Hot air drier.

FIELD OF THE INVENTION

0001THIS INVENTION relates to a hot air drier and is more specifically concerned with apparatus for providing a stream of hot unsaturated air which may be used, for example, for body drying, or for clothes drying.

STATE OF THE ART

0002Hot air driers usable either for body drying or for clothes drying are described and illustrated in United Kingdom Patent Application Nos. 2,222,944; 2,020,970; 2,243,546; 2,140,295; 2,146,522; United States Patent Nos. 3,418,452; 2,977,455; 3,621,199; 4,685,222; 3,878,621; 4,756,094; 3,449,838; 3,128,161; Patent Co-operation Treaty International Patent Application Nos. WO 80/01872; WO/91/07900; WO 91/05503; and finally Australian published Patent Application No. AU-A-11175/88.

0003All of the above driers use a blower to provide the air stream and an electric heating element through which the air is passed prior to delivery to the point of use. This may be a shower cubicle in the case of a body drier, or a rack on which clothes are draped, in the case of a clothes drier.

0004In order to dry wet objects, the water to be dried off must first be raised to its evaporation temperature, and then the latent heat of evaporation must be provided to convert the water into steam. This is accompanied by expansion, with the result that a small amount of water generates a large amount of water vapour. When drying is carried out in a poorly ventilated space such as a room, the water vapour raises the temperature and humidity in the room to an often uncomfortable level. Also, condensation of the water vapour on cooler surfaces in the room can promote dampness and rot, and also staining of glass surfaces such as windows and mirrors. Because of the relatively large amount of energy required to operate a hot air drier, and the attendant inconveniences mentioned above, electrically operated driers tend only to be used in domestic premises for small portable items such as hair driers.

OBJECT OF THE INVENTION

0005An object of this invention is the provision of improved hot air drying apparatus.

SUMMARY OF THE INVENTION

0006In accordance with the present invention apparatus for providing a stream of hot dry air to a confined space, comprises first means defining a first air path leading from outside the apparatus into the confined space, second means defining a second air path leading from the confined space to an air outlet, an electrical heater in the first air path, and, means for driving air through at least one of said paths to produce air circulation to and from the confined space; in which apparatus a heat exchanger is provided having two separate air flow passages in good heat exchange relationship, the first flow passage being connected in the first air path and the second flow passage being connected in the second flow path to extract heat from the air leaving the confined space and to use the extracted heat to pre-heat the air flowing through the first air path towards the confined space. The confined space may comprise a large bag or a small shower cubicle of much the same volume. The dimensions of the confined space will be matched to the drying ability of the apparatus to achieve optimum drying performance.

0007The invention enables the fresh air being drawn into the first air path to be pre-heated before flowing past the heating element. The energy expended by the heating element to carry out drying is thus reduced. In consequence, the size of the heater can be reduced, and the running costs to carry out drying are also reduced, or, conversely the rate of drying a given quantity of clothing can be increased for the same running costs.

PREFERRED FEATURES OF THE INVENTION

0008Preferably the heat exchanger is of counter-flow type which operates with an efficiency of between 80%-90%. A construction of heat exchanger of this type and particularly well suited for use with the present invention is described in the Applicant's United States Patent No. 5,078,208, hereby inserted by way of reference.

0009Suitably the blower unit and electrical heater are contained in the first air path downstream of the first passage and the second air path is provided with an exhaust fan. Preferably, the exhaust fan is located upstream of the second passage. It is preferred to have the exhaust fan operated by a motor which also operates a second fan located upstream of the first passage of the heat exchanger. The motor may be controlled by a switch responsive to either the temperature or the humidity of the air entering the second air path attaining a pre-set level.

0010The motor of the fans is not operated during an initial phase of the drying. Instead, the air in the confined space is re-circulated through the heater so that its temperature rapidly rises to a level at which optimum drying takes place. The motor is then switched on to remove the humid air at drying temperature from the confined space and simultaneously replace it with fresh air obtained from the first passage of the heat exchanger by way of the heating element and blower unit.

0011The apparatus may include a drying assemby usable to dry clothes and comprising a rack or a set of parallel cords which can be erected inside the confined space. The hot air discharged into the confined space is arranged to pass upwardly between the clothes to absorb moisture from them. Much of the heat of the humidified air leaving the bag is subsequently recovered by the heat exchanger.

INTRODUCTION TO THE DRAWINGS

0012The invention will now be described by way of examples, with reference to the accompanying drawings, in which:-

IN THE DRAWINGS

0013<ul id="ul0001" list-style="none"><li>FIGURE 1 is a perspective view of a casing of a wall-mounted drying cabinet showing a drying rack assembly in its stowed position;</li><li>FIGURE 2 shows the cabinet of figure 1 with the drying rack assembly in its erected horizontal position and a non-permiable flexible bag defining a confined space in which clothes drying is to take place;</li><li>FIGURE 3 is a front view of the cabinet with the front of its casing removed to show internal detail and air paths through the cabinet;</li><li>FIGURE 4 is a vertical section through the casing of figure 3 and taken on the line and in the direction indicated by the arrows IV-IV in figure 3; and,</li><li>FIGURE 5 is a broken cross-section through figure 3 taken on the line and in the direction indicated by the arrows V-V in that figure, the rack assembly being omitted.</li></ul>

DESCRIPTION OF PREFERRED EMBODIMENT.

0014Figure 1 shows a cabinet 1 having a casing 2 to the opposite sides of which are two arms 3 are pivoted at their upper ends at 4. The lower ends of the arms 3 carry a box structure 5 which can be swung forwardly to the position shown in figure 2 at which it is held by manually-releasable latches 10.

0015The box structure 5 comprises a top fixed plate 6 and a vertical plate 7 joined between the intermediate portions of the arms 3 and having a second plate 8 pivoted to its under edge at 9. The plate 8 has a stowage position shown in figure 1, at which it extends in spaced parallel relationship to the plate 6 and an operating position, shown in figure 2, at which it fills the space between the plate 7 and the front face of the casing 2.

0016The underside of the plate 8 is provided with a set of parallel drying cords 11 which, when the plate 8 is in its operating position shown in figure 2, extend horizontally beneath the plates 8 and 6 and are secured to the front edge of the plate 6 and the back edge of the plate 8. When the plate 8 is in the stowed position of figure 1, the cords are contained inside the cavity of the box structure 5 provided between the plates 6,7 and 8.

0017A bag 12 which is normally also stowed in the box structure 5 and which is made from a light thin plastics material, has its mouth attachable by an easily- removable, continuous connection, such as may be provided by a VELCRO strip (VELCRO is a registered trade mark), to the outsides of the arms 8, the front of the box structure 5 and the back of the cabinet 2, as shown in figure 2. The bag 12 , is about 1.8 metres high, which is sufficient to totally enclose clothes suspended from the cords 11 for drying. The bag 12 has, at its lower end, an outlet valve 13 to allow water dripping from the clothes to be collected without wetting the floor beneath the drier.

0018The lower front of the casing is provided with a hot-air outlet grill 14 which is manually movable along a vertical arc so that it discharges hot air at a desired angle between the horizontal and the vertical. The positioning of the grill 15 is achieved by turning a knurled wheel part of which protrudes from the front of the cabinet alongside the grill, as shown at 15.

0019The casing 2 is provided above the level of the pivots 4 with an air inlet grill 16 which may be opened or closed by a knurled knob 17 positioned alongside the grill 16. A second air inlet opening 28 is provided in the top of the casing 2 and the two inlets are selectively openable so that closure of the grill 16 automatically opens the inlet 28, and vice-versa. The air inlet 28 is connected to an air inlet duct if the cabinet is sited in a shower cubicle, so that outside ambient outside air is drawn into the cabinet for carrying out drying, rather than air sucked into the cabinet through the grill 16. A humid air outlet 29 is also provided in the top of the casing 1 for venting to waste air which has been used for drying.

0020The casing 2 is provided beneath the level of the pivots 4 with a second air inlet grill 19 which extends parallel to the grill 16 and is positioned so that it lies in the upper zone of the confined space enclosed within the bag 12, to suck hot humid air out of the bag.

0021Figures 3, 4 and 5 show the interior of the casing.

0022Hot air is provided to the grill 14 from a cowl 20 which receives air from a tangential flow fan 21. The fan 21 draws air through an electrically-operated heater 22 comprising two, independently-operated heating elements each of 0.9 kilowatts rating. This air may come from an outlet manifold 24 of a heat exchanger 25, or, by way of an aperture 26 in the cowl 20, from a plenum 27 provided on its outside with the inlet grill 19.The inlet of an air passage 30 of the heat exchanger 25 opens through a manifold 48 into the plenum 27. the outlet end of the air passage 30 is referenced 31 and opens into one compartment 32 of a chamber 60 formed in the upper end of the casing 2 and divided by a partition 61 into two compartments 32,33 respectively. The outlet 29 leads out of the compartment 32 to an exhaust.

0023As shown in figure 3, a motor 40 drives two fans or impellers 41 and 42. The impeller 41 is arranged at the air inlet manifold 48 to drive air from the plenum 27 into the air passage 30 of the heat exchanger 25. The second impeller 42 is mounted in a space 50 provided with the grid 16 and communicating selectively with the openings in the grid 16 and the air inlet 28, the choice being effected by operation of the switch 17 (see figure 1).

0024The impeller 42 operates to draw air from the space 50 into a second passage 45 of the heat exchanger 25. The heat exchanger is of counterflow type. It comprises a stack of parallel pockets each containing a platen of almost identical parallel gas flow passageways. The gas flow through neighbouring pockets is almost in true counterflow. The gas inlets and outlets to the passageways are arranged on adjacent sides of two corner regions of the heat exchanger stack. Tests have shown that such a construction of heat exchanger is easy and cheap to manufacture and will provide a thermal efficiency of 80% or more.

0025The second compartment 34 of the chamber 60 communicates with the space 50 by way of an opening closable by operation of the switch 17 so that the impeller 50 either draws in air from the inlet 18, or from the grill 16. The compartment 34 also communicates through a channel 63 arranged between one side of the casing 2 and the heat exchanger 25, with a further compartment 65 in which is mounted a motor 66 driving the radial fan 21. The channel 63 provides cooling air to the motor 66.

0026A temperature or humidity detector 70 is mounted in the plenum 27. This controls operation of the motor 40 and switches it on, if the temperature of the air entering the plenum 27 is higher than a pre-set value. When the cabinet is operating as a drier, this temperature is conveniently about 50° Centigrade. If the detector is responding to humidity, it switches on the motor 40 when the humidity rises to about 85%. A further temperature sensor 71 is provided adjacent the air entry side of the cowl 20 to switch off the heater 22 if the air temperature exceeds a pre-determined but adjustable value.

OPERATION OF THE THE PREFERRED EMBODIMENT

0027With the cabinet in the configuration shown in figure 1 it may be used as a space heater. the motor 66 and the heater 22 are operated but the motor40 is not. The fan 21 then sucks air from the grill 19 by way of the plenum 27 and the opening 26, and delivers the heated airthrough the grill 14 in the required direction. The temperature in the room is maintained at a chosen value by the sensor 71.

0028If the cabinet is to be used to dry clothes, the arms 3 are raised from the position shown in figure 1 to the position shown in figure 2. The plate 8 is turned about its hinge 9 so that the space between the arms 3 and the casing 2 is blanked off by the plates 6,7 and 8 which provide an effective ceiling to the bag 12. The movement of the plate 8 automatically exposes the grid of suspension cords 11 over which the clothes to be dried are draped. The bag 12 is then hung in the position shown in figure 2 to enclose the clothes completely so that there is virtually no escape of air from within the bag 12 otherwise than through the cabinet 1.

0029Drying of the clothes takes place in two phases. In the first phase the motor 66 and the heating element 22 are energised. As the temperature and humidity of air initially drawn out from the bag 12 are low, as the clothes are usually cold and wet, the motor 40 is not operated. Air is then drawn out of the bag 12 via the grill 19 and flows through the opening 26 into the upper end of the cowl 20. This air is re-circulated repeatedly through the bag and heater so that its temperature and humidity rapidly rises to the point at which the detector 70 responds. Although the re-circulated air expands during heating, very little of the volume increase escapes into the surrounding room, as the passages through the heat exchanger 25 remain open.

0030When the detector 70 responds to the temperature or humidity in the air attaining the pre-set value, it operates the motor 40. The impellers 41,42 then force air through the primary and secondary passages 30 and 45 of the heat exchanger 25. As the two impellers are identical and are driven at the same speed, they produce substantially the same air flow through each of the passages. As is clear from figure 3, the passage 45 supplies air from either the grill 16 or the inlet 28 to the heater 22 and the fan 21. Simultaneously the passage 30 carries hot saturated air drawn into the plenum 27 to the outlet 29. As the two passages are in counterflow and in good heat exchange relationship, the incoming air is preheated by heat extracted from the outgoing air, so that the heating element 22 only has to provide the thermal losses of the heat exchanger 25. Its rating necessary to maintain the drying temperature is thus very much less than would be the case were the heat exchanger not present.

0031For optimum drying, the grill 14 should be turned to the position shown in figure 2, at which it directs air into the lower part of the bag 12. This not only assists in maintaining the shape of the bag, but ensures that the hot and relatively dry air flows upwardly between the clothes on the cord rack. These clothes extend in vertical rows parallel to the cords 11 so that the hot air flows evenly past both sides of the clothes before entering the grill 19 of the cabinet. Rapid and effective drying is thus obtained.

0032Should the clothes be very wet when placed in the drier, they will inevitably drip into the bag 12. Some of this drip waterwill evaporate from the bag during operation of the drier. The remainder can be removed by operating the valve 13.

0033When drying is completed, the bag is opened by detaching its mouth and the clothes are taken from the rack assembly. The plate 8 is then released and turned about its hinge so that the cords 11 are once again contained in the box structure 5. The catches 10 holding up the arms 3 are then released and the arms 3 swung down to the positions shown in figure 1.

0034It will be noticed that the cabinet described can be used as a space heater, or it may be used in its space-heating configuration in a shower cubicle to perform body drying. If the cabinet is to be used for clothes drying, such drying takes place without any significant escape of hot humidified air into the surrounding room. Thus many of the objectionable characteristics of currently available clothes drying cabinets are avoided. If the cabinet is mounted in a shower cubicle having a door, the use of a bag 12 is still preferred as the effectiveness of drying is a function of the volume of the confined space. As long as the confined space is matched to the characteristics of the apparatus, optimum and therefore fast drying conditions can be obtained. Very often a shower cubicle will have a volume substantially larger than that of the bag and in such a situation drying of clothing will inevitably take place more slowly, unless the bag 12 is used.

0035The use of the inlet 28 as an alternative to the grill 16 allows outside air from an external source to be preheated in the heat exchanger, rather than partially saturated air from a shower cubicle in which the cabinet may be mounted providing the fresh air supply.

0036In one example of a drier constructed as described above, the following particulars were present: <ul id="ul0002" list-style="none"><li>Cabinet was 500mm. high, its depth was 150mm. and its width was 600mm. The depth of the cabinet with the arms extended horizontally, as shown in figure 2, was 700mm..</li></ul>

0037The motor40 was rated at 80 watts, and the motor 66 was rated at 80 watts. The fan was a TORIN tangential fan delivering 100 litres of air per second. The impellers 41,42 each delivered 50 litres per second of air. the heating element 22 has two separately operable 0.9kilowatt heating elements. During the initial phase of drying, both elements are operated. Once the motor 40 is operated the second phase of drying commences, keeping the heat high and the air saturated when it leaves the bag 12. When the humidity drops below a predetermined level which signifies that the clothes are nearly dry, the heating element is reduced from 1.8 kilowatts to 0.9 kilowatts. This saves energy while maintaining a high rate of drying.

0038The compartment 65 is hermetically sealed from the interior of the cowl 21 so that the motor 66 is unaffected by the temperature of air flowing through the cowl 20.