Results 53 to 60 of 60
02-07-2013, 08:00 PM #53
Then multiply the CFM airflow * 4.5 if at sea level & that result times the enthalpy difference. That's supposed to give you the Btu.
You don't use the static pressure number.
02-07-2013, 09:12 PM #54
my bad, I was looking at it all wrong.®
02-07-2013, 09:29 PM #55
I really recommend you take the time to learn how to do the calculations by hand, using a psychrometrics chart, and what it all means.
Once you gain a good understanding of it, retire the charts, and get a good psychrometrics app for your smart phone, preferably one that will calculate cooling and mixed air processes, and use it in the course of service calls.
You will be amazed at how it demystifies some problem systems, the system that is the subject of this thread is a prime example.
Unfortunately for the OP, there has been a 2.5 year parade of techs , including a manufacturers tech rep, that have utterly failed to diagnose the problem, even done thousands of dollars worth of useless repairs under warranty, because they either didn't take the air side readings necessary to see what the system was really doing, or they utterly failed to understand what the readings were telling them.
Sadly, even the most basic training in air side diagnostics is hard to come by in most areas.If more government is the answer, then it's a really stupid question.
02-08-2013, 11:18 PM #56
Thank you very much for the words of wisdom. This is something I was never taught in school, so it rather overwhelming to comprehend at the moment. I talked to my service manager about using psychometric charts and calculations, he gave me a lot of good information on it, and showed me a few things. I am also signed up for a few classes next month paid by the company. Not to say I will be a pro at in the next month or two but I'm sure I will be better off.
02-08-2013, 11:41 PM #57
It always struck me as strange that most 2 year college and tech school HVAC programs teach almost nothing about AIR...
One thing that you will find immediately helpful in understanding things, and how to apply it on service calls in the field, is the Testo AC & Refrigeration Application Guide.
Good stuff for anyone doing HVAC service, regardless of experience level.
A smart dude named Jim Bergman wrote it while he was working for Testo.
Last edited by mark beiser; 02-08-2013 at 11:59 PM.If more government is the answer, then it's a really stupid question.
02-09-2013, 11:50 AM #58
Mark, from what I have witnessed, we need a total retraining of service techs; few pay much if any attention to 'first & foremost' getting airflow right. I also believe they need to be certified as to, at the least, their knowledge. These horrible shortcomings need to be eliminated if we are to begin to reduce the wasteful use of energy...
I've seen some unbelievable A/C add-ons, on older belt-drive blower oil furnaces that will literally blow your mind when it comes to extreme low airflow; that should never happen to an HVAC consumer. Plus, most of them are left that way until a furnace change-out many, many long years later!
Few homes are energy efficiency rater/audited, & then after retro-work is done, have a room by room heat-gain heat-loss performed for proper equipment sizing & airflow to each room. Only the proper sequenced Best Practices will yield total optimal efficiency & optimally reduced energy utility bills.
02-09-2013, 09:07 PM #59
I attended a trade school that mainly tough the basics of electricity and refrigeration.. I had to learn everything from there in the field. I spend most nights reading on this site and reading articles on subjects that trouble me most. If i had a call that I didn't get or didn't understand why something happen, more than likely you'll find me reading what I can when I get home. My education started when I started my first day of work.®
02-09-2013, 10:33 PM #60Professional Member*
- Join Date
- Jun 2007
- Round Rock
I may or may not have read this. If it's a reciprocating 2 speed compressor. Bristol brand I believe had a problem shifting to high. I put about the same year model on this house and it worked great for a while, then would crap out and run again then crap out. Never not cooling, just not very well. It's a flaw with the compressors, I think there was some bulletin on them. I got a brand new unit for my customer with a scroll compressor. I had another one which was about a 2009 recip. They could get a brand new scroll for cost basically, they got a much better unit for a small amount more. When the crankshaft reverses positions in the compressor, it doesn't shift all the way as I recall. I think getting a little blow by in the 1st cylinder or not enough. I don't remember all the details, but was a problem.I like DIY'ers. They pay better to fix.