VENTILATION SYSTEM

Abstract: An air treatment installation comprising a supply-air system (1) with a cooling battery (13) for energy-saving dehumidification of a first air flow flowing through the supply-air system, whereby the cooling battery imparts a chill to the first air flow. The supply-air system (1) comprises a first heat exchanger (10) arranged upstream of the cooling battery (13) and a second heat exchanger (15) arranged downstream of the cooling battery (13). The heat exchangers are connected to a closed passive system for transfer of heat past the cooling battery. At thermal balance in the first air flow, the passive system transports a cooling effect past the cooling battery, which, between the heat exchangers, lowers the temperature and hence the dew point in the first air flow.

Description: Ventilation system TECHNICAL FIELD The present invention relates to an installation for dehumidification of a gas. More particularly, the invention relates to a ventilation system for treatment of air to a plurality of spaces enclosed in a building or the like. In particular, the invention relates to a ventila- tion system on ships or other installations at sea, so- called offshore installations. The invention relates especially to an air-treatment installation arranged in such a system. BACKGROUND ART Spaces onboard a ship are normally ventilated by means of fresh air which is filtered and treated such that it provides the desired temperature and humidity. In an air treatment installation, a supply-air fan ensures that fresh air is sucked in and is pressed further in a system of ducts. In the same way, an exhaust-air fan ensures that exhaust air is sucked back through an exhaust duct and released into the open. The supply air and the exhaust air pass, separate from each other, through a rotating hygroscopic heat exchanger, a so-called enthalpy wheel, which is arranged to transfer moisture and heat from one of the systems of ducts to the other system of ducts. The supply air is also given the desired properties such as purity, the proper temperature, the necessary pressure, the proper humidity, etc. For these purposes, the air-treatment installation comprises inter alia devices for cooling, heating and moistening the supply air. In ships, and in particular in passenger ships, considerable demands are placed on an air treatment installation. The installation should be able to offer a comfortable indoor climate, whether the ship travels in tropical waters or in arctic waters. Known air treatment installations occupy large spaces in the ships, which spaces could otherwise yield a good economic return. The fresh air, which is needed to create sufficient ventilation, normally only constitutes a minor part of the air volume which is supplied to the spaces of the ship. The remaining part, which constitutes about 70%, is used for balancing thermal and cooling loads. The maximum air volume is often determined by the cooling requirement when operating in tropical waters . The free air is here very warm and contains a considerable amount of moisture. To efficiently dehumidify the air, the air is cooled down whereby the so-called dew point is passed and condensation occurs . To this end, the air is allowed to pass through a cooling battery, on the cold surfaces of which the water condenses and runs off. The cooling battery is supplied with a cooling agent of about 5-15 degrees Celsius (°C) . As cooling agent there may be used a cooling liquid of the type water, salt solution, glycol water or the like, as well as an evaporated agent. Normally, an air treatment installation serves a plurality of cabins and other spaces through a branched system of ducts for supply and exhaust air. All the spaces are thus supplied with the same treated air in spite of the fact that the different rooms may have a very varying need of comfort and cooling requirement. A comfort level with a uniform temperature of about 22-24 C should be offered under all circumstances and in all climates. According to one known system for ventilation of ships, a so-called cold-air system, the air treatment is arranged such that the admitted fresh air is cooled down such that condensed water may be separated. Thereafter, the cooled supply air is transported in a duct which serves a plurality of spaces. The air is then tempered such that each space which is served by the duct is given a sufficiently cool environment. It is thus the space which has the greatest cooling requirement - which is normally determined by the highest thermal load - that dimensions the temperature of the departing supply air. To this end the air ducts have to be insulated and provided with a diffusion barrier where it passes through spaces where the surrounding air is hotter than that in the duct. One reason for this is that the air in the duct shall not be heated too much. Another reason is that the warmer air which surrounds the duct often contains water which would be condensed on the otherwise cold duct surface. Such condensate easily causes formation of mould or other sanitary inconvenience. In individual spaces with less thermal load, the supply air is after-heated in the respective space. Such after-heating is normally performed with a so-called electric battery, in which the air passing through is supplied with heat from an electric resistance. One disadvantage with this system is thus that additional energy must be supplied and another disadvantage is that the insulated ducts are space-demanding. According to another system for ventilation of ships, a so-called hot-air system, separation of condensed water is performed in the same way as above. Thereafter, the air is heated to comfort level and is transported to a plurality of spaces through uninsulated ducts . The temperature of the departing supply air is in this case dimensioned by that individual space which has the smallest cooling requirement, which is normally determined by the lowest thermal load. For the other spaces, individual after- cooling of the air is required. An advantage with this ventilation system is that the supply air may be trans- ported in uninsulated ducts, which saves both weight and space. A disadvantage is, however, the energy waste which occurs by first cooling the air, then heating the air and finally after-cooling the air. Thus, there are substantially two principles of ventilation in ships, namely one where cold air is transported to the cabins and is there heated as required, and one where hot air is transported to the cabins and there after- cooled as required. Common to both systems, however, is that the fresh air is first cooled down such that the moisture is condensed away. For this, energy is first needed to cool the air and then additional energy is needed to heat the air again. SUMMARY OF THE INVENTION The object of the present invention is to achieve a dehu- midification system which is more energy-saving than prior art systems. More particularly, the invention seeks to suggest ways of creating a ventilation system which dehu- midifies the air in a more cost-efficient way than hitherto known systems. The ventilation system shall permit the use of uninsulated and thus less space- demanding ducts, which includes a weight reduction and a greater economic yield from the available building volume. This object is achieved according to a first aspect of the invention of an air-treatment installation according to the characteristic features described in the characterizing portion of the independent claim 1 and with a method according to the characteristic features described in the characterizing portion of the independent claim 6. From a second aspect of the invention, the objects are achieved with a dehumidification plant according to the characteristic features described in the characterizing portion of the independent claim 8 and with a method according to the characteristic features described in the characterizing portion of the independent claim 9. Advantageous embodiments are described in the characterizing portions of the dependent claims. The air treatment installation according to the invention comprises a bypass-coupled heat-exchange system by means of which heat may be extracted from the passing air at a first point and again be supplied to the air at a second point. This second point may be placed upstream or downstream in relation to the first point. Between the first point and the second point, a device for supply or removal of heat from the air flow is arranged. In this context the fact it made use of that the air, without any external energy addition, for a short distance is temporarily cooled in order, for example, to be dehumidified, whereupon the air is again supplied with the separated heat. Especially in ships which operate in tropical waters, the described function is desirable and energy- saving. For operation in arctic waters, the reverse function may instead be of use. The air treatment installation according to the invention may also comprise an energy-recovery system in the form of a so-called enthalpy wheel, which is adapted to transfer moisture and heat between supply air and exhaust air in the installation. Such an enthalpy wheel is thus placed between the two interconnected heat exchangers . In this way, according to the invention, both heat and moisture are transferred between exhaust air and supply air with a typical efficiency of 70-80 % by causing the enthalpy wheel to rotate at a certain speed. In certain climate situations, it may be an advantage to transfer only moisture between supply air and exhaust air without also simultaneously transferring heat. The heat exchangers which are bypass-connected on either side of the enthalpy wheel may, in this connection, be used for apparently creating a different working situation for the enthalpy wheel. The heat which is normally transferred simultaneously with the moisture may thus be eliminated by utilizing the interconnected heat exchangers in such a way that, for example, relatively colder (e.g. 18 C, RH 35%) outdoor air is allowed to lower the air temperature after the air has passed through the first exchanger, the enthalpy wheel and finally the second exchanger. In this way, the supply air may be moistened by moisture from the exhaust air (e.g. 25 C, RH 60%) without suffering the increase in temperature which would normally result from the heat transferred with the moisture. Thus, with the bypass-connected heat exchangers, heat may be removed from the air flowing through the enthalpy wheel and then again be supplied to the air after the enthalpy wheel. The enthalpy wheel is thereby given a working situation whereby only moisture is transferred. This causes the total efficiency of the air treatment installation to increase. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail in the following by description of an embodiment with reference to the accompanying drawing, wherein Figure 1 shows a ventilating installation according to the invention. DESCRIPTION OF PREFERRED EMBODIMENTS The air-treatment installation belonging to a ventilation system, and schematically shown in Figure 1, comprises a supply-air system 1 and an exhaust-air system 2, which are interconnected by an energy-recovery system 3. This is exemplified in the figure by a so-called enthalpy wheel. Two filled arrows in the figure shows the direction of flow of the exhaust air and two unfilled arrows show the direction of flow of the supply air. The air-treatment installation according to the figure shows only the core in a complete ventilation system for, for example, a ship. Thus, the system may, at both ends, be connected to a system of ducts, not shown. The exhaust-air system shows in the direction of flow first a filter 4, then a sound attenuator 5, an empty space 6, the enthalpy wheel 3 and finally an exhaust fan 7. In the same way, the supply-air system shows in the direction of flow a damper flap 8, a filter 9, a first heat exchanger 10, an empty space 11, the enthalpy wheel 3, an empty space 12, a cooling battery 13, an empty space 14, a second heat exchanger 15 and finally a supply-air fan 16. The term cooling battery here refers, in a broad sense, to an apparatus which, in a gas flowing through, is capable of supplying or removing heat from an external system. The first heat exchanger 10 is connected to the second heat exchanger 15 in a closed system via a conduit 17. In the conduit 17 , a medium flows which transports energy from the first heat exchanger 10 to the second heat exchanger 15, or the reverse. The interconnected heat exchangers thus permit energy to be obtained from the air at a first point and be supplied to the air again at a second point upstream or downstream of the first point. This makes it possible, among other things, to reduce the temperature and the water content of the incoming fresh air such that an efficient dehumidification may be achieved. 8 In tropical waters the fresh air is hot and moist. The fresh air must therefore be both cooled and dehumidified to be able to ventilate the spaces of a ship with good comfort. The air must then be so cooled and dehumidified that it is able to absorb and transport away, for example, moist and heat emitted in the cabins. In typical situations in tropical waters, the ratio between the temperature of the fresh air in degrees Celsius/relative humidity is about 33/80. The air is cooled by the first heat exchanger 10 to, for example, 22 °C . When passing through the enthalpy wheel 3, moisture is removed from the supply air and heat is supplied from the exhaust-air system, whereby the temperature rises to about 25 °C . Thereafter, the air passes through the cooling battery 13, whereby the air is cooled to about 11 °C while being dehumidified. Then, the air passes through the second heat exchanger 15 which is connected to the first heat exchanger 10. Here, the heat, which was previously separated from the supply air, is supplied. The previous reduction of the air tempe- rature of 11 units of degree is thus returned here and increases the temperature of the air by a maximum of 11 units of degree. Before the supply-air fan the temperature is thus 22 °C and after the fan, which provides an addition of about 2 units of degree, about 24 °C. Under typical conditions in arctic waters the above- mentioned ratio is instead -10/50. The first heat exchanger 10 now supplies heat to the cold fresh air so that it is heated to about -5 °C . The enthalpy wheel now supplies from the exhaust-air system both heat and moisture such that the air is heated to about 18 °C . The cooling battery 13 now operates as a heating battery and heats up the air to about 30 °C, whereupon the second heat exchanger carries away the heat which was previously supplied to the supply air. Thus, before the supply-air fan the temperature is about 20 °C and after the fan about 22 °C. A great advantage when using the system under winter conditions is that the risk of the enthalpy wheel freezing is largely eliminated. Although advantageous, the air-treatment system according to the invention is not limited to the embodiment described above. Thus, other heat-extraction systems may also be used to extract heat and supply heat to an air flow again. The agent which connects the two heat- extraction units may consist of electricity as well as a liquid or a gas, and also of a mechanical device. What has been described above for air is also true, in general, of a gaseous medium which is desired to be dehumidified in an efficient way.

Claims: 10 CLAIMS 1. An air treatment installation comprising a supply-air system (1) with a cooling battery (13) for energy-saving dehumidification of a first air flow flowing through the supply-air system, whereby the cooling battery imparts a chill to the first air flow, characterised in that the supply-air system (1) comprises a first heat exchanger (10) arranged upstream of the cooling battery (13) and a second heat exchanger (15) arranged downstream of the cooling battery (13), which heat exchangers are connected to a closed passive system for transfer of heat past the cooling battery, whereby, at thermal balance in the first air flow, the passive system transports a cooling effect past the cooling battery, which, between the heat exchangers, lowers the temperature and hence the dew point in the first air flow. 2. An air treatment installation according to claim 1, characterised in that a liquid cooling agent passes through the passive system which comprises the first heat exchanger (10) , the second heat exchanger (15) and a conduit (17) interconnecting the heat exchangers. 3. An air treatment installation according to claim 1 or 2, characterised in that the air treatment installation comprises an exhaust-air system (2) through which a second air flow flows, whereby, between the supply-air system and the exhaust-air system, a heat-recovery system (3) is arranged, which is adapted to transfer moisture and heat between the first air flow and the second air flow. 4. An air treatment installation according to claim 3, characterised in that the heat-recovery system (3), in the supply-air system (1) , is arranged between the first heat exchanger (10) and the second heat exchanger (15). 11 5. An air treatment installation according to claim 4, characterised in that the heat-recovery system (3) comprises an enthalpy wheel . 6. A method for energy-saving dehumidification of an air flow flowing through a cooling battery (13) for external supply of a cooling effect, characterised in that a first heat exchanger (10) is arranged upstream of the cooling battery (13) and a second heat exchanger (15) is arranged downstream of the cooling battery (13), which heat exchangers (10, 15) are connected to a closed passive system, whereby, at thermal balance in the air flow, a cooling effect is transported past the cooling battery, whereby, between the first heat exchanger (10) and the second heat exchanger (15), the temperature and hence the dew point are reduced. 7. Use of an air treatment installation according to claims 1 to 5 or a method according to claim 6 for offshore installations or for the manufacture of a ship. 8. A dehumidification plant comprising a duct (1) and a cooling battery (13) arranged therein for supply or removal of heat in a gas flowing through the duct and the cooling battery (13), characterised in that the duct comprises a first heat exchanger (10) arranged upstream of the cooling battery (13) and a second heat exchanger (15) arranged downstream of the cooling battery (13), which heat exchangers are connected to a passive system for transfer of heat past the cooling battery. 9. A method for energy-saving dehumidification of a gas, wherein the gas is brought to flow through a cooling battery (13) for external supply of a cooling effect, characterised in that heat is extracted from the gas at a first point (10) upstream of the cooling battery (13) and 12 is supplied to the gas at a second point (15) downstream of the cooling battery (13) in a passive closed system, whereby, at thermal balance in the flowing gas, a cooling effect is transported past the cooling battery, whereby, between the first point and the second point, the temperature and hence the dew point are reduced.

Inventors: GOETMALM OERJAN, GOETMALM, OERJAN
Applicants: FLAEKT AB, GOETMALM OERJAN, ABB FLAEKT AB, GOETMALM, OERJAN
Application year: 1999
Main classification: F24F3
IPC codes: F24F3, F24F5