A centrifugal fan arrangement having an adjustable effective fan blade height, a control system for said centrifugal fan arrangement and a method for controlling said centrifugal fan arrangement

Abstract

The disclosure relates to a centrifugal fan arrangement (10) comprising: an inlet (16) for an incoming flow of air; a front shroud (13) which is arranged concentrically around said inlet (16); a back plate (14); and a plurality of fan blades (15) extending from the front shroud (13) and defining an effective fan blade height (h); said fan arrangement (10) being configured for generating a volume flow of air at a corresponding pressure. Furthermore, the fan arrangement (10) is configured so as to be operated with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement (10).

Description

[0001] TITLE

[0002] A CENTRIFUGAL FAN ARRANGEMENT HAVING AN ADJUSTABLE EFFECTIVE FAN BLADE HEIGHT, A CONTROL SYSTEM FOR SAID CENTRIFUGAL FAN ARRANGEMENT AND A METHOD FOR CONTROLLING SAID CENTRIFUGAL FAN ARRANGEMENT

[0003] TECHNICAL FIELD

[0004] The invention relates to a centrifugal fan arrangement comprising: an inlet for an incoming flow of air; a front shroud which is arranged concentrically around said inlet; a back plate; and a plurality of fan blades extending from the front shroud and defining an effective fan blade height (h); said fan arrangement being configured for generating a volume flow of air at a corresponding pressure.

[0005] The invention also relates to a control system for a centrifugal arrangement of the above-mentioned kind.

[0006] The invention also relates to a method for controlling a fan arrangement which comprises: an inlet for an incoming flow of air; a front shroud which is arranged concentrically around said inlet; a back plate; and a plurality of fan blades extending from the front shroud and defining an effective fan blade height (h); said fan arrangement being configured for generating at volume flow of air at a corresponding pressure.

[0007] BACKGROUND

[0008] In the field of air treatment systems, it is known to install so-called heating and ventilation air conditioning (HVAC) systems in buildings of different types. An HVAC system generally comprises an air handling unit (AHU) which is configured for an intake of fresh supply air into a building and for discharge of air from the building. To this end, the AHU normally comprises an extract air channel and a supply air channel.

[0009] An AHU normally comprises at least one fan which is configured for inducing a flow in the air ventilation ducting system. In general, when the AHU includes a supply air channel and an extract air channel, there is a fan provided in both the supply air channel and extract air channel. In this manner, supply air and extract air can be fed through these channels and through the ventilation system.

[0010] Furthermore, an AHU is often provided with a heat exchanger arrangement which is configured so as to provide an exchange of heat from the exhaust air to the intake air. Such an AHU can consequently be used for optimizing the energy consumption in an HVAC system.

[0011] Systems for demand-controlled ventilation (DCV) are also often used in buildings and are configured with a plurality of sensor devices in order to provide relevant information for controlling the ventilation in the building based on demand and on information from the sensor devices.

[0012] A fan which is often used in an air handling unit is constituted by a centrifugal fan in which air is drawn in a direction which is parallel to a fan motor shaft and diffused in a radial direction, generally perpendicular to said motor shaft, i.e. generally perpendicular to the direction of the intake of air. A centrifugal fan of a known type normally comprises a front shroud, a back plate and a plurality of fan blades which are located between the front shroud and the back plate. The fan blades define an effective fan blade height, which according to prior art is the length or height of the fan blades extending between the front shroud and the back plate and contributing to generating a flow or air.

[0013] During a configuration of a HVAC ventilation system, for example in a building with a number of rooms and spaces, it is common that such a system is dimensioned in accordance with a predetermined requirement for an air flow which should be generated by one or more centrifugal fans. The magnitude of the required air flow is normally based on a specified need for ventilation of supply air and extract air.

[0014] In this manner, the rooms and spaces of the building can be provided with a suitable flow of incoming and outgoing air. It should be noted that a centrifugal fan of conventional type operates in a manner so that its efficiency varies with the air flow and with the pressure generated within the fan arrangement during operation. This is normally described with reference to a so-called optimal system curve of the fan. This means that the efficiency of the fan can be maximized at specific, and optimal, air flow and pressure values. As a consequence, the efficiency of the fan will decrease during operation of the centrifugal fan at other air flow and pressure values than the optimal values (i.e. where the efficiency is optimized).

[0015] In the field of fan arrangements, it is common to refer to the system curve in order to describe the relation between the flow and the pressure of a fan and in order to define an optimal system curve (taking into account both the flow and the pressure) along which the fan presents an optimal coefficient of efficiency.

[0016] The system curve outlines the required static pressure to move a specific air volume for a particular duct system with connected workstations. The pressure is proportional to the volume flow, according to the following: p oc Qn(1.7 < n < 2.0)

[0017] In summary, at a specific rotation speed of the fan, there is a specific air flow value and a corresponding pressure value where a maximum efficiency of the fan is obtained.

[0018] In order to maximize the efficiency of the centrifugal fan - which for example is advantageous for maintaining a low energy consumption of the fan and, in fact, the entire ventilation system - there is consequently a desire to operate the fan at the specified air flow and pressure values at which a maximum efficiency is obtained. This means that it is suitable to use a specific type of centrifugal fan which has a maximum efficiency at the specified air flow and pressure for which the ventilation system has been designed. However, the above-mentioned strategy for designing and operating a ventilation system involves a challenge in that a ventilation system often must allow for changes in the air flow demand during operation, so-called demand controlled ventilation system (DCV). For example, a ventilation system of the above- mentioned type may be used for serving a number of individual rooms in a building, such as small office rooms and large meeting rooms. With today's HVAC system, it is necessary to allow an individual control of the airflow to each one of these rooms.

[0019] Using a fan arrangement which is optimized for a given system curve consequently means that the efficiency will be decreased in the event that the fan should be operated at different air flow / pressure values. With reference to the discussion above, this is obviously a disadvantage as regards the efficiency of the fan arrangement.

[0020] In summary, many of today's ventilation systems are configured to be used with one or more centrifugal fans which are chosen to be operated at a specified air flow value. As explained above, changes of the air flow in different parts of the ventilation system may lead to disadvantages as regards the efficiency of the fans.

[0021] Consequently, with regard to the technical field of ventilation systems involving operation of centrifugal fans, there is a need for further improvements. In particular, there is a need to provide an improved efficiency for systems involving centrifugal fan arrangement as described above.

[0022] The patent document DE 19812437 teaches a fan arrangement having an inner plate which can be displaced and positioned at a given position in relation to a back plate. The purpose of the arrangement according to DE 19812437 is to provide an arrangement which is adapted to predetermined operating points and volume flow control. However, the arrangement according to DE 19812437 involves an important disadvantage in that the efficiency of the fan decreases as the displaceable plate is moved further away from the back plate. Consequently, the problem regarding the inefficiency of a fan arrangement will not be solved by means of the arrangement according to DE 19812437. A further disadvantage with the arrangement according to DE 19812437 is that it is not configured for being used in a situation involving instantaneous changes in the air flow, DCV.

[0023] In summary, there is a need for further improvements in this technical field. In particular, there is a need to provide an improved efficiency for the centrifugal fans described above.

[0024] SUMMARY

[0025] An object of the invention is to provide improved ventilation arrangements which solves the above-mentioned problem and which offers an improved efficiency of an HVAC system.

[0026] The above-mentioned object is achieved by a centrifugal fan arrangement comprising: an inlet for an incoming flow of air; a front shroud which is arranged concentrically around said inlet; a back plate; and a plurality of fan blades extending from the front shroud and defining an effective fan blade height (h); said fan arrangement being configured for generating a volume flow of air at a corresponding pressure. Furthermore, the fan arrangement is configured so as to be operated with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement.

[0027] Generally, the invention is based on the principle that a distance or height (d) which corresponds to an “effective fan blade height” is defined, and also that a suitable value of this height (h) can be determined so as to obtain an optimized efficiency of the fan arrangement. The fan arrangement can then be operated with an optimized fan blade height.

[0028] The principles of the invention can be implemented in different ways. Below, a number of embodiments will be described in detail.

[0029] According to an embodiment, the fan arrangement is arranged so that the plurality of fan blades extend between the front shroud and the back plate; and that the fan arrangement comprises an additional plate which is arranged between the front shroud and the back plate, and which is movable in an axial direction of the fan arrangement. Furthermore, the additional plate is configured to be selectively positioned with a distance to said front shroud which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement.

[0030] The advantage of this embodiment is that the additional plate can be controlled instantaneously by means of a computer-based system to be adopted to any required changes in the air flow / pressure. As a result, the fan arrangement can be configured so that it always has an optimal efficiency generally independently of the air flow which is induced (and a corresponding pressure in the fan). This leads to a reduction in energy consumption of the fan arrangement and the ventilation system.

[0031] According to an embodiment, each one of the fan blades has a leading edge and a trailing edge, and the diameter of the additional plate is greater than a diameter which is defined by the position of each trailing edge of said fan blades.

[0032] According to an embodiment, the additional plate is arranged at least partly generally parallel to the back plate.

[0033] According to an embodiment, the additional plate is formed with openings corresponding to the cross-sectional areas of each of the fan blades, allowing the additional plate to be displaced along the fan blades while rotating during operation of the fan arrangement.

[0034] According to an embodiment, the additional plate is configured so as to be displaced by means of a motor arrangement which is arranged externally to the fan arrangement.

[0035] According to an embodiment, the motor arrangement comprises a fan motor which is arranged with an actuator extending within an output shaft of said fan motor and through said back plate; said actuator being attached to the centre of said additional plate.

[0036] According to an embodiment, the back plate is provided with a sealing extending along the periphery, and that said additional plate is formed with a peripheral section which is in contact with said sealing.

[0037] According to an embodiment, the additional plate is disc-shaped with said peripheral section in the form of a rim section which extends generally perpendicularly towards the back plate.

[0038] According to an embodiment, the additional plate is provided with a plurality of guiding pins extending from the underside of said additional plate and through the back plate, in order to maintain the additional plate generally parallel to the back plate.

[0039] According to a further embodiment, said back plate is formed with openings corresponding to the cross-sectional areas of each of the fan blades, allowing the back plate to be displaced along the fan blades while rotating during operation of the fan arrangement. According to a further embodiment each of said fan blades are arranged in a telescopical manner and comprising a first fan blade section and a second fan blade section which can be telescopically displaced in relation to each other.

[0040] There is also provided a control system for a centrifugal fan arrangement as mentioned above. According to an embodiment, the control system comprises: an input unit for providing a parameter value corresponding to said effective fan blade height (h); a control unit for determining, based on said parameter value, a desired setting of fan arrangement using said effective fan blade height (h); and an output unit for arranging the fan arrangement with said fan blade height (h), which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement.

[0041] The above-mentioned object is also obtained by means of a method for controlling a fan arrangement which comprises: an inlet for an incoming flow of air; a front shroud which is arranged concentrically around said inlet; a back plate; a plurality of fan blades extending from the front shroud and defining an effective fan blade height (h); said fan arrangement being configured for generating a volume flow of air at a corresponding pressure. Furthermore, the method comprises: operating the fan arrangement with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement.

[0042] The invention is particularly useful within the field of air treatment systems, in particular heating and ventilation air conditioning (HVAC) systems for buildings of different types.

[0043] In the context of this disclosure, the term “mode of operation” is used for describing a functional characteristic of a centrifugal fan in which the efficiency of the fan varies with its supplied air flow. The efficiency of the fan can be regarded as the ratio between the power which is used in the form of an air flow and the power which is consumed by the fan. This means that the fan has a mode of operation in which a specified air flow value and a corresponding pressure value gives a maximum fan efficiency value. From this follows that different types of centrifugal fans - i.e. having different dimensions, design, power consumption etc.

[0044] - may have mutually different modes of operation and different air flow values corresponding to the maximum fan efficiency.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The invention will now be described more in detail with reference to the accompanying drawings, in which:

[0047] Figure 1 shows an air handling unit (AHU) of a type which is used in a heating and ventilation air conditioning system;

[0048] Figure 2 shows a perspective view of a centrifugal fan of a type which can be used in accordance with the present disclosure;

[0049] Figure 3 shows a perspective view of an additional plate which is used in the centrifugal fan;

[0050] Figure 4a shows a side view of a centrifugal fan of a prior art type, i.e. which is generally known as such;

[0051] Figure 4b shows a side view of the centrifugal fan in Figure 4a, but in a different mode of operation than in Figure 4a;

[0052] Figure 5 shows a side view of the centrifugal fan according to this disclosure, in a first mode of operation;

[0053] Figure 6 shows a further side view of the centrifugal fan, in a second mode of operation; Figure 7 is a graph which shows how the coefficient of efficiency of the centrifugal fan varies depending on the position of the adjustable plate;

[0054] Figure 8 shows an embodiment of the fan arrangement which comprises a number of guiding elements;

[0055] Figure 9 corresponds to Figure 8 but shows the embodiment in a perspective view which shows the underside of the fan arrangement;

[0056] Figure 10 shows an embodiment of the fan arrangement which comprises a motor arrangement;

[0057] Figure 11 a shows a further embodiment with a guiding element;

[0058] Figure 11 b corresponds to Figure 11 a but in a different operating condition;

[0059] Figure 12a shows yet another embodiment with a guiding element, including an enlarged portion of the central part of the fan arrangement;

[0060] Figure 12b corresponds to Figure 12a but in a different operating condition;

[0061] Figure 13 is a perspective view which shows an embodiment of the fan arrangement which comprises a sealing arrangement;

[0062] Figure 14 is a cross-sectional view which shows the same embodiment as Figure 13;

[0063] Figure 15a is a side view of a first alternative embodiment of the fan arrangement, in a first mode of operation; Figure 15b is a side view of the first alternative embodiment but in a second mode of operation;

[0064] Figure 16a is a side view of a second alternative embodiment of the fan arrangement, in a first mode of operation; and

[0065] Figure 16b is a side view of the second alternative embodiment but in a second mode of operation.

[0066] DETAILED DESCRIPTION

[0067] Different embodiments of the present invention will now be described with reference to the accompanying drawings. The arrangements described below and defined in the appended claims can be realized in different forms and should not be construed as being limited to the embodiments described below.

[0068] Referring to Figure 1 , there is shown an embodiment of an air handling unit (AHU) 1 in which the present invention can be used. In particular, Figure 1 discloses an AHU 1 which comprises an air ventilation ducting system 2 with an extract air channel 3 and a supply air channel 4.

[0069] The extract air channel 3 comprises an extract air inlet 5 which is connected to the air ventilation ducting system 2 for exhausting air from the interior of a building via an extract air outlet 6 for discarding extract air to the environment. The supply air channel 4 comprises a supply air inlet 7 for inlet of fresh air from the external environment and a supply air outlet 8 for guiding fresh air to the air ventilation ducting system to be distributed via the air ducting system 2 to a building.

[0070] The air handling unit 1 is configured for regulating and ventilating air as part of a heating and ventilation air conditioning (HVAC) system, which is previously known as such. The extract air channel 3 and the supply air channel 4 are in a heat exchanging relation via a heat exchanger 9 in order to exchange heat between the extract air and the supply air. The extract air channel 3 is provided with a centrifugal fan arrangement in the form of an extract air fan 10, in order to induce a flow of extract air from the building via the air ventilation ducting system 2. In a corresponding manner, the supply air channel 4 is provided with a supply air fan 1 1 for inducing a flow of fresh air in the supply air channel 4 in order to distribute supply air to the building via the air ventilation ducting system 2. The AHU 1 is also connected to an electronic control unit (ECU) 12 for control of the fans 10, 11 and their operation, as will be described in greater detail below.

[0071] Figure 1 shows schematically an embodiment with an AHU 1 which comprises a pair of centrifugal fans 10, 11 which are configured in accordance with the present disclosure. Each AHU 1 may include further devices such as dampers for controlling the flow, additional air treatment units, e.g. humidifiers, filters or additional heat regulating devices such as a heat pump or electrical heaters, as well as sensors for sensing relevant parameters concerning air quality and temperature of the air.

[0072] According to further embodiments, the invention can be used in other applications (which are not shown in the drawings), for example an air handling unit of the single direction type which only provides flow of air in one direction. For this reason, such an air handling unit comprises a supply air channel but no extract air channel. Fresh air is then guided through an inlet and further via an air outlet and to an air ventilating ducting system in order to distribute fresh air to a building. The air handling unit is furthermore provided with a fan, such as the above-mentioned centrifugal fan, in order to induce a flow of fresh air into the air ventilating ducting system.

[0073] A further example of an air handling unit (not shown in the drawings) is a unit which comprises an extract air channel but no supply air channel. The air handling unit is therefore designed to only provide a flow of extract air from a building. The extract air is guided from an air ventilating ducting system to the air handling unit via an extract air inlet guided through the AHU to a supply air outlet to the environment. The air handling unit is further provided with a fan, such as the above-mentioned centrifugal fan, to induce a flow of extract air in the air ventilating ducting system.

[0074] The above description gives a few examples of different kinds of air handling units which may suitably be used for the present concept, involving centrifugal fans 10, 11 of generally the type as will be described in the following.

[0075] Figure 2 shows a perspective view of a fan arrangement in the form of a centrifugal fan 10, i.e. a fan which can be used for example as the above- mentioned extract air fan in the arrangement shown in Figure 1 . Sometimes centrifugal fans are referred to as radial flow type fans, or radial fans.

[0076] The fan 10 shown in Figure 2 is based on a concept for centrifugal fan arrangements which comprises a generally circular front shroud (also known as front disc) 13, a back plate 14 and a multitude of fan blades 15 which are interposed between the front shroud 13 and the back plate 14. Each fan blade 15 is formed with a leading edge 15a and a trailing edge 15b. The leading edge 15a is closer to the center axis of the fan 10 than the trailing edge 15b, so that the leading edge 15a will “meet” the flow of air entering through an inlet in the form of a hole 16 in the front shroud 13. The trailing edge 15b of each blade 15 is positioned further away from the centre axis of the fan 10 than the leading edge 15a, normally relatively close to the vicinity of the periphery of the back plate 14.

[0077] The above-mentioned type of centrifugal fan is often referred to as a backward curved centrifugal fan, or a centrifugal fan with backward curved blades. It should be mentioned that according to further embodiments, the concept according to this disclosure is also applicable to centrifugal fans with forward curved blades. Also, fans which are used in ventilation systems are often also referred to as low- speed centrifugal fans, in order to distinguish them from fans within other technical fields.

[0078] According to an embodiment, the front shroud 13, the back plate 14 and the fan blades 15 are produced as separate units which are assembled together by attaching each one of the fan blades 15 to the front shroud 13 and back plate 14 by any suitable means, e.g. by welding or by screws. Although not shown in detail in Figure 2, the fan 10 is suitably provided with attachment means for attaching the fan blades 15 to the front shroud 13 and to the back plate 14. As an alternative, the fan 10 could also be moulded as a single piece.

[0079] Each fan blade 15 has an upper edge which is in contact with, and faces towards, the front shroud 13 and a lower edge which is in contact with, and faces towards, the back plate 14. Also, each fan blade 15 has a blade body with a first side and a second side.

[0080] As mentioned above, in the centre of the front shroud 13 there is provided an inlet in the form of an opening or hole 16 through which incoming air may enter into the fan 10 in an axial direction, as indicated schematically by means of arrows in Figure 2. Air will enter through the hole 16 when the fan arrangement is operating and the fan 10 is rotating so that an air flow will be directed through the fan 10, in a radial direction along the periphery of the fan 10, in all radial directions. The blades 15 of the fan 10 are designed to produce a radial flow of air and together with the back plate 14 and the front shroud 13, which are functioning as guides, so as to redirect the axial air flow entering in the front shroud 13 to provide an induced radial flow which is discharged at the outer periphery.

[0081] The centrifugal fan 10 shown in Figure 2 is designed with a predetermined outer diameter d1 , which is chosen to fit into an opening with a corresponding diameter in an air handling unit 1 (see Figure 1 ), i.e. either in the extract air outlet 6 or in the supply air outlet 8 (or both). A further diameter d2 is also shown in Figure 2. In the context of the present invention, this further diameter d2 is defined as the outer diameter of the arrangement of the fan blades 15, or more precisely, the diameter of a circle which is formed by the outer positions of the trailing edges 15b during rotation of the fan 10.

[0082] In its most general form, the disclosure relates to a fan arrangement 10 with a plurality of fan blades 15 which extend from the front shroud 13 and which define an “effective fan blade height” (h), or “operating fan blade height” (h), i.e. a height or length of each blade which together contributes to the ability of the fan to generate an airflow. An important principle of the fan arrangement 10 is that it is configured so as to be operated with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency of the fan arrangement 10. As will be described below, this optimal efficiency is generally independently of the volume flow and pressure of the fan arrangement 10, as regarded along a system curve of the fan arrangement 10. This object can be achieved in accordance with several embodiments, as will be described below.

[0083] Initially, according to first embodiment which is described in Figure 2, the fan arrangement 10 comprises a further plate 17. This additional plate 17 is arranged generally parallel to the above-mentioned back plate 14 and is also adjustable in the sense that it can be displaced in a direction which is generally perpendicular to plane along which the back plate 14 and the additional plate 17 extend. This corresponds to the axial direction of the fan arrangement 10. The additional plate 17 has a diameter which preferably is greater than the diameter d2 which is defined as the outer diameter of the blades 15, as described above.

[0084] As will be described in greater detail below, the displacement of the additional plate 17 is suitably carried out by means of a motor arrangement (not shown in Figure 2). It will also be described below that the displacement of the additional plate 17 can be carried out during operation of the fan arrangement 10, i.e. during rotation of the fan with the fan blades 15, depending on certain input parameters.

[0085] In order to allow a displacement of the additional plate 17, it is formed with a number of openings 18 having dimensions which are slightly larger than the cross- sectional area and shape of each of the fan blades 15. This is shown in Figure 3, which is separate perspective view of the additional plate 17. These openings 18 consequently allows the additional plate 17 to be displaced, i.e. moved, along the fan blades 15 between different positions extending between a first position close to the upper side of the back plate 14 and a second position close to the underside of the front shroud 13. The actual operation of this displacement will be described in greater detail below.

[0086] The diameter d3 of the additional plate 17 as indicated in Figure 3 is suitably equal to, or slightly larger than, the above-mentioned diameter d2 (see Figure 2) which is defined by the diameter of a circle which is formed by the outer positions of the trailing edges 15b. According to the embodiment in Figure 2 and Figure 3, the diameter d3 of the additional plate 17 is not greater than the diameter d1 of the back plate 14.

[0087] The purpose of the adjustment or displacement of the additional plate 17 is to adapt the fan arrangement 10 to a given or desired operation involving a given air flow and pressure. As mentioned initially, it can be assumed that the AHU 1 (see Figure 1 ) is configured to be used with one or more centrifugal fan arrangements as shown in Figure 2 which are optimized to be operated at a very specific magnitude of the air flow / pressure within the fan. This relates to the system curve of the fan which was described initially. Using the arrangement with the additional plate 17 which can be moved along the fan blades 15, it will be possible to obtain an operation of the fan arrangement 10 in which the additional plate 17 is positioned so that an optimized effective fan blade height h is selected, which means that a maximum coefficient of efficiency is reached by the fan arrangement 10 generally independently of the flow and pressure and along the specific system curve which is associated with the fan arrangement 10. In this way, an advantage relating to a minimized energy consumption for the fan can be achieved.

[0088] If any changes to the required air flow / pressure should be necessary, the fan can be adapted with a suitable displacement of the additional plate 17 which corresponds to the change in air flow. In this manner, the additional plate 17 will be positioned with a distance h to the underside of the front shroud (se Figure 2) which provides a maximum coefficient of efficiency generally independently of the volume flow through the fan 10.

[0089] The principles on which this disclosure is based will now be explained more in detail with reference to Figures 4a, 4b, 5 and 6, in which Figures 4a and 4b show a fan arrangement 10' of a generally known type.

[0090] With reference to Figure 4a, there is shown a fan arrangement 10' of generally known type, which comprises an inlet shroud 13', a back plate 14' and a number of fan blades 15' as described initially. The distance between the underside of the front shroud 13’ and the upper surface of the back plate 14' is generally designated as h'. During operation of the fan arrangement 10', a flow of air is generated as indicated in a schematical manner by means of a number of arrows in Figure 4a.

[0091] It is assumed that the height h' is chosen to a value which is adapted to the required air flow during operation, so that an optimum coefficient of efficiency of the fan arrangement 10' is obtained at the chosen air flow. When the fan 10' is properly configured for a given magnitude of the air flow, the stream of air will follow the internal shape of the fan 10’ without any substantial disturbance or turbulence, as shown by the arrows. This will contribute to an optimal coefficient of efficiency of the fan 10’.

[0092] With reference to Figure 4b, there is shown a situation in which the magnitude of the air flow is changed (which might occur often during use of a fan arrangement in a modern HVAC system). In such a situation, the air flow through the fan arrangement 10' will generate a turbulent flow of air within a certain section of the fan arrangement, as indicated by means of reference numeral 19 in Figure 4b which comprises a number of “turbulent” lines. This can be explained with reference to a flow separation which occurs on the pressure side and the suction side of each fan blade (when the fan arrangement is not operated at the maximum efficiency point) which generates such turbulence, which consequently affects the efficiency in a negative way.

[0093] Due to the substantial amount of turbulence, the overall efficiency of the fan arrangement 10' will be decreased.

[0094] Referring now to Figures 5 and 6, the principles of the present disclosure will be described. Figure 5 generally corresponds to Figure 2 and shows a fan arrangement 10 having an inlet shroud 13, a back plate 14, a number of fan blades 15 and an additional plate 17 which can be displaced in a manner as described above, i.e. in the axial direction of the fan arrangement 10. Also, the additional plate 17 is at least partly positioned between the back plate 14 and the front shroud 13 and is according to the embodiment in Figures 5 and 6 generally parallel to the back plate 14. The distance between the underside of the front shroud 13 and the upper surface of the back plate 14 is designated as h. During operation of the fan arrangement 10, a flow of air is generated as indicated in a schematical manner by means of a number of arrows.

[0095] In a manner which generally corresponds to Figure 4a, the height h is chosen to a value which is adapted to the required air flow and pressure during operation, so that an optimum coefficient of efficiency of the fan arrangement 10 is obtained. As shown in Figure 5, the stream of air through the fan 10 follows the internal shape of the fan 10 without any substantial disturbance or turbulence. It should be noted that the fan arrangement 10 according to Figure 5 is operated with the additional plate 17 being arranged at a position slightly above the upper side of the back plate 14.

[0096] With reference to Figure 6, there is shown a mode of operation with a lower required flow of air in the ventilation system in question. In such a situation, the additional plate 17 has been displaced so that the value of the height h is slightly lower than the corresponding height h in Figure 5. In other words, the additional plate 17 is now positioned closer to the front shroud 13 than in the mode of operation shown in Figure 5. This means that the fan arrangement 10 in Figure 6 is operated with a slightly lower value of the effective fan blade height h, as compared with Figure 5.

[0097] The values of the height h in Figure 5 and 6, respectively, are determined based on certain input parameters. Suitably, current values of the air flow, air pressure and rotational speed of the fan 10 are used for calculating a height h which is selected so that the efficiency of the fan arrangement 10 is optimized. This is illustrated by means of air flow lines in Figure 6 which are generally free from turbulence. It should be noted that values of the height h are chosen so that a maximum coefficient of efficiency is provided independently of the volume flow (and corresponding pressure) which is induced by the fan arrangement 10.

[0098] This means that the ventilation system in which the fan arrangement 10 is used is operated at conditions in which the efficiency of the fan arrangement 10 can always be maximized by allowing operation along the maximum system curve of the fan through suitable selection of value of the height h. This is an advantage as regards the energy consumption of the ventilation system. This advantage is further illustrated in Figure 7, which is a diagram showing the relationship between the air flow and the coefficient of efficiency of the fan arrangement 10. Figure 7 shows in particular that the coefficient of efficiency is maximized in all modes of operation, i.e. independently of the magnitude of the air flow. More precisely, the curves in Figure 7 represent the relationship between the air flow and the coefficient of the fan at a number of different modes of operation, which are distinguished by the required air flow / pressure in the fan arrangement.

[0099] As shown in Figure 7, a number of different heights hi , h2, h3, h4 are calculated depending on the above-mentioned input parameters, where each one of these heights correspond to a given required air flow. In particular, it can be noted that the efficiency of the fan will be optimized and equally high independently of the air flow.

[0100] Figure 8 is a side view of an alternative embodiment of the fan arrangement 10. This embodiment generally corresponds to the one shown in Figures 5 and 6 but is configured in a manner so that the additional plate 17 is provided with a number of pins 20 which extends from the underside of the additional plate 20 and towards the back plate 14, and also through the back plate 14. The pins 20 are configured so as to constitute a number of guiding elements which ensure that the additional plate 17 is positioned and also displaced in a manner so that it is always parallel with respect to the back plate 14.

[0101] Figure 9 is a perspective view corresponding to Figure 8 but regarded from a view from below the back plate 14. Figure 9 shows in particular how the guiding pins 20 extend through the back plate 14 and project out of the underside of said back plate 14.

[0102] Figure 10 shows a fan arrangement 10 according to an embodiment which includes a motor arrangement 21 which is configured for displacing the additional plate 17 in a manner as described above and on demand. As shown, the motor arrangement 21 is arranged externally with regard to the fan arrangement 10, suitably in a manner wherein it comprises a fan motor 22 which is arranged with a linear actuator 23 extending towards the additional plate 17. The linear actuator 23 extends within an output shaft 24 of said fan motor 22. Also, the linear actuator 23 extends through the back plate 14, as shown in Figure 10. Furthermore, the actuator 23 is attached to the centre of the additional plate 17 so that the position of the additional plate 17 can be set as required.

[0103] Figure 10 also shows that the motor arrangement 21 comprises a control system based on an input unit 25 which is configured for providing values related to at least one parameter which is used for control of the distance (h) between the additional plate 17 and the back plate 14. According to an embodiment, the parameters which are used are the current air flow, the pressure and the rotation speed of the fan arrangement 10. Although not shown in the drawings, it should be noted that the arrangement according to Figure 10 comprises suitable sensor devices for the varies input parameter, such as for example a pressure sensor which can be mounted in an input duct of an air handling unit 1 such as the one shown in Figure 1 . Also, a signal corresponding to the rotational speed of the fan can be provided by the motor 22.

[0104] It is also possible to use further input parameters for controlling said height (h), such as for example the torque of the fan or the power of the motor 22.

[0105] Furthermore, the input unit 25 is connected to a control unit 26 which is configured for determining - based on the at least one parameter mentioned above - a suitable position (i.e. a suitable height h) of the additional plate 17. Also, the control unit 26 is connected to an output unit 27 for setting the additional plate 17 at said given height h corresponding to an effective fan blade height. The embodiment shown in Figure 10 comprises an output unit 27 which controls the linear actuator 23 which is arranged in connection with the electric motor 22.

[0106] Figures 1 1 a and 1 1 b show a further embodiment of the invention, comprising a fan arrangement 10 which generally corresponds to Figure 8, with a back plate 14, an additional plate 14, a linear actuator 23 and an output shaft 24 of a (not shown) motor. According to this embodiment, the back plate 14 and additional plate 17 are formed with a slightly raised centre portion. Also, this embodiment comprises a guiding element 20' in the form of a tubular element 28 which is fastened to the underside of the additional plate 14 and extends along the outside of the output shaft 24 and through the back plate 14 so as to project out of the underside of said back plate 14. The purpose of the guiding element 20' is to ensure that the additional plate 17 is maintained in a position which is generally parallel to the back plate 14 during operation of the fan arrangement 10.

[0107] In order to clearly show the operation of the embodiment according to Figures 11 a and 1 1 b, the fan arrangement 10 is shown in two different positions which can be achieved during operation, having a different distance h between the additional plate 17 and the underside of the front shroud 13 (i.e. with different values of the effective fan blade height h), in accordance with the description above.

[0108] Figures 12a and 12b show yet another embodiment of the invention, including a section which is shown in an enlarged form, comprising a fan arrangement 10 which generally corresponds to Figure 8, with a back plate 14, an additional plate 17, a linear actuator 23 and an output shaft 24 of a (not shown) motor for operating the fan. To this end, the output shaft 24 is connected with the back plate 14. Also, a tubular element 28 is arranged around the output shaft 24 and connected to the additional plate 17. According to this embodiment too, the back plate 14 and additional plate 17 are formed with a slightly raised centre portion. Also, this embodiment comprises a screw 29 or a similar component which is mounted through the tubular element 28 and which extends into a guiding track 30 which is formed along the output shaft 24. In this manner, the additional plate 17 can be maintained in a position (by arranging the screw 29 in a suitable position) which is generally parallel to the back plate 14 during operation of the fan arrangement 10, i.e. so that the additional plate 17 does not come into contact with the fan blades during movement of the additional plate 17.

[0109] In order to clearly show the operation of the embodiment according to Figures 12a and 12b, the fan arrangement 10 is shown in two different positions which can be achieved during operation, having a different distance h between the additional plate 17 and the underside of the front shroud 13 (i.e. with different values of the effective fan blade height h), in accordance with the description above.

[0110] Figure 13 shows a perspective view of an embodiment of the fan arrangement 10 which furthermore comprises a sealing arrangement 28 which is arranged along the periphery of the back plate 14. More precisely, the sealing arrangement 28 is based on an additional plate 17' which according to this embodiment is form as a plate of generally same type as described above (see for example Figure 2) but being formed with a peripheral section in the form of a circular rim 29 which extends from the additional plate 17' and towards the back plate (not visible in Figure 13.)

[0111] The sealing arrangement 28 is shown in further detail in Figure 14, which is a cross-sectional view showing the alternative additional plate 17' and its rim 29. The sealing arrangement 28 further comprises a sealing ring 30 which extends along the edge of the back plate 14 in a manner so that the insider of the peripheral section 29 is in sealingly contact with the sealing ring 30.

[0112] It should be noted that, as opposed to the embodiment shown in Figures 2 and 3, in which the diameter d3 of the additional plate 17 is not greater than the diameter of the back plate 14, the diameter of the additional plate 17 in Figure 13 is slightly greater than the diameter of the back plate 14. This is due to the fact that the additional plate 17 extends with its rim 29 outside back plate 14, including the sealing 30.

[0113] It should also be noted that the embodiment which is shown in Figures 13 and 14 can be operated by means of a motor arrangement of the same type as shown in Figure 10.

[0114] Furthermore, it should be noted that the embodiment which is shown in Figures 13 and 14 can be equipped with the arrangement of guiding pins 20 which is shown in any one of Figures 8-11 . In summary, the present disclosure relates to a centrifugal fan arrangement 10 which comprises an inlet 16 for an incoming flow of air, a front shroud 13 which is arranged concentrically around said inlet 16; a back plate 14; and a plurality of fan blades 15 extending from the front shroud 13 so as to define an effective fan blade height (h). The fan arrangement 10 is furthermore configured for generating a volume flow of air at a corresponding pressure. In particular, the fan arrangement 10 is configured so as to be operated with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve which is associated with said fan arrangement 10.

[0115] The principles of the fan arrangement according to the disclosure can be obtained in several ways. A first embodiment was described with reference to Figures 2, 3, 5 and 6. This embodiment is based on the concept that the additional plate 17 is configured to be positioned with a distance (h) to said back plate 14 which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve which is defined for the fan arrangement 10 in question.

[0116] Two further embodiments will now be described. In particular, it will be explained that the fan arrangement can - in its broadest form - be arranged without any additional plate.

[0117] With reference to Figure 15a, there is shown a fan arrangement 10 which generally corresponds to conventional technology, i.e. with a front shroud 13, a back plate 14 and a number of fan blades 15. However, according to this embodiment, the back plate 14 is formed with a number of openings which correspond to the same type of openings shown with reference numeral 18 in Figure 3. However, according to Figure 15a, these openings 18 are provided in the back plate 14 (see Figure 15b). Also, the back plate 14 is movable generally parallel to the front shroud 13, which means that the effective fan blade height h can be determined to a specific value which provides a maximum coefficient of efficiency of the fan arrangement 10, generally independently of the volume flow and pressure, along a system curve which is defined for the fan arrangement 10. Movement of the back plate 14 can be carried out according to the same principles as described above with reference to Figures 1 1 a, 11 b, 12a and 12b, i.e. with a motor and an actuator.

[0118] The fan arrangement 10 is shown in two different positions (i.e. according to Figures 15a and 15b) which can be achieved during operation, having a different distance h, i.e. having different values of the effective fan blade height h, in accordance with the description above.

[0119] A further embodiment is shown in Figures 16a and 16b, i.e. in the form of a fan arrangement 10 which generally corresponds to conventional technology, i.e. with a front shroud 13, a back plate 14 and a number of fan blades 15. However, according to this embodiment, the fan blades 15 are configured in a telescopic manner, i.e. having two sections 15a, 15b, which can be displaced in relation to each other in a manner so that a first section 15a is displaced into a second section 15b. In this manner, the effective fan blade height h can be chosen so as to provide a maximum coefficient of efficiency of the fan arrangement 10, generally independently of the volume flow and pressure, along a system curve which is defined for the fan arrangement 10.

[0120] The telescopic movement of the fan blades can be carried out while moving the back plate 14 according to the same principles as described above with reference to Figures 11 a, 11 b, 12a and 12b, i.e. using a motor and an actuator.

[0121] The fan arrangement 10 is shown in two different positions according to Figures 16a and 16b which can be achieved during operation, having a different distance h, i.e. having different values of the effective fan blade height h, in accordance with the description above. The fan arrangement according to the disclosure is particularly suitable for use in HVAC arrangements in buildings where there is need to control the air flow continuously on demand in various parts of the buildings. Finally, the inventive concept is not limited to the embodiments above but can be varied within the scope of the appended claims.

Claims

CLAIMS1 . A centrifugal fan arrangement (10) comprising: an inlet (16) for an incoming flow of air; a front shroud (13) which is arranged concentrically around said inlet (16); a back plate (14); and a plurality of fan blades (15) extending from the front shroud (13) and defining an effective fan blade height (h); said fan arrangement (10) being configured for generating a volume flow of air at a corresponding pressure; characterized in that: the fan arrangement (10) is configured so as to be operated with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement (10).

2. A centrifugal fan arrangement (10) according to claim 1 , wherein said fan blades (15) extend between the front shroud (13) and the back plate (14); wherein said fan arrangement (10) comprises an additional plate (17; 17') which is arranged between the front shroud (13) and the back plate (14), and which is movable in an axial direction of the fan arrangement (10); and wherein the additional plate (17; 17') is configured to be selectively positioned with a distance (h) to said front shroud (13) corresponding to the effective fan blade height (h) which provides said maximum coefficient of efficiency generally independently of said volume flow and pressure, along said system curve being associated with said fan arrangement (10).

3. A centrifugal fan arrangement (10) according to claim 2, wherein: each one of the fan blades (15) has a leading edge (15a) and a trailing edge (15b), andthe diameter of the additional plate (17) is greater than a diameter (d2) which is defined by the position of each trailing edge (15b) of said fan blades (15).

4. A centrifugal fan arrangement (10) according to any of claim 2 or 3, wherein: the additional plate (17) is arranged at least partly generally parallel to the back plate (14).

5. A centrifugal fan arrangement (10) according to any one of claims 2-4, wherein: the additional plate (17) is formed with openings (18) corresponding to the cross-sectional areas of each of the fan blades (15), allowing the additional plate (17) to be displaced along the fan blades (15) while rotating during operation of the fan arrangement (10).

6. A centrifugal fan arrangement (10) according to any one of claims 2-5, wherein: the additional plate (17) is configured so as to be displaced by means of a motor arrangement (21 ) which is arranged externally to the fan arrangement (10).

7. A centrifugal fan arrangement (10) according to claim 6, wherein: said motor arrangement (21 ) comprises a fan motor (22) which is arranged with an actuator (23) extending within an output shaft (24) of said fan motor (22) and through said back plate (14); said actuator (23) being attached to the centre of said additional plate (17).

8. A centrifugal fan arrangement (10) according to any one of claims 2-7, wherein: said back plate (30) is provided with a sealing (22) extending along the periphery, and that said additional plate (17) is formed with a peripheral section (29) which is in contact with said sealing (30).

9. A centrifugal fan arrangement (10) according to claim 8, wherein:the additional plate (17) is disc-shaped with said peripheral section (29) in the form of a rim section which extends generally perpendicularly towards the back plate (14).

10. A centrifugal fan arrangement (10) according to any one of claims 2-9, wherein: the additional plate (17) is provided with a plurality of guiding elements (20; 20') extending from the underside of said additional plate (17) and through the back plate (14), in order to maintain the additional plate (17) generally parallel to the back plate (14).11 . A centrifugal fan arrangement according to claim 1 , wherein: said back plate (14) is formed with openings (18) corresponding to the cross-sectional areas of each of the fan blades (15), allowing the back plate (14) to be displaced along the fan blades (15) while rotating during operation of the fan arrangement (10).

12. A centrifugal fan arrangement according to claim 1 , wherein: each of said fan blades (15) are arranged in a telescopical manner and comprising a first fan blade section (15a) and a second fan blade section (15b) which can be telescopically displaced in relation to each other.

13. A control system (25) for a centrifugal fan arrangement (10) in accordance with any one of the preceding claims, characterized in that the control system (25) comprises: an input unit (25) for providing a parameter value corresponding to said effective fan blade height (h); a control unit (26) for determining, based on said parameter value, a desired setting of fan arrangement (10) using said effective fan blade height (h); and an output unit (27) for arranging the fan arrangement (10) with said fan blade height (h), which is chosen with a value which provides a maximumcoefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement (10).

14. A control system (25) according to claim 13, wherein said fan arrangement comprises an additional plate (17; 17') which is arranged between the front shroud (13) and the back plate (14), and which is movable in an axial direction of the fan arrangement (10); wherein said control system (25) comprises: a control unit (26) for determining, based on said parameter value, a desired position of the additional plate (17) corresponding to a given distance (h) to the front shroud (13); and an output unit (27) for setting the additional plate (17) at said given distance (h).

15. A control system (25) according to claim 13 or 14, wherein: said output unit (28) comprises a motor arrangement (21 ) comprising a fan motor (22) which is arranged with an actuator (23) extending within an output shaft (24) of said fan motor (22) and through said back plate (14); said actuator (23) being attached to the centre of said additional plate (14).

16. A method for controlling a fan arrangement (10) which comprises: an inlet (16) for an incoming flow of air; a front shroud (13) which is arranged concentrically around said inlet (16); a back plate (14); and a plurality of fan blades (15) extending from the front shroud (13) and defining an effective fan blade height (h); said fan arrangement being configured for generating at volume flow of air at a corresponding pressure; characterized in that said method comprises: operating the fan arrangement (10) with an effective fan blade height (h) which is chosen with a value which provides a maximum coefficient of efficiency generally independently of said volume flow and pressure, along a system curve being associated with said fan arrangement (10).

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