AU2019201541B2

AU2019201541B2 - An air conditioning system and a method of operating an air conditioning system

Info

Publication number: AU2019201541B2
Application number: AU2019201541A
Authority: AU
Inventors: Kerry Lee Evans; Subhash Singheshwar Jha; Stephen James Pople
Original assignee: TEMPERZONE Ltd
Current assignee: Temperzone Ltd
Priority date: 2018-03-08
Filing date: 2019-03-06
Publication date: 2025-02-27
Anticipated expiration: 2039-03-06
Also published as: AU2019201541A1

Abstract

An air conditioning system for controlling the temperature and humidity of a conditioned space is provided. The system comprises a first refrigerant circuit comprising a first indoor coil and a reheat heat exchanger and a second refrigerant circuit comprising a second indoor coil. The system further comprises ducting comprising at least one inlet which is in fluid communication with the conditioned space, the ducting configured to direct inlet air over the first and second indoor coils in parallel, from the indoor coils to the reheat heat exchanger, and from the reheat heat exchanger to one or more outlets which are in fluid communication with the conditioned space. The system can select different modes of operation depending on the temperature and humidity of the air in the conditioned space, thereby reducing energy consumption. 15 (NY 00 r-4 r-. JF I L i -r r-4 LI -- -- -- "I I, r*-4

Description

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AN AIR CONDITIONING SYSTEM AND A METHOD OF OPERATING AN AIR CONDITIONING SYSTEM TECHNICAL FIELD

The present invention relates to an air conditioning system and a method of operating an air

conditioning system.

BACKGROUNDART

Most commercial buildings, for example supermarkets, have systems which condition the interior air.

Air conditioning of large spaces can be energy intensive and can result in large electricity supply costs.

As well as wishing to minimise these costs, businesses are increasingly aware of the reputational

benefits of being seen to minimise energy use.

In addition to temperature control, an important function of air conditioning systems is

dehumidification, that is, removing moisture from the air. One measure of the amount of moisture in

the air is its "dew point". The dew point is the temperature to which the air must be cooled to become

saturated with water vapour (assuming other variables remain constant). A high dew point indicates

relatively humid air, while a low dew point indicates relatively dry air. Another measure is relative

humidity, which represents the amount of water vapour present in air expressed as a percentage of the

amount needed for saturation at the same temperature. By contrast, absolute humidity is a measure of

the total mass of water vapor present in a given volume of air.

Dehumidification is usually achieved by lowering the temperature of the air below its dew point, such

that some of the water vapour in the air condenses, thereby lowering the absolute humidity of the air.

.0 Reheating this air results in conditioned air which has a lower relative humidity. However, heat is

released by the change of phase from water vapor to liquid water during the condensation process, and

the air conditioning system must expend energy to remove this heat.

All references, including any patents or patent applications cited in this specification are hereby

incorporated by reference. No admission is made that any reference constitutes prior art. The

discussion of the references states what their authors assert, and the applicants reserve the right to

challenge the accuracy and pertinency of the cited documents. It will be clearly understood that,

although a number of prior art publications are referred to herein, this reference does not constitute an

admission that any of these documents form part of the common general knowledge in the art, in New

Zealand or in any other country.

Unless the context clearly requires otherwise, throughout the description and the claims, the words

"comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an

exclusive or exhaustive sense, that is to say, in the sense of "including, but not limited to".

It is an object of the present invention to address the foregoing problems or at least to provide the

public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing

description which is given by way of example only.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided an air conditioning system for

controlling the temperature and humidity of a conditioned space, the system comprising:

• a first refrigerant circuit comprising an indoor coil, a reversing valve, an accumulator, a variable

speed inverter compressor, a modulating valve, an outdoor coil, a first electric expansion valve,

a second electric expansion valve and a reheat heat exchanger;

• a second refrigerant circuit comprising a second indoor coil, a second reversing valve, a second

accumulator, a second variable speed inverter compressor, a second outdoor coil, and a third

electric expansion valve;

• ducting comprising at least one inlet which is in fluid communication with the conditioned

space, the ducting configured to direct inlet air, comprising air from the at least one inlet, over

the first and second indoor coils in parallel, from the indoor coils to the reheat heat exchanger,

and from the reheat heat exchanger to one or more outlets which are in fluid communication

with the conditioned space.

Preferably the system is operable in a plurality of modes, the modes comprising:

• a first mode wherein the air supplied to the outlet(s) is dehumidified and cooled relative to the

air in the conditioned space; and

• a second mode wherein the system does not change the absolute humidity of the air as it

travels from the inlet(s) to the outlet(s) and the the air supplied to the outlet(s) is cooler than

the air in the conditioned space.

Alternatively, the system is operable in a plurality of modes, the modes comprising any two or more of the following:

• a first mode wherein the air supplied to the outlet(s) is dehumidified and heated relative to

the air in the conditioned space;

• a second mode wherein air supplied to the outlet(s) is dehumidified relative to the air in the

conditioned space, but the temperature of the air supplied to the outlet(s) is substantially

equal to the temperature of the air in the conditioned space.

• a third mode wherein the air supplied to the outlet(s) is dehumidified and cooled relative to

the air in the conditioned space;

• a fourth mode wherein the air supplied to the outlets is heated relative to the air in the

conditioned space, but the absolute humidity of the air supplied to the outlet(s) is

substantially equal to the absolute humidity of the air in the conditioned space;

• a fifth mode wherein the system does not change the temperature or humidity of the air as

it travels from the inlet(s) to the outlet(s); and

* a sixth mode wherein the system does not change the absolute humidity of the air as it

travels from the inlet(s) to the outlet(s) and the the air supplied to the outlet(s) is cooler

than the air in the conditioned space.

Preferably the system is capable of operating in each of the six modes.

According to a second aspect of the present invention there is provided a method of operating an air

conditioning system comprising:

• a first refrigerant circuit comprising an indoor coil, a reversing valve, an accumulator, a

variable speed inverter compressor, a modulating valve, an outdoor coil, a first electric expansion valve,

a second electric expansion valve and a reheat heat exchanger;

accumulator, a second variable speed inverter compressor, a second outdoor coil, and a third expansion

valve;

space, the ducting configured to direct inlet air, comprising air from the least one inlet, over the

first and second indoor coils in parallel, from the indoor coils to the reheat heat exchanger, and from the reheat heat exchanger to one or more outlets which are in fluid communication with the conditioned space, the method comprising: i) determining the temperature and dew point of the air in the conditioned space; ii) operating the system in a first mode if the dew point of the air in the conditioned space is above a preselected maximum dew point and the temperature of the air is above a preselected maximum temperature; and iii) operating the system in a second mode if the dew point of the air in the conditioned space is below a preselected maximum dew point and the temperature of the air is above a preselected maximum temperature; wherein, in the first mode, the air supplied to the outlet(s) is cooled and dehumidified relative to the air in the conditioned space; and in the second mode, the system does not change the absolute humidity of the air as it travels from the inlet(s) to the outlet(s) and the air supplied to the outlet(s) is cooler than the air in the conditioned space.

Preferably the method further comprises:

operating the system in a third mode if the dew point of the air in the conditioned space is above a

preselected maximum dew point and the temperature of the air is above a preselected maximum

temperature;

operating the system in a fourth mode if the dew point of the air in the conditioned space is above a

preselected maximum dew point and the temperature of the air is between preselected maximum and

minimum temperatures;

operating the system in a fifth mode if the temperature of the conditioned space is below a preselected

minimum temperature,

operating the system in a sixth mode if the dew point of the air in the conditioned space is between a

preselected maximum and minimum dew point and the temperature of the conditioned space is

between a maximum and minimum preselected temperature, wherein,

* in the third mode the air supplied to the outlet(s) is dehumidified and cooled relative to the

air in the conditioned space;

• in the fourth mode the air supplied to the outlets is heated relative to the air in the

• in the fifth mode the air supplied to the outlets is heated relative to the air in the

substantially equal to the absolute humidity of the air in the conditioned space; and

• in the sixth mode the air supplied to the outlets is the same the temperature and humidity

as the air in the conditioned space.

According to a further aspect of the invention there is provided an air conditioning system for

controlling the temperature and humidity of a conditioned space substantially as herein described with

reference to the accompanying drawings.

According to a further aspect of the invention there is provided a method of operating an air

conditioning system substantially as herein described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is

given by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of an air conditioning system of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to Figure 1, an air conditioning system according to one embodiment of the present invention

is generally referenced by arrow 100. The system comprises at least two separate refrigerant circuits.

A first refrigerant circuit 101 comprises a first indoor coil 1, a first reversing valve 2, a first accumulator

3, a first variable speed inverter compressor 4, a first modulating valve 5, a first outdoor coil 6, a first

electric expansion valve (EEV) 7, a second electric expansion valve 8 and a reheat heat exchanger 9.

Unless the context clearly requires otherwise, reference herein to a "coil" describes a heat exchanger which can operate as an evaporator (preferably a direct expansion evaporator) or a condenser, as required.

A second refrigerant circuit 102 comprises a second indoor coil 11, a second reversing valve 12, a

second accumulator, a second variable speed inverter compressor 15, a second reversing valve 12, a

second outdoor coil 13, and a third electric expansion valve 14. In some embodiments (not shown) the

second refrigerant circuit 102 comprise additional components, for example a second modulating valve,

a fourth electronic expansion valve and a second reheat heat exchanger, so that the second refrigerant

circuit 102 can operate in the same manner as the first refrigerant circuit 101.

In some embodiments one or both reversing valves 2, 12 may be omitted, although these embodiments

may not be capable of the modes of operation described below in which the respective indoor coils

operate as condensers.

Ducting 20 directs inlet air (typically comprising a combination of return air from one or more inlets 21

which are in fluid communication with the conditioned space, and fresh air 19 from outside the

building) over the first and second indoor coils 1, 11 in parallel (i.e. air which flows over one indoor coil

does not flow over the other). From the indoor coils 1, 11, the inlet air travels over the reheat heat

exchanger 9 and is then directed as supply air to one or more outlets 22 (for example diffusers) which

are in fluid communication with the conditioned space.

A controller 16 controls the compressors, EEVs, reversing valves and modulating valves based on

information from one or more temperature sensors 23 which sense the temperature of the conditioned

space or inlet air, one or more humidity sensors 24 which sense the humidity of the conditioned space

or inlet air, one or more temperature sensors 25 which sense the temperature of the supply air, one or

more temperature sensors 29, 33 which sense the temperature of the refrigerant returning to the

compressors, one or more temperature sensors 27, 31 which sense the temperature of the refrigerant

exiting the compressors, one or more pressure sensors 28, 32 which sense the pressure of the

refrigerant as it evaporates, and one or more pressure sensors 26, 30 which sense the pressure of the

refrigerant as it condenses.

Operating modes

Possible modes of operation of systems in accordance with embodiments of the invention are

described below. Modes are described below in no particular order, and reference to a system being operable with any particular mode does not infer that it is necessarily also operable with lower numbered modes.

In one embodiment the system may be capable of operating in at least Mode 3 and Mode 6 as

described below. In another embodiment a system may be capable of operating in Mode 3, Mode 6 and

at least one other mode as described below. In a further embodiment a system may be capable of

operating in each of the seven modes described below, as required. In a still further embodiment of the

invention the system may be capable of operating in any two or more of the modes described below.

Mode 1 - Heating and dehumidifying

A first mode may be used where the air in the controlled space must be both dehumidified and heated,

that is, where heating alone will not lower the relative humidity (i.e. lower the dew point) of the air

sufficiently.

In this mode, the first reversing valve 2 is set such that first indoor coil 1 operates as an evaporator and

the first outdoor coil 6 operates as a condenser. Inlet air is cooled and dehumidified by the first indoor

coil 1.

The second reversing valve 12 is set such that the second indoor coil 11 operates as a condenser and

the second outdoor coil 13 operates as an evaporator. Inlet air is heated by the second indoor coil 11.

The inlet air from the first and second indoor coils is combined and then passed through the reheat heat

exchanger 9 and heated to a temperature above the target temperature of the conditioned space, and

then directed to the conditioned space.

The controller 16 varies the speed of the compressors, the opening of the EEVs 7, 8 and the setting of

the modulating valve 5 to achieve a set temperature and humidity for the supply air.

Mode 2 - Dehumidification

This mode is used when the humidity of the air in the controlled space is higher than required (i.e. the

dew point is too high), but the temperature of the air in the controlled space is within a preselected

"target" range.

coil 1 and is then re-heated by the reheat heat exchanger 9 to a temperature approximately equal to

that of the temperature in the controlled area.

In this mode the second circuit 101, if provided, may not operate in order to conserve power.

Mode 3 - Cooling - High latent heat

This mode is used when the dew point of the air is higher than a preselected maximum and the

temperature of the conditioned space is lower the preselected target temperature range. In this mode

the first reversing valve 2 is set such that the first indoor coil 1 operates as an evaporator and the first

outdoor coil 6 operates as a condenser. Inlet air is cooled and dehumidified by the first indoor coil 1,

with the inverter compressor speed controlled to achieve an evaporating temperature which is below

the set dew point of the conditioned space. The first modulating valve 5 may direct relatively little

refrigerant flow to the reheat heat exchanger 9, so the inlet air from the first indoor coil 1 is reheated to

a relatively low minimum temperature only. Preferably the reheat temperature is selected to minimize

condensation in the ducts.

The second reversing valve 12 may also be set such that second indoor coil 11 operates as an

evaporator and the second outdoor coil 13 operates as a condenser. Inlet air is cooled and dehumidified

by the second indoor coil 11.

The supply air is supplied to the conditioned space at a temperature below the set temperature range,

but at or above a minimum supply air temperature.

Mode 4 - Heating

This mode may be used where the temperature of the air in the controlled space is below the target

temperature range.

. In this mode, the first reversing valve 2 is set such that the first indoor coil 1 operates as a condenser

and the first outdoor coil 6 operates as an evaporator. Inlet air is heated by the first indoor coil 1.

In this mode the controller 16 varies the settings of the compressor(s) and first EEV 7 to try to hold the

condensing temperature at a preselected temperature. The second EEV 8 is used to maintain a positive

pressure on the outlet check valve of the reheat coil to balance the refrigerant charge.

The supply air is supplied to the conditioned space at a temperature above the target temperature

range.

Mode 5 - Air circulation

This mode may be used where the relative humidity and temperature are both within the preselected

set ranges. In this mode the compressors 4, 15 do not operate, so the air is circulated by the system

without change to the temperature or humidity of the air.

Mode 6 - Cooling - High sensible heat

This mode may be used where the air in the conditioned space needs to cooled but not dehumidified.

As with Mode 3, the first reversing valve 2 is set such that the first indoor coil 1 operates as an

evaporator and the first outdoor coil 6 operates as a condenser. However, in this mode the

temperature of the first indoor coil 1 is set to a higher temperature than Mode 3, preferably just above

the dew point of the inlet air. In this way the inlet air is cooled but not dehumidified, and energy

consumption is minimized by performing only sensible cooling of the inlet air. The second refrigerant

circuit 102 preferably operates in substantially the same manner.

The inlet air from the first and second inlet is combined and then passed through the reheat heat

exchanger 9 and to the conditioned space. In this mode no additional heat needs to be added to avoid

condensation, and so the reheat heat exchanger is not in operation.

Mode 7 - Standard Cooling

This mode may be used where cooling is required in combination with a small amount of

dehumidification. This mode is similar to Mode 3. However, in Mode 7 the system reduces energy use

by setting the evaporator temperature higher than in Mode 3. As with Modes 3 and 6, the inlet air from

the first and second inlet is combined and then passed through the reheat heat exchanger 9 and heated

to a minimum supply air temperature.

Exemplary set points

Table 1 below sets out non-limiting examples of evaporator temperature set points, condenser set

points and supply air temperature set points for an embodiment of the present invention.

Table 1

Mode Evaporator set point Condenser set point Supply air set point

1 6°C 44°C N/A

2 6°C N/A 21°C

3 6°C N/A >10°C

4 N/A 44°C N/A

5 N/A N/A N/A

6 12°C N/A N/A

7 10°C N/A >10°C

In some embodiments the evaporator set point may be periodically or continuously varied, and may be

calculated as a function of, or an offset to, the conditioned space dew point.

When in Mode 4, the controller 16 may vary the evaporator temperature to minimize energy use while

ensuring the system receives sufficient energy to operate at the required condenser set point. Similarly,

during Modes 2, 3, 6 and 7 the controller may vary the condenser temperature to minimize energy use

while rejecting sufficient energy to allow the system to operate at the required evaporator set point.

Those skilled in the art will appreciate that the present invention provides systems and methods for

conditioning air which are effective and which minimize or at least reduce energy use.

The invention may also be said broadly to consist in the parts, elements and features referred to or

indicated in the specification of the application, individually or collectively, in any or all combinations of

two or more of said parts, elements or features.

Where in the foregoing description reference has been made to integers or components having known

equivalents thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments

described herein will be apparent to those skilled in the art. Such changes and modifications may be

made without departing from the spirit and scope of the invention and without diminishing its

attendant advantages. It is therefore intended that such changes and modifications be included within

the present invention.

Aspects of the present invention have been described by way of example only and it should be

appreciated that modifications and additions may be made thereto without departing from the scope

thereof.

Claims

WHAT WE CLAIM IS:

1. An air conditioning system for controlling the temperature and humidity of a conditioned space,

the system comprising:

a second electric expansion valve and a reheat heat exchanger;

electric expansion valve; and

* ducting comprising at least one inlet which is in fluid communication with the conditioned

with the conditioned space.

2. The air conditioning system of claim 1 wherein the system is operable in a plurality of modes,

the modes comprising:

air in the conditioned space; and

* a second mode wherein the system does not change the absolute humidity of the air as it travels

from the inlet(s) to the outlet(s) and the the air supplied to the outlet(s) is cooler than the air in

the conditioned space.

3. The air conditioning system of claim 1 wherein the system is operable in a plurality of modes,

the modes comprising any two or more of the following:

• a first mode wherein the air supplied to the outlet(s) is dehumidified and heated relative to the

air in the conditioned space;

conditioned space, but the temperature of the air supplied to the outlet(s) is substantially equal to the temperature of the air in the conditioned space;

• a third mode wherein the air supplied to the outlet(s) is dehumidified and cooled relative to the

air in the conditioned space;

conditioned space, but the absolute humidity of the air supplied to the outlet(s) is substantially

equal to the absolute humidity of the air in the conditioned space;

• a fifth mode wherein the system does not change the temperature or humidity of the air as it

travels from the inlet(s) to the outlet(s); and

* a sixth mode wherein the system does not change the absolute humidity of the air as it travels

the conditioned space.

4. The air conditioning system of claim 3 wherein the system is capable of operating in each of the

six modes.

5. A method of operating an air conditioning system, the air conditioning system comprising:

a second electric expansion valve and a reheat heat exchanger;

expansion valve; and

first and second indoor coils in parallel, from the indoor coils to the reheat heat exchanger, and

from the reheat heat exchanger to one or more outlets which are in fluid communication with

the conditioned space,

the method comprising:

i) determining the temperature and dew point of the air in the conditioned space; ii) operating the system in a first mode if the dew point of the air in the conditioned space is above a preselected maximum dew point and the temperature of the air is above a preselected maximum temperature; and iii) operating the system in a second mode if the dew point of the air in the conditioned space is below a preselected maximum dew point and the temperature of the air is above a preselected maximum temperature; wherein, in the first mode, the air supplied to the outlet(s) is cooled and dehumidified relative to the air in the conditioned space; and in the second mode, the system does not change the absolute humidity of the air as it travels from the inlet(s) to the outlet(s) and the air supplied to the outlet(s) is cooler than the air in the conditioned space.

6. The method of claim 5 further comprising the steps of:

i) operating the system in a third mode if the dew point of the air in the conditioned space is

above a preselected maximum dew point and the temperature of the air is above a preselected

maximum temperature;

ii) operating the system in a fourth mode if the dew point of the air in the conditioned space is

above a preselected maximum dew point and the temperature of the air is between preselected

maximum and minimum temperatures;

iii) operating the system in a fifth mode if the temperature of the conditioned space is below a

preselected minimum temperature,

iv) operating the system in a sixth mode if the dew point of the air in the conditioned space is

between a preselected maximum and minimum dew point and the temperature of the

conditioned space is between a maximum and minimum preselected temperature,

wherein,

air in the conditioned space;

* in the fourth mode the air supplied to the outlets is heated relative to the air in the

* in the sixth mode the air supplied to the outlets is the same the temperature and humidity

as the air in the conditioned space.