Technical field

The present invention relates to a rotary heat exchanger disposed at an air handling unit, and the handling of airflow leakage around the rotor in the rotary heat exchanger.

Background of the invention

In air treatment technology there exists a variety of different solutions to prevent air leakage around a rotating heat exchanger, arranged in an air handling unit. The rotary heat exchanger is a particularly efficient variant of heat recovery device, for energy exchange between two air streams, but just because the rotating part - the rotor - is rotating, the rotor must have a certain space/gap to the surrounding surfaces and separation walls and the like. The spaces in the air handling unit are sealed in relation to each other to avoid, for example, the air from a room getting mixed with the fresh air supplied to the room, which air in that case gets a lower air quality. To minimize leakage around the rotor generally a brush seal, or another edge seal which can withstand wear, is arranged on the rotor or on the surrounding plates which encloses the periphery of the rotor and connects to the inner surfaces of the unit. Moreover, the surrounding plates are in turn sealed towards interior surfaces to prevent air from leaking around these. Because of the moving part - the rotor - it is almost impossible to completely avoid leakage and therefore it is important that the pressure setup in the air handling unit is controlled, so the airflow leakage that occurs, and that is impossible to avoid, so to speak runs in the right direction, i.e. supply air is allowed to leak to exhaust air but not the opposite. This is well known technique which has been used during a long period of time. Further, there is a so called purging sector adjacent to the part of the rotor where the rotor at its rotation, so to say rotates from the exhaust air to the supply air side. The purging sector is a short circuit between the exhaust and supply air, which, as a result of the pressure difference between the supply (higher pressure) and exhaust air (lower pressure), blows away the exhaust air from the channels in the sector, before they enter into the supply air. Focus on the currently existing solutions have been to, in different ways find good seals, why solutions regarding the periphery seal and the seal between the air handling unit internal surfaces and separation walls against the rotating rotor has been developed. For example, there are different forms of labyrinth seals, which tasks are to ensure that a high pressure drop is caused, in air leakage path passing the seal, by a more or less advanced geometry of the seal. The pressure drop will then counteract the leakage flow around the rotating rotor whenever possible. Another known solution is presented in US 7 849 913 B2, where the focus instead is on managing the pressure conditions around the rotor. The leakage problem in this case has been solved by that the rotor are enclosed in a rotor housing, provided with a front wall and a rear wall, which have a respective opening for the front surface and the rear surface of the rotor wheel, to allow through-flow through the rotor in a conventional manner. Around the edges of the openings, adjacent to the rotor's periphery, is any kind of conventional seal mounted and the rotor housing is sealed / closed against other surfaces, and thus a space with a virtually closed volume of air around the rotor is created. The leak that occur will take place around the periphery of the rotor and adjacent to the separation between upper and lower half of the rotor / the unit. The space around the rotor is in the US application connected to a pressurizing source, which by the addition of external air to the space always makes sure that the current pressure around the rotor is higher than any other pressure of the air flowing through the rotor, from the parts of the air handling unit that connects to rotor. This is done by monitoring the pressure in the unit and the rotor housing, and regulation of the pressurizing source. The device is aimed primarily at plants in explosive environments, and it points out that the pressure around the rotor absolutely must be higher than the pressure in the gas / air flows through the rotor, to thereby ensure that any leakage that occurs is with air from the pressurizing source, which "pumps" in the clean air in the rotor housing. Furthermore, there is a discussion of using temperature monitoring and heating of the external air that is supplied through the pressurizing source. This solution, however, is energy intensive as it constantly will be supplied external air, and that the plant requires equipment provided for this, measuring and control equipment, monitoring equipment, etc., in addition to the usual pressure and temperature sensors and control devices which for other reasons anyway is necessary for the normal operation of a conventional air handling unit.

Disclosure of the invention

With the present invention the object is achieved to solve the above mentioned problems by an air treatment device according to the preamble of claim 1 , where a rotor in a rotary heat exchanger is enclosed in a housing - a rotor housing - which is sealed both towards the rotor periphery and towards surrounding interior surfaces of an air handling unit, in which the rotary heat exchanger is disposed. This forms an air volume around the rotor. The device is characterized in that it comprises a pressure compensation means arranged between the rotor chamber, with its air volume, and an outdoor air chamber. As the rotor rotates, there must be a gap towards adjacent separating walls in the air handling unit and towards connecting cover plates, which in all rotary heat exchangers must be positioned around the periphery of the rotor to force the air to pass through the rotor channels. These gaps are minimized with various types of seals, but as previously described, it is impossible to prevent some leakage. The invention therefore take care of the problem by ensuring that the leaking air is leaking from the rotor chamber air volume and out of the rotor chamber through correct pressure balance, that is, "in the right direction", whereby no contaminated air can leak into the supply air, and in addition it is only the cleanest air that is allowed to leak, i.e. the outdoor air. This is done by the air handling unit is adjusted by conventional means such as throttling plates and/or dampers and the like, so that the pressure in the outdoor air chamber, before the rotary heat exchanger, is higher than any other pressure, which surrounds the heat exchanger, and the pressure compensation means ensures that equate the pressure in the rotor chamber and the pressure in the outdoor air chamber. These two pressures are at least approximately equal, but may differ slightly due to a possible slight pressure drop in connection with the pressure compensation means. The leaking air around the rotor is of course minimized in a conventional manner because leakage air is not in any way desirable. In this way different forms of advanced "labyrinth seals" is not needed, but more simple seals can be used around the rotor and the rotor chamber instead. There are further no need of external pressure sources and thereto additionally provided monitoring equipment (in addition to the conventional devices that possibly still are needed for the operation and management of the facility), but a very simple pressure compensation means replaces these energy-maintenance demanding devices. Further, it is possible and even desirable that the above described purging sector also is connected to the rotor chamber, why this also obtains the same pressure as the rotor chamber.

According to a preferred embodiment of the device are a number of measurement devices deployed in the air handling unit for recording of the pressures to be monitored, so that a thereto arranged control device, on the basis of the measured pressures, ensures that the pressure in the outdoor air chamber is the highest. For example, by controlling the supply and exhaust fan the pressures in the unit is balanced so that the outdoor air chamber has the highest pressure in relation to the other chambers surrounding the rotor chamber, whereby also the rotor chamber air volume essentially gets the same pressure through the pressure compensation means. The leakage around the rotor will therefore take place with the cleanest air and in the right direction out from the rotor chamber, which prevents

contaminated exhaust air to penetrate into the supply air. Thus there is no need of external pressurizing sources as in older solutions, but the control equipment is balancing the pressures in the air handling unit for handling of the leakage flow, for proper pressurization in the outdoor air chamber and thus in the rotor chamber. According to another preferred embodiment, at least one damper is arranged in the second air stream to provide additional ability for controlling and balancing of the pressure drops in the air handling unit and around the rotary heat exchanger. According to a preferred embodiment is the pressure compensation means in its simplest form a hole in the front wall of the rotor chamber, that is, in the front wall between the rotor chamber and the outdoor air chamber. This is a very simple and cost effective solution that is suitable for most cases, when the space with the highest pressure and the cleanest air - the outdoor air chamber - is arranged in direct connection to the rotor chamber. Through a simple punching is a pressure compensation means achieved, that is sufficient to ensure that the sealed rotor chamber basically has as high pressure as the outdoor air chamber and higher pressure than other surrounding areas, whereby the leakage flow is controlled in the "right direction". Compared to the above known technology is the cost and simplicity very advantageous in the present solution.

In an alternative embodiment of the device is the pressure compensation means a suitably dimensioned tube connecting / short cutting the pressure set between the outdoor air chamber and the rotor chamber, by that the tube is connected with one end in the rotor chamber and its other end in the outdoor air chamber. This may be necessary for solutions where the outdoor air chamber and the rotor chamber are not arranged adjacent to each other, but one still wants to use the simple solution which is permitted by the pressure compensation means. In an alternative embodiment of the device is the pressure compensation means a suitably dimensioned pipe connecting / short cutting the pressure set between the outdoor air chamber and the rotor chamber, by that the pipe is connected with one end in the rotor chamber and its other end in the outdoor air chamber. In the same manner as immediately above, this solution may be appropriate when pressure compensation between the outdoor air chamber and the rotor chamber must take place although they are located at a distance from each other.

In a preferred embodiment of the device is the rotor chamber designed as a complete casing, which in this case comprises both the so-called front wall and the rear wall, which so to speak covers the periphery of the rotor and the surrounding internal surfaces of the air handling unit. The casing further also comprises four gables arranged around the rotor in its length direction and connecting to the front wall and the rear wall, so that a complete casing enclosing the rotor, but with openings in the front wall and the rear wall for the flow of the exhaust air flow and outdoor air flow through the rotor. Thus, the rotary heat exchanger can be delivered and installed as one part that is sealed towards the surrounding and which in its front wall comprises the pressure compensation means. From a second aspect of the invention the object is achieved to solve the above mentioned problems by a method of controlling the leakage at a rotary heat exchanger in an air handling unit according to the preamble of claim 7, where a rotor at a rotary heat exchanger is enclosed in a housing - a rotor housing, which housing comprises an air volume surrounding the rotor. The invented method therefore takes care of the above described problem by make sure that the leaking air is leaking from the air volume of the rotor chamber and out from the rotor chamber by correct pressure balance, i.e. in the "right direction", whereby no contaminated exhaust air can leak to the supply air, and further it is only the cleanest air that is allowed to leak, i.e. the outdoor air. This is done by that the air handling unit is adjusted so that the pressure in the outdoor air chamber, before the rotary heat exchanger, is higher than all other pressures surrounding the heat exchanger, and that a pressure compensation means makes sure to equalize the pressure of the rotor chamber with the pressure of the outdoor air chamber. These two pressures are at least approximately equal, but may differ slightly due to a possible small pressure drop in connection with the pressure compensation means. The leaking air around the rotor is of course minimized in a conventional manner because leakage air is not in any way desirable. In this way different forms of advanced "labyrinth seals" is not needed, but more simple seals can be used around the rotor and the rotor chamber if wanted. According to a preferred embodiment of the invented method it is ensured that the outdoor air chamber always has the highest pressure and thus also the pressure in the rotor chamber, at all operating points of the air handling unit, by registering the pressures in some parts in the air handling unit and through a control equipment regulate the pressures to always fulfill this criteria.

By the invention a number of advantages are achieved compared to prior art.

Ensuring of minimal leakage airflow and that the leakage, so to speak, is in the right direction.

- No need of advanced "labyrinth seals" thus conventional rotor seals can be used. - A simple and cost efficient solution without high installation and operating costs.

- A simple pressure compensation between outdoor air chamber and rotor chamber although if these are positioned at a distance from each other.

Short description of the figures

Below schematic figures shows:

Fig.1 shows a principal picture of an air handling unit 4 with a rotary heat exchanger 3, according to the invention as well as an enlargement showing a pressure compensation means 27, which is short-cutting the air between an outdoor air chamber 25 in the air handling unit 4, and an air volume 16 of a rotor chamber 6 at the rotary heat exchanger 3. Fig.2 shows a variant of a rotary heat exchanger 3, designed as a complete housing 29 and comprising the pressure compensation means 27 in the form of a hole in a front wall 7 of the housing 29.

The constructive design of the present invention is apparent in the following detailed description of an embodiment of the invention with reference to the accompanying figures showing a preferred, but not limiting embodiment of the invention.

Detailed description of the figures

Fig.1 shows a principal picture of an air handling unit 4 with a rotary heat exchanger 3. The air handling unit 4 comprises a supply air fan 1 arranged in a first air stream 17 and an exhaust air fan 2 arranged in a second air stream 18. The rotary heat exchanger 3 is arranged to exchange energy between the first and the second air stream 17, 18. The first air stream 17 sucks in outdoor air 23, which preferably passes a damper 28 and a filter 32 before it arrives an outdoor air chamber 25, then passes through a rotor 5 of the rotary heat exchanger 3, in conventional manner. After the air passed the rotor 5 it is termed supply air 24 and arrives thus to an supply air chamber 26, to then pass through the supply air fan 1 and out of the air handling unit 4 as supply air 24. The second air stream 18 sucks in exhaust air 19, which preferably passes a damper 31 and a filter 32 before it arrives to an exhaust air chamber 21 , after which it passes through the rotor 5 of the rotary heat exchanger 3, in conventional manner. After the air has passed through the rotor 5 it is referred to as extract air 20 and thereby arrives to an extract air chamber 22, then to pass the exhaust fan 2 and out of the air handling unit 4 as extract air 20. So far this is in a conventional way and by conventional technique. What distinguish the invention is that the rotor 5 is arranged in a rotor chamber 6, which is sealed towards surrounding interior surfaces 14 within the air handling unit 4, preferably by that the rotor chamber 6 comprises a front wall 7 and a rear wall 8, which are sealed towards interior surfaces 14 of the air handling unit 4 by means of edge seals 15, but between the rotor periphery and the, at the periphery connecting front wall 7 and rear wall 8, are respectively arranged peripheral seals 13 in a conventional manner. These can for example have the form of brush seals or other forms of seals. The front wall 7 and the rear wall 8 comprises a respective opening 9, 10 which reveals front surfaces 1 1 , 12 of the rotor 5, to allow through flow through the rotor. By that the rotor 5 is disposed in the rotor chamber 6, is an enclosed air volume 16 formed around the rotor 5, which according to the invention achieves essentially the same static pressure p ₁₆ as the static pressure p ₂ s of the outdoor air chamber 25, in that a pressure compensation means 27 is provided to short- cut the air pressure. In the most preferred embodiment, when the outdoor air chamber 25 connects to the rotor chamber 6, the pressure compensation means 27 is a hole in the wall - the front wall 7 - dividing the chambers 6, 25 from each other. In the figure are not shown pressure sensors, control equipment etc. which are used to balance the pressure set in the air handling unit 4 along with for example frequency control of the fans 1 , 2, and along with outdoor air damper 28 and/or exhaust air damper 31. By the control equipment it is ensured that always the pressure in the outdoor air chamber 25, which has the cleanest air, always is the highest pressure, and thus the air volume 16 surrounding the rotor 5, automatically holds the clean air of higher pressure than the other chambers 21 , 22, 26. The air which then leaks around the rotor 5 leaks therefore always in the right direction and it is always the cleanest air that leaks. Through this device, no advanced peripheral seals must be used around the periphery of the rotor to prevent air leakage, but this does of course not mean that such packaging can be used together with the inventive device. Fig.2 shows an alternative embodiment wherein the rotary heat exchanger 3 is designed as a "closed" housing 29, which encloses the rotor 5 through the front wall 7 and rear wall 8 and four side gables 30. These form the rotor chamber 6, which encloses the air volume 16, in the same way as the previously described embodiment in Figure 1 , and the rotor chamber 6 is sealed against leakage except some leakage that occurs between the rotor 5 and the openings 9, 10 at the peripheral seal 13, and also at a purging sector, as previously described. Here it is also sufficient with a simple type of peripheral seal 13, for example in the form of a brush strip, between the rotor 5 periphery and the walls 7, 8 as the leak that occurs here is controlled regarding that it is clean air and that the pressure in the rotor chamber 6 is controlled. In the front wall 7 is the pressure compensation means 27, in the form of a hole, arranged and in that half of the air handling unit that connects to the outdoor air chamber 25. As described above is the pressure controlled an adjusted to be highest in the outdoor air chamber 25, wherein also the pressure in the rotor chamber 6 by the pressure compensation means 27 is the same, or at least in principle the same. At least, the pressure is regulated so that the pressure in the air volume 16 of the rotor chamber 6 always is slightly higher than the surrounding other chambers - exhaust air chamber 21 , supply air chamber 26 and extract air chamber 22. P A R T S L I S T

1 = supply air fan

2= exhaust air fan

3= rotary heat exchanger

4= air handling unit

5= rotor

6= rotor chamber

7= front wall

8= rear wall

9= opening

10= opening

11 = front surface

12= front surface

13= peripheral seals

14= interior surfaces

15= edge seals

16= air volume

17= first air stream

18= second air stream

19= exhaust air

20= extract air

21 = exhaust air chamber

22= extract air chamber

23= outdoor air

24= supply air

25= outdoor air chamber

26= supply air chamber

27= pressure compensation means

28= damper

29= housing

30= gable

31 = damper

32= filter