GB2351345A

GB2351345A - Desiccant cooling system

Info

Publication number: GB2351345A
Application number: GB9912257A
Authority: GB
Inventors: Zyl Robert Peter Van
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-27
Filing date: 1999-05-27
Publication date: 2000-12-27
Also published as: GB9912257D0

Abstract

An air conditioning system allows for the simultaneous drying and cooling of an airstream. The system comprises a counter-current heat exchanger, with forward passages 2 and reverse passages 4 separated by an impervious wall 1. The forward passages are lined with a desiccant 3, and the walls of the reverse passages are wetted with water 5. In operation airstream 6 passes through the forward passages and is dried by the desiccant. The stream is then split into an exit flow 7 and an auxiliary stream 8, which is passed through the reverse passages 4. Latent evaporation of the water in these passages cools the forward passages 2 and the air passing through them. It is claimed that this apparatus cools the air from the forward passages and the water in the reverse passages below the dew point of the incoming air, allowing desiccants to be used that operate at high relative humidities, which can be regenerated at modest temperatures.

Description

2351345

DESICCANT COOLING SYSTEM DESCRIPTION

FEELD

The present invention relates to a desiccant cooling system, wherein the drying and cooling processes occur simultaneously.

BACKGROUND AND DESCREPTION OF PRIOR ART

Current desiccant systems utilise absorbents to reduce the moisture content of air, before and/or after cooling the air in one or more indirect evaporative heat exchangers. Various types of indirect evaporative heat exchangers have been utilised in these conventional desiccant systems. One of the most effective classes of evaporative heat exchangers was developed by Rotenberg et at. in US patent 5,187,946, by Maisotsenkc, et a]. in US patent 4,977,753, and by Ray in US patent 1,986, 529. These evaporative coolers utilise counter-current heat exchangers, in which one set of passages is wetted. Their evaporative heat exchangers can theoretically achieve cooling down to the dew point temperature, by various means including reversing a portion of the cooled, dry gases into the wetted passages to be utillsed as the direct evaporative stream.

If the relative humidity of the incoming air is low, desiccants must be chosen that are able to absorb moisture at low relative humidity. These desiccants require high temperature air for their regeneration. These systems are therefore often unsuitable for applications where the temperature of the regeneration heat source is low, such as heat collected by solar panels.

Multiple-stage systems, such as that defined by Tsimerman in US patent 5, 050,391, can partially solve this problem by utilising a first indirect evaporative cooler to reduce the temperature (and thus increase the relative humidity) of the incoming air before passing it through the desiccant dryer. However, the temperature or the air rises again as it passes through the desiccant dryer, thus reducing its relative hurruidity once more.

One method of preventing a drop in the relative humidity of the air being dried, is to cool it during the dehumidification process. To achieve this, the desiccant may be coated on de of a heat exchanger, while an auxiliary cooling stream (typically chilled water one si I Z.

or air) is passed through the adjacent passages. The auxiliary cooling stream directly cools the heat exchanger, and thus indirectly cools the desiccant and the dehumidified air stream. To be effective the cooling stream must be substantially colder than the dehumidified air stream, thus also requiring a cooling process. Evaporative cooling of ambient air is unlikely to achieve the necessary auxiliary stream temperature without being dried, thus repeating the problem of the primary air stream.

I.

SLqvgvLkRY In the present disclosure is a simple apparatus and method for simultaneously cooling and desiccant drying air that solves this problem. It comprises a counter-current indirect/direct evaporative heat exchanger of which the forward passages are coated with desiccants, and a portion of the cool, dry air stream exiting the forward passages is redirected into the wet passages in the counter-current direction, to act as the auxiliary, evaporatively cooled stream.

By this means, both the water from the wet passages, and the air from the dry passage may be cooled to below the dew point temperature of the incoming air, while desiccants may be utilised that absorb water predominantly at high relative humidity and can be regenerated at modest temperatures.

PREFERRED ENMODIMENT OF THE rNVENTION A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing. The apparatus comprises a counter-current heat exchanger in which the passages are separated by an impervious wall (1). The passage walls of the forward side (2) are coated with a liquid or solid desiccant (3), while the passage walls of the counter current side (4) are wetted with water (5).

A forward stream of air (6) is passed through the forward passage (2) where it is dried by contact with the desiccant (3), and cooled by heat exchange with the counter-current air stream (8) through the wall (1). The forward air stream (6), upon exiting the forward passage (2) is split into two strearns the supply air stream (7), and the counter-current air stream (8). The counter-current air stream (8) is reversed and passed through the counter-current passage (4) where it is humidified by contact with the water (5), and warmed by heat exchange with the forward air stream (6) through the wall (1).

The latent heat required for evaporation in the counter-current passages (4), is taken from the counter-current air stream (8), the liquid water (5), the heat exchanger matrix (1), the forward passage air stream (6), and the desiccant (3), thus transferring heat released by sorbtion in the dry forward passages (2). The forward air stream (6) and desiccant (3) are indirectly cooled by the evaporation process in the counter current passages (4), thus reducing (or even preventing) the drop in relative humidity of the forward air stream (6) as It is dried. By this process, the forward air stream (6) is both cooled and dried, while the desiccant (3) can be selected to operate at high relative humidity, thus regenerating at lower temperatures than usual.

Z.

Claims

I. An apparatus and method for simultaneously cooling and desiccant drying air, comprising a counter-current indirect/direct evaporative heat exchanger of which the forward passages are coated with desiccants, and a portion of the cool, dry air stream exiting the forward passages is redirected into the wet passages in the counter-current direction, to act as the auxiliary, evaporatively cooled stream. By t1iis means, both the water from the wet passages, and the air from the dry passage may be cooled to below the dew point temperature of the incoming air, while desiccants may be utifised that absorb water predominantly at high relative humidity and can be regenerated at modest temperatures.
2. An apparatus and method for simultaneously cooling and desiccant drying air, comprising a counter-current indirect/direct evaporative heat exchanger of which the forward passages are coated with desiccants, and a portion of the cool, dry air stream exiting the for-ward passages is redirected into the wet passages in the countercurrent direction, to act as the auxiliary stream. By this means, both the water from the wet passages, and the air from the dry passage may be cooled to below the dew point temperature of the incoming air.
The invention of claim 1, in which desiccants that absorb water predominantly at high relative humidity are used, and can be regenerated at modest temperatures.
4. The invention of claims I or 2, in which the cooled water from the wet passages, is drawn off as the cooled fluid.
5. The invention of claims I or 2, in which a portion of the air exiting the dry, forward passages, is drawn off as the cooled and dried fluid.
6. The invention of claims 1,2,3 or 4, in which the vapour exiting the wet passages is drawn off as the humidified fluid.
7. An indirect/direct evaporative heat exchanger substantially as described herein with reference to the figures of the accompanying drawings.

S.

Amendments to the claims have been filed as follows I An apparatus and method for simultaneously cooling and desiccant drying air, comprising a counter-current indirect/difect evaporative heat exchanger of which the forward passages are coated with desiccants, and a portion of the cool, dry air stream exiting the forward passages is re-directed into the wet passages the counter-current direction, to act as the auxiliary, evaporatively cooled stream. By this means, both the water from the wet passages, and the air from the dry passage may be cooled to below the dew point temperature of the incoming air, while desiccants may be util-ised that absorb water predominantly at high relative hurruidity and can be regenerated at modest temperatures.

The invention of claim 1, in which desiccants that absorb water predominantly at high relative humidity are used, and can be regenerated at modest temperatures.

The invention of claims I or 2, in which the cooled water from the wet passages, is drawn off as the cooled fluid.

The invention of claims I or 2, 'in which a portion of the air exiting the dry, forward 44 passages, is drawn off as the cooled and dried fluid.

The invention of claims 1,2,3 or 4, in which the vapour exiting the wet passages is drawn off as the humidified fluid.

An indirect/direct evaporative heat exchanger substantlafly as described herein With reference to the figures of the accompanyl ng drawings.

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