Year: 2017

As we have mentioned in several previous articles, many blended refrigerants have glide, which simply means they boil and condense over a range of temperatures instead of just one temperature.

As an example consider refrigerant R407c, it is a zeotropic blend which means it has enough glide that it makes a big difference if you fail to take it into account.

For example, on an evaporator coil running R407c the refrigerant leaving the TXV will begin boiling at the bubble point, let’s say that the pressure in the evaporator is 80 PSIG that bubble temperature will be 40°.

Now as the refrigerant continues boiling the temperature will begin increasing towards the Dewpoint which is 50.8°. Any temperature gained ABOVE 50.8° on a R407c system at 80 PSIG is superheated, meaning the refrigerant is completely vapor.

So we calculate superheat as temperature above the dew point and subcool as temperature below the dew point and the condensing temperatures and evaporator temperature aren’t fixed but they GLIDE between the bubble and dew and back again when the refrigerant is changing state.

But what does this mean for evaporator and condensing temperatures when calculating target head pressure (condensing pressure) and suction pressure (evaporator pressure) also known as evaporator TD and condensing temperature over ambient?

The simplest way is to use the midpoint between the dew and bubble points to calculate CTOA and DTD.

In the case above you would simply calculate 50.8° + 40° = 90.8 | 90.8 ÷ 2 =  45.5° average evaporator temperature or midpoint

Emerson points out that evaporators would be better calculated using 40% of bubble and 60% of dew but the extra complexity generally doesn’t make enough difference to mention.

I made this video to demonstrate further

 

— Bryan

There are several types of Ice Machines but in this article we will focus on Cuber style and Flaker or Nugget style. Both types produce Ice but the process of freezing and harvesting is a little different. The application in which the Ice will be used will determine what style of machine is needed. I primarily work with Restaurants and Hospitals so my article will be geared in that direction.

Let’s start by simplifying the ice making process, if we take water and circulate it over an evaporator that is below freezing we will at some point start to freeze that water, once our Ice has formed we than harvest the ice and start our process again. That’s about as simple as it gets

The  steps to make Ice seem simple take water and freeze it, but It’s not that simple. Making Ice cubes is actually a pretty complicated process, with several critical steps that must be met for the process to work correctly. The first step starts with properly cleaning the water that will be made into ice to remove any impurities, water itself naturally contains minerals and those minerals are an Ice Machines worst enemy. The minerals lead to calcium buildup which causes issues with the ice machine. A quality ice machine install will have a high quality water filter system installed that was sized properly and has the appropriate filters inside that are chosen after a water quality test has been performed. Once we have properly filtered water we bring the water into a reservoir inside the machine and the water waits until the machine is ready to make Ice.

Among all the ice machine manufacturers there are several methods that the machine will tell itself that the ice storage bin is low on Ice and to turn on, the most common methods are a thermostat and or some sort of mechanical control that is actuated by ice buildup, subsequently telling the machine that the ice is low and it’s time to turn on.

Cuber style ice machines

Assuming the machine is ready to turn on, most brands of ice machines will start in a pre-chill, which means we cool the evaporator with no water running over it, this is done to try and prevent slush from forming. Than by means of a water pump the machine will start to circulate the water over the evaporator, and that water will continually run over the evaporator and down into the sump than it will be pumped over the evaporator again, each time it passes over the evaporator the water will get colder and colder and eventually a little bit of the water will start to freeze to the evaporator plate, this process will continue over and over again until the ice is the proper thickness. The thickness can be determined by many methods including a thickness sensor, water level monitoring, and or a timer. Once it’s time to harvest the ice the most popular method is to introduce hot refrigerant from the discharge of the compressor into the evaporator and subsequently melt the ice off the evaporator from the inside out while running a little bit of water over the cubes to assist dropping the cubes off the evaporator. The harvest cycle is usually terminated by a timer that is in the circuit board. Each manufacturer has their own unique way of making and harvesting the ice. With all cuber style ice machines the harvest cycle is very dependent on maintaining an adequate high side pressure as their defrost depends entirely on it. When the machine is self contained and located indoors its not too hard to maintain the proper head pressure because the building will likely be conditioned, however on remote systems where the condenser is located outside we utilize head pressure control valves (headmasters) to back up the refrigerant in the condenser to reduce the condensing capacity of the condenser and subsequently raise the head pressure.

Flaker or Nugget style Ice machines

These machines have a unique way of making ice they utilize a round cylinder evaporator that has an auger inside of it that is turned by a high torque gear motor. The auger sits directly In the center of the evaporator with less than 1/16th of an inch clearance on either sides and the auger is always spinning it has the shape of a corkscrew. The machine will have a water reservoir that supplies water to the evaporator whenever it gets low. The machine will start to freeze the water and as it becomes ice the continually turning auger will force the ice up to the top of the evaporator and out of a nozzle that will shape the ice into the desired style (Crushed, Flaked, and or Nugget). It is important to notice that with this style of ice machine the harvest cycle happens when the ice gets thick enough for the auger to scrape it off and it both freezes and harvests the ice at the same time.

— Chris Stephens

P.S. – we have a new podcast out on ice machines HERE enjoy

My Grandfather is a really interesting guy. He grew up working in the Pennsylvania coal mines starting at the age of 7 or 8 and then worked as well driller, and a plumber, also went to HVAC school, and did some gas work worked a while as an electrician, welder, diver and ended up as an aircraft salvage man.

One of his favorite phrases is to call adjustable wrenches and channel locks (slip groove or tongue and groove pliers) “shoemakers tools”. I literally have no idea WHY he would call them that, or why he thought it was so funny to call them that but he certainly didn’t mean it as a compliment.

It is usually best to use a properly sized socket or wrench to do a job rather than reaching for a “multi-purpose” wrench, but every tool has a purpose and if you are going to use a tool it’s best to use it properly. I know this is basic, but we cant assume everyone has a grandpa like mine.

Pull Don’t Push (When You Can)

Whenever possible orient the wrench so that you are pulling rather than pushing (Yes, I know I’m awkwardly pushing in the GIF below) . This is a much more smooth and natural motion and you will be able to apply more force.

Pipe Wrenches are Special

A pipe wrench is only for working with pipe, NOT nuts, and bolts. I know this should be obvious but I worked with a guy once who treated a pipe wrench like a regular wrench and left a lot of damaged bolt heads in his wake.

A pipe wrench has sharp, angled teeth that will grip in one direction and release in the other direction. Open the jaw wide enough that the pipe sits in about the center of the pipe wrench unlike a typical where the object to be turned sits all the way in the back of the jaws.

Keep in mind that a pipe wrench will leave marring on the surface of the pipe, if you don’t want it to be damaged you can use a leather (or even rubber) strap around the pipe to protect it before using the wrench. A leather belt can do the trick.

Turn the Wrench Toward the Bottom Jaw

Maybe there is an exception to the rule, but not in any of my wrenches. If you turn the wrench toward the bottom jaw they will grip properly and be less likely to slip. In order to tighten vs. loosen just flip the wrench over and turn the opposite direction

Righty Tighty is Annoying

Half my childhood was HAUNTED by the phrase righty tighty, lefty loosey. IT IS ROUND! there is no right or left unless it is a reference to another direction (the top). It’s better said as clockwise tighty… and yes, I know that doesn’t sound cool.

— Bryan

 

 

 

 

 

Like we often do in these tech tips, we will start with the common and more practical explanation of saturation and then move to the more technical and nerdy explanation later.

When we say “at saturation” or “saturated” in the HVAC/R trade we are generally referring to refrigerant that is in the process of changing from liquid to vapor (boiling) in the evaporator or vapor to liquid (condensing) in the condenser.

We generally look at a set of gauges or find the temperature on a PT (Pressure – Temperature) chart that matches a particular refrigerant and pressure and we call that the saturation temperature.

So when a tech connects gauges to the liquid line (high side) of a system and they look at the needle they will refer to the pressure in PSI and the temperature for the particular refrigerant as saturation temperature. On the gauge above the refrigerant in the system is R22 (green scale) they would say that the pressure is 200 PSI and the saturation temperature is 102°F.

To be even more specific, a tech might say that the condensing temperature of this system is 102°F because the saturated state is occurring during the process of condensing in this particular case.

From a practical standpoint in a refrigeration circuit when we say saturation we are referring to –

the pressure and temperature a refrigerant will be if both liquid and vapor are present at the same time and place

One of the most common cases where we will see refrigerant at saturation is inside systems that are off as well as inside a refrigerant tank. If you were to connect a gauge to tank (like this Testo 550 shown) the refrigerant pressure inside the tank will be equal to the pressure that correlates to the saturation temperature of the tank (I know that’s a mouth full but it’s really pretty simple).

In the case of the refrigerant shown above the room temperature is 71.9°F and the refrigerant is R-422D. All I had to do was connect the Testo 550 and select R422D and the saturation temperature (show above the psi on the right) is EXACTLY 71.9°F. In this case, we can say the saturation PRESSURE of R422D is 136.8 PSI at 71.9°F or that the saturation TEMPERATURE is 71.9°F at 136.8 PSI.

Either way, what are saying is that there is both liquid and vapor present inside the tank so it is at SATURATION or in the saturated state if you would rather. So as techs we see refrigerant at saturation pressure and temperature when the system is off, inside a tank and when it is in the midst of boiling in the evaporator or condensing in the condenser.

Now for the more in-depth explanation

I will warn you that this is a bit of a beating around bush explanation, but I’m writing the explanation I wish I had been given early on… so be patient young grasshopper.

 

Let’s start with a dictonary definition of saturation –

The state or process that occurs when no more of something can be absorbed, combined with, or added.

So when something is “full” and can hold no more of something it is said to be saturated, like a sponge saturated with water, or air saturated with water vapor or a in this case, a liquid saturated with kinetic energy.

Many (including Wikipedia) will define saturation as the boiling point of a liquid. This definition is correct but can lead to a misunderstanding. Just because a liquid is at its boiling point doesn’t mean it is actively boiling. The refrigerant in an air conditioner is technically at the boiling point when the system is completely off. Refrigerant in a tank is at saturation (so long as it has some liquid in the tank) even though the refrigerant is static (nor flowing).

In nature, gasses (vapor) and liquids are free to move around and interact with one another with the predominant pressure being atmospheric pressure (14.7 psia at sea level).

You may have wondered why water exposed to the air will evaporate even though it has not reached the boiling temperature? This is because the temperature of a substance is the AVERAGE kinetic energy of the molecules in a substance not the specific kinetic energy of every single molecule. While there may not be enough energy for the entire substance to boil, there is enough energy in a few of the molecules to break free from the surface.

This is why when sweat evaporates off of your skin your skin cools. The highest energy molecules are leaving and taking themselves and their high energy ways with them! 

Translation – Some molecules have more energy than others and are able to escape the liquid form out in nature and we call this evaporation. This evaporation can be measured but it happens below the boiling point and when a substance is uncontained it results in less and liquid remaining.

Translation of the Translation – If you leave water out in a pan it will eventually disappear even when it isn’t boiling

Now if you put a liquid in a jar and screw the lid on, some of the molecules will escape the liquid bonds and fill the void in the jar until pretty soon the jar will be at equilibrium (static) pressure with an equal number of molecules condensing back into the liquid as those that are escaping. The more active the molecules in the jar the more pressure there will be in the jar. Since the definition of temperature is the average kinetic energy of the molecules you can translate that as “The hotter the jar the higher the pressure” or “The higher the pressure the hotter the jar”.

Different liquids have a more or less tendency to escape the liquid form (evaporate), liquids that have a very high tendency to escape will evaporate more quickly and have a higher “vapor pressure” and are also said to be more “volatile”. Alchohol or gasoline are liquids that are more volatile and have a higher vapor pressure at atmospheric pressure than water and disappear quickly even when the ambient temperature is below their boiling point.

Some Liquids (like vacuum pump oil for example) have a very low tendency to evaporate and are said to have very low volatility and a low vapor pressure.

Liquids with low boiling temperatures (like most refrigerants) are very volatile and have a higher vapor pressure than liquids that remain a liquid at atmospheric pressure. We know that refrigerant does more than evaporate at atmospheric pressure and normal atmospheric temperature, it literally BOILS.

A liquid boils when the vapor pressure of the liquid matches the atmospheric pressure. At that point the liquid molecules begin to break free rapidly and if they are uncontained they will simply fly away like water vapor out of an open pot.

If the molecules are boiling and contained they will begin increasing the pressure as they boil until the temperature of the liquid no longer increases and it hits equilibrium between the vapor pressure of the liquid and the pressure inside the vessel (tank, pressure cooker etc..).

Once the vessel is allowed to reach a state of perfect equilibrium it may no longer be boiling but it can still be at the boiling point, that exact POINT of equilibrium between vapor pressure and temperature is the SATURATION POINT. 

So long as the pressure remains constant on a boiling or static vapor/liquid mixed substance we can say that it is at saturation temperature because it remains at the same temperature until either

  1. The pressure changes
  2. The substance is fully boiled

But it is important to remember that it is the vapor pressure of a liquid substance being equal to the pressure around it that results in saturation and then boiling or in the opposite direction, condensing.

Also… Evaporators should be called boilerators but I’m doing being nerdy for now.

— Bryan

 

 

 

 

If you are used to simple, straight cool split systems you know that the low voltage to the outdoor unit is usually VERY simple with just a Y (contactor power) and a C (common) connected to the outdoor unit in many cases. When the condensing unit controls are strictly two wire low voltage there is no continuous low voltage power so there is also no timers or other logic in the condensing unit. Usually, in these cases, the LV wires connect directly to the contactor coil.

A heat pump needs to be able to switch between heat and cool and defrost which brings in the necessity for more control conductors and complexity.

A heat pump defrost board like most modern controls contain both loads and switches to control different functions.  because it has timers and some basic “logic” the board requires a power supply and for most residential split system boards this power comes from the C (common) and R (hot) terminals from the indoor 24v transformer.

The defrost board also utilizes the constant power on the defrost board R terminal to backfeed voltage through the W2 wire back to the secondary heat inside whether it be heat strips, furnace or hydronic secondary heat.

This helps to counteract the cooling effect that occurs when the heat pump when it shifts from heat to cool mode for defrost. This function is an important thing to test on heat pumps to reduce cold draft complaints during the winter.

Simply force the board into a defrost and check for 24v between w2 and c at the outside board to confirm proper operation or check the secondary heat via ammeter or visual confirmation during the defrost cycle.

— Bryan

I walked into a supply house the other day and I was looking at “universal” expansion valve on the shelf. The friendly guy behind the counter saw me and walked over, after saying hello he offered

“That’s a great valve, it’s even balanced port”.

Now I am a bit of a trouble maker, I should have just nodded and said “uh huh” but instead I asked, “what does balanced port mean?”. The counter guy sort of half shrugged and said “I guess it means it works on a lot of different systems?”

I would bet that most people in the industry have heard the term “balanced port” and figure it sounds like a good thing but don’t really know what it does. Not long ago, I would have been one of them.

We have all been taught that there are three forces that act on an expansion valve –

  1. Bulb Pressure is an opening force
  2. Evaporator Pressure (external equalizer) is a closing force
  3. The Spring is a closing force

while the system is within its design operating conditions these forces are the primary forces at work that allow the valve to “set” the evaporator outlet superheat.

There is a fourth force and that is the opening force applied by the refrigerant passing through the needle. When the inlet (liquid line) pressure is within the normal operating range this force is accounted for in a normal TXV. In cases where the liquid pressure is higher than usual the force will be greater allowing more flow through the coil and when it is less it will allow less flow.

The result of this effect is fluctuating superheat based on liquid pressure which may be acceptable in small amounts but can become unacceptable quickly on systems that require accurate evaporator feeding or systems that have a wide swing in condensing temperatures and pressures.

Sporlan largely solved this particular issue in the 40’s when they brought the “balanced port” valve to market. While the technology is nothing new it has been improved on over time.

Balanced port TXVs can vary in design but they solve this problem by allowing the inlet pressure to effect the top and bottom of the needle (orifice) equally. This eliminates (or reduces) the liquid pressure as an opening force and instead turns it into a “balanced” force that neither opens or closes the valve.

If you have an application where the head pressure is allowed to change or “float” over a wide range, the balanced port TXV is a great choice.

— Bryan

 

 

First, let’s state the obvious and clear the air a bit. The photo above is SUPER CHEESY! But this story is about three bad techs who don’t know it so three models clearly posing in clean clothes makes as good of a proxy for a bad tech as anything else.

First off, I’m not being negative about the trade or making fun of people, the point of this story is to identify some traits that many of us may exhibit or see in others techs and it can be hard to identify our own issues or issues within your organization. See if any of these techs sound a LITTLE TOO FAMILIAR and maybe we can learn something. Before you ask… No, these are not real people…. probably… maybe

Randy the Drama King

Randy, like most dramatic people who work in the trades, doesn’t see himself as being dramatic. He just thinks he is being constantly disrespected by management and co-workers and customers are crazy and the dispatcher is out to get him and it’s always about to rain and that ladder (and every ladder) looks unsafe.  These things aren’t DRAMA they are FACTS in Randy’s world and if you question this reality you get added to the long list of people who are disrespecting him.

Randy starts conversations with customers with phrases like “you aren’t going to want to hear this” or “Do you want the good news or the bad news”. He also tends to pass blame to his coworkers or his company because they are just clueless and he knows what’s REALLY going on.

Randy is actually a good tech, but he get’s in a lot of conflicts with coworkers, customers don’t always like his negativity (or as he calls it “being honest”) and he is inefficient and largely unpopular with other techs and management. Randy knows people think poorly of him because everyone is conspiring against him with that blankety-blank dispatcher Donna!

Randy always feels persecuted by the people around him and usually has something negative or conspiratorial to share about every topic. Politics, The weather, customers, co-workers, spouses… you name it.

Here is a test you can take to see if you might be a bit of a Randy

  • You have more than 5 people you are ticked off with or avoiding at any given time
  • You consistently see “danger” around you that nobody else sees
  • During work hours you have multiple conversations over 5 minutes with others about things that are “wrong”
  • You use a lot of negative and fear-inducing language with customers

If you find you are allowing negativity and drama get to you the best practice is to give yourself a break from negative speech. Like your grandma used to say, “If you don’t have anything nice to say”. Negativity is a hard habit to break but the best time to start is now and the best antidote for negativity is gratefulness.

Bob the Excuseful  

Yes, excuseful is a word… I made it up and I like it.

Bob is confident that he would be able to do his job if he was just given the proper training and tools and enough time to do the job and enough sleep and wasn’t forced to work these ridiculous hours. Bob often wonders if he should go back to school and get his degree in …. something and all the courses he would take if his cheapskate boss would just invest in him.

Sure he was given a book and sent to a seminar last month but that was all THEORY, he is a hands-on learner and he CANNOT learn from books or videos or seminars or anything unless he can get his hands on it.  Once he DOES get his hands on it he can’t be held responsible for any mistakes he makes because he has to be SHOWN what to do and how to do it and if he isn’t SHOWN how can he be held responsible? Now, when he is shown, he is a hands-on learner so he can’t learn things by being shown… he needs to do it himself.

His truck may be a mess but he would clean it if he ever had time with these ridiculous hours but in the slow season that is his one time of the year to relax, you can’t expect him to take his own time during the slow season to clean his van can you?

Here are some indications you may be struggling with a bit of Bobish excusefullness

  • You feel jealous when others succeed  and immediately give some reason why they have an advantage over you
  • You read fewer than 5 books last year but still feel like your lack of education is someone else’s fault
  • You find yourself using “hands-on learner” as a reason for failing to understand something
  • When you don’t understand something you call or text someone rather than looking up an answer yourself
  • You have a sense that your lack of progress is due to a lack of “opportunity”

The best way to stop making excuses is to begin living and working with what old-timers called “grit” or “gumption”. This means doing whatever it takes to solve problems, making excellence a goal and going after it no matter the barriers. Start by reading and learning on your own, don’t wait for someone to show you or tell you, go get it yourself.

Todd the Careless

Todd knows he is just forgetful, he TRIES to remember to tie down his ladder and put the caps back on and close his back doors on his van but he just forgets sometimes OK!

Sometimes Todd get’s defensive when other techs call him out for leaving the panel off or “forgetting” to clean the drain, but usually Todd just apologizes and says he will do better next time, but he knows he won’t because he didn’t do it on purpose, it just …… happened.

Some of the “Grouchy” old techs have told him that doesn’t seem to care about his job, but they are WRONG! (in Todd’s mind) he does care, he just has other things going on in his life and in his mind and sometimes accidents happen… like the time he stepped through the attic ceiling, or the time he slipped on the ladder, and that one time he rear-ended that car in the parking lot… oops

You may be a Todd if ….

  • You regularly make mistakes where you “just forgot”
  • You find yourself looking at your phone, texting and using social media during the workday
  • Your mind is preoccupied with personal matters during work and while driving

We have entered a new era of carelessness due to the advent of smartphones, social media, and texting. Many of us find our minds constantly distracted by things other than work during the work day and it leads to poor outcomes, mistakes and safety hazards. everything from climbing a ladder, to driving, to filling out a service call requires ATTENTION and distraction can lead to costly and dangerous mistakes. The best advice is to put the distractions way during the work day… unless it is reading this article. Just remember to put the panels back on and run test the equipment when you are done.

— Bryan

 

 

 

 

 

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