Significance of condenser air temp split?

[Sgt. Dookie]

I'm still new in the trade and just wrapped up my first season of summer maintenances. After a while I started wondering if the difference between air entering the condenser and leaving is significant, it's something I never checked during maintenances. Is there a normal range it should be? Is there any correlation between that and the head pressure, sub cooling, charge or anything? Or is it just an incidental value that doesn't necessarily mean anything? I don't remember learning about that value in school. Should the condenser air temp split be an important thing to check during a maintenance?

[1972torino]

Never really used cond. temp split. I always used head pressure and sub cooling.

[Mooshman812]

From what I know, the higher the split the lower the efficiency of the unit, be it from being plugged, old, rough shape, high load, etc. I may be wrong but I was taught that in school. Others will be able to verify if I am correct or not for sure though.

[northeastbeast]

its significant because you can tell what your head pressure should be by the td across the condenser coil. in school we were taught 30 degrees td across the coil as a general rule. so you take ambient temp add the td across the coil and then find the corresponding pressure with that temperature on the chart to see if its what it should be

[Mooshman812]

its significant because you can tell what your head pressure should be by the td across the condenser coil. in school we were taught 30 degrees td across the coil as a general rule. so you take ambient temp add the td across the coil and then find the corresponding pressure with that temperature on the chart to see if its what it should be

As far as hvac or refrigeration? Both? High efficiency(probably anything above 10 seer based on books date) coils should have less than 10 degree rise for resi... Again school taught me that, don't really use it cause I'm more refr than ac. Also I may be wrong


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[itaintme]

Not really a good rule of thumb to follow. Too many variables that can temporarily affect it.

Better to stick to the factory specs of SC and SH.

[northeastbeast]

Not really a good rule of thumb to follow. Too many variables that can temporarily affect it.

Better to stick to the factory specs of SC and SH.

how do you always get factory specs of superheat and sub cool?

[Mooshman812]

If available always use factory specs. If not I usually use condensing along with acceptable SH/SC
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[Sgt. Dookie]

Books say condensing pressure should be ambient temp (in my original question, the incoming air temp) plus 30 degrees. In reality I've seen 20 or so degrees normally. But that's not what I'm asking.. I wonder about the incoming air vs leaving air temp. If the indoor split is 17-20, and heat energy cannot be created or destroyed, the condenser needs to reject the same amount of heat if the coil and airflow were the same. But the surface area of the condenser is much larger, therefore the split will be less. Maybe half? 8-10? I just don't know if this number is valuable in a troubleshooting situation or not

[Mooshman812]

Without tapping onto system I would say its at a minimum a good way to gauge if the condenser is operating the way it should be. But there are also a lot of other variables to consider as well.

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[syndicated]

Books say condensing pressure should be ambient temp (in my original question, the incoming air temp) plus 30 degrees. In reality I've seen 20 or so degrees normally. But that's not what I'm asking.. I wonder about the incoming air vs leaving air temp. If the indoor split is 17-20, and heat energy cannot be created or destroyed, the condenser needs to reject the same amount of heat if the coil and airflow were the same. But the surface area of the condenser is much larger, therefore the split will be less. Maybe half? 8-10? I just don't know if this number is valuable in a troubleshooting situation or not

You're comparing apples to oranges here.
A proper system has a condenser sized to approx 125% of the evap coil's surface area so that it can also reject the heat of compression.
The condenser is also operating in an area of unfettered airflow (ideally), as opposed to the evap which is in a controlled environment.
The condenser will also loose a certain small amount of heat due to radiation and conduction to its surroundings.
The only useful info I think can be gleaned from measuring this value is to show if your coil is plugged.

[54regcab]

You're comparing apples to oranges here.
A proper system has a condenser sized to approx 125% of the evap coil's surface area so that it can also reject the heat of compression.
The condenser is also operating in an area of unfettered airflow (ideally), as opposed to the evap which is in a controlled environment.
The condenser will also loose a certain small amount of heat due to radiation and conduction to its surroundings.
The only useful info I think can be gleaned from measuring this value is to show if your coil is plugged.

My 2 ton unit must be an oddball 4.5sqft of evap coil with 16sqft of condenser coil.

[itaintme]

how do you always get factory specs of superheat and sub cool?

EXPERIENCE AND GOOD TRAINING ARE HOW I LEARNED. sorry ..cap stuck for a sec.

SC is listed on unit name plate. Super heat can be be obtained reasonably successfully using a refrig charging card.

[northeastbeast]

EXPERIENCE AND GOOD TRAINING ARE HOW I LEARNED. sorry ..cap stuck for a sec.

SC is listed on unit name plate. Super heat can be be obtained reasonably successfully using a refrig charging card.

I was talking refrigeration equipment or package roof top units. your talking resi splits i take it?

[bobster]

Should the condenser air temp split be an important thing to check during a maintenance?

Yes. It tells you about the airflow through the coil.

[bobster]

But the surface area of the condenser is much larger, therefore the split will be less. Maybe half? 8-10? I just don't know if this number is valuable in a troubleshooting situation or not

There are factors other than surface area that affect the heat transfer rate from the coil. Airflow is one of those factors. Coefficient of heat transfer of the coil surface (which can be affected by dirt) is another.

If the split is too high, it usually means there's not enough airflow through the coil. Which usually means it's dirty and/or clogged up.

[itaintme]

Yes. It tells you about the airflow through the coil.

That's true but the OP was asking about using 30* above ambient as a way to as a determination of proper system operation of a tuned system For trouble shooting the temp rise off the condenser is a must-do.

[bobster]

That's true but the OP was asking about using 30* above ambient as a way to as a determination of proper system operation of a tuned system For trouble shooting the temp rise off the condenser is a must-do.

Really? Here's what I read that he said:

"Books say condensing pressure should be ambient temp (in my original question, the incoming air temp) plus 30 degrees. In reality I've seen 20 or so degrees normally. But that's not what I'm asking.. I wonder about the incoming air vs leaving air temp."

My understanding of his question(s) was he wanted to know of what value the air temperature rise across the condenser coil was.

[itaintme]

Really? Here's what I read that he said:

"Books say condensing pressure should be ambient temp (in my original question, the incoming air temp) plus 30 degrees. In reality I've seen 20 or so degrees normally. But that's not what I'm asking.. I wonder about the incoming air vs leaving air temp."

My understanding of his question(s) was he wanted to know of what value the air temperature rise across the condenser coil was.

And my intent was meant to say: There are many varied opinion on what the condenser discharge temp over ambient should be. I have heard values of 10*F to 35*F over ambient that were big used by techs despite the age or efficiency of the system.

A rule of thumb with such a wide spread is not good practice.
And as I stated there are to many variables to consider to make it useful.

Case in point: Would you charge a unit to 30*F over ambient on a 70* day with low IDWB?.

This is why I am against most rules of thumb.

[bobster]

And my intent was meant to say: There are many varied opinion on what the condenser discharge temp over ambient should be. I have heard values of 10*F to 35*F over ambient that were big used by techs despite the age or efficiency of the system.

A rule of thumb with such a wide spread is not good practice.
And as I stated there are to many variables to consider to make it useful.

Case in point: Would you charge a unit to 30*F over ambient on a 70* day with low IDWB?.

This is why I am against most rules of thumb.

I don't think of it as a "rule of thumb". It is a design parameter. Q = u * A * TD. 30 to 35F for standard efficiency condensers, 20 to 25F for higher efficiency equipment (bigger coils).

If you get no useful information from it, don't use it, but that's what it is used for, which was the question.

As to your question, I would never charge using condenser temperature split. I use SH or SC depending on the metering device.