guidebook on medium freon compressors interfacing? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2019, 09:28:13 pm
content: I am kinda thinking about some kind of high capacity outdoors located pump/tank/radiator combo that would do some kW of cooling at a decent flow to cool various power electronics things for a power electronics lab (i.e. heat loads). It would have 2x flow meter and 2x pressure meter and differential temperature in addition to a pump controller and a tank. I wonder if you can mount it to a overhang or something. Something that does not look like a industrial site. Maybe built to look like a wall extension.If you had that capability you can add cooling jackets to vacuum pumps and other things too. And put little heat exchangers behind equipment that generates lots of heat to keep the room cool. Like a rack of commercial equipment with a suction fan. Then you can run stock linear high power supplies.It would beat the shit out of a extraction vent (omfg don't you hate that corrugated tubing shit?) if you need to move something around, especially if you put a grid of metal plates on the ceiling to which you can attach magnetic hooks if necessary to suspend heat extraction piping.But what if you can also add a compressor and a heat exchanger to the system and used chilled coolant (i don't want to run freon lines).I have a litron heat exchanger I was going to use for something, with quite a high capacity, brazed brass meant for inert fluid transfer.Does anyone have a guidebook on how to select a compressor to interface with a heat exchanger? (an advanced one that assumes you know how to setup a leak free clean freon system).I am not interested in peltiers for this application. It would be a habbitat thing.

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2019, 11:03:30 pm
content: do you just need to build the system to match some kind of pressure differential across the compressor? and thermal differential. DO you need some kind of flow measurement? I assume the heat exchanger metals need to conform to some kind of differential too so you don't freeze destroy them. If the differential are met during operation based on the geometry of the compressor it means the pump flow is adequate?I don't understand the freon heat exchanger too much. It is a four inlet network. Are you supposed to let the gas vaporize in it? Or is liquid freon supposed to pass and expand later? I assume it would flood/foam out if there was boiling liquid in such a small area. So you ensure there is no phase change in the heat exchanger in a freon/liquid interface?What is a suitable compressor type for something in the 10kW cooling range? Are home HVAC units capable of such operation?its something like this, i got a slam dunk deal on it a while backhttp://www.directindustry.com/prod/hofmann-beijing-engineering-technology-co-ltd/product-200015-2034350.html?utm_source=ProductDetail&utm_medium=Web&utm_content=SimilarProduct&utm_campaign=CA

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2019, 11:11:31 pm
content: is it a specific gas that requires licensing or just the concept of a compressor?it would be used to cool a liquid loop. does that qualify as HVAC?

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2019, 11:16:19 pm
content: Quote from: blueskull on January 15, 2019, 11:13:43 pmits not a buisness, is OSHA still relevant?What is the downside other then increased power cost? It would all be outside and elevated (the gas system). I know its dangerous to put indoors or near a structure that can accumulate the gas. You would use the proper equipment to charge the system as not to cause enviromental damage. A simulant could be used at increased pressure to check for leaks.

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2019, 11:25:40 pm
content: the idea is to use a compressor connected to a heat exchanger to cool a water loop so that freon is not run into a lab. Like with peltiers but not so enviromentally unfriendly. But also with a real professional heat exchanger not dipping a refrigerator into a barrel. I wanted it compact. And to minimize tank size. And with a custom radiator for the compressor thats built nice/wide surface area/easy to clean. Like do it with real parts in a custom engineered solution to a nice form factor with high quality throughout.

author: amyk
author_rank: Super Contributor
timestamp: January 16, 2019, 01:33:47 am
content: Quote from: blueskull on January 15, 2019, 11:13:43 pmThe "duster air" cans basically contain refrigerant (usually 134 or 152 these days), you can find videos of people recharging AC systems with them. So do the propellants in other types of aerosol cans, and of course people release those into the environment all the time... you're probably being better for the environment and making better use of the gas to put it in a closed refrigeration system, yet the EPA probably thinks that illegal... go figure.For the OP, this is probably something you'll find the answer to in refrigeration books and forums (not the kind full of commercial servicers, mind you --- they'll just brag about their EPA license and tell you to piss off), because you don't seem to be asking much in the way of electronics.

author: coppercone2
author_rank: Super Contributor
timestamp: January 16, 2019, 01:35:15 am
content: its kinda scary to go there with youtube video like DIY HVAC.They seem to be very aggressive towards this sort of thing. hungry hungry contractorshttps://www.youtube.com/channel/UCFxf3hjNRSQ706L3jgDYnBwkind of a shocker for me. I have found more then 1 of thesecompare to electricians, plumbers, mechanics..... usually those just complain on youtube comments (in regards to horrific worksmanship) but these guys got their own channels . I just want the engineering questions answered, I have a feeling those forums will not be too fruitful and rather painful to post on. I am not dealing with people that think putting dust-off in a tube and brazing it shut is some kind of entitlement that requires 2000 hours of training. Give me a fucking break, they seem like the kind of people that would want home depot to be illegal. 1 crappy contractor van probobly puts out more pollution then all the leaking HVAC systems. I would use better quality parts with less leak chance then them anyway.I am serious like half a decade ago I used to watch this one H-VAC channel and holy shit he was venomous as FUCK. THen he acts high and mighty because he managed to build some kind of shitty PLC out of a fucking arduino (for a big ass apartment building no less) and barely knew what goes into making a good electrical control system. It's like all Gerber (the multitool company) level advertising with these guys. Like bro if you wanna be professional don't throw 800lb of air conditioner into a parking lot and break the concrete like your 5 years old. You got a nice big flat roof to work on, cut it into small parts so you don't destroy the freaking building. Disrespectful to the property owner and scary for neighbors.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 16, 2019, 02:19:43 am
content: EPA 608 is very easy to get. But if it's a one off DIY project, just get a few window A/C units and hack them putting the evaporator into a tank - that avoids having to mess with the refrigerant plumbing. Keep in mind 1kW is equal to about 3400BTU/hr.If you do decide to open up the loop, I suggest replacing the cap tube with a TXV and spending the extra $10 or so for a sight glass. It's much easier to get right compared to a cap tube.

author: richard.cs
author_rank: Super Contributor
timestamp: January 16, 2019, 08:10:10 am
content: So you want to chill a water loop? What about a beer chiller from a bar? They have two halves, one looks like the outside half of an ac unit but contains the whole heat pump, cooling a water loop that snakes off indoors in 2x ordinary hose pipe to the other half that actually cools the beer.

author: coppercone2
author_rank: Super Contributor
timestamp: January 16, 2019, 09:11:48 am
content: I don't like the form factor of commercial solutions. I wanted to make a very specific radiator geometry in mind.and their heat exchangers are likely of low quality. And I don't like the vending machine look. I don't want a eyesore. I am thinking like a long thing designed into a duct shape and designed in solidworks.1x not economically viable prototype.

author: Rerouter
author_rank: Super Contributor
timestamp: January 16, 2019, 09:33:50 am
content: Start from the simplest approach, you need a pump, a heat load, a heat dump (radiator) and an expansion valve to drop the pressure,The cooling effect you get is from a pressure drop initiating a phase change, if the pressure drop is enough that it wants to change phase then you also get a boost from the latent heat of the phase change,When a material reaches a point where it wants to change phase, generally it involves energy from the outside, e.g. water becoming steam needs additional energy from its surroundings, and vice versa when it condenses it gives off a similar amount of energy, this is how your refrigerator works.So you design your loop around this phase change, just pressure vs temperature, pick a chemical and you can likely find its temperature / pressure phase chart online. So you need a pump that can reach a pressure where it becomes a liquid at your desired temperature range. but is a gas when not under operating pressure.Most refrigeration loops do not use pressure feedback, only temperature feedback, run the pump for X time, then start to crack the expansion valve, you should see your heat load start cooling quite rapidly, then regulate the valve position to balance how much you want the inside to be cool, vs not heating up the radiator so much your fluid boils back to a gas, or so cold on the valve that it freezes over (that valve will be the coldest part of your loop in general)

author: coppercone2
author_rank: Super Contributor
timestamp: January 16, 2019, 10:17:44 am
content: is it possible to have continuous control rather then the on/off control? like fully analog

author: Rerouter
author_rank: Super Contributor
timestamp: January 16, 2019, 11:01:55 am
content: Cheap expansion valves are self regulating. Focus instead on varying the speed / power to the compressor if you want to regulate it, be aware most are rated at a certain duty cycle, you can drive them at the equivilent power duty cycle constantly, but dont try and run the name plate rating full tilt or you will cook it,As the pump compresses the gas it heats up much hotter than simply the electrical power fed in, same reason why the valve gets cold from the pressure dropping over it.You will have probably noticed with just about every fridge and aircon out there that they pump up and then they cool, there is pressure for the valve to drop, and the compressor can usually provide way more flowrate than the system needs, so the simplest control method is have the pump cycle every so often.

author: dmills
author_rank: Super Contributor
timestamp: January 16, 2019, 03:54:47 pm
content: Note that not all compressors do well with variable speed, some need to be running at pretty much full song to get the lubrication to work correctly.There are plenty of non obvious refrigerants, some of which have issues of their own:Propane for example works well as anyone who has had a high flow application from a too small tank can tell you, but leaks can be bad news.CO2 is workable, just got to keep the pressure high enough to get a liquid phase.Anhydrous ammonia, dangerous as hell, but it works....I am guessing that nitrous oxide would work (oxidation hazard however), being as it is physically similar to CO2 in most respects.However, water has a HUGE specific heat capacity, and unless you are running a **BIG** load for long periods, a big tank and passive cooling usually does well and has none of the annoying issues of lines freezing and similar nonsense that refrigerated plants can suffer from.

author: coppercone2
author_rank: Super Contributor
timestamp: January 16, 2019, 06:43:09 pm
content: LOL nitrous oxide. The movie Bad Sheep comes to mind.Why is this fucking spark moving so slowly man..............?Is there a compressor that does not have problems with lubrication at low duty cycles?Can you maybe cut oil grooves into it or modify the oil grooves with a chisel to change the lubrication properties?The main reason I wanted to do the custom heat exchanger is because I thought I can minimize the tank size. If you can some how match the thermal extraction of energy by water from the freon (using flow) then you can get away with the minimum tank size, which would be enough to fill the hoses, pump and DUT with a bit extra to spare. Then if you get a leak in the lab its maybe like 2 gallons tops? I imagine with a on/off compressor you would need a big thermal average.I know how to do this with peltiers but the problem is I would be too cheap to turn it on. If I was rich I would.Another idea might be to use a small water volume with LOTS of copper to act as a non fluid thermal averager. Given how ridiculous this already is, buying a few copper bricks might not be the worst idea. It might be the cheapest and most reliable option actually. Like build a tank around a jenga stack of copper sheets.Then you can add a high resolution mode where you turn on the peltier heat exchanger and interface that with some inline RTDs connected to the DUT (like voltage sense).I am just thinking now if you can use the compressor to cool the peltiers too in addition to cooling the process.The problem is though, you would still want a custom radiator, even if you gut a water chiller unit.Am I correct in thinking the model of this is basically a SCR-switched preregulator (the compressor is gonna have a really really crappy time constant compared to the peltiers) connected to a shunt regulator? What a weird electrical supply that would be (analogy wise).Then you can use those shady-mixed hydraulic/electrical connectors to just retrieve a RTD signal and provide flow on a nice manifold. (who would use this to actually carry power o_O). There is a mil-spec one that looks like a DSUB with coaxials but the coaxials are supposedly 0 leak plug connectors (yea ok maybe in a fucking clean room). But it would be harmless with a RTD and a 1/4 inch coolant line for small prototypes.If you do this put a little mesh under your manifold that goes to a drain tank so you don't get drips or leaks on your work table.I am saying this because 90% of thermal products look like they belong in the loading bay of the nostromo. And they are equally likely to house evil creatures.youtube.com/watch?v=NFiLVrux4V8 . Yea thats why you don't use evaporative cooling.

author: Yansi
author_rank: Super Contributor
timestamp: January 16, 2019, 07:14:02 pm
content: Quote from: amyk on January 16, 2019, 01:33:47 amVery good point! Those "air" dusters are typically filled with an R134A refrigerant. It is I think one of those requiring quite low head pressure in the system and can cool down to quite some temperature.That's because you couldn't fit very much compressed air in the can, and it would also require substantial pressure, which is dangerous. R134a or Butane can live in a can with a rather low pressure at room temp.Also, lighter gas (butane) or such can be used for a diy refrigeration system.

author: coppercone2
author_rank: Super Contributor
timestamp: January 16, 2019, 07:15:53 pm
content: oh yea man with duster, you can buy this thing at harbor fright which is like a penetrator for a can of duster so you can securely match it to your cars air compressor. It looks like something Henry the eighth would use on 'missing ladies'.edit: don;t know whats its called, I saw it on a youtube car mechanic channel before. It looks like a ring with a brass nozzle in it with a screw thread that connects to a hose, so you put the can inside of it and the thing works like one of those 'pipe clamps' that you are supposed to use in a emergency to stop a leak in your wall if you don't have access to a shutoff valve.wow wtf, I can't find any reference to it. It came in a crappy pack like old action figures in the 90's where you have a paper backpeel and a front plastic clam. It was like 5$.Ah here is one version of something similar

author: amyk
author_rank: Super Contributor
timestamp: January 17, 2019, 01:26:42 am
content: The phrase you're looking for is "side can tap".

author: David Hess
author_rank: Super Contributor
timestamp: January 18, 2019, 03:18:39 am
content: They make units for chilling an antifreeze solution which you then pump through whatever heat exchanger you want. Why not use one of those instead of trying to design an air conditioner from scratch?

author: coppercone2
author_rank: Super Contributor
timestamp: January 18, 2019, 03:43:09 pm
content: still probobly going to the be the size of a refrigerator and look like shit, + I was always interested in making oneI find it to be a very interesting design challenge as well. You get to test your skills in brazing, pipe bending, high tightness joints, etc.