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.

Air Flow and Duct Design

Airflow across the indoor coil on residential heat pumps, or straight cooling systems, is always a topic of interest for the more astute members in HVAC technical circles…and rightly so. Proper airflow, or more accurately the lack thereof, may well be the HVAC industry’s most cited culprit for substandard equipment performance and efficiency. The importance of design airflow has received even more attention with the entrance of the 13 SEER standard.

There was a time when I would occasionally call Mfg Tech Reps looking for assistance in diagnosing my daily headaches. The first question they ask…”What’s the airflow?”. Well, actually that was usually the second question. The first question was…”What’s the model number?” (a little humor intended there). One distributor tech rep I know, designed a little pamphlet that is essentially a booklet of FAQ’s…the little black book lists several measurements to take, after which the answer to the question is usually obvious. Mfg’s technical guru’s no doubt spend a lot of time troubleshooting low airflow issues, when their true purpose in life, is more one of addressing questions regarding  the exotic  particulars of the equipment.

Commercial ducting systems are necessarily designed to carry the required volume of air, at the least cost. Least costs involves duct size and fan power requirements, among other things. I assume the engineers find the optimum combination of duct size and fan motor horsepower to produce the needed airflow for the least amount of initial costs and long term operating expense…

Residential systems aren’t designed that way. The equipment mfg’s stick a blower / motor combination in the air handler or furnace and tell you it’ll blow the required air so long as you build the duct system big enough to accommodate the limits of the blower / motor combination…which is usually defined in terms of ESP…external static pressure. So you work backwards finding a duct size that won’t choke down the indoor blower, which is reasonably simple enough if you have a Manual D or reasonable facsimile.

It behooves all of us to have at the very least, some comprehension of rudimentary airflow dynamics within a piece of duct. Just enough to understand why some “rules of duct design” need to be accepted and followed. Following the rules will carry you to the most successful duct system design, minimizing the number of potential  flow headaches to have to deal with afterward. Designing out the headaches to begin with is far better than working them out afterward.

Airflow inside a duct or pipe is all about resistance to flow.  Any time air flows through a piece of duct or pipe, it will encounter some resistance, which consumes some of the energy pushing the air through the duct. The net effect is reduced flow. The factors that produce the resistance are numerous. The best case scenario is round, metal, straight pipe, offering the least amount of resistance. Lined rectangular metal, ductboard and flex get progressively worse in terms of resistance. Then, changes in direction or  cross-sectional area, passage through a register, a filter, electric heat element, heat exchange coil, transition or past a take-off add more resistance. Any deviation from the round, metal, straight pipe scenario will create additional disturbances that negatively affect the airflow, requiring some consideration of the deviation in respect to the total system design. And, the only way to compensate for the distubances in most cases is to reduce the velocity of airflow through the duct…and the only way to do that is increase the duct size.  In some cases, improving the “geometry” of the piece of duct, reduces the disturbance…like substituting a radius elbow for a mitered 90.

Duct design via Manual D has been beautifully simplified for those of us neither mentally equipped nor necessarily interested in navigating through the heavy duty engineering design approach. Most all the “disturbance” factors have either been estimated at some direct loss in inches water column (IWC)  pressure, or converted to a value called “equivalent length”. The equivalent length conversion allows us to simply add a linear value to the the straight duct sections, rather than try to calculate an actual pressure loss value for some duct fitting. For example, a 90 deg radius elbow might have an equivalent length of 30 ft.  That simply means the elbow will create the same resistance as 30 ft section of straight pipe. So, a 15 ft run-out with an elbow stuck in somewhere, would have a total effective length of 15 + 30 = 45 ft.

The gist of the friction loss method is a friction rate factor determined by the longest duct run and available static pressure. Then the friction rate factor is applied to a friction loss chart or ductulator to size the duct sections, based on the volume of air they will carry.  So long as you don’t make any huge errors in estimates or arithmetic, the final results  are almost guaranteed to work.

I have over the years seen statements made by so called intelligent and educated individuals offering arbitrary friction rate values for residential duct design, like 0.1 or 0.08. They are saying essentially, size the duct for a specific friction loss value without any regard to the actual duct system  geometry requirements. The value they offer is probably a number that would indeed result in a duct system adequate for the blower capability. But depending on the actual duct system requirements, the value could  be lower than needed, resulting in oversized duct and a waste of material.

The information in Manual D is all most of us need to both understand the mechanics of airflow and design residential duct systems. It is an excellent reference resource to keep on a shelf in your library.

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Troubleshooting: How Stuff Works…and Breaks

So, maybe you’re thinking troubleshooting heat pumps is about Ohm’s Law, psychrometric charts, Mollier diagrams, sensible heat ratios, COP’s and…etc., etc…? There are a lot of scientific principles explaining how heat pumps do what they do. And at some point in our training we eventually have to deal with some of the science in understanding heat pump operation…electricity, magnetism, thermodynamics, fluid flow dynamics…stuff like that. But fluency in scientific principles generally won’t get you to a diagnosis. I can remember a time early in my career when I could recite a lot of science to heat pump owners, but couldn’t tell them why it wasn’t working like it’s supposed to…and then there’s the engineer who posted the following comment at this website:

“..Brilliant blog! I’m just starting to wade through this stuff. Ended up here after looking for answers on diagnosing reversing valves…I’m the engineer learning how to be the tech (geothermal) for the last 3 years and I find practical/applied stuff like this invaluable. Your strength is being able to recall the time when you didn’t understand the problem and relating to that person now trying to figure it out…”

So, just what does one need to know, in order to troubleshoot? Let’s look at a hypothetical situation…

If you walk into the bathroom and flip the light switch, most of the time the light comes on. That’s a simple result of an enormous amount of science and engineering. In order for that light to come on, Ben Franklin had to discover electricity, Edison had to invent the lightbulb, Tesla and Westinghouse had to develp AC power generation…but all you and I have to know is simple circuitry: when the light switch closes, a circuit is completed allowing voltage to be supplied, causing current flow which makes the light burn. And as long as the light comes on each time the switch is flipped, we don’t generally give it a second thought.

But when the light doesn’t come on, what are the options? Well, you could go to the breaker panel and check for a tripped breaker or even take a  meter and confirm the breaker is actually transferring voltage to the circuit. If that didn’t reveal the problem, you could move to the switch and see if there is a problem there…voltage in, voltage out. If you still don’t find the problem, checking the fixture for voltage would be the next thing to do. If after all that, you haven’t found the problem, then your last test would be continuity through the bulb…

But what do we usually do when the light doesn’t come on, after the  switch is flipped? Just change the bulb, right? And why do we change the bulb  before doing all that other stuff? Because most of us know the bulb is the weak link in the chain, the most likely candidate for failure. And how do we know that? Simply from years of replacing bathroom lightbulbs…

So the conclusion of the story is…? Troubleshooting residential heating and cooling equipment is, most of the time, all about knowing how stuff works and how stuff breaks. In the  bathroom light scenario, we use our knowledge of how stuff breaks to get us to a quick and probable diagnosis. But on the few occasions where the bulb isn’t the problem, we can use our knowledge of how stuff works and “test” our way to a solution.

Let’s look at another example closer to reality for us:

Suppose you go on a 10 SEER / R-22 system service call in July, and after making some pressure and temperature measurements, come up with the following numbers:

Suction pressure… 58 psi

Head pressure…….200 psi

Superheat……………2 F

Subcooling………….15 F

An experienced technician can look at the numbers and immediately see a problem with the suction pressure / superheat values,  know what the problem is and the most likely cause…low airflow across the indoor coil, due most likely to a dirty coil. His conclusions are part science and part experience. Normal suction pressures are closer to 70 psi by design with normal superheats closer to 10 F. Most 10 SEER equipment is fixed orifice, meaning superheats  vary with operating conditions. Low suction pressure, with low superheat, is the classic symptom of low evaporator air. There’s not enough heat available to boil off the refrigerant inside the coil, resulting in less refrigerant vapor produced and excessive liquid remaining in the coil. Dirty coils being the cause is mostly a product  of experience.

Knowing how things work tells us what heat pumps are supposed to do and what it takes for them do it. With that knowledge, you can always figure out what’s wrong with a failed system. Knowing how things break quite often tells you where to start the troubleshooting process…

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R-410A…Ready or Not?

Just in case someone hasn’t been keeping up, 12/31/09 is the last day for legal manufacture of R-22 equipment…and may end up being the last day of legal installation of R-22 equipment. I’m no  authority on the EPA regulations governing the phase-out of R-22 or R-22 equipment, but from what I read the EPA has “adjusted” the definition of “date of manufacture” from when it was made, to when it’s installed…

If you remember, when the 10 SEER equipment efficiency standard was plowed under to make room for the 13 SEER standard, many wholesalers and contractors stockpiled a lot of 10 SEER equipment to sell after the new standard went into effect, with no legal ramifications to contend with. But if you were thinking about filling up the company shop and parking lot (or garage in my case) with a bunch of Goodman 22 units the last week of December, 2009 …better reflect on that course of action a little longer. And stay more in tune with the ongoing internal activities of our friends at the EPA. I don’t believe the final ruling has been set in 15% silver  yet, but again don’t take my word for what is or isn’t.

For many, the execution date set for 22 equipment will be just another ho-hum day… no parades, no memorial services. The combination of nixed mismatches of 13 SEER equipment with pre-13 SEER equipment, plus the already existing  availability of 410A equipment, led some percentage of contractors to accepting the inevitable and ditching R-22 powered systems long past. But there are always those reluctant to change, if for no reason other than human nature. For me, I didn’t want to continue selling something that was about to become, essentially, obsolete. Nor did I want to speculate as to what it might cost to add a couple of pounds of “Freon-22″ (or Nu-22 for that matter) in 2015+…

And I’m not passing judgment on what anyone has or has not, is or is not doing. It remains, after all, a free country. And for sure, if the manufacturer’s keep making the stuff, somebody will keep buying it…just don’t get caught without a chair when the music stops.

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For Technicians Only…

..and I should add, techs who are a little weak in diagnostics. We always credit experience for expertise in some skill, regardless of the skill. Experience has always been the best teacher whether you’re working with heat pumps or airplanes…but experience is a somewhat generalized term leaving the inexperienced individual with little assistance in improving his skills level. In preparing presentation material recently for some “Troubleshooting Heat Pumps” seminars, I  came up with a better way (I believe) to illustrate just what experience teaches us, relative to troubleshooting.

It helps to understand the mentality needed for troubleshooting equipment as opposed to building equipment. Heat pump technology is a product of several sciences. But a heat pump unit is the application of those same sciences. And if the unit was designed and manufactured around the scientific principles, it will do what it’s supposed to do…the science is built-in at the factory. So, as technicians, we aren’t required to verify or confirm the science, just the designed operation. So…whether or not we really understand all the implications of the Second Law of Thermodynamics isn’t really an issue. The Second Law of Thermodynamics may explain in scientific terms how or why a heat pump can cool / heat the house, but it won’t tell you the filters are dirty…So just what is it we need to know in order to troubleshoot equipment? For lack of a better expression, I’m going to say, knowing how stuff works, or knowing what stuff is supposed to do. And then you can extend that definition a little and add, …and what it takes to make it do it.

As an illustration, the electricity / magnetism principles that explain why/how a motor “runs”, won’t really help you diagnose a motor that isn’t running…if it isn’t running, some of the science is obviously missing. And if it isn’t running, then it’s not doing what it’s supposed to do. If you know or can figure out what it takes to make it run, you can diagnose the failure….and what does it take to make it run, or do what it’s supposed to do? Voltage source? that’s a good place to start. Closed switch? yep. Unbroken wires/circuit connecting the voltage to the switch to the motor? absolutely. Decent bearings? a must. Good capacitor? of course.

So if you find a motor not doing what it’s supposed to do, now you know what items to test, check, etc., to determine why the motor isn’t doing what it’s supposed to do. Isn’t that far simpler than than trying to measure or analyze the magnetic fields? I would think so…

I believe you will eventually discover diagnostics is more about understanding what the engineers intended the equipment to do, than understanding the scientific principles behind just how it does it. So, when the situation has you stumped, think in terms of what the device, part or system is supposed to do and what might keep it from doing it. Some skill with that approach will help you get you through the service calls…

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TROUBLESHOOTING HEAT PUMP SYSTEMS…INDOOR / OUTDOOR TEMPS VS SUPERHEAT W/ FIXED ORIFICE SYSTEMS

..If you look at a superheat charging chart for a fixed orifice system, you quickly see the required superheat varies with outdoor and indoor conditions. As the outdoor temperatures vary, so does the required superheat…pretty much the same relationship for indoor temperatures. Why? The net force pushing liquid through the metering device is the difference in the head and suction pressures, more or less. And I would guess the designers figure in some maximum outdoor temperature in conjunction with some minimum indoor temp and come up with a minimum superheat value for “worst case” scenarios.

The point being, if the outdoor temperature is 75F you don’t won’t want a “beer can cold” suction line…because by the time the afternoon temperature hits mid-90’s, the increased head pressure will have increased the “net force” pushing the liquid through the orifice, and the system will be overcharged, resulting in a lower than desired superheat.

Likewise, if the indoor temps are “high”, superheats will be high. Most charging charts use indoor wetbulb as the control variable, since wetbulb temps include the humidity factor. As indoor wetbulb goes down, the superheat will decrease, everything else being equal. The following clip demonstrates variations in superheat with outdoor conditions.

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TROUBLESHOOTING HEAT PUMP SYSTEMS…R-22 VS R-410A

Unless you’ve been living under a rock for the past several years, you know R-22 is on the way out and R-410A appears to be the manufacturer’s weapon of choice for heat pump and comfort cooling equipment. If you’ve already encountered a 410A system and had a less than pleasant experience, possibly attempting to correct or understand what appeared to be abnormally high system pressures, your confusion may be with a misunderstanding of mechanical refrigeration, rather than the refrigerant.

Mechanical refrigeration is all about heat transfer and temperatures, especially boiling and condensing point temperatures. The whole point of a refrigeration system is that of creating a heat sink or low heat energy level, causing heat to transfer from a higher energy level. For comfort cooling applications, the indoor coil operates at a temperature lower than that of the indoor air temperature, and I’ll say in the 40ish degree range. When the system is in operation, the indoor air is pulled through the coil, where some of it’s heat is transferred to the coil. That heat is then carried to the outdoor coil, where it is transferred to the outdoor air. When heat pumps are operating in the heat cycle, the outdoor coil has a temperature less than the outdoor air temperature. Then the heat in the outdoor air transfers to the refrigerant in the outdoor coil, is carried to the indoor coil, where it is transferred to the indoor air. So, the dynamics of a mechanical refrigeration system simply control the refrigerant temperatures within the indoor and outdoor coils, maintaining a continuous process of heat transfer, in whatever direction is needed.

I don’t claim or even pretend to know, the engineering details necessary for the design of refrigeration systems. But I have a reasonably good idea of how they’re supposed to operate, relative to system pressures, subcooling and superheat, and particularly with comfort cooling and heat pump applications. And so long as I know what refrigerant the system uses, and have a way to convert pressures to saturated temperatures, I’m comfortable with the system. We’re all probably guilty of becoming familiar with system pressure measurements, and forgetting what we’re actually measuring, which is the saturated refrigerant temperatures in the evaporator and condenser coils. Once we see what those numbers are, we then measure the suction line and liquid line temperatures so superheat and subcooling values can be calculated. With the system pressures / saturated temperatures, superheat and subcooling values, we can make an intelligent decision about the operation of the system.

An R-22 system operating in the cool cycle on a hot summer day will usually run a suction, or low side pressure, of 75 psi or so. And the superheat could range from 5 to 15 degrees depending on the type metering device, equipment brand and outdoor temperature. An R-410A system would be running around 120 psi low side, but would have a similar superheat range, again depending on the metering device, brand and outdoor temperature. The difference in pressures is due simply to the difference in saturated temperature / pressure characteristics of the two refrigerants. So long as your gauges have a “temperature conversion scale” for the type refrigerant you’re working with, and you know what the evaporator temperature is supposed to be, you can analyze the system for proper charge and operation, whether or not the pressures are “familiar”.

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TROUBLESHOOTING HEAT PUMP SYSTEMS…OPEN CONTROL VOLTAGE CIRCUITS

One of the more frustrating and difficult situations with heat pump diagnostics is open circuits in the control wiring. There is a logical process to follow when attempting to locate the failure…

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TROUBLESHOOTING HEAT PUMPS SYSTEMS…REFRIGERANT LEAK DETECTION DEVICES

No doubt, my most frustrating service issue has been locating refrigerant leaks. And I’ll be the first to admit it was due to my own ignorance, from simply not doing a little research. I started out with a cold sensor technology electronic detector, bought a second cold sensor electronic detector and eventually concluded electronic detectors were pretty much worthless, at least for my desires and needs.

Next , I let someone talk me into the ultrasonic detector method. I never found the first leak using it. In fact, I couldn’t find a leak in my truck tire with the thing…so much for ultrasonics.

When I discovered the fluorescent dyes, I thought my leak search headaches were over. And to a certain extent, locating some leaks did prove to be much easier. So long as the black light would shine on the leak area, and it was reasonably dark around the suspect area, and the dye was actually coming out of the leak, I was in pretty good shape. But then there’s the waiting period between injecting the dye, and actually seeing it exit the puncture…and the mess…and all the paraphernalia required to actually locate a leak…

At some point I walked into my favorite wholesale house and told the manager, “Today is the day I buy my last leak detector…if it doesn’t do what I need it to do, I’m just gonna’ slit my wrists, and let my wife collect the insurance…” I bought another electronic detector with heated sensor technology…I had done a little research. That turned out to be one of the finer moments in my service career. It worked so well and was so reliable, I didn’t believe it for a while. But once I finally gained some confidence with the tool, my leak search issues were mostly a thing of the past. I can find most leaks now about as fast as I can access the equipment…especially those pesky indoor coils. Add to the detector’s capabilities my knowing where to look, and my batting average is close to 1000. The biggest problem I’ve had recently was a 410A leak that didn’t want to sniff out well.

Before I get too many people overly irritated with my conclusions, let’s back up a minute or two and pay some due respect to the aforementioned devices and methods. I’m sure there is some useful purpose for electronic detectors that use cold sensor technology. I just don’t believe it’s the residential sector. They will indeed detect refrigerant…but they also detect other stuff, so you never know for sure if the alarm is refrigerant or some other unknown something.

The ultrasonics are revered by some folks, who claim good success in finding leaks. I’m not gonna’ call those same folks liars.

The dyes are absolutely an option for some situations. If for whatever reasons you need to pinpoint the location of a leak, that’s the way to go, unless you want to try the bubble solutions.

But for me, most of the time, I just want to know if a coil is leaking, or an accumulator, or a service valve, or a liquid line filter or whatever. If the coil is leaking, I’ll replace the coil…if the accumulator is leaking, I’ll replace the accumulator.

Most of the repairable leak sources are visible via oil deposits. The electronic detector will usually get you in the general vicinity, and the oil, along with some bubble solution will show you the target.

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TROUBLESHOOTING HEAT PUMPS…DIAGNOSING PSC MOTORS

A common failure with residential equipment condenser and blower motors is not actually the motor, but the run capacitor. Probably the majority of the time, the capacitors fail “open”…the motor can’t develop the necessary torque to actually begin rotation. So, it justs sits in a “stalled” condition, pulling above normal amps…the video gives some thoughts on the subject.

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