AU644798B2 - Improvements in airconditioning - Google Patents

Description

4bAUSTRALIA~4 PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE P/00/01 I Form Short Title: Irnt. Cl: Application Number- Lodged: "-ompiete specification-Lodged: .**Accepted: Lapsed: Published: ecePriority: Related Ant: 64 4'79 8 *00 6 TO BE COMPLETED BY APPLICANT Name of Applicant: SlI1ANE WEST Address of Applicant: 349 Annandale ,Street S0S 0 ANNANDALIE NSW Actual Inventor: SHANES' WES oR S'El iU2 15888 06/07/90 Address for Service: 3249--iAnarelale Street n~ Comlee peifcaio fr heinvention entitled: IMPROVEMENTS IN AIRCONDITIONING The following statement is a full description of this invention, including the best method of performing it known to me:- Note: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm In depth and 160 mm In wirith, on tough white paperobf good quality and it is to be Inserted inside this form.

1 4599/78--L Printed by C. J. THomI'SON, Cbamonwvcalth Government Printer, Canberra 2 Technical Field The present invention relates to air-conditioning and more particularly to a method for controlling the growth of bacteria in cooling towers of airconditioning systems, and to an improved air-conditioning system.

Background Art There has been recognition for more than ten years of the problems of bacterial growth in the cooling towers of modern air-conditioning systems with particular regard to legionella pneumophila bacteria. Cooling towers provide an ideal environment for bacterial growth with water temperatures in the range S. 10 20 to 400C. Public authorities have or are introducing legal requirements for maintenance to eliminate or reduce the chance of bacterial infection emanating from cooling towers, which may be drawn into the external air intake of the air conditioning system and fed throughout a building. It has also been recognised that bacteria, such as legionella, not only provides a threat to occupants of 15 airconditioned buildings but also to the public passing by or near to an "infected" S. cooling tower.

Existing cooling tower maintenance consists of the addition of biocides such as sodium hypochlorite. The environment of the bacteria is doused with "biocides and the biofiim removed with high pressure hoses. For safety reasons full protective equipment is required to be worn by maintenance personnel including full face airline respirators with compressor or compressed air bottles, overalls, gloves and boots. These maintenance procedures are typically carried out in daylight hours and require the air-conditioning system to be shut down.

The cooling towers of air-conditioning systems act as a water filter and thereby collect many atmospheric contaminants which, when held in the sump of the cooling tower, provide a breeding ground for legionella and other bacteria. As will be appreciated, cooling towers have been designed to function as dissipaters of heat without due regard to potential microbiological problems.

3 One object of the present invention is to provide a method for controlling the population of bacteria in cooling towers without, or with the reduced, application of chemical biocides.

Another object of the present invention is to provide an improved air conditioning system which allows for measures to reduce bacterial populations.

Summary of the Invention According to one aspect the present invention provides a method for reducing the population of legionella organisms in the coolant water of airconditioning systems, comprising 10 periodically heating the coolant water so as to attain a temperature generally in excess of 650C, and maintaining said coolant water at a temperature in excess of 650C for a period of time sufficient to reduce the population of legionella organisms.

According to another aspect the present invention comprises an improved o 15 evaporative air-conditioning system, of the type including a coolant water circuit, characterised in that said coolant water circuit includes heating means for to periodically raising the temperature of said coolant water to in excess of 650C, and maintaining said coolant water at a temperature in excess of 650C for a 9* period of time sufficient to substantially reduce the population of legioneila organisms.

The method and system of the present invention can be applied to original equipment during manufacture or applied by retrofitting to existing airconditioning systems. To kill legionella bacteria a temperature of 650C is appropriate and experience will determine a suitable dwell time for the circulating water at an appropriate temperature which is necessary to effectively kill the bacteria. It is preferred that a temperature in excess of 800C is used.

Dwell time varies with the system design, but typically is at least 15 minutes.

By redesign of cooling towers the introduction of short duration heating to the cooling tower water should be able to be effected. Such heating could be 4 achieved by microwave energy, the use of refrigerant heat exchange systems, conventional electrical element heating, or any other suitable method.

Brief Description of Drawings Aspects of the present invention will now be described by way of example with reference to the accompanying drawings, in which:- Fig. 1 is a schematic of a conventional air-conditioning system with a wet cooling tower; and Fig. 2 is a schematic of a wet cooling tower in accordance with one embodiment of the invention.

10 Detailed Description Referring to Fig. 1, a generally conventional air conditioning system is illustrated. Modification of the system according to the present invention provides for heating of the cooling water in the cooling water circulation system V.00 10 to raise the temperature of that water to a temperature and for a dwell time 15 sufficient to kill all or most bacteria present in particular, legionella o.

Sa pneumophila.

Such heating may be achieved by additional heating of the water within condenser 11 or by heating the water in some other part of the circulation system 10. Additional heating of the water in system 10 may be achieved by the provision of a further heat exchanger or by restricting the flow of water through condenser 11 while compressor 12 is operating to thereby simultaneously increase the dwell time and the temperature of the water of system 10 in condenser 11 to the desired levels.

Referring to Fig. 2, this shows a wet cooling tower 20 in which the water in reservoir 30 is agitated by a turbulence generator 31, and the cooling water passes through a filter box 32 as it leaves reservoir 30 on its path through the water circulation system.

Along the path of the water through the circulation system it is heated to a temperature high enough to kill bacteria and maintained at that temperature for a predetermined period of time. The heating of the water to kill bacteria is schematically indicated by heat exchanger 33. The necessary heating could be provided by an electrical resistance heating element 35 or microwave heating in reservoir It will be appreciated that the cooling system is preferably heated during some part of the day or week when the air-conditioning system is not in use for instance, at night or on the weekend. This ensures that normal air-conditioning need not be interrupted to clean the system.

Atop cooling tower 20 there is preferably positioned a hood or duct 34 which serves the dual purpose of preventing direct sunlight contacting the 10 cooling water, which would promote algal growth, as well as providing a specific direction to the outlet aerosol from the cooling tower. By directing the cooling tower outlet in specific directions there can be greater surety that potentially S" contaminated droplets from the cooling tower are directed away from the fresh *l air inlet of the air-conditioning system.

15 Preferably a system constructed according to the present invention also provides for agitating water in the cooling tower sump or reservoir. Such agitation has been found to be unfavourable to bacterial and algal growth. In addition the agitation of the reservoir water should lift the sludge build up and improve its drainage from the reservoir on a periodic basis.

Preferably filters are provided for the cooling tower water which can collect particulate material and dead bacteria which would otherwise provide a food source for live bacteria.

Preferably tortuous path filters and/or drift eliminators are added to the cooling tower to prevent contaminated aerosols leaving the air-conditioning system.

Preferably the sump or reservoir of the cooling tower is reshaped to improve draining and flushing to aid sludge removal. This could be done by forming the reservoir into a downward funnel-shape with the drain at the lowest point of the funnel.

6 It will be recognk--. i by persons skilled in the art that numerous variations and modifications may be made to the invention as described above without departing from the spirit or scope of the invention as broadly described.

Claims (9)

1. A method 4- dtvththe population of legionella organisms in the coolant water of air-conditioning systems, comprising the steps of: periodically heating the coolant water so as to attain a temperature generally in excess of 650C; and maintaining the coolant water at a temperature in excess of 65°C for a period of time sufficient to reduce the population of legionella organisms. s*ee

2. The method according to claim 1, wherein said periodic heating occurs during periods when the building is not required to be airconditioned :9 The method according to claim 1 or claim 2, wherein said period of time is in excess of 15 minutes.

4. The method according to any one of the preceding claims, wherein the temperature is raised to over 8000.

5. An improved air-conditioning system, of the type including a coolant water circuit, characterised in that said coolant water circuit includes heating means for periodically raising the temperature of said coolant water to in excess of 650C, and maintaining said coolant water at a temperature in excess of 650C for a period of time sufficient to substantially reduce the population of legionella organisms.

6. The system according to claim 5, wherein the system is arranged such that said periodic heating occurs during periods when the building is not required to be airconditioned ease a a 0 0 00 9 @9 9 9 S 8

7. The system according to claim 5 or claim 6, wherein said period of time is in excess of 15 minutes.

8. The system according to any one of claims 5 to 7, wherein the temperature is raised to over 800C.

9. A method of reducing legionella populations in cooling water substantially as hereinbefore described.

10. An improved air-conditioning system substantially as hereinbefore described with reference to figure 2. Dated this 4 August 1993 SHANE WEST WATERMARK PATENT TRADEMARK ATTORNEYS LEVEL 4, AMORY GARDENS, 2 CAVILL AVENUE, ASHFIELD NSW 2131 CALI. lu