FIELD

[0001 ] The present invention relates to ventilation systems, and more particularly to air conditioning systems.

BACKGROUND OF THE INVENTION

[0002] Buildings require a make-up air supply to replace air exhausted from the building by other ventilation systems such as toilet and kitchen exhausts.

[0003] Make-up air that is supplied in hot humid climates with a high absolute humidity that has not been dehumidified can cause mold and mildew to form in the building when the temperature in the space is lowered by an air conditioning system.

[0004] Typical air conditioning systems are temperature controlled and do not fully dehumidify all the makeup air being drawn into the space.

OBJECT

[0005] It is the object of the present invention to overcome or ameliorate the above disadvantages, or to at least provide a useful alternative.

SUMMARY OF INVENTION

[0006] There is disclosed herein an air conditioning system for delivering air to a building enclosure. The air conditioning system includes a first refrigeration circuit having a first compressor, a first heat exchanger, a second heat exchanger, and a first expansion valve; and a second refrigeration circuit having a second compressor, a second evaporator, a second condenser, and a second expansion valve. The air conditioning system further includes a controller in communication with the first and second refrigeration circuits and configured to operate the first

refrigeration system when the air is above a predetermined humidity to provide air at a first predetermined temperature to the second refrigeration circuit. The controller is further configured to operate the second refrigeration circuit to cool the air received from the first refrigeration circuit to a predetermined dew point temperature and subsequently warm the air to a second predetermined temperature.

[0007] Preferably, the first refrigeration circuit includes a reversing valve, and the controller is configured to operate the reversing valve to direct refrigerant flow through the first refrigeration circuit based on a

predetermined air temperature and humidity, wherein in a first flow direction the first heat exchanger acts as a first condenser and the second heat exchanger acts as a first evaporator, and in a second flow direction the first heat exchanger acts as the first evaporator, and the second heat exchanger acts as the first condenser.

[0008] Preferably, the air conditioning system includes a first housing to house the first compressor and the first heat exchanger, and a second housing to house the second compressor, the second evaporator, the second condenser, and the second expansion valve, along with the second heat exchanger (associated with the first refrigeration circuit) and the first expansion valve.

[0009] Still preferably, the first housing is positioned outside the building enclosure, and is configured to eject heat absorbed in the first

refrigeration circuit outside the building enclosure, and the second housing is positioned inside the building enclosure and ducted to receive outside air, cool and reheat it and deliver it within the building enclosure.

[00010] Preferably, the first housing includes a first air duct for drawing air from outside the building enclosure. [0001 1 ] Still preferably, the first housing includes one or more fans operatively associated with the first air duct to draw air through the first refrigeration circuit.

[00012] Preferably, the second housing includes a second air duct for air delivery within the building enclosure.

[00013] Still preferably, the second housing includes one or more fans operatively associated with the second air duct to draw air through the second air duct.

[00014] In a preferred embodiment the controller includes a first sub controller operatively associated with the first refrigeration circuit and configured to regulate the speed and capacity of the first compressor based on temperature and humidity, and a second sub controller operatively associated with the the second refrigeration circuit

components and configured to regulate the operation of the second refrigeration circuit based on temperature and humidity.

[00015] Still preferably, the first sub controller and the second sub controller are in communication with each other.

[00016] Preferably, the first compressor is a variable speed compressor to adjust the flow rate of refrigerant through the first refrigeration circuit to alter the first refrigeration circuit cooling and/or heating capacity depending on ambient air conditions.

[00017] Still preferably, the second compressor is a fixed speed compressor and sized to gain only enough heat to reheat air from its required dew point temperature to its supply temperature.

[00018] Preferably, the first compressor is controlled by the first sub controller to a speed to ensure that heat removed by the first refrigeration circuit from air passing through the first evaporator is adjusted such that when further heat is absorbed by the second evaporator from the same passing air, the air temperature is lowered to its dew point set temperature and not overcooled.

[00019] Preferably, the first evaporator is placed upstream of the second evaporator.

[00020] Preferably, the air conditioning system includes one or more temperature sensors in communication with one or more sub controllers.

[00021 ] Still preferably, the air conditioning system includes humidity sensors in communication with one or more sub controllers.

BRIEF DESCRIPTION OF DRAWINGS

[00022] Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings wherein:

[00023] Figure 1 is a schematic side elevation of an indoor assembly for an air conditioning system according to the present invention;

[00024] Figure 2 is a schematic plan view of the indoor assembly of Figure 1 ;

[00025] Figure 3 is a schematic side elevation of and outdoor assembly for the air conditional system according to the present invention; and

[00026] Figure 4 is a schematic illustration of an air conditioning system according to the present invention. DESCRIPTION OF EMBODIMENTS

[00027] In the accompanying illustrations there is schematically depicted an air conditioning system 100 according to a preferred embodiment of the present invention. As best seen in Figure 4, the air conditioning system 100 comprises two independent refrigeration circuits 10, 20. The air conditioning system 100 is configured to deliver ventilation makeup air at a controlled air temperature and humidity to a building enclosure (not shown).

[00028] A first refrigeration circuit 10 includes a first compressor 32, a first heat exchanger 35, a first expansion valve 36, a second heat exchanger 37, and a reversing valve 34.

[00029] A second refrigeration circuit 20 includes a second compressor 23, a second evaporation coil 21 , a second expansion valve 25, and a second condenser 22.

[00030] As best seen in Figures 3 and 4, the compressor 32, the first heat exchanger 35 and the reversing valve 34 are housed in an outdoor assembly 18.

[00031 ] As best seen in Figures 1 , 2, and 4, an indoor assembly 28 houses the entire second refrigeration circuit 20 along with the second heat exchanger 37 and the expansion valve associated with the first refrigeration circuit 10.

[00032] Figures 1 and 2 show schematics of the indoor assembly 28. In this embodiment, the indoor assembly 28 includes a housing 1 1 having an internal divider wall 12 to form an air duct 13 in which the second heat exchanger 37, the evaporator, 21 , and the condenser 22 are housed, and a compartment 14 in which the expansion valves 25, 36 are housed along with a programmable logic controller (PLC) 51 (described below). The air duct 13 has one or more fans 15 to draw outside air through the air duct 13 from the intake, or entry point 16 to the exhaust, or discharge point 17 to cool, dehumidify and reheat the air.

[00033] The first and second heat exchangers 35, 37 can serve as either an evaporator or a condenser respectively, depending on the temperature of the outside air. This allows for heating of air in the indoor assembly 28 if necessary. The evaporator 21 which is operatively associated with the second refrigeration circuit 20 is positioned downstream of the second heat exchanger 37, and the condenser 22 is located downstream of the evaporator 21. A fan 15 draws outside ventilation makeup air through air duct 13 and delivers it to an exhaust, or discharge outlet 17.

[00034] The compartment 14 houses the second refrigeration circuit 20, which comprises the compressor 23, the thermal expansion valve 25, and connecting pipework 27 with filters, dryers and other components normally found in an air conditioning refrigeration circuit. The compartment 14 also houses an electronic thermal expansion valve 36 operatively associated with the first refrigeration circuit 10.

[00035] Referring to Figure 3, the outdoor assembly 18 comprises a housing 31 , a compressor 32, an oil separator 33, a reversing valve 34, a heat exchanger 35, a suction accumulator 38 with connecting pipework 39 with filters, dryers and other components normally found in an air conditioning system, all operatively associated with the first refrigeration circuit 10 and a variable speed fan 40 to draw air through the outdoor assembly 18 to pass through heat exchanger 35.

[00036] By placing the evaporator 37 before the evaporator 21 both reduces the required cooling load in the first refrigeration circuit 10 and raises the evaporating pressure (temperature) of the first refrigeration circuit 10 to minimize the difference between the first refrigeration circuit evaporator and condenser pressures 35, 37. Based on a typical operating condition for this air conditioning assembly 100, reducing this pressure difference will typically lead to an increase in the compressor 32 in the first refrigeration circuit 10 coefficient of performance (COP) of between 0.4 and 0.6 thereby reducing the energy required for any cooling load.

[00037] A programable logic (PLC) 50 located within the outdoor assembly 18 is configured to regulate the operation of the first

refrigeration circuit 10 and to communicate with a second PLC 51 located within the indoor assembly 28 which regulates the operation of the second refrigeration circuit 20.

[00038] As shown in Figure 4, a temperature sensor 53 is positioned within the outdoor assembly 18 to measure the refrigerant discharge gas temperature from the compressor 32, and another temperature sensor 54 is positioned to measure the temperature of the refrigeration circuit coil 35 and provide a signal indicative of these temperatures to the controller 50.

[00039] Also shown in Figure 4 are temperature sensors 52, 55 and 56 to measure outside air temperature, and air temperatures off refrigeration coils 37 and 22 respectively. A humidistat 57 is positioned to measure outdoor air humidity. The temperature and humidity sensors provide a signal to the PLC 51.

[00040] Fan 15 runs continuously to supply ventilation air to the building enclosure.

[00041 ] When the outside air humidity exceeds a predetermined set point the first refrigeration circuit 10 will operate. The compressor 32 will cause hot refrigerant gas to flow through pipework 39 to oil separator 33 then to reversing valve 34 which direct the hot refrigerant gas to flow to heat exchanger 35 which acts as a condenser to cool and condense the refrigerant to liquid, the liquid refrigerant then flows to the thermal expansion valve 36, then heat exchanger 37 which will function as an evaporator and cause the refrigerant liquid to evaporate to a gas by absorbing heat from the passing air and return to the compressor 32 via the reversing valve 34 and the suction accumulator 38. The fan 40, which is controlled by the PLC 50 will vary in speed based on the temperature difference measured between the outside air and the condenser 35 to ensure full refrigerant condensation occurs in the condenser 35. Hot refrigerant gas temperature measured at sensor 53 is used to ensure the compressor 32 does not overheat.

[00042] Temperature sensor 55 which is positioned to measure the temperature leaving the evaporator 37 communicates with PLC 51 which communicates with PLC 50 to cause the speed of the compressor 32 to increase or decrease to maintain a predetermined air temperature leaving the evaporator 37.

[00043] Once the air temperature leaving the evaporator 37 has reached its preset temperature, the second refrigeration circuit 20 will start operation. Air entering the inlet 16 of the indoor assembly 28 has been precooled to a predetermined set point temperature when passing through the evaporator 37. The cool air leaving the evaporator 37 is further cooled when passing through a second evaporator 21 to a preset dew point temperature to ensure it has the correct preset absolute humidity. This cold air then passes through the condenser 22 where it is warmed to predetermined set point temperature.

[00044] The air temperature leaving the indoor assembly 28 is monitored by temperature sensor 56 and communicated to the PLC’s 51 , 50. The PLC’s are configured to vary the speed of the compressor 32 to meet the programmed air condition requirement. [00045] The compressor 32 is a variable speed compressor, and as the ambient outside air temperature and humidity change the compressor 32 will increase or decrease its speed to maintain a constant air temperature leaving the evaporator 37. The PLC 50 is configured to control the compressor 32 to a speed to ensure that the heat removed by the first refrigeration circuit 10 from air passing through the evaporator 37 is adjusted such that when further heat is absorbed by the second

evaporator 21 the air temperature is lowered to its dew point temperature and not overcooled.

[00046] Because the air temperature reaching the second evaporator 21 is constant, the additional air cooling from the evaporator 21 and air heating from the condenser 22 remain the same unless the speed of the compressor 23 is varied.

[00047] The compressor 23 may be either a fixed or variable speed compressor depending on the variation in supply air temperature required. If the compressor 23 is a fixed speed compressor, the temperature of the air entering the building enclosure cannot be varied without effecting the absolute humidity of the air. A desired increase in temperature will increase the absolute humidity but the relative humidity in the duct 13 will remain approximately the same.

[00048] Since the second refrigeration circuit 20 is sized only to gain enough heat to reheat the air from its required dew point temperature to its supply temperature, it is smaller in size than the first refrigeration circuit 10.

[00049] In the above description the first PLC 50 is described as being located in the outdoor assembly 18 and the second PLC 51 is described as being in the indoor assembly 28. It is within the scope of the present invention for the first PLC 50 to be located in the indoor assembly 28 and the second PLC 51 is located in the outdoor assembly 18 or remotely. [00050] The above described invention provides an energy efficient ventilation system to supply fresh make-up air to an enclosed space at a predetermined humidity and temperature using two independent refrigerant circuits to cool the air to a desired dew point temperature and then reheat the air to maintain a comfortable space condition.

[00051 ] For example, to cool air from a condition of DB35C / WB26C to a desired condition of DB13C/ WB13C requires cooling of 43.4 kw / kg of air. On a 35°C day with a refrigeration condensing temperature of 50°C and an evaporating temperature of 8°C to achieve a 13°C air temperature, the COP of the compressor would typically be about 3.8 requiring 1 1.4 kw of electrical energy to power the compressor to perform this cooling load.

[00052] If there was a second refrigeration circuit combined with the first refrigeration circuit to reduce the air from DB35C / WB26C to DB15.5C / WB15.5C, then first circuit cooling load would be 36.5 kw/kg air. Since the evaporation temperature of the first refrigeration circuit has been raised by 2.5°C to 10.5°C, then the first refrigeration circuit compressor COP will increase from the original 3.8 to 4.2 requiring 8.7 kw electrical energy to power the compressor for this reduced cooling load. The second refrigeration circuit will lower the air condition from DB15.5C / WB15.5C to the same original condition DB 13C/ WB13C and discharge this heat back to the cooled air stream to reheat the air, then the condensing

temperature will reduce to the compressor minimum of approximately 30°C and with an evaporating temperature of 8°C to achieve the 13°C air temperature, the COP of the second refrigeration circuit compressor would typically be around 7.2 requiring 0.96 kw of electrical energy to power this second compressor to remove the second cooling load of 6.9 kw. The total electrical power required for this second option is 9.65 kw (8.7 first circuit+0.96 second circuit) versus the original first single cooling system option requirement of 1 1.4 kw, a power saving of approximately 15%. [00053] Advantageously, by having the second refrigerant circuit completely within an indoor unit, no third pipe connection is required between the indoor and outdoor units to supply hot gas for air reheating.

[00054] Although the invention has been described with reference to a specific example, it will be appreciated by those skilled in the art that the invention may be embodied in other forms.