WO1992014973A1

WO1992014973A1 - A method of and a distribution device for introducing air into a room

Info

Publication number: WO1992014973A1
Application number: PCT/FI1992/000037
Authority: WO
Inventors: Seppo Juhani Leskinen; Tapani Eino Antero Ahokas
Original assignee: ABB Fläkt AB
Priority date: 1991-02-14
Filing date: 1992-02-12
Publication date: 1992-09-03
Also published as: DE69219320T2; EP0571478A1; FI90466C; DK0571478T3; DE69219320D1; FI910729A0; FI90466B; EP0571478B1; ATE152232T1; AU1257592A; FI910729A

Abstract

A method of introducing air into a room by passing supply air (A) into a distribution device (1) ending in the room (2) and by blowing the air from the distribution device through air supply openings (8, 9) into the room. In order to control the introduction of air even when the supply air is considerably warmer than the room air, the supply air is introduced into the distribution device selectively through two separate independent flow paths (4, 5) into the air supply openings, whereby the supply air is subjected to flow conditions required for heating at the air supply openings (8) of one flow path and correspondingly to flow conditions required for cooling at the air supply openings (9) of the other flow path. A distribution device carrying out the method comprises at least two separate alternative flow ducts (4, 5) for supply air, the flow ducts being provided with separate air supply openings (8, 9) which provide different flow conditions in the separate flow ducts.

Description

A method of and a distribution device for introducing air into a room

This invention relates to a method of introduc- ing air into a room, in which method

- supply air is introduced into a distribution device ending up in a room; and

- the supply air is blown from the distribution device through air supply openings into the room, - whereby the supply air is passed in the dis¬ tribution device through at least two separate flow paths into separate air supply openings, and

- the supply air is subjected to flow condi¬ tions at the air supply openings of each flow path, which flow conditions differ from the flow conditions at the air supply openings of the other flow paths.

To supply air into a room, various devices have been developed, which can be divided roughly into three main groups: So-called mixing air distribution devices usually introduce the air into the upper portion of the room at a single point at a rather high rate through various slits, nozzles or openings. Air flow¬ ing through them catches with it great quantities of ambient room air and mixes with it. The entire air mass contained in the room is thus brought into motion and is mixed so that it becomes nearly homo¬ geneous both in temperature and in impurity content.

Due to the high flow rate, disturbing noise occurs easily. Large air jets are difficult to control. If the flow rate of air is too high, dis¬ turbing draught occurs. On the other hand, if the flow rate is too low, dead areas where the air does not change are liable to occur. The control of temperature conditions is made difficult by the influence of thermal forces on the air jet in spite of mixing. If the supply air is warmer than the room air, the air jet bends upward, and so the air in the lower portion of the room does not change. If the air is colder, it bends downward and causes draught. It is thus possible only to some extent to control the room temperature by adjusting the temperature of supply air. The air flow cannot either be adjusted to a very great extent without causing the above- described disadvantages.

In the so-called displacement air distribution, air is introduced at a low rate directly into the occupied zone through a rather large surface.

Draught and noise problems are usually avoided if the temperature of the supply air and the room air is the same. If the temperature difference increases to 2-3 degrees, thermal forces begin to control the flow. When the supply air is colder than the room air, the flow "drops", the flow rate increases due to the thermal forces, and draught occurs on the floor level. If the supply air is warmer than the room air, it rises upward where the exhaust is also usually positioned. This results in a so-called short-circuit flow and poor air change within the occupied zone. Accordingly, the room temperature cannot be adjusted significantly. As there is no air jet which would catch room air with it, the moving air mass is small and the flow is thus liable to disturbances. Convection flows, machines bringing the air into motion, people moving in the room, various flow obstacles etc. may affect the flows of air in the room. This may result in poor local air change. The air flow can be adjusted within wide limits without causing problems. Recently, a so-called active displacement has been developed which eliminates part of the dis¬ advantages of the displacing air distribution. The air distribution is divided over a large surface. Air flows into the room through small nozzles at a high rate and puts a great air mass into motion. As the air jet from a small nozzle is small, no noise problems occur in spite of the high rate. The flow rate of air in the small jet drops rapidly, so that draught does not occur easily. As a great quantity of air is brought into motion, disturbances affect the flow only locally, and so the air change is even throughout the room. Due to the high mixing ratio of supply air and room air, the temperature differences are levelled out, so that even cold air can be intro- duced into the occupied zone without causing the flow to "drop". Not even a temperature difference as high as 15 degrees causes floor draught.

If, however, the supply air is considerably warmer than the room air, a small temperature differ- ence causes the air to rise away from the occupied zone even after forceful mixing.

The air flow can be adjusted within wide limits. Active displacement is thus very suitable for use in cooling, but only limitedly in heating. This way of air distribution is described in Finnish Patent Specifications 79608, 73513, 72800 and 71417.

Finnish Patent Specifications 75421, 73514 and 70320 disclose air distribution devices in which supply air flowing through separate flow ducts is subjected to different flow conditions. These air distribution devices comprise two separate flow ducts at the air inlet end, through which ducts the supply air flows into the room space. Both ducts are, how¬ ever, arranged to be used simultaneously, that is, part of the supply air flows through one duct and part through the other duct. The purpose of such an arrangement is that the air flows passing through the two ducts supplement each other to achieve desired flow conditions. The device thus comprises only one air distribution system.

The object of the present invention is to provide a method which avoids the above-mentioned disadvantages and enables a faultless operation of an active displacement in particular even in cases where the supply air is considerably warmer than the room air. The room temperature can thus be fully controlled and adjusted. This object is achieved by means of a method according to the invention, which is characterized in that the supply air is introduced selectively through one or more separate independent flow paths.

The invention is based on the idea that the supply air is passed from the distribution device into the room through two alternative flow paths so that, depending on the flow path through which the air is blown into the room, different flow conditions are created for the supply air by means of different air supply nozzles. When heating is required, one flow path is used for the supply air, and when cool- ing is required only the other flow path is used. In cases where neither heating nor cooling is needed, the supply air can be introduced partly through both flow paths.

The invention is especially suitable for an active displacement but it can also be applied to other air distribution methods to improve their prop¬ erties.

The invention is also concerned with an air distribution device for applying the above-described method. The air distribution device is characterized in that the distribution device comprises closing means for separating the flow ducts from each other, and that each flow duct forms an independent air dis¬ tribution means, the independent air distribution means operating simultaneously together or separate¬ ly-

The basic idea of the distribution device is that the air supply openings, such as nozzles, are divided into at least two separate groups into which the supply air can be passed selectively through the separate flow ducts. The number and direction of the nozzles, the air flow rate in the nozzles and even the size and shape of the nozzles may be different in each group. One and the same air distribution device thus provides two or more different air distribution systems independent of each other, e.g. one for winter conditions and one for summer conditions, and the properties of the systems can be adjusted almost continuously from one system to another. In the following the invention will be described in greater detail with reference to the attached drawing, in which

Figures 1 and 2 show one embodiment of a distribution device according to the invention in a side view and in a section along the line II-II shown in Figure 1, respectively;

Figures 3A and 3B illustrate schematically the flow pattern of air blown into a room from the dis¬ tribution device when cooling is required and when heating is required, respectively; and

Figure 4 is a side view of another embodiment of the distribution device.

The air distribution device shown in Figures 1 and 2 of the drawings comprises an elongated supply pipe 1 connected at one end to a feed -system for supply air A and extending into a room 2 to be air- conditioned. The pipe is installed horizontally above the occupied zone of the room. The supply pipe is divided with a central partition plate 3 into two longitudinal halves which form two flow ducts 4 and 5 separate from each other. The flow ducts 4 and 5 end in a solid end plate 6 of the supply pipe. At the forward end of the partition plate there is a change¬ over damper 7 formed of a flap plate and mounted pivotably to the partition plate. The change-over damper is pivotable between two extreme positions, in which it closes fully either one of the flow ducts. The change-over damper can also be positioned in intermediate positions in which both flow ducts are partially open. Essential is that the adjustment of air flow in the upper flow duct and the lower flow duct of the supply pipe takes place in opposite directions, that is, when the flow in one duct is restricted, the other duct opens. The change-over damper may be manually operable or connected to a suitable adjusting device.

A great number of nozzles 8 are mounted in the mantle surface of the upper flow duct 4 of the supply pipe. The nozzles 8 introduce supply air radially into the room. Similarly, a great number of radial nozzles 9 are mounted in the mantle surface of the lower flow duct. The nozzles of the upper duct have smaller flow openings than the nozzles of the lower duct. Figures 1 and 2 illustrate the operation of the distribution device when cooling is aimed at, that is, when the supply air A is colder than the room air. The change-over damper 7 is thereby turned so as to close the lower flow duct 5, so that air is supplied into the room only through the nozzles 8 of the upper flow channel 4.

Figure 3A shows schematically a flow pattern created in the room when the room is to be cooled. Air jets B from the upper nozzles 8 of the supply pipe are directed upward and sideward and bring with them so-called induction air from below and are mixed with it. Since the air in the jets is colder than the ambient air and thus heavier, the jets tend to bend downward. The jets create a small vacuum below the supply pipe, and this vacuum tends to bend the down¬ wardly bent flow, which no longer has any temperature and density differences, to the side and again upward. Forces acting in different directions create a double turbulent flow shown in Figure 3A, in which the main direction of flow is upward in the middle and downward at the edges. Even though the flow rates are extremely low, they can be proved experimentally. As is typical of forced turbulent flows in general, the turbulence is extremely stable as compared with the magnitude of the impulse that created it, and it resumes its original shape very rapidly after a dis¬ turbance.

The distribution device operates in the way described above even when the supply air is slightly warmer than the room air. At a state of equilibrium, the vacuum below the supply pipe is equal to the thermal lifting action caused by the density dif¬ ference. If the temperature difference increases, the flow bends upwards, and the supply air no longer enters the occupied zone. The situation is com¬ plicated as the stability of the turbulence decreases with decreasing temperature difference. Thereby even a minor disturbance, flow obstacle, or the like, may totally change the nature of the flows. When the supply air is warmer than the room air, the pivoting change-over damper 7 is turned into a position shown by broken lines in Figure 1. The flow of supply air into the upper flow duct 4 is thereby prevented, and the supply air flows into the room only through the nozzles 9 of the lower flow duct 5. Air jets C are directed downward and take room air with them from above the supply pipe. Thermal forces bend the jets upward. If the flow im¬ pulse is selected suitably, the flow pattern shown in Figure 3B is achieved.

If the nozzles 8 and 9 of both flow ducts are similar, the impulse can be affected only by varying the number of the nozzles 9 of the lower duct, as a result of which the flow rate in the nozzles also changes. In order to make the warm air enter the occupied zone, the impulse and flow rate in the nozzles 9 generally have to be clearly greater than in the nozzles 8 of the upper flow duct, that is, the number of the lower nozzles 9 has to be smaller than that of the upper nozzles 8. In the air distribution device of the type shown in Figure 1, a reduction in the number of the nozzles 9 also affects favourably the direction of the nozzles. The sector within which the nozzles are positioned decreases with decreasing number of nozzles, and the jets are directed in a more downward direction and in a more centralized manner.

The flow rate in the nozzles 9 of the lower flow duct cannot, however, be increased without restrictions: the pressure loss or noise level easily increases too much. This problem can be solved in the system according to the invention by selecting the nozzles 9 so that they are of a different type than the nozzles 8 so that the impulse of the nozzles 9 and especially the so-called throw is greater than that of the nozzles 8.

For reasons of manufacturing techniques, for instance, it may be advantageous that the nozzles 8 and 9 are identical. A flow of desired type can be achieved by inserting a few large nozzles amongst the nozzles 9 of the lower duct. These large nozzles provide carrier jets which carry the air into the occupied zone. This kind of arrangement is also advantageous in that the mixing ratio of supply and room air remains at a high value.

If the nozzles 9 of the lower duct have to be dimensioned for a high heating effect, that is, for a great temperature difference, which has to be adjusted from zero to maximum effect, the flow from the nozzles 9 may be too forceful and cause draught in the occupied zone when the temperature difference is small. The distribution device operates faultless-

• ly even when a small proportion of the supply air is allowed to enter through the nozzles 8 of the upper duct by using the change-over damper 7.

The air flow and thus the flow rate in the nozzles 9 of the lower duct decreases, and so the impulse and throw of the air jet are also decreased. Additionally, the supply air flowing slowly from the nozzles 8 is drawn by the air jet from the nozzles 9 and is mixed with it, whereby the temperature of air in the jet rises and the thermal lifting action in¬ creases, tending to more intensely slow down the downwardly directed jet. Furthermore, the flow from the nozzles 8 in the opposite direction brakes the flow from the nozzles 9, decreasing the impulse and throw of the jet. In this way the flow field can always be modified such that the supply air scavenges the entire occupied zone without causing dis- advantageous draught. The embodiment of the distribution device shown in Figure 4 deviates from the one described above only in that the closing means for the separate flow ducts 4 and 5 of the supply pipe 1 is a so-called butterfly damper 10. This damper comprises two semi¬ circular plates fixed perpendicularly with each other and mounted pivotably to the partition plate perpen¬ dicularly to it. The damper 10 operates similarly as the change-over damper 7 described above. The drawings and the description related to them are only intended to illustrate the idea of the invention. In their details, the method and the distribution device according to the invention may vary within the scope of the claims. The supply pipe of the distribution device may be rectangular, el¬ liptical, etc. in cross-section, and the ratio be¬ tween its length and diameter may vary. The partition plate may be angular, curved, etc. It need not be parallel to the central line of the pipe, or to the sides of a rectangular pipe, in the longitudinal direction. The pipe is shown to be straight, but it may also be conical and it may comprise reducing fittings, etc. The change-over damper may be e.g. a guide blade adjuster. In place of nozzles, the air supply openings of the supply pipe may be mere open¬ ings, holes or the like.

The pivotable change-over damper may be re¬ placed with an arrangement comprising a control plate fixed to the partition plate 3. The partition plate is mounted in such a way that it turns about the central line of the pipe 1. By turning the partition plate through 180 degrees, the supply air can be guided either into the nozzles 8 or into the nozzles 9. A disadvantage of this arrangement is that the air cannot be guided partly into the nozzles 8 and partly into the nozzles 9 without substantially altering the direction of the air jets and the flow field created by them. Large partition plates, often several metres in length, are difficult to mount in bearings, which is also considerably more expensive than the simple damper shown in Figure 1. The shape of the pipe 1 is also limited.

If the partition plate 3 is a circular arch having a radius slightly smaller than that of the pipe 1 and turning about the central line of the pipe, it forms a closing plate which can be turned to close the nozzles 8 or the nozzles 9. The disad¬ vantages are the same as in the embodiment described above. An advantage is a smaller pressure loss as the air flows into the nozzles through the entire cross- sectional area of the pipe 1.

The partition plate 3 can also be made stationary, the pipe 1 being mounted to rotate about it. In this embodiment and in the preceding embodi- ment, the partition plate may also be positioned out¬ side the pipe 1.

Claims

Claims :

1. A method for introducing air into a room, in which method - supply air (A) is introduced into a distribu¬ tion device (1) ending up in a room (2); and

- the supply air is blown from the distribution device through air supply openings (8, 9) into the room, - whereby the supply air (A) is passed in the distribution device (1) through at least two separate flow paths (4, 5) into separate air supply openings (8, 9), and

- the supply air is subjected to flow condi- tions (B, C) at the air supply openings (8, 9) of each flow path, which flow conditions differ from the flow conditions at the air supply openings of the other flow paths, c h a r a c t e r i z e d in that the supply air (A) is introduced selectively through one or more separate independent flow paths (4, 5).

2. A method according to claim 1, c h a r a c ¬ t e r i z e d in that the supply air (A) is intro¬ duced selectively through different flow paths (4, 5) when heating is required and when cooling is re- quired.

3. A method according to claim 1, c h a r a c ¬ t e r i z e d in that the supply air (A) is intro¬ duced partially through both flow paths (4, 5) when heating and cooling are not required.

4. A distribution device for introducing air into a room, the distribution device (1) being con- nectable to a pipe for supply air (A) and provided with openings (8, 9) for blowing supply air into a room (2), the distribution device (1) further co - prising at least two separate flow ducts (4, 5) for the supply air (A), the separate flow ducts (4, 5) being provided with their own air supply openings (8, 9) arranged to create different flow conditions (B, C) for the supply air flowing through each of the separate flow ducts (4, 5), c h a r a c t e r i z e d in that the distribution device comprises closing means (7; 10) for separating the flow ducts (4, 5) from each other, and that each flow duct forms an independent air distribution means, the independent air distribution means operating simultaneously together or separately.

5. A distribution device (1) according to claim 4, the distribution device being formed of a pipe, c h a r a c t e r i z e d in that the distribution device (1) is divided by an axial partition wall (3) into two longitudinal flow ducts (4, 5), and that a closing flap (9; 10) is provided at the forward end of the partition wall, the closing flap being pivot¬ able into positions blocking the flow of the supply air (A) into either one of the flow ducts.

6. A distribution device according to claim 5, c h a r a c t e r i z e d in that the position of the closing flap (9; 10) is adjustable between the positions closing each flow duct (4, 5).

7. A distribution device according to any of claims 4 to 6, in which the air supply openings (8, 9) are nozzles, c h a r a c t e r i z e d in that the nozzles (8, 9) of the separate flow ducts (4, 5) are unequal in size and/or number.

8. A distribution device according to any of claims 4 to 7, c h a r a c t e r i z e d in that the nozzles (8, 9) of the separate flow ducts (4, 5) are substantially opposite in direction.