Vapor Absorption Airconditoning v/s Vapor compression

I also have few questions related to your question.

Are you not happy with Vapor compression system for refrigeration in automobiles?

Do you feel that Vapor absorption system for refrigeration is better than Vapor compression system for refrigeration, if yes in what ways?

Have you enquired with OEM like Dephi, Denso, Subros etc, why they use Vapor compression system only for refrigeration why not Vapor absorption? OR you are requesting us to enquire on behalf of you?

Are you aware of shortcomings of Vapor absorption system?

Please reply me on the above before I react to your questions.

Yes. i am not happy with vapor compression system

Reason:

1)As its what which is consuming lots of power from the engine.

2)Statistics say that only 35 - 40% of energy is converted into mechanical work the rest goes waste as engine heat and exhaust which can be utilised for Vapor absorption.

3)Reduced vibrations as no compressor. On size of VAR i am little confused. I hope we can make it compact with the microscale hat transfer technology and miniaturization of absorber and deabsorber.

4)I have gone thru website of OEMS all use Vapor compression. i didnt enquire. can u on behalf of me and forum?

5) Yes i am aware of shortcomings - COP is low and many other, however we engineers should think how to overcome these shortcomings while its benificiary in terms of Zero ODP and Global warming.

Now i would request all the HVAC engineers and mechanical engineers or the people with the knowledge in this domain, reply to this thread.

Naik, Adsorption systems are less efficient that those based on compression and expansion. That is why they exist on the margins of society, where electricity is scarce, but heat can come from various fuels. Adsorption systems are also dependent on a stable and level platform to allow gravity and capillary forces to move fluids around - a moving car is not stable enough.

links

http://en.wikipedia.org/wiki/Absorption_refrigerator

I'm new to this so correct me if I'm wrong, but aren't absorption systems used in RVs and boats? Those platforms are certainly not very stable.

Thanks nitesh for your quick response, in fact I'm late. I do not agree with 1 & 2, because more energy is required for VAR system due to very poor COP, almost 20 to 25% of VCR system. VAR system is viable only when lot of waste heat is available. Waste heat from exhaust is not sufficient to run a VAR system of required capacity. In large engines waste heat from exhaust is used at turbocharger and preheating of inlet air for combustion to improve engine efficiency. Besides this following are the other reasons not in favour of VAR system in automobiles:

1. "Reduced vibrations as no compressor" I agree with you but vehicle itself is like vibrating platform in which is not desirable for VAS system.

2. There are only two types of VAR system I know, Ammonia-Water and Water-LiBr. Both systems have its own shortcomings with respect to automobiles.

- Ammonia is a toxic gas, any minute leak also may be uncomfortable.

- LiBr work with vacuum. Any small air ingress in the system may cause very heavy corrosion in piping and equipments. LiBr leak may badly affect other areas of automobile.

As these issues are related with safety and health hazard, OEM's are not venturing in to it. But still let-us hope that these issues will be suitably addressed by engineers in future.

Thanks for the Reply. Looking forward for some more comments to make the point strong enough for not to go with Vapor absorption.

Hello,

you are quite right, the vapour absorption cycle does not figure in the auto industry. I have been planning to build a unit for years. There are a number of issues with the vapour absorption cycle.

1) you could use the ammonia version, but in an accident there could be additional health issues (over the accident itself). The other alternative is the lithium bromide version.

2) The LiB generally involves pumped fluid which negates some of simplicity that could be possible and adds reliability issues. Additional to this is that these systems can get crystallisation, whereby the salt accumulates in certain areas and the system has to be decrystallised. This is often done automatically on big commeercial units.

3) The Coefficient of Performance (COP) of a vapour compression unit is around 4, the COP of the LiB units is about 1.

4) the energy to drive the LiB units is free (heat in the water of the engine) but due to its low temperature, the radiator (evaporator) must be large.

None of this is impossible, I still plan to build a unit at some stage to see what the issues are in practice.

Thanks Smeaton for the reply. Yes i know these problems. but we need to think above it to see how can these problems are overcome. Do you have any ideas on it. please do share. happy to see the confidence you still have to build the vapor absorption system of airconditioning.

1) I also find these problems - cost, corrosive nature, low working pressure, COP, High heat rejection rates.

Wat else problems you are aware apart from these. Any remedies for it?

That is a research opportunity, the physical principle to use is heat absorption, to improve the process a new absorber, better then ammonia and LiB, have to be developed. This is the first road block. The second is: the absorption principle can work on a moving and shaking vehicle? After these 2 are overcomed, others will come.

"The Coefficient of Performance (COP) of a vapour compression unit is around 4, the COP of the LiB units is about 1."

Good to know the comparison of COP as 4:1.

How about the comparison of net weight per ton of chilling? This again would be a discouraging figure:)

The good aspect of adsorption is the use of heat from combustion, solar, or waste sources which mitigates the low COP. If that heat was turned into electricity via carnot devices and then used to power a vapour compression fridge you would add a high degree of complexity to the system and toss away most of the apparent COP advantage.

An absorption fridge can last for hundreds of years, the only failure mechanism being corrosion from the outside into the various coils to cause loss of the fluid integrity of the system. With care, the exposed parts can be made immune to corrosion at added expense, of course.

You are right there.

I have heard of 45 year old gas fridges that have failed because the burners were clogged. The absorption cycle was still working fine.

Not many vapour compression cycles could achieve that. Then there is the CFC problem. Ammonia and hydrogen are natural products in the environment.