• Early experiments with evaporative cooling using ether and alcohol
• The birth of closed-loop refrigeration systems
• Dangerous early refrigerants like ammonia and sulfur dioxide
• The game-changing invention of Freon (R-12) in 1930
• Environmental concerns leading to CFC and HCFC phase-outs
• Modern refrigerants and their trade-offs between stability and flammability

Learn why we’ve come full circle, revisiting some of the earliest refrigerants with a modern twist. The history of refrigerants is an interesting one!

The post History Of Refrigerants appeared first on Kalos Services.

Natural refrigerants include ammonia (NH3, R-717), carbon dioxide (CO2, R-744), and propane (R-290). Ammonia was a common refrigerant before the rise of R-11 and R-12, but the latter refrigerants were safer to work on. However, R-11 and R-12 damaged the environment, and ammonia has little impact. The other natural refrigerants also tend to have smaller environmental impacts than many of the chemical blends on the market today.

This article will cover the three most common natural refrigerants, their most common uses, and safety considerations.

A BRIEF HISTORY OF NATURAL REFRIGERANTS

Before compression refrigeration became commonplace, ammonia was the refrigerant in absorption refrigeration systems. Absorption refrigeration was a breakthrough of Michael Faraday in 1824. That breakthrough led to the use of ammonia in inventions like the “Icyball” in the 1920s (shown above). Ammonia was first used as a refrigerant in compression refrigeration machines in 1876. Carbon dioxide also came on the scene as a refrigerant in the early 1900s, though its use as a refrigerant was proposed in a British patent in 1850. Both refrigerants were natural and easy to come by.

However, CFC development also occurred in the 1920s. CFCs were effective at moving heat, were stable, and were non-toxic. They replaced ammonia and carbon dioxide in many refrigeration applications. Carbon dioxide mostly faded out of the picture and disappeared from use. On the flipside, ammonia didn’t completely go extinct, as it remained in use in large industrial applications. Propane became a common refrigerant in self-contained small refrigeration; RV refrigerators were and still are common uses for propane.

In the 1980s, the industry became aware of a major problem with CFCs. They depleted the ozone layer and had a significant negative impact on the environment. So, CFCs are no longer in widespread use. That opened the door for HCFCs and HFCs. Like CFCs, HCFCs contain chlorine, which breaks down the ozone layer. So, those have since been banned from production or importation (though R-22 systems still exist today). Many HFCs have a high global warming potential, and they are slowly going through a phase-down period.

These regulations, as well as new technologies, have opened the door for natural refrigerants to reenter the commercial and industrial refrigeration space.

SAFETY

The “natural” refrigerants all have different degrees of safety. ASHRAE classifies refrigerants based on toxicity and flammability. Low-toxicity refrigerants belong to Class A, and more highly toxic ones belong to Class B. In terms of flammability, a refrigerant may be part of Class 1, 2L, 2, or 3. The higher the number, the more likely a refrigerant is to catch fire (with 2L representing mild flammability).

At the time, CFCs were attractive because they were Class A1; they were non-toxic and would not catch fire. R-22 and R-410A are also A1 refrigerants, and many of their replacements are A2Ls. Of the natural refrigerants, only CO2 is an A1.

Ammonia is the only toxic natural refrigerant; it is also mildly flammable, so it’s a B2L. It’s worth noting that it may be the only “toxic” refrigerant of the naturals, but it’s easy to detect. Refrigerants with low toxicity could be deadly if they go undetected, as they displace oxygen and may asphyxiate people in closed spaces. Ammonia is lighter than air, so it will rise. Carbon dioxide and propane, both non-toxic but capable of displacing oxygen, are heavier than air; they will displace air from the bottom up, so alarms should be mounted at a low point in the room.

The propane we use in refrigeration is NOT the same kind you can pick up for your grill. However, many of the same precautions should be taken; propane is highly flammable in both forms.

Propane belongs to a family of substances called “hydrocarbons,” along with propylene and isobutane. Those refrigerants are highly flammable, but they aren’t highly toxic. Therefore, propane is an A3 refrigerant. Propane is also colorless and odorless, so you likely won’t be able to detect a propane leak with just your senses. In those cases, a static or electrical spark could be deadly, so a lot of care needs to go into the design and maintenance of propane systems.

ENVIRONMENTAL IMPACTS

Since natural refrigerants are NOT synthetic chemicals, they are abundant and easy to source. Also, unlike CFCs and HCFCs, none of them deplete the ozone layer.

Moreover, the natural refrigerants discussed in this article all have a very low global warming potential (GWP). We calculate GWP as a ratio that uses carbon dioxide as a baseline; CO2 has a GWP of 1, so a refrigerant that has a GWP of 5 has FIVE TIMES the environmental impact of CO2.

For some context, R-404A, which is common in commercial refrigeration systems, has a GWP of 3922. In other words, a single pound of R-404A has the same environmental impact as 3922 pounds of CO2. By comparison, R-410A (common in residential and light commercial HVAC) has a GWP of 2088. However, both of those refrigerants are going through a phase-down due to their high GWP. R-454B, which is an A2L replacement for R-410A, has a GWP of 466.

On the other hand, propane or R-290 has a GWP of 3. That’s the highest GWP of the three natural refrigerants in this article, with CO2 coming in second place with a GWP of only 1. Ammonia has NO global warming potential, meaning that it is the most environmentally-friendly choice. All three of those choices have very low GWP, meaning that they make good choices for the environment; they also likely won’t be in the crosshairs of future refrigerant phaseouts and transitions.

COMMON APPLICATIONS FOR EACH “NATURAL” REFRIGERANT

In many cases, these “natural” refrigerants are impractical for small-scale refrigeration; propane is an exception, as it is a common refrigerant for small, self-contained refrigerators

Ammonia is one of the most common refrigerants in industrial refrigeration. Industrial refrigeration systems are often much bigger than grocery systems; you may find ammonia as a refrigerant in chemical plants, large cooling operations, pharmaceutical facilities, and refineries.

Carbon dioxide is common in commercial refrigeration, but it can come in a few different forms. That is because carbon dioxide can be used above or below its critical point. The critical point refers to the temperature and pressure at which a fluid is neither a liquid nor a vapor and does not obey the pressure-temperature relationship. Systems that stay below the critical point are called “subcritical,” and systems that go above the critical point are “transcritical.” In transcritical systems, the part traditionally called the “condenser” becomes a gas cooler, which helps reduce the temperature of that fluid. Due to CO2’s low critical point (87.8 degrees), we see very few subcritical systems in Florida because they simply don’t work.

CO2 can work by itself or work in a system with other refrigerants. The other refrigerant could be an HFC like R-404A, or it may even be ammonia or propane. CO2 may also be used in medium-temp or low-temp refrigeration, though it is common to “cascade” it with another refrigerant; a cascade system often uses multiple refrigerants to achieve medium-temp and low-temp refrigeration at the same time. These systems have heat exchangers that help cool the condenser of the low-temp circuit while boiling off some of the refrigerant in the medium-temp circuit.

There are also some great resources if you want to learn more

We barely scratched the surface of natural refrigerants, but we hope you have a better idea of why these fluids can be great, sustainable options for large-scale commercial refrigeration. Here are some resources you may choose to consult if you wish to learn more:

• Emerson educator Don Gillis gave a thorough presentation about CO2 (and mentioned the others) at a trades event at Kalos. You can watch that HERE. It’s mostly aimed at technicians, but it’s a deep dive into the world of CO2 in commercial refrigeration.
• The HVAC School Podcast, operated by Kalos President Bryan Orr, also covered propane in a few episodes. HERE is an episode featuring Alejandro Rios from True Refrigeration. HERE is another R-290 episode featuring a representative from Embraco, a compressor manufacturer.

The post What Are Natural Refrigerants? appeared first on Kalos Services.

Sometimes, technicians have to add refrigerant, but it’s usually not because the refrigerant “goes bad” inside the system. Refrigerant doesn’t typically “wear out” in the way that we might imagine. However, blended refrigerants can cause a drop in performance when their mix becomes uneven. This article will explain why refrigerant doesn’t “go bad” as we might imagine, how blended refrigerants can “go bad,” and why we might need to add refrigerant to a system.

HOW REFRIGERANT WORKS

A/C and refrigeration systems absorb heat and reject it somewhere else.

Inside the air handler of an A/C unit, cold liquid refrigerant moves through the evaporator coil. The blower moves air over the coil. Since the air is warmer than the refrigerant, it loses some of its heat to the refrigerant. As the refrigerant absorbs that heat, it boils; the fluids used in A/C and refrigeration systems have much lower boiling points than water. The refrigerant is under pressure in an HVAC system, so the boiling point is typically around 40 degrees Fahrenheit in a typical residential A/C unit. (However, at atmospheric pressure, R-410A has a boiling point below -55 degrees Fahrenheit!)

Once it has boiled off, the now-vapor refrigerant moves to the compressor, where it is squeezed into a smaller volume and gets a lot hotter. The discharged vapor then moves to the outdoor unit, where the outdoor temperature is far lower than the vapor temperature. A fan blows over the coil, and the hot vapor loses some of its heat to the cooler air. As it loses heat, it becomes a liquid again.

After the refrigerant becomes a liquid, it returns to the indoor unit and undergoes a pressure drop before repeating the cycle at the evaporator coil.

The refrigerant does that over and over, and it doesn’t wear out in the process. It simply changes from liquid to vapor and back again as it absorbs and rejects heat.

Grocery refrigeration systems work similarly; evaporators absorb heat from inside the refrigerated boxes, and the condenser rejects that heat outside. There are usually many compressors, and the refrigeration cycle takes place with the help of large racks that can control multiple evaporators and compressors.

WHY MIGHT I NEED TO ADD REFRIGERANT?

Refrigerant doesn’t wear out, but it can leak at fittings, valves, or through pinhole leaks in the copper or aluminum. Leaks are likely when a joint or valve has been poorly brazed in. Corrosion on the evaporator coil or line sets can also cause pinhole leaks.

Many leaks are usually very slow, but they negatively impact your equipment’s ability to remove heat. A smaller volume of liquid in the evaporator coil won’t be able to absorb as much heat as a larger amount. The smaller volume will also heat up more than a larger volume, and it may lead to overheating in the compressor as well.

So, we can add more refrigerant in the short term. Even though the production of R-22 was banned in 2020, it is still legal to add R-22 to older systems. However, recharging the system can be very costly due to the lack of newly produced stock.

A long-term solution would be to replace the leaking components, which could be a line set, valve, or even an evaporator coil. An HVAC technician should do thorough leak detection and pinpoint the location of a leak before offering to replace a leaky component.

However, significant leaks can cause even more trouble in systems that use blended refrigerants.

WHAT CAN HAPPEN TO BLENDED REFRIGERANTS?

Some blended refrigerants can “go bad,” but it’s not in the way we think they can.

R-410A is an example of a refrigerant blend. R-410A uses R-32, which is a good refrigerant but is flammable. To temper the refrigerant’s flammability, manufacturers mix R-32 with R-125, which is a flame suppressant. The R-410A example goes to show that whenever you mix refrigerants, you mix chemicals with different properties.

Those different properties cause those refrigerants to have “glide,” which is a range of boiling points based on all refrigerants in the mixture. R-410A has very little glide, but refrigerants like R-407C have significant glide. R-407C consists of R-32, R-125, and R-134A. When there is a leak, the higher-pressure refrigerants leak out faster than the others in the mixture. The uneven losses cause “fractionation,” which causes the refrigerant’s chemical makeup to change, leading to swings in temperature and pressure. Those dramatic swings can cause poor performance.

For that reason, technicians must add blended refrigerants to HVAC systems in the liquid state (not vapor). HVAC technicians must also check tanks and systems for leaks. A significant leak in an HVAC or refrigeration system may cause fractionation, but even small leaks can alter the chemical makeup of refrigerants stored in upright tanks.

If there is a reason to suspect that fractionation has occurred inside a system, it’s typically best to have an HVAC technician recover all of the remaining refrigerant in the system. Then, the technician would charge the system with brand new refrigerant (and make sure to add it in the liquid state).

Pure refrigerants (like R-22 and R-32) simply won’t wear out. They can deplete if there are leaks, but they don’t stop working. The same is somewhat true (but more complicated) for blends; the refrigerant doesn’t completely stop working, but the fractionation caused by leaks may cause a performance decline.

All of this is to say that refrigerants don’t get dirty and break down like car oil. Refrigerants can do the same job over and over again for several years at a time. Leaks are often the culprits of performance concerns, not the refrigerant “wearing out” or “going bad.” That said, if you notice a decline in your system’s performance, it’s a good idea to contact an HVAC/R professional to find out if any leaks or other potential issues are causing your HVAC/R system to perform poorly.

The post Does Refrigerant Go Bad or Wear Out? appeared first on Kalos Services.

Oil separators take the discharge gas from the compressor and separate the oil from the refrigerant. That way, the refrigerant proceeds to the condensing unit, and the oil returns to a reservoir for use near the compressor.

Commercial oil separators come in three main varieties, but they all accomplish the same task: separate oil from the refrigerant and send it back to the reservoir. This article will look at three different types of commercial oil separators; it will explain how they work and take a look at each type’s benefits and drawbacks.

IMPINGEMENT SEPARATOR

The oldest type of oil separator is the impingement-style separator. These separators use screen socks or filters that separate the inlet and outlet; the gas passes through the filters, and the oil vapor gathers into large droplets. As the refrigerant passes through the outlet, the oil droplets drip to the bottom of the separator and into a vessel. Inside the separator, a baffle prevents the vapor from shortcutting and bypassing filtration.

Three different separation processes are at work in the impingement separator. The first and most intuitive process deals with the screen socks; when the gas comes into contact with the screen sock, oil gets stripped from the mixture. There are also two changes in velocity that happen inside the separator: a change in speed and a change in direction. A change in the speed at which the gas moves causes some oil to be ejected from the refrigerant; think about slamming the brakes on a fast-moving car and having all the car’s contents slide to the front. Changes in the direction also cause some oil to separate from the refrigerant; think about taking sharp turns with a car and having the contents slide around.

Impingement separator benefits

Impingement separators have remained in use for a long time due to their reliability. These separators also happen to be some of the least expensive on the market, and they don’t have parts that need semi-regular replacement. System designers can also oversize these separators without a huge impact on efficiency.

Impingement separator drawbacks

The impingement separator tends to be less efficient than some of the newer models; these are only around 80% effective. When oil remains in the gas, it travels through the rest of the refrigerant circuit and may clog up the pipes if it gets stuck in low-lying areas.

A pressure drop can also occur across an undersized separator when the screen socks get clogged with debris. As with a dirty A/C filter, debris is a restriction; without adequate room for the remaining fluid to pass through, the pressure builds on one side and is much lower on the other.

CENTRIFUGAL SEPARATOR

The centrifugal separator is a bit simpler and more straightforward. It simply relies on centrifugal (spinning) force and layers of screen mesh along the side to separate the oil and drain it out.

The discharge gas enters the separator at an angle. The angle of entry causes the discharge gas begins moving in a vortex-like motion inside the separator can. As the gas maintains that circular motion, the oil stays on the outer side of the vortex. Since the oil is on the outer side, it comes into contact with the screen mesh; the oil comes together in larger droplets and drains out as it drips down the mesh.

Another type of separator, the helical separator (pictured below), uses the same principle with a slightly different process. Instead of there being a mesh on the side of the can, there are plates all around it. The heavier oil droplets collide with these plates and drain downward.

Centrifugal separator benefits

Centrifugal separators tend to be highly efficient when the system designer adheres to correct sizing guidelines. When sized properly, a centrifugal separator can be 99% effective.

These separators also have a low pressure drop and are reliable, as there are no filters that need replacement.

Centrifugal separator drawbacks

Sizing is much more critical for centrifugal compressors than the other commercial oil separators.

Oversizing and lower-load conditions can significantly decrease the efficiency of centrifugal separators. Smaller cooling loads will cause the discharge gas to enter the separator at a lower velocity, making it harder to fling the oil to the sides of the can.

COALESCING SEPARATOR

The coalescing separator sends discharge gas through an inlet at the bottom and uses a filter to strain the oil from the discharge gas. As discharge gas moves into the separator, oil collects on a filter (made of a material resembling fiberglass). The filter works from the inside out, so the oil droplets get larger and larger because they coalesce as they move through the filter. When the oil reaches the outside of the filter, gravity allows it to drain into a sump.

Like the other types, coalescing separators need the discharge gas to have enough velocity. If the discharge gas is moving too slowly, the oil particles might be able to weave through the filter instead of colliding with the fibers. Unlike the other types, coalescing separators need to have their filters replaced on occasion. They also come with a removable flange that allows you to access the filter, and there are some costs associated with filter and flange replacement.

Coalescing separator benefits

When sized properly, coalescing separators can be more than 99% efficient. The nature of the coalescing separator also allows it to remove other contaminants from the discharge gas, which can prevent pipe restrictions that negatively affect performance.

Coalescing separator drawbacks

The filters of coalescing separators need replacement from time to time, which makes these separators a bit pricier than the other types. Dirty filters can cause a large pressure drop, and they may even rupture in extreme cases. So, maintenance is especially critical and may be pricey.

Overall, each oil separator has its benefits, drawbacks, and appropriate uses. When efficiency is less of a concern than price, the good old impingement separator will be best. If you want an efficient, reliable option and can work with tight sizing parameters, then the centrifugal separator could suit your system best. Instead, if you’re willing to spend a bit more on maintenance but want the best possible efficiency and contaminant removal, then the coalescing separator is ideal.

Ultimately, there is no best option that will suit everyone. Each facility manager’s “ideal” oil separator will vary by budget and each individual refrigeration system’s needs.

The post Commercial Oil Separators appeared first on Kalos Services.

In HVAC/R trade school classes, many instructors liken the compressor to the human heart. They do it with good reason; the compressor pumps refrigerant from one side of the system to the other, and most commercial refrigeration systems can’t work without compressors. (Note: there ARE some ways to provide refrigeration without a compressor. You can read about those on HVAC School at https://hvacrschool.com/refrigerant-cycles-without-compressors/.)

But what do commercial refrigeration compressors do? How can we monitor their behavior and maximize their efficiency?

This article will explain the basic functions of commercial refrigeration compressors, go over various types of compressors, and describe how we can make compressors as efficient as possible.

BASIC COMPRESSOR FUNCTIONS

The compressor has two main jobs: compress vapor refrigerant and circulate it through the system. Overall, the compressor’s main goal is to circulate the most pounds of refrigerant with the lowest possible energy usage (in watts). We can measure that rate of circulation in pounds per minute (lb/min) or pounds per hour (lb/hr); we call that the mass flow rate.

Although compressor size is one of the main factors that control the mass flow rate, the mass flow rate may also change depending on how dense the refrigerant is. When the refrigerant is denser, we can expect higher mass flow rates. However, when the suction pressure is low and the refrigerant is less dense, we can expect lower mass flow rates.

The suction pressure is also a variable in the compression ratio, which also affects the mass flow rate. When we find the compression ratio, we take the head pressure (on the high side of the system after the compressor) and divide it by the suction pressure (coming from the evaporator at the box). In general, refrigeration compression ratios should be higher than residential and light commercial HVAC compression ratios. However, they still shouldn’t be too high, as that is a sign of inefficiency.

In other words, a high compression ratio will lead to a lower mass flow rate.

When a compressor is operating, it also regulates the pressures of the evaporator and condenser. The evaporator is where the refrigerant absorbs heat from the refrigerated box and maintains the temperature. On the other side, the condenser rejects heat from the system. The compressor does a balancing act between the two; as more the evaporator absorbs more heat, the compressor heat output increases. That then makes the condenser reject more heat, thus increasing the mass flow rate.

OTHER NOTABLE COMPRESSOR FUNCTIONS

Compressors have motors, which may overheat. As a result, many compressors contain a means of cooling their motors via air or water. Air-cooled compressors pass air over the compressor to keep it cool. On the other hand, water-cooled compressors contain a water jacket that allows water to cool the compressor without actually coming into contact with the motor. In many cases, companies that offer both air-cooled and water-cooled models will have nomenclature that distinguishes the two. In some cases, the suction gas (refrigerant) may also be used to cool the compressor.

The compressor also contains oil that lubricates the bearings and keeps the compressor from experiencing mechanical wear. A refrigerator’s oil system ties in with the compressor, where oil mixes with the refrigerant. Upon discharge, the oil is separated from the refrigerant inside an oil separator, and it gets stored in a reservoir separate from the compressor. Refrigerant has an affinity for oil, and we have to try to keep it from migrating into the compressor crankcase when the system is off; we can stop migration with crankcase heaters, liquid line solenoid valves, pump-down solenoids, and hard shutoff TXVs.

COMPRESSOR TYPES

We use a few different ways to classify compressors.

We classify compressors based on whether they open or not. Hermetic compressors have their motors completely sealed within the compressor body; these can’t be taken apart without cutting into them. On the other hand, semi-hermetic compressors keep the compressor and motor in the same space, but that space is a sealable chamber that can open and close if we add or remove screws. Both hermetic and semi-hermetic compressors have set operating ranges; if the compressor operates outside the manufacturer’s published operating range, then it won’t run at its full efficiency.

Open compressors have motors that are separate from the actual compressor and don’t have the same sealed chamber found in the other two types.

Compressors come in a few more categories based on how they operate: reciprocating, scroll, and screw. Each compressor type has its benefits, drawbacks, and ideal applications. (Some are better for industrial refrigeration. There is also a fourth type, centrifugal, which is usually very large and often used in large manufacturing plants.)

RECIPROCATING COMPRESSORS

Reciprocating compressors contain pistons, which go down to draw the refrigerant in and go back up to “press” the refrigerant into a smaller volume before discharging it. These compressors are common in all sorts of HVAC and refrigeration systems and tend to be quite durable. However, they are not the most energy-efficient option on the market because not all of the vapor is discharged through the piston. Semi-hermetic configurations are quite common.

Some of the good folks at Emerson did a compressor tear-down class for HVAC School. You can see how a reciprocating compressor’s pistons work by clicking HERE. (Note: the link takes you to the exact timestamp of the piston examination. You are welcome to watch the entire demonstration, but it is almost 50 minutes long. The demonstration also features a scroll compressor at the very end.)

SCROLL COMPRESSORS

Scroll compressors tend to be quite efficient. These compressors have two scrolls, which are spiral-shaped plates that fit inside each other; These scrolls compress refrigerant by oscillating an orbiting scroll within a fixed scroll. (You can see what these scrolls look like in a quick video by Kalos President Bryan Orr HERE.) There is oil between the scrolls so that they can make contact with each other repeatedly without wearing each other down; signs of wear on the scrolls indicate that liquid refrigerant has gotten into the scrolls and washed the oil away. Scroll compressors tend to be rather compact and are often hermetic.

Some manufacturers may have scroll compressors that are designed for specific temperature applications; for example, Emerson’s Copeland compressor line has different types of scrolls that can be used in low or medium-temperature refrigeration.

SCREW COMPRESSORS

Rotary or screw compressors contain one or two screws and compress the gas between the screw notches. The double-screw variety shares some similarities to scroll compressors in the way that they compress the refrigerant into a smaller space. As a result, screw compressors tend to offer more capacity and control over operation than reciprocating compressors. Screw compressors tend to be large and well suited for industrial refrigeration, though they are also suitable for some grocery refrigeration applications.

HOW CAN WE MAXIMIZE THE COMPRESSOR’S EFFICIENCY?

One of the most important ways we can increase efficiency is by decreasing the compression ratio. Some simple ways we can reduce compression ratio include keeping the condenser clean and making sure the suction line is of the proper size. Refrigeration contractors can control those two main things with maintenance and proper installation. However, there are a few other ways that facilities managers can keep compression ratios low.

You’ll typically get relatively low compression ratios when you keep your set temperatures within or slightly above the equipment’s design temperatures. In other words, it’s unwise to use coolers as freezers or set the box temperature down from 36 degrees to under 20 degrees. You can also try your best to keep good airflow moving through a refrigerated case; keep products spaced out whenever possible to allow for better circulation and airflow. You’ll also have an easier time keeping your products’ temperatures under control if you make sure the products aren’t crowded in the refrigerator.

Figuring out how commercial refrigeration compressors can work at the top of their game can help save energy and money. However, efficient compressors with low compression ratios are also less prone to premature failure; high compression ratios are often responsible for overheating, which can cause a compressor to fail. So, paying attention to your compressor is vital to the longevity and efficiency of your equipment.

The post Commercial Refrigeration Compressors appeared first on Kalos Services.

Parallel rack refrigeration systems are very large and contain multiple compressors piped together in parallel. All of the coolers attached to the rack system share the same refrigerant and oil charge, so a parallel rack system is an efficient way to keep several units cold at once. These refrigeration systems are so large that they typically require their own motor rooms, which are usually located on the rooftops of grocery stores.

We’re going to share a few secrets about parallel rack refrigeration and show you where and how the magic happens. We’ll also cover some special safety concerns with parallel rack motor rooms.

PARALLEL RACK ANATOMY

We can see a few different types of rack refrigeration systems, including direct expansion (DX) and carbon dioxide (CO₂) systems. This time, we’re going to focus on the DX rack refrigeration system.

Like most other compression-refrigeration systems, parallel rack refrigerators operate on a refrigeration cycle. In other words, they use refrigerant to absorb heat, compress that refrigerant, reject heat from the refrigerant, and drop the refrigerant pressure to restart the cycle.

However, parallel racks may have several evaporators and multiple compressors piped together. All of the compressors are tied into the same piping system, so they all discharge hot, high-pressure gas into a discharge header. That discharge header then leads into a common discharge line that goes to the condenser. However, some of the discharge gas may tie into the A/C system for reheat purposes.

From the condenser, the refrigerant travels to the liquid receiver. That receiver can store liquid refrigerant when it’s not actively moving through the system. Then, the refrigerant passes through a filter-drier. It then goes through the liquid line to the remote liquid header. That’s where the evaporators connect the liquid header to the suction header.

Each evaporator has a pressure-regulating valve, which can help the system achieve near-100% runtime between defrosts. The evaporators allow the refrigerant to absorb heat from the coolers below, and the refrigerant turns into a gas. From there, the gas moves to the suction header, through the suction line, and back to the compressors.

OIL SYSTEM

Rack refrigerators also use oil to keep the compressor lubricated. Without oil, the bearings would wear out very quickly, leading to compressor failure and heavy replacement expenses.

To keep the compressor lubricated, oil moves with the refrigerant through the compressor and separates from it again in the discharge line. Discharge gas carries oil and refrigerant to the oil separator, which removes the oil from the refrigerant and sends it back to an oil reservoir for storage. When the oil goes back into the piping, it leaves the reservoir, passes through an oil filter, and goes into one of the oil regulators. The oil regulators feed oil into the compressor, which allows the bearings to stay slick and prevent excess wear.

These oil components have sight glasses, which are little windows into the system that let you see the oil inside the piping and parts.

ELECTRICAL COMPONENTS AND CONTROLS

To keep the compressors all running, each rack will have an electrical panel with the compressor contactors. The contactors are just the places where the wiring comes together.

Each compressor will have its own breaker, and that’s important because one compressor can shut down without affecting the others. If all compressors were on a single breaker, then one compressor shutdown or failure would cause the entire rack to go down.

The rack will usually also have a controller. Controllers can take inputs and turn those into signals for the relay board inside the panel, which can control vital functions like defrost. We likely won’t use every single function on a relay board; those boards need to be programmed to fit the rack and its parts. There may also be a motor saver near the controller.

MOTOR ROOM HAZARDS

Motor rooms are generally on building rooftops, and they may contain one or multiple refrigeration racks.

Because motor rooms are secluded areas, some employees may be tempted to get out of work by taking breaks in those motor rooms. Our techs occasionally see litter like chip bags in motor rooms, which indicates that people may have been hanging out there when they really shouldn’t have been. That’s actually very concerning to us because motor rooms may have other hazards, including exhaust fans and electrical components. With so much refrigerant and electrical power in a single confined space, it’s no surprise that motor rooms can be dangerous places. It’s best that facilities managers inform their employees of the following risks of injury or death:

ELECTRICAL HAZARDS

NOBODY except authorized contractors should touch electrical components. Only those who have received proper training should open electrical panels and touch the parts inside the panels. There should also never be any open wiring in a motor room. If anybody works on a refrigeration unit and needs to disconnect the power, they should lock or tag out the equipment at the power supply so that nobody can start the equipment while it is being worked on.

RESPIRATORY HAZARDS

Refrigerant leakage is also another potential concern, as we can inhale it and damage our bodies. Normally, refrigerant leakage outdoors isn’t a big deal when it comes to our health; we’re surrounded by fresh air, so a little bit of refrigerant won’t stay near us in large amounts for long. However, motor rooms are small, and rack refrigeration systems carry a lot of refrigerant. That refrigerant can displace oxygen very quickly if it were to leak into a confined space like the motor room. So, everyone who enters the motor room should know the exit and watch out for signs of refrigerant inhalation. Some symptoms of refrigerant poisoning include dizziness, headache, and nausea.

For maximum safety, facilities managers would be wise to post signage warning employees of the hazards present in the motor room. (And unauthorized employees should stay out of motor rooms altogether.)

BEHIND THE SCENES

Kalos Services is also an industry leader in HVAC and refrigeration education through the global training resource, HVAC School. Kalos technician Eric Mele has made several educational videos about commercial refrigeration on the HVAC School YouTube channel, including a tour of a DX parallel rack motor room:

(Note: The motor room is a loud place. Closed captioning is available by pressing the “CC” button.)

Learn more about our commercial refrigeration services HERE.

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If you own or manage a restaurant, supermarket, or convenience store, you’ll know that defrost is a regular part of your refrigeration system operation. Refrigerators must defrost anytime the coils drop below freezing, 32°F. 

When the temperatures dip below freezing, any moisture on the coil will freeze. As that water freezes, it forms layers of ice on the coils. Those layers of ice prevent the refrigerant in the system from absorbing heat inside the fridge. As a result, the refrigerator will have a harder time keeping products cool. You may end up with food spoilage, which may negatively affect profits and present food safety hazards. 

Defrost can be as simple as shutting the compressor off for a while. It can also involve complicated procedures like reversing the refrigerant flow to send hot gas through the coils. We’ll cover these different methods and the controls that manage the defrosting process.

DEFROST METHODS

In the olden days, we used to take everything out of the refrigerator and unplug it. We’d have to wait for several hours for the ice to melt, or we’d speed up the process with a makeshift ice pick (whether that be a screwdriver or a piece of cutlery) or a hairdryer. 

Of course, those methods are wildly impractical for commercial refrigerators. Nowadays, we have much more efficient ways of defrosting refrigeration systems.

Off-Cycle Defrost

The off-cycle defrost is the simplest and most common method of all. As its name suggests, this method turns the system off and naturally lets the ice melt off the coil. When the system turns off or pumps down, the evaporator fans keep running, which forces the system to defrost.

The off-cycle defrost is only practical on smaller medium-temperature coolers, as the air needs to be above 32°F. So, you will most commonly see off-cycle defrost on coolers for produce and beverages, as those should never freeze.

Electric Defrost

Remember when I said that some people used to use hairdryers to defrost their home refrigerators? The same principle is at play with electric defrost; we use electric heat to melt the ice off the coils.

As with off-cycle defrost, electric defrost relies on timers and other similar controls to signal when to start and stop the process. 

Although electric defrost is effective on a wide range of equipment, it is a long and slow process. Applying external heat is much less effective than using internal heat to melt the coils (as with hot gas defrost). So, it can take a long time to heat those coils and expend a lot of energy. On top of that, you may only get a partial defrost from electric heat. Partial defrosts leave some ice and moisture on the coil, making the refrigerator more prone to refreezing.

Hot Gas Defrost

The final common method uses hot gas within the system to heat the coils from the inside. A valve de-energizes and creates a pressure differential; that pressure differential reverses the flow of hot discharge gas and sends it to the evaporator. The system has two actuating valves that help control the flow direction, and the discharge gas behaves as it does in heat pump applications. Since discharge gas may exceed 200°F, it can melt ice off the coil with relative ease. Most supermarket refrigerators will use this method.

Hot gas defrost control strategies are expensive to install, but the method’s quality and versatility typically help offset the price. Discharge gas runs through the entire coil and does a better job of reaching the entire coil than external electric heat. 

As with electric defrost, the hot gas method requires the fan to be off during and after the defrosting procedure.

CONTROL STRATEGIES

All of those methods would be a real pain for us to control on our own. With so much product and profits at stake, remembering the exact time parameters would put a lot of pressure on us.

Luckily, we can rely on plenty of control strategies to automate the defrosting process. 

Cold Controls (Constant Cut-In)

One of the most common controls is the automatic cold control, also known as the constant cut-in. 

These controls have sensing bulbs in the evaporator that pick up the temperature. The controls refer to a fixed cut-in point and an adjustable cut-out point; the cut-in temperature is above freezing, usually in the upper 30s, and the cut-out temperature may be as low as around 10°F. 

When the bulb senses that the system has reached the fixed cut-in point, the control closes and turns the compressor on. Later, the control opens when the bulb detects that the evaporator temperature has reached the cut-out point. The compressor turns off and remains inactive until the bulb senses that the system has reached the cut-in temperature again. 

The logic behind cold controls is that they will stop the compressor after frost has had some time to accumulate on the coils. They will only turn the system on again if the freezing conditions are no longer present.

Defrost Timers

We use timers in medium-temperature applications to help us manage off-cycle defrosts. Timers help us determine when our refrigerators shut off and for how long. 

A cold control only activates whenever the sensor relays a signal for the control to open or close, making it unpredictable. Defrost timers allow us to control the defrost parameters directly instead of relying on sensors to send signals to the circuit board.

We may also use timers with the other two defrost types, electric and hot gas. However, these applications are a bit more complicated. 

Defrost termination on electric and hot gas defrosts requires a failsafe and a fan delay.

Defrost Termination Thermostat and Failsafe

Termination is critical on electrical or hot gas defrost systems. While we want to ensure that the coil is completely ice-free, defrosting strategies use up a lot of energy and may overheat the coil; we want to stop the defrost process before the coil gets too hot.

On systems that use electricity or hot gas for defrosting the coil, there will typically be a defrost termination thermostat. This device senses when the coil is free of ice and stops the defrost. In other cases, the thermostat stops the defrosting process when the coil reaches 55-60°F to ensure that the coil has no ice whatsoever.

On rare occasions, the termination thermostat may malfunction and fail to terminate defrost. In those cases, we could face severe product losses. To avert that crisis, the failsafe steps in to stop the defrost after a set amount of time. The failsafe time is the maximum amount of time that a system will stay in defrost; it will often be in the 20-40-minute range.

When the termination thermostat kicks in, the system resumes normal operation. However, the fans shouldn’t turn on until the coils have had some time to drain. If the fans were to turn on immediately, they’d blow melted ice all over the place. You’d get a gross, slushy mess in the refrigerated box if that were allowed to happen. So, these applications have a fan delay. The fan delay prevents the fan from starting until a certain coil temperature is reached, usually around 30°F. The logic is that the refrigerator will have had some time to drain all of the melted moisture by the time it cools back down to the set temperature.

As you can see, each defrost method has its advantages, drawbacks, and appropriate uses. The same is true of the control strategies. Nevertheless, each method and control helps protect perishable products in supermarkets, restaurants, and other food sale or preparation facilities.

For more information on the causes and prevention of frozen cases, check out our article on the subject.

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Most refrigerators are simply not made for chilling food to freezing temperatures in a short span of time. Some fast-food restaurants use “flash freezers” that can bring warm products down to a freezing temperature. “Blast chillers” serve a similar purpose. However, many restaurants, grocery stores, and small farming operations lack flash-freezing equipment. Those businesses will likely have to consider the possibility of hot pull downs.

WHAT IS A HOT PULL DOWN?

“Hot pull down” refers to a condition in which the refrigerator has difficulty removing heat from the box. The phenomenon is due to the box having a much higher heat load than normal. You will most often see hot pull downs on startup after a long time of non-operation or when loading the box with hot food.

Most refrigerators are designed to maintain a product’s temperature or bring it down slowly, not bring it down to below-freezing temperatures in a snap. Many people will not deal with a “hot pull down” if they freeze foods that were already frozen from the market or wholesaler. Leftovers from the medium-temperature fridge likely won’t cause a hot pull down if they move to the freezer; they have already had their temperature brought down, and that temperature will continue to fall slowly.

However, hot pull downs can be a problem if you’re dealing with warm, really fresh products, like those chickens in the image above. For example, a small-time or self-sustaining chicken farmer may need to store chicken carcasses after slaughtering and cleaning them. Many large-scale meat storage facilities have chillers that can rapidly reduce temperatures, but many smaller farmers don’t have those and may only have a commercial refrigerator at best. Those freshly-slain chickens had body temperatures exceeding 100°F, so it will be tough for the refrigerator to pull the carcasses down to a safe temperature at once. (A safe temperature for meat storage should not exceed 40°F! Read more about food safety guidelines HERE.)

WHY IS IT DIFFICULT TO PULL THE TEMPERATURE DOWN?

The cooling ability of a refrigerator depends on two main design factors: capacity and coil-feeding range.

Capacity refers to the ability of a cooling system to remove the most heat over time. As with A/C systems, refrigerators use refrigerant (“Freon”) to absorb heat and carry it away from the conditioned space. In the case of a refrigerator, that “conditioned space” is the refrigerator box. A refrigerator that has a hard time with hot pull downs may not have enough refrigerant in it to absorb heat from the box quickly enough, even if it has the appropriate amount of refrigerant for the system design.

The coil-feeding range refers to the metering device’s ability to feed low-pressure refrigerant into the evaporator coil. Metering devices, such as the TX valve in the picture above, reduce the pressure of the refrigerant before feeding it into the evaporator. In the case of a hot pull down, the evaporator coil starves because the metering device can’t feed it with enough refrigerant to handle the heat load. That refrigerant will exit the evaporator at a very high temperature, making it unable to cool the compressor and likely to overheat it.

In short, the refrigerator simply doesn’t have enough refrigerant to handle such a sudden, intense heat load. So, the fridge struggles to bring the product temperature down at best and could suffer compressor damage at worst.

WHAT SHOULD I DO TO PREVENT A HOT PULL DOWN?

Keeping the box temperature low is the key to preventing a hot pull down.

The best thing you can do is wait for food to cool down before you stuff it in the refrigerator. That way, you lessen the heat load inside the box when the food goes in. When your refrigerator isn’t straining to regulate temperature, you decrease your likelihood of compressor failure. 

You can also prevent the box temperature from rising if you ensure that there is good circulation inside. Ensure that there is adequate spacing between all the products in the box. When air circulates better, the products don’t retain heat as much, and the refrigerator is more effective at keeping the box (and food) cool.

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However, ice machines are also important in the commercial sphere. The types of ice machines you’ll find in commercial kitchens and hotels are called package ice makers. These machines come mostly pre-installed from the factory, and they can typically make cubes or flakes of ice. Personal preference is not a factor that we consider for ice usage in the commercial sphere; each ice type has a distinct job.

We’ll cover how ice machines work and then describe the differences between cube and flake ice. We will also cover what we use each ice type for and why they are ideal for their respective uses.

HOW ICE MACHINES WORK

Like A/C units and refrigerators, ice machines operate on a refrigeration cycle. They move heat away from water to freeze it, and it rejects that heat elsewhere.

So, the most critical element of an ice machine is the evaporator, which absorbs heat from the space. Water fills that space, and then the evaporator removes heat from that water, effectively freezing it. That frozen water then collects in a storage bin, where the ice remains until it is ready for consumption or other uses. 

ICE CUBES: THE BASICS

Cube ice machines freeze water in batches. Water fills a sump with a grid, and it freezes on the grid. Once the ice is ready to drop, the ice machine goes into a harvest cycle. The harvest cycle is a hot gas defrost, which sends hot gas from the compressor to the evaporator. Then, the ice releases itself as the evaporator warms. When the ice falls off, it accumulates in the storage bin until it is ready for use. 

Cube ice’s main use is for human consumption. You will find ice cubes in your drinks at restaurants and self-serve soft drink dispensers.

ICE FLAKES: THE BASICS

Instead of having a sump with a grid, flake ice forms in a long cylinder that fills with water. The cylinder’s walls absorb heat. As the water freezes, an auger rotates in the center of the cylinder, compressing ice flakes as they freeze and moving them towards the top of the cylinder. When the flakes reach the top, they get pushed through a chute and fall into the storage bin.

You can use flake ice for human consumption, but we typically use pure flaked ice for storage and display purposes. For example, buffets may keep cold food in bowls and bins that get wedged in flake ice. Another example of flake ice usage is the storage and display of fresh fish at the market.

When restaurants use flake ice for human consumption, you would typically see “nuggets” instead of flakes. Ice nuggets are compressed flakes that are round, soft, and easy to crush with your teeth. You can find these nuggets in some cocktails at restaurants (or Wawa specialty iced coffee).

QUALITY STANDARDS FOR ICE CUBES AND FLAKES

Even though ice cubes and flakes are just frozen water, they have different quality standards. While some of these quality standards certainly overlap, some features that are desirable for ice cubes are undesirable for ice flakes and vice versa.

Quality standards start with the water. In ice cubes and flakes, purer water is always more desirable. You can get a rough idea of the water’s purity by examining an ice cube. Water that does not have any minerals or trapped air will freeze first. As the water freezes, mineral-laden water and air bubbles move towards the center of a cell on the grid until they eventually freeze. You will yield an ice cube that looks cloudy in the middle. Cloudy ice comes from hard water, which has a high mineral and air content, and it’s less desirable than clear ice.

One area where cubed and flaked ice differ is their desired hardness. In ice, hardness refers to its ability to decrease the temperature of something. (Don’t confuse ice hardness with water hardness. Harder water actually decreases ice hardness because the high mineral content reduces the ice’s ability to remove heat from a beverage or product.)

Ice cubes are dense, and many ice machines that produce cubes wash out the minerals, making the cubes as hard as possible. Cubed ice should typically be in the 95-100% hardness range. On the other hand, flaked ice will naturally be softer because the machine cannot wash out the mineral content, and more air is present during the freezing process. Flaked ice will ideally have a hardness value of around 70%.

Regardless of which ice type your business utilizes, the best way to make sure you get the best possible ice is to keep your machines clean. When cleaning ice machines, a nickel-safe sanitizer works best, not harsh chemical cleaners. No matter if you’re a restaurant owner serving Coca-Cola, a bar owner serving specialty cocktails, or a market manager who wants to keep their products fresh, proper ice machine cleaning and maintenance will give you the best-quality cube and flake ice.

References:

Silberstein, Eugene, et al. Refrigeration & Air Conditioning Technology. 9th ed., Cengage, 2021.

Wirz, Dick. Commercial Refrigeration for Air Conditioning Technicians. 3rd ed., Delmar, 2021.

These sources are some of the top training and educational materials that we recommend for our technicians. They are truly the guides of the HVAC and refrigeration industries.

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When the liquid refrigerant enters the evaporator coils, it absorbs heat from the environment. It’s tough for the refrigerant to absorb heat when the coils are covered in thick layers of ice. Food may spoil if the refrigerator can’t keep the surroundings cool. 

Retail managers may want to know what they can do to prevent or fix frozen cases in their stores. Luckily for them, there are some steps they can take to help prevent their cases from freezing. I’ve spoken to Nathan Orr to help talk about frozen cases, control strategies for retail managers, and defrosting. Nathan Orr leads the Kalos Services heavy mechanical division. He is also the VP and a co-owner of the company.

Freezing causes

Based on the service calls that we receive, we see four leading causes of freezing. Your refrigerator may freeze due to one or a combination of the following situations.

Poor airflow

One culprit of freezing is poor airflow across the evaporator coils. The causes of low airflow are the same as in air conditioning, such as broken blower motors or dirty evaporator coils.

Evaporator coils can become insulated with grime, which hinders airflow and makes it harder for the refrigerant to remove heat from the environment. When the refrigerant can’t absorb heat properly, it may stay too cold, and the water moisture along the coils may freeze.

Improper drainage

Another common cause is that water drainage can’t properly escape. Condensate drains remove water moisture from the area around the evaporator coils. When the drains can’t do their job, the condensate stays and may freeze.

Defrosting issues

Issues with your defrost cycles may also cause the coils to freeze. Defrosting is the process that melts the frost from the coils, whether that means turning the system off for 25-45 minutes or using electrical or gas defrosting methods. Freezing may occur when the defrost cycles are too short. Electrical defrost controls may also develop mechanical issues that lead to freezing.

Frozen environmental conditions

One of the most frequent causes of frozen refrigerator cases is cold environmental conditions. 

When you leave a walk-in or swinging glass door refrigerator open, humid outside air enters the case. When you let moist air get into the refrigerated space, you allow moisture to accumulate. That moisture will then freeze on your equipment. 

I’ve found a frozen case in my store. What can I do?

While checking up on your units, you notice that the evaporator coils have frozen over. As a facilities manager, what can you do?

First, you should see just how much frost is on the coils. If it’s a small amount, then there’s a strong chance that you won’t need to do anything. A little bit of frost will always form on the coils, and a proper defrost cycle should take care of it.

But what if there’s a heavy ice buildup? That’s when you should call a service technician. You can’t do much to solve the problem on your own.

However, there are some things you can do to make it easier for the techs to solve your problem. Before you call a technician, there are two things you can do.

The first thing you can do is take pictures of the freezing. That way, the service technician can see exactly what you saw, and they may diagnose and solve the issue more easily. 

The second thing you can do is turn off the circuit. Some units have a hand valve that you can turn to power the circuit off.

Again, these aren’t required, but your service technicians will appreciate you if you can take these basic steps to make their jobs easier. 

What can I do to prevent frozen cases?

There is one main prevention method for frozen cases. (It will also make your service techs will love you.)

Keep the refrigerator doors closed whenever possible. 

That’s it. Just keep the doors closed whenever you can. When people keep the doors open too much and cause the case to freeze, they usually won’t know what caused the issue and make a service call without a specific issue. The technicians will test every element of the refrigerated system, and then they’ll conclude that the doors were left open too long. Prevention is the only cure, so those service calls are a waste of time for everyone.

Now, we understand that it will be difficult to control the glass doors on the sales floor. Some customers keep the doors wide open while they figure out which ice cream flavor they want. That’s uncontrollable, and technicians typically understand that challenge. However, you can still reduce the probability of frozen coils on your other refrigerators if you can keep those doors closed whenever you’re not actively stocking or removing product.

Electric vs. gas defrost

An article on frost prevention wouldn’t be complete without a quick overview of defrosting methods. We’re going to discuss the differences between electric and gas defrost.

Electric defrost uses an electric device to defrost the system. (They’re like giant hairdryers.) Gas defrost uses energy within the system to defrost, usually by reversing the refrigeration cycle via a valve. (The image above shows a gas defrost valve.) The hot, high-pressure vapor that usually goes to the condenser after compression goes to the evaporator, and the heat melts the ice on the coils. As a result, the gas defrost process is quite rapid.

Conversely, electric defrost is long and slow. It takes a long time for the external heat to warm the coils, possibly resulting in partial defrost. Partial defrost is undesirable and may lead to frost buildup and freezing over time.

However, gas defrost isn’t perfect either. Because the process is so fast, you may end up steaming water near the coils. That isn’t a terrible thing, but it may look alarming. The main downside is that gas defrost may overheat the case if it lasts too long. Case overheating may lead to food spoilage or decreased food quality, negatively affecting profits and customer satisfaction.

When you oversee market refrigeration practices, you’re bound to see freezing at some point. Even though there isn’t much that you can do about it as a manager, there’s no need to panic. At Kalos, our technicians are well equipped to troubleshoot freezing, whether that means replacing a blower motor, checking the defrost controls, or advising you to keep the doors closed more often. It’s still good to know what causes freezing and how you can prevent it to the best of your abilities.

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