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Believe it or not the most educational stuff come from the dissection of vague questions. I think most people gain something when everyone throws in their two cents or past experiences, even if it doesn't pertain to the exact question. Especially when it results into meaningful dialogues and debates.

Yikes! Guess I should hire me a lawyer before my next post on this thread.


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Originally Posted by mark beiser

The OP's question wasn't particularly clear, as he asked if a psychrometer was required to accurately "calculate" superheat.

Would you have been happier if we had just simply said "yes," and left it at that, with no explanation as to why, and no response to the incorrect "no" answers?

No, in the post you quoted of me I clearly stated that I guess I misunderstood'But for the record in my humble opinion superheat and subcooling to me are just two numbers, what you do with those numbers where you plug them into who's ever charging chart or psychrometric chart Or factor is all part of the equation And part of the bigger picture! Some people reading this post Would be happy just to understand what sub cooling and superheat are! I was happily moving on Until you dragged me back in by quoting me, Now can I just go back to watching Pawn Stars? Kirk out

Originally Posted by joegrind

the OP Originally asked a very simple question , Everybody is offering up opinions and charging procedures for equipment that he never asked for, All are valid and differ depending on the equipment On.

Would you have been happier if we had just simply said "yes," and left it at that, with no explanation as to why?

The OP's question wasn't particularly clear, as he asked if a psychrometer was required to accurately "calculate" superheat.
It wasn't a question that has a simple yes or no answer.
Technically the simplest accurate answer would have been "It depends."

Just the fact that the question was asked, and the unclear way it was asked, indicate that the OP is seeking a greater understanding of the subject.
To simply give a yes or no answer would have been a disservice to the OP.

Don't slag me for simply trying to answer his question and not offer opinions above and beyond

You got on us a little for not just giving a simple answer...

Originally Posted by mark beiser

It the calculation isn't of what the superheat will be, but of what it should be, which varies with differences in the wet bulb temperature of the air entering the evaporator coil, and the dry bulb temperature of the air entering the condenser coil.
Measuring the wet bulb temperature of the air entering the evaporator coil requires the use of a wet bulb thermometer, or a psychrometer.

If you don't take the measurements, and do the calculation to determine what the superheat should be, what good is taking the measurements to know what it is?



The chart you are speaking of is not for charging, it is for determining if the system is operating within its design parameters.
On TXV systems, the wet bulb temperature is not needed for either of the 2 charging procedures AS/Trane have used.

the OP Originally asked a very simple question , Everybody is offering up opinions and charging procedures for equipment that he never asked for, All are valid and differ depending on the equipment On. Don't slag me for simply trying to answer his question and not offer opinions above and beyond

Originally Posted by andersonbe06

Is a sling psycrometer required to acuaratly calculate superheat and subcooling as well as a temperature probe. All we have at work is a laser\infered thermometer . Thanks guys and gals

To measure superheat/subcooling you do not need a psycrometer. All you need is the existing pressures vs. the PT chart settings based on your low side temperature and high side temperature (heat pump sensitive) respectively. To determine if you have the correct superheat you will need a psycrometer as a minimum to determine indoor WB as well as the R/A temperature entering the coil (keep in mind you may have a certain level of heat gain if you take your reading from inside the conditioned space. The closer to the evaporator the better) and your OAT. There are other methods and formulas that can be used as listed in this thread, but this would be the bare bones approach to measuring superheat/subcooling and calculating the required superheat/subcooling. I hope this helps

Originally Posted by git-r-dun

Only one person has mentioned airflow so far though. There is no point in taking any of these measurements and using that formula (which doesn't have an air volume factor in it) if you can't determine the total amount of heat content in the air that you are conditioning. So how many cfm/ pounds of air is this formula based on? Would anyone even notice if they had a 15 degree SH and their designed SH was suppose to be 12 based on that formula? And would they add refrigerant to drop SH to design conditions rather than finding that the blower is moving a higher volume of air or a fresh air duct is present or ducts are not fully sealed in the attic? We are in a greatly technical field with constantly changing conditions, the only thing we tend to do is hang on to rule-of-thumbs and homemade formulas. In the end though that truly gets us close enough.

My Jerry Springer final thoughts speech

That is why, whenever possible, I measure the return WB and DB temperature of the air as it actually enters the coil, and while I'm there, measure the supply air DB and do the TEET calculation.

Only one person has mentioned airflow so far though. There is no point in taking any of these measurements and using that formula (which doesn't have an air volume factor in it) if you can't determine the total amount of heat content in the air that you are conditioning. So how many cfm/ pounds of air is this formula based on? Would anyone even notice if they had a 15 degree SH and their designed SH was suppose to be 12 based on that formula? And would they add refrigerant to drop SH to design conditions rather than finding that the blower is moving a higher volume of air or a fresh air duct is present or ducts are not fully sealed in the attic? We are in a greatly technical field with constantly changing conditions, the only thing we tend to do is hang on to rule-of-thumbs and homemade formulas. In the end though that truly gets us close enough.

My Jerry Springer final thoughts speech

Originally Posted by joegrind

Maybe you got me on a technicality, maybe I've been out of the residential arena for too long! I guess I don't understand how it can be calculated as it is a real-time measurement of the here and now I don't know of an application where you project what the superheat will be

It the calculation isn't of what the superheat will be, but of what it should be, which varies with differences in the wet bulb temperature of the air entering the evaporator coil, and the dry bulb temperature of the air entering the condenser coil.
Measuring the wet bulb temperature of the air entering the evaporator coil requires the use of a wet bulb thermometer, or a psychrometer.

If you don't take the measurements, and do the calculation to determine what the superheat should be, what good is taking the measurements to know what it is?

Originally Posted by walterc

Trane prefers the subcooling method for TXV's.

However if you use their supplied chart on some systems with TXV's- you must know the wet bulb.

I don't use the wet bulb chart much, so I'm not sure when they quit using them.

The chart you are speaking of is not for charging, it is for determining if the system is operating within its design parameters.
On TXV systems, the wet bulb temperature is not needed for either of the 2 charging procedures AS/Trane have used.

Trane prefers the subcooling method for TXV's.

However if you use their supplied chart on some systems with TXV's- you must know the wet bulb.

I don't use the wet bulb chart much, so I'm not sure when they quit using them.

Originally Posted by DDC_Dan

Joe, the OP did not say measure, he said calculate. I (and others I imagine) think he is asking if the sling psychrometer (or other means of measuring WB) is needed to calculate the target SH or SC, not just to measure it. So, to measure, not required. To calculate the target, required. Agreed?

Maybe you got me on a technicality, maybe I've been out of the residential arena for too long! I guess I don't understand how it can be calculated as it is a real-time measurement of the here and now I don't know of an application where you project what the superheat will be, Anyway my bad if I misunderstood it, I just asked simple questions in the past only not to get answered But was offered a whole slew of other opinions not related to the question Cheers

Originally Posted by joegrind

So the answer is no you do not need a sling psychrometer to measure superheating or subcooling!

Joe, the OP did not say measure, he said calculate. I (and others I imagine) think he is asking if the sling psychrometer (or other means of measuring WB) is needed to calculate the target SH or SC, not just to measure it. So, to measure, not required. To calculate the target, required. Agreed?

Originally Posted by andersonbe06

Is a sling psycrometer required to acuaratly calculate superheat and subcooling as well as a temperature probe. All we have at work is a laser\infered thermometer . Thanks guys and gals

The original posters question has distorted throughout the thread is a simple yes or no question as superheat is the temperature above the refrigerant saturation and subcooling is a temperature below refrigerants saturation at specific temperatures and pressures. So the answer is no you do not need a sling psychrometer to measure superheating or subcooling! As other posters have mentioned A gauge, temperature probe, and the pt chart is what is required to measure the units Superheat and subcooling. There are definitely some handy tips being offered and useful information,,

I seen that one too but counter Guy was a little skeptical on its performance.

Originally Posted by timberlinemd

Got a Fieldpiece pocket digital psychrometer from my supplier today for $60!

I got mine for 52$.

Got a Fieldpiece pocket digital psychrometer from my supplier today for $60!

Originally Posted by Mr Bill

But they work great to get the grease right when cooking hot wings.

They do have their place in the right application.

Originally Posted by rundawg

I too have never been a fan of infrared thermometers for measuring liquid and suction line temperatures.

But they work great to get the grease right when cooking hot wings.

Oh its available at united refrigeration, and about $90 bucks.

I recently picked up on a nice digital psychrometer made by SUPCO #dsp1000. Very nice and accurate, give DB,wb, rh, and dew point. Highly recommend it.