GB2436801A

GB2436801A - Electrically heated hot water bottle and docking station

Info

Publication number: GB2436801A
Application number: GB0705842A
Authority: GB
Inventors: Carl Ernest Alexander
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-04-08
Filing date: 2007-03-23
Publication date: 2007-10-10
Also published as: GB0607121D0; GB0705842D0

Abstract

A bedside bed-warming system includes reheating stations that electrically heat one or more compatible hot water bottle-like modules up to a safe temperature. Direct connection or inductive methods are preferred for power transfer. Latent heat evolution at about 45 deg C 495 from capsules holding a wax is a preferred way to simulate a higher effective specific heat than water at a steady temperature, although water will do. Another method is use of an internal battery that has been recharged, then discharged through a heater inside the module under electronic temperature-regulated control.

Description

« •

2436801

TITLE Improvements in bed warmers

FIELD

5 This invention relates to a bedside bed-warming means analogous to the hot water bottle.

BACKGROUND

This invention relates to bed-warming devices that use portable modules that receive energy, and then deliver that energy to the local environment as heat. A well-known version of this sort of device 10 is the domestic hot-water bottle which evolved from bedpans containing hot coals when rubber bottle technology was developed. Hot-water bottles have a number of disadvantages including: (1) the amount of heat stored is good for perhaps two or three hours only and drops continuously during use so encouraging people to start at too high a temperature, (2) the initially filled hot water bottle is capable of causing tissue damage by overheating body parts in contact, especially if used with 15 elderly or unconscious persons, (3) the process of filling a hot-water bottle with hot water often results in spilt hot water, while air rushes out of the bottle during filling, causing pain or scalding to the person filling the bottle, and (4) the water heated for use is mostly wasted. The inventor expects that rises in the cost of energy will tend to encourage the use of hot-water bottles and analogous devices as opposed to whole-house heating, along with thermally insulating clothing, coverings and 20 bedding.

DEFINITIONS

"Portable heating means" refers to a derivative of a hot water bottle modified to be used as part of

1

1 «

the invention.

25 "Rewarming station" refers to a closable cabinet within a bed heating system, each station including a separately temperature-regulated energy supply for rewarming a portable heating means.

"Bed heating system" refers to a combination of at least one rewarming station (usually two) and a supply of the portable heating means. This is usually a bedside appliance but may be used in an institution providing bed care to a number of people, with perhaps 6-12 individual reheating 30 stations..

"Effective Specific Heat "describes the amount of heat output required to cause unit mass of a substance to fall from a first to a second temperature and if that fall includes a change of state then the descriptor includes the amount of heat evolved during a change of state. In a variation adapted to describe instances where the unit mass includes electrochemical storage of energy (battery) and 35 active electronics means to controllably release said energy, effective specific heat measures the amount of heat evolved from an item of a certain weight while the battery is controllably discharged from an initial full charge. The term also includes "normal" specific heat of substances where no change of state is involved.

40 PRIOR ART

Schnoor in US 2004/0102823 describes a flat bag, holding a mixture of vegetable oil and paraffin wax, for use as a heating pad. Noppel et al in US 5069208 describe a cooling or heating pad including cells containing material that can change state and take in or supply latent heat. Feback et al in US 6615906 describe a "latent heat body" somewhat optimised to store latent heat but without 45 focus on heating pads for bed warmer use. Boys in US 5450305 describes a variety of suitable induction-heating power supplies, (see Fig 6 herein).

OBJECT

It is an object of this invention to provide an improved device or combination of devices for bed

2

50

warming purposes, or at least to provide the public with a useful choice.

STATEMENT OF INVENTION

In a first broad aspect this invention provides a bedside system or bed-warming device including at least one rewarming station each capable of re-warming a portable, sealed heat source herein called 55 a "portable heating means" capable of releasing heat during use though constrained to release it at no more than a predetermined, safe temperature. A cold portable heat source is placed inside the station and left to reach an operating temperature.

Optionally each bed warming device contains a mass of material having an effective specific heat at least about the same as for water. (Equivalent: 0.238 kJ/kg per degree C).

60 In one option, the latent heat properties of selected materials are employed in order to extend the duration of supply of heat from a given mass at a medically safe temperature.

In a related aspect, the invention provides a sealed bed warmer in a configuration physically similar to that of a known hot water bottle, including a granulated form of a substance (preferably a wax or mixture of waxes) that melts and freezes within a desired temperature zone; the substance being 65 restricted within a plurality of envelopes thereby forming filled cells, and a fluid for transporting heat about the contents selected from a range including water and oil.

In a first alternative version, the sealed bed warmer is provided with externally accessible electric contacts leading to an internal resistive wire heater so that the contents of the bed warmer may be warmed from time to time by the passage of electricity derived from an external supply of 70 electricity.

Preferably the external supply is at a low voltage hence providing compatibility including maximum power transfer conditions with lead-acid storage cells and/or safety considerations. Optionally the external supply is at a higher voltage so that current loading at connectors is less..

Preferably the external supply is physically brought to a connector compatible with that of the 75 portable heat source and is located within a closable rewarming station having thermal insulation properties so that the bed warmer to be heated is held warm within the closed box during and after

3

the heating process until it is ready for use.

Preferably the internal resistive wire heater is in series with a reversible thermally actuated switching means, so that current flow in the wire is interrupted as soon as the thermally actuated 80 switching means has been sufficiently heated to enter an open-circuit state and so that the bed warmer cannot be heated above a safe predetermined temperature.

Optionally an internal, thermally actuated switch or resistor is connected separately to external control means within the rewarming station.

Preferably the presence of the internal wire prevents the bed warmer from being heated in an 85 ordinary microwave oven to an unsafe temperature.

In a second alternative version, the sealed bed warmer is provided with an internal resistive wire heater in the form of a closed loop having an area, so that the contents of the bed wanner may be wanned by inductive power transfer from time to time by collecting a changing magnetic flux within the area and converting it into electricity so that the bed warmer may be heated from the exterior 90 without direct electrical contact.

Preferably the closed loop includes a thermally actuated switching means so that the maximum temperature is able to be limited.

Optionally the closed loop includes a tuning capacitor so that the closed loop may serve as a resonant secondary winding, in which case the thermally actuated switching means may act to 95 destroy resonance.

Preferably the inductive power transfer is carried out at a frequency of over 20 kHz.

In another option, the sealed bed warmer includes electrochemical reversible storage means comprising at least one rechargeable battery and means for controllably discharging said battery through an included resistance so as to maintain the sealed bed warmer at or about a predetermined 100 temperature, using an associated temperature sensor and control means..

Preferably the sealed bed warmer includes a loop of wire capable of serving both as an inductive power transfer pickup, as previously described in this section, during charging of the battery, and as a heat dissipating device during discharge, so that the sealed bed warmer may be (reloaded from the

4

exterior without physical contact.

105 Alternatively a direct electrical connection can be used during charging of the battery

In one option a charged bed warmer according to the fourth version is provided with externally accessible control means that is capable of switching off the charged bed warmer until required.

PREFERRED EMBODIMENT

110 The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention.

Throughout this specification unless the text requires otherwise, the word "comprise" and variations such as "comprising" or "comprises" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of 115 integers or steps.

DRAWINGS

Fig 1: is a diagram showing a sealed hot water bottle (portable heat source) having a fill including cells holding material having desired latent heat properties.

120 Fig 2: is a diagram showing an unsealed (closable) hot water bottle including cells holding material having desired latent heat properties.

Fig 3: shows a sealed hot water bottle (portable heat source) including within the fill a closed loop of wire.

Fig 4: shows a closed loop of wire with series components including a thermal cutout.

125 Fig 5: shows an open loop of wire with external electrical connections and a thermal cutout.

Fig 6: shows a prior-art (Boys) inductive heating circuit having a resonant primary loop 10b

5

(provided by way of example).

Fig 7: shows a cross-section through a re-heating bedside unit including (in this embodiment) an inductive heating power supply.

130 Fig 8: is a block diagram of a bed wanner employing a rechargeable battery as a source of energy.

Fig 9: is a perspective view of one embodiment of an actual bedside unit.

There is an overall desire to economically provide an easily replenishable bed-warming module or portable heat source that delivers heat at a safe temperature in a convenient and safe manner as a substitute for the well-known rubber hot water bottle. Some ways to exploit Effective Specific Heat 135 held by a mass are:-

1. Use of specific heat of water or similar (reversible). The specific heat of water is 0.238 kJ/kg per degree, hence a 30 degree fall in temperature releases about 7.14 kJ per kilogram. (Examples 1, 1A, IB)

2. Use of latent heat of e.g. solidifying wax or other suitable material (reversible). The Effective 140 Specific Heat, if just the latent heat is exploited, is (for paraffin wax) about 60 kJ/kg over the small eventual change in temperature. (The Effective Specific Heat is clearly higher than that for cooling water but that paraffin wax example has a higher than desirable melting point, so is indicative only.) On its own, this aspect may be covered by the prior art.

3. Use of heat evolved by a chemical reaction (not reversible, dangerous, and justified for search 145 and rescue or military applications, rather than in domestic areas.) For example the burning of paraffin wax releases about 42,000 kJ/kg although only some of that heat would be captured under a controlled burning process.

4. Conversion of stored electricity into heat (using a battery that is preferably rechargeable). The specific energy of a fully charged Ni-Cd battery is about 45 kJ/kg and newer types of battery

150 such as lithium can store several times that amount. A Ni-Cd battery can be fully charged and then discharged perhaps 700-1000 times in its life and electronic control of the heat output gives a safe and controllable mode of usage. The power may be dissipated as heat within a portable heat source containing a battery, or carried by connecting wires to warmed clothing. All possible inefficiencies during discharge (such as within semiconductors) are converted to heat and are

6

155 captured as useful output in this application. The "bed feel" problems of a hot water bottle analogue containing palpable hard lumps may be overcome.

EXAMPLE 1

Fig 1 shows a bed warmer or portable heat source comprising a rubber or like envelope 100, having 160 a handle 102 and a hollow interior filled with cells 101 each cell holding an amount of paraffin wax (or other latent heat-effective material), separated by water (or an oil) which serves to redistribute the heat. This portable heat source may be heated by thermal contact or by microwave energy but in those cases there is no inherent protection against overheating. To start with the external appearance of the invention as put in practice, Fig 9 shows the appearance of a finished bedside unit 900, 165 including support legs 901, two reheating stations (902, 903) with lids 904, and a control panel 905 including, in this example (from top), a timer, a temperature control (which may prove incompatible with safety requirements), and means to charge the portable heat source more quickly. The power cord 907 is also visible. A lifting handle (906) of one portable heat source is also shown. The outer case 908 is thermally, electrically, and if necessary, electromagnetically screened. Similar units 170 could be made to be mounted under a shelfor in other convenient places. A corresponding portable heat source (hot water bottle) is shown at 1000; the majority of the surface 1001 being waterproof, flexible, and of relatively low thermal conductivity (like a hot water bottle cloaked in a knitted woollen cover) and this example including a special connector 1002 (though this particular example with sharp edges may be lacking in "bed feel". Fig 11 shows an institutional version 1100, 175 configured for mounting on a wall. 1101 is one of nine closable lids, each bearing an example control panel 1102 with indicator lights to show when the contents are up to the predetermined temperature. One portable heat source (hot water bottle) is shown extending from an opened lid at 906.

This invention relates to a bedside system relying on portable heat sources each of which comprises 180 a mass having a high effective specific heat, at least as high as water, as exhibited at a preferred working temperature of at most about 45-65 deg C (the priority being, of course, not to provide a dangerously hot bed-warmer in contact with a person Scalds and bums can be produced. The threshold of normal subjects for pain from hot objects is at about 52 deg C, at which temperature protein degradation commences, so a bed warming device should not be used at or over this

7

185 temperature. Furthermore, the poor peripheral circulation of some persons including diabetes patients raises the risk of tissue damage with bed warmers at even under 45 deg C and many hospitals and care providers simply will not use hot water bottles at all. The inventor accepts that temperature selection is the domain of medical care experts and simply provides a personal contact heating system, the maximum temperature of which can be adjusted to an accurate [redetermined 190 value which, it is hoped, will lower some of the barriers to the use of hot water bottles. The means for adjustment may be concealed from unauthorised access.

Reference is made herein to a "wax" as being a material that melts or freezes in the desired range at normal pressures. Preferred materials will be non-toxic, non-allergenic, non-reactive and generally safe and acceptable, and will preferably exhibit a large latent heat of melting/freezing (which is, of 195 course, reversible) in terms of joules per kilogram. Different waxes can be mixed together to approximate a desired melting temperature although the sharpness of the melting point may be lost. Apart from waxes (such as paraffin (hydrocarbon) or bee wax there are other acceptable materials including various "plastics" which are hereby imported into the ambit of the invention. For example, the components of at least some types of "hot glues", or chemical modifications thereof, are or can 200 become suitable. Eutectic mixtures of metal salts also have latent heat properties; this specification embraces all materials having like properties. On reduction of temperature (as when in use) the temperature of the portable heat source usefully remains fairly constant for a period, while the wax gradually freezes and latent heat is evolved, thereby providing a high Effective specific heat over a limited range. Paraffin wax which may be used in a low melting-point mixture is a potentially 205 combustible material if it escapes, but is otherwise not dangerous or toxic.

In this Example, a rubber (or equivalent waterproof flexible material) portable heat source reasonably similar in external appearance and characteristics to existing water-filled hot water bottles is provided, but in a sealed, closed configuration containing (a) water holding in free suspension (b) optionally also closed capsules or cells of a mixture of wax and (c) an optional air 210 pocket, each cell having a volume of perhaps about 1 ml so that the user feel of the hot water bottle is reasonably similar to that of existing water-filled hot water bottles. The water is provided as a heat transfer medium for capsules containing wax, or as a material having latent heat in its own right. The cells are preferred so that the wax does not congeal as one solid lump as would happen without use of cells. The heat diffusion distance into the centre of any one cell is small, so that the 215 overall temperature response is rapid. An oil could be substituted for the water. A partially insulating jacket made for example of a woollen or polyester fabric may be provided over the outer

8

rubber (or like) surface of the hot water bottle in order to extend its operating (cooling) period, reduce inherent danger of tissue damage, improve the "feel", and make it impractical to overheat the hot water bottle by immersion in a container of hot water.

220 A cell or capsule holding wax as intended for use herein in large numbers can be made for example by heat-sealing a pellet of wax into a polyethylene tube to form short packets (cells) holding wax, which may be separated apart or remain in the form of a segmented tube.

The warming (and, by symmetry) the cooling behaviour, in reverse of an Example 1 portable heat source during application of a constant amount of energy from cold is as follows:

225 1. The temperature of the bottle rises at a steady rate dependent on the overall specific heat and amount of the mixed water and suspended closed blisters of frozen wax until...

2. the wax starts to melt at its melting point, whereupon the temperature of the portable heat source remains relatively constant for a period while the input energy is converted as latent heat into melting the wax present, until ...

230 3. all the wax has melted, whereupon the temperature of the portable heat source rises again. At least one type of thermal cutout may be relied on simultaneously, to avoid overheating.

Fig 2 shows a variant portable heat source again employing the fill of wax capsules and allowing conventional addition of hot water from an external supply through a funnel 201 and removable seal 202 in order to add heat in an uncontrolled manner to the bed warmer. A sieve 203 prevents escape 235 of the cells holding wax during emptying. It may be found that several replacements of hot water are required in order to cause sufficient wax to melt, and then the heated bed warmer has the advantage that it will last longer in use than a water-only version. Clearly, this option undoes several of the advantages (such as no splashing or water waste) of the invention cited elsewhere in this specification, but does teach another, low-technology method of putting energy into the portable 240 heat source.

Figs 3, 4 and 5 show more preferred embodiments of this invention. In all cases, electricity is brought into the portable heat source during a rewarming process, and converted into heat by conventional means such as by passing it through an internal, immersed heating wire 301 having a resistance. (Preferably this wire is lightly yet effectively insulated in order to protect against 245 corrosion or electrolytic effects). For example, if a 12 volt DC supply was connected to an internal

9

coil of wire having a 1 ohm total resistance then 144 watts of heat would be generated within the wire by the 12 amperes flowing, and this would soon warm a thermally enclosed bed warmer. Optionally, one or more conventional resistors may be used for the dissipation of heat, but wire on its own is effective, better distributed, and cheaper. It is desirable that the electric current 250 connections be protected from unauthonsed user modification. The inventor thinks that having portable heat sources heated or recharged by non-approved means (especially with mains electricity) is dangerous. Electrocution, steam explosions, and scalding of end-users can happen.. The electrical contents might be complementary to other connectors, or they might preferably be disguised as something else (such as brass edging around the bed warmer) yet still remain usable by the purpose-255 designed heating unit. Safety interlocks may be used. It is clear that once a resistively heated bed warmer of this type is disconnected from the heating current, it immediately becomes electrically quiescent and electrically safe for use in a bed even if there are one or more exposed connectors. Reference to 12 volts is made in part because this bed heating system may be run from a 12 volt storage battery kept charged by sustainable energy. Other voltages, such as 110 or 220 volts may be 260 less demanding of connector capacity; yet more demanding of wire insulation.

The active components (wax-filled cells, wire coil, water) may be supplied for assembly pre-packed in a bladder 302 such as a sealed plastic bag ready to be inserted into a sealed rubber (or the like) exterior bag, useful if a rubber goods factory making portable heat sources is separate from another factory.

265 In order to help prevent these portable heat sources from being reheated and overheated in a microwave oven, which may lead to unsafe in-bed conditions, or even steam explosions inside the oven, the coil serves as a metallic energy absorber immersed inside the bottle.

In Fig 3, a portable heat source 100 (as per Fig 1) is shown including a closed loop of wire 301 that may be supplied with electricity by inductive power transfer (also see Figs 4, 6 and 7) or by direct 270 physical connection (Fig 5) using connectors 501 and 502 to an external source. In Fig 4, the closed loop of wire is depicted with a series-connected thermal cutout device 402, which is preferably a switch that opens if the surrounding temperature exceeds a predetermined level such as 46 deg C. The switch would close again when the temperature drops to 45 deg C for example, so that if the bed warmer was held within an activated rewarming unit it would hold its temperature at between 45 275 and 46 deg C until taken out for use. (Either the switch carries the heating current, or it may be separately connected through the connector to a control input of the heating supply so that its contacts do not carry a heavy current. In that case it may be a thermistor, not a switch). Fig 4 also

10

shows an optional tuning capacitor 401 which has the effect of making the wire loop a resonant secondary at some intended frequency, and thereby enhancing the transfer of inductive power by 280 increasing the maximum current. The capacitor is incompatible with direct current heating and would not be used in a Fig 5 embodiment. When in use, significant resonant current flows in the coil causing ohmic losses in the wire itself (including skin effect, if high frequency currents exist) that results in heating of the surrounding water and hence the wax inside the blisters.

Inductive power transfer techniques, using a circuit such as the prior-art example shown in Fig 6, 285 results in the formation of an alternating magnetic field at perhaps 25 to 50 kHz that is generated inside a bedside wanning unit (Fig 7). The alternating magnetic field that is radiated from the coil 10b passes through the bed warmer and intersects the coil 301 inside the bed warmer, generating electricity within the coil and having the effect of moving energy into the wanning module. This technique has the advantage that no metal parts traverse the wall of the wanning module which may 290 be a rubber bag as used in conventional hot water bottles, but is permanently sealed. There is no need to ensure that a physical electrical connection occurs. Of course, ordinary electric connectors could be used while remaining within the ambit of the invention - as per Fig 5. It should be noted that a physical connection carrying reasonably high currents (such as 12 amperes) may generate intense local heat if a poor connection is made and this heat may damage the bed wanner wall or 295 cause a fire. In addition, users cannot maliciously tamper with the wanning bed warmer such as to overheat it because they have no electrical connections to access.

Therefore a bed warmer replenishment unit (bedside device) comprises part of the overall invention and would be physically and electrically matched to the warming modules (portable heat sources). Externally, the replenishment unit (see section 700 in Fig 7) would appear similar in all 300 embodiments and would contain one or two pockets (rewarming stations) 703 for holding portable heat sources 100, and portable heating means (e.g. primary winding 10b) but those could also be heating wires that simply heat the interior of the replenishment unit) for heating the bed warmers by contact when placed inside the pockets. That may be too slow a process. A 24 hour time switch 705 may be used to disable the bed wanner until the time switch is activated; when the user expects to 305 go to bed or shortly before, so that less electricity is wasted.

A typical bedside system is located by a person's bed and would restore the energy within a bed wanner in about 5 to 30 minutes, whereupon the person can lift the protective lid 701 and remove a bed warmer. Through the night, if one bed wanner goes cold, the person would reach into the box, remove the other one, and put the cold one back. Termination of replenishment can be controlled

11

310 electronically such as by sensing battery charge amount, or internal temperature. Two stations provide for a double bed, for example. Many stations might be used in a rest home.

Fig 6 shows an example inductive heating power supply circuit and this prior art circuit will be described by way of example. 15B represents a DC power source. 12B and 14 are high-inductance coils used to supply current to the resonant circuit, made up of capacitor 13b and inductance 10b 315 (shown in section as "OOO" and "XXX" in Fig 7). Either side of the resonant circuit is connected to the return supply of the power source alternately, at or about the resonant frequency of the circuit, through power switching devices 18b and 18b', which are activated as required by controller 19b.

A circuit of this type can be adapted for the present application such as by including a load detector, having the effect of switching the circuit off unless a secondary winding is present within the space 320 covered by a field generated in the primary winding, and can be provided with 24-hour timing circuits as previously mentioned. The lid 701 should be connected to a switch to turn off the primary circuit if the lid is opened. The exterior of the bedside system 700 should preferably include a metal so that the inductive fields do not leak out of the box, which is inefficient and may give rise to safety issues. At the same time the box walls should have good thermal insulation properties, also to 325 increase efficiency. Another safety device is one to sense the weight of the portable heat source presently inserted. If the weight is zero, or below a predetermined weight, (such as if the portable heat source has lost some or all of its fluid), the heating circuit is disabled.

Each portable heat source should control its own heating process. A portable heat source can be left inside the charger until it is needed, where it will be raised or topped up to the intended maximum 330 temperature from time to time. Charging is always halted once the portable heat source in the charger is hot enough, as determined by the thermal cutout device. The primary circuit may be arranged to charge up two "bottles" in adjoining compartments, so that one can be re-warmed while the other is in use.

A different means for measuring temperature during the reheating process is to use, at each warming 335 station, an infra-red thermometer (using a Melexis MLX90614 device, for example: Melexis, Concord, NH, USA) ) based on a thermocouple principle, which "looks at" the bed warmer being warmed and provides an accurate indication of temperature. The internal thermal switch should be retained as a backup or safety device for preventing overheating, since if a bed wanner was inadvertently heated to boiling point it would probably explode. Hence a relief valve may also be 340 preferred as a safety measure.

12

EXAMPLE 2 (electrochemical)

Rather than use a bulk property of latent heat of a selected material or mixture, a bed-warmer module visually similar to that of the preceding example(s) emulates a mass having a high effective specific heat by using electric batteries, in which reversible ion chemistry can store effective 345 amounts of energy. The amount of energy storage available per unit weight is at least as good as a wax. (Consider how hot a laptop computer becomes, when operating from its battery supply while on one's knees). The module uses a rechargeable battery as a store of energy and uses one or more active electronic modules to maintain a user-compatible heating surface at a predetermined temperature. The heating surface is heated by controlled current from the battery as long as there is 350 energy in the battery. Preferably each electronic module is:

1. adjustable for temperature, within a safe upper limit (also, high temperatures tend to reduce battery life)

2. reliable - and perhaps the temperature transducer is internal to an integrated circuit in order to minimise parts count and wire breakages,

355 3. fail-safe - using PTC thermistor sensors so that an open circuit simulates an over-hot module,

4. capable (with extra internal equipment) of logging its usage - which may be of use in medical care.

It may also be cold even if filled - until activated. Fig 8 is a block diagram of this embodiment of the invention. 801 is a rechargeable battery (or assembly of batteries). 802 is a control device that in 360 a first mode rectifies coil current (derived from coil 301 when in the charging mode, or meters out battery current to the coil as direct current when in the discharge mode. 802 preferably includes a resonating capacitor and means to detect when the battery has become charged. The metering out process includes a feedback loop comparing the internal temperature as detected by thermal sensor 803 in relation to a predetermined target temperature. If the portable heating device uses resistive 365 wiring buried within in the exterior wall, temperature sensing may be carried out by other wiring buried within in the exterior wall.

Again, the bed wanner is supplied inside a user-friendly covering, and is supplied together with an electrically driven reloading device (as per Fig 7) capable either of reheating one or more modules

13

or of recharging some other batteries which can then be slipped into the module in order to replace 370 discharged batteries. The module (or modules) and reheating device are intended to replace the hot-water bottle as a way of keeping people warm. While a rechargeable battery could start a fire if shorted out when charged, careful design shall minimise that risk. The user-friendly covering, in more detail, shall provide an external perception of softness rather than a hard heavy battery within. Starting at the exterior there is an option of a textile covering (analogous to prior-art hot water bottle 375 covers of wool, cotton or other materials) over a rubber or analogous waterproof, preferably flexible layer. Inside the waterproof flexible layer shall be probably a gel-filled sac containing and protecting the hard material of the electronic assembly. The "gel-filled sac" may be made of a gel which is preferably thermally conductive. Convective heat transfer as with a relatively low-viscosity fluid may be the simplest approach to thermal conductivity. Another approach is to embed heating wires 380 in the waterproof flexible layer, and connect these to the discharge circuit.

It will be appreciated that inductive power transfer is an efficient way to reload a battery because the secondary winding behaves as a constant-current source.

It will also be appreciated that a charged battery does not have to be actively discharging straight away. In other words, bed warmers using electronic energy storage as described herein can be in a 385 cold state with respect to temperature even if charged up, and be switched off until needed. A suitable switch to initiate discharge might be closed by passing the device over a strong magnet. A status indicator such as a LED lamp (off/full/in use) would be useful.

The electronic bed warmer of Fig 8 may also be connected to clothing or footwear that includes warming wires to be substituted for coil 301 when in discharge mode, useful in cold countries or for 390 motorcyclists for electrically heated socks and gloves for example.

INDUSTRIAL APPLICABILITY and ADVANTAGES

The higher Effective Specific Heat provides longer-lasting heat from the bed warmers than if water is used.

The use of latent heat release provides a reasonably constant temperature output as long as the 395 energy is present.

Dangers of conventional hot water bottles (such as scalding with hot water when filling, and overheating of body parts in contact) are absent.

14

Waste of hot water is abolished.

A bed-ridden person can replace a cold bed warmer from a bedside re-warming unit as and when 400 required.

Heat energy is conserved - the only item heated is the hot water bottle.

Finally, it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and 405 spirit of the invention as set forth in the following claims.

15

Claims

I Claim:

1. A bed heating system using at least one rewarmable, permanently sealed portable heat source (not unlike a hot-water bottle) for warming a bed by giving off heat from an

410 internal mass of heated material; the material substantially comprising water, wherein the bed heating system includes a bedside device having at least one rewarming station including temperature-limited heating means for electrically heating a compatible portable heat source; each rewarming station including means for detection of the temperature of the portable heat source, means for producing a form of energy capable 415 of transmission into the interior of the portable heat source, and means for halting the supply of energy if that temperature exceeds a predetermined temperature, so that the portable heat source can conveniently be warmed and later re-warmed, and so that energy and effort can be conserved.

2. A portable heat source for a bed heating system as claimed in claim 1, capable of giving 420 off heat passively from an internal mass of heated material having an effective specific heat of more than one; the material substantially comprising a plurality of capsules suspended in water, each capsule containing a selected wax or resin, capable of changing state from a solid to a liquid or vice versa at or about the predetermined temperature.

425 3. A portable heat source for a bed heating system as claimed in claim 1 or in claim 2, wherein the portable heat source includes a flexible, waterproof external wall of at least one layer having a moderate thermal conductivity, even if wet, similar to that of a conventional rubber hot-water bottle provided with a woollen fabric jacket.

4. A bed heating system as claimed in claim 1, wherein each rewarming station includes 430 weight-sensitive sensing means capable of disabling the supply of energy unless a portable heat source of at least a predetermined weight is within the rewarming station, so that energy will not be fed into an empty rewarming station or one containing an abnormally light portable heat source such as one that has lost its charge of water.

5. A bed heating system as claimed in claim 3, wherein the rewarming station is capable of 435 generating a compatible electric current and using a complementary set of reconnectable electric connectors to transmit the electric current into an immersed electrical resistance inside the portable heat source.

16

6. A bed heating system as claimed in claim 5 wherein the electric connectors are of a type selected so as to render difficult any unauthorised connection to the immersed

440 resistance.

7. A bed heating system as claimed in claim 3, wherein the rewarming station includes means for generating an alternating magnetic field at a frequency; the field passing through the portable heat source in order to transmit energy into magnetic field interception means inside the portable heat source; the current induced within the

445 interception means to be resistively converted into heat.

8. A bed heating system as claimed in claim 7 wherein the magnetic field interception means is a secondary winding made resonant at the frequency in order to improve the efficiency of coupling and so as to render difficult any unauthorised attempt to heat the portable heat source; the portable heat source being contactless.

450 9. A bed heating system as claimed in claim 5 or claim 8, wherein the wiring inside the portable heat source includes at least one temperature-sensitive electrical fuse or like means capable of opening at or about the predetermined temperature, so that operation of the fuse interrupts the process of heating and serves as a second safety action.

10. A bed heating system as claimed in claim 1 wherein the means for detection of the

455 temperature of the portable heat source is selected from a range including one or more of: (a) thermopile means comprising part of the rewarming station for receiving infra-red energy radiated from the portable heat source, (b) a device within each portable heat source capable of changing electrical resistance in response to the temperature; connected to connecting means and hence to electronic temperature assessment

460 means, and/or (c) a like device comprising part of the rewarming station brought into effective thermal contact with the portable heat source during a reheating procedure.

11. A bed heating system as claimed in claim 1, wherein the bedside device further includes timing means capable of initiating a heating process within one or more rewarming stations at a predetermined time so that, for example, the bedside device will

465 hold heated portable heat sources ready for bedtime.

12. A bed heating system as claimed in claim 1, wherein the bed heating system is adapted for institutional use by being able to heat six or more portable heat sources at one time.

17

13. A bed heating system using at ieast one rewarmabie, permanently seated portable heat 470 source (not unlike a hot-water bottle) for warming a bed by giving off heat from an internal energy storage device wherein the bed heating system includes a bedside device including at least one recharging station providing recharging means for electrically charging a battery contained within a compatible portable heat source; each recharging station including means for halting the supply of energy once the battery is 475 charged; each portable heat source including means to discharge the battery through resistive heating means including temperature-limiting control means so that the portable heat source cannot exceed a predetermined temperature chosen in relation to a risk of tissue damage by overheating to an infant or an elderly or comatose person when the portable heat source is in contact with the skin of that person, so that the 480 portable heat source can conveniently be loaded by absorbing electrical energy and later discharged by giving out heat energy, and so that energy and hot water can be conserved.

14. A bed heating system as claimed in claim 13, wherein electricity is provided to the portable heat source in the recharging station by direct electrical connection.

485 15. A bed heating system as claimed in claim 14, wherein electricity is provided to the portable heat source in the recharging station by inductive power transfer.

16. A portable heat source as claimed in claim 14 or in claim 15, wherein discharge and consequent provision of heat can be switched on or off.

490

18