Marine Refrigeration Question

[Guest]

Hi all

 

I have recently replaced the engine in my boat and now I am faced with the task of remounting the freezer compressor and plumbing up the condenser.

 

On the old engine, the raw water ran through the condenser before cooling the engine.

 

The new motor needed more water to cool it (1 inch pipe) so upgraded the skin fittings etc...

 

The problem I now have is the existing condensers diameter is too small to connect to the engine cooling system.

 

Do I

 

1) Upgrade the condenser to a larger one (Quoted $1700.00 just for the condenser)

 

2) Hook up a small electric pump and cool separately (Might need to upgrade the alternator for this one?)

 

Or do you have any other suggestions? Go electric?

 

As it stands now I have not started mounting the compressor so anything goes. I am looking at at least $2000 to get this freezer going

[Atom Ant 0]

What about an electric freezer? You may need a bigger alternator depending on what you already have or maybe a smart charger like a Next Step would do the job depending on alternator output. But then you would have to consider battery capacity. Having gone through it all I went electric and simply upgraded by alternator, charging system, and batteries. May not be the best for you but it worked well for me.

[grant 40]

could you insert a junction off your new hose to run to the condenser?

[banaari 27]

So problem is: The original configuration was that the engine's ENTIRE raw water supply ran through the condensor first.

But now the condensor would, if plumbed inline as before, constrict the intake and prevent the engine cooling properly.

 

Could you: Plumb the condensor in PARALLEL with a bypass pipe?

i.e. some of the raw water intake comes via the condensor and some via the bypass.

[too_tall 15]

In the setup we have, which is a 1 hp DC guneret system dating back to the 80's, there is a separate pump which feeds the condenser with salt water. Totally independent to the engine. As I put in an 80 amp smart charger, it means that we can run the compressor without running the motor when at the marina, and indeed, we generally run it for not more than 20 minutes twice a day, so we often do one of those runs without running the motor as we have significant battery capacity.

 

So to get back on topic, there is a smallish Jabsco diaphragm pump installed. It has its own through hull - something I would rather was tee'd off another through hull, but it is how it is at the moment. Uses about 4 amps - nothing if your running a engine driven compressor. There is no significant pressure requirement and I think it requires 7 litres per minute - and that is enough for a 1hp compressor - much larger than your average domestic freezer has in it.

[Kestrahl 6]

I can recommend the Isotherm electric units, they are pretty easy to retro-fit to an existing freezer box and come all pre-gased etc

[Guest]

So problem is: The original configuration was that the engine's ENTIRE raw water supply ran through the condensor first.

But now the condensor would, if plumbed inline as before, constrict the intake and prevent the engine cooling properly.

 

Could you: Plumb the condensor in PARALLEL with a bypass pipe?

i.e. some of the raw water intake comes via the condensor and some via the bypass.

 

Yes that's correct. That sounds like a good idea but how would it work? Would it overload the water pump?

[Guest]

I can recommend the Isotherm electric units, they are pretty easy to retro-fit to an existing freezer box and come all pre-gased etc

 

Thanks mate I will look into that as an option

[Guest]

I think given the feedback the best option is to run the compressor off the engine and a separate electric water pump for the condenser. I think it only needs 7l per minute so a smallish pump will do the trick

[Grinna 2]

I've got a brand new Flojet premium quad series 12v electric pump for sale on trademe at the moment. It's suitable as a shower drain pump and can cope with running dry. Flow rate is 3.3 gal/min or 12.5 L/min. They retail for $315 but you can have it for $200 if you're keen.

[mattm 98]

Don't do it!!! I work as a marine sparky, as well as doing marine refrigeration. Engine drives are no longer the way to go. They leak gas by design, are expensive to maintain and older systems can fail often, I could go on but I won't. Just don't do it. Get an isotherm dc system. The biggest aircooled kit, which will run a massive freezer retails for $1495, will run for 10 years, are totally sealed systems and use around 5a when running ( half the time if speced correctly). You can leave them on when the boats at the dock if you have shore power and a charger, so it's cold when you get to the boat, you can run it while racing so the beers cold after the race, they have a thermostat, so temp is accuratly controlled so you don't give the mrs food poisoning on your summer cruise. They dont pre heat you engine water causing a higher running temp, you can clear out the old pipe work and not clutter the engine with the compressor etc. you can turn the thermostat up or down and have a fridge or freezer as required, again, I could go on. We typically spec 220ah of batteries minimum (two 6v 220ah batteries are best if they fit). If you have a new motor, it will likely have about a 120a alternator which is plenty. Install by someone who knows hat they are doing is usually around 4 hours depending on your boat. The cost of the kit may be less depending on the size of your freezer. Cheers. Ps, don't do the engine drive

[erice 732]

good review of an isotherm system here

 

http://www.ventspleen.com/?p=646

[Guest]

good review of an isotherm system here

 

http://www.ventspleen.com/?p=646

 

Thanks for the post Eric. I like the look of this system so will crunch some numbers

[Atom Ant 0]

This is basically what I was saying earlier on. All you need to do is have enough power generation to cover the electrical requirements to run it, and all your other electrical needs. I have a 50 litre isotherm portable fridge freezer. It's like an big chilly bin only it has a sealed danfos unit in it and can run on 12/24/240 volts. I fill it up at home and run it on 240 volts to get it down to temp, then on the day of use, I unplug it, take it to the boat, put it in place, plug it in, and away it goes. Its consumption over 24 hrs is around 1 amp as it runs approx 20 minutes in the hour.

 

A built in one is more or less the same unit and the same rules apply. There are various models and so you could build in a 12/240 volt model if you want.

 

A compressor system is just big bucks waiting to be spent.

[Guest]

It's a shame because I was told its a $17,000 custom made ocean air freezer unit.

 

My main concern is I have no idea if, when I put it all back together again it will work ok. I'm guessing it has not been run for a long time...

 

The compressor has tested ok and it made a small hissing sound when I removed its so that means the pipes are still ok

 

The electric system sounds like the way to go but it seems a real shame throwing away allot of what is already in place...

 

I would like to run the compressor off the engine because that means I don't have to upgrade the alternator / batteries / charging system.

 

Bloody freezers!!!

[Island Time 1,235]

Personally, I don't entirely agree with throwing out the engine driven compressor. Yes, they loose gas over time, depending on the type of compressor. BUT, they are FAR more powerful than any electric unit, (several HP) and will pull down your freezer way faster.

 

I'm not sold on the isotherm units. They can draw a lot, and air cooling is not very efficient.

 

On I.T. I have an ozefridge, as well as an engine driven compressor. They are completely seperate systems, so we have a failsafe. The engine compressor brings the cabinet down, and the electric unit keeps it there. The OZEFRIDGE has water cooling, but unlike other keel cooled systems, it uses fresh water from the tank, and returns it a little warmer. This unit draws 4.5 amps, and was running about 30% of the time on the equator, keeping the freezer at -16 to -21c for the icecream! It was really fantastic.

 

A friends boat was with us. He has dual Isotherm units, one fridge, one freezer. Total draw is 13 amps! He switched it off and did not use it. Ours has been on since installlation 3 years ago...

[mattm 98]

You are right, the engine drives are faster at pulling a warm box down, but the dc system can run all the time, it dosnt need to be fast because it's job is 90% done when it turns back on- the box is already cold as the unit turns on and off as required, not as you run the engine. If you go racing weekly, you run the motor for 10 or 15 minutes on the way out, not enough too cool your beer, if you have dc, its running at the dock when you get there and the beer is already cold . If you are a cruiser, the box stays a constant temp during your entire voyage, rather than being too cold on days you use the motor a lot and too warm other days. 13 amps is much more current than two modern isotherm units need. Your friend has something wrong. We constantly remove engine drives and fit dc systems, maybe 30 in the last few years, everyone is happy. A few are apprehensive at first and keep the engine drive also, only to remove it after a year or so as they never use it.

Also Royale, if the system only made a small hiss there is probably a leak. If you opened up a fully charged system and dumped it (illegal) it would blast gas out for 5 to 10 minutes, staying liquid/ gas refrigerant and oil all over the place. Also, if the system has been open you will need a new sight glass and dryer, as well as a nitrogen pressure test and flush, a long vacuum, it also never hurts to acid wash the heat exchanger while the system is empty. All engine drive systems are custom made, regardless of the cost, don't throw away good money after bad.

[Steve Pope 243]

What would be the recommended size of solar panels required to cope with the load from a battery driven fridge / freezer??

[Island Time 1,235]

mine used to work fine with 2 36watt flexible panels. That was about the same power as the fridge required - maybe a little less, but not much. It will depend on the installation, - efficiency of the freezer unit and the box, including insulation.

 

My unit cools a well insulated freezer of 295 ltrs, and thru a common tank (engine driven, not always used) also the freezer (also 295ltrs - yes it is big!). it draws 4.5 amps when running, and runs about 1/4 of the time here in Auck at this time of year. It is water cooled, so is more efficent, and uses a be80 compressor, which is also more efficent than the danfoss ones that are common.

 

For safety's sake i'd work on a 50% duty cycle (on 50% of the time - ONCE COLD). If you switch on the electric unit when ariving at the boat, and then put in unfrozen food, it can take several days to freeze it all.

 

Unfortuantely now my solar panels are old, and only produce about 1/2 what they used to....

[Guest]

You are right, the engine drives are faster at pulling a warm box down, but the dc system can run all the time, it dosnt need to be fast because it's job is 90% done when it turns back on- the box is already cold as the unit turns on and off as required, not as you run the engine. If you go racing weekly, you run the motor for 10 or 15 minutes on the way out, not enough too cool your beer, if you have dc, its running at the dock when you get there and the beer is already cold . If you are a cruiser, the box stays a constant temp during your entire voyage, rather than being too cold on days you use the motor a lot and too warm other days. 13 amps is much more current than two modern isotherm units need. Your friend has something wrong. We constantly remove engine drives and fit dc systems, maybe 30 in the last few years, everyone is happy. A few are apprehensive at first and keep the engine drive also, only to remove it after a year or so as they never use it.

Also Royale, if the system only made a small hiss there is probably a leak. If you opened up a fully charged system and dumped it (illegal) it would blast gas out for 5 to 10 minutes, staying liquid/ gas refrigerant and oil all over the place. Also, if the system has been open you will need a new sight glass and dryer, as well as a nitrogen pressure test and flush, a long vacuum, it also never hurts to acid wash the heat exchanger while the system is empty. All engine drive systems are custom made, regardless of the cost, don't throw away good money after bad.

 

 

Right, you have now convinced me that electric is the way to go

 

No point spending $$$$ mounting compressor, plumbing condencer, gasing a system I am not even sure works!!!

 

Next question if I may. Where is the best place to get this DC system from? I have about a 65L freezer box and I'm keen to keep it as a freezer if possible