SE527241C2 - Flow stabilized ventilation system - Google Patents

Abstract

The invention relates to a method in which the dominative drop in pressure of a flow stabilised ventilation system is established across the supply air terminal devices of respective rooms. By using supply air terminal devices that include several nozzles of noise minimising construction and numbers for leading air into the room, it is possible to allow a drop in pressure of up to 250 pascal across the device without exceeding office noise limits. The invention obviates the need for throttles, constrictions and sound dampening means. Because the dominative drop in pressure is established across the supply air terminal device, and because said device is a nozzle-type device, there will be relatively little change in the airflow through the sytem conduits and through the supply air terminal devices as a result of pressure changes in the system.

Description

20 25 30 35 527 241 2 Technical and economic requirements 7) The driving power of fans should be kept low both for economic reasons and due to unwanted sound stringing. 8) The pressure distribution between ducts (often of different lengths) must be balanced in a reasonable way due to technical and economic requirements.

Common system solutions There are several different types of installations (system solutions) that meet the above functional requirements. The requirement for fresh air and the requirement for the right temperature in a building can be solved in several ways. Of crucial technical-economic importance is how the fresh air and heat are distributed to and from the premises where it is used within the building.

Regarding the heat and cooling transport, it can be - Waterborne from a local power plant (oil boiler, electric boiler, cooling unit), - airborne from a local power station (oil boiler, electric boiler, cooling unit), - produced in the rooms (electric radiator, fireplace , cooling units).

The fresh air can come via - a local exchange in the building (mechanical ventilation), -in direct connection between rooms and outside air (air gaps under windows).

In spaces with high comfort requirements, points 1-8 above must be met well. Decisive for what the technical solutions look like today has been and is a number of technical-economic factors such as construction costs, installation costs, component costs, the authorities' regulations, in addition to how well the functional technical requirements have been met. These factors, together with technical innovation ability, have guided developments in the ventilation industry. Developments in Sweden with high demands on both heating and cooling in office spaces have over time led to ventilation solutions that are characterized by: 10 15 20 25 30 35 527 241 I. The heating and cooling supply takes place from a (nearby) central to the room with water as an energy-bearing medium.

II. The fresh air is distributed to and from the rooms via a pipe network from a local exchange.

III. The regulation of fresh air volume, heating and cooling takes place "near or in the room where people work.

The above preferred design thus requires equipment for introducing fresh air into the room and at the same time heating or cooling it so that the right comfort is obtained. The main technical advantages of this focus on the system solution are: - A water-borne energy transport entails a small dimensioning of lines, etc. because water can carry a lot of energy per kg of medium. Water is also easy and efficient to exchange heat between different systems.

- The separation of air and energy transports entails a pure cultivation of the components and functions within each system.

This in the long run leads to cheaper components and higher functional reliability.

- The requirement to be able to regulate the indoor climate in each room means in reality that a control system must be in each room, which is why it is logical to be able to control the temperature control of the fresh air in this place.

- The existing technical system solutions according to the above offer many advantages, but there are still significant disadvantages that you struggle with.

Disadvantages of current system solutions If you want to develop the best existing system solutions, you can consider the following points of view: Water-borne energy distribution according to I exists and they work well. Regarding the regulation of fresh air both in terms of quantity and temperature, there are a plethora of methods and components and it leads too far to go into specific ones here. However, product development has been concentrated on components and in many cases their place in a system has been neglected. In the long run, they should be necessary to start from primarily improving the system and from this point of view select or develop components. At present, it is more or less the case that the system becomes the sum of components without the total system function being examined. This relationship is understandable but not good. The main reason should be in the interest of manufacturers to sell their own components and in a conservative corps of plumbing consultants who do not primarily adopt news.

The distribution of fresh air from a central (fan room) to (office) spaces and the distribution of the exhaust air back requires a duct system and different types of regulations to control the air flows. It is of interest here to see which factors are dimensioned for the system. a) The size of channels with accessories costs money. Smaller dimensions become cheaper and encroach less on spaces at the expense of the flow rate in pipelines. b) Large fan effects with large pressure drops increase the possibility of restricting the flow in the duct systems a lot for control purposes. c) The number of fan exchanges in a building is expensive and is normally limited to a single or a few. This often results in long pipe systems with many branches. d) The control of flows in different ducts often takes place via sequential choking of ducts in order to achieve a specified pressure drop across the local supply air devices in the rooms. e) Energy recovery between supply and exhaust air is economically important. The methods vary but normally require that an exhaust air system exists. Thus, there are requirements for dual duct systems. (f) Structures included in subsystems mentioned in subparagraphs (a) to (e) above must also be designed in such a way that no generating sound levels are generated. 10 15 20 25 30 35 527 241 Low noise levels in office premises have perhaps become the most significant dimensioning factor in modern ventilation systems. This is partly due to the fact that the requirements for sound comfort have increased and partly due to the fact that a cheap design to cope with the factors according to a) to e) is in conflict with low noise levels.

The types of sound generated are of several types and all cause inconvenience.

Infrasound can be generated in duct systems without being heard and cause discomfort and nausea. Audible sounds are definitely generated in the ducts and fan motor sounds and vibrations are transmitted along with them through the duct systems and into the rooms. Last but not least, disturbing sounds are generated by the supply air devices that ultimately disperse air in a specific room. In order to remedy these inconveniences, different types of silencers are often introduced along the duct system and the pressure drop across the supply air devices is in practice always specified by the manufacturer to a maximum value in order for the sound level from it to remain within stipulated limits.

Known ventilation systems can thus be considered to include a fan control panel which supplies supply air via a supply line. Along the supply line, channels are delimited, which lead into each room. The ducts open into one or more supply air diffusers in the rooms. The fan control panel should supply the air with an overpressure of the order of 100 Pa to meet existing needs for dampers, throttles, mufflers, etc. along the supply line to finally deliver supply air with a pressure of about 20 Pa just before the supply air device.

The requirement for the highest pressure drop (approx. 30 Pa) over a conventional supply air device is due to the desire to avoid annoying noise at the supply air device. This in itself leads to requirements for dampers / throttles in the ducts to ensure that the air pressure on the inlet side of the supply air diffuser is at most as great (approx. 30 Pa). But such pressure-reducing dampers / throttles also produce noise, which in turn requires the installation of silencers that are expensive both in terms of cost and installation. Since the pressure drop across the conventional supply air device must be low, it is usually required that the air flow of the supply air device is adjustable, for example with a throttle, so that a correct and desired supply air flow to the room can be set. The supply air flow adjusting throttle, in turn, has a tendency to produce noise and usually requires the supply air device to contain sound-absorbing agents.

The measurement of the air flow through the supply air device, and the setting of this, is a time-consuming and costly work effort, and presupposes that the supply air device is adjustable.

An object of the invention is to provide techniques with which the mentioned inconveniences can be completely or partially eliminated. The object is achieved with a ventilation procedure according to the independent method requirement. The purpose is also achieved with a ventilation system according to the independent system requirement.

Embodiments of the invention are set forth in the appended dependent claims.

The invention is based on the concept of using a supply air diffuser which has a wall with a plurality of air nozzles which let the supply air into the room. The nozzles are designed to cause the least possible flow disturbances and thereby the least possible noise development. The design of the nozzles for this purpose belongs in itself to the state of the art. The number of nozzles at constant flow does not affect the sound generation of the supply air diffuser.

This means freedom to construct supply air devices dimensioned for pressure drops between 60-250 pascals at stipulated flow and (quiet) sound level, which is impossible with conventional supply air devices. The pressure drop through the supply air diffuser is essentially established only by the nozzles.

The nozzles are usually designed with an opening diameter in the size range 4-7 mm. For a tested embodiment, the diameter of 5.7 mm was chosen. The nozzle has a softly rounded funnel shape and tapers all the way to its outlet. The mutually equal nozzles in the supply air device each pass through an air flow which is well defined and which to a relatively small extent varies with the magnitude of the pressure drop. It is therefore possible for a designer to designate a supply air device that meets the sound requirements for a certain room with a given desired supply air flow and pressure drop.

Because the supply air device itself can take care of a large pressure drop, no pressure-reducing and noise-inducing throttles are required in the supply air ducts. The need for noise attenuation for control dampers and the like in the supply air device is also eliminated, because control can be done in a silent manner by blocking or exposing a number of nozzles in a device.

The invention will be described in the following in an exemplary form with reference to the accompanying drawing.

Fig. 1 Fig. 2 Fig. 3 schematically shows a ventilation system for a building. shows a section taken along line II-II in Fig. 1. shows a section taken along line III-III in Fig. 2. shows a section taken along line IV-IV in Fig. 3.

Figs. 5A-5C show successive steps in the manufacture.

FIG.

FIG.

FIG.

Fig. 10 of a supply air device according to the invention. shows an alternative supply air diffuser. shows an axial section through a nozzle. shows another embodiment of a supply air device. shows a nomogram. shows another embodiment of a supply air device.

Fig. 1 schematically shows a building with a fan center 1, an air supply line 2 and a plurality of branches 3 branched along it, which lead to respective supply air diffusers 4 in associated rooms 5. The rooms can be considered to have different needs for supply air flows. . The pressure P1 at the outlet of the fan control unit 1 drops to P2 at the end of the line 2. In rooms 5, the air pressure P0 must of course be atmospheric pressure.

The wires 3 can be of different lengths.

In a practical situation, the pressure difference between P1 and P2 can amount to about 30 Pa. In order to prevent a change in the air outflow in one room from having a strong effect on the air outflow in other rooms, it is appropriate to have the fan exchange 1 establish a pressure P1 of the order of 100 Pa below atmospheric pressure and to ensure that most of the pressure drop taken up over the supply air devices.

Figs. 2-4 schematically show a supply air device comprising a straight circular-cylindrical plate jacket 41 which at the outer end 42 is closed with a plate end, and which at the inner end 48 is connected to the end of the duct 3.

The sheet metal jacket 41 is provided with a plurality of nozzles 43 (Fig. 7).

The supply air devices and nozzles are designed to offer an air flow with minimized noise generation. The nozzles 43 are for that purpose designed to cause the least possible disturbance in the air flow out through the nozzle. The inner wall of the nozzle is therefore smooth and continuously curved and connects continuously to the sheet metal jacket. Furthermore, the wall of the nozzle 43 is arranged to be conical all the way to the outlet mouth 44. The nozzle has a substantially circular cross-section. All nozzles 43 in supply air 4 should be of equal design. The inner surface of the nozzle should be smooth and have a good shape accuracy, and furthermore the nozzle should be made so that it lacks sharp edges, burrs, surface irregularities and the like which could cause noise.

The effective surfaces of the nozzle may be coated for this purpose. Alternatively, the nozzles can be embossed with stamps which ensure a good dimensional accuracy and a fine surface finish for the nozzles when these are made of a sheet metal piece. With reference to Figs. 5A-C, the air device 4 can be manufactured by providing a hole 44 in a first operation, for example a drilling operation or a punching operation, in a first operation, for example a drilling operation or a punching operation. 'for each nozzle 43 to be manufactured. As shown in Fig. 5B, the plate 140 is subjected to an embossing operation adjacent to the hole 44 ', to form the nozzle 43 in the still flat plate 140. As shown in Fig. 5C, the plate according to SB can then be bent so that two opposite edges thereof are connected. to form the supply air device shown in Figs. 2-4.

Each nozzle 43 offers at the specified pressure drop a certain air flow, which varies surprisingly little with a change in the pressure drop. Therefore, in a plant of the type indicated, the supply air diffuser 4 can be designed in advance so that it offers a predetermined air flow, simply by providing the relevant supply air diffuser with a corresponding number of nozzles. By using relatively small nozzles, a relatively large number of nozzles is required, for example at least 50, in order to produce a sufficient air flow to an ordinary office space, and thereby the noise level becomes particularly low.

In Fig. 3 it is indicated that the nozzles 43 are arranged in a row and directed generally parallel. This achieves the advantage that the supply air is introduced into the room as a curtain. This curtain can be used to offer an ejector effect in connection with a diffuser nozzle, whereby ambient air in the space 5 is sucked into the ejector nozzle by the air jets flowing out through the nozzles 43. The sucked-in air nozzle can then pass a heat exchanger. Thanks to the relatively high velocity of the air, which flows out through the nozzles 43, a good mixing effect is also achieved with respect to the mixture between the supply air and the air already present in the room. Furthermore, a high efficiency of the heat exchanger is obtained, since the inlet speed of the supply air into the drain directly or indirectly offers high air velocities through the heat exchanger.

A special feature of the system according to the invention is that the supply air device 4 can let the supply air through with a high pressure drop without producing any annoying noise, nor does it produce any disturbing noise if the pressure drop were noticeably higher than the nominal one. The ventilation system therefore does not normally need to have any pressure-reducing dampers or the like in the line system between the fan control unit 1 and the various supply air devices. Since no pressure-reducing and noise-generating dampers need to be used, no expensive silencers need to be installed next to them.

An essential feature of the supply air devices according to the invention is that they discharge the supply air to the room in question via nozzles 43 which amount to a minimum number in order to meet the sound level requirements.

When establishing a ventilation system according to the invention, the designer knows the desired air outflow from the respective room 5. A standard nozzle with an opening diameter of, for example, 5.7 mm has usually been chosen, whereby a dimensioning model (nomogram according to Fig. 5) can build up. The designer can then, with knowledge of the current pressure drop level PUP2-P0, optimize the supply air devices and order or have these manufactured, for example with a suitable number of nozzles. When the plant is then built up, the relevant supply air diffuser 4 will offer the calculated air flow with good accuracy even if the pressure drop would have a relatively large deviation from the dimensioning pressure drop. Furthermore, the noise generation at the supply air device would not increase in a troublesome manner if the pressure drop deviates significantly from the nominal one.

Of course, it is possible to manufacture supply air diffusers so that a selected number of the nozzles can be completely shielded. The supply air diffuser can thus be prefabricated with a relatively large number of nozzles, whereby in a given situation the nozzles that are not required for the supply air diffuser to deliver the desired air flow are shielded. The shield can of course be designed in many different ways, ranging from individual plugs for the individual nozzles 43, to various forms of slides which allow complete shielding or exposing of a plurality of nozzles by displacing the slide.

As can be seen from Fig. 8, a supply air device according to Figs. 2-4 may lack nozzles in its outer end portion, and there contain a cylindrical slide 141 which is provided with a resiliently smooth and sealing. surface layer 142 of, for example, a soft plastic on its outer circumference along its length. The cylindrical slide may be coupled to a coaxial screw 144 extending through the end 42 and engaging a nut 145. The screw is provided at the outer end with a handle 146 which can be rotated by hand.

By turning the handle 46, the slide 141, 142 is thus displaced axially in the pipe jacket 141 so that the slide can be brought to positions where it completely covers and shields a selected number of nozzles 43 which are axially separated along the jacket 41. The screw 144 may be provided with visible markings in the area outside the nut 145 / end 42, the markings 147 being readable against any reference, for example the free short end of the nut 145, the arrangement being such that the inner end 148 of the slide 141 is located between adjacent nozzles 43 when the marking 147 coincides with the reference. The markings 147 can of course also be arranged to indicate the number of nozzles which are shielded by the slide 141.

In the supply air device according to Fig. 3, the nozzles are shown lying in a row and directed parallel in the same direction, but it should be clear that the nozzles can of course be directed in different directions, if desired. An advantage of the invention is that the nozzles offer a relatively high speed, and that by choosing a certain mutual orientation for the nozzles a desired and favorable flow pattern for the air leaving the supply air device can be achieved.

It is preferred to slightly vary the mutual distance between adjacent nozzles 43, so that the risk of resonant effects that could cause noise can be avoided. Furthermore, it is preferred to position the nozzles relative to each other in a manner known per se in such a way as to avoid noise reflection problems.

The specific design of a nozzle 43 in order to minimize the development of noise under the indicated conditions is in itself well known and can be taken from the literature.

A ventilation system according to the invention is flow-stabilized, and has the dominant pressure drop across the supply air devices. 10 15 20 25 30 35 527 241 12 Because the noise development at the supply air diffuser is low, thanks to the smooth, softly rounded noise-minimizing design of the nozzle, it is possible to establish a high pressure drop across the air diffuser / nozzles without annoying noise. By choosing a smaller nozzle opening and a larger number of nozzles, the noise development can be significantly reduced for one and the same flow. You can supply a supply air diffuser with a slightly too large number of nozzles, whereby for adjustment purposes you can expose or plug a selected number of nozzles in order to be able to fine-tune the air flow that begins in the room at a certain measured pressure in the supply air diffuser.

The number of nozzles can be selected in the range 20-500 and preferably in the order of 100. For a supply air diffuser, which is designed for a dimensioning pressure drop of 100 Pa, a pressure drop of up to 250 pascals can be allowed without the noise development being troublesome. , if desired.

An advantage of a nozzle-type air diffuser is further that an increase in the pressure drop across the diffuser results in a much smaller increase in the air flow. It is therefore possible, for example, to shut down up to a third of the ducts 3 (the air diffusers 4) without troublesome changes in air flow and noise occurring in the other air diffusers.

A supply air diffuser for an ordinary office space suitably has at least 50, preferably about 80, or more nozzles. Fig. 10 schematically shows a supply air device which has a first part which is connected to the supply air duct and which is dimensioned for a suitable air flow to this room. This air valve is shown connected via an opening and closing valve, to an additional air valve which can be dimensioned, for example, for an air flow as large as the first part, the number of nozzles suitably being equal and the nozzles having the same size.

By opening the valve, a doubling of the air inflow into the room is then established, essentially without noise increase, and above all this is achieved without the need for any further measures.

A further advantage of the supply air diffuser and the system is that by clogging a smaller proportion of the nozzles in a supply air diffuser (in order to locally regulate the air inflow in a certain room) there is no significant effect on the air flows which flows through the other supply air devices in the plant.

The air pressure P1 that the fan control panel 1 is to supply to the duct system must be understood so that the air pressure in question is provided at the end of line 2 in the area closest to the lines 3. The fan control unit itself could be located at a relatively long physical distance from this entrance in the duct system. would need to deliver at its outlet a higher pressure which falls to a minimum of 70 pascals at the input of the actual duct system 9.

Claims (8)

527 241 14 P a t e n t k r a v A method for supplying supply air to a plurality of rooms (5) in a building, wherein a fan exchange is caused to supply air with a pressure of at least 70 pascals above atmospheric pressure at an inlet (9) to a duct system, which comprises supply air ducts which via a or several supply air devices (4) open into the respective room (5), characterized in that supply air devices having a plurality of substantially equal air outlet nozzles with a noise-reducing design are used, which define the pressure drop across the supply air device, that the duct system is designed to ensure than the pressure drop through the duct system from the inlet (9) to the inlet of the supply air device (4), that the pressure drop across the supply air device is dimensioned for a value in the range 60-250 pascals, and that the nozzles have a free diameter of not more than 8 mm by selecting the number of air-flowing nozzles. Method according to claim 1, characterized in that the pressure drop through the duct system up to the supply air devices (4) is limited to between 0.1 and 1 times the pressure drop across the supply air device to the room. Method according to claim 1 or 2, characterized in that the pressure drop of the supply air device is dimensioned for a value in the range 80-150 pascals. Method according to one of Claims 1 to 3, characterized in that in order to reduce the development of noise under otherwise equal conditions, the number of nozzles in the supply air device is increased and the size of the nozzles is reduced. Method according to one of Claims 1 to 4, characterized in that a number of nozzles amounting to at least 20 and preferably to at least 50 and preferably at least 70, and preferably at most 500, are selected for a supply air device. 527 241 Method according to one of Claims 1 to 5, characterized in that the air flow through a supply air diffuser is adjusted by exposing or shielding nozzles. Flow-stabilized ventilation system for supplying supply air to a plurality of rooms in a building, the system comprising a fan control panel (1) which is arranged to introduce air into a duct system (2, 3) with an overpressure of at least 70 pascals relative to the atmospheric pressure. comprising supply air ducts (3), each of which via one or more supply air devices (4) opens into the respective room, characterized in that the supply air device has a plurality of mutually equal nozzles (43) through which the supply air is introduced into the room (5), that the nozzles are formed to give a low noise development during the air flow, that the nozzles are arranged to determine the pressure drop through the supply air device, that the nozzles have a free diameter of at most about 8 mm, and that the duct system is designed to ensure that the pressure drop across each nozzle is greater than the pressure drop through the duct system leading to the supply air device, the pressure drop across the supply air device being dimensioned for a value in the range 60-250 pascals, whereby to the air flow of the air diffuser is adjustable by selecting the number of open nozzles. Flow stabilizing ventilation system according to claim 7, characterized in that the number of nozzles in each supply air diffuser is at least 20 and preferably at least 50.