Refridgeration Question

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ashskett

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Hey all, I am new here but I hope that somone can help me with a refridgeration issue. I have just taken over a 47ft Lagoon Catamaran and have set about fixing and changing many things to satisfy the owners requests. One issue we have is the on board freezer. We currently have a seawater cooled Megafrost unit installed. It is a 230V system that comes with a dedicated inverter so it can be powered by the service batteries.

The problem we have is that this system drains the batteries far too quickly, it has a very large draw. The solution I have suggested is to replace it with a WEACO Coldmachine 94 12V air-cooled compressor. My question is this: Currently we have a large hold-over plate installed inside the freezer box, can we keep this installed for use with the WEACO 94 or do we need to change the plates?

Hope someone can help! Thanks....
 
It would sound like the previous owner had the freezer set up to run when charging batteries or connected to shore power, hence the large holding plate and inverter arrangement. The seawater cooling will keep the waste heat generated by the fridge out of the boat and as Vyv has said is more efficient than air cooling. Running a freezer is a power hungry past time and while I agree there is some inefficiency in the inverter the rest of the set up seems sensible. You need to consider how the boat will operate, and where, to understand how power will be generated or imported so you can set up a charging routine that allows the freezer to be run efficiently. I would suggest that if the boat is going to be mainly self sufficient on 12v batteries and charging arrangements you should just change to a 12v water cooled unit but retain the holding plate. You should be aware however that the holding plate will initially take more power to bring down to temperature and ideally you would run the freezer when a charging source is operating (engine or generator). I would also suggest you need to consider your total power consumption against the service battery size. Hope that helps.

Yoda
 
A 47ft Lagoon was never intended to be a frugal user of power. It is quite large for a cat and most of the one's I've seen in Greece don't try to run things like deep freezers from the batteries but from a plumbed-in generator which is running most of the time. It is also more likely than not that such a vessel would also have air-con in at least two cabins. There is, after all, plenty of space for a genset. Make sure you get one with a water seperator in the exhaust so that we can ALL get some sleep! £3500 to £5000 should get a suitable installation but expect to pay up to £8000 for one that will run air-con too

Chas
 
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Thirty years ago I worked for a chilled food company and came to work one Monday morning. As I drove past the distribution yard to get to the staff car park I noticed all the huge trunker artics had been repainted over the weekend with the new company livery and logo.

Across the sides and tailgate of all the trailers it said "Company Name Refridgerated Transport" in huge letters.

To get to my office I had to walk past the Distribution Manager's office. As I walked past he asked proudly "Do you like the new livery". I answered, "It's lovely, except that someone has mis-spelt refrigerated"

He looked out of his window, shouted something I can't repeat, and shot past me saying "That's ten thousand effing quid down the pan!"

Not having a go at the OP - it just brought back a lovely memory from a long time ago. ;)

Richard
 
Regfrigeration

I would strongly suggest that you look at the dedicated inverter set up. If you can measure the AC current drawn by the compressor both on mains 240vac and on the inverter. Then measure current drawn by the inverter when supplying the compressor, you might find there are huge losses in the inverter. Or more specifically the freezer running on the inverter. You would expect better than 80% power efficiency from the inverter and no more AC current on inverter as on 240VAC mains.
It is my guess that the inverter may be a modified square wave type when Induction motors as used in domestic refrigerators must be fed with true sine wave inverter.
What happens roughly is that all the power in the AC components that are not true 50 hertz are wasted heating the motor. So a purchase of a true sine wave inverter of appropriate power (be careful of start up current) may reduce DC consumption dramatically.
Perhaps you could borrow a true sine wave inverter to try out and compare.
While an inverter to domestic freezer compressor will be inefficient I would think that its advantages being water cooled may make it more efficient on current draw at 12v than the proposed replacement.
In any case if the existing freezer is working oK on 240vAC just add the proposed 12v freezer to the box along side the existing system. good luck olewill
PS a simple check of the inverter apart from its label is to try to run a household fan on the inverter. Compare its speed and operation to 240VAC mains. If it seems queer on the inverter you will have similar problems with the freezer.
 
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ashskett said:
Hey all, I am new here but I hope that somone can help me with a refridgeration issue. I have just taken over a 47ft Lagoon Catamaran and have set about fixing and changing many things to satisfy the owners requests. One issue we have is the on board freezer. We currently have a seawater cooled Megafrost unit installed. It is a 230V system that comes with a dedicated inverter so it can be powered by the service batteries.

The problem we have is that this system drains the batteries far too quickly, it has a very large draw. The solution I have suggested is to replace it with a WEACO Coldmachine 94 12V air-cooled compressor. My question is this: Currently we have a large hold-over plate installed inside the freezer box, can we keep this installed for use with the WEACO 94 or do we need to change the plates?

Hope someone can help! Thanks....
Click to expand...

I wouldnt change just the compressor and not change the evaporator plates if the current system is quite old you may find the refrigerants used in the old system are not compatible with the new stuff which is now more ecologically safe.

If you are changing the system any way take a look at the water cooled version of the cold machine, water is a better system in hotter climates for several reasons, the air cooled variety will likely be vented inside the vessel thus raising the internal temperatures and the cooling of the system in hot air is also less efficient so the compressor has to work harder to achieve the required temperature thus consuming even more power from your already tired battery bank.



look at: the cold machine 97 (water cooled) suitable for larger sized cabinets and has a larger danfoss compressor unit, then look at the cooling plates underneath and decide what best suit your needs

Id also take a look at the 240v or 12/24 volt automatic swithing unit (mps50), which will automatically go over to a 240v (also available for 110v) when plugged into a mains supply which will also conserve your battery bank.

I have no connection to the company other than having just ordered £1500 quids worth of kit from them, they were very helpful.
 
Thanks all the the replies, I think I have a clearer idea of what needs to be done, but not 100% yet!

William: Inverter theory is interesting, The Inverter installed is a CLD Marine OSD800 but I can't find out if it is square or sine wave. Unfortunately I don't know anyone who will be able to lend me a true sine wave inverter to test (I am in Tahiti right now).

Ribrage & Yoda: I have contacted WEACO and indeed, the refrigerant used in the Cold Machine 94 (R134a) is different to what we have now (R22). So by the sounds of it the plates will defiantly have to be changed. I have looked at the water-cooled version of the cold machine and I am moving closer to this. I am still concerned about the power consumption though...does anyone have any experience with the water-cooled Cold Machine 97?

RichardS: Entertaining story, thanks for that! Back to school for me I think... :)

Charlesswallow: Dedicated genset sounds slightly like an overkill for me, but thanks for the suggestion.
 
ashskett said:
Thanks all the the replies, I think I have a clearer idea of what needs to be done, but not 100% yet!

William: Inverter theory is interesting, The Inverter installed is a CLD Marine OSD800 but I can't find out if it is square or sine wave. Unfortunately I don't know anyone who will be able to lend me a true sine wave inverter to test (I am in Tahiti right now).

Of course I was assuming that the existing freezer works fine on 240VAC. If it is running low on gas it will possibly freeze but run for long periods rather than the hoped for shorter periods of running. Indeed it might be worth just getting a fridge man to check the gas charge first. Then I think I would be inclined to buy a sine wave inverter mail order and replace existing dedicated one. If it doesn't solve the problem the old inverter will be good as a spare.
http://www.altronics.com.au/index.asp?search=Inverter+sine+wav&area=srch&Submit=SEARCH or
http://www.jaycar.com.au/productRes...+wave&keyform=KEYWORD&SUBMIT.x=19&SUBMIT.y=12
These pages shows a few sine wave inverters from Australia of course you need to know the start up power requirements of the compressor. good luck olewill Oz$=67 UK pence
Click to expand...
 
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