WO2006024066A1

WO2006024066A1 - Air conditioning system

Info

Publication number: WO2006024066A1
Application number: PCT/AU2004/001190
Authority: WO
Inventors: Neville Walter Williams; Brian Victor Stockwell
Original assignee: The State Of Queensland (Acting Through Its Department Of Public Works)
Priority date: 2004-09-02
Filing date: 2004-09-02
Publication date: 2006-03-09
Also published as: AU2004322949A1; CN101052844A; EP1787065A1

Abstract

An air conditioning system having multiple modes for cooling an enclosed indoor space. One of the modes is preferably a hybrid combining an evaporative system with a water pre-cooler system. The modes are activated or deactivated by a controller that monitors the indoor and outdoor temperatures, and also the temperature of water in the pre-cooler. The controller preferably maintains a relationship between the indoor temperature and the water temperature.

Description

AIR CONDITIONING SYSTEM

FIELD OF THE INVENTION

This invention relates to air conditioning systems, in particular but not only to a system having multiple modes of operation, including a hybrid mode in which the temperature of water used in an evaporative system is controlled by a refrigerative system.

BACKGROUND TO THE INVENTION

Conventional evaporative coolers use a fan to draw air through pads or other media saturated with water, before delivering the air into, a room. Evaporation of the water withdraws sensible heat from the air stream and thereby cools but generally also increases the relative humidity of the air. The sensible cooling effectiveness of the cooler depends on the temperature of the water and increases as the water temperature is reduced below the wet bulb temperature of the outdoor air. A water temperature lower than the outdoor air wet bulb temperature also tends to lower the absolute humidity of the air passing through the evaporative medium. Existing evaporative air conditioning systems have only limited temperature control over the air delivered by the evaporative cooler. Existing evaporative air conditioning systems also have limited capability to control the temperature of the enclosed indoor space within predetermined threshold limits. Also, existing evaporative air conditioning systems generally do not combine multiple modes of operation.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved air conditioning system, or at least to provide an alternative to existing systems.

In one aspect the invention may be stated as air conditioning apparatus for an enclosed space, including: an air delivery system that delivers air from the outside of the space to the inside of the space, an evaporative system which cools the air passing through the

Substitute Sheet (Rule 26) RO/AU delivery system by the evaporation of water, a pre-cooler system which cools the water before evaporation in the evaporative cooler, and a controller that provides multiple modes of operation by activating and deactivating the air delivery system, the evaporative system and the pre-cooler system, according to predetermined outside and inside temperature thresholds.

In another aspect the invention may be stated as air conditioning apparatus for an enclosed space, including: an air delivery system that passes air from outside the enclosed space to inside the enclosed space, an evaporative system which cools the air passing through the delivery system by the evaporation of water, a pre-cooler which cools the water before evaporation in the evaporative cooler, and a controller which activates the evaporative cooler when the temperature of air inside the space rises to a predetermined threshold, and which activates the pre-cooler when the temperature of the water in the evaporative cooler rises to a predetermined threshold.

LIST OF FIGURES

Preferred embodiments of the invention will be described with .respect to the accompanying drawings of which: Figure 1 shows air conditioning equipment with refrigerative and evaporative cooling systems and multiple modes,

Figure 2 is a table containing typical temperature control data for use of the equipment in a greenhouse,

Figure 3 is a table containing typical temperature control data for use of the equipment in a schoolroom,

Figure 4 shows simplified air conditioning equipment having a limited number of modes, and

Figure 5 is a psychrometric diagram outlining a combined evaporative and refrigerative cooling mode for the system in Figure 1.

Substitute Sheet (Rule 26) RO/AU DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings it will be appreciated that the equipment can be constructed in many different ways for a range purposes. The equipment described here is given by way of example only. Psychrometric processes will be well understood by a skilled reader and need not be described in detail.

Figure 1 shows an air conditioning system that operates to cool an enclosed space 10, such as a greenhouse or a room in a building. In a fully functional form the system has multiple modes including natural ventilation, forced ventilation, two or more cooling modes and possibly a heating mode. The modes of operation are determined to suit the geographical location and physical characteristics of the particular space, and to enable energy efficiency. The large arrows indicate airflow. The system includes an air delivery arrangement such as a main duct 11 that carries outside air into the space and may also include a recirculation duct 12 for heating purposes. A fan 13 draws or blows air through the main duct, with the air passing into and out of the space through apertures governed by motorised dampers 14, 15. The space may also have windows that are open or closed by human operators when required. A heating element 16 may also be provided in the main duct 11 so that the system may provide both cooling and heating modes if required.

The air conditioning system in Figure 1 has an evaporative cooling subsystem 20 including an evaporative medium 21, a water reservoir 22, and a pump 23 by which the water is drawn from the reservoir and released or sprayed onto the medium through pipe 24. In this example the evaporative medium is oriented vertically above the reservoir so that water raised by the pump drains down over the medium back into the reservoir. A range of different evaporative systems might be used. Outside air travelling through the duct 11 must pass through the evaporative medium and is able to exchange heat with the water on the medium. The arrangement also typically includes an electronic descaling device 34.

In a preferred form the descaling device 34 has treatment windings 35 that generate an electromagnetic effect in the surrounding water. In this example, the windings 35 are

Substitute Sheet (Rule 26) RO/AU located on a section of the pipe 24 that is folly submerged in the reservoir water. The descaler 34 and its windings 35 act to neutralise the bonding mechanism of a range of scale forming minerals thereby preventing crystallisation or reactions between the minerals that may form scale within the reservoir or pipe. The windings 35 generate a signal with a set of specific resonance frequencies that travels throughout the water stored in the reservoir as well as up and down the water stream in pipe 24. Other descaler systems may also be suitable.

The evaporative cooling subsystem 20 in Figure 1 operates in conjunction with a pre- cooling subsystem 25 that cools the water in reservoir 22 before passage over the evaporative medium 21. The pre-cooling subsystem may include a conventional heat transfer device such as a refrigerative compressor/condensing set that passes refrigerant through a refrigerant evaporator 26 immersed in the reservoir 22. Without pre-cooling, the temperature of the water tends to stabilise at the wet bulb temperature of the outside air passing through the evaporative medium. Also without pre-cooling, the dry bulb temperature of the air after passing through the evaporative medium depends on the saturation efficiency of the medium and will not be lower than the wet bulb temperature of the outside air. With pre-cooling the temperature of the water can be reduced below the wet bulb temperature of the outside air and thereby enhance the overall cooling effect of the air conditioning system. The absolute humidity of the air passing into the space 10 can also be reduced to a predetermined threshold so that relative humidity in the space does not rise above a predetermined threshold.

A controller 30 in Figure 1 receives data from a number of temperature sensors that are located in the air conditioning system, and possibly other sensors if required. The controller operates the dampers 14,15, the heating element 16, fan 13, the evaporative cooling system 20 and the pre-cooler 25 in response to the data. A sensor 31 determines the dry bulb temperature To of the outside air. A sensor 32 determines the temperature Tw of the water in the reservoir 22. A sensor 33 determines the dry bulb temperature Ti of the air in the enclosed space 10. The air conditioning system has multiple modes of operation and the controller has an electronic interface that allows a user to determine thresholds and

Substitute Sheet (Rule 26) RO/AU operational ranges for different modes according to the values of T₀, Tw, T₁. Preferred temperature thresholds are set by the user for heating and cooling of the space 10, and for the temperature of the water in the reservoir. A relationship between the temperatures of the space and the reservoir is preferably maintained by the controller, such as a fixed temperature difference set by the user. If a user adjusts the preferred temperature of the space, the controller correspondingly adjusts the temperature of the reservoir.

In a fully functional system such as shown in Figure 1, the operational modes for space 10 may include four cooling modes: (1) "natural ventilation" in which the motorised dampers 14, 15 are opened to allow natural air flow, (2) "mechanical ventilation" in which the dampers are open and the fan 13 is activated to enhance the air flow, (3) "evaporative air conditioning" in which the evaporative system 20 is activated and (4) "hybrid air conditioning" in which the pre-cooler is also activated. Warming modes may also be provided, including (5) "dead band" in which the dampers are closed and no other components are activated, and (6) "heating" in which the element 16 and fan 13 are activated. Occupants of the space are also expected to open or close any windows. In the cooling modes preferably all of the air that passes into the room is exhausted through the damper 15. In the heating mode, up to about 90% or more of the air may be recycled through duct 12. The characteristics of each mode, such as the range of temperatures over which the mode is active, are determined by the functional requirements of the particular space.

Figures 2a and 2b are tables indicating operation of the system in Figure 1 through a range of modes as might be used to condition the air space inside a greenhouse located in Queensland, Australia for example. Setpoints of 15°C and 24⁰C have been set by the user for heating and cooling, to meet requirements during winter and summer periods for example, with a setpoint of 10⁰C for the water in the reservoir. In Figure 2a, as the outdoor temperature To rises, during the morning for example, and the system moves through a sequence of modes from heating to hybrid cooling in order to maintain the inside temperature Ti. In Figure 2b, the outdoor temperature falls, during the evening for example, and the system moves through the sequence of modes in reverse order.

Substitute Sheet (Rule 26) RO/AU Figures 3 a and 3b are tables giving another example of the operation of the system in Figure 1, with a range of modes as might be used to condition the air space inside a school classroom in Queensland, Australia. A single indoor setpoint of 24°C is required for the classroom during the day. In Figure 3 a the temperature rises during the morning for example and operation of the air conditioning system changes from heating to cooling. In Figure 3b the temperature falls during the afternoon and again operation of the systems moves through a sequence of modes.

Figure 4 is an example of a simplified air conditioning system having only the capability to function in the various cooling modes. As in Figure 1, the system operates to cool an enclosed space 10, such as a greenhouse or a room in a building. The large arrows indicate airflow. The system includes an air delivery arrangement such as a main duct 11 that carries outside air into the space. A fan 13 draws air through the main duct, with the air passing into and out of the space through fixed apertures (not shown). The space may also have windows that are open or closed by human operators when required.

The evaporative cooling subsystem 20 in Figure 4 includes an evaporative medium 21, a water reservoir 22, and a pump 23 by which the water is drawn from the reservoir and released or sprayed onto the medium through pipe 24. The evaporative medium is oriented vertically above the reservoir so that water delivered by the pump drains down over the medium back into the reservoir. Outside air travelling through the duct 11 must pass through the evaporative medium and is able to exchange heat with the water on the medium. The pump/pipe arrangement typically also includes an electronic descaling device 34 with windings 35.

The evaporative cooling subsystem 20 in Figure 4 operates in conjunction with a pre- cooling subsystem 25 that cools the water in reservoir 22 before passage over the evaporative medium 21. The pre-cooling subsystem includes a heat transfer device such as a refrigerative compressor/condensing set that passes refrigerant through a refrigerant evaporator 26 immersed in the reservoir 22. A controller 30 receives data from a range of

Substitute Sheet (Rule 26) RO/AU temperature sensors and operates the evaporative cooling system 20 and the pre-cooler 25. A sensor 31 determines the dry bulb temperature To of the outside air. A sensor 32 determines the temperature Tw of the water in the reservoir 22. A sensor 33 determines the dry bulb temperature Ti of the air in the enclosed space 10. An electronic interface allows a user to determine thresholds and operational ranges for different modes according to the values of To, Tw, Ti. The scope of the modes of operation and setpoints for the temperature of the space 10 and the water in reservoir 22 are determined to suit the geographical location and functional requirements of the particular space.

Figure 5 is a psychrometric diagram outlining operation of the air conditioning system in Figure 1 for an outdoor air summer temperature of To= 34°C dry bulb and 28⁰C wet bulb (i.e. 64% relative humidity). The predetermined indoor air and water temperatures are respectively T₁ = 24°C and Tw = 9°C. The horizontal and vertical axes in this diagram are dry bulb temperature and absolute humidity respectively. The lines of constant relative humidity are those that curve upwards to the right and where the 100% relative humidity, or saturation, is represented by the top curve. Lines for determining wet bulb temperature slope upwards to the left and are read at the saturation line using the horizontal axis. For example, a dry bulb temperature of 30°C at 50% relative humidity corresponds to a wet bulb temperature of 22°C, while at 100% humidity the wet bulb temperature matches the dry bulb temperature. A high temperature is less uncomfortable when humidity is low.

In Figure 5, the outdoor air at condition A passes through the evaporative medium 21 to reach condition H, having a lower temperature and slightly higher relative humidity. The wet bulb temperatures are indicated by K and J respectively, and the absolute humidity by O and P respectively. The air at condition H is delivered to the space 10 and mixes with air in the space to reach condition E, and to be exhausted through aperture 15. The temperature of the water in reservoir 22 is indicated by condition L and is generally a function of the required room condition E, a fixed temperature difference of 15°C for example. Water exits the evaporative medium at condition M and lies below the dewpoint temperature N of the air supplied to the space. Water vapour therefore precipitates from

Substitute Sheet (Rule 26) RO/AU the air as it passes through the evaporative medium and the wet bulb temperature drops from condition K to condition J.

It will be appreciated that an air conditioning system of the kind described above can provide cooling through a range of operational modes and that the range of each mode can be controlled according to the requirements of local users. It will also be appreciated that a range of different components may be used to construct the system without limitation to the particular components described above.

Substitute Sheet (Rule 26) RO/AU

Claims

1. Air conditioning apparatus for an enclosed space, including : an air delivery system that delivers air from the outside of the space to the inside of the space, an evaporative system which cools the air passing through the delivery system by evaporation of water, a pre-cooler system which cools the water before evaporation in the evaporative system, and a controller that provides multiple modes of operation by activating and deactivating the air delivery system, the evaporative system and the pre-cooler system, according to predetermined outside and inside temperature thresholds.

2. Apparatus according to claim 1 wherein the controller operates a first cooling mode in which the air delivery system alone is activated.

3. Apparatus according to claim 1 wherein the controller operates a second cooling mode in which the air delivery system and the evaporative system are activated.

4. Apparatus according to claim 1 wherein the controller operates a third cooling mode in which the air delivery system, the evaporative system and the pre-cooler system are activated.

5. Apparatus according to claim 1 further including apertures for natural air flow through the space, wherein the controller opens and closes the apertures according to predetermined temperature thresholds.

6. Apparatus according to claim 5 wherein the controller operates a fourth cooling mode in which opening of the apertures alone is activated.

Substitute Sheet (Rule 26) RO/AU

7. Apparatus according to claim 1 wherein the controller sequentially activates the air delivery system, the evaporative system and the pre-cooler system as indoor and outdoor temperatures rise through predetermined thresholds.

9. Apparatus according to claim 1 further including heaters, wherein the controller activates and deactivates the heaters according to predetermined temperature thresholds to provide heating in the space.

10. Air conditioning apparatus for an enclosed space, including : an air delivery system that passes air from outside the enclosed space to inside the enclosed space, an evaporative system which cools the air passing through the delivery system by evaporation of water, a pre-cooler system which cools the water before evaporation in the evaporative system, and a controller which activates the evaporative system when the temperature of air inside the space rises to a predetermined threshold, and which activates the pre-cooler when the temperature of the water in the evaporative system rises to a predetermined threshold.

11. Apparatus according to claim 10 wherein the controller maintains a predetermined relationship between the threshold for the temperature of the water and the threshold for the temperature of the space.

12. Apparatus according to claim 10 wherein the predetermined threshold for the temperature of the air in the space is set by an operator.

13. Apparatus according to claim 11 wherein the relationship between the threshold for the water and the threshold for the space is set by an operator.

Substitute Sheet (Rule 26) RO/AU

14. Apparatus according to claim 10 wherein the controller activates the pre-cooler when the temperature of air outside the space and or the air inside the space rises to a predetermined threshold.

15. Apparatus according to claim 10 wherein the wet bulb temperature of the air passing through the evaporative system is reduced by the pre-cooler system.

Substitute Sheet (Rule 26) RO/AU