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JTHAW 29-09-2015 07:30

Old Grunert Refer Freezer rehab ?'s...
5 Attachment(s)
for the experienced...
on my new to me 36', I have an old grunert rfrig/freez...see pics...It is in very serviceable condition, compressor runs; probably installed early-mid ninties....earlier?.....holding plates...etc.....where is the best place to get all the info needed to maintain/fix/learn? keeping/fixing it for cruising tropics, down islands...2 newer 900 cca sealed agm batteries now with 65 amp cart 6 volt batteries in the future....a very knowledgable cruiser tells me he would prefer this to his older adler B...he said install a new evaporator and get gauges...then get and keep moisture out of the tubing and the thing will run forever...
informed thoughts , advice....?..

SV THIRD DAY 29-09-2015 10:55

re: Old Grunert Refer Freezer rehab ?'s...
Remember the line from Jaws "get a bigger boat" or something like that.
Well with that system the line is "get a bigger battery bank and alternator" because the amps needed to run that system is going to kill you. The are great systems but will lock you into a huge energy deficit unless you are in the 700W+ solar array range.

Since holding plates rarely "wear out" I would look at converting from your power hog compressor to a more efficient 12v system so that you could have a chance to run the system from solar. We do 3-4 of these type of conversions a month. (usually after the cruiser struggles for a season with having to run their engine all the time to keep the batteries full) Recycle the holding plates and go with a new compressor set-up and at the same time get rid of that maintenance nightmare pumped water cooling.

Oh...and upgrade that 65A alternator for a 100A, you won't regret it because the No 1 problem cruisers have out there is keeping their batteries charged up. It's not storms, or pirates, or corrupt customs officials...its waking up to dead batteries.

Cheechako 29-09-2015 11:02

re: Old Grunert Refer Freezer rehab ?'s...
They were great units, heavy duty, quality built etc. But they suck amps like a tornado! At least mine did. It was a 1/2 HP belt drive unit.

colemj 29-09-2015 11:34

Re: Old Grunert Refer Freezer rehab ?'s...
Holy cow, that thing draws 40A. You are going to be spending all your time charging your batteries to keep up with that load - particularly so if your insulation is old or thin.

As someone who has spent the past 7 years in the tropics, with plenty of solar and a generator and an extremely well-insulated box, I wouldn't be able to power manage the boat with that on it. At least not without several hours of generator run every day. I suggest taking Rich's advice to heart and convert it to a Danfoss 12V air cooled system.

Refrigeration will still be your largest power consumer, and you may still need to intensely manage power, but at least you will have a fighting chance.


JTHAW 29-09-2015 12:44

Re: Old Grunert Refer Freezer rehab ?'s...
3 Attachment(s)
many thanks for the replies guys.....conversion it is...s/v Third Day...ball park figure for conversion is....??? lowest possible $? ? I can do most of the work myself...

further: The insulation is old...I can dig out and vacuum 2 sides and shoot canned expanding foam from Lowes....suggestions, pictures....on how to get to the aft/ engine room bulkhead side and outboard side old insulation out????
hate chopping up original gelcoat fiberglass though...first thought is to cut through the aft bulkhead, jump down the cockpit locker to access...all 3 of the below pictures are of the aft bulkhead taken while sitting down in the cockpit locker....on the other side of the bulkhead( behind the red filter) is old foam insulation...
all pics and detailed suggestions very much I am going to have to do this.....details please.....thanking ya'll in I to keep the holding plates in the box? the giant hog compressor and the power control box underneath...these are shown in the 1st set of pics...probably remove the black box and grunnert gauges too?...correct?...

JRM 29-09-2015 13:21

Re: Old Grunert Refer Freezer rehab ?'s...
I did this project this spring before my trip. I got lucky and my system was already empty (original 1975 plates) so I didn't have to vacuum any refrigerant. Still, I put in two Danfoss based Isotherm kits, figure $1800-$1900 each for a fridge and a freezer. I completely cut out the old box, and built a new one with stitch and glue, lined it with bathroom liner panels, and good sheet insulation. Figure $400 for the box and insulation. Then I had to rebuild the countertop and put on new Formica, so probably another $150 there.

Then a new electrical subpanel, new wiring to it, new lid made, etc. The problem with a project like this is the feature creep kills you. I probably dropped $50 just in fasteners. And like many things, if you cut corners it'll end up costing later in energy and things like condensation in the insulation.

It's awesome though. Worth every penny just to have the beer cold!

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JRM 29-09-2015 13:28

Re: Old Grunert Refer Freezer rehab ?'s...
8 Attachment(s)
Some pics from my phone.

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SV THIRD DAY 29-09-2015 14:10

Re: Old Grunert Refer Freezer rehab ?'s...
I think JRM got it pretty right in terms of costing.
$1495 for the compressor/condensing unit plus a few hundred dollars in tubing, fittings, thermostat, etc. So I always tell clients to figure $2K out the door to not undershoot a budget. Depending on your box size you could go with the classic spill over freezer/refrigerator set-up or if you have too large a box or want to have two different temp plates in each box (freezer and refrigerator) then you would have two compressor systems running, one for each box.

In terms of insulation, I like the RMax PolyIsocyanurate that you can buy in 4ft x 8ft sheets at Home depot for about $25ea. They have 1/3 more R value than the pink board and that to me is more important than the differences in moisture absorption. Sure the pink stuff (or blue) is hydrophobic and won't absorb any water...but you can make the RMax PolyIso water tight and needed 1/3 LESS insulation to get the same R-value. At the end of the day...R-value is damn important to energy usage.

Cover the RMax polyiso panels with foil tape.
Line the new box with the fiberglass wall board from home depot
Caulk the seams and boom....done....go cruising.

Richard Kollmann 29-09-2015 15:04

Re: Old Grunert Refer Freezer rehab ?'s...
A belief or conclusion on the web held with confidence but not substantiated by positive knowledge or poof most likely is wrong. You may presently have the best refrigeration for your live aboard lifestyle. Small 12 volt refrigeration is not going to always be the correct answer. A lot more quantifying data is require when making a reasonable decision as to keeping or replacing the present system.

I suggest you spend a few days operating system as you would when cruising. If the two refrigerated areas are each 4 cu ft or larger it will be a challenge to switch to small 12 volt refrigeration when cruising in the tropics. To adjust your test data to tropical conditions add 4% of per degree of increased seawater temperature amperage or daily compressor run times. I suggest you use 86 to 90 degrees as tropical water temperatures. During testing box temperatures must be maintained at desired operating temps.

As far as present insulation efficiency this can be evaluated easily buy checking insulationís exterior temperature against ambient cabin air temperature. If insulation exterior temp is 4 to 5 degree F colder than cabin air insulation it is usable. If this delta T is high enough to cause exterior moisture condensation additional insulation in that area is needed.

The term energy hog can apply to any refrigeration system when the daily energy demand exceeds the Btu capacity of a system. Any boat refrigeration system that performs well with 70 degrees seawater and ambient air temps will require double the energy in 95 degree F temperatures. If a small 12 volt compressor in a hot climate is installed in a 5 cubic ft freezer box it will run less efficient than it would in a 4 or 3 cubic ft box..

JRM 29-09-2015 15:44

Re: Old Grunert Refer Freezer rehab ?'s...
Many thanks to Mr. Kollmann, who's information I used extensively for my project. I had originally thought to go with a keel cooler system, but after spending time on his site and searching his posts here, I scaled down my box sizes, increased my insulation, and went air cooled with additional airflow through the compressor area.

My boat had a huge ice box in which a giant engine driven spillover system had been installed. With about 2 inches of 40 year old foam insulation. I thought about filling in some of the box, but in the end, built my own to maximize efficiency. I've set it up so that the compressors are interchangable, and either condenser can run the whole box as a fridge in the event of a failure.

I played conservative with my power usage calculations, and was pleasantly surprised to find performance exceeded my expectations.

Thanks again for all the time you invest in the cruising public.

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colemj 29-09-2015 17:30

Re: Old Grunert Refer Freezer rehab ?'s...
For the first time, I have to disagree with Richard Kollman on this. With the OP's 1976 insulation, modest battery bank, modest solar generation (assumed-if any), and small alternator, there is no way a 40A draw compressor with an additional water circulation pump is going to be power-manageable in the tropics.

Few people we have met cruising are able to manage this draw without significant generator or engine run time (actually, we haven't met a single one). There are several threads where Flying Pig has a system drawing less than this that he can't keep up with - and he has significant power generation capabilities and a newly constructed, well-insulated box. We have met others with these types of systems and they are essentially engine-driven systems, since no one can operate them without also running their engines.

I would hate to be out cruising and not be able to leave the boat for more than a few hours without my food spoiling. One would be a slave to the refrigerator and miss out on some great travel opportunities.

Of course, if the unit is operable, then operate it and see what you get. If inoperable, then I wouldn't throw any money into it for testing purposes.

Also, we run a 4cf freezer with a spillover into a 6cf reefer on a single air-cooled BD50 and large evaporator plate (surrounds almost the entire freezer compartment). This works a charm and uses 50-60 Ahr/day in the equatorial tropics. Our boxes are well-inslulated, but that is 90% of the challenge with efficient refrigeration, of course.


SV THIRD DAY 29-09-2015 20:48

Re: Old Grunert Refer Freezer rehab ?'s...

Originally Posted by colemj (Post 1926088)
Our boxes are well-inslulated, but that is 90% of the challenge with efficient refrigeration, of course.

To help underscore the point about insulation take a look at the photos below. What you are looking at is a roughly 140 Cubic Foot refrigerator that we make for an outfit in Papua New Guinea that air lifts these systems into remote villages so the village can have a community refrigerator for their food/produce. The walls are 12 inches thick of Polyisocyanurate (the same stuff sold at Home Depot I mentioned earlier) giving an approximate R-Value of 80. There is a 4ft x3ft x 3 inch holding plate covering the back wall with two independent cooling loops that are frozen down by two of our standard off the shelf BD50 type capacity air cooled CoolBlue systems. Given the remote nature of the villages they wanted two compressors for redundancy rather than one larger compressor.

There are a few things a cruising boat can't have enough of:
Solar, Insulation in your Ice Box, and Cold beer!

The 1000W of solar with 500AH LiFePO4 battery back up keeps things purring along. It was a fun project and I'm still trying to angle a trip out to Papua New Guinea for a service call...but my wife says not without her!

Just shoot me an email if you have any questions specific to your set-up and I will be happy to help:

Dave Lochner 30-09-2015 09:33

Re: Old Grunert Refer Freezer rehab ?'s...
We have just finished our second year with a 1993 vintage Grunert Refrigeration system. Two large cold plates, water cooled. No freezer.

Yes, the system draws around 40 Amps when running. However, we found that in moderate temperature (highs 75-85) and 72 degree water the unit runs about twice a day for 30 minutes each time. When the box is full and cold, it runs less frequently.

One week this summer, someone (probably the skipper) forgot to turn on the shore power and left the refrigerator running all week. After 5.5 days the batteries were still at 60% SOC (460 AH, 4 GCs). The current draw was only about 40 AH a day.

A well insulated box is essential with money and effort spent on those upgrades probably a better investment than new compressor units.

ramblinrod 30-09-2015 20:19

Re: Old Grunert Refer Freezer rehab ?'s...
On my personal boat, I removed a perfectly performing 40 year old 120 Vac refrigeration system with holding plate, to install a new NovaKool 12Vdc / 120Vac refrigeration system, both air cooled. It pained me to remove a perfectly performing system that was part of the purchase decision.
But the new DC system uses so little power it is amazing. With only 100 W of solar (we are adding 300 W more) we need to run the engine (35 A alternator) 1/2 hr per day, 30C daily high, 20c nightly low.

I have installed several of these systems for customers and all have been happy. If you install refrigeration, and won't be on shore power, solar is a must, wind generation if you are in an area where you will often be anchored on15 knots plus, for many hours every day.

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