Engine driven refrigeration

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Hans
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Engine driven refrigeration

Post by Hans »

After 4 years my refrigeration problem with a Grunert engine driven system has been solved at last. In case somebody else faces this same problem:
On the 45ft is installed a Grunert engine / shore power driven refrigeration system. From the beginning I had problems with the engine driven holding plates. They worked when tested in harbor, but only to fail after some time at sea, sometimes after a couple of hours or after max. two days ( never worked any longer, and they didn't work again during that trip, they only started working again after the boat had been left alone for a couple of weeks in the marina ?!) Quite an erratic problem. I asked many experts in different harbors to solve this problem. Resulting in: topping up gas, new evaporator, new solenoids, new compressor and new clutch. In short: almost a new system. Problem stayed. But always because the clutch stopped engaging due to power loss I found out. ( Became something like an expert myself after seeing all these guys working on the fridge.) Last time happened when I left Newport for Bermuda, where the system had been declared to work properly. Clutch didn't engage again due to a fault in the power. I checked the power cable to its origin: a connection box behind the panelling. Inside a wiring diagram. Showed the power to be connected via an oil pressure switch on the engine. This switch or the connections to it proved to be faulty. I bypassed this circuit, since then no more problems; cold beer every dat at last!
Hans Hansen, Makkum,The Netherlands.
Freedom 45AC #47 "Scherezade".

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GeoffSchultz
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Re: Engine driven refrigeration

Post by GeoffSchultz »

I struggled with the Grunert system until I decided to rip the whole thing out. It was designed for the coastal cruiser who is either motoring a lot and/or is plugged into shore power on a nightly basis. If you're trying to run this off of your batteries, you're screwed.

My original goal was to replace the 120V compressor with a 12V compressor and retain the engine drive system. After doing that I discovered that design didn't work well. Thus I ended up ripping out the engine drive and just using a 12V compressor. If I had to do it all over again, I'm not sure that I'd end up with the solution that I have, but it certainly works well.

My first attempt at solving this was to replace the 120V system with a 12V system that I designed and built from parts purchased at http://www.rparts.com. I do not recommend this path for the feint of heart as it requires a lot of reading and engineering, but the end result was that I had a very robust system that I could maintain anywhere I went. You also become quite popular when people find out that you understand refrigeration and have gauges, leak detectors and an evacuation pump! ;) If I were to redo this, I would probably go with a very efficient evaporator plate system, but you can easily find 12V systems for holding plates. Note that this also required changing from R12 to R134A, but that's a good thing. Photos of the system are at http://www.geoffschultz.org/BlueJacket/Refrigeration/

One of the major issues is that the holding plate is a dual coil system, with one coil loop being driven by the engine compressor and the other by the 120V compressor. One coil is on the front side of the plate and the other coil is on the back side of the plate. The engine compressor does a great job of freezing the entire plate, but the 120V compressor takes a long time to freeze the entire plate and thus draws a lot of power.

Getting back to the system...The system did not perform as I expected at all as the 12V compressor was running much longer than anticipated. After quite a bit of research and sole searching, I determined that the problem was that the 12V compressor coil loop took much too much time to freeze the plate completely though and that the only solution was to remove the engine drive system and combine both loops into one. Sue looked at me like I was crazy when I told her that I was going to do this, but once I did it, the system ran great.

Another great addition was Carel electronic thermostats which turn the system on when the plate temperature rises above a preset temperature. This keeps the temperature in the freezer and refrigerator fairly constant. You don't want both plates running at the same time, so I have it set up such that the freezer gets priority over refrigerator plates.

Being an engineer, I installed run hour meters to keep track of both the refrigeration and freezer run times. This allowed me to fine tune the thermostats for the turn-on and turn-off temperatures. Right now the combined run time for both sets of plates is around 3 hours a day and it uses about 85 AH in very hot environments.

I also replaced the foam in the refrigeration hatches with Vacuum Insulted Panels (VIP). You can read about this at http://www.freedomyachts.org/viewtopic. ... &hilit=VIP. This really helped as it changed the R value of the hatches to R40-R80.

One easy thing that you can do to improve the efficiency of your current system is to add a water cooling loop to the 120V system. Mine was air cooled, which is very inefficient.

Sorry if this is just kind of a brain dump and not well organized, but it's a complex problem, especially when you're trying to refit an existing system.

-- Geoff
BlueJacket
1997 Freedom 40/40
http://www.GeoffSchultz.org

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Hans
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Re: Engine driven refrigeration

Post by Hans »

Geoff, this is a lot of interesting and helpful info, a pity I am not an engineer and be able to work on it myself. Good to read that you installed a 12V system on the Grunert holding plates. I asked the same some time ago,( love the 12V Adler Barbour system on the 38, it's from '89 and still working fine and silent!) was told it to be impossible and was quoted a complete new system for 15-20K. Well, that's too much even for cold beer. The Grunert works fine now and see how long it lasts. Good tip: the water cooling on the 120V, I have a air cooled system now and which seems to run 24/24 in the tropics and heating up the aft cabin as bonus as well! I asked whether the 120V system could be removed, it's very inefficient but does takes up a lot of space in the cockpit locker which is already too small for the boat in my opinion. I was told that this was impossible without ruining the whole system. Was this a correct answer in your opinion?
You improved the insulation. Only the lid or the whole box? How do you regard the insulation of the fridge/ freezer boxes done by the yard, any big improvements to make here?
Hans Hansen, Makkum,The Netherlands.
Freedom 45AC #47 "Scherezade".

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GeoffSchultz
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Re: Engine driven refrigeration

Post by GeoffSchultz »

Hans,

There's no reason that the 120V system can't be replaced. The major issue is that you'll be going from R12 or R22 to something like R134A. The oil used in compressor is different and requires flushing the system of the old oil. I think that I used denatured alcohol and just ran it through the system with a pump. You also need to change out the expansion valves, but that's pretty much involves just selecting the correct R134a expansion valve and unscrewing the old R12 on and installing the new one. This is not difficult. Believe me, I designed the by reading Calder's boat refrigeration book (which I can't really recommend) and figuring out how all of the pieces worked together. If anything, I way over engineered it, but it will last for a LONG time. If there's one thing that just works on BlueJacket, it's the refrigeration. And how many boats do you know that can say that?

You should be able to buy a pre-configured 12V compressor system that hooks up to your existing tubing. I searched for "12V marine refrigeration cold plate" and saw quite a few. With that you should be able to replace the Grunert.

Probably your biggest issue is having the dual coils in your cold plates. The Grunert just can't freeze through the engine drive side very quickly and as a result has to run and run and run...If you were to simply remove the engine drive and install a "U" on the plate to join the 2 sets of coils, your system would probably run MUCH better than it does right now. I know that it's scary to think about getting rid of the redundant dual systems, but it will run much better. Believe me, I've been there and it was a huge leap of faith to do that.

As far as my insulation goes, I just replaced it in the hatches. I could feel that they were cooler relative to the rest of the box. I would have loved to have done the entire box, but I didn't want to remove whole thing and install VIPs.

I think that if you install the water cooled loop that you'll see a large improvement. Water conducts 14x more heat than air.

-- Geoff
BlueJacket
1997 Freedom 40/40
http://www.GeoffSchultz.org

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Hans
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Re: Engine driven refrigeration

Post by Hans »

Normally I am in awe when I see the plumbing, compressors, solenoids and all other stuff which makes up the refregeration system and give it a wide berth. Reading your comments starts to make me less anxious about this, and reading that you have a good working, almost noiseless system on 12V which takes only 85 Ah daily sounds more then tempting. I do have to read and make myself familiar with these systems, you talk about R12, R22 or R 134a and I don't even know waht this is, also about oil in the system while I thought that the system workes on compressed gas like freon or something. But you make it sound human instead extraterrestial, so when I start living aboard I'll problably take up the work, problably in a year or so, maybe two. Can I contact you then for details when I miss something? Would you advise to install a U turn on the existing Grunert plates or just install new holding plates if you change the whole system? At least it looks like there's a new challenge for improving the boat.
Hans Hansen, Makkum,The Netherlands.
Freedom 45AC #47 "Scherezade".

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GeoffSchultz
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Re: Engine driven refrigeration

Post by GeoffSchultz »

R12 is the freon gas that old systems used. It's very efficient, but also destroys the ionosphere and has been phased out. R22 is commonly used in air conditioning systems and while not as bad to the ionosphere, is also being phased out. R134a is very commonly used in automobiles and many appliances. All compressors have some sort of oil that circulates with the compressed gas to lubricate the compressor. R12 used mineral oil and R134a uses ester oil. If the 2 are mixed, the form a sludge, which is not good. Thus you need to flush all of the ester oil out of the system before switch to R134a.

I will state that my system is far from noiseless. It's got a big compressor and motor and you can definitely hear it run. That's the biggest downside of it. If I were to do it again, I'd probably use a Danfoss compressor, which is what you have in the Grunert system. They are very reliable, quiet and very energy efficient.

There's no reason to get new holding plates. The ones that you have are very good and will work well. As I said, the issue is that currently one side of the plates is chilled by the engine drive and other other side is chilled by the Gunert. The engine drive is incredibly powerful using 1-2 HP form the engine and freezes the entire plate very quickly. The Grunert side has a 1/8 HP motor and takes a LONG time to freeze the plates all of the way through.

Another issue that I didn't discuss is that the way that the current system is designed, both plates can chill at the same time. This causes too much gas to be flowing through the system and is inefficient as the Grunert compressor can't move that amount of gas. I solved this with a relay that only allows one of solenoids for the plates to be open at any given time. In my case I gave the freezer priority over the refrigerator.

Cooling is caused by a allowing the gas to expand due to a pressure differential. This is what the expansion valves do. The control the amount of gas flowing through the plate and restrict the flow based upon the temperature that they sense. There are different expansion valves based upon the type of refrigerant, flow rate and the temperature that they'll be working at. The refrigeration cold plates freeze at a higher temperature than the freezer plates do.

I'll be glad to answer any questions that I can. However, I'm not a refrigeration expert. I just play one in this forum and my answers are worth every $ that you pay for them! :lol:

-- Geoff
BlueJacket
1997 Freedom 40/40
http://www.GeoffSchultz.org

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Hans
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Re: Engine driven refrigeration

Post by Hans »

Thx again Geoff, I will start with some reading, have the Nigel Calder's Mechanical and Electrical Manual here at home. Will be busy for some time as I have to work also.
Will report or ask later, but thx for all the info sofar. Enough stuff to think about.
Hans Hansen, Makkum,The Netherlands.
Freedom 45AC #47 "Scherezade".

jdpandlp
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Re: Engine driven refrigeration

Post by jdpandlp »

I redid the refrigeration on White Wings, a 39 Express, 8 years ago and have been pleased with the result both in the Chesapeake Bay and Florida.

I redid the box with poured insulation. I did away with the unuseable space from the deep V at the bottom and closed of the drain. The flat bottom to the box greatly eased construction and did away with having to cool unusable space. I installed a 12V Cool Blue system. They configured the holding plate to the space I had. I use a single plate for the freezer and fridge. The divider is movable to allow me to change the proportion of the space between freezer and fridge as needed. The divider is insulated and has movable openings to control the cold air movement between the two sides for fridge temp control. The insulated divider was a later change to stop the beer and milk next to the divider from freezing.

The total box size is 5.5 cubic feet. The Cool Blue unit will hold 5 degrees in the freezer and 40 degrees in the fridge in a Chesapeake Bay August for about 35 amp/hrs. I have never seen a daily usage higher than 33 amp when I had a meter connected to the unit. My house bank is 2 AGM 8Ds so I have sveral days of margin waiting for the sun to come back out for the panels to work.

It was a simple installation that has (and will for a long time I hope) given me good service with heavy usage. Unit is in service about 20 months of every 24. Maintenance is limited to cleaning the fan and fins on the unit once a year. I have never had to add 134A.

Hope this helps

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