A low-velocity supply air terminal device

Abstract: A low-velocity supply air terminal device (10) intended for use in rooms that require an air supply comprises an inlet (11) which can be connected to an external supply air duct, an air distributing unit (18) for distributing exiting supply air to said room, and an inner space (14) which is open to the inlet (11) and extends in the longitudinal direction of the device (10) from the inlet (11) to its bottom (16), for transporting and distributing air to the air distributing unit (18). The space (14) is delimited laterally by an inner air permeable wall (19) of the air distribution unit (18) and, when applicable, also by the outer wall (12) of the device. The device (10) also includes a perforated plate (15) for throttling the flow of supply air. The perforated plate (15) is intended to favour distribution of the supply air vertically and uniformly to the air distribution unit (18) arranged in the form of a distribution plate in the inner space (14) at a distance of at least 50 mm and at most 300 mm from the inlet (11), therewith delimiting an upper part (14A) of the inner space from a lower part (14B) thereof. The invention also relates to a method of measuring the airflow in a low-velocity supply air terminal device at a distance of between 50 mm and 300 mm from the air inlet of said device with the aid of a measuring nipple provided in the perforated plate.

Description: The present invention relates to a low-velocity supply air terminal device of the kind defined in the preamble of Claim 1 and a method of measuring the airflow rate of such devices. Low-velocity supply air terminal devices have long been available commercially and obtained their breakthrough at the beginning of the 1980s, These devices are designed for different applications and areas of use, although a common feature is that they are chiefly intended for use in public places where a supply of fresh air is required, for instance in offices, hotels and conference rooms, restaurants, lobbies, theatres, cinemas, and, at times, also in domestic premises. Several designs and models of supply air terminal devices for the aforesaid purposes are illustrated and described in our product catalogues relating to such devices. These devices may thus have different designs and constructions depending on the use for which they are intended, and may be flat, semi-circular or quadrantal in shape or even fully circular, and may include an air-impermeable outer wall which is intended to be placed adjacent a wall in the room in which the device is used, or may have two such outer walls which are mutually angled for placement in a corner of a room, or may completely lack such outer walls when the device is intended to be placed somewhere else in the room. However, a common feature of all low-velocity supply air terminal devices is that they have an inlet which can be connected to an external supply air duct or channel, and a distribution unit for distributing air into the room in which the device is placed. Connecting with both the inlet and the air distributing unit is an inner space which is open towards said inlet and which extends in the longitudinal direction of the device from its inlet to its bottom. This space is intended for transportation of the air from the inlet and distribution of the air to the air distributing unit and is delimited laterally by an inner air-permeable wall of the air distributing unit and, when applicable, also partially by the outer wall or walls of said device. The inner air-permeable partition wall of the air distributing unit that lies proximal to said space may have the form of a plate provided with nozzles or functionally corresponding apertures, although said partition wall may alternatively comprise a filter wall or the like, possibly supported by a net-like wall structure or some other simple construction. Hereinafter, embodiments of low-velocity devices that include perforated plates will be mainly described although it will be understood that other types of air distributing units are fully analogous in this context. It is also known to utilize a perforated plate for throttling airflow in conjunction with low-velocity devices, for instance for measuring induction. For instance, WO 89/03961 teaches throttling of supply air through a perforated plate arranged in the inlet, so as to increase the velocity of the airflow and therewith generate an induced airflow. A mixture of primary and secondary (induced) air then leaves the device. The air flow to known low-velocity devices is controlled by measuring the pressure in the duct immediately upstream of a perforated plate mounted in the inlet of said device, as described in EP-A-0493350. Since the pressure drop across a low-velocity device is relatively low, it is necessary to include the perforated plate in order to increase the pressure so that a measurable value will be obtained. The plate has a number of negative consequences, however, among other things because the energy losses increase at the same time as the sound level rises. The throttling effect caused by the perforated plate increases the velocity of the air entering the device and present therein, therewith further increasing the sound level. The maximum airflow into the device is therefore limited in practice by the level of sound that can be tolerated. Another problem with these devices is that the process of measuring airflow is very sensitive to disturbances upstream in the duct system, for instance by a 90-degree bend immediately upstream of the device, which can result in serious measuring errors. There is a need to be able to increase the air capacities of low-velocity supply air terminal devices without generating disturbing sound levels. There is also a desire to eliminate possible sources of error when measuring airflow. The object of the present invention is to provide a low-velocity supply air terminal device which has a greater airflow capacity with the level of sound generated by the device kept unchanged, and to provide a method of measuring the airflow in such devices. The inventive low-velocity supply air terminal device has the features set forth in the following Claims 1-6, while the inventive method comprises the method steps set forth in Claims 7 and 8. The inventive low-velocity supply air terminal device thus includes a perforated plate disposed in the inner space of said device and delimiting an upper part of said space from a lower part thereof so as to favour distribution of the supply air from the inner space in a vertical direction to the distribution unit, said upper part having a length or vertical extension of at least about 50 mm and at most about 300 mm. By using a so-called distribution plate inside the device, more specifically in the space downstream of the inlet, instead of an inlet-mounted measuring plate, the flow conditions into the device are surprisingly improved significantly, because part of the supply air passes out through the air-permeable partition wall of the air distribution unit and out through the outer front plate of said unit without first passing through the measuring plate. This reduces the sound level with an unchanged airflow due to a lower pressure drop, therewith greatly favouring indirectly the capacity of said device. The upper part of the inner space shall not be too short, since the volume of air passing to the distribution unit upstream of the distribution plate will then be too small and the pressure drop will not be greatly reduced. Neither should the upper space be too long, since this would render the plate more or less inoperative as an air distributor. The distribution plate may have varying configurations and be made of mutually different materials without deviating from the inventive concept, although it is preferred that the plate will be circular and have round holes that are distributed essentially uniformly over the full area of the plate. The cross-sectional area of the plate is preferably equal to the cross-sectional area of said space, although a given, although lower, effect will also be obtained with plates of smaller area. The distance from the inlet to the plate, i.e. the height or vertical extension of the upper part of the inner space may vary within the aforesaid limits of 50-300 mm, although, for the aforesaid reasons, the best effect is obtained at a distance of from 100-200 mm from the inlet, this effect varying slightly in relation to the dimensions of the inlet and in relation to the cross-sectional area of the device downstream of the inlet. It can be said generally that when a plate which throttles the airflow is placed in the inlet, as taught by the known technique, it will function solely as a measuring plate and will not function to distribute air in a vertical direction as in the case when the plate is placed at a distance from the inlet in accordance with the present invention. It can, however, in this case also function for measuring purposes. It is true that the measuring pressure will be lower than when measuring in the inlet of the device, although this is more than well-compensated for by the fact that the measuring process will be less sensitive to disturbances, as explained in more detail hereinafter. The distribution plate is conveniently provided with round holes that have a diameter of between 3 mm and 10 mm and has a free area within the range of 40-60%. The plate may include a nipple in the centre of the plate for measuring air volumes. According to the invention, air volumes are measured immediately upstream of a plate provided in the device downstream of the inlet at a distance of between 50 and 300 mm therefrom, and with the aid of a nipple mounted in the plate. The invention increases the capacity of a given low-velocity supply air terminal device from between 15 and 50% when the area of the distribution plate is equal to the inner cross-sectional area of the device, i.e. equal to the area of said space. It is also found that measuring of the airflow is no longer disturbed by flow conditions immediately inwards of the device, and consequently a, e.g., 90-degree bend can be placed immediately upstream of the inlet without exceeding the highest recommended measuring error (5%). The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows an inventive low-velocity supply air terminal device obliquely from above according to one embodiment having a semi-circular distribution unit and a rear outer wall, and Figure 2 illustrates schematically the same device with the outer cover plate removed. Figure 1 illustrates a supply air terminal device 10 having in an upwardly delimited upper part 17 of the device an shown inlet part 11, which has the form of a circular hole in the illustrated case, for connection with a supply air duct (not shown). The device further includes a rear outer wall 12, normally comprised of sheet metal. The device 10 is delimited outwardly by a semi-circular front plate 13 which, although not shown, has openings for supply air distributed over the whole of its surface. Shown at the inlet part is the upper part 14A of an inner space 14 which continues from the inlet 11 straight down through the device 10 to a bottom part 16, which has the form of a plate in the illustrated case. The Figure also shows a horizontal air distribution plate 15 mounted in the space 14 at a distance from the inlet 11 and delimiting a lower part 14B of the space 14, in accordance with the Figure 2 illustration. Figure 2 is a transparent illustration of the same device 10 as that shown in Figure 1, although with the front plate 13 of said device removed for the sake of illustration. Figure 2 shows the upper part 17 of the device, containing the inlet 11 and the distribution unit 18 in the form of a flat perforated plate 19 which is bent at three locations so as to form part of a hexahedron with bent flanges 20, so that the plate 19 has a plane connection with the rear outer wall 12. The plate 19 of the distribution unit 18 is provided with openings 21 for receiving air distribution nozzles (not shown). The horizontal distribution plate 15 also includes openings 22, here shown in a preferred embodiment as round holes, dispersed over the whole of the plate 15. The openings 21 in the plate 18 are intended to receive distribution nozzles for exiting air, for instance nozzles of the kind described in our European Patent Specification EP-B-0507756.

Claims: A low-velocity supply air terminal device (10) intended to be placed in rooms in which a supply of air is required and including an inlet (11) which can be connected to an external supply air duct, an air distribution unit (18) for distributing exiting supply air to said room, an inner space (14) which is open to the inlet (11) and extends in the longitudinal direction of the device from its inlet to its bottom (16), for transporting air and distributing said air to the air distribution unit (18), said space (14) being delimited laterally by an inner air-permeable wall (19) of the air distribution unit (18) and, when applicable, also by the outer wall (12) of said device, wherein said device (10) also includes a perforated plate for throttling supply air, characterised in that in order to favour distribution of the supply air vertically uniformly to the air distribution unit (18), the perforated plate (15) has the form of an air distribution plate which is mounted in the inner space (14) at a distance of at least 50 mm and at most 300 mm from the inlet (11), therewith delimiting or separating an upper part (14A) of the inner space (14) from a lower part (14B) thereof A low-velocity supply air terminal device (10) according to Claim 1, characterised in that the distribution plate (15) is a disk that has round holes distributed essentially uniformly over the whole of its area. A low-velocity supply air terminal device (10) according to Claims 1 and 2, characterised in that the cross-sectional area of the distribution plate (15) is essentially the same as the cross-sectional area of the space (14). A low-velocity supply air terminal device (10) according to Claims 1 and 2, characterised in that the distribution plate (15) is placed at a distance of 100-200 mm from the inlet (11). A low-velocity supply air terminal device (10) according to Claims 1-3, characterised in that the distribution plate (15) is provided with round holes (22) having a diameter of between 3 and 10 mm and has a free area in the range of 45-60%. A low-velocity supply air terminal device (10) according to Claims 1-4, characterised in that the distribution plate (15) has provided in its centre a nipple for measuring airflow. A method of measuring the airflow in a low-velocity supply air terminal device according to the preceding Claims, characterised by measuring said airflow at a distance of between 50 mm and 300 mm from the air inlet of said device. A method of measuring the airflow in a low-velocity supply air terminal device according to Claim 7, characterised by measuring said airflow with the aid of a measuring nipple provided in a perforated plate.

Inventors: HENRIKSSON SVEN-OVE, SVENSSON ANDERS, HENRIKSSON, SVEN-OVE, SVENSSON, ANDERS
Applicants: STIFAB FAREX AB
Application year: 1999
Main classification: F24F13
IPC codes: F24F13