BACKGROUND In recent years, with increased interest in reduction of a building's carbon footprint and power grid loading, there has been substantial research done on building systems relying on renewable energy, in particular, for air conditioning systems integrated with solar panels. There are two main ways of harnessing solar energy in an air conditioning system. The first way relates to solar-power assisted air conditioning which utilises solar energy to power air conditioner components such as, for example, compressor, fan coil, and so forth. The second way relates to solar-heated air conditioning which utilises solar energy to heat up working fluid, increasing both temperature and pressure of refrigerant. In the second way, a solar collector is located downstream of a compressor where solar energy is utilised to increase temperature and pressure of the refrigerant. However, it is noted that the current ways of harnessing solar energy in an air conditioning system can be improved in relation to energy consumption.

SUMMARY In a first aspect, there is provided a solar air conditioning system, the system comprising: a solar collector configured to heat and compress working fluid to a predetermined temperature and a predetermined pressure; and a compressor downstream from the solar collector, the compressor including at least one sensor configured to determine temperature and pressure of the working fluid for determination of a work load of the compressor. It is advantageous that the work load of the compressor is reduced when the at least one sensor determines the temperature and pressure of the working fluid to be the predetermined temperature and the predetermined pressure respectively as the solar collector compensates for the reduced work load of the compressor, and preferably, the predetermined temperature and pressure is dependent on an amount of solar energy harvested at the solar collector.

There is also provided a method for conditioning air, the method comprising: heating and compressing, in a solar collector, working fluid to a predetermined temperature and a predetermined pressure; and determining, using at least one sensor in a compressor, a temperature and a pressure of the working fluid. Advantageously, the work load of the compressor is reduced when the at least one sensor determines the temperature and pressure of the working fluid to be the predetermined temperature and the predetermined pressure respectively as the solar collector compensates for the reduced work load of the compressor, and preferably, the predetermined temperature and pressure is dependent on an amount of solar energy harvested at the solar collector.

DESCRIPTION OF FIGURES In order that the present invention may be fully understood and readily put into practical effect, there shall now be described by way of non-limitative example only, certain embodiments of the present invention, the description being with reference to the accompanying illustrative figures, in which: Figure 1 shows a schematic view of a solar air conditioning system of the present invention. Figure 2 shows a pressure-enthalpy diagram of the system of Figure 1 .

Figure 3 shows a graph denoting power consumption of a compressor in the system of Figure 1 and a compressor of a conventional air conditioning system. Figure 4 shows an embodiment of a solar collector as used in the system of Figure 1 .

Figure 5 shows a process flow of a method for conditioning air of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a system and method for conditioning air, and provides enhancements compared to other air conditioning systems. For example, discharge air temperature of the system downstream from a condenser of the system is lower compared to other air conditioning systems under identical cooling load conditions. Correspondingly, less energy is dissipated to the ambient environment, and thus, less energy is consumed compared to other air conditioning systems.

Referring to Figure 1 , there is shown a schematic view of a solar air conditioning system 20. The solar air conditioning system 20 comprises a solar collector 26 configured to heat and compress working fluid to a predetermined temperature and a predetermined pressure upstream of a compressor 24 so as to reduce the work done by the compressor 24, the compressor 24 being downstream from the solar collector 26, the compressor 24 including at least one sensor 25 configured to determine temperature and pressure of the working fluid at which a work load of the compressor 24 can be reduced. The solar air conditioning system 20 can also include other typical components of an air conditioning system such as, a condenser 22, an evaporator 28, and a throttling valve 30. The pre-determined pressure and temperature of the compressor 24 is dependent on an amount of solar energy which is harvested by the solar collector 26. The higher the amount of solar energy harvested by the solar collector 26, the higher the pre-determined pressure and temperature of the compressor 24. Moreover, it should be noted that reducing the work load of the compressor 24 refers to reducing the work load of compressing a gas in the compressor 24 (as indicated in points 2 to 3 in Figure 2). Correspondingly, power consumed by the compressor 24 is reduced as well as the electricity consumed by the compressor 24.

Referring to Figure 4, there is shown an embodiment of the solar collector 26. The solar collector 26 includes a plurality of u-shaped copper pipes 64 sheathed with evacuated glass tubes 66, the copper pipes 64 being for passage of the working fluid. The solar collector 26 also has an inlet 60 and an outlet 62 for respective ingress and egress of working fluid which is a gas such as, for example, Refrigerant R407c. It should be appreciated that the solar collector 26 is configured to carry out heat absorption and compression via the copper pipes 64, and ambient heating via the evacuated glass tubes 66. The copper pipes 64 are submerged in a liquid medium to aid in storing thermal energy to be transferred to the working fluid via the copper pipes 64. The solar collector 26 also includes a vent 68 to minimise build-up of pressure due to evaporation of the medium.

During use of the solar air conditioning system 20, the work load of the compressor 24 is reduced when at least one sensor 25 determines the temperature and pressure of the working fluid to be the predetermined temperature and the predetermined pressure respectively (as discussed earlier). An increase in pressure and temperature upstream of the compressor 24 is dependent on an amount of solar energy which is collected. The higher the amount of solar energy harvested, the higher the increase in pressure and temperature upstream of the compressor 24.

Referring to Figure 1 , it should be noted that the working fluid undergoes two compression stages, firstly in the solar collector 26, and subsequently in the compressor 24, during circumstances when the compressor 24 is operational under reduced work load conditions. These conditions reduce power consumed by the compressor 24 as the total work done is shared by both the solar collector 26 and the compressor 24. In comparison to typical air conditioning systems, the work done is typically fully carried out by the compressor. Figure 2 shows a pressure-enthalpy diagram of the solar air conditioning system 20. Reference is also made to Figure 1 for the following description. The solar air conditioning system 20 follows through points 1 - 2 - 3 - 4 - 5 - 1 . Starting from point 3, working fluid leaves the compressor 24 at a higher pressure gaseous state at pressure P3 and temperature T3 and enters the condenser 22. Heat is rejected to the surroundings at the condenser 22, and the working fluid leaves the condenser 22 as subcooled liquid at temperature T4. Subsequently, from point 4 to 5, the working fluid is expanded through the throttling valve 30, thus, lowering both its pressure and temperature. At point 5, the working fluid at a lower pressure P5 and temperature T5 enters the evaporator 28 which absorbs heat from an ambient refrigerated space. The process after the evaporator 28 differs from other air conditioning systems. For typical air conditioning systems, the post-evaporator process is represented by process 1 - 3 (compressor work). In this regard, a compressor has to compress the working fluid from a lower pressure P1 and temperature T1 to the condenser pressure P3 and temperature T3. In the system 20, the working fluid undergoes two compressions, first by the solar collector 26 (process 1 -2), then followed by the compressor 24 (process 2-3).

In the system 20, the compressor 24 will operate at reduced load condition to cause a state of the working fluid to transition to a temperature (T3) and pressure (P3) after the solar collector 26. For instance, the solar collector 26 compresses the working fluid during process 1 - 2. Since the operating condition of the condenser 22 is at pressure P3 and temperature T3, the compressor 24 compresses the working fluid from state point 2 (temperature T2, pressure P2) to state point 3 (T3, P3). This is possible as a flow regulator/check valve (not shown) is installed between the evaporator 28 and the solar collector 26 in order to maintain uni-directional flow. As the pressure of the working fluid increases along solar collector 26, the flow regulator regulates the flow in such a way so that the flow is always from the evaporator 28 to the solar collector 26, not the other way around. Figure 3 shows a first line 40, denoting power consumption by a compressor of a typical air conditioning system, while a second line 42 denotes power consumption by the compressor 24 of the solar air conditioning system 20, with both the air conditioning systems having identical cooling loads. It should be noted that the first line 40 indicates higher power consumption at longer durations compared to the second line 42. This shows the lower power consumption of the solar air conditioning system 20. It should be appreciated that the compressor 24 of the solar air conditioning system 20 consumes reduced power as the work load is shared with the solar collector 26. Referring to Figure 5, there is shown a process flow of a method 80 for conditioning air. The method 80 can be carried out using the solar air conditioning system 20 as described earlier, or can be carried out using any other system and apparatus. The method 80 will be described using components of the solar air conditioning system 20 for the sake of clarity,

The method 80 comprises heating and compressing, in a solar collector 26, working fluid to a predetermined temperature and a predetermined pressure (82) such that the work done by the compressor 24 is reduced. The predetermined temperature and the predetermined pressure is dependent on the amount of harvested solar energy. The higher the amount of solar energy harvested by the solar collector 26, the higher the pre-determined pressure and temperature of the compressor 24.

The method 80 includes determining, using at least one sensor 25 in a compressor 24, a temperature and a pressure of the working fluid (84). The work load of the compressor 24 is reduced when the at least one sensor 25 determines the temperature and pressure of the working fluid to be the predetermined temperature and the predetermined pressure respectively. It should be noted that with the application of the method 80, if the work load of the compressor 24 is reduced, power consumption of the solar air conditioning system 20 is correspondingly lower even though the solar air conditioning system 20 is able to provide a cooling load which consumes more power for other air conditioning systems.

Whilst there have been described in the foregoing description preferred embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the present invention.