MK1 Fridge

[lustyd]

Started a little project over xmas. Step one was learning to solder pipes, but here is step two, the mk1 fridge. Yes, it's missing a few bits and bobs, but it is holding vacuum. Next step will be adding cap tube and checking that vacuum can be maintained before moving on to building an evaporator. With the exception of the compressor and electronics I'm hoping to build out the whole thing. Not because I need a fridge, it just seemed like a fun project!

 

[[194224]]

I can see why it would be a fun project. Yes you can buy one saving time and money perhaps but whatever you learn while doing things like that can have long lasting value that you can't reduce to Pounds and hours. Good for you.

 

[vyv_cox]

Not sure about soldering. My son builds and modifies fridges as part of his business. All his pipework joints are brazed. You probably need oxy-propane, although I think a good propane torch might do it.

 

[lustyd]

Braze vs solder doesn't seem important for the pipework from what I can tell. The cap tubes seem to get brazed mostly but seem to also be people soldering those. Brazing is certainly on my list though.

 

[superheat6k]

Plumbing solder is simply not suitable for a fridge system intended to last. That said silver solder for most joints is an overkill. MAPP gas with a Rothenberger Copper alloy solder rod is our norm, and MAPP is hot enough for the tiny pipework you are using. It must be pre-cleaned and the Rothenberger rods will take without additional flux.

I also note you have created a pipe loop - a working evaporator requires an inlet and an outlet at either end of the evaporator.

What vacuum are you achieving and how are you achieving it ?

Professionally we look for < 3 torr (3mm of a mercury (Hg) column where 1 atmosphere is 760 mm / Hg), this requires a decent vacuum pump, and the tiny vac scale on the standard fridge manifold in your photo only shows a very coarse 30" vacuum scale (i.e. 760 torr over ~ 5mm of gauge deflection). We never rely on this for a proper evacuation, only a Torr / MM HG / Millibar gauge. (1 Torr = 1.33 Millibar). Electronic ones only show a readable level < 12 Torr.

The reason we need such a low vacuum (NB this is high by freeze drying standards) is to achieve a contaminant free and dry pipe system, and this also requires the local ambient above 10oC, or entrained moisture might not flash off. Leave any moisture contaminants in the system at your peril.

May I ask how are you going to purchase and charge the refrigerant and what are you thinking of using ?



NB this is a typical evaporator (on the left) and couple of compressors (on the right) we work with on a daily basis (330 kW unit) ...




And the same unit finished ...

 

[lustyd]

I am certainly not a pro. The vac pump is a 1 stage so also not pro and not capable of tight levels of vacuum. It's not intended to last, but from everything I've seen I would disagree, brazing vs soldering is a choice of which part you want to fail, not whether it will fail. Soft copper on a boat connected to a hard joint is probably worse than hard copper and a softer joint. It also seems that some connections can''t take the heat anywayso soldering is necessary. Realistically, if the pipes can hold the vacuum it makes no real difference to the project. I'm not building a real fridge, I'm building the skills to fix a fridge in an anchorage on a boat with minimal stuff.

The above may be entirely wrong, part of my reason for posting is feedback from people like you so I will gladly read further comments.

 

[lustyd]

Rothenberger rods

you mean rolot S2? I'm trying to work out which ones to buy for learning. There are a lot of options! This is leading me towards an f-gas course so eventually I will learn properly but for now I have zero skills so the course cost isn't worth it, especially since I have a completely unrelated career!

 

[Daverw]

lead solder will slowly give, brazing just as easy with copper tech rod and turbo torch, it has flux in the rod, just clean copper and heat. To get some just call at your local climate centre

 

[lustyd]

Brazing may be just as easy but I don’t carry nitrogen around on the boat. Why would lead free solder slowly give? Seems just as likely that annealed copper would split on a boat

 

[Daverw]

Not sure why you want nitrogen for brazing as you only need the turbo touch which uses Mapp gas to get a higher temp, lead will creep at the higher pressures of what could be 20 Bar on the high side. Fridge copper is not the same as plumbing copper as it needs to cope with higher pressures. Some of our systems are designed for over 100 Bar and tested at 132 Bar, you should hear the creeks and groins during those tests.

even though your just starting to play with this, don’t forget you are working with what is classed as a pressure system and the basics are best learned first correctl.

 

[dankilb]

Lots of uses for MAPP on the boat too (un-seizing things etc.).

 

[lustyd]

Not sure why you want nitrogen for brazing as you only need the turbo touch which uses Mapp gas to get a higher temp, lead will creep at the higher pressures of what could be 20 Bar on the high side. Fridge copper is not the same as plumbing copper as it needs to cope with higher pressures. Some of our systems are designed for over 100 Bar and tested at 132 Bar, you should hear the creeks and groins during those tests.

even though your just starting to play with this, don’t forget you are working with what is classed as a pressure system and the basics are best learned first correctl.

Nitrogen is needed if brazing to avoid soot on the inside which will cause issues for the filter or cap tube. This much seems pretty obvious and is demonstrated nicely all over the web.

I never mentioned lead but I assume you're referring to any solder process. This seems to be in dispute and lots of differing opinions on the subject even from professionals. I see no reason the relatively low pressures of a refrigeration system would cause a problem for a good soldered joint. From what I can tell the use of brazing is rooted in not needing to clean and use flux rather than for any strength reason. I agree that if you're at 100bar it may be different, but a boat fridge isn't at 100 bar, or even 10 bar from what I can see.

It seems an F-gas course is now the only route to getting hold of gas, so I'll likely have to do it at some point to finish the project. Once I work out what brazing rods to buy I will have a go and just ignore the soot etc. for now.

 

[Daverw]

Back purging not really an issue unless large bore, never bother on small stuff as braze takes seconds. Yes was referring to lead solder. For your info I’m a refrigeration engineer for over 30 years so done thousands of joints. Not sure why you think your high side will be so low, being a boat makes no difference as it’s about ambient temp.

just also comment that the system design is more about pressure drops, compression ratios and superheat/ heat transfer, pipe sizes are critical within this as well as refrigerant spec. You have to factor in gas velocities and oil return.
But good luck with your project.

 

[lustyd]

Not sure why you think your high side will be so low

A quick bit of Google. As a professional, what pressure in barg do you think the average r134a yacht fridge uses on the high side? I do understand that various factors come into play, but yacht fridges are extremely standard at this point so a lot of that is largely irrelevant. Please do post any relevant info/links here, it's very useful to have information from a professional.

 

[Daverw]

Not googled but actually measured a couple of systems last year, in summer and air cooled ranged from 15 Bar to 18 Bar, very dependant on size of condenser, air flow and location, R134a is now very difficult to get hold of and try not to look at the price. You are correct that most yacht fridges are simple and use mostly two sizes of compressor so duty’s are basically the same.
I would suggest for you to play and get of an old domestic fridge and use the evaporator out of this, it will be far better that you can make, condenser is easy especially if you want to try and make a water cooled one. Also look at the theory of superheat and sub cooling as these are the fundamentals.
if you want I have a good book somewhere that you can have for the cost of posting which will tell you far more than google

 

[Stingo]

if you want I have a good book somewhere that you can have for the cost of posting which will tell you far more than google

What is that name of this book, please? An ISBN will help. I´m in Portugal, which complicates buying & shipping from the UK, so that is not an option.

 

[Daverw]

Principles of Refrigeration, by Roy Dossat, ISBN 0-13-717687-2

not sure if it’s in print anymore as mine is dated 1991
this was the bible at the time

 

[penfold]

I think I will get a copy too.

 

[Stingo]

Principles of Refrigeration, by Roy Dossat, ISBN 0-13-717687-2

not sure if it’s in print anymore as mine is dated 1991
this was the bible at the time

Thank you. Amazon, Spain might be my friend.

 

[lustyd]

Thanks, I'll hopefully be moving on to more of the theory at some point. Being in a less practical career (let's call it computers) my plan is to learn some of the physical skills first, then some theory and eventually probably do the f-gas 1 course. As you say, the gas is hard to get these days without it, although somehow Halfords still seem to be selling cans of the old stuff and I can't work out how they are an exception to the law. What's worrying for yachtsmen is that every country seem to have their own certificate so if I get it in the UK I'd then need an EU one and US one if the trip were long enough. And all to save money and be able to DIY fix the fridge It is fun though, so I think worth it.