US20060137099A1 - Convective cushion with positive coefficient of resistance heating mode - Google Patents

Abstract

A cushion that is heated convectively using a positive coefficient of resistance type resistive heating element that is provided with heat exchanging surfaces, includes a mattress pad, seat or the like with a bottom surface secured around its perimeter to an air permeable top surface, forming a plenum and containing tubular spacer material therein. The plenum is connected to a power unit housing a blower, a heating module and a controller unit. The heating module preferably includes a PTC type heating element in conduction with a base plate and a number of heat exchanger fins. Preferably the heating element is sandwiched between a pair of the base plates and the heat exchanger fins, and there is a seal between the base plates to minimize air flow from the blower from passing there between. A remote control for the user's convenience may be provided, and a foldable antenna attachable to the convective unit facilitates wireless communication between the remote control and controller unit. The user resting atop the cushion is able to control the blower and heating module to deliver air of a desired temperature and quantity to the cushion and through the top surface. The invention advantageously replaces the current carrying, conductive wires and insulation found inside prior art heated mattresses, enhancing safety and performance while at the same time offering a cooled or ventilated capability.

Description

CROSS REFERENCE TO RELATED DOCUMENTS
• This application is continuation-in-part of utility patent application Ser. No. 11/024,073 (filed Dec. 27, 2004) entitled “Variable Temperature Cushion And Heat Pump.”
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to temperature controlled mattress pads, seats or other cushions, and more particularly to such a cushion that is heated by a positive temperature coefficient (PTC) element and ventilated as well.
• 2. Description of the Related Art
• Resistance wires oftentimes with PTC resistive elements are the conventional way of heating a cushion by conduction. This suffers from certain disadvantages, however, including that the electrical conductors are located within the cushion itself. Over time, the wires, carbon fiber strips or the like being subject to repeated weight loads and mechanical stresses may become physically damaged causing sparks from short circuits, and an occasional fire. Voltages as low as 6V can produce noticeable sparking, even at current levels in the 1-200 milliamp range.
• Insulation is commonly used in the prior art, not only to limit peak heating at the conductor but also to spread the heating effect out (or average it) over the surface to be heated. The disadvantage here is that it takes longer to reach an adequate heating level, because of the drop in heating efficiency caused by the insulation. The overall efficiency of the heating apparatus is compromised as the insulation slows the heating of the outer surface of the cushion.
• Additionally, resistance heated type, prior art mattress pads don't offer cooling or ventilation. This is a major disadvantage in many parts of the world where the population lacks means such that air-conditioning is unavailable and a substantial portion of the year relaxing or sleeping is uncomfortable due to very warm ambient air conditions.
OBJECTS OF THE INVENTION
• Accordingly, it is an object of the present invention to construct a temperature-controlled cushion that is heated without the conventional resistance wires or PTC resistive elements in conductive mode within the cushion itself,
• It is a further object of the present invention to construct such a cushion while minimizing the use of insulation.
• It is a still further object of the present invention to provide such a cushion that also includes a cooled or ventilated mode.
• It is a still further object of the present invention to provide such a cushion that includes convenient controls for the user.
• It is a still further object of the present invention to provide such a cushion that is simple and relatively inexpensive to manufacture.
• It is a still further object of the present invention to provide an accompanying power unit that is quiet and compact, and located remote from the cushion;
• These and other objects of the present invention will become apparent upon reference to the following detailed description and accompanying drawings.
SUMMARY OF THE INVENTION
• Disclosed is a new approach for a cushion that is heated convectively using a positive coefficient of resistance type resistive heating element that is provided with heat exchanging surfaces, or alternatively a thermoelectric device with heat exchanging surfaces, or a Stirling Cycle heat pump with PTC heater mounted on the cold head and heat exchanging surfaces attached to the PTC heater and/or cold head.
• The present invention includes a mattress pad, seat or other cushion with a bottom surface secured around its perimeter to an air permeable top surface (forming a plenum or air-flow structure) and containing tubular spacer material or equivalent therein. The plenum has an opening for a (preferably insulated) air duct which leads to a power unit housing a blower, a heating module and a controller unit. Besides obvious uses in the home or an automobile, the invention as disclosed herein may also be used for patient warming in medical and surgical settings.
• The heating module preferably includes a PTC type heating element in conduction with a base plate and a number of heat exchanger fins. Preferably the heating element is sandwiched between a pair of the base plates and the heat exchanger fins, and there is a seal between the base plates to minimize air flow from the blower from passing there between. A remote control for the user's convenience may be provided and a foldable antenna attachable to the convective unit facilitates wireless communication between the remote control and controller unit, although corded remote control may also be utilized or the controls located on the power unit itself. The power unit may include multiple PTC elements including of varying capability to allow the user to more precisely control the output temperature of the air, and may include a speed control for the blower.
• The user resting atop the cushion is able to control the blower and heating module to deliver air of a desired temperature and quantity to the cushion and through the top surface. The advantages of the subject invention over the prior art in heating mode for mattress pads, seats and other cushions are substantial. Since there are no current conducting wires or carbon fiber strips within the cushion structure, the convective cushion is much safer than the prior art when used as a mattress pad. This is because the PTC heating element is located remotely from the cushion and is connected to the cushion only with an air duct hose, eliminating all mechanical stress to any electrical wires from weight applied to the sleeping or seating surface. Because the heating medium is air, and not hot current conductor wires, it isn't necessary to use insulation to spread the heating effect over the entire surface of the cushion. By using air, the heating effect is gentle and effective without the need for insulation, so the overall heating mode efficiency is higher and more evenly distributed over the heated surface.
• The present invention, besides replacing basic electric resistance wire heated mattress pads as well as other resistance element heated cushions, also offers a feature that the prior art cannot using the same equipment and that is a ventilation mode for warm weather. By causing ambient air to move within the air flow structure (which is much more efficiently done with tubular spacer fabric as described elsewhere herein, and in U.S. Pat. Nos. 6,263,530 and 6,085,369, but can be done less efficiently with other air flow structure materials), a meaningful percentage of excess body heat can be removed during warm weather while the user is seated on or sleeping on the cushion of the subject invention.
• As long as ambient temperature is below the user's body skin temperature (which averages out to approximately 96 degrees Fahrenheit over much of the body), there must (according to Newton's Law of thermal transfer), be a thermal exchange between the source of heat at a higher temperature (body skin surface), and a heat sink at a lower temperature, by ambient air under forced convection (macrocosmically) and free convection, (microcosmically). The terms macrocosm and microcosm simply refer to the relatively large bulk air flow (or forced convection), produced through the cushion air flow structure by the blower and the relatively very small air convection movement (free convection), produced at the microcosmic level by the delta T or difference in the relatively warm air nearest the user's skin and the relatively cool air brought into close proximity via forced convection. The microcosmic level is that level within the padding and textiles which is the interface between the user and the air flowing through the cushion.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• FIG. 1 is a side elevation view of the convective cushion of the preferred embodiment of the present invention placed atop a conventional mattress;
• FIG. 2 is a plan view of the convective unit with a portion of the housing removed to show its contents;
• FIG. 3 is an enlarged plan view of the PTCresistive heating element30;
• FIG. 4 is an end view of the assembly ofFIG. 3;
• FIG. 5 is another side elevation view of the same assembly, in the air flow direction, looking through the heat exchanger fins;
• FIG. 6 is a cross-sectional view of the air duct;
• FIG. 7 is a side view of the convective unit with an optional attachable folding antenna with an attachedair duct hose40 to convey conditioned air to the cushion.
• FIG. 8 is a side view of a convective seat cushion for a vehicle with a compact power unit installed at the bite line between the seat and backrest in accordance with an alternate embodiment;
• FIG. 9 is a side view of the power unit optionally installed at the front of the seat;
• FIG. 10 is a cross-sectional view of the power unit optionally installed at the top of the backrest;
• FIG. 11 is a front elevation view of the cushion with a damper valve for regulating the airflow;
• FIG. 12 shows the modified airflow ofFIG. 8 when the damper valve is closed;
• FIG. 13 shows the modified airflow ofFIG. 9 when the damper valve is closed; and,FIG. 14 shows the modified airflow ofFIG. 10 when the damper valve is closed.
LISTING OF REFERENCE NUMERALS
• convective cushion10
• plenum12
• airimpervious bottom surface14
• air-permeabletop surface16
• vent17
• tubular spacer material18
• power unit20
• housing21
• blower22
• circuit board box24
• adaptor26
• air outlet27
• air duct inlet28
• PTCresistive heating element30
• heat exchanging fins32
• power terminals34
• PTC heating element36
• base plates38
• air seal orgasket39
• air duct hose40
• flexible air duct42
• insulated sleeve44
• sleeve splines46
• remote IR sensor,detector50
• length ofwire52
• articulated folding strut,antenna60
• IR sensor62
• adapter plug64
• hingepoints66
• vehicle seating cushion130
• seat rest132
• backrest134
• compact power unit150
• straight air duct194
• special air duct195
• special duct196
• Zipper™ valve ordamper198
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Initially referring toFIG. 1, shown is theconvective cushion10 placed upon a conventional mattress, including aplenum12 constructed of abottom surface14 secured around its perimeter to atop surface16. Thebottom surface14 is preferably air impervious, although placement on a conventional mattress may render an air permeable surface largely impervious. Thetop surface16 is air-permeable although sufficiently impervious that a greater air pressure can be maintained inside the enclosed space.
• Inside theplenum12 istubular spacer material18 or equivalent. U.S. Pat. Nos. 6,085,369 and 6,263,530 pioneered the use of suchtubular spacer fabric18 as an air flow structure for seats, mattresses, mattress pads, and other articles of furniture that can be sat on or laid down upon. Although the preferred embodiment of this invention utilizes the sametubular spacer fabric18 as described in the issued Feher '369 and '530 patents, it is possible to utilize other air flow structures such as Muller Textile's 3 Mesh or Strahle and Hess' assembled woven tube fabric, as well as any other air flow structure; however there may be substantially reduced levels of performance when compared totubular spacer material18 as disclosed in the above U.S. Pat. Nos. and herein.
• FIG. 2 shows apower unit20 for theconvective cushion10, which includes ablower22 for blowing air across one a PTCresistive heating module30 including heat exchanging surfaces32 (seeFIGS. 3-5), and pushing the air into theplenum12 for heating thecushion10. Alternatively, thePTC module30 need not be energized, resulting in a ventilating function as a result of circulating ambient air through the cushionair flow structure12. ThePTC heating module30 withheat exchanging fins32 is located in anadaptor26 that matches themodule30 to theblower air outlet27 and theair duct inlet28 in the most aerodynamically efficient manner within the space limitations of thepower unit20housing21 dimensions. Details such as a power cord and plugs and sockets are not shown.
• Also shown inFIG. 2 is abox24 for any necessary or desired electrical circuits for mode switching, switching between multiple heaters, on and off, etc., plus wireless remote control circuits if desired. A speed control printed circuit board may be incorporated in thespace24 shown inFIG. 2, which could be used to control heating as well as ventilation by coordinating PTC elements with AC power control to regulate air flow, perhaps offering more flexibility in comfort settings than the simplest form which relies solely on the PTC switch temperature characteristics of the PTC elements with a fixed air flow rate.
• Thebox24 may optionally include a Triac or other semiconductor power control for the PTC heating elements to enable the PTC elements to operate below their switch temperature design point. The PTC element switch temperature is the temperature at which the resistance starts to rise exponentially. Theelements36 are called Positive Temperature Coefficient because, unlike NTC, or Negative Temperature Coefficient type materials, the electrical resistivity rises with increasing temperature, instead of dropping with increasing temperature. Most materials exhibit PTC characteristics because increasing temperature causes more ionic movement, crystal lattice vibration, and/or molecular motion, any of which can interfere with electron mobility. The switch temperature of ceramic PTC devices is determined by the amount of doping with certain elements, such as strontium, for example, before firing.
• In order to operate thePTC heating elements36 below their design point switch temperature it is necessary to either increase the heat load beyond the capabilities or rating of the elements, by increasing air flow beyond the design point for example, or by reducing voltage to the elements, which reduces the power rating of the elements relative to the load. For a mattress pad application of theconvective cushion10 it may be more desirable to use a power reduction instead of an air flow increase, in order to maintain a very low noise level for a comfortable sleeping environment.
• FIG. 3 shows thePTC heating module30 withheat exchanging fins32 running in the Y axis andpower terminals34 on the right side. TwoPTC elements36 can be seen, represented by dashed lines, mounted in the middle of theheat exchangers32. Thepreferred PTC elements36 are rated 50 Watts each and 120 VAC, with a switching temperature of about 38-45 deg. C. max., and are manufactured by Advanced Thermal Products, Inc. of Saint Mary's, Pa. Other elements with different power and voltage ratings can be used; however the above is the preferred embodiment because it is unnecessary to produce air at more than about 45 deg. C. max. to affect good heating performance and using elements rated for 120 VAC eliminates the need for a power supply which reduces the cost of the product while increasing product reliability. If a more powerful heating effect is desired, it is a simple matter of using higher rated elements or more of the same power ratedelements36.
• FIGS. 4, 5 show thePTC heating elements36 mounted between twobase plates38 of theheat exchangers32. Theseplates38 are heavier than thefins32 and serve to spread the heat outward from thePTC heating elements36 to the far edges of theheat exchangers32 as efficiently as possible without excessive thickness and weight. An air seal orgasket39 is also shown in this view the purpose of which is important. Theseal39 prevents air flow between the twoheat exchangers32, which forces all of the air flow through thefins32, increasing thermal transfer efficiency. The reason that this became an issue was that the thickness of the PTC heating elements rated for 120 VAC is twice that of PTC heating elements rated for 12-24 VDC. The extra thickness results in a gap of sufficient size to permit excessive air flow between the two heatexchanger base plates38. Theseal39 addresses this issue to produce a more efficient apparatus that operates reliably at or very close to the switch temperature.
• The PTCheating module assembly30 can be made with asingle heat exchanger32; however such an arrangement would not be as efficient from a thermal point of view. Theheat exchangers32 are preferably made of copper, although aluminum or any other thermally and electrically conductive material can also be used. Although solder can be used to bond thePTC heating elements36 to the heatexchanger base plates18, a flexible adhesive with good thermal and electrical conductivity is preferred to prevent excessive stress buildup andpossible PTC element36 cracking due to differences in coefficient of thermal expansion (CTE) between thePTC heating element36 material and theheat exchanger32 material, which can be substantial, for example, approximately10:1 for thePTC elements36 and copper.
• Referring back toFIG. 1, thepower unit20 may be mounted on the floor, with a flexibleair duct hose40 attached to one end of theconvective cushion10, which is preferably at the foot of the bed. Although it is possible in some instances to introduce air into theconvective cushion10 at the head of the bed it is preferred to put the air in at the foot of the bed for several reasons. Thepower unit20 is designed to be very quiet, however it is not totally silent so the father away it is from the user's ears the better. For heating mode, the extremities tend to require more heating than the trunk of the body; therefore putting the warmed air in at the foot puts the warmest air in at the place where it's needed most, the extremities, or feet and legs. Lastly, there may not be enough space between the bed and the wall at the head of the bed to accommodate theair duct hose40.
• FIG. 1 shows how some of the air percolates or vents up through thecushion10, which is enclosed in atextile envelope12 and secured to, in this case, a bed, resulting in ventilating or heating air flowing under the covers (not shown), however most of the ventilating or heating air flows through thecushion10air flow structure18 and vents out at the end17 opposite from where it entered.
• FIG. 1 also shows how to achieve an infra-red type remote control with theconvective cushion10 as a mattress pad. Ordinarily, thepower unit20 is placed on the floor at the foot of the bed in order to enable a short length of air duct hose and to minimize blower noise perceived by the user. Unfortunately, this places thepower unit20 out of the line of sight of an infra-red (IR), type remote control, which is less expensive than a radio frequency (RF), type remote. The more expensive RF remote has the advantage of not requiring a line of sight to function. Shown is connecting a remote IR sensor, ordetector50, to thepower unit20 with a length of wire52 (most beds are at least6 feet in length, so the length ofwire52 needed is at least that long, plus approximately three feet for slack), to enable the user to use an IR remote (not shown) without a line of sight to thepower unit20. Alternatively, either an IR or RF type remote may be designed to be used with thePTC power unit20 in order to enable control of ventilation, or heating, and degrees of ventilation and heating, without the need for a cord connecting the remote to thepower unit20.
• The solution ofFIG. 7 is to place anIR sensor62 on the end of an articulated folding strut, orantenna60, attached to thepower unit20. When theantenna60 is unfolded vertically, the user has a line of sight to the IR detector orsensor62, enabling use of the IR type remote control. TheIR sensor strut60 should be capable of extending vertically at least24 inches or more, and can be attached to thepower unit20 permanently or can use anadapter64 to plug into thepower unit20 housing before or after unfolding. A telescopic strut (not shown) could also be used, but managing the wire on the inside during collapse of the telescopic type of antenna is more complex and bulky than using afolding strut60 with rotary electrical contacts at the hinge points66. Thefolding antenna60 design can be such that the middle leg folds to nest within the top leg and the bottom leg folds to nest within the middle leg, etc. The legs can be made of flat strips of metal or plastic with the top leg overlapping the middle one and so on. Power to thesensor62 and signals from thesensor62 can be transmitted to thecontrol circuit24 in thepower unit20 via either wires in theantenna60 or via the arms of theantenna60 and a third wire if the arms are made of conductive material or if they are provided with conductive circuit traces and rotating contacts in the joints.
• FIGS. 1, 6 and7 show thePTC heater assembly30 withblower22 connected to themattress pad10 via a length offlexible air duct40. A good example of such anair duct42 is known as Uniloop, made by Flexhaust, Inc. It is important for good performance of thepreferred embodiment10 to ensure that there is low heat loss in theair duct42 in cold weather and in heating mode. Although there are numerous materials and techniques that can be used to make a flexible insulated air duct for the purposes of the subject invention, one example is to make aninsulation sleeve44 for the Uniloop air duct hose out of Volara, made by Voltek Corp., which is a polymeric foam with very small closed cells enabling a relatively high R rating, or insulation rating for a relatively thin material cross section. In this case a Volara sleeve or layer approximately 0.08″ thick produces very good results. A preferred form of theVolara insulation sleeve44 would be extruded withinternal splines46 as shown inFIG. 6 to create small air gaps between thesleeve44 and theair duct42 to enhance the insulation performance of the sleeve with minimal bulk.
• This is one way of making an insulatedair duct hose40 for thepreferred embodiment10 that remains flexible and non-bulky while enabling higher performance and efficiency for the subject cushion or mattress pad in heating mode under cold ambient air temperature conditions. However it is configured, an insulatedair duct hose40 is important for best cold weather heating mode performance, especially because the air delta T in heating mode is substantially higher than in ventilation mode, in which there is no delta T because ambient air is being used for ventilation. If a source of air cooled below ambient is used, then theinsulated air duct40 will improve efficiency, however, not to the same extent, as active cooling mode delta T will still usually be less than half that of heating mode delta T. For example, heating mode may easily entail an air delta T of 45+ deg. F., while active cooling mode with thermoelectric or Stirling Cycle devised as disclosed in some of my other patents, will generally not exceed 20-30 deg. F.
• Referring toFIGS. 8-14, an alternate embodiment vehicle seating cushion may be described, in particular application of the PTC air heating and ventilating system to a seat cushion consisting of a seat rest and backrest capable of sustaining internal air flow that will communicate thermally and convectively with the user contacting surfaces, in communication with the PTC power unit or air heating and ventilating system, via a variety of optional air pathways. As shown inFIG. 8, preferably acompact power unit150 is installed proximate the “bite line” or separation between theseat rest132 andbackrest134 portion of thecushion130, with astraight air duct194 running from the mouth162 of thepower unit150 to thecushion130. This set up is preferred as conditioned air entering the middle portion of thecushion130 is more easily evenly distributed throughout theseat rest132 andbackrest134. Alternatively, thepower unit150 can be installed forward of theseat rest132 with a special air duct195 (FIG. 9) or above and aft thebackrest134 with special duct196 (FIG. 10). These configurations are useful for use with seats that do not have an opening or slot at the “biteline” between the seat and backrest cushion of the seat upon which the PTC cushion is to be installed, in order to facilitate installation of the cushion.
• Note the airflow direction through thecushion130 varies depending upon where thepower unit150 is placed, with the air primarily exiting thecushion130 remote from thepower unit150. The set up with thepower unit150 forward theseat rest132 is advantageous for ease of control in that thepower unit150 controls could be located directly on theunit150 and easily accessible between the user's legs when seated on thecushion130. When thepower unit150 is located aft of the user, a wired control extends to the user or to a location accessible to the user or a remote wireless control could be used.
• FIG. 11 shows a Zipper™ valve ordamper198 installed in the middle portion of thecushion130. Thedamper valve198 serves to control the air flow between theseat rest132 andbackrest134 portions of thecushion130. For example, when thepower unit150 is installed at the bite line and thevalve198 is completely closed, air flows only through thebackrest134 and not the seat rest132 (FIG. 12). Other examples, when thepower unit150 is installed atop thebackrest134 and thevalve198 closed air flows again only through the backrest134 (FIG. 13), or when thepower unit150 is installed forward theseat rest132 and thevalve198 closed air flows only through the seat rest132 (FIG. 14), in both these instances the air exiting thecushion130 through theduct194 at the bite line. It is also possible to open or close thevalve198 to intermediate positions in order to vary the thermal effect of the cushions, by controlling the amount of air flowing through the cushions.
• The present invention has been described in connection with preferred and alternate embodiments, but it is understood that modifications will occur to those skilled in the appertaining arts that are within the spirit of the invention disclosed and within the scope of the claims.

Claims (22)

1. A selectively-controlled convective cushion comprising:

a plenum defined by a bottom surface secured around its perimeter to a generally air permeable top surface and containing tubular spacer material therein;

a power unit located remote from the plenum but in fluid communication with the plenum, and housing a blower in fluid communication with a heating module;

a controller unit in communication with the blower and the heating element;

whereby a user resting atop the cushion is able to control the blower and heating module to deliver air of a desired temperature and quantity to the cushion and through the top surface.

2. The selectively-controlled convective cushion ofclaim 1 wherein the plenum has an opening at one end, and further comprising an air duct with one end sized to be received into the plenum opening and a second end extending to the power unit.

3. The selectively-controlled convective cushion ofclaim 1 wherein the heating module comprises a PTC type heating element in conduction with a base plate and a plurality of heat exchanging fins.

4. The selectively-controlled convective cushion ofclaim 3 wherein the heating element is sandwiched between a pair of the base plates and the plurality of heat exchanging fins.

5. The selectively-controlled convective cushion ofclaim 4 further comprising a seal between the base plates to minimize air flow from passing there between.

6. The selectively-controlled convective cushion ofclaim 1 further comprising a remote control in communication with the controller unit.

7. The selectively-controlled convective cushion ofclaim 6 further comprising a foldable antenna attachable to the power unit to facilitate wireless communication between the remote control and controller unit.

8. The selectively-controlled convective cushion ofclaim 8 wherein the controller unit includes a speed control for the blower.

9. The selectively-controlled convective cushion ofclaim 2 wherein the air duct comprises an outer shell and an inner insulating sleeve with an air gap there between.

10. The selectively-controlled convective cushion ofclaim 1 further comprising a vent at the opposing end of the plenum.

11. The selectively-controlled convective cushion ofclaim 1 wherein the bottom surface of the plenum is generally air impermeable.

12. The selectively-controlled convective cushion ofclaim 1 wherein the plenum is adapted to be placed on a conventional mattress.

13. The selectively-controlled convective cushion ofclaim 3 wherein the power unit comprises a plurality of PTC type heating elements.

14. A convective mattress pad comprising:

a plenum defined by a bottom surface secured around its perimeter to a generally air permeable top surface, the plenum containing an air flow structure and having an opening at one end;

an air duct with one end sized to be received into the opening and a second end extending outside the plenum;

a power unit housing a blower in fluid communication with a heating module and connected to the second end of the air duct;

a controller unit in communication with the blower and the heating element; and,

wherein the heating module comprises a PTC type heating element in conduction with a base plate and a plurality of heat exchanging fins.

15. The mattress pad ofclaim 14 wherein the heating element is sandwiched between a pair of the base plates and the plurality of heat exchanging fins.

16. The mattress pad ofclaim 14 further comprising a seal between the base plates to minimize air flow from the blower from passing there between; and

17. The mattress pad ofclaim 14 further comprising a remote control in communication with the controller unit.

18. The mattress pad ofclaim 17 further comprising a foldable antenna attachable to the power unit to facilitate wireless communication between the remote control and controller unit.

19. The mattress pad ofclaim 14 wherein the controller unit includes a speed control for the blower.

20. The mattress pad ofclaim 14 wherein the air duct comprises an outer shell and an inner insulating sleeve with an air gap there between.

21. The mattress pad ofclaim 14 further comprising a vent at the opposing end of the plenum.

22. The mattress pad ofclaim 14 wherein the air flow structure is tubular spacer material.

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