EXPANSI ON VESSEL I N A HEATI NG OR COOLI NG SYSTEM

FI ELD OF THE I NVENTION

5

The present invention relates to a method of determ ining a functional condition of an expansion vessel in a heating- or cooling system . I n particular, it relates to such a method in which the determ ination includes generating at least one tem porary pressure increase in liquid flowing in the system and m easuring and analysing the resulting pressure response.

BACKGROUND OF THE I NVENTION

A heating system installed e.g. in a house typically com prises a heat source, such5 as a boiler, which is used to heat liquid, such as water, flowing in the system . The generated heat is used for heating the surroundings, typically via radiators or floor heating. The consum ption of heat normally varies during the day and depending e.g. on the outdoor tem perature. It is generally preferred to keep the pressure in the heating system more or less constant, and for this purpose, the system 0 typically comprises an expansion vessel with an internally arranged elastic mem brane which separates a volume of gas, such as air or nitrogen, from the liquid flowing in the system . When the temperature in the liquid increases, the volume thereof increases accordingly, and the expansion vessel com pensates by the gas being com pressed. Thus, it works as a sort of overflow tank that absorbs5 the extra pressure thereby helping to keep the system stable. Sim ilar considerations apply to a cooling system .

If the expansion vessel is not working correctly due to a broken m em brane, the increased liquid volum e and pressure due to the increase of liquid tem perature0 fills up the expansion vessel and can dam age parts of the system and lead to leakage, e.g. at the pressure relieve valve or at gas venting locations. Sym ptom s of a faulty expansion vessel can be hard to verify, since the expansion vessel is a closed unit and the m em brane cannot be visually inspected. The user or service technician can experience a drop in system pressure and water in the appliance,5 which continues refilling of the system . These symptoms can result in m any service technician call-outs, before the actual problem of the expansion vessel is detected. If there is a com bined failure on the pressure relieve valve and expansion tank, very problem atic failures in the system piping or inside the appliance, can occur.

The sym ptom s caused by a faulty expansion vessel can, besides the m entioned problem s, cause exchange of otherwise well-functioning system com ponents, such as the pressure relieve valve, sensors, the gas-venter or the pump. Som etim es it is erroneously believed by the service technician that the pum p is causing these sym ptom s in the system . However, a fully functional returned pum p is defined as a “NFF” (no failure found) , and there is no warranty in this case. Furtherm ore, scrapping a functional pum p is not sustainable.

Hence, an im proved method of determ ining a functional condition of an expansion vessel in a heating- or cooling system would be advantageous.

OBJECT OF THE I NVENTION

It is an object of the present invention to provide a m ethod with which the functional condition of an expansion vessel in a heating- or cooling system can be determ ined in a more efficient and reliable m anner than with known methods.

It is another object of the present invention to provide a m ethod with which the functional condition of an expansion vessel in a heating- or cooling system can be determ ined without having to disassem ble any parts of the system .

It is a further object of the present invention to provide an alternative to the prior art.

I n particular, it may be seen as an object of the present invention to provide a method that solves the above-m entioned problem s of the prior art. SUMMARY OF THE I NVENTI ON

Thus, the above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a m ethod of determ ining a

5 functional condition of an expansion vessel in a heating- or cooling system , wherein the system com prises: pipes connecting elem ents of the system , a pum p for circulating liquid through at least a part of the system , an expansion vessel arranged and configured to equalize pressure in the liquid when the expansion vessel is intact , and at least one pressure sensor configured to m easure a pressure in the liquid, the m ethod com prising the following steps: generating at least one tem porary pressure increase in the circulating liquid, 5 by use of the at least one pressure sensor, determ ining a pressure response representing the resulting pressure in the liquid as a function of tim e, com paring the determ ined pressure response with known data representing a corresponding pressure response of the system when the expansion0 vessel is intact, and based on the com parison , determ ining the functional condition of the expansion vessel.

The m ethod could be used in a HVAC-system . A HVAC-system is a system for5 heating, ventilation , and air conditioning and is used to control the tem perature, hum idity, and purity of the air in an enclosed space with the aim of providing therm al com fort and acceptable indoor air quality.

The functional condition to be determ ined will typically be whether or not the0 m em brane in the expansion vessel is intact and functioning as intended to seal off a gas-cham ber from the liquid in the system . As will be explained in further details below, such a gas-cham ber will act as a spring to provide pressure equalization to the system . I n the following, the expansion vessel will be referred to as containing air as that is the m ost com m on gas used. However, it could also5 be another gas, such as nitrogen . The “elem ents” of the system could e.g. be a heat exchanger, a boiler, or a pum p.

The expansion vessel will typically be connected to the suction side of the pump, but the scope of protection also covers system s in which it is connected to the pressure side of the pump.

The at least one pressure sensor could be analogue or digital; it could e.g. be a piezoelectric sensor, a capacitive sensor, or a sensor based on strain gauges.

The tem porary pressure increase could also be referred to as a pressure stim ulus or a pressure pulse.

By “resulting pressure” is m eant the pressure resulting from the temporary pressure increase.

I n presently preferred em bodim ents of the invention, the method and the system are configured to determ ine the functional condition of the expansion vessel as a faulty condition when the expansion vessel is defect.

The com parison between the determ ined pressure response and known data m ay com prise determ ining a num erical value of the difference there between. The subsequent determ ination of the functional condition of the expansion vessel may then comprise determ ining whether or not this numerical value has exceeded a predefined threshold.

The at least one pressure sensor may send output signals to a controller, and the controller m ay be used to determ ine the pressure response based on the output signals. The controller may further be used to determ ine the functional condition of the expansion vessel. The controller may e.g. be an electronic or mechanic controller.

The pressure response resulting from the generated tem porary pressure increase may have a lower pressure level when the expansion vessel is defect than when it is intact. This effect is related to the norm al functioning of an expansion vessel and will be described in relation to the figures.

The at least one tem porary pressure increase may be generated by ram ping up and down the speed of the pum p from zero differential pressure. Typically, the pump is ram ped up from stillstand, i.e. from a speed of 0 RPM, to a speed which has to be selected depending on the specific system . At least for som e systems, alternative ways of generating the temporary pressure increase would be to provide a water ham mer pulse by quickly opening and re-closing a valve to a water supply, or to m anually tap on a pipe of the system by a tool.

I n som e embodim ents of the invention, the system comprises one pressure sensor arranged: on a suction side of the pum p, or on a pressure side of the pump.

For both options, the pressure sensor m ay e.g. be arranged in a branched off pipe leading towards the expansion vessel. An exam ple of such an embodim ent will be shown in the figures.

I n alternative em bodiments to the ones with only one pressure sensor, the system may com prise two pressure sensors arranged on a suction side of the pum p and on a pressure side of the pump, respectively, the m ethod comprising the following steps: by use of the two pressure sensors, determ ining a first pressure response and a second pressure response, respectively, comparing the two pressure responses with two known data representing corresponding pressure responses of the system when the expansion vessel is intact.

The scope of protection also covers em bodiments in which the system com prises more than two pressure sensors. By having two or more pressure sensors, it m ay be possible to increase the precision of the m easurem ents and/or to ensure that any defects in the expansion vessel is correctly detected even if one of the pressure sensors does not work correctly. I n presently preferred em bodim ents of the invention, the heating- or cooling system is degassed before the step of generating the at least one tem porary pressure increase. Hereby it can be avoided that any gas, typically air, present in the system would act in m anner resem bling the functioning of an intact expansion vessel. Thus, such gas would make a system with a defect expansion vessel erroneously look as if the expansion vessel was still intact. Degassing can also be referred to as venting or air-venting.

I n a second aspect, the invention relates to a device com prising a controller configured to carry out a method according to the first aspect of the invention.

I n som e embodiments of the invention, the device is a pum p or a boiler configured to be included in the heating- or cooling system .

Alternatively, the device is a separate device configured to com m unicate with the heating- or cooling system without being a part thereof. It m ay e.g. be a device used by a service technician travelling around and providing service to heating- or cooling system s, e.g. in private hom es or other facilities.

The first and second aspects of the present invention m ay be combined. These and other aspects of the invention will be apparent from and elucidated with reference to the em bodim ents described hereinafter.

BRI EF DESCRI PTION OF THE FIGURES

The method and device according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of im plem enting the present invention and is not to be construed as being lim iting to other possible em bodim ents falling within the scope of the attached claim set.

Figure 1 schem atically shows the functioning of a known expansion vessel. Figure 1 .a shows an intact m em brane and figure 1 .b shows a broken and thereby defect mem brane. Figure 2 schem atically shows an em bodim ent of a heating system which has been used for the tests perform ed during the developm ent of the invention.

Figure 3 is a flow diagram of a m ethod according to the invention.

Figure 4 shows a tem porary pressure increase that was used in tests performed as part of the developm ent of the invention.

Figure 5 shows the pressure response to the tem porary pressure increase of figure 4 for a system as in figure 2 in which the expansion vessel is intact.

Figure 6 shows the pressure response to the tem porary pressure increase of figure 4 for a system as in figure 2 in which the expansion vessel is defect.

DETAI LED DESCRI PTI ON OF AN EMBODI MENT

Figure 1 schematically shows the functioning of an exemplary known expansion vessel 1 . The expansion vessel 1 com prises an internally arranged elastic mem brane 2 which separates an air volum e 3 from the liquid 4 flowing in the system as shown in figure 1 .a. When the tem perature in the liquid 4 increases, the volum e of the liquid increases accordingly, and the expansion vessel 1 com pensates by the air in the air volum e 3 being compressed. Thus, it works as a sort of overflow tank that can help in bringing the pressure in the system back to a norm al level. Or in other words: the air that is present in the expansion vessel 1 acts like a spring. I n this way, it absorbs the extra pressure, thereby helping to keep the system stable. As described above, if the mem brane 2 is broken as shown in figure 1 .b, the whole of the inner cham ber of the expansion vessel 1 may become filled with liquid 4, and the expansion vessel 1 thereby loses its function. The result m ay be damage to other parts of the system or leakage.

Figure 2 schem atically shows an example of a heating system 5 com prising different elem ents exem plified by a radiator 6, a flow m eter 7, a heat exchanger 8, and an expansion vessel 1 . The radiator 6 could also be floor heating. The illustrated system 5 is connected to a dom estic hot water supply 9. The system 5 further com prises pipes 10 connecting the elem ents of the system 5 and through which the liquid 4 flows. A pump 1 1 is used for circulating the liquid through the system 5. The pump 1 1 is provided with a venting valve 12. The expansion vessel 1 is arranged and configured to equalize pressure in the liquid when the expansion vessel 1 is intact as described above in relation to figure 1 .

I n the em bodim ent in figure 2, the system com prises two pressure sensors each configured to m easure a local pressure in the liquid. The pressure sensors are marked as P1 and P2, respectively. However, in other embodim ents, there is only one pressure sensor, or the one or more pressure sensors are arranged at other locations. The pressure sensors P1 , P2 send output signals 13 to a controller 14. I n this embodiment, the determ ination of the functional condition of the expansion vessel 1 is perform ed by use of a separate device 15 com prising the controller 14, the device 15 being configured to com m unicate with the heating- or cooling system 5 without being a part thereof. However, as described above, the controller 14 m ay alternatively be com prised in a pum p 1 1 or a boiler (not shown) which is included in the heating- or cooling system 5.

The controller 14 is used to determ ine the pressure response based on the output signals 13. I n this em bodim ent, the controller 14 is further used to determ ine the functional condition of the expansion vessel 1 as will be explained in further details in the following.

The m ethod according to the first aspect of the invention com prises the following steps as shown in the flow diagram of figure 3:

A: Generating at least one tem porary pressure increase in the circulating liquid. B: By use of the at least one pressure sensor P1 , P2, determ ining a pressure response representing the resulting pressure in the liquid 4 as a function of tim e. C: Comparing the determ ined pressure response with known data representing a corresponding pressure response of the system 5 when the expansion vessel 1 is intact.

D: Based on the com parison, determ ining the functional condition of the expansion vessel 1 .

As mentioned above, the m ethod m ay further com prise a first step E of degassing the system 5 before the step of generating the at least one tem porary pressure increase. Since this is a preferred step, but a step which is not essential for the scope of protection in its broadest terms, it is shown with a circle in the figure.

The following figures show some of the experiments that have been perform ed during the developm ent of the invention. They were m ade on a system 5 as shown in figure 2; i.e. with two pressure sensors P1 ,P2 arranged on a suction side and on a pressure side of the pum p 1 1 , respectively. The pressure increase was generated by ram ping up and down the speed of the pump 1 1 from zero differential pressure as shown in figure 4, where time is shown on the x-axis and the speed of the motor driving the pum p is shown on the y-axis.

Figure 5 shows the pressure response obtained by applying the temporary pressure increase in figure 4 to a system in which the m em brane of the pressure vessel is intact and thus functioning as intended. The system pressure was 1 .5 bar. The two lines in the figure show the resulting pressure responses as measured with pressure sensor P1 and P2, respectively. As m entioned above, two pressure sensors P1 , P2 were used in these experim ents even though there will typically only be one sensor implemented in a system 5 when installed e.g. in a household.

Figure 6 shows the corresponding response as in figure 5 but now for a system 5 in which the m em brane 2 of the expansion vessel 1 is defect so that there is no air, or substantially no air, in the expansion vessel 1 . As seen by comparing figures 5 and 6, the pressure response resulting from the generated temporary pressure increases has lower pressure levels when the expansion vessel 1 is defect than when it is intact. Therefore, by com paring an actual pressure response with known data representing a corresponding pressure response of the sam e system when the expansion vessel 1 is intact, the functional condition of the expansion vessel 1 can be determ ined.

The following is an exam ple of a method according to the invention which can be perform ed by a service technician or installer when inspecting a heating system 5 com prising an expansion vessel 1 . As a first step, the service technician ensures that the system 5, including the radiators 6, is air-vented and pressurized. Hereafter a procedure can be initiated via a user interface, which will prepare the system 5 for expansion vessel diagnostics. Furtherm ore, the controller 14 of the device 15 will send a pressure signal, e.g. via LI N, to the pum p 1 1 . The pump 1 1 will use the signal as a reference level, when the pum p 1 1 is not running. A threshold is predefined in the pum p 1 1 or sent to the pump via the LI N control, where the pump 1 1 should send a fault signal back if the threshold is passed showing that the expansion vessel 1 is not responding as expected, typically because the m em brane 2 is dam aged. This information can be acted upon im m ediately by the service technician, if present at the location of the system 5. Alternatively, it can be stored in a fault log, showed as a fault code in the display, or inform ed via a cloud solution that the expansion vessel 1 should be checked, so that the service technician or the user of the system 5 can take appropriate action.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way lim ited to the presented examples. The scope of the present invention is set out by the accom panying claim set. I n the context of the claims, the term s “com prising” or “com prises” do not exclude other possible elem ents or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as lim iting the scope of the invention. Furtherm ore, individual features m entioned in different claim s, m ay possibly be advantageously combined, and the m entioning of these features in different claims does not exclude that a com bination of features is not possible and advantageous.