Can you unconfuse me?

This is a big site. I’ve been through some discussions, but I still have confusion/questions. I really haven’t found what I am looking for. I joined this site because I am search of answers. You guys seem really nice and friendly. I like that. I hope you can lend some assistance.

To start, I am not a Refrigeration Engineer. I’m actually a sailboat owner. 6 years ago, I had a problem with my refrigerator on my boat. I pulled into a marina and the Service Manager suggested that I replace the unit with something entirely different. For a unit that had AT MOST 100 hours on it, I could not put my head around spending the money for another system. That started my quest to learn refrigeration.

I read as much as a could on the Internet, ordered boat refrigeration books, talked to specialists, etc. I now have a good understanding of the components and how a refrigeration system works. To make a long story short, I found the problem with the installation of the LO side connection. This resulted in corrosion on the connection that resulted in a pinhole in the evaporator bin. This has been fixed.

The problem that I have now is that I want to get away from the aluminum evaporator bin and convert to stainless holding plates. This has energy conservation benefits for my application. The problem that I am having is in the application of the products. For example, if I use a seawater condenser and an air-cooled condenser in series in the Bahamas, then move my boat to Canada, I may have to turn off the seawater condenser and possibly partially block the air cooled condenser (so I am told). Why does this make sense? If I move my boat to cooler climates, then why would I restrict the cooling capacity of my condensing units? I don’t get that. Wouldn’t it be more efficient?

If I think back to Gary’s tutorial, the best outcome is to have the condensing unit condense the vapor to liquid right at the output of the condenser. That makes sense to me. It seems most efficient. If I add in changing environmental conditions, then the saturation point changes. Right? I could be condensing at some point before or after or not fully condensing at all??

If my thinking about this is correct, then the question come down to what parameters can we control? Should I set a PID loop around the evaporator that regulates the temperature differential that increases and decreased the condensers to make the system most efficient for example? But condensing temperature is going to change with pressure right? So, the set points will change. Is that right?

I’m pretty much convinced that I will need to design and build and custom system to handle the varying conditions that a boat may go through. I just don’t know how to approach it. Any information (links) on how to approach this would be most appreciated. Please unconfuse me.

THANKS!
Mark

It seems you enjoy learning, so I am not going to give straight answers.
You understand the parts of the system but you do not yet understand the system (very common)
Always start at the beginning, what are you using the refrigeration process for? So it could be said that this is afixed variable or a constant. So what ever you do this constant needs to be maintained!
Draw out your system, let nature do what it does to the refrigeration cycle (variable water temp, air temp) and see what happens to the rest of the refrigeration "loop", can each every component handle the new set of differences.

http://myboatsgear.com/newsletter/200915.asp

looks interesting link for novice

http://ir.library.oregonstate.edu/xm...pdf?sequence=1

more good info but looks like water cooled is the best & simplest option all round.

Hi windseeker

Bahamas, must say first I am very green of your location, you lucky fella

There is a book I can highly recommend - its book number is

ISBN 0-13-027270-1 The Principles of Refrigeration (5th Edition)

It's not cheap - about 150usd - But commonly known as the refrigeration bible over here

this will give you the knowledge you need to understand your over-condensing problem in cooler climates

The system needs a minimum pressure differential in order to push the liquid through the metering device into the evaporator. In low temp ambients, the high side pressure can drop to the point where the evap is starved.

On an air cooled system, you would want to control the fan to raise the condensing pressure to maintain the minimum differential.

On a water cooled system, you would control the water flow with a water regulating valve.

Under extremely cold conditions, you may need to go to a flooded condenser system.

Quote:

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Originally Posted by chillerman2006

Hi windseeker

Bahamas, must say first I am very green of your location, you lucky fella

There is a book I can highly recommend - its book number is

ISBN 0-13-027270-1 The Principles of Refrigeration (5th Edition)

It's not cheap - about 150usd - But commonly known as the refrigeration bible over here

this will give you the knowledge you need to understand your over-condensing problem in cooler climates

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Or an even better option

http://prostores1.carrierzone.com/se...com/StoreFront

cant u fit a condenser fas speed controller to maintain ur head pressure in low ambient conditions

You can add a condenser fan speed control but they are expensive. A condenser fan cycle control would work.
There is also a device called a head master that is a 3 way valve that bypasses the air cooled condenser at a set ambient outside air temp.

I want to thank all of you for your input. I will read/look into all of these one by one. Right now, I'm working through Post #4. Even though I am not freezing fish, the paper is really interesting. It even inspired an idea about regulating compressor speed with falling Low pressure. There are some devices out there that kinda do this, but they are all open loop. If I can do it closed loop without sacrificing energy efficency, then it could be worth it. I'll keep you posted. Thanks again! You guys are great!

I ended up ordering the book Chillerman recommended (ISBN 0-13-027270-1). Though, I'm sure the other books are fantastic, I'm hoping that this one will answer my questions. One day . . . if this becomes a career vs. an obsession, I will get them. This link here provided by Ranger1 is exactly my system.

http://myboatsgear.com/mbg/product.asp?prodID=1618

I am in the process of re-installing this unit with the fixed evaporator leak. When I took it out, the coils we neatly wrapped, tie-wrapped and screwed to the bulkhead. Re-installed, they do not lie in the exact position.

Quick Question: I have some conflicting information. The return line is 1/4" and the pressure line is 5/16" Do I need to insulate the return line? I've also read the that the HI and LO lines need to be close together. For now, I have tie wrapped them together. Is this correct?



BTW Chillerman, I'm not in the Bahamas yet. It's a goal and a dream. :) !!! That's one of the reasons why I'm doing all this. I would sell myself short in saying that is the only place. I would like to go much further. Brazil?

Quote:

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Originally Posted by Windseeker

Quick Question: I have some conflicting information. The return line is 1/4" and the pressure line is 5/16" Do I need to insulate the return line? I've also read the that the HI and LO lines need to be close together. For now, I have tie wrapped them together. Is this correct?

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Return line, Yes

Hard question for me ! (two lines together)

This can have benefits & downsides

If it was originally designed like this I would say yes

If the lines are insulated together, it will do two things it will lower the discharge temp & assist cooling the refrigerant to a liquid (help with condensing higher climates) but it will also increase the suction superheat at the compressor inlet.

If the evaporator is set up without the lines touching, you have a certain amount of cooling for the compressor, heat from the discharge pipe will be transfered to the suction pipe if they are together, using up the cooling meant for the compressor. Shortening its life.

I think it would be a good idea to have the pipes running together in one insulation, transfering heat from the discharge pipe, its just you need to set up the expansion valve to compensate for this if its not how it was originally designed/setup

ps. dont try & absorb that book all at once, it is full of info some very technical but from your original post, I think it will be a very good purchase, it has the basics right through to all the industry formula's, pictures, diagrams & graphs, hope you enjoy it

chillerman, ask him what brazing rods he's using!

Quote:

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Originally Posted by install monkey

chillerman, ask him what brazing rods he's using!

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None hopefully !!!

I've heard thats a very fine art sweating rubber...

I did not even notice that, obviously, just thought as usual copper tube, der

your too quick for me mate

So that blows that idea out the water then :D

if you fancy some fresh fluff, check your email,

its real fun, am off there in 5