EP4317830A1 - A heating assembly having an active silencer - Google Patents

Abstract

Providing an assembly for heating water in a building, in particular a heat pump, wherein the assembly comprises an active silencer to continuously attenuate disruptive frequencies generated by a fan within the assembly at any given fan speed thereby actively dampening the variable noise generated by the fan.

Description

• The invention relates to an assembly for heating water in a building, in particular a heat pump, wherein the assembly comprises an active silencer. Additionally, the invention relates to an active silencer for use in a heating assembly such as a heat pump.
• Heating of water in buildings, such as heating water of a central heating system or heating of water for domestic use, may be accomplished by means of a heat pump system. Such a heat pump system may either be a ground source heat pump (GSHP) system or an air source heat pump (ASHP) system. In a GSHP system, calories are exchanged between the ground and a fluid, in particular being air or water. The calories in the ground may be extracted by capturing calories in a water table or by circulating a water-based circuit in the ground. In an ASHP system calories are exchanged between the air and a fluid, in particular air or water.
• A heat pump system typically comprises at least one first heat exchanger for capturing calories from a first source, at least one second heat exchanger for transferring captured calories to a second source, and a refrigerant loop between both heat exchangers to transport the captured calories from the at least one first heat exchanger to the at least one second heat exchanger. The at least one first and second heat exchangers together with the refrigerant loop form, at least a part of, a heat exchanging circuit.
• The heat exchange achieved can be used to cool or heat the desired medium. Among the most commonly used circuits for an air source heat pump, the medium to be heated can be a heating water circuit and/or a sanitary water circuit.
• In the case of a heat pump that only heats domestic water, it is called a heat pump water heater (HPWH). Heat pump water heaters can be either monobloc or split.
• The most common solution is to have a monobloc heat pump water heater. The water tank to be heated and the heat pump are part of the same product. This product is installed inside so as not to cause too much heat loss to the tank filled with hot water. To operate the heat pump, a flow of air passes through the evaporator and exits cooled. In order to maximize the efficiency of the heat pump and depending on the installation environment, the user can choose to use ambient air from the installation site, air from the ventilation ducts (partially heated by the building's consumption) or outside air. The same applies to the air outlet of the heat pump. As this air is colder than the air entering the building, the choice can be made to cool the installation site or to expel the air outside the installation site.
• In general, in order to optimize the performance of the product without lowering the temperature of the installation site, it is chosen to duct at least the air outlet of the heat pump water heater to the outside.
• Typically, ASHP, and especially ASHP water heaters, systems further comprise a fan creating an airflow between the outside air and the heat exchanging circuit to exchange calories with a thermodynamic system. This fan may also be ducted in order to bring the airflow from the outside and guiding the airflow through the inside of a building into a heat pump system. When ducted, the airflow coming from the fan is ultimately pushed or pulled outside the house after the airflow passed the heat pump system. The fan creating the airflow may have a variable speed. This leads to a variable thermic power output available to the heat exchanger and so a variable power and variable performance of the product. Depending on the heating requirement, the heating condition and the environment of the product, the system can regulate this power and performance.
• A fan usually creates noise. The noise level, or acoustic profile of a fan, is linked to among others to the amount of fan blades, the shape of the fan blades but also to the speed at which the fan is turning. With variable fan speeds, the noise generated by the fan also varies according to the sound pressure level or power. The sound spectrum of a fan consists of marked peaks at the Blade Passing Frequency (FBP) of the fan and its harmonics. The FBP is equal to the fan speed in rpm, divided by 60 and multiplied by the number of blades. The sound power is related to additional parameters. When the airflow is ducted, the airflow pushed or pulled outside the building may be directed to neighboring buildings and the noise generated by the fan may as such be noticeable at the neighboring buildings. As such, the fans generate an undesired and possibly annoying noise pollution.
• It is therefore desired to obtain a heating assembly, in particular an air source heat pump, in particular an air source heat pump water heater, wherein the assembly comprises an active silencer. Such an active silencer may be based on a Helmholtz Resonator which allows active dampening of the variable noise generated by the fan. Such an active silencer will adapt itself based on the fan speed or any parameter influencing the fan speed, assuring a constant noise reduction.
• The object of the invention is obtained by an assembly for heating water in a building, in particular a heat pump, the assembly comprising a fan, a duct connected to the fan, and an active silencer connected to the duct, wherein the active silencer comprises an enclosed cavity and a volume changing member positioned within the enclosed cavity wherein the volume within the enclosed cavity is varied by means of the volume changing member depending on the fan speed or any parameter used to regulated the fan speed during operation of the assembly .
• The assembly for heating water in a building may be a heat pump or heat pump system such as an ASHP system, especially an air source heat pump water heater. The fan may be any fan suitable for creating an airflow between the outside air and a heat exchanging circuit within the assembly. The fan may be positioned within the heat pump. The fan may be positioned before or after the heat exchanger within the heat pump according to the direction of the air flow. Alternatively, the fan may be positioned within the duct. The duct may be any pipe or tube suitable for guiding an airflow. The duct may be a cylindrical pipe. The active silencer may be attached substantially perpendicular, parallel or in any other suitable angle to the duct. The active silencer may be attached to the duct as a T-junction. As such, the active silencer may comprise a neck portion. The enclosed cavity of the active silencer may have a cylindric, spherical, parallelepiped, or any other hollow shape suitable to comprise a volume changing member within the cavity.
• The volume changing member may be any suitable means to vary the volume within the enclosed cavity. The volume changing member may, for instance, be a balloon-like member or a piston-like member. As such, the volume changing member may vary the volume within the enclosed cavity by means of expansion and contraction of the member or by means of movement of the member. Preferably, the volume changing member is a movable piston. The piston may be moved using an endless screw.
• Parameter used to regulate the fan speed may be, amongst others, the temperature of the water to be heated within the assembly, the temperature of a refrigerant used within the assembly, the temperature of the air anywhere within the assembly, the operating mode of the assembly, the pressure drop of the installation and/or the pressure of the refrigerant used within the assembly. The fan speed is mainly set based on the power to be delivered to the heat pump system. The fan speed is decreased or increased based on the amount of power to be delivered. The amount of power to be delivered is based on the temperature of the water to be heated compared to the set temperature for the water. The refrigerant temperature may vary to influence the performance of the heat pump at different operating modes and can be varied by adjusting the fan speed. The air temperature within the system may also be varied using different fan speeds to, for instance, prevent freezing of the system if the air is too cold. In different operating modes, the fan speed may change to, for instance, boost the fan speed when overconsumption is expected or to reduce the fan speed when setting the assembly to a silent or stand-by mode.
• As the size or the position of the volume changing member within the enclosed cavity relates to the fan speed or any parameter used to regulated the fan speed in the assembly, the size or position may change upon each change in fan speed or of said parameter. Thus, the size or the position of the volume changing member may continuously vary during operation of the assembly. With this continuously varying size or position of the volume changing member, the volume within the enclosed cavity also varies continuously. Due to the varying volume within the enclosed cavity of the active silencer, and the active silencer being in connection with the duct, the active silencer may attenuate the disruptive frequencies generated by the fan causing noise, and travelling via the airflow through the duct, at any given fan speed. Thus, an active dampening of the variable noise generated by the fan is obtained.
• The dimensions of the active silencer may be, in general, defined by the following formula, $$f=\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">c</figure-callout>}}{2\pi }\times \sqrt{\frac{S_{\mathit{neck}}}{V_{\mathit{cavity}}\times L_{\mathit{cavity}}}}$$

  

  wherein, f is the frequency of the fan, c is the speed of sound in the air, S is the surface of the neck of the active silencer, V is the volume of the enclosed cavity and L is the length of the enclosed cavity. Furthermore, the speed of sound c is dependent on the temperature measured in Kelvin and may be equated a c = 20,05 · √T. The speed of sound c may thus vary with different air temperatures.
• When the active silencer has a cylindrical shape, the dimension of the active silencer may be defined by the following formula, $$f=\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">c</figure-callout>}}{2\pi }\times \sqrt{\frac{{\mathit{<figure-callout\; id="2"\; label="\pi R\; neck"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">\pi R</figure-callout>}}_{\mathit{neck}}^{\mathit{}}}{{\mathit{<figure-callout\; id="2"\; label="\pi R\; cavity"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">\pi R</figure-callout>}}_{\mathit{cavity}}^{\mathit{}}\times h\times \left(L_{\mathit{neck}}+1.5R_{\mathit{neck}}\right)}}$$

  

  wherein, f is the frequency of the fan, c is the speed of sound in the air, R(cavity) is the radius of the enclosed cavity, h is the height of the enclosed cavity, L(neck) is the length of the neck portion and R(neck) is the radius of the neck portion. Furthermore, the speed of sound c is dependent on the temperature measured in Kelvin and may be equated a c = 20,05 · √T. The speed of sound c may thus vary with different air temperatures.
• With the speed of sound c varying at different air temperatures, measuring the air temperatures within the assembly may be preferred to adjust the position of the volume changing member within the active silencer to not only accommodate for the varying fan speed but also the varying speed of sound c as a result from a different air temperature.
• In an embodiment, the volume changing member positioned within the enclosed cavity is a piston comprising a step motor and an endless screw attached to the step motor. The step motor is electronically connected to a logic board or programmable card. The logic board or programmable card may receive information on the fan speed or any parameter used to regulate the fan speed in the assembly during operation of the assembly. The piston may be any suitable piston mechanism to change the volume within the enclosed cavity. The step motor drives the endless screw. The endless screw may, as such move the piston up and down within the enclosed cavity thereby continuously moving the piston. The step motor may receive an input from the logic board or programable card based on the fan speed, any parameter used to regulate the fan speed in the assembly, or a combination of both. The logic board or programable card may be situated anywhere within the assembly for heating water and may be directly or indirectly electronically connected to a tachometer or a temperature sensor.
• In an embodiment, the logic board or programable card is electronically connected to a tachometer of the fan to read-out the fan speed during operation of the assembly. The logic board or programable card may continuously receive the actual fan speed. The logic board or programable card may use a lookup table or a calculation method to send a driving signal to the step motor based on the received fan speed. As the actual fan speed may continuously vary, the logic board or programable card may continuously send a different value for the driving signal to the step motor. Thereby, the endless screw is continuously adjusted and as such continuously moving the piston.
• In an embodiment, the parameters used to regulate the fan speed in the assembly are chosen from the temperature of the water to be heated, the temperature of a refrigerant used within the assembly (1), the temperature of the air, the pressure drop of the system, an operating mode set during operation, or any combination thereof. The fan speed is mainly set based on the power to be delivered to the heat pump system. The fan speed is decreased or increased based on the amount of power to be delivered. The amount of power to be delivered is based on the temperature of the water to be heated compared to the set temperature for the water. The refrigerant temperature may vary to influence the performance of the heat pump at different operating modes and can be varied by adjusting the fan speed. The air temperature within the system may also be varied using different fan speeds to, for instance, prevent freezing of the system if the air is too cold. In different operating modes, the fan speed may change to, for instance, boost the fan speed when overconsumption is expected or to reduce the fan speed when setting the assembly to a silent or stand-by mode.
• In an embodiment, the logic board or programable card is electronically connected to a temperature sensor to read-out the temperature of the water, the refrigerant and/or the air.
• In an embodiment, the active silencer is connected to the duct via a T-junction. The active silencer may be fluidly connected to the duct via said T-junction. The active silencer may thus be connected perpendicular to the duct with the piston moving in a direction perpendicular to the duct. Alternatively, the active silencer may also be connected in parallel to the duct with the piston moving in a direction parallel to the duct.
• In an aspect of the invention, an active silencer for dampening variable fan noise in an assembly for heating water in a building, is provided wherein the active silences comprises an enclosed cavity and a volume changing member positioned within the enclosed cavity wherein the active silencer is connected to a duct of an assembly for heating water in a building and the volume within the enclosed cavity is varied by means of the volume changing member depending on the fan speed in said assembly or any parameter used to regulated the fan speed during in the assembly during operation of the assembly. As the size or position of the volume changing member within the enclosed cavity relates to the fan speed or any parameter used to regulate the fan speed, the size or position may change upon a change in fan speed, or any parameter to regulate the fan speed, recorded within an assembly for heating water in a building. Thus, the size or position of the volume changing member may continuously vary during operation of the assembly. With this continuously varying size or position, the volume within the enclosed cavity also varies continuously. Due to the varying volume within the enclosed cavity of the active silencer, and the active silencer being in connection with a duct within the assembly, the active silencer may thus attenuate disruptive frequencies generated by the fan causing noise, and travelling via the airflow through the duct, at any given fan speed. Thus, an active dampening of the variable noise generated by the fan is obtained.
• The active silencer may be attached substantially perpendicular or parallel to a duct within the assembly. The active silence may be attached to the duct as a T-junction. The enclosed cavity of the active silencer may have a cylindric, spherical, parallelepiped, or any other hollow shape suitable to comprise a volume changing member within the cavity. The volume changing member preferably is a movable piston. The piston may be moved using an endless screw.
• In an embodiment, the volume changing member positioned within the enclosed cavity is a piston comprising a step motor and an endless screw attached to the step motor wherein the step motor is electronically connected to a logic board or programable card comprising information on the fan speed or any parameter used to regulate the fan speed in the assembly during operation of the assembly. The step motor is electronically connected to a logic board or programable card. The logic board or programable card may comprise information on the fan speed or any parameter used to regulate the fan speed in the assembly during operation of the assembly. The piston may be any suitable piston mechanism to change the volume within the enclosed cavity. The step motor drives the endless screw. The endless screw may, as such move the piston up and down within the enclosed cavity thereby continuously moving the piston. The step motor may receive an input from the logic board or programable card, calculating the number of steps the motor with have to makes based on the fan speed, any parameter used to regulate the fan speed in the assembly, or a combination of both. The logic board or programable card may be situated anywhere within the assembly for heating water and may be directly or indirectly electronically connected to a tachometer or a temperature sensor.
• In an embodiment, the logic board is electronically connected to a tachometer of the fan to read-out the fan speed during operation of the assembly. The logic board may continuously receive the actual fan speed. The logic board may use a lookup table or a calculation method to send a driving signal to the step motor based on the received fan speed. As the actual fan speed may continuously vary, the logic board may continuously send a different value for the driving signal to the step motor. Thereby, the endless screw is continuously adjusted and as such continuously moving the piston.
• In an embodiment, the parameters used to regulate the fan speed in the assembly are chosen from the temperature of the water to be heated, the temperature of a refrigerant used within the assembly (1), the temperature of the air, the pressure drop of the system, an operating mode set during operation, or any combination thereof. The fan speed is mainly set based on the power to be delivered to the heat pump system. The fan speed is decreased or increased based on the amount of power to be delivered. The amount of power to be delivered is based on the temperature of the water to be heated compared to the set temperature for the water. The refrigerant temperature may vary to influence the performance of the heat pump at different operating modes and can be varied by adjusting the fan speed. The air temperature within the system may also be varied using different fan speeds to, for instance, prevent freezing of the system if the air is too cold. In different operating modes, the fan speed may change to, for instance, boost the fan speed when overconsumption is expected or to reduce the fan speed when setting the assembly to a silent or stand-by mode.
• In an embodiment, the logic board is electronically connected to a temperature sensor to read-out the temperature of the water, the refrigerant and/or the air.
• In an embodiment, the active silencer is connected to the duct via a T-junction. The active silencer may be fluidly connected to the duct via said T-junction. The active silencer may thus be connected perpendicular to the duct with the piston moving in a direction perpendicular to the duct. Alternatively, the active silencer may also be connected in parallel to the duct with the piston moving in a direction parallel to the duct.
• In an aspect of the invention, a method for actively dampening variable fan noise in an assembly for heating water in a building, is provided wherein the method comprises the steps of determining the fan speed directly from a fan for creating an airflow and/or the air temperature of said airflow within the assembly, and setting the volume of an active silencer by means of a volume changing member within the active silencer connected to a duct for guiding airflow based on the determined fan speed; wherein the fan speed is determined by means of a tachometer of a fan and/or any parameter to regulate the fan speed, and wherein the volume is set by means of a step motor attached to the volume changing member. The fan for creating an airflow generates noise when operated. The amount of noise is correlated to the speed at which the fan is operating. The fan speed may be directly determined by means of a tachometer of said fan, or indirectly determined by means of a parameter for setting the fan speed. With the fan speed determined directly or indirectly, a volume changing member within an active silencer may be expanded, contracted or positioned accordingly and as such the size or position of the volume changing member may change upon a change in fan speed or a parameter for setting said fan speed. Thus, the size or position of the volume changing member may continuously vary during operation of the assembly. With this continuously varying size or position, the volume within the enclosed cavity varies continuously as well. Due to the varying volume within the enclosed cavity of the active silencer, and the active silencer being in connection with the duct, the active silencer may attenuate disruptive frequencies generated by the fan causing noise, and travelling via the airflow through the duct, at any given fan speed. Thus, an active dampening of the variable noise generated by the fan is obtained.
• In an embodiment, the parameters used to regulate the fan speed in the assembly are chosen from the temperature of the water to be heated, the temperature of a refrigerant used within the assembly, the temperature of the air, the pressure drop of the system, an operating mode set during operation, or any combination thereof.
• In an embodiment, the volume changing member is a piston moving within the active silencer. The piston may comprise a step motor and an endless screw attached to the step motor. The step motor is electronically connected to a logic board or programable card within the assembly for heating water in a building. The logic board may comprise information on the fan speed or any parameter used to regulate the fan speed in the assembly during operation of the assembly. The piston may be any suitable piston mechanism to change the volume within the enclosed cavity. The step motor drives the endless screw. The endless screw may, as such move the piston up and down within the enclosed cavity thereby continuously moving the piston. The step motor may receive an input from the logic board or programable card based on the fan speed, a parameter to regulate said fan speed, or a combination of both. The logic board may be situated anywhere within the assembly for heating water and may be directly or indirectly electronically connected to a tachometer or a temperature sensor.
• In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

Figure 1

shows a schematic representation of an assembly according to the present invention.

Figure 2

shows a schematic representation of an active silencer according to and embodiment of the present invention.

Figure 3

shows a schematic representation of an assembly according to an embodiment of the present invention.

Figure 4

shows a table representation of the acoustic pressure at varying resonator frequencies of a fan.

Figure 5

shows a graphical representation of the acoustic pressure level for a particular blade pass frequency.

Figure 6

shows a graphical representation of the acoustic pressure level for a particular blade pass frequency.

Figure 7

shows a graphical representation of the acoustic power level for a particular blade pass frequency.

• With reference to Figure 1, an assembly 1 according to the present invention is shown. The assembly 1 is an example of a ASHP water heater. The assembly 1 comprises a heat pump module 2 to which a first duct 4a and a second duct 4b is attached. The assembly 1 further comprises a fan 3. An active silencer 5 is attached to first duct 4a. As can be seen, the active silencer 5 is attached in a T-shape fashion and perpendicular to the first duct 4a. The active silencer 5 comprises an enclosed cavity 6 which comprises a volume changing member 7 in the form of a piston. The volume changing member 7 comprises a step motor 8 and an endless screw 9. An end-of-stroke sensor 10 is provided to be able to detect the end of the movement of the volume changing member 7 during operation of the active silencer 5. The step motor 8 is electronically connected to a logic board or programable card not shown in Figure 1. The logic board or programable card, not shown, is further connected to the heat pump module 2. Lastly, the active silencer 5 comprises a neck portion 11 which connects the enclosed cavity 6 to the duct 4a.
• In Figure 2, an active silencer 5 is shown. The active silencer 5 comprises an enclosed cavity 6 which comprises a volume changing member 7 in the form of a piston. The volume changing member 7 comprises a step motor 8 and an endless screw 9. An end-of-stroke sensor 10 is provided to be able to detect the end of the movement of the volume changing member 7 during operation of the active silencer 5. The step motor 8 is electronically connected to a logic board or programable card not shown in Figure 2. The active silencer 5 further comprises a neck portion 11 which connects the enclosed cavity 6 to an air duct.
• Figure 3 shows the same assembly 1 as shown in Figure 1 however the active silencer 5 is now attached in a T-shape fashion but parallel perpendicular to the first duct 4a.
• In Figure 4, a table is shown representing the acoustic pressure at varying resonator frequencies of a fan. In particular, the blade passing frequency (BPF) is shown in the left column. The BPF is calculated with the following formula. $$\mathit{FBP}\left(\mathit{Hz}\right)=\frac{\mathit{<figure-callout\; id="60"\; label="Fan\; Speed\; rpm"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">Fan</figure-callout>}\mathit{Speed}\left(\mathit{rpm}\right)\left(\mathit{}\right)}{60}\times \mathit{Number}\mathit{of}\mathit{blades}$$

  
• Furthermore, the acoustic pressure (L_P1) measured in decibels (dB) is shown for the resulting acoustic pressure measured at any given fan frequency when an assembly 1 would not comprise an active silencer 5. Also, the acoustic pressure (L_P2) measured in decibels (dB) is shown for the resulting acoustic pressure measured at any given fan frequency when having an assembly 1 according to the present invention which includes an active silencer 5. Lastly, the difference in acoustic pressure measured at any given fan frequency between an assembly 1 with and without an active silencer 5 is shown in the right column. As can be seen, the active silencer 5 reduces the acoustic pressure measured at any of the blade pass frequencies shown in the table.
• Figures 5 and 6 show a graphical representation of the acoustic pressure level, or sound pressure level, measured in decibel (dB) in relation to the frequency for a particular blade pass frequency for both an assembly 1 with and without an active silencer 5. In Figure 5, the acoustic pressure level on the Y-axis is shown against the frequency on the X-axis at a blade pass frequency of 196 Hz. In Figure 6, the acoustic pressure level on the Y-axis is shown against the frequency on the X-axis at a blade pass frequency of 157 Hz.
• Figure 7 shows the acoustic power level, or sound power level, measured in A-weighted decibels (dBA) in relation to the frequency for a particular blade pass frequency for both an assembly 1 with and without an active silencer 5. The acoustic power level on the Y-axis is shown against the frequency on the X-axis at a blade pass frequency of 157 Hz.
Reference Signs

1

assembly for heating water in a building

2

heat pump module

3

fan

4a

first duct

4b

second duct

5

active silencer

6

enclosed cavity

7

volume changing member

8

step motor

9

endless screw

10

end-of-stroke sensor

11

neck portion

Claims (15)

1. An assembly (1) for heating water in a building, in particular a heat pump, the assembly comprising:

   - a fan (3);

   - a duct (4a, 4b) connected to the fan (3); and

   - an active silencer (5) connected to the duct;

   wherein the active silencer (5) comprises an enclosed cavity (6) and a volume changing member (7) positioned within the enclosed cavity (6) wherein the volume within the enclosed cavity (6) is varied by means of the volume changing member (7) depending on the fan speed or any parameter used to regulated the fan speed during operation of the assembly (1).
2. The assembly (1) according to claim 1, wherein the volume changing member (7) within the enclosed cavity (6) is a piston comprising a step motor (8) and an endless screw (9) attached to the step motor (8) wherein the step motor (8) is electronically connected to a logic board or programable card comprising information on the fan speed or any parameter used to regulate the fan speed in the assembly (1) during operation of the assembly (1).
3. The assembly (1) according to claim 2, wherein the logic board or programable card is electronically connected to a tachometer of the fan to read-out the fan speed during operation of the assembly (1).
4. The assembly (1) according to claim 2, wherein any of the parameters used to regulate the fan speed in the assembly (1) is chosen from the temperature of the water to be heated, the temperature of a refrigerant used within the assembly (1), the temperature of the air, the pressure drop of the system, an operating mode set during operation, or any combination thereof.
5. The assembly (1) according to claim 4, wherein the logic board of programable card is electronically connected to a temperature sensor to read-out the temperature of the water, the refrigerant and/or the air.
6. The assembly (1) according to any of the preceding claims, wherein the active silencer (5) is connected to the duct (4a, 4b) via a T-junction.
7. An active silencer (5) for dampening variable fan noise in an assembly (1) for heating water in a building, wherein the active silences (5) comprises:

   - an enclosed cavity (6); and

   - a volume changing member (7) positioned within the enclosed cavity (6);

   wherein the active silencer (5) is connected to a duct (4a, 4b) of an assembly (1) for heating water in a building and the volume within the enclosed cavity (6) is varied by means of the volume changing member (7) depending on the fan speed in said assembly (1) or any parameter used to regulated the fan speed during in the assembly (1) during operation of the assembly (1).
8. The active silencer (5) according to claim 7, wherein the volume changing member (7) positioned within the enclosed cavity (6) is a piston comprising a step motor (8) and an endless screw (9) attached to the step motor wherein the step motor (8) is electronically connected to a logic board or programable card comprising information on the fan speed or any parameter used to regulate the fan speed in the assembly (1) during operation of the assembly (1).
9. The active silencer (5) according to claim 8, wherein the logic board or programable card is electronically connected to a tachometer of the fan to read-out the fan speed during operation of the assembly (1).
10. The active silencer (5) according to claim 8, wherein any of the parameters used to regulate the fan speed in the assembly (1) is chosen from the temperature of the water to be heated, the temperature of a refrigerant used within the assembly (1), the temperature of the air, the pressure drop of the system, an operating mode set during operation, or any combination thereof.
11. The active silencer (5) according to claim 10, wherein the logic board of programable card is electronically connected to a temperature sensor to read-out the temperature of the water, the refrigerant and/or the air.
12. The active silencer (5) according to any of the claims 7 to 11, wherein the active silencer (5) is connected to the duct (4a, 4b) via a T-junction.
13. A method for actively dampening variable fan noise in an assembly (1) for heating water in a building, wherein the method comprises the steps of:

    - determining the fan speed directly from a fan for creating an airflow and/or the air temperature of said airflow within the assembly; and

    - setting the volume of an active silencer (5) by means of a volume changing member (7) within the active silencer (5) connected to a duct (4a, 4b) for guiding airflow based on the determined fan speed; wherein the fan speed is determined by means of a tachometer of a fan and/or any parameter to regulate the fan speed, and wherein the volume is set by means of a step motor (8) attached to the volume changing member (7).
14. The method according to claim 13, wherein the parameter to regulate the fan speed is chosen from the temperature of the water to be heated, the temperature of a refrigerant used within the assembly (1), the temperature of the air, the pressure drop of the system, an operating mode set during operation, or any combination thereof
15. The method according to claim 13 or 14, wherein the volume changing member (7) is a piston moving within the active silencer (5).

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