Refrigerants vs Refrigeration
I continue to get the occasional question, worded something like, “..Hey, do them videos tell ya’ how to charge 410A systems?” And I go into an explanation about the DVD’s covering a review of refrigeration principles with R-22 and providing some discussion relative to 410A…or sometimes I just direct them here and suggest they may get their answer for the price of a websurf…
But, the question still takes me back a little, simply because I get the impression some people have never heard of any refrigerant other than R22, or never seen a refrigeration system containing any other refrigerant…I admit, I found out about the pressure thing with 410A indirectly from another tech, who had stumbled onto a R-410A system accidentally, with no knowledge of the refrigerant’s characteristics, and didn’t have a saturated pressure/temp chart for the alien chemical. All he knew was the suction pressure was near double what he was accustomed to seeing. He had the presence of mind to call someone who was familiar, and was quickly tutored as to what he was looking at.
But, if someone out there knows 410A exist, knows the saturated pressures are different, can get his hands on a P-T chart and is comfortable with the application of mechanical refrigeration principles, the question of how to deal with the system relative to it’s type of refrigerant, should be a no-brainer…or not even exist. It’s just another heat pump with another refrigerant…what’s not to understand?
Refrigerants are about pressures, if you want to talk about pressures. Someone, some time in history, designed a particular refrigerant for a particular reason, none of which I know. I just know there are more refrigerants to choose from these days than I can get in my truck at one time. I abandoned low and mid temp service work, just because of all the refrigerants. Use to, it was 12, 22 and 502. You could service about any system you went on with one of those 3 options. Then, with the initial demise of R-12 there were several retrofit drop-in’s available, with different folks choosing different strokes…and little convenience stores with 6 condensers, using maybe 4 different refrigerants, with some not identified…what a mess. But getting back to the point of the story, all the condensing units were still doing the same thing…cooling down the Budweiser and Miller 12 packs.
Refrigerants are about pressures, refrigeration is about temperatures. I’ve seen heat pumps running on R-12, R-22, R-500 and now, R-410A. And they all did essentially, the same thing…cool the house in the summer and warm it in the winter. And of course, they accomplish that by creating conditions conducive to heat transfer. Those conditions are indoor and outdoor coil temperatures. And the coil temperatures have been pretty much consistent since Day One of comfort cooling and heat pump applications.
We all tend to forget what we’re actually measuring when we hook up the gauges to a system. We grow dependent on pressure values and “beer-can-cold” suction lines, not thinking in terms of the saturated temperature of the pressure and it’s relationship with the temperature of the suction line. We’re just looking for 70 psi and a cold suction line. One positive aspect of servicing 410A equipment is the fact we’re all gonna’ have to go back to the basics for a while and actually think about saturated temperatures…at least until the 410A suction pressures become as familiar as the R22 have been, for so many years.
May 9, 2009 at 9:42 am
It took me a long time to finally understand the 410a thing. I distinctly remember asking guys what pressures do I want to see on a 410 system? Your video really made it easy to understand by putting a 22 and a 410 system side by side and comparing saturation temps at thier respective pressures. Now it seems so basic, but it was kinda tricky at first. One thing I was wondering about is your take on determining the type of metering device you are dealing with without having to go look.I have heard of a few different methods for doing this but I was hoping to get Mr. Wayne Shirleys opinion. I have really learned alot from your vids, by the way. I use the knowledge everyday, especially in troubleshooting shorts and in correctly diagnosing either low charge or low airflow. You definitely have a knack for making things easy to understand. I’m waiting for you to do one on airflow and understanding static pressure, velocity, CFM,etc…Anyway, just wanted to stop by and say hi, and would really like to hear your take on the metering device thing. Thanks Wayne.
May 9, 2009 at 8:03 pm
..yeah, as long as you have some idea what the system operating temps are supposed to be and P-T values for the particular refrigerant, analysis and diagnosis is pretty straight forward…
..most TXV’s close on the off-cycle pretty quick, because the evaporator and bulb pressures become equal, leaving only the spring force, which closes the valve orifice. I usually just kill the power and watch the pressures. If they don’t equalize pretty quick, I figure the system is TXV’d. That’s about the only trick I know. If you’re referring to liquid line restriction symptoms, and whether or not the problem is actually a restriction or faulty TXV, then you just have to eliminate restrictions, leaving only the TXV. Of course, most 10 SEER stuff is fixed, most 13+ SEER equipment is TXV’d…well, the 13 SEER brands I’ve dealt with are TXV from the factory. Some of the “non-premium” brands aren’t…I think Goodman is still shipping stuff (air handlers/”A” coils) with pistons…the few I’ve bought were…but for what it’s worth, adding the TXV and hardstart is worth the additional time and money…they perform better and commission much simpler. The superheat will get right almost immediately, leaving nothing to do but adjust the subcooling…there was a time when TXV’s were the rule instead of the exception…but no doubt, cost cutting on the part of mfg’s led to the cap tube/fixed orifice designs…
..I’m not a big fan of the static pressure/CFM/velocity stuff with residential equipment…it’s time consuming to do and maybe misleading at times…airflow dynamics is extremely complicated and just sticking a pitot tube in a hole somewhere doesn’t impress me all that much…I’d rather use the temperature rise formula if I got to have a CFM value to make somebody happy.
I finally realized with residential heat pump equipment, you either got enough (airflow), or you don’t…and the pressures/superheat will tell you that…if the suction is 60 psi (R22) in the cooling cycle and the superheat is low (normal for TXV), the airflow is low…and it doesn’t matter how much low, it just ain’t enough…
Velocities are whatever they are…Maximum recommended velocities are for noise considerations. But with residential equipment, particularly the supply side, decent friction rates usually result in decent velocities. Most residential noise will be at undersized supply registers and return air grills…you don’t generally “hear” the air moving through the ducting, regardless of the velocity…least I never have…
The science of heating and cooling is based on principles. Service work deals with the application of the principles…the two ain’t the same. It’s like the airflow thing. In the time it takes someone to run a bunch of test to confirm low airflow, I can access the indoor coil and scrape some crap off of it and get the system back in decent running condition.
Service work is all about “..finding the real problem, real fast…”. The most I ever want to do on a service call is connect the Testo or measure some voltages…if I gotta’ do more than that, it’s gonna’ be a bad day…
If I didn’t answer your questions, ask again…and thanks for the complimentary comments…
May 9, 2009 at 9:04 pm
Excellent!! The methods I had heard about and mentioned before involved having the system running and either disabling the condenser fan or restricting the condenser airflow with a blanket and observing the low pressure, if it rises directly proportional to high side you have an orifice, and if it lags behind the high side, you have a TXV. I have seen this method fail utterly. The watching for pressure eqaulization at the off cycle method makes total sense to me, and I cant wait to try it. It just makes me wonder why I didnt think of it to begin with. Probably because I’m still a beginner. As far as the airflow thing goes, a wise man once said, we have to assume on a service call that the system was up until recently operating satisfactorily, and our job is to return the system to that point where everyone was “cool”. You can take obvious factors like the state of the house, the number of animals living in the house, and the condition of the filters of course in conjunction with the low side pressure and superheat{or lack thereof}to accurately determine whether the problem is restricted airflow across the evap coil or not.That being said, I feel it would behoove me as a tech to actually understand the whole ” airflow scenario”,before I begin to make too many other than blatantly obvios decisions about a customers duct system. I can tell by listening to you that you have a pretty good comprehension of airflow, and while its not necessary to be an engineer, it would be very helpful to at least get my mind around the basics. Thank you so much for taking the time to help me out with these issues, my friend
May 10, 2009 at 7:19 am
The best airflow “book” I’ve found for us field folks is Manual D. I’ve got several reference type books that get deep into the physics of airflow, which always ends up being a mind numbing experience for me. Even with Manual D, I had to read it several, several times before things began to make sense. And every time I open it now, I have to re-learn some of the material.
With airflow in a piece of duct, the dynamic factor is total pressure, which is the sum of velocity and static pressures. Velocity pressure is simply the result of the energy or “throw” of the air created by the blower wheel. Static pressure is the result of “compression” of the air inside the duct (and is the “force” that pushes the air through the run-outs). If friction losses are disregarded, total pressure is constant…so, velocity and static pressures are inversely proportional. If one goes up, the other has to go down. So as duct cross-sectional area changes, velocity/velocity pressure changes, and static pressure changes…If duct size decreases, velocity/velocity pressure increases, while static pressure decreases, and vice-versa (you could/can have a negative, or near negative, static pressure in some locations of a duct system!).
Friction losses are the result of resistance to airflow, either as a result of “drag” or changes in duct geometry (turns, transitions,take-offs, etc.). Dynamic losses are proportional to the square of the velocity. So, increasing the velocity of the air by some factor, will increase the friction loss by a geometrically greater value.
Manual D takes all this stuff into consideration and provides simple, practical methods for designing/sizing duct systems…
With residential systems, it usually comes down to total effective length and available static pressure. Available static isn’t too hard to calculate, but total effective length can be tricky. For example, sometimes the run-out/branch duct closest to the air-handler can have more effective length than the run-out farthest from the air-handler…it doesn’t make sense, but goes back to airflow dynamics, a complicated field of study…
If I’ve learned anything over the years, it is simply the fact that most existing residential systems have, at the very least, some minor ailments associated with the overall performance, of the system. I think most installing contractors do/have done, a satisfactory job of sizing and installing the duct system, yet they had/have to, to be practical. The “perfect” duct system would cost more than anyone is willing to pay.
The biggest mistake I see with systems is undersized equipment as a result of high/vaulted ceilings, undersized flex and poor trunk/take-off geometry. I suspect some contractors use square-footage “rules of thumb” to calculate equipment tonnage, which is OK with 8′ ceilings…but 18′ foot ceilings require some additional thought (the equipment conditions the volume of air, not the square footage of the house). Fifty foot of 6″ flex duct won’t carry very much air, and 6 take-off’s over 2′ of trunk, isn’t efficient.
When someone (HO) complains a system “never has adequately cooled the house”, it’s probably an equipment sizing problem. When someone complains a room “has always been hot”, it’s probably a duct issue. Sometimes, the problem is insulation. Attics need to be loaded up with insulation, at least in the southern part of the country. I worked with a system for years, never paying any attention to the tonnage, just fixing mechanical/electrical problems. Finally one day, I discovered the equipment was 3 tons and the house was like 1000 sq ft, and always hot!!! I began shooting ceiling temps with an IR thermometer and some of the numbers were in the 90’s…there was an obvious insulation problem…ceiling and wall temps should be the same, or near the same, as room air temperature.
Fortunately, most service calls are equipment related, and fixable. Duct problems…? that’s maybe another horse of a different color…
July 26, 2009 at 12:50 pm
I remember some systems used R500. Yellow drum i believe.