Convert air conditioning units from R22 to another refrigerants

[mfqd]

Hi,

I'm trying to study the effects on efficiency (COP) if we consider to substitute the refrigerant in air conditioning units. Can anyone give me some guidelines? I didn't find yet any text related specificaly to this subject?

THANKS!!

 

[imok2]

mfad

This may interest you!

http://answers.google.com/answers/threadview/id/99414.html

 

[mfqd]

Hi,

I just saw your post now, so i will take a look with more time....

I found this table in a chapter of ASHRAE. What do you think about this? Can i assume the COP values to compare the fluids??

Thanks

 

[desnov74]

In a practical sense not much, most commercial refigerants is about the same. Just think about the operating pressures. Work in Work out.

Just look at the ASHRAE chart, only ethane and co2 are about half, all the rest are about the same.

 

[mfqd]

Dear desnov,

Can you be a bit more specific please? thanks! i'm not sure that i have undrestood completly what you are trying to say.

THANKS

 

[cdxx139]

Changing refrigerant in an existing system is typically not practical. A coil designed for R-22, typically will not handle the pressures required for an R-4xx

knowledge is power

 

[desnov74]

MFQD,
I'm just saying that in any vapor compressor cycle, the compressor is the "work-in" and the heat removed is the "work-out" ideal. See slide #5, I just googled this real quick. The presenter shows on slide #7 some basic expressions of COP. We can, see if the work in of the compressor, Win, gets hypothetically large then COP goes lower (h2-h3)/Win=COP.

http://web.me.unr.edu/me372/Spring2001/Vapor Compression Refrigeration Cycles.pdf

So going back to that ASHRAE chart, one can get an idea on the effect of the refrigerant on the COP.

 

[desnov74]

PS...........
For changing a system practically, you got a whole other set of issues as cdxx139 points out. Even when changing replacement refrigerants there are issues with oils and dryers etc. The selection of the refrigerant determines everything, compressor design/selection, sizing, etc.

 

[mfqd]

Dear desnov,

I know well that COP equations, but i would like to know what is the correct aproach to understand this well. What calculations must we use to estimate that a difference in COP value by chossing other fluids. Maybe an example would clarify this...

Thanks

 

[desnov74]

MFQD~

What is this for? Could you clarify so mabey I could try to help or ask someone else. I'm not sure if you're looking to retrofit a system, design a new one, or conduct a study of some kind.

 

[mfqd]

Ok,

I work in a company that has in one of it's services energy audits. I'm analysing what are the consequences in suggesting as an energy saving measure the change of refrigerant or aquiring new equipments of air conditioner (split type) with higher COP values.
For what i've analysed, changin the fluid will affect other things as pressure values involved in the cycle tha may damage the system. Also for what i've red , the effects on efficiency are low, but never in the way of increasing it. So i will discard this option as a energy saving measure.

But, when i was reading about this, i've started to remember about the refrigeration cycle and it's calculations, and how can i apply them in this case, just for interest in the subject...
Because of the change in pressures that exist when we change the refrigerant in an existing installation, i'm a bit confuse on how can i perform the calculations.

Maybe assuming an example, i can understand better.
I will suggest the follwoing example that i have in a book, for you to help me...

Here it goes:

We have a "real refrigeration cycle" (not Carnot) using R-134a. The mass flow is 0,05 kg/s. enters in the compressor at 0,14MPa and -10ºC and exits at 0,8MPa and 50ºC.Exits the condenser at 0,72MPa and 26ºC and is strangled to 0,15MPa.

With this we can calculte the cooling power, the power consumed by the compressor and the COP. the results are:
-cooling power: 7,93 kW
-compressor power: 2,02 kW
-COP: 3,93

I didn't explain the calculations because i assume that you can do them....

Now, what would be the new values if we substitute to R22 coolant?
My problem, as i said before, is that we can not assume the pressure and temperature values specified in the enunciation, because the change of fluid in that same system will change that same values...

I hope i made myself clear enough.

THANKS

 

[desnov74]

mfqd~

Your questions and responses are like a dog chasing its own tail.

 

[mfqd]

Ok,

If thats what you think.... maybe you are one of those who knows everything...sorry i'm not.

thats easy to say, but i think that you can't explain it so easly through calculations...

 

[desnov74]

" I didn't find yet any text related specificaly to this subject?"

But, when i was reading about this, i've started to remember about the refrigeration cycle and it's calculations, and how can i apply them in this case, just for interest in the subject... Because of the change in pressures that exist when we change the refrigerant in an existing installation, i'm a bit confuse on how can i perform the calculations.Maybe assuming an example, i can understand better.I will suggest the follwoing example that i have in a BOOK, for you to help me...

 

[mauricestoker]

A bit confused-you are proposing to swap R-134a for R-22 as an ECM? I would think that shutting off all outside air intakes might have a better economic payback, or removing all the filters to reduce static loss.

 

[mfqd]

No no, think i didn't myself clear...

This example is simply academic to understant through calculations the effects of a fluid change in an existing system. I know that this specific change is not correct.

 

[imok2]

mfad
For R-22 at the saturating condensing temp of 122*F and the saturating suction temperature of 46*F
With a heat load of 27,066 BTU/hr(7.93kw) the input will be 2.198 KW with an EER of 12.32 btu / Wh or COP 3.60 and a mass flo rate of 396lb/h and for
R134 at the same exact conditions of suction and dischargetemperatures. I get a compressor input of 2.17 KW with an EER of 12.47 btu/ Wh or a COP 3.65 and a Mass flo rate of 425lb/h

So it looks like a push at least at the conditions you gave

 

[imok2]

mfad
I changed the SSt to 14* F (-10C) and here’s what I got
For R-22 at the saturating condensing temp of 122*F and the saturating suction temperature of 14*F
With a heat load of 27,066 BTU/hr(7.93kw) the input will be 3.567 KW with an EER of 7.59 btu /Wh or COP 2.22 and a mass flo rate of 414 lb/h and for
R134 at the same exact conditions of suction and discharge temperatures. I get a compressor input of 3.586 KW with an EER of 7.55 btu/Wh or a COP 2.21 and a Mass flo rate of 458 lb/h
Again its a push and this is a correction of the evaporator SST of the above example

 

[KiwiMace]

Oak ridge national lab has an online heat pump model, which can be run as an air conditioner. Google the above.

For the kind of theoretical exercise you suggest, you can muck around with pretty much any parameter you like.

Make sure you read the instructions as the solver fixes certain variables to make the solution.

 

[KiwiMace]

Here it is...