How the Two Stage Heat Pump Works

here working on the refrigeration machine got a big new project if I can get this thing stabilized be well on my way to putting a heat pump in the house I got a few features that I haven't quite figured out how to work with yet pretty much none of them die it's a lot of fun so this is what I got going on here the last video mmm just trying to explain what this liquid separator here is for the low side but I thought I would just go ahead and overview the whole thing because I forget sometimes that people don't know what the hell it is that I'm doing included so the intention here is to build a test bench it's always been some kind of a test bench to just get a handle on different methods of brazing of fitting of bending and how well propane refrigerant works it's just a cheap I've barbecue grade propane pass through a little bit of filtration but more or less just just as it were as it was in the tank so this is the heat pump vapor compression heat pump picks up heat there to that coil with a fan discharges up here in this condenser with a fan both come out of air conditioners as well as this hermetic rotary compressor here third a half horsepower pretty small I think is like 7 CC displacement or something rotary so I'm just gonna kind of go through the different components and explain what they do this thing is set up so that with with luck I did it'll do something it'll do something once I actually fire it up tonight that it has essentially three main pressures use a high side pressure as you normally would in a system it's for condensing a high temperature vapor out of the compressor leaves a low temperature evaporator before picking up heat and in this case we have a medium pressure column two-stage compression ejector is the first stage and the electrically powered rotary compressor is a second stage out of the compressor we have high-pressure vapor shot through this quarter inch line loop-de-loop up the line into the condenser heat is driven off causes the vapor to condense discharges out the side here you see some these thermocouples that I have installed various spots hopefully a little bit sub cooled see there's a slight glass back there as it goes back up just service valve filter dryer comes up over the top pressure gage they're looking for any kind of pressure drop across the filter dryer and it comes on down into the ejector now it's not too simple in terms of it just being one single loop like a conventional vapour compression system it's not just four components there's more to it than that there's in a sense there's two loops that are going on at the same time and the overlap occurs in the ejector and in the separator column here so what kind of a low-pressure system going on between the the evaporator and the medium pressure column being compressed by the the the ejector or expresser expander and compressor at the same time no moving parts just a bunch of copper and then on the other side we have the high pressure side coupled to the medium pressure side between the ejector and and separator column there to the you know the compressor and the condenser up there so as I was saying the liquid coming from the condenser comes down through the ejector or picks up some vapor off the evaporator the low-pressure side the velocity of the liquid refrigerant coming through comes through a nozzle something like this that's actually placed down inside this this kind of sort of a venturi type device gains velocity through the tip here the pressure component from the high-pressure liquid is converted into kinetic energy velocity and great to a low pressure high velocity but low pressure which can draw a vapor off of the low pressure side the liquid refrigerant coming from the condenser everything coming out of the primary mode of nozzle it gives up some of the kinetic energy that it has to the low pressure refrigerant the mixture of those two comes through this quarter inch line that expands out through here slows down gains pressure and ends up at a pressure a medium pressure somewhere between the high pressure side and the low pressure side it's closer to the low pressure side I've only seen about 10 psi in here this column here there's one inch column separator column liquid can settle out there to the bottom get the laser pointer see if this helps at all so liquid can separate out into this column here save about two that point there and what liquid is separated out can come down through this line and then comes back up through this needle valve adjustable needle valve and then it allows me to put a little bit of restriction between the medium pressure column and the low-pressure side and it is an expansion device is a refrigerant control hasn't been tested yet hasn't been utilized I've used quarter inch valves for a similar purpose but I wanted something a little bit larger because the pressure difference between medium pressure column and the low pressure side is very small so I should continue to explain in the medium pressure column I just said the liquid can be drawn off and go to cooling work what vapor is produced because you're always going to have some flash gas that's produced from the in the ejector from the you know expanding refrigerant coming in from the high side and that vapor needs to be drawn back to the compressor which goes through this goofy line that I had to make up and comes back so yeah thermocouple there comes on back there we have this extra little quarter-inch in knob that's not used in this this setup here so that's pretty much you know the high side there okay in the low-side we also have a column it's got some nice sight glasses you see through them there's two cup three inch lines that terminate up there in the middle and then this one down here is just for the purpose of looking at liquid level now this column does something very similar to the medium pressure column this column is for the purpose of separating low pressure liquid from low pressure vapor liquid is intended to be maintained somewhere around the height of the sight glass around where this this line is here yeah a thermocouple on the backside here that'll take a liquid temperature so the refrigerant control feeds a little bit of liquid in here and that line terminates is the one line right there so you should be able to see liquid spewing out there hopefully not such a velocity that it's actually picked up by the suction line which loops back to the ejector so everything in this column names coil everything in this coil is that we all a low-pressure relatively speaking with all system now this column as I said it does the separation just as this one does here so vapor can be drawn off liquid settles to the bottom the evaporator itself rather than just having a line going in it from say you know a refrigerant control and then exiting going straight back to the compressor and in a simple favorite compression system this is a flooded evaporator and by that I mean in the entire inside surface of the coils are should be more or less wetted at all times the velocity of the refrigerant passing through those coils is more or less dictated by the heat carrying capacity of the refrigerant of the liquid refrigerant the surface area of the coil the you know obviously the pressure the delta T between the temperature the the coil and the surrounding ambient environment and then of course you know other things like you know he made it even amount of airflow across it but what I'm trying to say is that because it's wet it all the time there's pretty good heat transfer coefficients to to to warm the the the saturated liquid inside and cause it to immediately start to boil a bewdley lowers the density of this this mixture has a lower density than just the liquid itself the vapor and picking up some liquid is pushed up through this line here exits out through that line just like the refrigerant control that feeds this terminates right there in the view of the sight glass and I should be able to see the amount of liquid that's being carried over by this this coil so we need to just review we've aligned coming out of the bottom just feeding liquid off of a separator column to the coil and then we align coming off the top the coil and then into the top more you know upper space here to separate some of the vapor and the liquid it could have terminated towards the bottom and there never been some bubble England I want to keep the liquid in the bottom as calm as possible so hoping that's a that works for that so so again you know the amount of circulation that goes through there it's kind of its dictated by a lot of variables hopefully there's enough circulation through there that vapor pockets aren't being you know are quickly being carried away you know washed away by some of the liquid and all the movement all the difference being the static head of the liquid sitting on this side and and the you know some more active head or whatever you want to call it the lower density vapor being you know drawn off it pulled off or produced or whatever yeah so time will kind of tell because of a mess with flooded evaporators a little bit here in the past but nothing quite of this this nature usually have a column that's you know the full height there but here I'm hoping to insulate these lines and actually be able to see the amount of overflow you know the thermos tightening effect somewhat similar to a you know solar thermal you know water heating insulation or something but you know with the added effect that we're actually having phase change going on in there so it's going to be violent so while all that is going on and vapors being produced liquid being recirculated and vapor being produced that vapor and then the low pressure conditions that need to be maintained to continue the heat trance and pulling heat out of the the environment in this case they'll local air that vapor is drawn back to the ejector and that vapor is accelerated till it meets the liquid and exiting through the primary mode of nozzle and there's an exchange of energy there the combined velocity is somewhat higher than the velocity entering from the vapor and lower than the velocity of the liquid exiting the primary mode of nozzle the same relationship with pressures and what exits is a mixture that's at a pressure somewhere in the middle so that's kind of our second state or excuse me our first stage compression that that occurs and is essentially powered by this compressor but the intention is that there's no extra energy expended by the compressor in order to provide that compression because that energy that that pressure component of the enthalpy of the incoming liquid refrigerant that that pressure component would normally be lost converted into internal energy and you know internal energy ends up causing flash gas and we lose some of the the liquid that could be carrying heat for our purpose and it's just being circulated around and around and around just for the compressor in this case I'm trying to use some of that work to do some compression for that and I'm I know it works I don't know exactly how well it works other than I've achieved 810 psi whether or not it's better than a system without an injector I don't have any comparison anyway so you know we have our first stage compression there and vapor from that stage is drawn off and goes to the compressor to finish it off so you know by doing this first stage here and even even raising the suction pressure for the rotary compressor by 10 psi that now ultimately reduces the compression ratio that the compressor has to to perform and if you lower the compression ratio Plus work the compressor has to do by having a higher suction pressure coming back to the compressor you know say we're maintaining 40 psi there but the compressor only you know sees 50 psi the density of the of the suction gas being drawn into the veins of the rotary compressor it's a higher density gas so the for each rotation of the the compressor there's more mass flow through the compressor so it's higher volumetric efficiency generally at least that's the intention so time will tell I'm gonna change me me yeah I'm gonna change my vacuum pump oil I don't let her sit on the pump for a while and drawing you water that might be out I actually flush this coil out with water so uh I knew that could be a problem but it just takes a long time with a vacuum pump to get her out and later on this evening we'll do a pressure test with this ugly ugly epoxy and make sure everything's good to go there and no doubt will have some leaks in some of my ugly-ass flare fittings but they my god they are convenient so hopefully we'll be running tonight once I get some preliminary tests it seems like it's good to go I can insulate all this crap and that won't be so ugly anymore right anyway thanks for watching and we'll see you next time

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