WO1990003540A1

WO1990003540A1 - Ventilation method

Info

Publication number: WO1990003540A1
Application number: PCT/FI1989/000178
Authority: WO
Inventors: Erkki Aalto; Teuvo Pellinen; Jouni Laurikainen; Erkki Asikainen
Original assignee: Halton Oy
Priority date: 1988-09-23
Filing date: 1989-09-25
Publication date: 1990-04-05
Also published as: FI81901B; FI884383A0; FI884383A; EP0389605A1

Abstract

The invention concerns a ventilation method, wherein isothermic or lower-temperature intake air is brought into the space (H) to be air-conditioned from one or several intake-air devices (10) and in which method air contained in the space (H) to be air-conditioned is removed from the zone (K) for gathering of contaminations in the space to be air-conditioned and/or directly from convection-air flows (17) that contain contaminations. In the method intake air is passed into the zone of stay from outside the zone of stay, advantageously by means of an intake-air device placed above said zone of stay, so that the intake-air flow does not substantially prevent or disturb the carriage of contaminated convection flows (17) into the zone (K) for gathering of contaminations in the room space (H). When the convection flows formed in the room space (H) increase, i.e. when the boundary layer of contaminations sinks to a lower level, an increasing proportion of the warm air in the zone for gathering of contaminations is induced as secondary air into the intake-air flow so that a sinking of the boundary layer of contaminations to an excessively low level is prevented.

Description

1 Ventilation method

c The invention concerns a ventilation method for spaces with mechanical air-conditioning, wherein air is blown into, and removed out of, the air-conditioned space. Ventilation is used for the supply of clean air into the breathing zone, where the people stay, and, in a corre¬ sponding way for removing contaminated air out of the same space. -jQ It is required that the operation of the ventilation is such that a per-son who stays in the air-conditioned space does not have a dis¬ agreeable sensation, such as draught, because of the air-conditioning. Moreover, the temperature in the space must be such that a pleasant atmosphere is obtained in view of the purpose of use of the space.

15

At present, primarily two ventilation methods are used, which are displacement ventilation and mixing ventilation. In the mixing ven¬ tilation, an almost optimal distribution of temperature is obtained. In such a case, the intake air, which is blown in at a high velocity, 0 mixes the air in the room substantially completely, and therefore, in the room space, both the temperature and the concentration of contaminations are substantially invariable.

In the mixing ventilation method, along with the intake air, a large 5 secondary flow of air is induced, and the air in the whole space is mixed so that the heat generated by the sources of heat and the amount of contaminations generated by the sources of contaminations are mixed in the air volume of the whole space. Thereby, in the whole space, there are a uniform temperature and a uniform concentra- 0 tion of contaminations. Thus, in the zone of stay, there is the same temperature and the same concentration of contaminations as in the exhaust air.

In the displacing ventilation method the intake air is brought 5 straight into the zone of stay without mixing the intake air and the room air with each other. Thereby distinct vertical distributions of temperature and concentration are formed in the room space. By this 1 method, the air in the zone of stay can be made clean. The flows coming from the sources of contamination or from the sources of heat can rise to the ceiling zone. Owing to the scarce mixing of the air, the temperature of the air at the level of the intake-air member is

5 substantially the same as the temperature of the intake air. Thereby, when intake air of low temperature is employed, a temperature gradient is formed in the space to be air-conditioned. A major part of this gradient is formed in the zone of stay in the space to be air- conditioned, whereby the person who stays in the room is subjected ^■|0 ^to draught. The difference in temperature between the neck and the ankles causes an unpleasant atmosphere.

In the invention, it has been realized to supply fresh air into the space to be air-conditioned at the proximity of the boundary layer

^■{5 of contaminations formed in the room. According to the invention, the fresh air is blown out of the intake-air device vertically from the top downwards. By means of the method in accordance with the invention, a more uniform distribution of temperature is obtained in the zone of stay of the space to be air-conditioned. Moreover, when

20 ^tne method of the invention is used, the boundary layer cannot sink into the zone of stay of the space to be air-conditioned, which is the case when the displacement ventilation method is employed.

The method in accordance with the invention is mainly characterized 25 in that in the method intake air is passed into the zone of stay from outside the zone of stay, advantageously by means of an air distributor device placed above said zone of stay, so that the intake- air flow does not substantially prevent or disturb the carriage of contaminated convection flows into the zone for gathering of con- 30 taminations in the room space and so that, when the convection flows formed in the room space increase, i.e. when the boundary layer of contaminations sinks to a lower level, an increasing proportion of the warm air in the zone for gathering of contaminations is induced as secondary air into the intake-air flow so that a sinking of the 35 boundary layer of contaminations to an excessively low level is prevented. The invention will be described in the following with reference to the accompanying figures.

Figure 1 is a schematical illustration of the ventilation method in accordance with the invention.

Figure 2 illustrates the relative temperature at different points of the room height with different ventilation methods.

Figure 3 illustrates the relative concentration of contaminations with different ventilation methods at different points of room height.

Figure 4 shows a more detailed comparison of the concentrations of contaminations when the ventilation method of the invention and the displacement ventilation method are used. hat is shown is the con¬ centration of contaminations at different points of room height..

Figure 5 is a more detailed illustration of the distribution of temperature in the room space when the method of the invention and the displacement ventilation method are used. The horizontal axis represents the temperature^", and the vertical axis the room height.

Figures 6A to 6C show the measurement curves from a comparison of three different ventilation methods.

Fig. 6A shows measurement results related to mixing ventilation. Fig. 6B shows measurement results related to the displacement ventilation method, and Fig. 6C shows measurement results related to the method in accordance with the present invention.

Figure 7 illustrates a preferred embodiment of the method in accord¬ ance with the invention.

Fig. l is a schematical illustration of the ventilation method in accordance with the invention.

Air is brought vertically from the top downwards out of an intake- air device 10. From the intake-air device 10 the air is discharged into the room space H to be air-conditioned as a primary air flow, i.e. as an intake-air jet 11. The intake-air jet 11 operates as an inducing air jet and draws along a secondary air flow from the proximity of the boundary layer R of contaminations, advantageously from above said layer. The secondary air flow 12 and the primary air flow, i.e. the intake-air flow 11, are mixed together, and the overall air flow 13 is carried into the space H to be air-conditioned, e.g. into a room, into its zone of stay Hτ_. In the ventilation method of the invention, in the upper part of the space H to be air-conditioned a layer of contaminations is formed, whose concentration of con¬ taminations differs radically from the concentration of contaminations present in the rest of the room space. The lower part of said layer K of contaminations, wherein the concentration of contaminations is increased in the space to be air-conditioned abruptly, is, in the present patent application, called the boundary layer R of contami¬ nations. Said boundary layer R can be observed clearly either by means of measurements and/or visually.

Air is removed from above the boundary layer R of contaminations into an exhaust-air duct 14. In the figure the exhaust-air flow is denoted with the arrow 15. The room space may comprise several sources of contaminations or convective sources of heat 16. The contami¬ nations-air flow or the convection-air flow out of said source is carried upwards in the air space H, and said flow is denoted with the arrows 17. Air is removed out of the space H either directly out of the convection flow 17 and/or out of the contaminations layer K in the space H.

In the method of the invention air is blown downwards in the room space H from the proximity of the boundary layer R into the zone H^ of stay. By means of said downward blowing, part of the air placed above the boundary layer is passed to be mixed with said down-blow air 11. As the boundary layer attempts to sink, by means of the downward blowing in accordance with the invention the boundary layer is readjusted to the correct location determined by the intake-air device 10. The invention will be described in more detail in the following with reference to the accompanying graphs of comparison.

Fig. 2 shows the relative distribution of temperature as a function of the height of the room space. The curve f^ denotes the displace¬ ment ventilation method, the curve f2 denotes the mixing ventilation method, and the curve f3 denotes the ventilation method of the present, invention. The horizontal axis represents the relative temperature, and the vertical axis the room height. From the graph it is seen that in the displacement ventilation the difference in temperature between the lower part of the room space and the boundary layer R of contaminations, occurring in the displacement ventilation, is high. In the mixing ventilation, the distribution temperature in the room space is by and large invariable (curve 2 . When the method of the invention is employed, wherein air is blown at the proximity of the boundary layer R downwards, a considerably smaller temperature gradient is obtained in the zone of stay, compared with the case of displacement ventilation. Thus, by means of the method in accordance with the invention, more favourable conditions are achieved in the zone of stay. A high difference in temperature increases a sensation of draught and an unpleasant atmosphere. According to the invention, it has been possible to reduce said temperature gradient considerably in comparison to the displacement ventilation method.

For the distribution of temperature, the following formula is used:

- t_t x 100 %, wherein

- t_t

t^ - temperature of measurement point t_t - temperature of intake air t- - temperature of exhaust air

For the relative concentration of contaminations, the following formula is used:

C_j. - C_t

C - x 100 %, wherein

Cp - C_t C^ - concentration of contaminations at measurement point

C_t - concentration of contaminations in intake air C_p — concentration of contaminations in exhaust air.

In laboratory measurement the concentration of contaminations is the concentration of the marker gas 1^0, which is passed to above convec- tive sources of heat. In a normal room space, corresponding con¬ centrations of contaminations consist of any detrimental and removable contaminations that are carried along with air, such as carbon dioxide (CO2 in respiration air, tobacco smoke, etc.

In Fig. 3, in a corresponding way, said ventilation methods have been compared in respect of the concentration of contaminations. Fig. 3 shows the curves of comparison fι_, f2, f3. The curve f^ relates to displacement ventilation, the graph f2 relates to mixing venti¬ lation, and the curve f3 relates to the method of the invention. The horizontal system of coordinates represents the relative con¬ centration of contaminations, and the vertical system of coordinates represents the height of the room space. From the figure it can be seen that in displacement ventilation and in the down-blow method in accordance with the present invention there is a steep increase in the concentration of contaminations at a certain level in the room space. Thus, in said methods, there is a boundary layer R of con¬ taminations. At the height level concerned the concentration of contaminations increases steeply. From the graph it is seen that, when the method of the invention or a pure displacement ventilation method is used, the concentration of contaminations in the zone of stay is by and large the same. In the mixing ventilation method (curve f2) the relative concentration of contaminations is the same, i.e. 100 %, in the whole room space.

Fig. 4 is a more detailed view of the curves of comparison when the method of the invention and the displacement ventilation method are used. The method of the invention is represented by the curves al,a2,a3 drawn in solid lines. The pairs of values related to the displacement ventilation are illustrated by means of dashed lines as the curves bl,b2,b3. In a corresponding way, the measurement points in the graph illustrating the method of the invention are denoted with Bal,Ba2,Ba3, and the corresponding points in the displacement ventilation method are denoted with Bbl,Bb2,Bb3.

The curves al.bl illustrate a case in which the intake-air flow and the exhaust-air flow are sufficient in view of a convection flow. The boundary layer R of contaminations is placed above the zone of stay H^ in the space H to be air-conditioned, e.g. a room space, and remains in a stable position. By means of the method of the inven- tion, in respect of the concentration of impurities, equally good conditions are obtained in the zone of stay as when the displacement ventilation method is employed.

When the convection air flows are increased in relation to other air flows, the boundary layer R still remains at the same level when the method of the invention is employed. Said situation is illustrated by the curve a2. In said case the concentration of contaminations becomes somewhat higher in the zone of stay. In a corresponding situation with the displacement ventilation method, the boundary layer tends to be lowered to the zone of stay H_]_. Said stage is illustrated by the curves b2 and b3. Thereby the concentration of contaminations in the breathing air is increased abruptly. The curves a3 and b3 illustrate a stage in which the convention air flow or the air flow coming from sources of contaminations have increased further. When a displacement ventilation method in accordance with the curves bl...b3 is employed, a person present in the zone of stay H^ in the room H must stay in contaminated air. When the method of the invention is employed, the boundary layer R still remains at the correct level, and the air in the zone of stay is still of considerably higher purity than in the upper part of the room H.

Fig. 5 illustrates a corresponding comparison of the down-blow method of the invention and the displacement ventilation method by means of curves of temperature. In Fig. 5 the horizontal axis represents the temperature, and the vertical axis the height level in the room. The difference in temperature between the lower part of the room and the upper part of the zone of stay H^ is considerably higher in the displacement ventilation method than when the method of the invention is used. For example, when the curves s.ι -^° ^are compared with each other, the difference in temperature between the boundary layer R and the floor level in the room is D_]_ when the method of the invention is employed and D2 when the displacement ventilation method is used. From the curves in the figure it is seen that D2 is considerably higher than D_j_. This means that, when a normal displacement ventila¬ tion method is employed, there is a considerable difference in tem¬ perature between the shoulders and the feet of a person staying in the zone of stay, and said difference in temperature results in disagreeable draught. Thus, when the down-blow in accordance with the invention is used, said unfavourable temperature gradient is avoided and the pleasant atmosphere in the space to be air-conditioned is improved. When the method of the invention is employed, said reduced temperature gradient is retained under all circumstances

(curves al...a3). In the method of the invention, above the intake- air device, in the air space placed there, a steeper temperature gradient is formed than in the air space placed below the intake-air device. The vertical temperature gradient in the zone of stay proper i^{s at} the maximum 1.5°C per metre. When the method of the invention is employed, the maximum velocity of the intake-air flow 11 at a distance of 0.5 m from the air-distributor device 10 is no higher than 1 m/s.

Iⁿ the method of the invention, the location of the boundary layer is determined so that it is at the level of, or above, the location of the intake-air device. Now the air flows, i.e. the intake-air flows and the exhaust-air flows as well as the convection-air flows mentioned above, together with the generation of contaminations, determine the concentration of contaminations that is reached in the space to be air-conditioned.

When the boundary layer of contaminations attempts to sink to a level lower than the level of installation of the intake-air device, the concentration of contaminations in the intake-air jet is in¬ creased. An increased secondary air flow from the boundary layer again raises the level of the boundary layer R, and in this way the boundary layer is adjusted to the level of the intake-air device. Thus, the boundary layer cannot be formed below the level of the intake-air device, but the method attempts to raise the boundary layer to above the level of installation of the intake-air device.

When the down-blow method in accordance with the invention is used, an approximately invariable temperature is obtained in the zone of stay. However, an upward carriage of a larger amount of contamina¬ tions rising along with the convection flow is not prevented, nor is formation of the boundary layer R prevented.

In the method of the invention, fresh air is introduced into the room space by blowing it at a low velocity from above into the zone of stay in the intake air; secondary air flow is mixed into the primary air flow as a 0.1...10-fold, most advantageously as a 0.1...3- fold quantity in relation to the volumetric flow of air in the primary air flow 11, whereby a substantially invariable temperature is pro¬ duced in the air in the zone of stay. Out of the space to be air- conditioned, air is removed at the proximity of the ceiling or from ^a location where the concentration of contaminations in the air is highest. The location of the intake-air device 10 is chosen so that rising of the so-called convection flows and of contaminations carried along with them into the zone of exhaust air to the proximity of the exhaust-air duct is not prevented.

Advantageous locations are occasional zones of stay, such as halls, corridors, areas at the side of walls, in front of doors. The ven¬ tilation method of the invention is used most advantageously in spaces where there are heat loads of low surface temperature, such as people. Advantageous objects of use of the method of the invention are lodging premises, office premises, dwellings, classrooms, con¬ ference rooms and nursing premises. Also, passenger cabins are advan¬ tageous objects of use for the ventilation method of the invention. The level of the intake-air device measured from the floor, i.e. the installation height, is determined at the same level as the desired lowest allowed level of the boundary layer R of contaminations. Figures 6A to 6C are more detailed graphs of comparison illustrating the air-flow method and based on laboratory measurements. Fig. 6A relates to the mixing ventilation method and illustrates the distribu¬ tion of temperature in a room space and the distribution of concentra- tion of contaminations in a room space. Fig. 6B relates to the dis¬ placement ventilation and illustrates the distribution of tempera¬ ture in a room space and the distribution of concentration of con¬ taminations in a room space, and Fig. 6C relates to the down-blow method in accordance with the invention and illustrates the distribu- tion of temperature in a room space and the distribution of concentra- tion of contaminations in a room space.

Fig. 7 illustrates an embodiment of the invention wherein the zone K of gathering of contaminations placed above the zone of stay 20 is separated from the upper part of the zone 19 of temporary stay by means of a wall 18 extending downwards from the ceiling. By means of the wall 18, mixing of the most contaminated air in the upper part of the zone K for gathering of contaminations as a secondary air flow 12 into the intake-air jet 11 blown out of the intake-air device 10 i^s restricted. In the embodiment shown in Fig. 7, air is introduced out of the intake-air device 10 placed in the zone 19 of temporary stay, and air is removed out of the layer K of contaminations placed above the zone 20 of stay proper through an exhaust-air duct 14 placed in the ceiling. The air flow that is removed is denoted with the arrows 15 in Fig. 7. The convection flows are denoted with the arrows 17 in Fig. 7.

Claims

WHAT IS CLAIMED IS:

1. Ventilation method, wherein isothermic or lower-temperature intake air is brought into the space (H) to be air-conditioned from one or several intake-air devices (10) and in which method air contained in the space (H) to be air-conditioned is removed from the zone (K) for gathering of contaminations in the space to be air-conditioned and/or directly from convection-air flows (17) that contain contaminations, c h a r a c t e r i z e d in that in the method intake air is passed into the zone of stay from outside the zone of stay, advantageously by means of an intake-air device placed above said zone of stay, so that the intake-air flow does not substantially prevent or disturb the carriage of contaminated convection flows (17) into the zone (K) for gathering of contaminations in the room space (H) and so that, when the convection flows formed in the room space (H) increase, i.e. when the boundary layer of contaminations sinks to a lower level, an increasing proportion of the warm air in the zone for gathering of contaminations is induced as secondary air into the intake-air flow so that a sinking of the. boundary layer of contami- nations to an excessively low level is prevented.

2. Ventilation method as claimed in claim 1, c h a r a c t e r ¬ i z e d in that in the method the temperature gradient in the zone of stay (H^) in the space (H) to be air-conditioned is reduced so that intake air is made to flow out of the intake-air device (10) in the zone of stay (H^) in the space (H) to be air-conditioned from the top downwards and so that thereby part of the warm air present in the boundary layer (R) of contaminations in the space (H) to be air-conditioned is mixed into the intake-air jet (11), whereinafter the intake-air jet (11) is mixed further into the air in the zone of stay (H^) and mixes said air.

3. Method as claimed in claim 1 or 2, c h a r a c t e r i z e d in that air is removed out of the space (H) to be air-conditioned from the zone (K) for gathering of contaminations from above the intake- air device (10) through an exhaust-air duct (14) placed at the proximity of the ceiling of the space (H) to be air-conditioned.

4. Ventilation method as claimed in any of the preceding claims, c h a r a c t e r i z e d in that above the intake-air device there is a steeper temperature gradient than underneath said device.

5. Ventilation method as claimed in any of the preceding claims, c h a r a c t e r i z e d in that the intake-air flow is passed into the zone of stay proper, i.e. to the principal zone of stay, through a transit zone or through temporary zones of stay, e.g. through corridors, halls, and that the zone (K) for gathering of contaminations is advantageously at least partly separated from the temporary zone of stay by means of a wall (18) so as to restrict mixing of the intake-air jet (11) and the contaminated air present in the zone (K) for gathering of contaminations.

6. Ventilation method as claimed in any of the preceding claims, c h a r a c t e r i z e d in that in the zone of stay proper the vertical temperature gradient is at the maximum 1.5°C/m.

7. Ventilation method as claimed in any of the preceding claims, c h a r a c t e r i z e d in that the maximum velocity of the intake- air flow (11) at a distance of 0.5 metre from the air-distributor device is no more than 1 m/s.

8. Ventilation method as claimed in any of the preceding claims, c h a r a c t e r i z e d in that, when the intake-air flow arrives in the zone of stay, the intake-air flow contains advantageously a 0.1...10-fold quantity of secondary air, in relation to the primary air flow (11), and most advantageously a 0.1...3-fold quantity in relation to the primary air flow (11) .

9. Use of the ventilation method as claimed in any of the preceding claims, c h a r a c t e r i z e d in that the method is used in spaces in which there are heat loads of low surface temperature, such as, for example, people.

10. Use of the ventilation method as claimed in any of the claims 1 to 8, c h a r a c t e r i z e d in that the method is used in lodging premises, office premises, dwellings, classrooms, conference rooms, nursing premises, or other, corresponding premises, such as, for example, passenger cabins.