Scroll Compressor Exposed: Understanding Its Mechanical Magic

sponsored by Danos scroll compressors look something like this they come in many shapes and sizes depending on their capacity and also the technology used inside them they basically convert electrical energy into mechanical energy we call them scroll compressors because inside we find two metal spiral-shaped Scrolls which causes the compression we can find them used in equipment like air compressors but we will be focusing on the refrigerator versions for this video we commonly find them used in air conditioning systems heat pumps rooftop units crack units walk-in coolers and we also find them grouped together for larger commercial cooling applications with the DSG scroll compressor by Danos our sponsor you can design a new generation of sustainable scroll systems increasing Energy Efficiency with ultra low gwp refrigerants the DSG Scrolls feature a broad operating map making them perfect for ultr low gwp chillers and heat pumps their ability to handle reversible applications is perfect for Comfort it and process cooling the DSG range provides unmatched flexibility for both cooling and heating needs its versatility Innovative design and topnotch efficiency have set new high standards allowing oems to design a new generation of sustainable HVAC systems and acceler the decarbonization of the cooling and heating sectors check out the link in the video description to learn more and see the specifications for the entire range do check them out links down below compressors are the heart of the refrigeration system they push the refrigerant between all of the components the refrigerant is a special fluid which can easily change between a liquid and a gas the compressor pushes this around the entire refrigeration system through the condenser the expansion valve and evaporator and then back to the compressor compressors simply trap a quantity of refrigerant and then compact this into a smaller volume to increase the pressure the molecules are then tightly packed together and so they Collide more often the pressure and the temperature will therefore increase we send this high temperature high pressure superheated Vapor refrigerant outside to the condenser the condenser is a simple heat exchange danger the hot refrigerant flows through the tube while cooler ambient air is blown over the outside of the tube the refrigerant is a much higher temperature and so the heat flows from the refrigerant through the tube wall and into the cooler ambient air the removal of heat causes the refrigerant to condense back into a liquid it leaves the condenser as a high press medium temperature liquid and this flows into the expansion valve these valves are either mechanical or electronic design and you can watch our detailed videos on how they work but they basically use a sensor to monitor the superheat at the exit of the evaporator they will then open and close small amounts to control how much refrigerant can flow through the evaporator which controls the superheat value superheat basically means the refrigerant has been boiled to a point where it is completely gas no liquid can exist at that point the nozzle of the expansion valve holds back the liquid refrigerant as it passes through it will expand into the empty space just like a spray water bottle we force liquid through a nozzle which vaporizes it and it expands into a liquid Vapor mixture with more space we have a drop in pressure the molecules can move around more and so the temperature drops this then flows into the evaporator which is another heat exchanger inside the property the refrigerant again flows through the tube with the air of the room flowing over the tube but this time the thermal energy of the air is going to flow through the tube wall and into the low pressure refrigerant the low pressure allows the refrigerant to boil very easily just like this vessel filled with low pressure refrigerant my hand has enough thermal energy to cause it to boil and so the heat of the room is enough to boil the refrigerant because it has a very low boiling point the ref ref turns into a gas and carries The Unwanted heat of the room away it exits as a low pressure low temperature slightly superheated Vapor the refrigerant is then sucked into the compressor to repeat this process when we look at the compressor we have the main protective shell we also find the low press suction Inlet and the high press discharge Outlook there is also an electrical connection for the power supply and controls this is hermetically sealed meaning all the compon components are sealed inside so we can't access them but also dirt can't enter and the refrigerant can't escape when we remove the shell we see there is a mechanical section and an electrical section at the bottom we usually find some type of support with a bearing built into this the shaft will sit within this bearing and Rises up through the compressor connected to the shaft is the rotor surrounding the rotor is the motor stator there is a small gap between between the stator and the rotor the stator remains stationary but the rotor rotates the stator has a number of coils of wire these are energized to create an electromagnetic field the magnetic field interacts with the rotor causing it to rotate the rotor is attached to the shaft and so this also rotates attached to the coil is a temperature sensor typically this is a PTC type sensor as the coil temperature increases the PTC resistance also increases at a certain temperature the sensor will cut the power to protect the motor otherwise the heat of the coil will melt the enamel insulation causing a short circuit and the STA would just burn out coming back to the shaft we can notice the top of the shaft is offset from the center the scroll will attach to this but because the scroll is offset we have an imbalance on the shaft so we find some counter weights attached to the top and the bottom of the rotor to try and correct this at the top of the shaft we find the compressor housing we usually find a bearing within this to help support the shaft during rotation the housing has some grooves cut into it another component called the olden ring has some ridges which will sit Within These grooves these allow it to slide back and forth the orbiting scroll also has some grooves cut into into it these will interlock with the ridges on the top of the olden ring allowing the scroll to slide back and forth perpendicular to the housing and the olden ring the offset of the shaft combined with the restrictions of the olden ring allows the scroll to orbit without rotating on its axis the orbiting scroll will sit within a fixed scroll this is connected to the shell and also the housing and so this is locked in position when the shaft rotates the orbiting scroll will now move within the fixed scroll this causes compression we will see how that works in just a moment the compressed refrigerant is then ejected from the center we typically then find a non- return valve here this design is a simple disc valve and that is pushed open to vent the refrigerant and it drops down when the compressor turns off to stop the back flow we might also find read valves used here these are basically thin sheets which Bend to open and vent the refrigerant but it will also drop down when the compressor turns off above this we usually find a heat shield the refrigerant leaving the compression chamber is a high temperature so this helps prevent heat transfer back into the compression chamber notice there is a void between the heat shield and the shell this area stores some refrigerant the refrigerant will exit the compression chamber imp pulses and so this storage chamber removes moves these pulses allowing a constant stream to exit the compressor some compressors will have a check valve at the compressor Outlet instead of the compression chamber but this works in a very similar way we might also find some sort of pressure relief valve built into the housing if the discharge temperature exceeds the design limit it will discharge the hot refrigerant gas down into the casing the motor winding temperature sensor will detect this rapid increase in temperature and it will cut the power to protect the motor in the bottom of the housing we find a reservoir of oil and residual liquid refrigerant some compressors will have a sight glass where you can inspect this oil level inside the shaft there is a small Channel with various exit points and there's also an opening at the lower section as the shaft rotates oil is sucked into this opening and the centrifugal force causes it to rise up the channel it will then exit at the various points to lubricate the bearings and surfaces the refrigerant is sucked into the shell from the evaporator it will typically hit some sort of Shield Plate because the refrigerant could be a mixture of liquid and gas the liquid will then drop down to the reservoir while the gas can continue to flow the refrigerant will then flow inside the casing through and around the motor now that might seem a bit strange but remember the motor is sealed within the shell a standard electrical motor uses a fan to blow ambient air over the casing and remove the unwanted heat of the stator electrical motors produce a lot of heat which needs to be removed otherwise it will destroy the motor so we use the refrigerant to collect and remove this unwanted heat the refrigerant will then flow upwards and into an opening on the side of the fixed scroll as the scroll orbits the wall will separate and a gap opens to allow some refrigerant inside the scroll then continues to orbit and the Gap closes a pocket of refrigerant is now trapped inside the walls will continue to orbit and this forces the refrigerant to move deeper into the compression chamber towards the center gradually the volume decreases which increases the pressure eventually the refrigerant will reach the center where it has reached its maximum compression the Scrolls then separate at the very center allowing the refrigerant to escape the scroll continues to orbit and the central Gap closes which forces any remaining refrigerant to exit and it then collects in the dome at the top during compression several pockets of refrigerant will be compressed simultaneously and this will give a continuous output scroll compressors can handle small amounts of liquid it can pass through without damaging the scroll plates the refrigerant exits the compression chamber as a high press high temperature super heated vapor and flows to the condenser a crank case heater is sometimes fitted this keeps the shell warm in cold climates and prevents the refrigerant condensing inside this prevents back flow and also stops the lubricating oil from diluting traditionally scroll compressors would just be turned on and off to control the cooling capacity the system is even either completely on or completely off there is no in between on larger systems with groups of compressors they would simply be turned on and off at different stages to try and meet the cooling demand this does give some modulation of capacity but it's not very good turning the system on and off causes pressure surges it also causes bad thermal control and also causes electrical surges the electrical motor has a fixed rotational speed so the only way to modulate the cooling capacity previously was to turn it on and off the diameter of the scroll the height of the scroll wall and also the motor's rotational speed is what controls the capacity and with traditional designs all of these were fixed properties one method developed known as the hot gas bypass uses a solenoid valve to recirculate some of the hot refrigerant back into the evaporator this creates a f false cooling load on the system it's very inefficient but it does keep the compressor running another common design is the digital compressor a solenoid valve recirculates refrigerant back into the suction light the fixed scroll can move up and down the pressure within the Dome holds the fix scroll down but a solenoid valve can open to release this pressure back into the suction line during this moment the Scrolls will disengage a tiny amount and so no refrigerant will be compressed in this time but the motor keeps running after a short duration the valve then closes the pressure builds up again and this pressure will force the scroll down and so the compression continues we control this in 15c intervals so if you need 50% capacity then the scroll will engage for 7.5 seconds and then disengage for 7.5 seconds newer designs use a variable frequency drive to control the speed of the motor and so the volume of refrigerant flowing around the system changes to match the current cooling demand this design uses an electronic expansion valve to achieve very precise control this gives us great Energy Efficiency and also optimal thermal control check out one of these videos to continue learning about Refrigeration engineering and I'll catch you there for the next lesson don't forget to follow us on Tik Tok Twitter link Lin Instagram Facebook and the engineering mindset.com

Channel: The Engineering Mindset

Views: 235,196

Keywords: scroll compressor, compressor, how scroll compressor works, scroll, hvac, hvac technician, hvac training videos, copeland scroll, hvac school, hvacr, building services, bryan orr, hvac instructor, hvac near me, heat transfer, hvacr videos, hvac training, digital scroll, hot gas bypass, superheat, compressor stages, condenser, evaporator, hvac videos, suction line, danfoss compressor, process engineering, hvac controls, hvac shop talk, ac, how it works, heat pump, hvac guy, cfm

Id: e_4ITFCQvts

Length: 14min 39sec (879 seconds)

Published: Sun Dec 03 2023