EEVs are like an easy button honestly. Very simple PID to control superheat. We use the Sporlan Kelvin II all the time but the temp transducer only works down to -60C. It wouldn’t be so bad except after that it commands the EEV full close and there’s not dry contact to command a compressor stop so yeah, guess what happens. Certainly makes you get your HPC logic down.
Other issue with the Kelvin II is that it’s pretty expensive. TBH it makes more sense to use a Siemens Logo or similar small PLC with a single PID loop and value chart to run the EEV. Next time I do one I’ll throw the program up on here and save everyone a couple hundred bucks.
The red lines indicate suction lines to the pump inlet, blue lines are discharge lines from the pump outlet.
The orange lines indicate a chiller of some sort–if its possible to push compressed refrigerant through there without creating some kind of compliance nightmare, i’m all about it.
The plan is to transfer -10C ethanol from a larger holding tank into that small tank (the centrifuge is a CUP-15 for size reference), and further chill that ethanol to -40C using the brazed plate. This is primarily because -10 or -20C chillers are about 1/4th the price for double the amount of kilowatts.
I’d prefer not to get an ultra-low chiller–not because they aren’t awesome (because they totally are)–but because they’re super expensive.
Anywho, does anyone know if compressed refrigerant will work?
Plate heat exchangers work great for these applications. There are some issues with vapor holdup on the evaporator but nothing drastic. Absolutely no problem with that design (other than some nitpicky stuff like a liquid accumulator and expansion device). Also, you can get brazed plates in the 1000psi+ MAWP range.
The condensing unit Im looking at has the same capacity at -40 as a Julabo presto which retails at $40k
Seems like the EEV will be a future upgrade for me, I was eyeing the johnson control eev(cause they have a price listed), which looks like it’d work for -40. Probably opt for a sporlan or emerson txv.
Duda diesel carries some big cheap BPHXs that I’ve used. I also troll eBay for SWEP and Alfa Laval units that are used/new-old stock. For the real badass applications Tranter maxchanger is an all welded stainless plate heat exchanger. We used one as an insterstage heat exchanger operating at like 1300psi once.
Only thing I will say about BPHXs is that they usually come with NPT threads which are fucking useless in a refrigeration system. I’d kill for someone who would make them with JIC ends instead. Usually we either weld the piping in directly or weld in a JIC adapter. In the past we brazed the threads directly but… I fucking hate brazing
Good call on the jic adapter welding and plate mfg recommendations, I will do some more searching there. I am also interested in dx cooling my processing recovery tubes as well.
Excerpt from the DX thread previously linked:
So Im not exactly understanding how it wont be stealing much mass if you grossly oversize the evaporator. Is there downsides? The inside jacket surface area is much greater than say a 1/2 ton bphx.
It has some good info on learning what some of the performance data means and what determines or influences capacity of the compressor and how that relates to the evaporators refrigeration effect.
Im sure what Im not getting is right before me, but it hasnt fully clicked yet, I think I have to re read the mit doc several more times.
“As superheat increases, Hsh increases &
Evaporator Refrigeration Effect increases (as long
as the superheat does not become higher than the
desired cooling temperature for the unit)”
“as long as the superheat does not become higher than the desired cooling temperature for the unit”
if 5°F to 10°F is normal super heat, and the desired cooling temp for the unit is -40. I dont understand.
This also is not clicking yet:
"Lowering the return gas temperature will
increase the density entering the
compressor, thus increasing the evaporator
mass flow. This will increase the evaporator
refrigeration effect. Increasing the
evaporator mass flow will also increase
compressor capacity but the return gas
temperature enthalpy (Hrgt) will decrease
reducing the change in enthalpy. This leads to a lower
compressor capacity. In most instances,
the enthalpy decrease will be greater than the mass flow
increase which will result in lower compressor capacities. "
Bascially trying to understand what determines the enthalpy decrease vs mass flow increase, cause it sounds like an easy way to increase capacity is to lower the return gas temps from the standard 65f, which in my cold ass location should be easy.
So yes, oversizing the evaporator will require more refrigerant in the system and will have more holdup volume. Other than that though, no real issue with it. The way to look at it is how an EEV works (TXVs do the same mechanically, just less ideally): an EEV looks at the pressure and temperature of the refrigerant entering the compressor and calculates the superheat from that. If that is less than the setpoint, it closes the valve which reduces the saturation pressure and also consequentially the temperature at the inlet of the evaporator (because the refrigerant is now boiling at a lower temperature). BUT the density is lower because of the lower pressure and therefore the compressor is moving less gas.
When the system is running initially (let’s say cooling a massive amount of hot solvent) the evaporator is getting all the heat it needs it boil a shitload of refrigerant. Only limited by heat exchange, the EEV goes full open and still has more superheat than the setpoint. Design note here: if you way oversize the EEV you can build a system that just pumps refrigerant in a circle without building any pressure differential so… Don’t do that. Anyways, if the evaporator is way oversized here, it will just ensure that you max out your expansion valve but ultimately you are cooling faster because the EEV doesn’t have to close to ensure superheat.
Move along to where we’re at temperature. The process fluid is very cold and that makes the EEV close a lot to bring the saturation temperature sufficiently below the process fluid temp, otherwise no refrigerant will boil and no superheat will be developed. The larger the heat exchanger (actually the higher “theta”), the more easily the refrigerant can find the heat to boil and therefore will operate at a higher pressure ie higher density ie more chooch.
What the MIT thing is probably saying is that a less superheated gas is denser and therefore lends more capacity than a more superheated gas, which is correct but the more important factor is that the system achieves that lower superheat by allowing a higher evap pressure at a given heat load. That higher evap pressure = denser gas = more chooch.
Lastly, what I’m saying about not “stealing mass” is talking about fade out capacity. The standstill pressure is the same across the entire system. It is a function of the density of that refrigerant, the volume, and the temperature. Let’s say we cap that pressure at 700psi (normal max pressure of refrigeration components FYI). If you know your system volume, you can derive how much mass you are allowed. Now, when allocating your volume between suction and discharge (ie more sense and less sense), a higher ratio of suction volume (evaporator size) to discharge requires less refrigerant mass because the density in the evaporator is lower. If you minimize your condenser volume as much as possible and still require too much mass for your standstill allowance, the only solution is to add more volume on the suction side, commonly by putting a tank that literally only serves the purpose of taking up volume. Obviously if you have an enormous evaporator, the tank might not be necessary. Does that make sense?
None of this applies with a fixed orifice lol. I skipped that part of my self-education so don’t ask me how it all works when you just use a hole.
If you are looking to DX exchange with a jacketed column, it’s as simple as setting your standstill pressure/mass allowance to a bit below the working pressure of the jacket, but if that’s low it’s going to mean you need a massive amount of fade out capacity or another more sophisticated design.
And on your last point, what you’re really saying is that a lower suction superheat is more efficient as that is absolutely correct. It is standard practice to reduce that as much as you can without worrying about liquid slugging. Incorporating a suction accumulator is a very easy effective way to drop from 10 R to 3-4 R superheat. Honestly though if this is your first chiller build, don’t sweat it too much, it’s really not a major capacity factor.
I do my best to try to pass along the information I’ve picked up. Seems like a more than fair trade to exchange knowledge about refrigeration (a subject that has tons and tons of accessible literature) in exchange for all the cutting edge secrets developed for the first time by the fine people of this forum.
Yes its very much appreciated. Im sure I can get it working, but understanding more fully can only help.
So looking at the performance data sheet for the awa2464zxdxc, what size of txv would you chose to optimally run at -40, a 1/5 or 1/4 ton to match the -40 rating/data, or a half ton for its -10 “nominal” range rating?
I am way over thinking it mainly because I would like to eventually get into cascade or autocascade usage, primarily because I would like to inject for extraction at a temp colder than -40, even -50 would be awesome, so Im trying to understand if its possible to “overclock” this Tecumseh unit to achieve lower temps than -40.
I am leaning towards a direct expansion application vs a plate or other exchanger. I am thinking of ordering a 6"x54" tube, with a wall thickness of 4mm which should have a collapse pressure of over 450. double jacket it. Roughly there would be 10sqft of evaporator surface area and near 1200cc of evap volume!
(obviously not the safe manner of thinking but the collapse pressure will be bolstered by the internal pressure which should rise pretty equally if using a propane dom mix as a solvent) Basically a dual permanent storage freezer/working vessel for the solvent.
Do it! We can do the math to make that safe. I don’t recommend placing any value on the internal pressure because leaks happen and then, well, yeah.
The biggest thing to look at is the compression ratio. -40 is right on the edge of what you can do with r404a. If you have to compress the vapor more than 10:1 it’s not going to work well. You can get up to 15:1with liquid or vapor injection but that’s a different compressor than you’re looking at.
Here’s the saturation table for 404: R404A (1).pdf (43.6 KB)
At -45C you’re at 14.9 psia. To condense at 43C, you need to be at 283 psia. That’s almost 20:1. I would suggest some sort of water cooled condenser to get your range down to a lower condensing temp.
I read on some other site that 404a in freezer applications the typical range is 6:1 - 13:1 which the awa2464 is a 13:1 @ -40evap and 90f condensing temps, so was only mildly concerned.
Whats with the higher btu capacity at 80F vs 90F but the watts goes down? typo?
Anyway, average temp at my location is very cold, I get maybe 4 or 5 days over 85f, average yearly temp is 1c. I will have a harder time keeping it above 40f than not for most of the time its in use.
Is there a sweet spot? To cold of ambient not good?
Maybe I should not be so concerned with a “pre built” condensing unit and source a compressor that can utilize a more suitable refrigerant? The amount of stuff on the schematic that is not a compressor and condenser does daunt me if I had to recreate all that.
I’d probably run an EFSE-1 (1 ton nominal) with an SX charge. You’re probably not going to find a better single stage refrigerant than 404a, just beware the issue. There is no such thing as too cold an environment, you basically just translate all the parameters down.
I’m used to sizing systems with the assumption that they’re going to be in a hot ass mechanical room. If you can keep the condenser on the colder side you can probably make it work. Just watch the discharge temp on the compressor, that high compression ratio will make it hot and if it gets over 200C it will start to burn oil.
Waiting on some quotes on the unit and hopefully expansion valve. Might have a hard time getting that one. Think I found the condensing unit for $1k though.
Got one price for the dx storage tank just using a simple design, not sure if it needs more consideration, should be okay with the intake and outake being opposite each other? I upped my diameter from 6" to 8" to lower the height and went with a 5mm wall thickness for the inner tank. Should hold 30lbs of propane.
Picked up a used condensing unit locally for a couple hundred: a Copeland C8AL-0151-TAC-001. Its a “receiver base” condensing unit. Will have to figure out the phase conversion though.
Heres some specs on the compressor it uses if anyone is interested: Copelametic EADA-020E-TAC (6000btu and 1.1KW cooling capacity)
Also picked up a keep rite freezer evaporator which doesnt have a name plate, but pretty sure it was paired with the condensing unit I picked up(restaurant auction)
The evap has a Danfoss TUAE valve rated to -40. I couldnt find a valve rated for lower than -40 at least without paying out the ass for a new one(over 500cad wtf)
Key items left:
Still havent decided on the DX tubing size but am getting it done up local vs china, looks like it’ll be around $1000cad for a 60-100lb pipe/tank.
Been a couple days since you posted this but I had a couple questions/points (other than nice score on the unit, looks like it should do well):
When you talk about DX coil what did you have in mind, just a straight up wort chiller style coil in the tank? You may have issues with liquid holdup in the evaporator unless you use run multiple coils through a distributor. That storage tank looks like it might work well in a “flooded evaporator” style (basically a giant suction accumulator) although you’re going to want a lot of insulation on the outside (vac jacket would of course be ideal but money is a thing lol).
Disclaimer: I’ve never used danfoss components since they told me to get bent so that part may be totally suitable but I honestly didn’t look for a cross
Lastly, whatcha gonna do with that evaporator if you’re DXing? Fun fact, most refrigeration components are either rated for 450psig or 700psig so you could probably work it in as additional condenser area if you needed it.
It was a nice score, I could also pick up a used 4hp tecumseh for around $1000, so anyone watching, do some searching for used/refurbed units, unfortunately a lot of restaurants are going under so freezer units are around.
The DX style is the latter of your guesses, like a big suction accumulator, or a 6inch(or 8") double jacket one end closed material spool.
I was going to use sch 5 pipe for the jackets, but cant source it locally so far. If I cant source it I will probably use Sch 10 for both the inner storage pipe, and the dx first jacket. For the outter vac jacket I will probably get some ghetto tek going and use a few kitchen stock pots with ends cut off and welded together as a outer pipe to avoid a 10 or 12 inch sch 10 weight and cost.
I still cant find the collapse pressure for 8" pipes so if I go with that size for the inside storage pipe I will opt for sch 40, which the only reason I hesitate on that is the thermal transfer hit with the thickness increase, but I dont think a 7 foot tall 6" pipe is ideal compared to a 5 foot 8" pipe.
Im 95% sure im going to use swagelok pipe adapters to plumb everything. If I could find flexable line set for 404a with low ambient temp rating Id use that too, but havnt found it yet, not sure if swagelok can make something up or what.
The reason for the high price on the TXV is the extreme or ultra cold charges, the SX and ZZC for the Sporlan and Emerson. Regular -40 type valves are all over for around $100
I picked up the walk-in evaporator because I thought I could scavenge the expansion valve off of it as it was cheaper than purchasing the valve on its own. Also we have wanted a walk in freezer for processing storage as well, so will pick up a replacement valve for it or buy a different one for the DX pipe.
Im not sure I’d need that much condensing power its very large compared to the condenser utilized by the unit. Its 8 or 10 foot long, youve kinda blown my mind with this prospect.
Honestly you probably won’t have an issue with hunting in your application which is what those specialty charges are for. Sounds like you’re basically going to be fully loaded above design temp until you reach design temp and then if your vessel does have a vac jacket, you won’t need much capacity to maintain your cooling. That means your TXV is going to be pretty fully open most of the time. I think you can probably get away with a regular LT charge.
As far as fabbing up the vessel, I definitely think vac jacket is the way to go if you can swing it. You’ll also probably find it much more economical to have someone roll plate for you than to use pipe. That’s a pretty standard vessel design, and pretty easy with a backing strip on the outer and middle wall. You will probably want to find/design around the torispherical heads. Flat heads even at these pressures/diameters will butcher your wall thickness calculations I think.
Lastly, hoses/fittings: there should be a plethora of options for hoses rated for -60 or so but they won’t be cheap. You may want to honestly consider hard piping; how often do you really move your rack? The only thing I will say is that you’ll hate your life if you let a single pipe thread on the refrigerant system. I would have JIC flare fittings welded on personally.
