TECHNICAL FIELD OF THE INVENTION

The present invention relates to a part of a ventilation arrangement intended to be flowed through by two air flows, i.e. supply air, preferably outdoor air, and exhaust air (indoor air) which, with the help of a air supply fan and an exhaust air fan, is transported through a heat exchanger and a two-stage electrofilter which is arranged to clean incoming air (outdoor air). The device is arranged to be equipped with a cleaning device.

STATE OF THE ART

There has been a strong focus in recent years on improved indoor air quality, especially with regard to airborne particle pollution in combination with systems with better, i.e. more efficient, use of energy. This has created an interest in air purification products such as filters for ventilation systems, filters for industrial use and air purifiers for homes and households.

The knowledge of how small inhalable (respirable) particles affect humans, especially particles from fossil fuel combustion, shows that there is a great need of being able to stop such particles with the help of ventilation filters before they enter an indoor environment. Achieving this with today's mechanical filters for the outside air in a ventilation system is not practically and economically possible due to the high pressure drop and the high energy demand that such solutions would entail. In that context, a filter with a high separation capacity is therefore needed, which is also effective with respect to nano-sized particles, without there being a significant pressure drop across the filter, such that the filter allows for air purification at relatively high air flow rates. It is of course also desirable to have a high level of service friendliness.

The standard air flow speed for a ventilation filter is relatively high and corresponds to approximately 2.4 m/s. The air flow rate for an electrostatic precipitator that meets the above requirements is within the same range.

In WO 97/46322 A1 a two-stage electrostatic precipitator with an ionization section is described, which is followed on the downstream side in the direction of air flow through the device by a so-called precipitator. The precipitator unit consists of two strip-like electrode elements which are multiple and with a gap distance "d" between the respective electrode elements wound around a central coil. Such a precipitator unit is to the greater part comprised of a cylindrical body. An air flow through the precipitator unit is directed in an axial direction through gaps that are formed between adjacent electrode elements and that are open to allow the passing air flow. The precipitator unit according to the above can advantageously be made of a specially designed paper in accordance with what is described in WO 03/013734 or of plastic as described in WO 2019/203708 A9.

In WO 2013/105885, a treatment of the edge sections of the circular capacitor is described, which enables a precipitator made of cardboard with a plastic layer over the surface to withstand washing with water or steam after the edge sections have been treated.

A limitation of the precipitator unit as described above is that the separation efficiency of the precipitator unit decreases as dust stick to the electrode elements of the precipitator unit and impairs its separating properties. This reduction in efficiency is strongly dependent on, among other things, the speed of the air flow through the gap between the respective electrode elements but is also dramatically affected when the relative humidity of the air increases to above about 70 - 80%. Specifically, the slower the air flow rate and the lower the relative humidity, the better the particle separation properties will be.

In order to achieve particle cleaning of relatively large air streams in an air flow duct, mechanical so-called bag filters are often used. To reduce the pressure drop across the bag filter, large filter surfaces are used, for example using V-shaped filter bags. The air stream passing through the filter thus passes the filter at a low speed in relation to the air flow speed in the air duct in which the bag filter is placed. This reduces the pressure drop across the filter. Despite such a construction of so-called bag filters, the pressure drop across mechanical filters and the energy required to achieve the forced ventilation through them accounts for a significant part of a ventilation system's operating costs. In addition to this comes the cost of replacing and depositing used filters.

The pressure drop across a circular precipitator unit is normally much less than through a mechanical bag filter and can also be kept constant if intermittent cleaning of the precipitator can be achieved.

Today's ventilation systems are often built around heat exchangers, for example rotary heat exchangers, counter-flow or cross-flow heat exchangers, which are protected from the pollution of the outside air by a mechanical filter on the upstream side, i.e. before the outside air passes the heat exchanger, and by a mechanical filter that is placed closest to the exhaust air connection to the ventilation arrangement. A purpose of the air supply filter is also to reduce outdoor particulate pollution compositions to protect people in indoor air environments. Due to relatively high pressure drops in air supply filters, the choice of air supply filter and its ability to handle the most harmful particles becomes a compromise between an acceptable pressure drop across the filter and the filter's ability of particle purification. In this context, it should be mentioned that a mechanical filter should not be replaced by a two-stage electrofilter placed in the air supply duct upstream of the heat exchanger as seen from the direction of air flow through it, since the particle separation capacity of the precipitator drops dramatically at a higher relative humidity than about 80%, which is a normal relative humidity in the outdoor air that constitutes the incoming air.

Today's ventilation systems have become relatively sophisticated with the use of different types of heat exchangers. The structure of the ventilation arrangement and thus its constituent components differ greatly from each other depending on the outdoor climate and desired parameter values, i.e. the properties of the supply air in terms of for example particle content, temperature and relative humidity.

BRIEF DESCRIPTION OF THE INVENTION AND ITS PURPOSE

An object of the invention is to improve the performance or at least offer an alternative way to cleaning air in a ventilation arrangement as described above.

Specifically, the object of the present invention can be described as creating a ventilation system with a very low pressure drop and thus with a very low energy requirement.

In addition, the invention can contribute to a minimized need for service and systems with significantly better properties when it comes to filtering the incoming outside air, i.e. the supply air.

According to a first aspect, the invention relates to a ventilation arrangement including a rotating heat exchanger arranged between two air flow ducts, of which one air supply duct and one exhaust air duct, at least one precipitator for a two-stage electrofilter with an associated high- voltage unit, whereby at least one fan is arranged to provide supply air and exhaust air and whereby electrode elements in the two-stage electrofilter are arranged for electrical charging of particles in the air supply duct, wherein the precipitator is located downstream of the rotating heat exchanger in the direction of air flow in the air supply duct. The basis of the present invention lies in the realization that a so-called rotating sorption heat exchanger can return the heat from the exhaust air to the supply air during cold seasons, or lower the temperature of the supply air during warm seasons at the same time as the relative humidity of the supply air decreases during the warm season downstream of the heat exchanger seen in the direction of air flow through it, whereby beneficial conditions are created for particle purification of the incoming outside air, i.e. the supply air, by means of precipitators in the comparatively drier air flow downstream of the heat exchanger.

To this can be added that a rotary heat exchanger as well as a precipitator, such as for example a circular precipitator, can be washed with, for example, steam or liquid, such as water. Washing with liquid is particularly practical if the rotary heat exchanger and/or circular precipitator is placed horizontally or inclined in an air flow duct with the possibility of runoff. It should be mentioned that the rotary heat exchanger after a completed cleaning preferably should be blown clean and dry before it is put back into use, why a blowing device may be arranged in connection with the rotary heat exchanger to blow dry the active parts thereof.

BRIEF DESCRIPTION OF THE DRAWING

In the following detailed description, the invention will be described with reference to the attached drawing, of which:

Fig. 1 shows a ventilation arrangement according to a specific embodiment of the invention.

DETAILED DESCRIPTION

In Fig. 1 , a ventilation arrangement 1 is shown with a rotating heat exchanger 10 placed vertically between two air flow ducts, comprising an air supply duct 2 and an exhaust air duct 3, which each include parts 2A and 3A, respectively, upstream of the rotating heat exchanger 10, and each part 2B and 3B respectively downstream of the rotary heat exchanger 10. Downstream of the heat exchanger 10 in the air supply duct 2B seen in the direction of air flow through it, a circular precipitator 6 is placed at an angle with respect to the direction of air flow through the air supply duct. The placement of the precipitator 6 downstream of the heat exchanger 10 is advantageous both because the humidity in the downstream air is lower than for the air in the inlet duct 2A upstream of the rotary heat exchanger 10, and that any return flow from the outflow of the exhaust air that escapes through the rotary heat exchanger 10 is cleaned of particles before it is passed on to the indoor air.

An ionization section is arranged upstream of the precipitator 6, which may comprise an ionization element 7, for example in the form of a carbon fibre brush, with a surrounding grounded counter electrode or grounded counter electrodes to charge the particles in the incoming air. In the schematically shown drawing, the counter electrode can form part of the inner wall of the ventilation drum, which for that purpose may be connected to ground. The ionization element 7 is connected to a high voltage source. The ionization section can either be placed downstream although preferably upstream of the rotary heat exchanger 10, but of course upstream of the precipitator 6.

An air supply fan 4 and an exhaust air fan 5 are shown very schematically in Fig. 1 . Both the air supply fan 4 and the exhaust air fan 5 can be placed as either suction or blowing fans, i.e. either downstream or upstream of the rotating heat exchanger in the ventilation arrangement. In the embodiment shown, the air supply fan 4 is a suction fan and the exhaust air fan 5 is a blowing fan.

The rotating heat exchanger 10 is equipped with a drive motor that causes the heat exchanger to rotate, which is a prerequisite for heat transfer in the shown embodiment and, in the case of the sorption heat exchanger type, the rotation also provides a transfer of moisture via the rotating heat exchanger 10. The drive motor is suitably arranged in a heat exchanger housing 11 which surrounds the rotating heat exchanger 10.

In this application, a sorption heat exchanger refers to a rotating heat exchanger which is arranged to be able to at least partially lower the humidity in the incoming air and may for example be of the HUgo® type provided by the German company Klingenburg Gmbh.

The circular precipitator 6 can be assembled with a circular frame in the form of a ring with spokes, whereby the precipitator 6 is arranged to rotate around its central axis during a purification process. A plate 12 extends between the precipitator's circular holder and the inner walls of the air flow duct, which forces all air to pass through the precipitator 6.

The ventilation arrangement 1 according to the present invention can be provided with both a cleaning device 9 for the rotary heat exchanger 10 and a cleaning device 8 for the precipitator 6. These are exemplified in Fig. 1 in the form of tubular elements which are placed radially and over at least half the diameter of the precipitator 6 and the rotating heat exchanger 10 and which on the respective underside are provided with a number of openings or a thin slit and are connected to a liquid source such as hot water or the like. The exiting liquid thus penetrates the gaps between the precipitator's band-like electrodes and removes the particle impurities deposited on the electrodes as it passes them. Corresponding cleaning is achieved on the rotating heat exchanger 10. The dirty liquid drips down to a drain or a container which, according to Fig. 1 , is placed on the bottom of the device and is led away from there.

In a not shown embodiment, the ventilation arrangement 1 is placed in a vertical direction, instead of as in Fig. 1 in a horizontal direction. In a vertically oriented ventilation arrangement 1 , the air supply duct 2 is preferably directed upwards and the exhaust air duct 3 downwards, which is advantageous from a moisture point of view because washing liquid can flow straight down through the slits of the precipitator and out of the ventilation arrangement 1 .

The cleaning equipment 8 and cleaning device 9 shown in Fig. 1 can of course be designed in different ways. They can, for example, include a short nozzle arranged to move radially along with the rotation of the precipitator or the rotating heat exchanger, whereby a more focused and stronger liquid flow may be achieved.

The ventilation arrangement 1 is designed so that the need for mechanical filters on the supply and exhaust air side is substantially reduced or even eliminated.

In Fig. 1 a complete ventilation arrangement comprising the invention is shown in a very schematic manner. A high-voltage unit (not shown) is arranged to provide the voltage of the ionization element 7 as well as the connection of the precipitator 6 and the respective electrode element to opposite poles. Other parts of the unit that are not shown in Fig. 1 are, for example, possible cooling units or heating units, humidifying units, dampers, air ducts and so on.

For the purpose of the invention, a rotating sorption heat exchanger constitutes a suitable choice of heat exchanger to be used up stream of the precipitator, as it reduces the relative humidity of the supply air even during warm parts of the year or in hot climates and thus is adapted for the precipitator's operating different conditions all year round. It should be noted that circular precipitators dramatically lose their particle precipitation capability at a relative humidity greater than 80%, making them essentially unusable in traditional ventilation arrangements in most parts of the world as the relative humidity is often above 80%.

In the embodiment shown in Fig. 1 , the rotary heat exchanger 10 is placed vertically and the precipitator is positioned in an inclined position. It is, of course, possible to arrange both the heat exchanger and the precipitator horizontally or vertically. An at least near-vertical orientation of both the heat exchanger and the precipitator is advantageous considering that the cleaning liquid from the distribution nozzle can then flow down by itself, which simplifies the cleaning process of heat the heat exchanger and the precipitator. The rotating heat exchanger 10 may be placed at an angle of between 0 and 25 degrees in relation to a vertical direction.

In a not shown embodiment where the ventilation arrangement is positioned such that both the air supply duct 2 and the exhaust air duct 3 extend in a vertical direction, the heat exchanger 10 may instead be positioned horizontally, specifically at an angle of between 0 and 25 degrees with respect to the vertical plane.

The at least one precipitator 6 for a two-stage electrofilter has a non-planar shape. Specifically, it may have a cone or dome shaped form.

The ventilation arrangement may comprise a precipitator arrangement including a second precipitator 6 for a two-stage electrofilter in addition to the at least one precipitator 6. The at least two precipitators 6 may be arranged in sequence in the air supply duct 2B. Preferably, at least one of these two precipitators 6 may have a central opening allowing part of the flow to pass unfiltered through said opening to instead be filtered be the next precipitator 6 seen in the direction of flow in the air supply duct 2.

With the very low and constant pressure drop across the filter, two successive circulating precipitators, both including suitable ionization sections, can be arranged one after the other in the direction of flow of the air to be purified.

The washing process of the precipitators can be achieved using sprinklers or an equivalent type of liquid supply.

The ionization electrode 7 shown in Fig. 1 in the form of a carbon fibre brush is just one embodiment among others and can be replaced with another known ionization chamber, for example equipped with so-called corona wires. The charging of the particles in the supply air can also take place upstream of the rotating heat exchanger 10.

In accordance with the invention, traditional mechanical filters are replaced by particle collectors in the form of precipitators 6, wherein a ventilation system with basically constant pressure drop is created, which reduces problems with leakage between the supply and exhaust air sides that can otherwise arise in rotating heat exchangers as a result of various and /or varying pressure drop on the supply and exhaust air side. This expands the theoretical use of rotary heat exchangers. As the system may be built around a built-in cleaning device, service requirements, disposal costs for mechanical filters and of course the environmental impact may be dramatically reduced.

In the example shown in Fig. 1 , intermittent washing of the rotating heat exchangers at least partially replaces the need for an exhaust air filter and air supply filter, which in traditional systems have the task of protecting the function of the heat exchanger. Both this function and the task of protecting indoor environments from outdoor pollution have been replaced by precipitators placed downstream of a rotary heat exchanger, possibly equipped with an intermittent cleaning device. Rotary heat exchangers can have a diameter of up to 3 meters. A reasonable size of circular precipitator can be 1 .2-1 .4 meters in diameter. In larger ventilation systems, several circular precipitators can of course be arranged next to each other in the air flow duct.

In the embodiment shown in Fig. 1 , intermittent cleaning of rotating heat exchangers is provided for. Of course, a mechanical filter or a circular two-stage electrofilter equipped with a purification plant can be used on the exhaust air side if desired. It is also conceivable to supplement the ventilation arrangement 1 with an air supply filter, preferably a filter of a lower filtration class than is customary when no precipitator is provided.