Gary McCreadie is one HVAC tech, the creator the and also the HVAC know It all Podcast

Refrigeration bike Explained

To collection this up properly, ns really should lug up the an initial time I placed some lackadaisical thought into refrigeration or waiting conditioning. I was a young teenager walking by the side of my residence on a warm summer day, we had actually a strength draining, inefficient beast of a window unit the intrusively hung out the side of the house, practically obstructing the go way.

You are watching: What is the refrigerants state when entering the metering device

It was outputting some major heat and also water was dripping indigenous the ago onto the ground. Ns walked into the house and it to be cooler and also less humid than it to be outside. Yes, I had actually an epiphany: to be the warm I felt comes from the gargantuan brown box in reality being attracted from my home and was the dripping water gift somehow siphoned indigenous the indoor air and being transferred outdoors?

I knew this had to be true, yet this to be pre-internet or the internet as we now know it today and the details I essential wasn't easily available. It wasn't until years later in trade institution that i learned the my concept was certainly correct.

Before we obtain started, if you're in search of a skilled online environment to comment on the trade, check out the subscription based HVAC understand It all app.

The Refrigeration cycle is a science,knowing it and knowing it well is a gift and a curse. Gift, together we service techs know, that is our bread and also butter, the method we do a living and administer for our families. A curse, yes, together we organization techs know, as soon as it it s okay hot exterior everyone and their brother in law wants or needs a favour. In order to know therefrigeration bicycle we have to understand just how refrigerant acts in ~ a system. We additionally need come understand just how refrigerant reacts once its bordering temperature alters as it concerns its pressure.

After reading this short article check out this video clip explaining the refrigeration cycle v a an ext visual experience

Let's take R410a, a popular refrigerant at the moment and also look at itssaturated temperature in ~ 72⁰F. Notification the press on the Danfoss RefTools Refrigerant Slider is 207.7 PSI. If we rise the saturated temperature of the same refrigerant to 80⁰F, the pressure boosts to 235.7⁰F. The first lesson below is the refrigerant pressure boosts with a temperature rise and also conversely refrigerant press decreases v a temperature drop.


I pointed out saturated temperature in the paragraph over so let's look at that and consider that lesson number two. Saturation is essentially the refrigerant's cook point, where it is a liquid and also a vapour in ~ the very same time. Together you can see native the over images on the Refrigerant Slider, R410a at atmospheric push boils in ~ -60.60⁰F. Let's to compare this to a boiling allude of water. Water at sea level will boil in ~ 212⁰F, (100⁰C) when the water reaches its boil point, the is a fluid (within the pot) and vapour (hovering above the liquid inside the pot) at the exact same time.

The water is in ~ itssaturated or boiling temperature. Utilizing water as an instance usually helps to understand this concept. But, water additionally follows the rules of pressure/temperature relationship as well. Water will certainly boil in ~ room temperature in a vacuum in ~ 29.92"hg (inches of mercury). By place a glass that water in an enclosed environment and also then progressively decreasing the press within that setting by creatinga vacuum, the water will boil, however at room temperature, that's right, it's not hot.

This is an practice that countless HVAC/R instructors usage to showcase that pressure and also temperature space related. Just like with refrigerant, together we drop the push we drop the saturated or boiling temperature of the water, this generally starts the wheel in movement for numerous students.

Check out this experiment at home boiling water at room temperature in a vacuum

We can't move on until we speak briefly about superheat and also sub-cooling, this are an essential factors to expertise the refrigeration cycle and also what is happening within a system. Superheat and also sub-cooling are frequently used come diagnose systems and to dial in the refrigerant charge.

Superheat In A Refrigeration System

Simply put, superheat is anything above the saturation point. Superheat ensures the problem is 100% vapour. If we take R410a again together our example and we look at itssaturation temperature in ~ 118 PSI, it coincides to 40⁰F. Now, this is a usual pressure/temperature partnership as it concerns an evaporator forcomfort cooling. We periodically refer to this as the saturated suction temperature or SST. If us were take it an yes, really temperature that the suction line and it to be measured in ~ 50⁰F our superheat would certainly be calculated in ~ 10⁰F.

Actual line temp 50⁰F - SST 40⁰F = Superheat 10⁰F

As we will certainly touch ~ above later, superheat in the suction line is required to ensure only vapour enters the compressor during a running cycle.

This short video clip explains just how to check evaporator superheat

Sub-cooling In A Refrigeration System

Sub-cooling is the contrary of superheat, it is anything below the saturation allude or boil temperature,sub-cooling guarantee the substance is 100% liquid. A common saturated condensing temperature in lull cooling is in the range of 100⁰F-110⁰F, let's stick v 100⁰F for this example. Utilizing R410a again, a saturated condensing temperature or SCT of 100⁰F coincides to 317 PSI. By taking theactual temperature the the liquid line andreceive a readingof 90⁰F, our sub-cooling because that this instance is 10⁰F.

SCT 100⁰F - Actual heat Temp 90⁰F = 10⁰F

Sub-cooling is essential in the liquid line to ensure our metering maker receives a full column that liquid.

The Four major Components

The refrigeration cycle can not take place without the following crucial components. Understand that plenty of bells and also whistles have the right to be thrown right into the mix as far as extr items in ~ a circuit, but for now we will focus on the four major pieces that the puzzle.

1) Compressor

Compressors come in many shapes, sizes and varieties but they all share the same roll, come facilitate the movement of refrigerant v a system. When the compressor is powered, itsjob is come take low pressure, short temperature refrigerant vapour from the suction line and compress it into a high pressure, high temperature refrigerant vapour right into the discharge line. Compressors room designed to relocate vapour through a system, no liquid.

Any liquid refrigerant the enters the compressor can reason damage and compressor failure. Many compressors save oil, the oil must be compatible through the type of refrigerant the system is utilizing. The oil is moves with the mechanism with the refrigerant and also keeps the compressor and also system components lubricated. Liquid refrigerant within a compressor can wash away compressor oil, causinginternal parts to fail.

Common species Of Compressors Are:


The term semi-hermetic simply shows the compressor is not fully sealed and also can it is in taken apart because that service. A completely hermetic compressor or believe can, as it's periodically referred to, is a completely sealed unit and can not be ar serviced.

This is a great compressor examine up list from Danfoss Cool


2) Condenser

The condenser is a heat rejection device. The refrigerantsystem picks up warmth in the evaporator and alsofrom the heat of compression (from the compressor itself) and also the condenser rejects or rids of the heat. A condenser can be waiting cooled, by utilizing a fan to move air across the coil and also fins, or water cooled by making use of a pump to move water despite a coaxial coil, brazed plate warm exchanger or condenser bundle.

Because the condenser obtain superheated refrigerant vapour native the discharge line, itsfirst job is to cool the gas by de-superheating it. Once the refrigerant get its saturation or cook temperature, the condensers next job is to sub-cool the refrigerant. This guarantee that as the refrigerant pipeline the condenser down liquid line, there is a complete column of liquid making itsway in the direction of the metering device.

Common types Of Condensers Are:

Traditional copper coil w/aluminum finsMicro ChannelCondenser BundleCoaxial CoilBrazed Plate heat Exchanger

2) Metering Device

A metering device can be adaptive, such as a thermal expansion valve or fixed, such as a capillary pipe or resolved orifice. Itsjob is to meter the sub-cooled liquid right into the evaporator. The metering an equipment separates the mechanism from the high pressure side andthe low pressure side.

As the sub-cooled fluid passes through the metering device, it create a speed gas. This way a portion of the liquid is immediately turned or flashed into a vapour because of the fall in pressure. A dominion of ignorance is 75% liquid and also 25% vapour entering the evaporator. To destruction a little deeper right into metering devices check out this article.

Common species Of Metering Devices

Thermal development ValveAutomatic growth ValveCapillary tubeFixed orificeElectronic growth Valve stepper motor

The future the metering refrigerant


Before us talk about the fourthmajor component, we have to briefly talk about sensible and also latent heat and the differences between them.

Sensible Heat

Sensible warm is the heat required to readjust the temperature that a substance. Because that example, if us take 80⁰F air and also remove 10⁰F so that air is now 70⁰F, we have done 10⁰F the sensible heat removal. The temperature regarded on a conventional thermostat display is an example of a changein wise heat.

Latent Heat

Latent heat is the heat forced to adjust the state that a substance. By an altering state us mean an altering water to a vapour or water vapour ago to a liquid, because that example.

4) Evaporator

Ah, because that me this is whereby the magic happens. The evaporator's task is come absorb heat and remove moisture from the air passing end it, if we space speaking in terms of a typical evaporator coil. A traditional coil removes latent heat and sensible warm from the air passing by. Latent warmth removal is responsible for removing moisture or humidity indigenous the air, together the humid air come into contact with the cold coil, water vapour clings come it, the vapour changes state indigenous a vapour to a liquid, known as condensation. The condensation is built up in the evaporator drain pan and exits via a drain line. As soon as the latent heat is removed (moisture native the air), sensible warmth removal is able come take ar at a higher pace.

Sensible heat removal, together previously disputed is responsible for dropping the temperature that the air. In chiller systems, the evaporator absorbs heat but not moisture, air does not pass end this form of evaporator. Chillers use an evaporator bundle, refrigerant and water or glycol enter the bundle and also heat is exchanged. Chiller bundles can only perform sensible warm removal. For this instance we will emphasis on a standard air over coil.

As refrigerant beginning the evaporator with the metering device, the pressure and also temperature are reduced. From our ascendancy of thumb above we offered a mixture that 75% liquid and also 25% vapour beginning the evaporator. The continuing to be liquid is boiled off together it absorbs warm from the waiting passing end the coil.

In theory, all of the liquid is boiled turn off in the evaporator, any included heat after boiling is additional, that added heat is know as supervisor heat. Superheat ensures that just refrigerant vapour pipeline the evaporator and also enters suction line. The compressor brings back the the superheated vapour and also re-begins the process.

Common varieties of evaporators are:

Finned Evaporator (A coil and also N coil)Evaporator bundlePlate evaporatorBare Tube

Check out a quick podcast illustration explaining the refrigeration cycle


The Cycle

Now the we have actually hammered down the significant components let's put the cycle together as one.

On call for cooling or refrigeration the compressor starts. The compressor, acting together a pump will certainly pressurize vapour refrigerant right into a high pressure high temperature gas into the discharge line.

The vapour refrigerant in the discharge heat issuperheated. The discharge heat feeds refrigerant right into the condenser, as refrigerant moves through the condenser the gas is cooled to eliminate the supervisor heat. The refrigerant moves into a saturated state (liquid and also vapourat the very same time) onceit is de-superheated. At this point, further heat is removed, the refrigerant i do not care a sub-cooled liquid together its temperature isnow below its boiling or saturation point.

The sub-cooled fluid enters the fluid line, at this point still in ~ a high pressure but reduced temperature. The sub-cooled liquid moves through the metering maker dropping itspressure and temperature as it flashes right into the evaporator. As air passes over the evaporator coil, the refrigerant absorbs heat.

The took in heat causes the refrigerant with its saturation or cook point. The refrigerant proceeds to absorb heat past that is saturation point, the additionalheat superheats the vapour.The superheated vapour enters the suction line and also is brought earlier to the compressor for the cycle come repeat itself.

Key Points

The compressor acts as a vapour pump to relocate refrigerant about the system. A compressor is not designedto pump liquid.

The condenser rejects warm picked up from the system (evaporator and also compressor) and also is responsible for ensuring that the refrigerant leave is a sub-cooled liquid.

The metering device regulates fluid refrigerant into the evaporator lowering the temperature and pressure. It is flashed into the evaporator together 75% liquid and also 25% vapour as a ascendancy of thumb.

The evaporator absorbs heat, from wait in a house for example, boiling turn off the continuing to be liquid refrigerant. The refrigerant choose up additional heat, the included heat is recognized as superheat. The superheated vapour moves into the suction line and back to the compressor.

Additional Components

As we have actually covered the four major components, there space a few additional components that are essential within a mechanism we will certainly cover as bonus material.

Pressure Switches

At minimum, systems have to be outfitted with high and low push switches to defend the compressor. There are numerous safety switches that we might discuss but high and also low pressure cut out is super necessary to any kind of system.

High push Switch

The high push switch can be uncovered on the discharge heat or the liquid line of any given system, the can likewise be placed directly top top the head of a semi-hermetic compressor. The monitors the mechanism pressure and also will shut down the compressor on a high push event. High pressure events can be brought about by a dirty condenser coil, defective condenserfan and also over fee for example.

The setting of the high push switch deserve to be adjustable or fixed depending on the format of switch the is utilized. The setup of the switch is dependent upon the refrigerant being used. Not all refrigerants produce the very same high side pressure and also need come have various settings. I have discovered that the cut-out setup usually sit in range of 140⁰F come 155⁰F saturation condensing temperature or SCT. If you look in ~ the pressure that autumn into the temperature variety for any given refrigerant, it's typically a great reference suggest for high push cut-out.

Low press Switch

The low push cut-out move is placed on the suction line, or even sometimes top top the compressor body together in the instance with some semi-hermetic compressors. Simply as the high push switch, low pressure switches have the right to be resolved or adjustable. Likewise again, the switch setup is dependent upon the refrigerant and application. Low press switches in lull cooling space usually set around or over a push that synchronizes to freezing. For instance, R410a at 32⁰F saturation synchronizes to a press of 101.6 PSI.

To defend the mechanism from freezing up, the switch setup will must be set in and around 101.6 PSI. As soon as speaking in regards come refrigeration, the low pressure switch is usually set up to shut under the device when it reaches set point or after a pump down. The setup will be based upon the site details application and also refrigerant being used and may call for some thought.

Low pressure switches in general will also protect the system in a low fee situation. If for instance the system had actually a leak and also lost its charge the low press switch would open up and also not enable the compressor come run.

Liquid heat Filter Drier

A liquid line filter drier is a very important accessory to many systems. The is installed in the liquid line together close to the metering an equipment as possible. Its task is come filter out any type of debris within a system and also remove trace quantities of humidity that can be current using a desiccant material.

Liquid Line sight Glass

A sight glass is an inline maker that is additionally installed in the fluid line, downstream (after) the filter drier. It gives an indication that a complete column of liquid is current entering the metering machine and likewise has a humidity indicator that changes colour in the existence of moisture within a system. A fluid line sight glass can likewise give indications that there is a difficulty in a system.


A recipient is a storage machine that storesrefrigerant in the off-cycle after a pump under or shop refrigerant till it's needed. An example of this is winter operation, in cold approximately temperatures much more refrigerant is necessary to pressurize the system. The refrigerant would be save on computer in the recipient in warmer approximately temperatures and as the ambient begins to drop, save refrigerant is used to maintain system pressure.

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Liquid heat Solenoid Valve

A liquid line solenoid valve is another inline component the is mounted in the liquid line. The is supplied in most instances to pump under a system. As soon as the valve is forced closed, the compressor continues to run, the refrigerant is pumped into the condenser/receiver. Together the evaporatorand suction line pressures drop, the low pressure switch will open cutting procedure to the compressor. Once the valve is opened during a call, the evaporator and suction line are pressurized by one inrush of refrigerant. The low push switch closes and the compressor re-initiates operation.

This image from the Danfoss RefTools app Troublehooter shows a liquid line filter drier, sightglass and also solenoid valve in collection with circulation moving from appropriate to left