coil 56, heat pump 58, electric resistance liquid heater 60, fossil fuel boiler 62, ice skating rink grid 64, and cold storage room 66.
Starting at top righ-t and proceeding down are shown examples of heat output equipment including agri-cultural or industrial process heater 70, water heater 72, heating coil in air duct 74, heat pump 76, radiant base-board heater 78, radiant floor heater 80, Rankine engine 82, absorption air conditioner 84, and air cool or cooling tower 86.
The various heat input devices shown 54-66 may all be used -to melt a PCM in tank 50 selected for -the appropriate temperature level of -that hea-t input device.
For example solar collector 54 may heat fluid-. 26 to 130F
: .
,.
z~
as it is being pumped t-hrough collector 54 on its way to tank 50. Pipe insultation 57 prevents substantial change in temperature of fluid 26. The reader will understand that insulation 57 should be distributed throughou-t the system but is omitted to simplify the drawing,. In tank 50 so~id PCM sodium thiosulfate pentahydrate, which melts at 118~F, will begin to melt by taking heat from fluid 26, dropping its temperature from 1300F or slightly less to perhaps 1250F
as it leaves tank 50 and is pumped back to collector 54.
After several hours, the length of time depending on the total area and spacing of small tubes 8 and 10, the PCM ~ ,~
will be totally melted except for what is in nucleating device tube 30 in Figure 1.
The hea-t stored in the above example in -tank 50 may be pumped via fluid 26 -to various heat outle-t devices on the right side when desired by suitable valve operation.
For example heating coil in air duct 74 may be selected and heating provided -to a structure, not shown, in the usual manner. Or water heater 72 may be heated by fluid 26.
Similarly agricul-tural process 70, such as grain drying, may be performed or room radiant heating 80.
If a higher temperature PCM were selected, such as trisodium phosphate dodecahydrate at 150F, or magnesium ,' chloride hexahydra-te at 243~F, solar collec-tor 54 could be utilized advantageously to supply heat to heat output devices such as baseboard radiation 78, Rankine engine 82, and absorp-tion air conditioner 84. Heat pump 76 could be best utilized with a PCM ,at 32 F or 55 F supplying heat to the evaporator.
In similar manner the other heat inputs may be advantageously connected through tank 50 to many of the heat outlet units. One example of each will be men-tioned.
: :' ::
Air coil 56 can be used to melt ice in -tank 50 created by operation of heat pump 76.
Heat pump 58 can be used during night off-peak hours to melt a 1180F PCM tank 50 which will in turn provide heat during the day to air coil in duct 74.
Electric heater 60 can supply heat to melt PC~
at 150F in tank 50 during off-peak hours to be used during the day in baseboard radiator 78.
Fossil fuel boiler 62 7 undersized for direc-t heating application in a church, can store heat ahead of time in tank 50 and release it into the church on Sunday morning through radiant heater 80.
Ice rink 6L~ can be kept frozen during peak daytiMe hours by coolness stored a-t 12F in a PCM such as 22% ethylene glycol and water the previous night by operation of heat pump 76.
Cold storage room 66 may si~milarly be kept cold by storing coolness from the heat pump during off-peak hours.
Cooling tower 86 can be operated at night to freeze a 55 F~PCM and supply air conditioning through air coil 56 in the day-time.
There are many other combinations for which thermal storage may be used. It will be understood that there may be multiple heat inlets and multiple outlets which may be interconnected in various cross-combinations. Fig.
5 illustratively shows ~only some of the possible heat input and heat output equipment that might be advantageously used.
Figure 6 is an enlarged cross-sectional view of a section of the thermal storage device 2. The section shows two layers of mat 8 spaced apart approxima-tely 1" by rubberized hair 22 which has an open wiry appearance.
~ ~ .
~ 14 -, ~ 2~ t Rubberized hair has very large air spaces within the matted structure and actually leaves most of the space for PCM
24 while also keeping the layers of mat 8 spaced properly.
The flexible tubing mat 8 is factory fabricated using small diameter -twin tubings 10 which are extended out of thermoplastic material suitable for a wide range of tem-perature and is corrosion resistant.
Area 24A of PCM denote the frozen crystals around the tubes during a discharging cycle when the PCM is giving up heat. Areas 24B between the tubes show the melted unfrozen part. During a charging cycle this would be reversed. Heat domain divider line 42 denotes the location equidistant between the tubes where heat flow divides between the domain of each tube. It should also be no-ted that whichever of -the -tubes 10 of each pair is connected to inlet header 16 will have more frozen PCM surrounding it during a discharge cycle because it is colder and will have more melted PCM surrounding it during a charging, , heating cycle. Fig. 6 is shown near the halfway point (close to the U-bends) so little difference in temperature is noted, and thus the frozen PCM 24A will be fairly symmetrical.
It is understood -that the charging or freezing ~eriod involves solid PCM being around the tubes and melted PCM being out halfway between the tubes, while the melting period involves melted PCM around the tubes and frozen PCM
a~ the halfway point. Since liquid can transfer heat by conduction and convection, that is, moving around within its melted space, while solid PCM can only transfer by conduction, the freezing up period will take longer.
', '' , EXAMPLE ~ 2~ ~
1. An electric utility company introduces an off-peak rate of $.060 per KWH for 10. A.M. -to 10 P.M.
and $.015 from 10 P.M. to 10 A.M. A small office building uses 20 tons of chilled water air conditioning at 44 F
from 9 A.M. to 6 P.M. during the summer season. The following will show the storage equipment as shown in the present invention which is required and how much operating cost is saved.
Ice at 32F provides 44 F water with a 12 differential. The amount of ice required is compu-ted as follows:
(a) 12 hours x 20 tons x 12,000 BTU's per hour per ton 144 BTU's per pound of ice 56 pounds ice per ( cubic foot requires 357 cubic feet of ice in -the PCM tanks 50 or 5OA. A 6 ft. diame-ter plas-tic -tank five feet high is a practical maximum size and this holds 120 cubic feet up to a 4 1/4 ft. level. Therefore three 6 ft. diameter tanks are required.
The spacing of the plastic tubes within the ice must be such that all the ice be melted in 9 hours and all the water refrozen in 12 hours because there is a time period described above when the rates are low. The spacing determines the total hea-t transfer area and thus the length of the spiral tublng mat to be installed in the tan~.
I have found that 14 BTU/hr/sq/ft./ F can be transferred from an ice slah on both sides of -the mat up to 1" thick.
Assuming an average temperature differential of 40F when freezing the ice, it would mean the chilled anti-freeze solution would enter at about 24F and leave at 32~F
with an average of 28~F. A refrigerant suction temperature . , ~;. .. . .
`:
.
- of about 180F produces this desirable temperature pattern.
The calculation, then, is as follows:
(b) 20 tons x 12,0~0 BTU/hr/ton 14 BTU/hr/ft i F x 4 F = 4,286 sq.f-t.
and with mats 4 ft. wide, this meant 4286/4 - 1072 running ft. of mat located in three 6 ft. diameter tah~s. Such -tanks have a combined cross-sectional area of 85 sq. ft. The spirally coiled mats take up substantially the whole space in the cylindrical tanks. Thus each coil path has a width of 85/1072 = .079 ft. or .95 in. Therefore 1072 running feet in the three tanks provide 357 running feet per tank.
I have found out that pressure drop consider-ations as a practical matter limit mats to about 90 ft. in length. Thus you install more -than one mat in each tank 3 4 mats per tank each 89 ft. long, or 12 89 ft. mats in all.
The spacer material would be ~95" less -the width of the mat which is .31", thus about 5/8". An alternative is to use 6 mats 60 ft. long which would raise the cost of more headers and U-bends but would reduce pressure drop, allow for more low, and provide faster response.
The present opera-ting cost of -the offlce building air conditioning equipment would be about (c) $.06/KWH x 12,000 BTU/hr/-ton 746 BTU/KWH x 3.0 C.O.P. $-32/ton-hr Assuming that this small office building is operating 25 weeks, 5 days per week at 50% of full load 9 hours per day. the calculation is as follows:
(d) 25 x 5 x 9 x .5 x 20 = 11,250 ton-hrs., or $3,600 cost.
Since the refrigeration suction temperature will be lower because of the freezing of the ice, about 18 F vs.
3~ F for chilled water, the C.O.P. (coefficient of perform-; ance) of the chiller heat pump can be assumed to be about 2.5 instead of 3Ø The cost is calculated as follows:
(e) $.015 x 12,000 = $.0g6/-ton-hr and for 11,250 ton-hrs, the cost would be $1,080. A
savings of $2,520 per year, or a savings of 70%, compared to operating without storage in the small office building.
II. Example II using sodium thiosulfate pentahydrate, a phase change material, PCM-118, which melts at 118 F, or 115 F in this case because of certain impurities, is to store heat for one cloudy day and -two nights during 30~F average temperature weather in a house that takes 50,000 BTU's/hr at O F. Since the design base is 65F, 35/65 x 50,000, or 26,923 BTU's per hour for 40 hours, or 1,076,920 BTUts must be able -to be s-tored.
With 92 BTUs per pound la-tent heat and 18 BTUs per pound sensible heat between 100 F, 1,076,920 BTUs divided by 110 BrrUs per pound shows -that 9,790 pounds of salt are requlred .
Since salts are more conveniently loaded at the factory into tank or tanks 50, the weight of loaded con-tainers is a factor, and a practical limit of about 1,000 pounds for shipping and moving into a house basement is assumed. PCM-118, with a specific gravity of 1.6, will store over 10q,000 BTUs and weigh about 1,000 pounds in a plastic container 2 feet in diame-ter and 4 feet high.
Ten such tanks 50 are needed for this example, ; providing about 1,100,000 BTUs. Heat transfer liquid from the solar collectors at about 1300F enters the tank tubing leaving at 116F for an average of 1259F,= 8 F above the ~usion point at llS~F. Opposite from the other example, charging the tank 50 involves melting liquid around the tubes first which speeds heat transfer by conventional motion of the liquid.
Assuming two sunny days to charge the tanks with heat~ assuming 900 BTUs per square foot per day from the - 18 - ~
': ' ' collectors~ and assuming 25,000 BTUs per hour are needed to hea-t the house during the 8 hour sunny days, -then 1,276~000 BTUs would be needed along with 1,476,000/900 x 2 = 820 sq. ft. of collector. The charging time is 16 hours (the two 8 hour solar days) and the discharging (freezing) time is 40 hours.
Since PCM-115 has a thermal conductivity about 1/3 less than ice, an overall coefficient of abou-t 5 BTU/
hr/ft / F from each side is reasonable, or 10 overall when the salt is solid. The partially liquid phase should be higher but can be assumed to be the same. The calcu-lation for the mat area would be Lo7TU0-- BTUs -- - - = 840 sq. Et.
hr ft2 F x 8 F x 16 hrs and with 4 feet high mats, it would mean 2L0 running feet divided into 10 -tanks, or 21 fee-t length per ma-t. Since the ten tanks are each 2.0' diameter, their area is 3.14 sq. ft., and 3.14 sq, f-t./21 ft. = .150 ft. or 1.8 in. is the width of each coil path of the spiral. Sub-tracting the mat thickness of 0.3 in., the spacer material is 1.5"
thick.
It is to be noted that since the salt shrinks as i-t freezes, the mol-ten salt should more than cover the tubes and the frozen salt will be totally wi-thin the height oE -the tubes in tank 50.
The headers 16 are made of ABS or CPVC plastic pipe with ABS or CPVC nipples 17 solvent ceménted to the headers for low cost, adequate heat resistance and elimin-ation of corrosion. The mat tubing is a medium or high density polyethylene with butyl rubber additive for flexi-bili-ty to aid in making tight sealing joints. Stainless steel U-bends and s-tainless steel tubing clamps are -the only metal in contact with the salt to avoid ga~Lvanic ac-tion.
.
i2~
The examples given are illustrative of various applications that may be made of phase change material thermal energy storage according to my invention. These examples are not to be thoughtof as limiting as to any particular use, dimension, or material. It is intended that various modifications which might readily suggest themselves to those skilled in the art be covered by the scope of the following claims.
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(e) $.015 x 12,000 = $.0g6/-ton-hr and for 11,250 ton-hrs, the cost would be $1,080. A
savings of $2,520 per year, or a savings of 70%, compared to operating without storage in the small office building.
II. Example II using sodium thiosulfate pentahydrate, a phase change material, PCM-118, which melts at 118 F, or 115 F in this case because of certain impurities, is to store heat for one cloudy day and -two nights during 30~F average temperature weather in a house that takes 50,000 BTU's/hr at O F. Since the design base is 65F, 35/65 x 50,000, or 26,923 BTU's per hour for 40 hours, or 1,076,920 BTUts must be able -to be s-tored.
With 92 BTUs per pound la-tent heat and 18 BTUs per pound sensible heat between 100 F, 1,076,920 BTUs divided by 110 BrrUs per pound shows -that 9,790 pounds of salt are requlred .
Since salts are more conveniently loaded at the factory into tank or tanks 50, the weight of loaded con-tainers is a factor, and a practical limit of about 1,000 pounds for shipping and moving into a house basement is assumed. PCM-118, with a specific gravity of 1.6, will store over 10q,000 BTUs and weigh about 1,000 pounds in a plastic container 2 feet in diame-ter and 4 feet high.
Ten such tanks 50 are needed for this example, ; providing about 1,100,000 BTUs. Heat transfer liquid from the solar collectors at about 1300F enters the tank tubing leaving at 116F for an average of 1259F,= 8 F above the ~usion point at llS~F. Opposite from the other example, charging the tank 50 involves melting liquid around the tubes first which speeds heat transfer by conventional motion of the liquid.
Assuming two sunny days to charge the tanks with heat~ assuming 900 BTUs per square foot per day from the - 18 - ~
': ' ' collectors~ and assuming 25,000 BTUs per hour are needed to hea-t the house during the 8 hour sunny days, -then 1,276~000 BTUs would be needed along with 1,476,000/900 x 2 = 820 sq. ft. of collector. The charging time is 16 hours (the two 8 hour solar days) and the discharging (freezing) time is 40 hours.
Since PCM-115 has a thermal conductivity about 1/3 less than ice, an overall coefficient of abou-t 5 BTU/
hr/ft / F from each side is reasonable, or 10 overall when the salt is solid. The partially liquid phase should be higher but can be assumed to be the same. The calcu-lation for the mat area would be Lo7TU0-- BTUs -- - - = 840 sq. Et.
hr ft2 F x 8 F x 16 hrs and with 4 feet high mats, it would mean 2L0 running feet divided into 10 -tanks, or 21 fee-t length per ma-t. Since the ten tanks are each 2.0' diameter, their area is 3.14 sq. ft., and 3.14 sq, f-t./21 ft. = .150 ft. or 1.8 in. is the width of each coil path of the spiral. Sub-tracting the mat thickness of 0.3 in., the spacer material is 1.5"
thick.
It is to be noted that since the salt shrinks as i-t freezes, the mol-ten salt should more than cover the tubes and the frozen salt will be totally wi-thin the height oE -the tubes in tank 50.
The headers 16 are made of ABS or CPVC plastic pipe with ABS or CPVC nipples 17 solvent ceménted to the headers for low cost, adequate heat resistance and elimin-ation of corrosion. The mat tubing is a medium or high density polyethylene with butyl rubber additive for flexi-bili-ty to aid in making tight sealing joints. Stainless steel U-bends and s-tainless steel tubing clamps are -the only metal in contact with the salt to avoid ga~Lvanic ac-tion.
.
i2~
The examples given are illustrative of various applications that may be made of phase change material thermal energy storage according to my invention. These examples are not to be thoughtof as limiting as to any particular use, dimension, or material. It is intended that various modifications which might readily suggest themselves to those skilled in the art be covered by the scope of the following claims.
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Claims (25)
1. In a heat exchange system capable of transferring the heat of fusion between a moving liquid and a stationary liquid-solid phase change material A. a tank formed of a material capable of with standing constant temperatures above and below the melting point of any phase change material within said tank;
B. a grid of closely-space, small-diameter flexible plastic tubes arranged to give multiple parallel liquid circuits with opposite direction of flow of the liquid in adjoining tubes;
C. spacer medium to provide substantially uniform horizontal spacing of said layers of plastic tubes throughout said tank;
D. a phase change material substantially filling said tank and surrounding said grid of uniformly spaced tubes;
and E. liquid supply and return headers connected to said grid of plastic tubes;
whereby said phase change material may be alternately melted and frozen uniformly throughout the mass of said phase change material as heat is added to and withdrawn from said system.
B. a grid of closely-space, small-diameter flexible plastic tubes arranged to give multiple parallel liquid circuits with opposite direction of flow of the liquid in adjoining tubes;
C. spacer medium to provide substantially uniform horizontal spacing of said layers of plastic tubes throughout said tank;
D. a phase change material substantially filling said tank and surrounding said grid of uniformly spaced tubes;
and E. liquid supply and return headers connected to said grid of plastic tubes;
whereby said phase change material may be alternately melted and frozen uniformly throughout the mass of said phase change material as heat is added to and withdrawn from said system.
2. In a heat exchange system capable of transferring the heat of fusion between a moving liquid and a stationary liquid-solid phase change material as claimed in claim 1 in which the tank is cylindrical with a top opening.
3. In a heat exchange system capable of transferring the heat of fusion between a moving liquid and a stationary liquid-solid phase change material as claimed in claim 1 in which the phase change material is pumped into the tank in liquid phase after the tank has been located for its position of use.
4. In a heat exchange system capable of transferring the heat of fusion between a moving liquid and a stationary liquid-solid phase change material as claimed in claim 1 in which the spacer means consists of a non-corrodible loose light-weight matting rolled up with the grid of plastic tubes into a spiral roll.
5. In a heat exchange system capable of transferring the heat of fusion between a moving liquid and a stationary liquid-solid phase change material as claimed in claim 1 in which the outer surface of the tank is insulated.
6. In a heat exchange system capable of transferring the heat of fusion between a moving liquid and a stationary liquid-solid phase change material as claimed in claim 5 in which the phase change material extends in a narrow projection out through the outer wall and outer insulation so that some of the phase change material will not melt when heat is added to the system thus preserving frozen crystals for nucleation purposes when heat is being extracted from the system.
7. The method of storing coolness and subsequently releasing it for use at a later time in air conditioning, refrigeration, and process functions comprising the steps of:
A. providing an open-top container;
B. uniformly spacing a grid of small diameter flexible plastic tubes within and substantially throughout said container;
C. substantially filling said container and surrounding said tubes with a phase change material (PCM) in its liquid state while leaving a region in the top of said container free of PCM for allowing room for expansion and contraction of the PCM during its change of phase;
D. arranging said tubes to give multiple parallel circuits with opposite direction of flow in adjoining tubes in said tank for providing generally uniform heat energy transfer into and out of said grid of flexible plastic tubes throughout the volume of said PCM;
E. connecting said tubes to supply and return headers;
F. connecting said headers through pumping and heat exchange means;
G. recirculating a liquid through said tubes at a temperature below the phase change temperature of said PCM causing the PCM to solidify; and H. at a later time when cooling is desired recirculating a liquid through said tubes at a temperature above said phase change temperature causing said liquid to be cooled and said PCM to melt, whereby the latent heat of fusion will be withdrawn from the PCM enabling the storing of coolness in the solid state, and subsequently the heat of fusion will flow from the recir-culating liquid to the PCM thereby cooling said liquid.
A. providing an open-top container;
B. uniformly spacing a grid of small diameter flexible plastic tubes within and substantially throughout said container;
C. substantially filling said container and surrounding said tubes with a phase change material (PCM) in its liquid state while leaving a region in the top of said container free of PCM for allowing room for expansion and contraction of the PCM during its change of phase;
D. arranging said tubes to give multiple parallel circuits with opposite direction of flow in adjoining tubes in said tank for providing generally uniform heat energy transfer into and out of said grid of flexible plastic tubes throughout the volume of said PCM;
E. connecting said tubes to supply and return headers;
F. connecting said headers through pumping and heat exchange means;
G. recirculating a liquid through said tubes at a temperature below the phase change temperature of said PCM causing the PCM to solidify; and H. at a later time when cooling is desired recirculating a liquid through said tubes at a temperature above said phase change temperature causing said liquid to be cooled and said PCM to melt, whereby the latent heat of fusion will be withdrawn from the PCM enabling the storing of coolness in the solid state, and subsequently the heat of fusion will flow from the recir-culating liquid to the PCM thereby cooling said liquid.
8. The method of storing coolness and subsequently releasing it for use at a later time in air conditioning, refrigeration, and process functions as claimed in claim 7 in which the tank is cylindrical, is made of plastic and has the multiple parallel circuits lying horizontally.
9. The method of storing coolness and subsequently releasing it for use at a later time in air conditioning, refrigeration, and process function as claimed in claim 8 in which the space means consists of a non-corrodible loose light-weight matting rolled up with the grid of plastic tubes into a spiral roll.
10. The method of storing coolness and subsequently releasing it for use at a later time in air conditioning, refrigeration, and process function as claimed in claim 7 in which the outer surface of the tank is insulated.
11. In a heat exchange system capable of transferring the heat of fusion of a stationary liquid/-solid phase change material between a moving liquid in said system and said phase change material, apparatus comprising:
A. an insulated tank formed of a material capable of withstanding temperatures above and below the melting point of any phase change material within said tank;
B. at least one grid of closely-spaced small diameter flexible synthetic conduits arranged within said tank to give multiple parallel liquid circuits through which said liquid can flow;
C. a phase change material substantially filling said tank and surrounding said grid of synthetic conduits with a region at the top of said tank being free of said phase change material for accommodating expansion and contraction thereof in the tank;
D. said grid of flexible synthetic conduits being arranged for flow of liquid in opposite directions in neighboring pairs of conduits in said grid for providing generally uniform transfer of heat energy between the liquid in the respective pairs of conduits and the phase change material throughout said tank;
E. spacer means in said tank associated with said grid for pro-viding substantially uniform horizontal spacing of said synthetic conduits and permitting free flow of the phase change material in its liquid state throughout said tank;
F. liquid supply and return headers connected to said grid of synthetic conduits for conducting said liquid into and out of said condui-grid;
G. heat supply means for adding heat to said liquid in said system;
H. heat removal means for withdrawing heat from said liquid in said system; and I. pumping means for recirculating said liquid through said conduit grid, headers, heat supply means and heat removal means; whereby said phase change material may be alternately melted and frozen uniformly throughout the mass of said phase change material as heat is added to and withdrawn from the recirculating liquid in said system.
A. an insulated tank formed of a material capable of withstanding temperatures above and below the melting point of any phase change material within said tank;
B. at least one grid of closely-spaced small diameter flexible synthetic conduits arranged within said tank to give multiple parallel liquid circuits through which said liquid can flow;
C. a phase change material substantially filling said tank and surrounding said grid of synthetic conduits with a region at the top of said tank being free of said phase change material for accommodating expansion and contraction thereof in the tank;
D. said grid of flexible synthetic conduits being arranged for flow of liquid in opposite directions in neighboring pairs of conduits in said grid for providing generally uniform transfer of heat energy between the liquid in the respective pairs of conduits and the phase change material throughout said tank;
E. spacer means in said tank associated with said grid for pro-viding substantially uniform horizontal spacing of said synthetic conduits and permitting free flow of the phase change material in its liquid state throughout said tank;
F. liquid supply and return headers connected to said grid of synthetic conduits for conducting said liquid into and out of said condui-grid;
G. heat supply means for adding heat to said liquid in said system;
H. heat removal means for withdrawing heat from said liquid in said system; and I. pumping means for recirculating said liquid through said conduit grid, headers, heat supply means and heat removal means; whereby said phase change material may be alternately melted and frozen uniformly throughout the mass of said phase change material as heat is added to and withdrawn from the recirculating liquid in said system.
12. The method of storing thermal energy and withdrawing it at a later time comprising the steps of:
A. providing an open-top container insulated on its outer surfaces;
B. outside of said container, fabricating a flexible grid containing a multiplicity of closely and uniformly spaced flexible small diameter conduits of synthetic material arranged to provide multiple parallel circuits for liquid flow;
C. connecting said conduits to supply and return headers;
D. positioning said flexible grid within said open-top container with said grid substantially uniformly spaced horizontally within said container and located throughout substantially the entire volume of said container;
E. providing a phase change material outside of said container and having a phase change temperature above the ambient temperature, and heating said material for causing said material to be in its liquid state;
F. substantially filling said container and surrounding said conduits with the phase change material in its liquid state while leaving a space in the top of said container for expansion and contraction of said phase change material;
G. covering said container with a tightly fitting top cover;
H. connecting said headers to pumping and heat exchange means;
I. filling said conduits, headers, pumping and heat exchange means with suitable heat exchange liquid;
J. recirculating the liquid through said conduits at a temperature below the phase change temperature causing the phase change material to solidify;
K. alternately adding heat to and withdrawing heat from the re-circulating liquid causing said material alternately to melt and solidify around said multiplicity of conduits throughout the mass of said phase change material and then released to the recirculating liquid; and whereby when the liquid is not flowing, the heat lost from the phase change material through the outer insulated wall of the tank will cause the phase change material adjoining said wall to solidify, thus preventing con-vection adjacent to the tank wall and creating additional insulation effect by the solidified material for impeding heat flow from the interior region of the material out through the solidified material adjacent to the insulated wall of the container.
A. providing an open-top container insulated on its outer surfaces;
B. outside of said container, fabricating a flexible grid containing a multiplicity of closely and uniformly spaced flexible small diameter conduits of synthetic material arranged to provide multiple parallel circuits for liquid flow;
C. connecting said conduits to supply and return headers;
D. positioning said flexible grid within said open-top container with said grid substantially uniformly spaced horizontally within said container and located throughout substantially the entire volume of said container;
E. providing a phase change material outside of said container and having a phase change temperature above the ambient temperature, and heating said material for causing said material to be in its liquid state;
F. substantially filling said container and surrounding said conduits with the phase change material in its liquid state while leaving a space in the top of said container for expansion and contraction of said phase change material;
G. covering said container with a tightly fitting top cover;
H. connecting said headers to pumping and heat exchange means;
I. filling said conduits, headers, pumping and heat exchange means with suitable heat exchange liquid;
J. recirculating the liquid through said conduits at a temperature below the phase change temperature causing the phase change material to solidify;
K. alternately adding heat to and withdrawing heat from the re-circulating liquid causing said material alternately to melt and solidify around said multiplicity of conduits throughout the mass of said phase change material and then released to the recirculating liquid; and whereby when the liquid is not flowing, the heat lost from the phase change material through the outer insulated wall of the tank will cause the phase change material adjoining said wall to solidify, thus preventing con-vection adjacent to the tank wall and creating additional insulation effect by the solidified material for impeding heat flow from the interior region of the material out through the solidified material adjacent to the insulated wall of the container.
13. In a heat exchange system capable of transferring the heat of fusion of a stationary liquid-solid phase change material between a moving liquid in said system and said phase change material, apparatus as claimed in Claim 11, in which:
said spacer means is fibrous and low density and has sufficiently large spaces therein for permitting said free flow of the phase change material in its liquid state.
said spacer means is fibrous and low density and has sufficiently large spaces therein for permitting said free flow of the phase change material in its liquid state.
14. In a heat exchange system capable of transferring the heat of fusion of a stationary liquid solid phase change material between a moving liquid n said system and said phase change material, apparatus as claimed in Claim 13, in which:
said spaces in said spacer means are also sufficiently small for preventing crystals of the solidified phase change material from falling through to the bottom of the tank.
said spaces in said spacer means are also sufficiently small for preventing crystals of the solidified phase change material from falling through to the bottom of the tank.
15. In a heat exchange system capable of transferring the heat of fusion of a stationary liquid-solid phase change material between a moving liquid in said system and said phase change material, apparatus as claimed in Claim 11, in which:
said insulated tank is at least two feet in diameter and at least four feet high.
said insulated tank is at least two feet in diameter and at least four feet high.
16. In a heat exchange system capable of transferring the heat of fusion of a stationary liquid-solid phase change material between a moving liquid in said system and said phase change material, apparatus as claimed in Claim 15, in which:
said insulated tank is sufficiently large to hold 12 cubic feet of the phase change material.
said insulated tank is sufficiently large to hold 12 cubic feet of the phase change material.
17. The method of storing thermal energy and withdrawing it at a later time as claimed in Claim 12 in which:
said step (E) of substantially filling said container and surrounding said conduits with a phase change material in its liquid state is carried out by further steps of:
delivering the phase change material in its liquid state in a heated tank truck to the site where said container is located, and pumping the phase change material in its liquid state from the heated tank truck through a hose into said container.
said step (E) of substantially filling said container and surrounding said conduits with a phase change material in its liquid state is carried out by further steps of:
delivering the phase change material in its liquid state in a heated tank truck to the site where said container is located, and pumping the phase change material in its liquid state from the heated tank truck through a hose into said container.
18. Heat storage tank apparatus for temporarily storing heat energy comprising:
A. a thermally insulated tank providing convenient access to its interior;
B. liquid supply and return headers extending within said tank;
C. at least one grid of closely-spaced small diameter conduits of flexible plastic material connected at their ends to the respective headers and arranged within said tank to give multiple parallel liquid circuits through which a heat-transfer liquid can flow;
D. said grid being a rolled-up grid of closely-spaced parallel flexible parallel conduits having a vertical axis and the respective layers of said rolled-up grid having a spiral configuration as seen from above;
E. said liquid flow being in opposite directions in neighboring conduits in each respective layer of said spiral configuration;
F. a liquid/solid phase change material substantially filling said tank and surrounding said grid of closely-spaced small diameter conduits;
G. spacer means in said tank associated with said grid for pro-viding substantially uniform horizontal spacing of said small diameter conduits of plastic material and permitting free flow of the phase change material in its liquid state throughout said tank; and H. said insulated tank, said flexible plastic conduits and said headers being formed of materials capable of withstanding temperature above and below the melting point of said liquid/solid phase change material;
whereby said phase change material may be alternately melted and frozen throughout the interior of the mass thereof as heat is added thereto or withdrawn therefrom by circulating heat-transfer liquid through said conduit grid.
A. a thermally insulated tank providing convenient access to its interior;
B. liquid supply and return headers extending within said tank;
C. at least one grid of closely-spaced small diameter conduits of flexible plastic material connected at their ends to the respective headers and arranged within said tank to give multiple parallel liquid circuits through which a heat-transfer liquid can flow;
D. said grid being a rolled-up grid of closely-spaced parallel flexible parallel conduits having a vertical axis and the respective layers of said rolled-up grid having a spiral configuration as seen from above;
E. said liquid flow being in opposite directions in neighboring conduits in each respective layer of said spiral configuration;
F. a liquid/solid phase change material substantially filling said tank and surrounding said grid of closely-spaced small diameter conduits;
G. spacer means in said tank associated with said grid for pro-viding substantially uniform horizontal spacing of said small diameter conduits of plastic material and permitting free flow of the phase change material in its liquid state throughout said tank; and H. said insulated tank, said flexible plastic conduits and said headers being formed of materials capable of withstanding temperature above and below the melting point of said liquid/solid phase change material;
whereby said phase change material may be alternately melted and frozen throughout the interior of the mass thereof as heat is added thereto or withdrawn therefrom by circulating heat-transfer liquid through said conduit grid.
19. Heat storage tank apparatus as claimed in Claim 18, in which:
G. said grid is rolled into a spiral roll configuration as seen in cross section looking downwardly.
G. said grid is rolled into a spiral roll configuration as seen in cross section looking downwardly.
20. Heat storage tank apparatus as claimed in Claim 19, in which:
H. said spacer means is low density matting having multiple spaces therein which has been rolled into said spiral roll configuration together with said grid, said matting and said grid being in alternate spiral layers as seen in cross section.
H. said spacer means is low density matting having multiple spaces therein which has been rolled into said spiral roll configuration together with said grid, said matting and said grid being in alternate spiral layers as seen in cross section.
21. Heat storage tank apparatus as claimed in Claim 19, in which:
I. said liquid supply and return headers extend generally vertically within said tank, and each of said conduits extends generally in a horizontal plane in a spiral having a reversal of direction near the center of said spiral roll configuration with the liquid flow in each conduit travelling generally in a horizontal plane from the supply header along an inward spiral path through the phase change material to said reversal of direction and then travelling in a generally horizontal plane along an outward spiral path through the phase change material, said outward spiral path being near to said inward spiral path.
I. said liquid supply and return headers extend generally vertically within said tank, and each of said conduits extends generally in a horizontal plane in a spiral having a reversal of direction near the center of said spiral roll configuration with the liquid flow in each conduit travelling generally in a horizontal plane from the supply header along an inward spiral path through the phase change material to said reversal of direction and then travelling in a generally horizontal plane along an outward spiral path through the phase change material, said outward spiral path being near to said inward spiral path.
22. Heat storage tank apparatus for temporarily storing heat energy comprising:
A. a thermally insulated tank providing convenient access to its interior;
B. liquid supply and return headers extending within said tank;
C. at least one grid of closely-spaced small diameter conduits of flexible plastic material connected at their ends to the respective headers and arranged within said tank to give multiple parallel liquid circuits through which a heat-transfer liquid can flow;
D. a liquid/solid phase change material substantially filling said tank and surrounding said grid of closely-spaced small diameter conduits;
E. spacer means in said tank associated with said grid for pro-viding substantially uniform horizontal spacing of said small diameter conduits of plastic material and permitting free flow of the phase change material in its liquid state throughout said tank;
F. means for preserving a small portion of the phase change material in its solid state in contact with the main body of the phase change material when the phase change material is being changed into its liquid state by adding heat energy thereto, thereby preserving frozen crystals of the phase change material for serving nucleation purposes when the phase change material is later being changed into its solid state by extracting heat energy there-from;
G. said insulated tank, said flexible plastic conduits and said headers being formed of materials capable of withstanding temperature above and below the melting point of said liquid/solid phase change material;
whereby said phase change material may be alternately changed into a liquid state and changed into a solid state throughout the interior of the mass thereof as heat energy is added thereto or withdrawn therefrom by cir-culating heat transfer liquid through said conduit grid.
A. a thermally insulated tank providing convenient access to its interior;
B. liquid supply and return headers extending within said tank;
C. at least one grid of closely-spaced small diameter conduits of flexible plastic material connected at their ends to the respective headers and arranged within said tank to give multiple parallel liquid circuits through which a heat-transfer liquid can flow;
D. a liquid/solid phase change material substantially filling said tank and surrounding said grid of closely-spaced small diameter conduits;
E. spacer means in said tank associated with said grid for pro-viding substantially uniform horizontal spacing of said small diameter conduits of plastic material and permitting free flow of the phase change material in its liquid state throughout said tank;
F. means for preserving a small portion of the phase change material in its solid state in contact with the main body of the phase change material when the phase change material is being changed into its liquid state by adding heat energy thereto, thereby preserving frozen crystals of the phase change material for serving nucleation purposes when the phase change material is later being changed into its solid state by extracting heat energy there-from;
G. said insulated tank, said flexible plastic conduits and said headers being formed of materials capable of withstanding temperature above and below the melting point of said liquid/solid phase change material;
whereby said phase change material may be alternately changed into a liquid state and changed into a solid state throughout the interior of the mass thereof as heat energy is added thereto or withdrawn therefrom by cir-culating heat transfer liquid through said conduit grid.
23. The method for freezing ice solid in a vertical cylindrical plastic tank without creating lateral expansion forces in the tank for cooling storage for use in air conditioning a building using electrical energy at "off peak"
rates including the steps of:
uniformly spacing a grid of small diameter spaced flexible plastic tubes within and substantially throughout the tank in the main lower portion of said tank;
arranging said tubes to give multiple parallel circuits with op-posite direction of liquid flow in adjoining tubes;
connecting said tubes to supply and return headers;
filling said tank with water in the main lower portion of said tank while leaving he top portion of the tank free of water to accommodate ex-pansion as the water is frozen into solid ice in the tank;
connecting said headers through electrically energized pumping and refrigeration means located outside of said tank and arranged for refrigerating anti-freeze liquid;
electrically energizing said pumping and heat exchange means during "off peak" hours of a 24 hour day for recirculating the anti-freeze liquid through said tubes at a temperature below the freezing point of water for causing the water in said plastic tank to freeze to solid ice around all of said adjoining tubes uniformly throughout the whole volume of water in said tank during said "off peak" hours;
said freezing of the water to solid ice around all of said adjoining tubes throughout the whole volume of water in said tank squeezing the extra water volume upwardly due to expansion of the freezing ice and thereby pre-venting rupture of the plastic tank as the whole volume of water freezes to solid ice;
during daylight hours when air conditioning is desired in the building recirculating the anti-freeze liquid through said tubes embedded in said solid ice and through second heat exchange means;
blowing building air past said second heat exchange means for cooling the building air by transferring heat energy from the building air into said recirculating liquid and for transferring heat energy from said recirculating liquid into the ice in said tank;
thereby providing air conditioning in the building while avoiding the use of electrical energy during hours of "peak" rates, and thereby advantageously avoiding rupture of the tank even though the water is frozen solid therein.
rates including the steps of:
uniformly spacing a grid of small diameter spaced flexible plastic tubes within and substantially throughout the tank in the main lower portion of said tank;
arranging said tubes to give multiple parallel circuits with op-posite direction of liquid flow in adjoining tubes;
connecting said tubes to supply and return headers;
filling said tank with water in the main lower portion of said tank while leaving he top portion of the tank free of water to accommodate ex-pansion as the water is frozen into solid ice in the tank;
connecting said headers through electrically energized pumping and refrigeration means located outside of said tank and arranged for refrigerating anti-freeze liquid;
electrically energizing said pumping and heat exchange means during "off peak" hours of a 24 hour day for recirculating the anti-freeze liquid through said tubes at a temperature below the freezing point of water for causing the water in said plastic tank to freeze to solid ice around all of said adjoining tubes uniformly throughout the whole volume of water in said tank during said "off peak" hours;
said freezing of the water to solid ice around all of said adjoining tubes throughout the whole volume of water in said tank squeezing the extra water volume upwardly due to expansion of the freezing ice and thereby pre-venting rupture of the plastic tank as the whole volume of water freezes to solid ice;
during daylight hours when air conditioning is desired in the building recirculating the anti-freeze liquid through said tubes embedded in said solid ice and through second heat exchange means;
blowing building air past said second heat exchange means for cooling the building air by transferring heat energy from the building air into said recirculating liquid and for transferring heat energy from said recirculating liquid into the ice in said tank;
thereby providing air conditioning in the building while avoiding the use of electrical energy during hours of "peak" rates, and thereby advantageously avoiding rupture of the tank even though the water is frozen solid therein.
24. Heat storage tank apparatus as claimed in Claim 18, in which:
the density of the phase change material is greater than the rolled-up grid of plastic conduits together with said elongated spacer members whereby the grid and elongated spacer members will tend to float up vertically when the phase change material is in its liquid state in said tank; and a rigid tank cover in retaining relationship with said elongated spacer members, whereby said rolled-up grid is prevented from rising up in spite of the buoyancy effect of the phase change material when it is in its liquid state.
the density of the phase change material is greater than the rolled-up grid of plastic conduits together with said elongated spacer members whereby the grid and elongated spacer members will tend to float up vertically when the phase change material is in its liquid state in said tank; and a rigid tank cover in retaining relationship with said elongated spacer members, whereby said rolled-up grid is prevented from rising up in spite of the buoyancy effect of the phase change material when it is in its liquid state.
25. In a heat exchange system capable of transferring the heat of fusion of a stationary liquid/solid phase change material between a moving liquid in said system and said phase change material, apparatus as claimed in Claim 11, in which:
more than one grid of closely-spaced small diameter synthetic con-duits are arranged within said tank to give multiple parallel liquid circuits through which said liquid can flow;
whereby in case of a leak in one such grid of conduits rendering the heat exchange system inoperable and thereby causing the phase change material to cool and solidify, said leaking grid can be closed off and another grid in said tank can be used to circulate said liquid for heating and melting the phase change material so that the liquefied phase change material can be pumped out of the tank as a liquid to allow repairs to be carried out on said leaking grid.
more than one grid of closely-spaced small diameter synthetic con-duits are arranged within said tank to give multiple parallel liquid circuits through which said liquid can flow;
whereby in case of a leak in one such grid of conduits rendering the heat exchange system inoperable and thereby causing the phase change material to cool and solidify, said leaking grid can be closed off and another grid in said tank can be used to circulate said liquid for heating and melting the phase change material so that the liquefied phase change material can be pumped out of the tank as a liquid to allow repairs to be carried out on said leaking grid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79091977A | 1977-04-26 | 1977-04-26 | |
| US790,919 | 1977-04-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1115264A true CA1115264A (en) | 1981-12-29 |
Family
ID=25152122
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA299,798A Expired CA1115264A (en) | 1977-04-26 | 1978-03-28 | Method and system for the compact storage of heat and coolness by phase change materials |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1115264A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110770524A (en) * | 2017-06-01 | 2020-02-07 | 松耐普有限公司 | Active crystallization control in phase change material thermal storage systems |
| CN111189348A (en) * | 2020-01-20 | 2020-05-22 | 中国科学院过程工程研究所 | Phase change energy storage box and use method thereof |
-
1978
- 1978-03-28 CA CA299,798A patent/CA1115264A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110770524A (en) * | 2017-06-01 | 2020-02-07 | 松耐普有限公司 | Active crystallization control in phase change material thermal storage systems |
| CN110770524B (en) * | 2017-06-01 | 2023-12-12 | 松耐普有限公司 | Active crystallization control in phase change material thermal storage systems |
| CN111189348A (en) * | 2020-01-20 | 2020-05-22 | 中国科学院过程工程研究所 | Phase change energy storage box and use method thereof |
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