WO2001061253A1

WO2001061253A1 - A flow-stabilised ventilation system

Info

Publication number: WO2001061253A1
Application number: PCT/SE2001/000284
Authority: WO
Inventors: Bengt Sellö
Original assignee: Soft Inneklimat Ab
Priority date: 2000-02-17
Filing date: 2001-02-13
Publication date: 2001-08-23
Also published as: SE0000517L; SE0000517D0; AU2001234283A1; SE527241C2

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

A FLOW-STABILISED VENTILATION SYSTEM

The present invention relates to a method of ventilation of the kind defined in the preamble of the accompanying independent method Claim 1.

The invention also relates to a ventilation system of the kind defined in the preamble of the independent claim directed to the system.

The invention also relates to a supply air terminal device as defined in the independ- ent claim directed towards the device. The supply air terminal device can be used in the inventive method and in the inventive system.

The invention is primarily related to the ventilation of spaces or rooms that are regularly occupied by people and that mostly constitute a workplace.

Of particular interest are indoor workplaces, on which high comfort requirements are placed, and particularly spaces in which low sound levels are a given requirement.

Background of the invention

The majority of workplaces and office spaces are ventilated via forced introduction of air into the rooms or spaces concerned, i.e. fresh air is supplied to the spaces in the building in question and exhaust air is removed from said spaces through the medium of one or more fans or blowers. In order for a ventilation system to be accepted by the relevant authorities and to meet the requirements of professional customers, the ventilation system must fulfil the following requirements.

Comfort requirements 1) The system must be capable of supplying and removing a specified quantity of fresh air to and from the building. 2) It must be capable of supplying each space or room in which people work with the stipulated flow of fresh air.

3) Ventilation must be effected in the absence of disturbing sound.

4) Ventilation shall be effected in the absence of wide variations of temperature in the spaces and rooms concerned.

5) Ventilation shall be effected in the absence of draft around the workplace.

6) It must be possible for the temperature of a (office) space to be controlled by persons using said space.

Technical-economic requirements

7) The fan driving power should be kept low, both for economic reasons and to prevent undesired sound generation.

8) The pressure distribution between conduits and ducts (often of different lengths) must be balanced in a reasonable manner, due to technical-economic requirements.

Typical system solutions

Several different types of installations (system solutions) that fulfil the above functional requirements are known to the art. The fresh air requirement and the re- quirement of an appropriate temperature in a building can be satisfied in several ways. The manner in which the fresh air and heat are distributed to and from the space or room used within the building is of a decisive technical-economical significance.

The heat or cold may be

- water carried from a local central unit (oil boiler, electric boiler, cooling unit),

- produced in the room or spaces concerned (electric radiator, fireplace, cooling unit).

Fresh air can be supplied via - a central local unit in the building concerned (mechanical ventilation) - direct connection between the rooms or spaces and outdoor air (air gaps beneath windows).

The requirements under points 1-8 above must be satisfied effectively in spaces on which high comfort requirements are placed. There are a number of technical- economical factors which decide how the technical solutions are implemented at present, these factors being building costs, installation costs, component costs, the rules and regulations laid down by the authorities, in addition to how well the functional technical requirements have been fulfilled. These factors have controlled de- velopment within the ventilation branch, together with the technical innovation ability within this field. Developments in Sweden, where high requirements are placed on both warm and cool atmospheres in office spaces, have, in the passage of time, resulted in ventilation solutions that are characterised in that:

I. Heat and cold are supplied to the room from a (nearby) central unit, with water as the energy carrying medium.

II. Fresh air is distributed to and from the room, via a duct network from a local central unit.

III. The volume of fresh air, heat and cold, is controlled close to or in the room in which people work.

These preferred system constructions require equipment for supplying fresh air to the room and, at the same time, heating or cooling the air so as to achieve the comfort desired. The main technical advantages afforded by this objective approach to the system solution are: - Water-carried energy transportation requires small dimensioning of ducts, conduits, etc., and water can carry very much energy per kg medium. Water is also light and can be used effectively to exchange heat between different systems. - The separation of air and energy transports enables cultivation of the components and functions within each system to be achieved. This results in cheaper compo- nents and higher functional security in time. - The necessity of controlling the air climate in respective rooms, means, in reality that a regulating system must be installed in respective rooms, and consequently it is logical to implement the control of the temperature of the fresh air at this place.

- Present day existing technical system solutions according to the above afford many advantages, although there are still significant drawbacks that must be overcome.

Drawbacks with present day system solutions

The following standpoints can be taken into account, when wishing to develop the best existing system solutions:

Water-carried energy distributing systems according to I above exist and function effectively. Many methods and components exist by means of which the control of fresh air can be achieved, both with respect to volume and temperature, these meth- ods and components being far too many in number to mention specifically in this document. However, product development has been concentrated on components, and their place in a system has been neglected in many instances. In the long run, it would appear necessary to take as a starting point primarily an improved system and to choose and develop components from this starting point. At present, the system will, more or less, be the sum of its components, without examining the total system function. Although this is understandable, it is not good. The main reason is believed to be found in the interest of manufacturers to sell their own components, and in a conservative body of civil-consultants who do not enjoy novelty at first hand.

The distribution of fresh air from a central plant (fan room) to (office) spaces, and the distribution of exhaust air back again requires the presence of a duct system and of different types of controls for guiding the air flows. It is of interest in this respect to view the factors that control dimensioning of the system.

a) The size of ducts and accessories cost money. Smaller dimensions are cheaper and take up less space, although at the cost of the rate of flow of the medium in the ducts, b) High fan powers with high pressure drops enhance the possibility of throttling the flow to a high degree in the duct systems, for regulating and control purposes. c) Building-installed fan centres are expensive and are usually limited to one or only a few. This often results in long conduit systems with many branches, d) The medium flow in different ducts is often controlled via sequential throttling of ducts, or conduits, in order to achieve a specified drop in pressure across the local supply air terminal devices in the various rooms. e) Energy recovery between supply air and exhaust air is economically important. Although the methods applied in this regard vary, the existence of an exhaust air system is normally required, f) There is therefore a requirement for a twin duct system. Constructions included in the sub-system mentioned under points a) to e) above, should also be de- signed so as to be quiet in operation.

Low sound levels in office spaces have perhaps become the most significant factor with regard to the dimensioning of modern ventilation systems. This is because of the increase in sound comfort requirements, and also because an inexpensive con- struction that manages the factors according to a) to e) are in conflict with low sound levels. Several types of sound generating systems exist and all have drawbacks.

Infrasound, i.e. inaudible sound, can be generated in duct systems. Such sound, however, is liable to cause feelings of unpleasantness and sickness. Audible sound is definitely generated in the ducts, and the sound of fan motors and vibrations are forwarded together therewith through the duct systems and into the rooms. Last, but not least, is the disturbing sound generated by the supply air terminal devices that spread air into a specific room. In an effort to overcome these drawbacks, different types of sound dampers or attenuators are often placed along the terminal system, and, in practice, the manufacturer always specifies the drop in pressure drop across the supply air terminal device at a highest value in order to keep the sound level from said device within stipulated limits.

Thus, known ventilation systems can be considered to include a central fan unit which delivers supply air via a supply line. The supply line includes delimited ducts that lead into respective rooms. The ducts open out into one or more supply air terminal devices in the rooms. The central fan unit will preferably deliver air at an overpressure in the order of 100 Pa in order to satisfy existing requirements with regard to throttles, constrictions, sound dampers, etc., along the supply line, so as to finally deliver supply air at a pressure of about 20 Pa immediately upstream of the supply air terminal device.

The requirement of a highest drop in pressure (about 30 Pa) across a typical supply air terminal device is due to the desire to avoid troublesome noise in the device. This results in the requirement of throttles/constrictions in the ducts in order to ensure that the air pressure on the inlet side of the supply device is at most as high as about 30 Pa. However, such pressure-reducing throttles/constrictions also generate noise, which in turn requires the installation of sound dampers, which are expensive both with respect to purchasing cost and installation cost. Since the drop in pressure across a typical supply air tunnel device shall be low, it is normally necessary to enable the air flow through the device to be adjusted, for instance with the aid of throttle means, so as to enable the flow of supply air to the room to be adjusted to a correct and desired level. The flow setting throttle means of the supply air terminal device has, in turn, a tendency to generate noise and normally requires the supply air terminal device to include sound damping means. Measuring of the air flow through the air supply device and setting of said device are time consuming and cost incurring tasks which assume that the supply air terminal device can be regulated.

One object of the present invention is to provide technology with which the afore- said drawbacks can be eliminated, either completely or partially. This object is achieved with a ventilation method according to the independent method claim.

The object is also achieved with a ventilation system according to the independent system claim.

The object is also achieved with a supply air terminal device according to the independent claim directed to said supply air terminal device.

Further embodiments of the invention will be apparent from the accompanying dependent claims.

The invention is based on the concept of using a supply air terminal device which has a wall that includes a large number of air nozzles which allow supply air to enter the room. The nozzles are designed to promote the least possible flow disturbances and therewith develop the least possible noise. The design of the nozzles in this respect belongs to the known standpoint of techniques. On the other hand, it is not part of the known technology for the number of nozzles used with a constant flow to influence sound generation of the supply air terminal device. At a stipulated flow and (quiet) sound level, this allows freedom in the construction of supply air terminal devices dimensioned for drops in pressure of between 60-250 pascal, which is not possible with conventional supply air terminal devices. The drop in pressure across the supply air terminal device is established substantially solely by the nozzles.

The diameters of the nozzles orifices are normally in the range of 4-7 mm. An orifice diameter of 5.7 mm was chosen for a test embodiment. The nozzle, or jet, has a gently rounded funnel shape and tapers all the way to its orifice. The nozzles in the supply device are mutually of the same size and each allows a well defined flow of air to pass through, this air flow varying with the magnitude of the pressure flow to a relatively small extent. It is therefore possible for a designer to provide a supply air terminal device that fulfils the sound requirements of a given room with a given desired supply of air and a given pressure drop. Because the supply air terminal device is itself able to manage a high pressure drop, no pressure reducing and noise promoting restrictions are required in the supply air ducts. The need to dampen noise from regulating throttles and the like in the supply air terminal device is also eliminated, since in this regard control can be achieved quietly by blocking or opening a number of nozzles in the device concerned.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.

Figure 1 illustrates schematically a ventilation system for installation in a building.

Figure 2 is a sectional view taken on the line II-II in Figure 1.

Figure 3 is a sectional view taken on the line III-III in Figure 2.

Figure 4 is a sectional view taken on the line IV-IV in Figure 3. Figures 5A-5C illustrate mutually sequential stages in the manufacture of an inventive supply air terminal device.

Figure 6 illustrates an alternative supply air terminal device.

Figure 7 is an axial sectioned view of a nozzle.

Figure 8 illustrates another embodiment of a supply air terminal device. Figure 9 is a nomogram.

Figure 10 illustrates another embodiment of a supply air terminal device.

Figure 1 illustrates schematically a building that includes a central fan unit 1, an air supply conduit 2 and a plurality of ducts 3 that branch off from the conduit 2 and that lead to respective supply air terminal devices 4 in affiliated rooms 5. The rooms can be considered to have mutually different requirements with respect to air flow. The pressure PI at the outlet of the central fan unit 1 falls to P₂ at the end of the conduit 2. The air pressure P₀ in the rooms 5 shall, of course, be atmospheric pressure.

The ducts 3 may have mutually different lengths. In one practical situation, the difference in pressure between P, and P₂ may be about 30 Pa. In order to prevent a change in the air inflow of one room having a strong influence on the air inflow in another room, it is convenient to allow the central fan unit 1 to establish a pressure P, in the order of 100 Pa above atmospheric pressure, and to take-up the greatest part of this drop in pressure across the supply air terminal device.

Figures 2-4 are schematic illustrations of a supply air terminal device that includes a straight circular-cylindrical metal sheet barrel or outer surface 41 which is closed by a metal plate wall at its outer end 42 and which is coimected to the end of the duct 3 at its inner end 48.

The barrel 41 is provided with a plurality of nozzles or jets 43 (Figure 7). The supply air terminal devices and the nozzles are constructed to allow air to flow ihere- through with minimised noise development. The nozzles 43 are constructed to this end to cause the least possible disturbance in the flow of air exiting through the nozzle. The inner wall of the nozzle is therefore smooth and curved continually and connected continually to the metal plate barrel. The nozzle wall is also conical in shape all the way to the nozzle outlet orifice 44. The nozzle has a generally circular cross-section. All nozzles 43 in the supply air terminal device 4 will preferably be of mutually similar design. The inner surface of the nozzle will preferably be smooth and shape accurate, and the nozzle will also preferably be constructed so as to lack sharp edges, burrs, surface irregularities and the like that may be instrumental in generating noise.

The effective surfaces of the nozzle may optionally be externally coated to this end. Alternatively, the nozzles may be embossed with stamps which ensure good shape accuracy and a fme nozzle surface fineness when said nozzles are produced from metal sheet. Referring to Figures 5A-C, the supply air terminal device 4 may be produced by providing in a flat sheet of metal 140 in a first operation, for instance a drilling operation or a punching operation, a hole 44' for each nozzle 43 to be pro- duced. As shown in Figure 5B, the metal sheet 140 is subjected to an embossing operation in the vicinity of the hole 44', to form the nozzle 43 in the still flat metal sheet 140. As shown in Figure 5C, the metal sheet according to 5B may then be bent or folded so as to join two mutually opposing sheet edges and therewith form the supply air terminal device shown in Figures 2-4.

Each nozzle 43 affords at said given drop in pressure a specific air throughflow that surprisingly varies very little when the drop in pressure changes. This enables the supply air teirninal device 4 to be pre- fabricated in a system of the type indicated above, so that said device will allow a pre-determined flow of air to pass through, simply by providing the device concerned with a corresponding number of nozzles. The use of relatively small nozzles will require a relatively large number of nozzles to be used, for instance at least 50, in order to lead sufficient air into a standard office space, whereby the noise level will be particularly low.

In Figure 3, the nozzles 43 are disposed in a line and directed generally parallel. The advantage afforded hereby is that the supply air will enter the room in the form of a curtain. In conjunction with a diffuser nozzle, this curtain can be utilised to obtain an ejector effect whereby ambient air in the room 5 is sucked into the ejector nozzle by the air jets that flow out through the nozzle 43. The room air sucked into the ejector nozzle can be caused to pass a heat exchanger. Because of the relatively high velocity of the air exiting through the nozzle 43, a good mixing effect is also achieved with regard to the mixture between supply air and the air already present in the room. Moreover, a high heat exchange efficiency is obtained, since the velocity at which the supply air enters the room affords, either directly or indirectly, high air velocities through the heat exchanger.

A significant feature of the inventive system is that the supply air terminal device 4 can allow supply air to pass through with a high drop in pressure without generating troublesome noise. Neither will troublesome noise be generated should the drop in pressure be significantly higher than its nominal drop. Consequently, the ventilation system need not normally include pressure-lowering throttles or the like in the conduit or duct system between the central fan unit 1 and the various supply air terminal devices. Because no pressure reducing and noise generating throttles need be used, it is unnecessary to install expensive sound dampers in this connection.

Another essential feature of the inventive supply air terminal devices is that they release supply air into the room concerned through the medium of nozzles 43 that are present in the smallest number for satisfying sound level requirements.

When establishing an inventive ventilation system the construction engineer will be aware of the air flow desired to respective rooms 5. Normally, the engineer will have chosen a standard nozzle with an orifice diameter of 5.7 mm ? for instance, therewith enabling a dimensioning model to be built-up (the nomogram according to Fig. 9). With knowledge of the relevant pressure level P,/P₂-P₀, the engineer is able to optimise the supply air terminal devices and to order such devices from an appropriate supplier or allow the same to be manufactured, for instance with an appropriate number of nozzles. Subsequent to having built-up the system, the supply air terminal device 4 concerned will deliver the calculated air throughflow with a high degree of accuracy, even though the drop in pressure may deviate relatively widely from the drop in pressure for which the system was dimensioned. Moreover, noise generation in the supply air terminal device would not rise to a troublesome level should the drop in pressure deviate essentially from the nominal drop.

A supply air terminal device may, of course, be constructed in accordance with the invention so as to completely screen-off a chosen number of nozzles. The device may also be pre-fabricated with a relatively large number of nozzles, wherewith those nozzles that are not required in order for the device to deliver the desired flow of air may be screened-off or closed in a given situation. Screening or closing of the nozzles may, of course, be effected in many different ways, for instance ways that range from the use of individual plugs for individual nozzles 43 to different forms of slides that permit nozzles to be screened-off completely or that allow a number of nozzles to be exposed and opened up by displacing the slide accordingly.

As will be seen from the Figure 8 illustration, a supply air terminal device according to Figures 2-4 may lack nozzles in its outer end part and may there include a cylindrical slide 141 which has a yielding, smooth and sealing outer layer 142 of, for instance, a soft plastic material on its outer circumference and along its length. The cylindrical slide may be coupled to a coaxial screw 144 that extends out through the wall 42 and engages a nut 145. The outer end of the screw is fitted with a handle 146 that can be turned by hand.

Thus, the slide 141, 142 can be moved axially in the barrel 141 by turning the handle 46, therewith enabling the slide to be brought to positions in which it fully covers and screens a chosen number of nozzles 43 disposed axially and discretely along the barrel 41. The screw 144 may include visible markings in the region located outwardly of the nut 145/the end wall 42, wherewith the markings 147 can be read against a reference, for instance the free short end of the nut 145, wherewith the arrangement may be such that the inner end 148 of the slide 141 will be situated between mutually adjacent nozzles 43 when the marking 147 coincides with the refer- ence. The markings 147 may, of course, also be adapted to indicate the number of nozzles that are screened-off by the slide 141.

In the case of the supply air terminal device shown in Figure 3, the nozzles are disposed in a line and are directed parallel with one another in one and the same direc- tion, although it will be understood that the nozzles may, of course, be directed in mutually different directions if so desired. One advantage afforded by the invention is that nozzles permit a relatively high velocity to be achieved, and that a desired and favourable air flow pattern can be achieved with respect to the air exiting from the device, by choosing a given mutual orientation of the nozzles. It is preferred to vary the spacing between adjacent nozzles 43 slightly, so as to avoid the risk of resonance effects that could otherwise cause noise. It is also preferred to place the nozzles relative to one another in a manner to avoid noise reflection problems, in accordance with known technology.

The specific design of a nozzle 43 with the intention of minimising noise development under the conditions indicated is well known to the art and can be found in the literature.

An inventive ventilation system is flow stabilised with the dominative drop in pressure across the supply air terminal device. Because noise development in the air supply terminal device is low, due to the smooth, gently rounded, noise-minimising design of the nozzle, it is possible to establish a high drop in pressure across said device/said nozzles in the absence of troublesome noise. The selection of smaller nozzle orifices and a large number of nozzles, enables noise development to be substantially reduced for one and the same throughflow. A supply air terminal device can be provided with a comparatively large number of nozzles, wherewith adjustments can be made to the device by exposing or plugging a chosen number of nozzles so that the air flow into the room can be finely adjusted for a given measured pressure in said device. The number of nozzles may be in the range of 20-500, preferably in the order of 100. With respect to a supply air terminal device that has been designed for a dimensioning drop in pressure of 100 Pa, a pressure drop of up to 250 pascal can be permitted without troublesome noise development, should this be desirable.

One advantage afforded by a nozzle-type supply air terminal device is that a rise in the drop in pressure across the device results in a much lower rise in the air through- flow. For instance, this enables up to a third of the ducts 3 (the supply air terminal devices 4) to be closed without resulting in troublesome changes in air flow and in the occurrence of noise in the remaining devices. A supply air terminal device for a typical office will conveniently have at least 50, preferably about 80, or more nozzles. Figure 10 illustrates schematically a supply air terminal device that has a first part which is connected to the air supply conduit and which is dimensioned for suitable air flow into the office. This part of the supply air teπninal device is shown connected to a further part of a supply air terminal device, via an opening and closing valve, wherewith this latter part may be dimensioned, e.g., for an air flow that is equally as large as the air flow through the first part, wherein the number of nozzles is suitably the same and the nozzles having the same size. Opening of the valve will therefore establish essentially a doubling of the air flow into the office, essentially without a noise increase, this being achieved above all without needing to take further measures.

A further advantage afforded by an inventive supply air terminal device and system is that blocking of a small number of the nozzles in a supply air terminal device (with the intention of locally regulating the inflow of air into a given room or space) will have no substantial influence on the air flows that exit through the remaining supply air terminal devices in the system.

The air pressure PI that the central fan unit 1 shall deliver to the duct system shall be discerned so that the air pressure in question is obtained at the end of the conduit 2 in the region nearest upstream of the ducts 3. The actual central fan unit could be located at a relatively long physical distance from the input to the duct system, wherewith the central fan unit would need to deliver at its output air higher pressure that falls to a lowest pressure of 70 pascal at the input 9 to the actual duct system.

Claims

C l a i m s

1. A method of delivering supply air to a plurality of rooms (5) in a building, wherein a central fan unit is caused to deliver air to an inlet (9) of a conduit system at an air pressure of at least 70 pascal above atmospheric pressure, said conduit system comprising supply air ducts which discharge into respective rooms (5) via one or more supply air terminal devices (4), characterised by using supply air terminal devices which have a plurality of air outlet nozzles that have a noise reducing construction and that define the drop in pressure across the supply air terminal device; and in that the conduit system is constructed to ensure that the drop in pressure across the supply air terminal device will be greater than the drop in pressure through the conduit system from said inlet (9) up to the inlet of the supply air terminal, device (4).

2. A method according to Claim 1, characterised by limiting the drop in pressure through the conduit system up to the supply air terminal device (4) to between 0.1 and 1 times the drop in pressure across the supply air terminal device in said room.

3. A method according to Claim 2, characterised by dimensioning the drop in pres- sure across the supply air terminal device for a value within the range of 60-250 pascal.

4. A method according to Claim 3, characterised by dimensioning the drop in pressure of the supply air terminal device for a value within the range of 80-0 pascal.

5. A method according to any one of Claims 1-4, characterised by increasing the number of nozzles in the supply air terminal device and decreasing the size of the nozzles, in order to reduce noise development under otherwise similar conditions.

6. A method according to any one of Claims 1-5, characterised by including in a supply air terminal device nozzles in a number reaching to at least 20 and preferably to at least 50 and more preferably to at least 70 and even more preferably to at most 500.

7. A method according to any one of Claims 1-6, characterised by exposing or screening-off nozzles in order to adjust the flow of air through a supply air temiinal device.

8. A flow stabilised ventilation system for delivering supply air to a number of rooms in a building, wherein the system includes a central fan unit (1) which is adapted to introduce air into a conduit system (2,3) at an overpressure of at least 70 pascal relative to atmospheric pressure, wherein said conduit system includes air supply ducts (3) each of which discharges air into respective rooms via one or more supply air terminal devices (4), characterised in that the supply air terminal device has a plurality of nozzles (43) through which supply air is discharged into the room; in that the nozzles are constructed for low noise development as air passes through said nozzles; in that the nozzles are adapted to determine the drop in pressure across the supply air terminal device; and in that the conduit system is constructed to ensure that the drop in pressure across the supply air terminal device is greater than the drop in pressure across the conduit system leading to said supply air terminal de- vice.

9. A supply air terminal device for carrying out the method according to any one of Claims 1-6, characterised in that the supply air terminal device has a plurality of nozzles whose number and construction are chosen to release air into the room with a minimised noise development at a drop in pressure from the supply air terminal device to the room in the order of at least 60 pascal.

10. A supply air terminal device according to Claim 9, characterised in that the device includes at least 20 nozzles and preferably at least 50 nozzles.

11. A supply air terminal device according to Claim 9 or 10, characterised in that the nozzles have mutually the same size and have a diameter smaller than 10 mm.

12. A supply air terminal device according to any one of Claims 9-11, character- ised by means for selective screening or exposing of nozzles in said device.

13. A supply air terminal device according to any one of Claim 8-10, characterised in that the nozzles have an orifice diameter of at most about 8 mm.