a/c books

billygoat22

Yes, I was looking at "Heating and Cooling Essentials" or "Residential Construction Academy HVAC".
I was also recommended "Troubleshooting and Servicing Modern A/C and Ref Systems" by John Tomczyks.

I have a number of books that cover superheat 101, so to speak, but they don't seem to go indepth on the subject. I came across a refrence about "approach temp", apparently the condensor temp is going to be pretty much X degrees above ambient, regardless, which falls in line with some of the rules of thumb and experiance. But I can't locate a source that covers the theorey behind it (and other questiona as well), and get a better understanding.

billygoat22

a/c books

I've been looking around for some books with some more detail than the more generic a/c books out there. For example, I've found an equation for superheat on HVAC talk site, but cannot find any equations of that nature in the books I have, and would like to get some deeper insight into it.
Most books just define superheat and give rather vague ideas on charging not much detailed than some of the rules of thumb out there. Even some of the manuf reps can't explain their own manuf charts when I ask certain questions.
Also, any books for standards for duct install, like healty house type standards or smacna standards? Not layout, but construction, insualtion install, execution type details.
Thanks for any ideas, two books in the bookstore look promising, but so did the others I bought.

Alan R. Mercurio_3

Bryan, There are some right here that you may be interested in?

Books & More

Your friend in the industry,
Alan R. Mercurio

www.oiltechtalk.com

Eugene Silberstein 3

I think you are on the right track and will be in good hands with any of the three books you have mentioned. I. of course, am partial the the second one you mentioned for obvious reasons.

Since it would be impossible to cover all subcooling theory here, I will attempt to clarify a few issues that tend to confuse many field technicians with regards to subccoling.

Although subccoling is an effective way to evaluate the operation of an air conditioning or refrigeration system, especialy those equipped with thermostatic eexpansion valves, it is important to understand what the subcooling number means about the refrigerant flowing in the system.

To take a step back for a minute, especially for those who are hearing the term for the first (or second) time, subcooling is defined as the condenser saturation temperature minus the temperature of the liquid line at the outlet of the condenser. When blended refrigerants are used, the bubble point temperatures are used for this calculation. For example, if the condenser saturation temperature for an R-22 system is 110 degrees and the temperature at the outlet of the condenser is 90 degrees, the subcooling measurement is 20 degrees.

Now for the goodies. Let's assume that we are charging a system that is equipped with a TXV. The system has just been evacuated and we added a holding charge of refrigerant to the system. Obviously, once the system is started, additional refrigerant will have to be added to the system. Once started, the TXV will be wide open, causing refrigerant to flow through the condenser coil very rapidly. The amount of time that the refrigerant will spend in the condenser coil is small.

In the condenser, refrigerant gives up heat to the air passing through the coil, allowing the refrigerant to desuperheat and then condense. Since the refrigerant is moving through the coil faster, it will condense at a point close to the outlet of the condenser coil. This will cause the subccoling measurement to be low, since the refrigerant is not able to give up a great deal of sensible heat once it has condensed.

As the refrigernt charge of the system in increased, the amount of time that the refrigerant spendsin the condenser coil increases. This gives the refrigerant more time to desuperheat, condense and then cool to a temperature below its saturation temperature. In this case, the subcooling measurement will be higher.

For this reason, low subcooling is an indication that the systemm charge is low, while excessively high subcooling is an indication that the system is overcharged.

Remember that one system parameter alone is not enough to definitively determine a system problem. High subccoling, in conjunction with other factors can lead to a determination of an overcharge, but not the subcooling by itself.... BE CAREFUL!

Here's the tricky part.... If low subcooling is an indication that the system charge is low, what is likely indicated by a subcooling measurement of ZERO?


Post your thoughts... The answer may surprise you!

billygoat22

Thanks for the replies. I'll probably go with the second book.

At zero subcooling

billygoat22

Thanks for the replys. I'll probably go with the seconnd book.

zero subcooling. Assuming the refrigerant is not contaminated with noncondensibles, either a non operating compressor or a no pumper? With no refrigerant flow the temp/pressure in the cond coil would match the ambient temp, so the saturation temp and coil temp would be the same- zero subcooling.

Eugene Silberstein 3

Ding! Ding! Ding!

You are correct!

When refrigerant stops flowing, it will reach the temperature of its surroundings and BINGO, ZERO subcooling. The refrigerant charge could be perfect.

Once again, BE CAREFUL!