404A head pressure to ambient rule of thumb

[kengineering]

I know that with other refrigerants there is a "rule of thumb" relationship with head converted to temperature in relation to the ambient. For example 134A we add 30-35*f to the ambient and covert the pressure to temperature to see if were in the ballpark. What would it be for 404A. Ken

[Gary]

Why would it be different for different refrigerants?

BTW, the rule of thumb I use is "saturated condensing temperature 20-35F over ambient", depending upon load... regardless of refrigerant.

[US Iceman]

The actual temperature difference utilized is based on the design TD of the air-cooled condenser. As a rule-of-thumb if you use the ambient temperature plus the design TD you will have the approximate condensing temperature.

Converting the condensing temperature to the pressure will provide an adequate estimate of the discharge pressure.

This will work for any refrigerant using an air-cooled condenser only.

The real trick is knowing what the actual design TD is. The numbers mentioned cover a wide range of old school technology to more modern methods.

[Gary]

The important thing to remember is that refrigeration is about temperatures, not pressures. The reason you are carrying a set of guages is to find out the temperatures.

If you have ten identical systems using ten different refrigerants, all you need to know is the proper saturated suction temperature (aka evaporating temperature) and the proper saturated condensing temperature (aka condensing temperature).

If you try to memorize all of the pressures for all of the refrigerants, you are doing things the hard way. If you know what the temperatures should be and have the right P/T chart in your pocket, you can work with ANY refrigerant.

[Gary]

The real trick is knowing what the actual design TD is. The numbers mentioned cover a wide range of old school technology to more modern methods.

Yep, we almost never know what the design TD is.

In the field, rules of thumb get the job done.

[US Iceman]

In the field, rules of thumb get the job done.


That's true. I tend to use a rule-of-thumb as a reality check to get me close. It is sort of like a sniff test. If it smells bad, it usually is.

This is a highly subjective test and not recommended on ammonia systems.:D

Most of the time being close is good enough to get you started.

[m3ae2002]

PLEASE P-H CHART FOR R404A ARGENT

[Dan]

www.sporlan.com/miscellaneous.shtm

[Peter_1]

PLEASE P-H CHART FOR R404A ARGENT

A very friendly intro you made here. This is the best website for the R404a- ph chart and other refrigerants: www.google.com

[lana]

PLEASE P-H CHART FOR R404A ARGENT

Hi there,
I sent a PM to you about this.
Find the attached file.
Better to download the CoolPack.
Regards,
Lana

[Triggerman]

The important thing to remember is that refrigeration is about temperatures, not pressures.

So right, Gary. And the most overlooked temperature goes along with this question.

DO NOT forget discharge superheat.

Best of luck.
Ben

[m3ae2002]

The actual temperature difference utilized is based on the design TD of the air-cooled condenser. As a rule-of-thumb if you use the ambient temperature plus the design TD you will have the approximate condensing temperature.

Converting the condensing temperature to the pressure will provide an adequate estimate of the discharge pressure.

This will work for any refrigerant using an air-cooled condenser only.

The real trick is knowing what the actual design TD is. The numbers mentioned cover a wide range of old school technology to more modern methods.
_what is the meaning of above paragraph ?

[US Iceman]

The real trick is knowing what the actual design TD is. The numbers mentioned cover a wide range of old school technology to more modern methods.


You were addressing this in your post. Ambient + TD = condensing temp.

Older air-cooled condenser were selected for much higher TD's while newer condensers are selected for much lower TD's.

Higher TD's = older selection parameters
Lower TD's = newer selection parameters

The first time you see a different system, you do not know what TD was selected to size the condenser. Therefore, you have to do some basic calculations to find this.

That's what I was trying to say before.

[lana]

Hi m3ae2002,

The air cooled condenser TD depends on ambient temperature. Usually, high TD is for colder ambient and low TD is for warmer ambient.

In here we take :
TD= 5-6°C for very hot areas like ta=50°C
TD=8-10°C for normal mbient ta=42°C
TD=12-15°C for colder areas ta=32°C

But as US Iceman mentioned, it is difficult to know the already installed condenser's TD unless you have the documentations.
I normally measure the ambient temperature and then add 10°C to it then compare it to the condensing pressure. This works here most of the time. (Because the condensers I work on are designed and manufactured by me :D ).

Hope this helps.
Cheers

[US Iceman]

(Because the condensers I work on are designed and manufactured by me :D ).


I think that is cheating.:rolleyes: Although it is probably easier to find the unit capacities!

[setrad7791]

I tend to dis-agree with sum statements here... Refrigeration is all about pressures, temperature is just a by product of refrigerants at a certain pressure!. Ofcourse that said we do obviously need to ascertain the correct temperatures to guide us in determining if their is a problem. But in relation to head pressure r404a should run between 1500-1800kpa in 90% of instances. if your head pressure is not correctly maintend between these figures you will begin to see over/under condensing which will make it difficult to pinpoint actual problems. If ambient temps are a factor in head pressure and their are no head pressure controls... i.e cycling fan, then the head pressure should be attained via other means, i.e blocking condensor/water on condensor, then correct operation can be diagnosed.

[Gary]

Given a full set of temperature readings, you can trouble shoot every problem the system has without knowing what the pressures are or what refrigerant is in the system... with one exception, i.e. non-condensables.

On the other hand, knowing the pressure without knowing the refrigerant is meaningless. Refrigeration is about temperatures.

[Triggerman]

Refrigeration is about temperatures.

I couldn't agree with you more (system wouldn't let me post simply "Ditto") :D

[lana]

Given a full set of temperature readings, you can trouble shoot every problem the system has without knowing what the pressures are or what refrigerant is in the system... with one exception, i.e. non-condensables.

On the other hand, knowing the pressure without knowing the refrigerant is meaningless. Refrigeration is about temperatures.

Hi,
Gary is right on point.

My friend, refrigeration is about temperature not pressure. We learn, work, suffer, endanger ourself TO PRODUCE SOME LOW TEMPERATE, not pressure:cool: .
Have you ever heard this " I build a chiller which produces 100 Psi? Of course not.
Everything is about temperature.
I suggest you read Gary's explanation again.
Cheers

[Makanic]

Democracy !!!!!

Is it a Vote? :)

I Vote Tempreture :)

[setrad7791]

Then maybe you should buy a set of gauges that only indicate temperature!!!!! pressure temperature relastionship is the base reference we work from.... In saying that i do agree temp is an important factor, but when were unable to measure temps due to unforseen circumstance i.e difficult locations what is the first thing we rely on to determine a problem... LOW OR HIGH SUCTION/DISCHARGE PRESSURES!!! when was the last time you grabbed a discharge line to ascertain the head pressure was to high? if.... when we do notice a hot liquid line the first thing we do is check the head PRESSURE!!!! temp my arse... pressure is EVERYTHING! p.S GARY.... IT WOULD BE LOVELY TO LIVE IN A WORLD WERE WE RECIEVE A FULL SET OF TEMPS.... BUT I PREFER TO WORK ON MY GAUGES AT THE COMPRESSOR AND NOT CRAWL AROUND TEMP CHECKING PIPEWORK AND HARD TO GET EVAPS! When was the last time someone asked you for the discharge temp? never....So in conclusion unless you work in the field and understand what it's like to actually service and fault find a system on location i suggest you take into account PRESSURES as they r a much more accurate basis of fault finding and problem solving!

[lana]

Hi there,

What is meant with "refrigeration is about temperature not pressure" is that we think about temperature. Of course we can not measure evaporating temperature or condensing temperature, but we can measure pressures. After that we have to find the corresponding temperatures.

NOW ,

When we say a water chiller's evaporating temperature is +3°C, then everything is clear. But if we say a water chiller's suction pressure is 65 Psi(g) then one would certainly ask what is the refrigerant? Because the pressure depends on the refrigerant but temperature is always temperature.

I hope this helps.

Cheers

[taz24]

When we say a water chiller's evaporating temperature is +3°C, then everything is clear. But if we say a water chiller's suction pressure is 65 Psi(g) then one would certainly ask what is the refrigerant? Because the pressure depends on the refrigerant but temperature is always temperature.

I hope this helps.

Cheers

Very well put.

Cheers taz.