Solar Powered Air Conditioner

Principles of Solar Powered Air Conditioning

1.The basic working principle of solar hybrid air conditioning

Summary of Operation:

In a Solar Hybrid  Air Conditioning System the sun is used as a heat source to reduce the energy needed to drive the cooling process of a typical air conditioning system which in turn reduces the electrical energy required to run the compressor.

The  Solar Hybrid  Air Conditioning System is similar to a standard a/c in that the refrigeration takes place by evaporating liquid with a very low boiling point. In both cases, when a liquid evaporates or boils, it absorbs energy in the form of heat and can continue to do so either until the liquid is all boiled or until everything has become so cold that the sub-zero boiling point has been reached.

The difference between the two is how the gas is changed back into a liquid so that it can be used again.  A standard air conditioning system uses a compressor to increase the pressure on the gas, forcing it into a liquid in the condenser coil. The change of state of the refrigerant starts to take place approximately 2/3rds of the way down the condenser.

The  Solar Hybrid Air Conditioning System uses a different method. It uses the heat from the sun to superheat the refrigerant which enables it to begin changing state in the top 2/3rds of the condenser coil.

By using this method it reduces the superheat of compression required to achieve the cooling process in the conventional cooling system as well as utilizing more of the cooling face of the condenser coil.

The conventional cooling system is only able to change a portion of the gas into a liquid state so that as it enters the metering device it is a saturated vapor.

The  Solar Hybrid  Air Conditioning process allows more of the refrigerant  to change state back into a liquid faster as well as allowing the transformation of more liquid into the metering device.

In our solar ac system the low pressure, low temperature refrigerant is compressed before being superheated in the heat exchanger of the solar absorption panel so that we now have both high pressure and superheated vapour.

Then the vapour is condensed into high pressure liquid at ambient temperature by passing through the condenser.

The high pressure liquid is converted into low pressure, low temperature liquid at room temperature when it passes through the capillary in the fan head.

This is achieved by throttling and decompression of the liquid into vapour at low pressure and low temperature.

This phase change absorbs energy out of the room in the condenser inside the fan head.

Air is blown through the condenser to distribute the cooling throughout the room.

Moisture forms on the surface of the condenser where it is piped away to top up the solar thermal heat exchanger.

In the heating cycle the condensers are reversed in sequence so that heat energy is released in the fan head instead of outside.

2. How much energy can be saved by solar hybrid a/c?

Comparison between Normal A/C and  Solar Hybrid

Product	Btu	Cooling(W)	Power(W)	EER	Saving
Conventional A/C	24,000	7200	3025	2.38	—
CSEA TKF72GW	24,000	7200	1884	3.82	37.71%
Conventional A/C	20,000	6000	2521	2.38	—
CSEA TKF60GW	20,000	6000	1546	3.88	38.67%
Conventional A/C	12,000	3500	1470	2.38	—
CSEA TKF35GW	12,000	3500	899	3.89	38.84%

3.      Can the Solar Hybrid A/C be installed by Do-it-yourself?

Only qualified tradesmen holding a CSEA Installation Certificate may install the CSEA Solar Hybrid A/C system. This is to ensure that installation is as per the installation manual and to qualify for the warranty.

4.      Warranty time and after sales service?

The warranty time for  solar hybrid a/c is 3years and the designed service life is 30 years. Most components are readily available locally, however, they are covered by the warranty in the warranty period.

5.     Does the solar collector need any special maintenance?

NO special maintenance is required once installed.

6.     Is the solar hybrid a/c 100% solar?

No. It still requires electric power to operate the compressor and the fans.

7.     How does the solar hybrid a/c work at night and in cloudy weather?

The  solar hybrid air conditioner works day and night and in rainy or cloudy weather. The solar panel will absorb and store solar thermal energy during the day. It only requires 4-5hours of sunshine for 15hrs continuous operation.

8.     What is the difference between Inverter a/c and solar hybrid a/c?

Inverter technology enables the a/c to operate at the most efficient compressor and fan speed when below full power. At full power it has no advantage over conventional a/c. Typically, an inverter will save up to 15% of the electricity required to operate except when it is on full power.

A solar hybrid a/c will continually save 38-50% over a conventional a/c and eliminate the high demand at peak times.

9.    What savings can I expect in my electricity bill?

	Output	RRP	CSE	kW/hr	Conv	kW/hr	Saving	Cost of	Saving	Payback
Model	kWth	Cost	EER		EER		kWe/hr	Elect	PA	years
35GW	3.5	$1,595	3.89	0.90	2.4	1.46	0.56	0.22	$269	5.92
60GW	6	$2,250	3.88	1.55	2.4	2.50	0.95	0.22	$459	4.90
72GW	7.2	$2,550	3.82	1.88	2.4	3.00	1.12	0.22	$537	4.75

Greenhouse Gas Saved over 10 years(Tonnes)

35GW 3.33

60GW 5.68

72GW 6.64

Supporting Data:

Heat Transfer

Heat transfer, or heat exchange, is a process of “heat migration” from one point, to another.

From a point of higher temperature to a point of lower temperature.

Tell me about heat transfer from the beginning, please.

What if I start at energy?

Energy is “the ability to do work”.

Work, in simple terms, is defined as force (F) applied to move any object, by a distance (x).

Hence, if the force required to move the object is larger, i.e. moving a train then the work done per distance moved is much larger than moving a bag of cotton.

The indestructible nature of energy:

Every atom has an internal energy.

This is due to the continuous motion of electron/s orbiting the neutron/s and proton/s. Electron has its own mass to move, so force is required. Electron has its own distance to move. Hence, energy is existent.

As long as the basic of all building blocks, namely electron, proton, and neutron exist, energy can neither be destroyed nor created.

Therefore, energy can only be transformed from one state, to another:

Consider a sample of gas, with a specified internal energy.Consider another sample of gas with lower internal energy.Now, due to the internal energy from the electrons, atoms or molecules will move in a specified random motion. The Speed that these particles (atoms or molecules) move, will depend on the internal energy. The higher its internal energy, the higher the speed of these particles.

Back to our samples of gas.

When these gases are brought into contact, the gas particles will start to collide with each other. Gas particles with higher internal energy, will collide with gas particles with lower internal energy.

Speed of these particles will be traded. The lower particles’ will increase in speed, and the higher gas particles’ speed will reduce speed.

Analogy

It is analogous to what happens when a white ball in snooker game hits a pack of snooker balls. Initially, the white ball will have a very high speed. As it impacts the pack of balls (which are initially at a standstill), the white ball will loose its speed tremendously, and the rest of the pack will gain some speed.

This is an example of how energy is transferred from one state, to another.

So, how can you say that heat is a form of energy?

A specific sample of gas, with temperature above 0 Kelvin, and a finite mass; has particles vibrating, rotating, or travelling at a high speed. In other words, these particles are moving.

Since these particles are in motion, the gas particles are doing work! Therefore, heat is a form of energy.

Change gas to liquid giving you cold :

Manufacturers of air conditioners use refrigerants because they have an attractive boiling temperature for heat exchange between air that we live in, and the refrigerant.

But, our atmospheric condition will not allow refrigerant to be in liquid state. Hence, we need to compress it enough, coupled with condensing it, to change the state from gas, to liquid. The energy from compression and condensation overcomes the internal energy of the refrigerant. Hence the state is changed from gas to liquid through compression and condensation.

This stage is coupled with compression, for two reasons:

1. to change the refrigerant’s state from high pressure gas to high pressure liquid
2. to avoid having a very large compressor to compress refrigerant beyond critical point – i.e. change gas to liquid without going through liquid-vapour phase. In other words, ensuring air conditioner efficiency.

Although compression alone may change the state of refrigerant from vapour to liquid, it is not efficient. A large amount of energy is consumed and you might not get cool air in the end. So, condensation is required. Condensation happens mainly in a heat exchanger, through a heat exchange process. The heat exchanger is known as the condenser.

Sneak peek into the basics:

Every atom and molecule of matter has a specific internal energy, as explained in the compression page. And due to this specific internal energy, different matter exists in different states (solid, liquid, or vapour) at a given pressure and temperature.

Solids will have atoms or molecules packed together very closely, hence the movement only involves rotation about each atom or molecule’s axis.

Liquid however, will have a close formation of molecules or atoms. The movement is much more flexible than solids, but still restricted to short distances. Liquid has higher molecule or atomic energy compared to solid, but lower energy compared to vapour.

Vapour has all the freedom in this world, to move in all directions possible, with large distances between each atoms or molecules, high speed and random in motion. It has the highest molecule or atomic energy between solid and liquid.

Our interest is in vapour and liquid phases, and the phase in between. The phase in between? Keep reading.

Condensation:

Condensation is defined as the state, when a vapour starts to change phase into liquid state, as a result of temperature drop.

It starts when a superheated vapour reaches its saturation point.

We have to bear in mind that condensation does not occur at a singular temperature. It occurs at different ranges of temperature. Reason being, the pressure of the vapour itself.

Compression page has explained that increasing the pressure will reduce the distance between the vapour molecules. Thus, vapour molecules will have lower net energy.

Decreasing the pressure will have a reverse effect, where the distance between the molecules will increase, and net molecular energy will increase.

So, if a gas or vapour has a higher net energy, more energy needs to be removed to reduce the distance between the molecules.

Similarly, lower net energy of vapour requires less energy removal for molecules distance to close.

What’s with all the molecule distance and energy removal?

As explained earlier, the molecule distance is a characteristic to different states of a matter. Solid, liquid, or vapour.

Energy can be in terms of work, or heat. And when condensation is in the picture, energy removal is in terms of heat.

Hence, as the pressure of the vapour increases, the heat removal required is smaller to condense it. This means that condensation of the matter starts to happen at a higher saturation (or boiling) temperature. This is good, as any temperature lower than the saturation temperature, means we will have a condensed liquid.

The flip side occurs for low vapour pressure.

Let us consider Refrigerant 12 as an example.

Referring to Rogers’ and Mayhew’s “Thermodynamic and Transport Properties of Fluids”:

• the saturation temperature at 1 bar is about -30 ^oC
• whereas the saturation temperature at 9.6 bar is about 40 ^oC

This means that we have to have ambient air at -30 ^oC for condensation of the refrigerant to occur at ambient pressure.

Well, if we have that kind of ambient temperature, we wouldn’t need cooling anymore would we?

You see, the ambient temperature for the compressed refrigerant does not have to be very low for condensation to occur. In fact the saturation temperature is higher than most ambient temperatures during hot summer. Hence heat exchange occurs from the refrigerant, to ambient air.

This is why we have to couple condensation with compression in air conditioner systems.

Bring the pressure up, close the gap between the gases, and remove the heat from the refrigerant to close the gap even more – we have liquid refrigerant!

Vapour, liquid and the phase in between:

This occurs when heat is continually removed from the vapour.

If all of the matter is in vapour form, then we call it superheated vapour, as there is no condensation.

Once the temperature drops to saturation line, we will have a mix of vapour and liquid. This, is the phase in between.

At this time, temperature will not drop. This is due to energy consumption of the atoms or molecules to bond and change phase from vapour, to liquid.

Temperature will not decrease until all vapour within an enclosed space is turned into liquid. This is the phase change.

Once in liquid form, the temperature will start to decrease again, until it meets freezing point. But that’s a different story.

Condensation in a real life example:

• Order a glass of iced lemon tea
• Watch condensation of water vapour happening on the glass