Technical Field

The present invention relates to a method of cooling air for air conditioning of a space in a building. The method comprises the generation of a flow of intake air for the space to be air conditioned and can be used generally in air conditioning, i.e. in areas having a hot climate as well as in areas having a medium hot climate. Background art

When cooling air in a conventional way in air condi- tioning equipments, the air is first cooled until it is saturated with moisture and is then further cooled, so that moisture is precipitated. The cooled, humid air is then forced into the space to be air conditioned. This method of cooling is effective but has the disadvantage that it requires a comparatively high power. Disclosure of Invention

The main object of the invention is to provide a method of cooling air for air conditioning equipments, the method requiring less power than the conventional method. According to the invention, this is achieved by first for¬ cing the air in the generated intake air flow to pass a dehumidifier containing a desiccating substance, so that the moisture content of the air is reduced, thus increasing the temperature of the air, and then cooling the air, and by forcing an air flow having a comparatively low moisture content to pass a substance that has absorbed moisture from the intake air, so that the moisture content of the desic¬ cating substance is reduced, i.e. so that the substance is regenerated, and the substance then can be reused for absorbing moisture in the intake.air. Preferably, the inta¬ ke air can after dehumidification first be cooled by heat exchange with an air flow and then be further cooled. Par¬ ticularly, if the air is compressed, before or after pas-

sing the desiccating substance, and|or solar heat can be supplied to an air flow for regeneration of the desiccating substance, a substantial improvement of the economy of the cooling method can be obtained. This improved economy is achieved by giving the dried and possibly compressed air a bigger temperature difference to the cooling medium, so that a portion of the heat in the dried air in a more effi¬ cient way can be carried off and possibly used for regene¬ ration of the desiccating substance, and by further heating the desiccating air flow by supply of solar heat, either directly by forcing the air flow along a surface exposed to direct sun radiation or indirectly by means of a solar energy equipment. Brief Description of the Drawing The method according to the invention will now be further explained below with refernce to the accompanying drawing. The drawing is a schematical cross section view through a building having an air conditioning system accor¬ ding to the invention. Best Mode for Carrying Out the Invention

The drawing shows a building 1 which is erected on a concrete base 2 or other suitable foundation. The building comprises a framework 3 which supports a wall cladding 4 and a roof cladding 5. Both the wall cladding and the roof cladding may consist of metal panels having a good thermal conductivity, for example aluminium panels.

The building has a pitched roof and is provided with an air vent 6 at an upper region of the roof.

A layer of porous insulating boards 7 is provided below the roof cladding 5 and in spaced parallelism with the roof cladding, the layer being supported by the frame¬ work 3. A narrow air channel 8 is provided between the roof cladding 5 and the porous boards 7, and this channel commu¬ nicates with the lower portion of the air vent 6. Due to the fact that the roof cladding consists of metal panels having a good thermal conductivity, the air in the channel 8 will be substantially heated, when the sun shines on the

roof cladding.

The porous boards 7 are preferably made of a material having good thermal insultaing properties and so designed that air from the interior of che building may flow up through the boards into the air channel 8, as indicated by the arrow 9. The boards may thus be made of a material that is inherently porous, for example an expanded rock wool material. Alternatively, the boards may be made of an impervious material, for example closed-cell expanded polystyrene, the boards being provided with apertures the¬ rethrough, so that the boards become capable to effectively permit the flow of air therethrough. These apertures are preferably positioned adjacent the eave, so that the air channel 8 becomes as long as possible. In the air vent 6 a dehumidifier 10 is provided con¬ taining a desiccant material, such as silica-gel, which can be regenerated, i.e. dehumidified, by means of comparative¬ ly dry air. This desiccant material is positioned in con¬ nection with an inlet pipe 11 for intake air to the buil- ding. After the dehumidi ication, which increases the inta¬ ke air temperature, the intake air is cooled and fed into the interior of the building through a pipe 12.

The dehumidifier 10 is preferably so designed that the used portion of the desiccant material after a predetermi- ned period of time can be exchanged, so that the intake air always passes a portion of desiccant material that can absorb moisture from the intake air, and so that the exhaust air passes a utilised portion of desiccant material for dehumidification of this portion, so that a utilised portion of the desiccant material is regenerated and thus can be used again. This can be accomplished by providing the desiccant material in cartridges in the dehumidifier and moving the cartridges by means of an appropriate mecha¬ nism between the inlet channel for the intake air and the outlet channel for the exhaust air. Thus, one cartridge can be used for drying the intake air, whilst one or more cart¬ ridges are being dried, i.e. regenerated, by the hot

exhaust air from the channel 8.

The dehumidification of the intake air increases the temperature of this air by for example 10-20 °C depending upon the initial content of mo sture of the intake air and the extent of the dehumidification.

The cooling of the intake air fed into the building can be achieved in many ways, for example by forcing the intake air to pass a heat exchanger which is also passed by cooler exterior air. Such a cooling of the intake air is possible due to the fact that the intake air after the dehumidification has a higher temperature. A further coo¬ ling of the intake air can then be achieved, either by pas¬ sing the intake air in a conventional way through a further heat exchanger with for example cooling water or by increa- sing the moisture content by causing the intake air to flow for example past a damp sheet or similar arrangement. The structural work shown on the drawing is primarily intended for geografical areas having a hot climate, because the exhaust air due to the presence of the air channel 8 bet- ween the roof cladding 5 and the insulating boards 7 partly to a high degree prevents solar heat form penetrating into the interior of the building, so called dynamic heat insu¬ lation, and partly is substantially heated, so that it can provide regeneration of the desiccant material in the dehu- midifier without further heat supply.

When the invention is utilised in geografical areas with only medium hot climate, it is normally not necessary to provide a dynamic heat insulation. In stead, it may be necessary to provide further heat supply to the air inten- ded to provide regeneration of the desiccant material, in case the direct sun heat is not sufficient. This can be achieved by means of solar energy devices.

However, when further heat must be supplied to the air intended to provide the regeneration of the desiccant mate- rial, it is difficult to achieve a substantial improvement of the operating economy with the present technology by starting the cooling procedure with a desiccating step. In

such cases, however, a substantial improvement of the ope¬ rating economy can be achieved by compressing the intake air before cooling. This will cause a further increase of the temperature of the intake air, so that heat easier can be carried off from the intake air by heat exchange with a flow of exhaust air or exterior air. This improvement is achieved by the fact that the temperature difference bet¬ ween the intake air and the exhaust air or the exterior air is increased. The temperature after the compression may be about 70 °C. When the intake air has this temperature, the cooling air will get a sufficiently low relative humidity to be able to provide the regeneration of the desiccant material without further heat supply.

After the initiating cooling of the intake air, a further decrease of the temperature of the intake air is achieved by expanding the intake air, before the intake air flows into the space to be air conditioned. Thus, in this case it is convenient to utilise the exhaust air, which has been heated by the intake air, for the regeneration of the desiccant material.

The compression can, of course, also be used in combi¬ nation with the above described dynamic insulation in areas with a hot climate.

The compression of the inlet air before the cooling can be made before or after the dehumidification and can be so balanced that the following expansion will give the required further lowering of the temperature of the intake air. Alternatively, a more substantial compression may be made, thus improving the heat transfer to the exhaust air or exterior air. In this case, a portion of the energy necessary for the compression can be recovered during the expansion.

Whilst the method according to the invention has been described in connection with a structural work that is pri- marily intended for use i areas with a hot climate, it is to ^' be appreciated that the method can be used generally, i.e. in areas having a hot climate as well as in areas

having a medium hot climate. When the invention is utilised in a hot climate, it is not necessary to use the air heated by the intake air for the regeneration of the desiccant material, because the air temperature necessary for the regeneration easily can be obtained from direct solar ener¬ gy. However, when the invention is utilised in a medium hot climate, it is convenient to use the heat carried off from the intake air for the regeneration of the desiccant mate¬ rial. The dehumidification can also be provided by means of many different devices. It is not necessary to provide the desiccant material in interchangeable cartridges, but the desiccant material may alternatively be provided in a rota- table drum having several sections, the drum being arranged to rotate, so that the different sections alternately are positioned in the channel for the intake air and in a chan¬ nel for heated exhaust or exterior air. Furthermore, other regenerable desiccant materials than silica-gel may be used. It is not necessary that the intake air is cooled by heat exchange with an air flow, but also other cooling media, for example water, may be used.