Such devices, systems and methods for treating air are used for treating the air of many types of spaces and premises, such as residential houses or industrial buildings by dehumidifying and purifying the air, and for producing negative pressure in the space being treated as well as for heating the air, if required. Systems according to the invention are used, in particular, when repairing buildings damaged by moisture or mould. Hereby it is important to prevent microbial cells from microbial growth, such as moulds, bacteria and yeast and rot fungi, from being conveyed beyond the working space, particularly into indoor air, because people exposed to such air might end up suffering from consequences for their health caused by their exposure to microbes. Typically, such consequences include eye and skin symptoms as well as symptoms of the respiratory tract, repeated respiratory infections and allergic illnesses. While repair work is under way, the microbe concentrations in the working space air may rise to even one hundred times the concentrations prior to the repairs.

Smelly and volatile compounds are also formed during the growth of many bacteria and mould fungi. As a result, complex mixtures of alcohols, aldehydes, esters, hydrocarbons and aromatic compounds are produced. The content of these compounds is usually very low in air, somewhere in the region of 1 to 100 ng/m3 but some of these compounds are highly irritant for people.

According to conventional prior art, the outside environment of a working space is protected by isolating

the working space and also maintaining a negative pressure within. If it has not been possible to remove a sufficient amount of moisture via the negative pressurizer by exhausting outdoors e.g. during the period the building is heated, a separate air dehumidifier has been used.

The prior art is hampered by a number of disadvantages: the moisture released during the drying of the structures is conveyed to the air in the space under repair work, where it can then be removed by leading the exhaust air of the negative pressurizer outdoors. This is, however, in practice often not possible particularly while the buildings are heated, whereby the air must be subjected to dehumidification by a separate air dehumidifier. This poses problems if space is scarce because separate equipment is required both for creating the negative pressure and for the dehumidification. In addition, the equipment used today for treating air during repair work is not very well suited for use when water damage in residential buildings is being repaired. This is because such damage often occurs in bathrooms which are too small for the equipment to fit in.

Drying water damage takes several days, during which time the equipment is in continuous operation. No attention has been paid to the noise caused by prior-art equipment, wherefore continuous use of such equipment will disturb those using the building. Furthermore, growth of filamentous fungi has been observed in the HEPA filters of negative pressurizers used while taking apart structures damaged by dampness, such growth fouling the expensive filters such that they become unserviceable too soon.

Volatile, gaseous and organic metabolic products, i.e. microbial VOCs, are released into air from such growth of filamentous fungi, such products penetrating particle filters and possibly causing irritant symptoms.

In US Patent Specification No. 5,090,972, a device for treating air e.g. for work involving asbestos is described.

Said device comprises a movable unit having a HEPA filter, an air dehumidifier and blowers for circulating air, as well as air passages for conveying air from the space where work is being done to the device, further to open air or back to the air inside the space where work is under way.

However, the device described in the document is, due to its structure, not particularly well suited for repair work involving damage caused by moisture or mould, because in the device the HEPA filter is arranged before the air dehumidifier. When used in buildings suffering from mould damage the HEPA filter has to function in damp conditions, whereby the filtration and throughput properties of the filter are impaired, and, worst of all, the filter risks contracting mould. Thus, the device described in the document solves a wholly different type of problem. In the device of the document, the purpose of the air dehumidifier is to participate in adjusting the air humidity in the working space such that it is optional for the asbestos removal process and for the working conditions of the workers.

The present invention aims at eliminating the above- described drawbacks and at achieving an entirely novel type of device, system and method for treating air.

The invention is based on arranging and dimensioning the elements of the device or system for treating air such that the relative humidity of air taken to the HEPA filter does not exceed 50 % while the device is in operation. In practice, this is achieved by placing the air dehumidifier before the HEPA filter in the flow path of air. The invention is also based on taking the air treated in the air treatment method from the space where work is being done to the HEPA filter dehumidified in a corresponding manner.

In more detail the device for treating air according to the

invention is characterized by what is stated in the characterizing part of claim 1, and the system for treating air is characterized by what is stated in the characterizing part of claim 6. The method for treating air according to the invention, then, is characterized by what is stated in the characterizing part of claim 9.

The invention offers considerable benefits.

By furnishing the device and system with a correctly positioned and dimensioned air dehumidifier the relative humidity of air filtered by means of a HEPA filter can be controlled such that it is less than 50 % while the system is in operation, whereby an essentially insignificant growth of microbes on the surface of the HEPA filter is attained. This makes it possible to use the invention to improve the result of air filtration and to extend the service life of HEPA filters.

When it is desirable to remove, e.g. solvent vapours or gases which are released by microbes and are hazardous to human health from the air being treated, the device or system is advantageously equipped with a gas filter.

When implementing the invention in an advantageous manner, work steps such as surfacing and grouting following repair work can also be safely speeded up. Such speeding up is based on air dehumidification whereby even the dehumidification of floats and surfacing materials occurs more rapidly. The dehumidification is advantageously performed using a device or a system having a gas filter or whose use involves exhausting the filtered air from the space being treated. This makes it possible to control emissions into the working air caused by the drying of surfacing materials, thus reducing the exposure of workers to for example solvent vapours.

In the following, the invention is described in more detail by means of a number of examples and with reference to the annexed drawings.

Fig. 1 is a schematic representation of a device for treating air according to the invention.

Fig. 2 is a schematic representation of a system for treating air according to the invention.

In the present invention, the term HEPA filter refers to a particle filter capable of filtering at least 99.97 % of particles having a size of 0.3 m, or any other filter device which can be used to almost completely remove particulate impurities such as microbes from air.

The gas filter 20 for its part is a filter which is used to remove volatile organic compounds. The adsorbent of the gas filter 20 may comprise, e.g. activated alumina impregnated with potassium permanganate, impregnated activated carbon, or preferably activated carbon.

The device according to the example depicted in Fig. 1 which is suited for single, separate targets consists of a body 6, to which an air dehumidifier 8, 9, 10 constituted by the combination of an evaporator 8, a condenser 9 and a compressor 10, is fixed, and to which a HEPA filter 2, a gas filter 20, a blower 3, a prefilter 5 and a hygrostate (not shown) are fixed.

The operation of the device of Fig. 1 is based on circulating the air being treated through the device such that most of the microbes are first removed from the air by taking it through the prefilter 5. In this manner it is possible to significantly reduce the fouling of the cooling coil 8 and clogging of the HEPA filter 2, thereby reducing the need for maintenance of the device and extending the

replacement interval of the expensive HEPA filters 2. After prefiltering 5 the air is dehumidified in the air dehumidifier 8, 9, 10 so efficiently that its relative humidity remains below 50 % whereby the multiplication of microbes on the surface of the HEPA filter 2 is prevented.

In this exemplifying device the condensing dehumidifier 8, 9, 10 is used connected such that the air being treated is cooled in the evaporator 8 to a temperature below its dew point and is thereafter drawn through the condenser 9 whereby thermal energy bound by the coolant is returned to the air being treated. Condensed moisture from the evaporator 8 is taken to e.g. the drain system.

After the evaporator 8 the air is drawn to the HEPA filter 2 which removes practically all particles in the microbial size range, that is, having a size of about 2 to 5 m. In this example the dimensions of the filter 2 are approximately 450 x 450 x 100 mm. The HEPA filter 2 must be fastened in position in a well-sealed manner in order for all the air to be filtered and for no by-pass leakage to take place.

From the HEPA filter 2 the air is drawn to a gas filter 20, preferably an activated carbon filter. The gas filter 20 is advantageously arranged after the air dehumidifier 8, 9, 10 in the flow direction of the air being treated. This is because the great humidity of the filtered air impairs the performance of most gas filters. The gas filter 20 is also advantageously placed after the HEPA filter 2 in the air flow direction, whereby the air reaching the gas filter 20 is dust free. Naturally, this will result in a longer replacement interval for the gas filter 20.

It is essential in the dimensioning of the gas filter 20 that the residence time-of the filtered air through the filter 20 is sufficiently long. This can be guaranteed by selecting the thickness of the filter material and the

cross-section of the filter such that they are sufficient with regard to the air flow rate through the filter. If the filter is not sufficiently thick for the air flow being treated, some of the gas meant to be filtered will penetrate the filter. On the other hand, the pressure loss caused by the gas filter 20 must not be too great. The dimensions of the gas filter 20 may be for instance about 450 x 450 mm and its thickness may be 150 to 200 mm.

Air from the gas filter 20 is drawn to a blower 3 whose task it is to effect the circulation of the air. After the blower part of the exhausted air is diverted from the space being treated, whereby the required negative pressure is generated in the space where work is being done. The rest of the air is returned to said space. The air treatment device of the present invention can be used to reach a total flow of about 450 to 550 m3/h when electric power of about 1 kW is used. The external dimensions of the exemplifying device are about 0.50 x 0.50 x 0.90 m and it is provided with fixing means for connecting air supply and discharge hoses.

An advantageous position for the blower 3 in the air flow being treated is after the HEPA and gas filters 2, 20, because it is then easier to prevent the air to be treated from passing the filters 2 and 20 unfiltered. Thus, the arrangement makes sealing of the device easier because the negative pressure sucks the filters against their backing surfaces. The phenomenon is due to the fact that when the blower 3 is arranged after the filters 2, 20 the filters 2, 20 operate in a negative pressure environment with respect to the surrounding air, whereby small leaks, if any, do not cause leaking of air into the space external of the device but on the contrary give rise to air flow from outside into the device.

A system (not shown) can be connected to the device which

monitors and controls the operation of the device. Such a system may comprise, for example, means for measuring and controlling air flow, temperature, humidity, and differential pressure. Pressure losses caused by the filters 2, 20, for example, are advantageously monitored by means of differential pressure instruments. This makes it easy to notice when the filters 2, 20 need replacing.

The exemplifying device may also be connected to an exhaust air passage along which the amount of air required to create the negative pressure is exhausted from the space being treated. This passage may comprise a lead-through which exploits standard dimensioning of windows and doors.

With ready-made lead-throughs the installation time of the passage may be significantly reduced. The lead-throughs may also facilitate the arrangement of ventilation without draught during the repair work.

The principle of the exemplifying embodiment intended for repairing large targets, for instance all the sanitary spaces in an apartment building at the same time, is shown in Fig. 2. The body 6 of such a system for treating air may consist of e.g. a container. Both medium pressure fans 3, which are used to take care of the continuous ventilation of the various spaces under repair work, and a high- pressure exhaust fan 11, which is used to remove by suction the contaminated waste formed during repair of the work space, are mounted in the body. With their control devices and automatics (not shown) both systems form their own entity inside the system. Connections are provided in the body 6 for a system of passages 12 through which air is supplied into and extracted from the work space.

The purpose of ventilation is to remove microbes and other impurities formed in the work space and to dehumidify the air by means of heated and, if necessary, dehumidified incoming air. The dehumidification of air can be performed

by means of an air dehumidifier 1. The connections for the passage system 12 are furnished with gate valves 13. The medium pressure fans 3 are controlled steplessly by means of a frequency changer (not shown), and thus the required air flow can be selected flexibly according to the size of the repair target. A heat recovery unit 4 is installed into the system, by means of which heat from exhaust air is transferred to incoming air. If energy released from heat recovery is, e.g. during severe frost spells, not enough to heat the air being supplied, an air preheater 7 is used.

The filtered and heated incoming air is supplied back into the work space without draught. The exhaust air is efficiently purified by means of the filters 2 before the regenerator, whereby microbial contamination is prevented as well as the drifting of impurities along with leakage air flows back into the space being repaired. In the case of the exemplifying system, the maximal air flow rate is 7000 m3/h, which will take care of the ventilation of about 20 average-size apartments at the same time.

The apparatus of Fig. 2 supplies air from the space external of the space under repair work through the system into the space being repaired and further through the system back to the space external of the space being repaired. Thus, the flow path of air comprises a first section through the system, the space being repaired and a second section through the system. In accordance with Fig.

2, the flow path of air is arranged such that both the air dehumidifier 1 and the space being repaired are arranged before the high-efficiency filters 2 in the flow path of air. In the system of Fig. 2 the air dehumidifier 1 is arranged in the first section of the path of air flow through the system and the high-capacity filter 2 in the second section through the system.

The operation of the arrangement is monitored and controlled by means of a system (not shown) comprising

measurement and control systems for air flow, temperature, humidity and pressure difference. A similar control system can also be used in apparatuses similar to the embodiment concerning devices for treating air in one single target space.

The system according to the example also has lead-throughs which make use of standard dimensions for windows and doors. By means of such ready-made lead-throughs the time required for installing the system of passages is considerably reduced. In addition, the lead-throughs make it easier to arrange ventilation during ongoing repair work without any draught.

In addition to cleaning and the removal of finely divided dismantling waste a high-pressure exhauster 11 is used for local exhaust during a dusting step as pick dressing.

Hereby the finely divided waste is removed into the space external of the space being repaired directly by suction, whereby there is no need to handle the waste indoors. The air filtration of the high-pressure exhauster 11 takes place in multiple steps such that most of the exhausted material is collected by the preseparator 14. Next, dust is removed by means of filters furnished with cleaning means 15, and is then exhausted outdoors. A dust collector tank is arranged under the preseparator 14, which tank is emptied at a dump area.

Within the scope of the invention even solutions deviating from the above-described embodiments are feasible: in devices such as the one depicted in Fig. 1 the air circulating device 3 could be arranged between the air dehumidifier 8, 9, 10 and the filters 2, 20 or before them.

The device is also operable such that the amount of air exhausted from the space being repaired is led entirely to the space external of the space being repaired. This could be considered e.g. when the work space is divided into sections. Hereby the device could be adjusted to exhaust air e.g. from a first section and to lead the filtered exhaust air into a second section.