how to use a refrigerant comparator

[ActiveEngineer]

Hi,

looking for guide on how to use a refrigerant comparator for working out suction pressure on all systems .

[frank]

Why do you want to work out the suction pressure for all systems?

[taz24]

Hi,

looking for guide on how to use a refrigerant comparator for working out suction pressure on all systems .


Your question is too vauge.

A comparator only converts pressure to temp or temp to pressure for the refrigerant you are using.

So you fit your gauges and read the pressure. You then slide the comparator along untill the line is at the same pressure displayed on your gauges. You then look up the refrigerant you want and where the line intersects the refrigerant line you have your temp.

You will have different pressures if you have different temps.

taz.

[ActiveEngineer]

Is there know such guide?

looking find out how you work out what the suction pressure/tempature

For the likes of a HVAC system running on r59 what suction tempaturte would be and how you work it out


Hope i have come over bit better this time cheers for any help you guys can give me

[taz24]

Is there know such guide?

looking find out how you work out what the suction pressure/tempature

For the likes of a HVAC system running on r59 what suction tempaturte would be and how you work it out


Hope i have come over bit better this time cheers for any help you guys can give me


Active Engineer.

Have you ever done any training?

I ask because the information you are asking for does not exist (not in the form you want) but you would know that if you had any training.

Why don't you introduce yourself and explain what you want. We can work from that point and perhaps give you some assistance.


taz

.

[Toosh]

Hi,

looking for guide on how to use a refrigerant comparator for working out suction pressure on all systems .
Hi Active, Have a look at this site
http://www.marineair.com/pdfs/L-2270.pdf, found by Google

Norm

[ActiveEngineer]

Active Engineer.

Have you ever done any training?

I ask because the information you are asking for does not exist (not in the form you want) but you would know that if you had any training.

Why don't you introduce yourself and explain what you want. We can work from that point and perhaps give you some assistance.


taz

.




Hello Taz,

I am a mechical tech and i work offshore in the north sea and have know refrigeration training at all.

Like my other questions i would like to know how you guys work out the suction pressure/temperature of systems.

suction pressure/temperature of a HVAC system running on R59 would be ?

[nike123]

Like my other questions i would like to know how you guys work out the suction pressure/temperature of systems.

suction pressure/temperature of a HVAC system running on R59 would be ?


You need to know design TD (difference between evaporation temperature and air/water/brine entering temperature) for your heat exchanger.
Subtract evaporator design TD from evaporator actual air/water/brine entering temp to obtain required evaporation temperature, and add condenser design TD to actual entering air/water/brine temperature to that condenser to obtain condensation temperatures.
Then convert that temperatures to saturation temperatures of refrigerant in system and you have your expected pressures. Now compare that with your measured pressures (or temperatures, if gauge has scale in temp. for that refrigerant) to establish is your system pressures are OK.

http://www.refrigeration-engineer.com/forums/showthread.php?t=11403&highlight=table

[ActiveEngineer]

This helps alot mate thank you very much.

[Gary]

It's not about pressures.

You convert the pressures to temperatures, but it's not about temperatures, either.

It is about temperature differences, i.e. subtracting one temperature from another temperature (subcooling, superheat, TD's, dT's, approaches, etc.). Any single pressure/temperature, by itself, tells you nothing useful about the system.

[ActiveEngineer]

Still looking for help regarding this matter..

Maybe i did not explain my self to well the first time..

What i would like to know is how suction pressure are related to operating tempatures.

For example,

A freezer with operating tempature of -21c, running on R404a with a suction pressure of 1 bar/14.7psi.

I checked a comparator and for that pressure that would give you a lp vapour tempature of -32c... i think.

So would that give you a 11 diff in tempature.

So is there a simple rule of thumb to follow when trying to work out suction pressure from your operating tempatures and is it the same for all refrigerant.

Hope this explains it better this time.

[FreezerGeezer]

Basically for heat to flow, there must be a temperature difference. So to absorb heat in the evaporator, the temperature of the refrigerant must be 6 deg. or more less than the temperature of what you're cooling. Any less would be inefficient. And obviously to reject heat from the condenser, the cooling medium must be colder than the refrigerant temperature, again by at least 6 deg.
It's many years sisnce I used R404a & LT systems, but the -32 for -21 case temp sounds right to me.

Hope that helps.

[Gary]

I would add that TD is primarily a matter of coil sizing. A larger coil transfers heat faster resulting in a lower TD. A smaller coil transfers heat slower resulting in a higher TD.

[icecube51]

maybe you need to download the "coolpack" program,and play a bit. you put in some numbers and it will calculate the outcom for you. you learn a thing or two.

Ice

[Josip]

Hi, ActiveEngineer :)


maybe you need to download the "coolpack" program,and play a bit. you put in some numbers and it will calculate the outcom for you. you learn a thing or two.

Ice

you should download above mentioned program, and under CoolTools:Auxiliary you can find

"COMPARISON OF REFRIGERANTS .... Comparison of three refrigerants in a simple refrigeration cycle" ...

... of course there is much more, then a thing or two, to learn ;)

Best regards, Josip :)

[murphyboy]

Still looking for help regarding this matter..

Maybe i did not explain my self to well the first time..

What i would like to know is how suction pressure are related to operating tempatures.

For example,

A freezer with operating tempature of -21c, running on R404a with a suction pressure of 1 bar/14.7psi.

I checked a comparator and for that pressure that would give you a lp vapour tempature of -32c... i think.

So would that give you a 11 diff in tempature.

So is there a simple rule of thumb to follow when trying to work out suction pressure from your operating tempatures and is it the same for all refrigerant.

Hope this explains it better this time.


usually you would be looking for a superheat (your TD) of around 7 degrees c, preferably 5 on freezer / cold store. it all depends on if its on a DX (direct expansion), fixed orifice, or capilary system.

but 1 bar on 404a sounds right to me

[frank]

usually you would be looking for a superheat (your TD) of around 7 degrees c, preferably 5 on freezer / cold store. it all depends on if its on a DX (direct expansion), fixed orifice, or capilary system.

but 1 bar on 404a sounds right to me
Would that be during pull down or approaching set point?

[icecube51]

look at the date of last post guy's.
and he never told anyone if he has learnd a thing (or two) ;-))

Ice

[Magoo]

September 2008 was a good month, original post date people.

[ActiveEngineer]

Boys and girls where can i find this cool pack program.

[nike123]

Boys and girls where can i find this cool pack program.

Ar you sure that you are active?;)
http://tinyurl.com/32u4a3k

[ActiveEngineer]

Ar you sure that you are active?;)
http://tinyurl.com/32u4a3k


Ha ha ha funny guy how cool is that, I like it.

Cheers for the info tho. don't really get on here to much as you can tell by my posts

Still don't really understand how you guys work out the suction pressure/temperature. like I said above I never served my time as refrigeration engineer so was just looking for a ball park figure.

[nike123]

Ha ha ha funny guy how cool is that, I like it.

Cheers for the info tho. don't really get on here to much as you can tell by my posts

Still don't really understand how you guys work out the suction pressure/temperature. like I said above I never served my time as refrigeration engineer so was just looking for a ball park figure.

You seems to not reading carefully!;)
Everything is alredy explained in this thread.
There is no simple way by looking in thumb and aligning it with evaporator bottom line. We must measure some temperatures, consider some factors, than we came with expected value for evaporation temperatures and than we convert that in pressures for refrigerant in question.

[Gary]

Still don't really understand how you guys work out the suction pressure/temperature. like I said above I never served my time as refrigeration engineer so was just looking for a ball park figure.

If you know the pressure it tells you the temperature. If you know the temperature, it tells you the pressure.