Fixing up some old marine refrigeration

[old_salty]

Hi all,

I'm new to this forum, and I hope to solve a problem.
I have read this thread (http://www.cruisersforum.com/forums/...de-135996.html), and the advice was fantastic, but I didn't want to hijack the thread, so here is a new one.

My wife and I own an old weekend type boat that had some custom made engine driven refrigeration aboard built by a company that no longer exists. It was gassed with R404A which has leaked out quite a while ago. I decided to pull the system to determine why the gas leaked and after quite a few swear words, I had the system removed and noticed several flares were not much past hand tight. There was probably the reason right away. I wasn't upset because I wanted to modernize the system anyway and perhaps convert it to R134A which is a lot cheaper here in Australia than 404.

I am not a licensed fridgie, but in my previous life, I was dealing in high pressure air and silver soldering pipework to handle 5000psi, so refrigeration pressures don't really phase me. I understand the fundamentals of refrigeration design, and, as far as I know, here in Australia, it's not illegal for me to work on a de-gassed system, and I only need a licensed person to re-gas (with the R134A).

Piping was generally 1/4" and 3/8". The cooling plates (1 fridge and 2 freezer) were eutechtic design. The plates all appear in good order. I intend to clean and flush them, and then pressure test to make sure everything is OK. Fridge size is 90 liter and freezer about 50 liter.

What I'd like to do is rebuild the system and use the existing Sanden compressor (SD7H13) and use it when the engine is running, and a 12V solar driven compressor for the rest of the time that the boat is idle, so that when we come aboard, we have a cooling "head start".

My first questions are, can I install 2 parallel compressors (engine driven and obviously large capacity) and electric (eg Danfoss BD50 - low capacity), and, do I need isolation valves?

I have sourced new Danfoss TX valves suitable for 134A,electronic thermostats, new dryer, receiver and accumulator.

Here is an image of the system


Thanks

[a64pilot]

I'm sure it can be done as my home AC units have two compressors each, small one for efficiency.

I do not know how to tell you to do it though, or if it's worth all the expense etc.

[SV THIRD DAY]

The more common way is to have independent 12v and engine driven system refrigerant loops either inside the same holding plate or in separate plates. Technautics has been building these type of engine driven/12v (or 120v AC) dual systems since....**** longer than I've been alive and In my opinion you will be asking for trouble trying to isolate off the engine driven and then BD50 compressor running on the same refrigeration loop.

If I had your boat and system, I would recycle the holding plates outfitted with new R134a TXVs and then install a dedicated 12v compressor on each fridge and freezer system and toss the engine driven system all together. Mixing the two on a common refrigerant loop playing with isolation valves is something abandoned by most manufactures long ago....for a reason.....trouble.

[old_salty]

Thanks Rich,
I was hoping that my post would attract your attention, and, thanks for the reply.
Firstly, being an older "salty", costs are an issue and I only have 65W solar capacity and 300AH of batteries. This really is a labor of love and a project to keep my mind and hands active above all.

Correct me please if I am wrong.

I assume that you only need to isolate (separate) the discharge lines between the engine driven Sanden and a BD50. This could be achieved easily with a 12V solenoid and a relay. After refurbishing the old system, the suction line accumulator would prevent slugging the BD50 (and the Sanden), and the receiver would buffer the system from over-charging. The receiver is about a liter (? pints), but the literature says BD-50 has a maximum refrigerant charge of 300 grams (or close I think).

Would the BD-50 handle the larger charge of refrigerant?

Thanks

[SV THIRD DAY]

300grams is 10.4Oz of refrigerant.
When we make a CoolBlue system using a BD50 (or BD35, or the Cubigel equivalent) a full charge is 24Oz based on the overall system design. So if you are using a dryer/receiver down stream of the compressor outlet for the refrigerant to be stored until called on by the TXV, then you can safety ignore the max refrigerant charge literature on the BD50. How will you KNOW your amount of correct charge for the system you are building? Well you could do some math...or just install a sight glass and let your eyes tell you when your charge is right or wrong.

Remember...they are giving the Max refrigerant volume for a different animal of a "critical charge system" with a critical fixed orifice where the balance of internal refrigerant loop volume and charge needs to be "just right", as Goldy Lox says, for good performance.

If you have the skills and access to a vacuum pump there is no reason you can't pull this project off and end up saving some valuable cruising kitty dollars in the process. I'm sure I'll be attacked by the usual chat room suspects, but hey...that's part of the fun of giving advice online...ha ha ha....what do I know, I just do this for a living anyway... I'm happy to help, so just ping me if you need any help/advice. Rich@cruiserowater.com

[old_salty]

As we say here in Australia... "You're a good man!". Thanks. I'd just like to point out to any knockers that I am not doing anything illegal. The refrigeration industry in Australia is locked down tighter than the crown jewels. It's impossible to get your hands on any refrigerant (including R134A) unless you are licensed.

Having said that, it's not illegal to build, re-plumb, design or rebuild anything to do with refrigeration AS LONG AS you get the gassing done by a licensed person who checks the system.

OK, over and out with the disclaimers.

Rich, the old system has a perfectly good cupro-nickel salt water condenser unit. In your opinion, is that worth re-using?

[SV THIRD DAY]

I'm a fan of air cooling for the smaller BD50 type systems....but for the engine driven system it just makes sense to use water cooling since you have water already pumping through engine. Since you are looking at a hybred engine/12v system it would seem pretty nutty to add in an air cooling loop when you already have a good water cooling loop in place. So I would give up a little power to run a sea water pump when the 12v unit is running and keep the simplicity of an entirely water cooled system.

[old_salty]

A quick question on changing from 404A to 134A.

The Sanden specs for oil say "SP-10 or Equiv" (which, from my research is a PAG-46 oil) and the Danfoss requires Polyolester oil. I think these oils are incompatible when mixed. Would this be a reason to run separate systems?

Have you also heard of the new PAOil which is non-hygroscopic?

[a64pilot]

Stupid question, why go hybrid? Is it t save the battery by using the engine to drive the compressor when it is running? If so, then that isn't logical as you have all the free power you could want from the engine alternator when the engine is running.
Your going to have to have an electric compressor anyway so your not saving money, in fact I think by going hybrid your adding cost and there is no benefit, a hybrid system is more complex and has more parts to break.
I hate to say Rube Goldburg, but unless there is something I'm missing?

[old_salty]

Hi,
Thanks for your reply. Please correct me if I'm wrong here, but the Sanden compressor is about 120cc and the Danfoss is about 3cc. Am I right in assuming that the Sanden will cool much much quicker?

I guess that I should say more about my requirements. It's not for cruising, but for long weekend use (3-4 days) where I want maximum cooling capacity for fishing and storage of food for the 3 days. The engine(s) are running for 8 hours a day (leaving 16 hours for the BD). I want the engine driven compressor to provide the grunt for the initial cool down in this situation. Apart from that, on lazy days, it would just be nice to keep the milk and beer (not necessarily in that order ) cold. Back on shore for 4 days, I'd like the system to hold some residual cold. If we don't go out for a few weeks, and, I'm down on the boat doing repairs, it would be just nice to have some cold storage.

Rube Goldburg... maybe. But I still want to do it

[a64pilot]

If your not keeping it cold all the time and allow it to reach ambient temp between weekends, then I can see the need of doing an oversized cooling system, but if your running the engines for 8 hours each day, may not need the electric half.
I am HVAC licensed, but not real experienced, in my limited experience I believe you will be far happier with independent systems if you need both engine and electric.
I believe however that since money seems to be a consideration, that if it's available a chunk of dry ice and rejuvenating your engine driven system will be far less expensive. A few kilos of dry ice will provide and astonishing amount of cooling and if slightly insulated will last longer than you may think, I used to wrap it in news paper and it would last a three day weekend and keep anything frozen in a regular cooler.

Now if the lure of just doing something neat is drawing you, by all means, but I would go with independent systems, plus that way you gain redundancy

[old_salty]

Food for thought. Thanks. Yeah, it IS about doing something neat. It keeps the brain going though...

If I went for independent systems, I'd like to rebuild the eutectic plates to be dual. I have access to a Stainless TIG workshop. Any design ideas with regard to pipe length etc

[Richard Kollmann]

Old salty, My recommendation would be to re commission present engine driven system and run engine one hour the first day and less each day there after as long as plates are frozen.
If holding plates are small less than one gallon of solution per cubic ft of freezer and ½ gallon per cu ft of refrigerator section compressor may need to run engine ½ hour twice a day.

Use a Refrigerant flush liquid to clean out all old oil from all components. Then seal all openings to keep moist air out.

Seawater condensers designs vary from different manufactures and are the only component that is be life limited do to electrolysis. I recommend a 24 pressure test with 200 psi of dry nitrogen.

Replace filter dryer and receiver if it is an automobile type filter/dryer and receiver.

New Danfoss TE expansion valve with a number one orifice would be my choice along with an engine drive pulley size that prevents compressor from ever exceeding 1600rpm at full engine max cruise. I would also install a low pressure switch.

I would install a permanent refrigerant pressure gauge for future monitoring as it will eliminate need for a licensed service engineer later.

Ester ISO 100 POE conversion oil is my choice for 134a refrigerant.

You can leak test system with 200 psi of dry nitrogen after all connections are secure. I prefer a 48 hour leak test.

Without knowing size of boxes or worst case heat degree days where you plan on cruising or whether boat is connected to shore power when not sailing I can not see any advantage to installing a Danfoss BD50 system. Your boats DC power grid is too small to support refrigeration and a freezer, As far as solar the question again is your boxes daily heat load need to be calculated first.
There are reasons why a hybrid dual compressor common refrigerant system is a bad idea the most important reason oil traveling with refrigerant will not always return to the correct compressor.
When boat with engine driven refrigeration is connected to shore power no one wants to run the engine one hour a day. I and others manufactures built plates with dual evaporator coils inside. Back then I would offer the second coil in each plate for $35 and suggest to owner the day will come when he may want to add the second 110 volt or 12 volt condensing unit.
If you can justify a second compressor condensing unit for shore power use there is a way. In several boats we placed a copper coil behind plate and coil pressure against plate maintained low box temperatures. This temperature did not freeze much eutectic solution but held plate near freezing point.

[Suijin]

Originally Posted by SV THIRD DAY

I'm a fan of air cooling for the smaller BD50 type systems....

Rich, why is that? I'm curious because I've been contemplating converting mine to a keel cooler, which I just assumed was more efficient. Can you elaborate?

[old_salty]

Hi Richard

Wow, that's about the most comprehensive answer that I could have expected!
If you or Rich Boren are ever in Sydney (Australia), I'll buy you both a cold beer.