WO1999036734A1

WO1999036734A1 - Improved air conditioning system

Info

Publication number: WO1999036734A1
Application number: PCT/AU1999/000030
Authority: WO
Inventors: John Francis Urch
Original assignee: Eco Air Limited
Priority date: 1998-01-15
Filing date: 1999-01-15
Publication date: 1999-07-22
Also published as: AUPP135998A0

Abstract

An air conditioning apparatus including a heat exchanger (7) and an evaporative coil (10). The heat exchanger (7) includes first and second air flow circuits adapted to provide heat transfer therebetween. The evaporative coil (10) is interposed between the first and second air flow circuits of the heat exchanger (7). The air stream flowing through the apparatus passes through the first air flow circuit and then through the evaporative coil, before being passed through the second air flow circuit of the heat exchanger.

Description

TITLE: IMPROVED AIR CONDITIONING SYSTEM

FIELD OF THE INVENTION

This invention relates to air conditioning apparatus for cooling and/or heating an

environment.

More specifically the present invention is concerned with improving the operating

efficiency of such apparatus.

BACKGROUND TO THE INVENTION

Air conditioning is commonly employed in buildings to provide a stream of air at a

controlled temperature and/or level of humidity.

A common form of air conditioning system employs a refrigerant which is

circulated through a refrigeration circuit to modify the temperature and/or humidity of an

incoming stream of air so that it is supplied to the space being ventilated under the

desired conditions. However, conventional air conditioners are relatively inefficient,

requiring large motors and consuming a considerable amount of power in order to

operate effectively. As a consequence, both the capital and running costs are relatively

high.

It is an object of the present invention to overcome or ameliorate at least one of the

disadvantages of the prior art, or to provide a useful alternative. SUMMARY OF THE INVENTION

The present invention provides an air conditioning apparatus including heat

exchanging means having first and second air flow circuits adapted to provide heat

transfer therebetween, and an evaporative coil, the evaporative coil being interposed

between the first and the second air flow circuits of the heat exchanging means such that

an air stream flowing through the air conditioning apparatus passes through the first air

flow circuit and then through the evaporative coil, before being passed through the

second air flow circuit of the heat exchanging means.

It has been discovered unexpectedly that by providing a heat exchanger with first

and second air flow circuits which are isolated from each other but which provide heat

transfer therebetween, and locating an evaporative coil in the air flow circuit between the

first and second air flow circuits of the heat exchanger so that an air stream passing

through the air conditioning apparatus passes through the first air flow circuit of the heat

exchanger, then through the evaporative coil, and subsequently through the second air

flow circuit of the heat exchanger, a favourable improvement in operating efficiency of

the air conditioning unit can be achieved.

Preferably the evaporative coil is connected to a conditioning unit of suitable size

for the overall performance required.

In a preferred form of the invention, the air stream is subsequently passed through

a water coil for further cooling or heating of the air stream. The air stream is then

preferably passed through a cooling pad prior to being directed into the environment. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described, by way of

example only, with reference to the accompanying drawings in which:

Figure 1 depicts a schematic sectional view of a first preferred embodiment of an

air conditioning apparatus in accordance with the present invention;

Figures 2a to 2c depict schematic sectional views of alternative embodiments of air

conditioning apparatus designed in accordance with the present invention;

Figure 3 shows a psychrometric chart illustrating an example of the temperature

and moisture conditions of an air stream at various stages whilst passing through the air

conditioning apparatus; and

Figure 4 shows a further embodiment of the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring to Figure 1, an air conditioning unit 1 designed in accordance with the

present invention is illustrated. The air conditioning unit 1 includes a casing or housing

2 having an air inlet 3 through which an air stream enters the air conditioning unit and an

air outlet 4 through which the air stream leaves the air conditioning unit. A suction fan 5

is provided to draw the air stream through the unit, with the flow of air through the unit

generally being indicated by the arrows 6. It is to be appreciated that the type of fan

used to circulate the air stream through the unit is not essential to the concept of the

invention.

In accordance with the invention the air conditioning unit includes a heat

exchanger 7. The heat exchanger includes first and second air flow circuits which are isolated from one another but which are adapted to provide good heat transfer

characteristics therebetween. One form of such a heat exchanger is described in detail in

Australian Patent No. 660,781 whilst another form of such a heat exchanger is disclosed

in International Patent Application No. PCT/AU96/00731, the full contents of both being

hereby incorporated herein by way of reference. The flow of air through the first air

flow circuit of the heat exchanger is illustrated by the solid lines and arrows 8, whilst the

flow of air through the second air circuit of the heat exchanger is indicated by the dashed

lines and arrows 9.

The air conditioning unit further includes an evaporative coil 10 which is located

in the air stream flow path between the first and second air flow circuits of the heat

exchanger 7.

The second air flow circuit communicates with a water coil 11 and cooling pad 12

which is preferably designed in accordance the cooling pad disclosed in International

Patent Application No PCT/AU95/00315.

A water collection tray 13 or the like is positioned beneath the evaporative coil 10

which acts to collect the moisture extracted from the air stream as it passes through the

coil. The water which is extracted from the air stream is directed to a reservoir or sump

14 positioned adjacent the water coil and cooling pad via a water drain, channel or the

like 15. The extracted water may then be utilised in the water coil and cooling pad. A

pump 16 may be incorporated in the unit to provide for the circulation of water through

the water coil 11. In an alternative arrangement, particularly suitable in hot, dry

environments or where more immediate cooling is required, mains water can be

introduced to the system to provide a supply of water for circulation in the water coil 11 with or without the refrigerant compressor system operating. In a further embodiment of

the invention, the water from the evaporative coil 10 may be pumped directly, via a

separate pump unit (condensate pump), to the head of the cooling pad in order to give

quicker cooling, particularly during start-up of the unit. Once the unit has reached

normal operating conditions the pump 16 may then be activated to circulate the water

collected in the reservoir or sump 14 through the water coil 11.

The operation of the air conditioning unit in cooling mode will now be described.

Upon entering the air conditioning unit via the air inlet 3, the air stream is directed

through the first air flow circuit of the heat exchanger 7. In passing through the first

circuit the air stream is cooled whilst the moisture content (humidity ratio) of the air

remains substantially constant. The air stream is then passed through the evaporative

coil 10 which acts to reduce both the temperature and moisture content of the air. Upon

passing from the evaporative coil 10 the air stream is then passed through the second

circuit of the heat exchanger whereupon the air stream absorbs heat from the first circuit.

This results in a reduction in the temperature of the air stream in the first circuit and an

increase in the temperature of the air stream flowing in the second circuit.

Upon leaving the second circuit of the heat exchanger, the air stream is passed

through the water coil 11 which acts to reduce the temperature of the air. The air stream

is subsequently passed through the cooling pad 12. The suction fan 5 acts to draw the air

stream through the unit and finally dispense the cooled air through the air outlet 4.

Figures 2a to 2c illustrate a variety of alternative configurations of the air

conditioning unit. Those components of the air conditioning unit in Figures 2a to 2c

which correspond with the components depicted in Figure 1 are provided with identical reference numerals. In the embodiments of Figures 2a to 2c the heat exchanger 7 is of a

cross flow type featuring first and second air flow circuits as described above. It should

therefore by appreciated that differing types of heat exchanger may be utilised in the

present invention.

The present invention may also be used in a reverse cycle mode for heating of the

environment. In this instance, hot water is circulated through the water coil 11. The

evaporative coil 10 then acts as a heating coil to improve the heating performance and

can be used in conjunction with the water coil 11 by employing a three-way diverter

valve to supply hot water to the water coil 11. Alternatively the water coil 11 may be

used in isolation from the evaporative coil 10.

Figure 3 illustrates a psychrometric chart which depicts an example of the air

temperature and moisture conditions of the air stream at various stages whilst passing

through the air conditioning unit. For the example shown, return air (shown as point A)

enters the air conditioning unit with a dry bulb temperature of 27°C and a wet bulb

temperature of 19°C. Upon passing through the first circuit of the heat exchanger, the

air stream is cooled to a dry bulb temperature of 17°C whilst moisture content (humidity

ratio) remains constant at 10.5 grams of moisture per kilogram of dry air (point B). The

air stream is then passed through the evaporative coil where it is cooled to a saturation

temperature of approximately 10.0°C to 11.5°C, with a moisture content of 8 grams of

moisture per kilogram of dry air (point C). The air stream then passes through the

second circuit of the heat exchanger whereupon the air stream is heated with a constant

moisture content to a dry bulb temperature of 20°C (point D). Upon passing through the

water coil the air stream is cooled to a dry bulb temperature of 16°C and a wet bulb temperature of 13°C (point E). The cooling pad then acts to reduce the dry bulb

temperature to 13.5°C whilst the wet bulb temperature is maintained at 13°C (point F).

A further embodiment of the invention is shown in Figure 4. In this case, the

water coil 11 extends through an upper partition separating the return air section and the

fresh air section. A duct entry 16 allows fresh air to pass through the top of the water

coil, thereby precooling the fresh outside air before entering path '8' while mixing with

the air in path '6'. In the heating cycle, a three way water valve can allow hot water

from a boiler to preheat the outside air, then heat the supply air to the required

temperature. In this mode, the cooling pad and pump would be switched off with the

cooling vapour compression coil.

Advantageously, it has been calculated that as a result of the present invention it is

possible to achieve an air conditioning unit of improved efficiency with substantially

higher air flows. Based upon the example above, it has been calculated that it is possible

to obtain the equivalent of 18 kilowatts of cooling with a 10 kilowatt unit designed in

accordance with the present invention. More particularly, it has been calculated that

with a 10 kilowatt air conditioning unit designed in accordance with the present

invention it is possible to cool an air stream flowing at a rate of 900 litres per second

from 27°C dry bulb temperature and 19°C wet bulb temperature to 13.5°C dry bulb

temperature and 13°C wet bulb temperature. Under the same conditions a conventional

10 kilowatt air conditioning unit would only achieve the equivalent cooling at an air

flow rate of approximately 500 litres per second. Based upon these calculations, the co¬

efficient of performance (COP) of an air conditioning unit designed in accordance with

the present invention is approximately 5.2:1, in comparison with a conventional air conditioning unit which would have a co-efficient of performance of 3: 1. Thus, the

invention represents both a practical and commercially significant improvement over the

prior art.

While the present invention has been described with reference to specific

examples, it will be appreciated by those skilled in the art that the invention may be

embodied in many alternative forms.

Claims

CLAIMS:-

1. An air conditioning apparatus including heat exchanging means having first and

second air flow circuits adapted to provide heat transfer therebetween, and an

evaporative coil, the evaporative coil being interposed between the first and the second

air flow circuits of the heat exchanging means such that an air stream flowing through

the air conditioning apparatus passes through the first air flow circuit and then through

the evaporative coil, before being passed through the second air flow circuit of the

heat exchanging means.

2. An apparatus according to claim 1, wherein the air stream enters the apparatus

through an inlet, and exits the apparatus through an outlet, for discharge to an

environment to be heated or cooled.

3. An apparatus according to claim 1 or claim 2 wherein said air stream is

subsequently passed through a water coil for further cooling or heating before being

discharged.

4. An apparatus according to any one of claims 1 to 3, wherein said air stream is

subsequently passed through an evaporative cooling pad prior to discharge.

5. An apparatus according to any one of the preceding claims, wherein the air

stream is drawn through the apparatus by means of a fan.

6. An apparatus according to any one of the preceding claims, further including a

water collection tray positioned beneath the evaporative cooling coil to collect

moisture extracted from the air stream passing through the coil.

7. An apparatus according to claim 6, wherein the water extracted from the air

stream is recirculated to a reservoir or sump, for utilisation in the water coil or the

evaporative cooling pad.

8. An apparatus according to any one of claims 3 to 7, further including a pump to

circulate water through the water coil.

9. An apparatus according to any one of claims 3 to 8, further including conduit

means arranged to introduce water from a mains supply for circulation in the water

coil.

10. An apparatus according to any one of claims 4 to 9, wherein water from the

evaporative coil is pumped directly to the evaporative cooling pad, to enhance cooling

during start up.

11. An apparatus according to any one of the preceding claims, being adapted to

operate in conjunction with a refrigerant compressor in either a normal cycle mode to

cool the environment into which the air stream is directed, or in a reverse cycle mode

to heat the environment.

12. An apparatus according to any one of the preceding claims wherein the heat

exchanging means includes a counterflow air to air heat exchanger.

13. An apparatus according to any one of the preceding claims wherein the heat

exchanging means includes a crossflow air to air heat exchanger.

14. An apparatus according to any one of claims 3 to 13 wherein the water coil

extends at least partially into the inlet to provide precooling or preheating of inflowing

air, upstream of the heat exchanging means. - i l ┬¼

ls. An apparatus substantially as herein described with reference to any one of the

embodiments of the invention shown in the accompanying drawings.