Hey there guys, Paul here, from TheEngineeringMindset.com. In this video, we're going to be looking at industrial
refrigeration system basics, with a focus on ammonia
refrigeration systems. We'll start at the basics and work our way up covering some typical
systems for single stage, two stage and cascade systems to help you learn the basics
of industrial refrigeration. I just want to take a moment to thank our partner Danfoss for sponsoring this video. Danfoss is on a mission to spread as much knowledge about modern
environmentally-friendly refrigerants as they can. This includes information about ammonia and how it works in their industrial
refrigeration solutions.
They have a collection of free ammonia eLessons available now at Danfoss Learning. Just follow the link in the video description below to start your first course. So where are we going to
find these types of systems? Industrial refrigeration
applications are typically used in places like cold food
storage, dairy processing, beverage production, ice
rinks and heavy industry, these sorts of places. These are large scale cooling systems. We've previously covered
other types of cooling systems for commercial buildings,
supermarket CO2 systems, chillers and chilled water schematics. Do check these out if you haven't already. Links are in the video description below. I just want to very briefly touch on why we use ammonia as a refrigerant. Ammonia occurs naturally
in the environment, it's available in abundant amounts. It has an ozone depletion rating of zero and a global warming potential of less than one. If we compare that to other common refrigerants such as R134a this has a GWP of 1,430, and then R404A has a GWP of 3,922. You can see why ammonia
is very beneficial to use.
Ammonia is also cheap to
produce and energy efficient to use. It has the capability
to absorb large amounts of heat as it evaporates. That's a really important aspect for a refrigerant to be of use, it also means that
pipes and components can be made thinner and smaller. Ammonia is toxic however and can also be flammable at certain concentrations. Most refrigerants are
odorless but ammonia gives off a very sour smell so it's easily noticed if a leak occurs. If ammonia leaks it will react with the carbon and water in the air to form ammonium bicarbonate which is a harmless washed compound. Now, for the engineering stuff. Let's look at some simplified
typical refrigeration systems. Single stage, this is the simplest ammonia industrial refrigeration system other than a direct expansion type, so we're going to start here. We start off with the
compressor, this is the heart of the system and is what pumps the ammonia refrigerant around
the refrigeration system to provide the cooling. It pulls in the refrigerant that has collected all the unwanted heat from the evaporator and compresses this into
a much smaller volume so that all that thermal energy is very tightly packed together, making the refrigerant very hot.
The refrigerant is sucked into the compressor as
a low pressure vapour and it leaves as a high pressure vapour. The high pressure refrigerant
vapour exits the compressor and flows to the condenser. The condenser cools the refrigerant down by pulling the unwanted heat out of the refrigerant and
discharging this heat into the ambient outside air. This is typically done by passing the hot
refrigerant through the inside of some small tubes and using a fan to force the cooler ambient
air across the outside of the tubes to cool it down
and carry the heat away.
Additionally, we'll
often find a small pump spraying water over the pipes, some of this will evaporate and
help carry more heat away. The refrigerant is sealed inside the pipe and does not come into contact with the air or water, it is always separated, the two never meet or mix. Only the heat of the refrigerant passes through the pipe wall and is carried away by the air and water. As the heat is removed
the refrigerant condenses into a liquid. So it leaves the condenser as a high pressure liquid
refrigerant and flows to the receiver.
The
receiver is a storage vessel for a reservoir of liquid refrigerant and holds any excess that's not in use. This allows it to maintain
a minimum head pressure and also perform under
varying cooling loads, providing a buffer. We'll likely find a line running between the receiver
and the condenser inlet, this is just to provide
pressure equalization and allows the liquid refrigerant to flow out of the condenser and into the receiver more easily.
The refrigerant then flows to the expansion valve which regulates the pressure and addition
of liquid refrigerant into the evaporator circuit. From the expansion valve
the refrigerant flows into the liquid separator,
the liquid flows to the bottom and is
typically then sucked in by some refrigerant pumps, these pumps ensure
correct circulation rate through the evaporators as
the cooling load varies. The refrigerant is then
pushed to the expansion valves of the evaporator which regulate the flow of refrigerant into the cooling load. The cold refrigerant enters
the evaporator and passes on the inside of some pipes inside the evaporator and a fan blows the warm room air across
the outside of these tubes. The cold refrigerant absorbs the heat so the air leaves much cooler and thus provides cooling to the space. As the warm air passes
across the evaporator pipes, it causes the ammonia to boil and evaporate as a part
liquid, part vapour mixture. As it evaporates it carries the heat away. Just like when water boils
in a pan, steam rises from the pan and carries the heat away. Again the refrigerant is sealed inside a pipe and it never comes into contact or mixes with the air, the two are always separated.
The refrigerant leaves the evaporator as a liquid/vapour mixture and heads back to the liquid separator. The refrigerant which is liquid falls down and repeats the cycle
through the evaporator. The refrigerant which is vapour, rises and is sucked
back into the compressor to repeat the entire cycle again. The refrigerant enters the compressor as a low pressure vapour refrigerant. Two stage, this is the next evolution of the industrial refrigeration
system which is suitable for low temperature refrigeration systems, providing high efficiency and low compressor discharge temperatures. We again have the refrigerant
flowing the same cycle but we have a few other
components and cycles. In this type we have a tank called the intermediate cooler which sits between the receiver
and the expansion valve. The main flow of refrigerant
passes through the coil inside the tank, the refrigerant passes through this and into
the main expansion valve just like the single stage system, it then continues its
flow via the separator, the evaporator and back to the separator. Another stream of refrigerant comes off the main line and is sprayed into the tank via an expansion valve to produce a cooling effect, as it is sprayed and
evaporates into the tank, it cools the submerged coil.
This sub cools the main
flow of refrigerant inside the coil before it flows to the main expansion valve. The vapour refrigerant being sucked out of the separator still
flows to a compressor, but this time we have two compressors, the refrigerant therefore flows to the low stage or booster compressor to increase the pressure. From here it flows and is released into the intermediate cooler which helps to condense the refrigerant. The vapour refrigerant is sucked out of the intermediate cooler and flows to the high stage compressor, where it will then flow back into the condenser to
repeat the entire cycle.
Cascade, this is the most advanced system, and these systems can become very complex. It's suitable for refrigeration
systems which require different temperature ranges
for their cooling loads and also makes it easier
and cheaper to comply with health, safety and
environmental regulations. It is a little daunting
when you first look at this system, but if
you've watched this video all the way through without skipping, then you should be able
to follow how it works. Just give yourself a
moment to trace the pipes and see where everything is flowing. These refrigeration
systems usually consist of two or more separate
refrigeration circuits, often using different refrigerants to provide a cooling effect. In this system we have two compressors except they are both
circulating refrigerant around separated circuits, a high temperature circuit and a low temperature circuit.
Connecting the two circuits
is a heat exchanger known as a cascade condenser. We've covered how heat exchangers work, as well as the different
types in our previous videos. Do check that out, links are in the video description down below. The cascade condenser acts as a condenser for the high temperature
circuit, but also an evaporator for the low temperature circuit. The two refrigerants can
be the same or they can be different and optimized
for each circuit. For example, we could use ammonia for the high temperature side and CO2 for the low temperature side. This would mean that less ammonia is used and the system would be
more efficient compared to a two stage ammonia only system.
I just want to thank Danfoss again for sponsoring this video. Don't forget to check out
their free ammonia eLessons by clicking on the link in the video description below. Okay, guys, that's it for this video, but if you want to continue your learning about refrigeration systems, then click on one of these videos on screen now, and I'll catch you there
for the next lesson. Leave your questions
in the comment section and don't forget to follow us on Facebook, Instagram, Twitter, as well as, TheEngineeringMindset.com..
