Solar Hybrid Reverse Cycle Air Conditioners 1

[FreddyNurk]

Not strictly a work related question, but more of a curiosity, and if theres likely to be a sensible answer, its here.
I've seen a number of advertisements recently regarding 'Solar Hybrid Reverse Cycle Air Conditioners'. Usual sort of thing, various quotes on efficiency improvements over standard reverse cycle air conditioners, inverter or DOL notwithstanding.
It appears that these devices operate by including a solar panel (though not an electrical type, rather the same sort of thing as found in a hot water system) in the refrigerant loop, usually before the compressor. A link to a typical supplier is here

With my somewhat limited understanding, I can't see how these would provide benefit in cooling a building. I can see that it'd be handy to gain extra heat from the sun if you're intending to heat the building but I can't see any benefit in using the sun to heat the refrigerant before it goes into the compressor. These units are also being advertised in my location which is in the Northern part of Australia, typically where air conditioners are not reverse cycle. They don't state any sort of absorption method being used, though it might be possible.

Any thoughts on whether this is a real development in terms of AC technology, or just another snake oil trend?

 

[MintJulep]

If by "reverse cycle air conditioner" you mean what we call a "heat pump" here in the Northern hemisphere then I'd suspect that the solar collector is used in heating mode only.

 

[trashcanman]

Get them to guarantee energy savings IN WRITING. Let them know you will see them in court if their claim is false. Too many scams out there.

 

[FreddyNurk]

trashcanman, I'm not looking to purchase at this stage, though I'd have been curious to see if it was worth using the equipment in some of our installations. Usual disclaimer though, 'up to' savings...

MintJulep, I believe we're talking about the same thing. Most ACs (at least the smaller domestic split systems) are used for cooling most of the time, reverse cycle refers to reversing the system thus using it for heating (thus the same thing). What I can't understand is why they'd want to market the units in an area where 'reverse cycle' often isn't installed as theres no need for heating, if thats the only benefit of having the panels.

 

[KiwiMace]

The panel will 'work' in both cooling and heating modes as it superheats (more) the refrigerant from the compressor discharge.

It is the amount of saved energy vs the additional cost of the system that is the dubious part. Compressed refrigerant is already rather hot, so I doubt there would be much in the way of savings. When I opened your link I was expecting to see the solar cell on the compressor inlet where you'd think it would do more work.

 

[tonyruff]

Hi Freddy, I am also from Australia. Put simply, the benefits of a split system solar air conditioner are the reduction of electricty usage. With certain brands of solar air con systems, such as this you don't actually need the sun for it to work. Just having exposure to daylight for 4 hours a day is enough to power it for 15 hours. And whether it's performing heating or cooling, the fact is, you are using up to 80% less energy, hence the reduction in electricity bills. Hope this helps.

 

[Compositepro]

The explanations on the website make no technical sense. It has all the earmarks of a scam.

 

[Drazen]

in your link there is better thermodynamical description that i could found elsewhere.

as far as i can comprehend, heat is introduced after evaporator, i.e. at compressor suction.

take a look at refrigeration cycle in wiki:

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

if point 1 is raised, i.e. temperature at suction is raised, this also means that compressor entrance enthalpy is raised. enthalpy lines are sloped, becoming parallel to saturation line, so that is not proportional increase, yet it is increase.

a compressor work equals enthalpy difference, so with fixed compressor outlet state point - entrance to condenser - higher compressor entrance enthalpy will mean less compressor work.

this is pretty apparent in refrigeration cycle diagram, but how it works in reality, that is another story. this is new concept and issues of actual efficiency, return on investment, reliability etc. are yet to be found.

 

[MintJulep]

The cartoon how it works diagram in tonyruff's link has the solar collector between the compressor and the condenser.

It's thermodynamically reasonable.

It is absolutely NOT 4 hours of sun = 15 hours of run time.

 

[Drazen]

you are right, mint, i did not look at illustration at all, i just looked at term "superheating" which mostly applies to evaporator outlet condition, as refrigerant is already superheated when entering compressor, and i can hardly figure why would they used term for compressor outlet, where vapor is very superheated already.

though, i admit to not fully understand how it works in such case. the whole process after compressor up to expansion valve lays on the same isobar. how can solar exchanger increase pressure? there should be some valve which separates pressure conditions between compressor outlet and rest of cycle up to expansion valve.

the other possibility is that there is interaction between compressor and solar heater, so solar heating changes compressor curve, though i am not sure can it be presented by method other than probe measuring.

 

[MintJulep]

Solar heat in equals increase in refrigerant enthalpy.

At least some part of that enthalpy could be exhibited as a pressure increase. Although most of it probably goes to increasing the superheat, which isn't very useful at increasing efficiency.

 

[urgross]

Has anyone on the forum had experience with reverse cycle chiller/heat pumps? I'm looking at alternatives for a project that the upfront costs for extending chilled water and steam lines destroys the LCCA, and nearest natural gas connection is on the wrong side of a secure site. Plenty of electricity available, but I want to avoid resistance heating. Temperature does go below 10*F routinely. Terrain is karst, so geo systems boring vertical is a crap shoot-never know when either perched water or chasms will be encountered. No room for slinkys. Any experience or comments would be appreciated, I haven't used RCC (other than tiny maritime installs).

 

[EnergyProfessional]

is this like this thread?
[URL unfurl="true"]http://www.eng-tips.com/viewthread.cfm?qid=348557[/url]

I today got an email claiming I would get $4.5 instantly and $10K monthly as soon as I wire the $250 processing fee to them (not sure why they just deduct that from my "for sure" $4.5 mio). I would put these solar assisted refrigeration cycles into the same category.