Frigoboat Keel Cooling Refrigeration in Temperate Cold water?

[westernspirit]

Looking for advice/experience from those who have keel cooled frigoboat systems in northern waters (for me pacific northwest). I have an older boat with converted icebox, older Sea Freeze Inc. BD35 compressor air cooled. I think poorly designed system with compressor in a settee compartment whose fan pulls from another compartment next to engine compartment. Basically doesn't get good fresh air circulation and frequently compartments in the summer even in PNW get into high 90's F with engine running. I've read various threads and inputs about importance of box insulation and this box is 36 years old so plan on rebuild. No easy way to completely rebuild without destroying galley cabinetry so I am planning on lining existing box with blue foam and then glassing in a new box liner. Current compressor draws 5.5 amps and even on cooler day with cabin in the 60's no engine heat doing about 80 Amphr/day; gets to 120 Amphr in summer almost running constantly, not compatible with my desire to be on the hook and use mostly solar for long periods . So I either have to design some elaborate air ducting system for the air cooled unit or go to keel water cooling. I think I will get a newer compressor with speed control to also help with efficiency. So after reading various opinions I am asking what are people really experiencing with their keel water cooling units in cold water?

[Cheechako]

Some people I know had it on their Gulfstar 43, they were very satisfied. Sailed to NZ and back with no isues from the PNW.
It sounds to me like you may have a black box/ or thermostat issue.... shouldnt be running that much up here.... I was using 100 AH per day in the carribean with a fan cooled unit and a poorly insulated box.

[Dockhead]

I have a somewhat different system -- the Isotherm Self-Pumping system. This is essentially also keel-cooling -- the coils are in a special through-hull used for a sink drain or deck drain. The natural movement of the boat pumps water back and forth over the coils.

It works extremely well, and a great benefit (like other keel-cooled systems) is you have no sea water pump or associated sea water plumbing.

It is interesting that the Isotherm system works with no apparent loss of efficiency when the boat is on the hard -- air circulates by convection through the through-hull and does the business.

Of course, cold water is no challenge to a refrigeration system which in any way uses the sea as a heat sink. So if you're in cold water, that's all the more reason not to use an air-cooled refrigeration system.

[roverhi]

The keel cooler type of Frig's will work better the colder the water they are in. It's all about drawing heat out of the coolant and colder water does that more effectively. In tropical waters, there are some places where water temp is so high that they are virtually ineffective. Fortunately, that's mostly places you wouldn't want to go.

[jr_spyder]

I'm nearing the end of installing two Frigoboat Keel Cooler systems - fridge and freezer - so can't yet comment on the efficiency. But I have to share this photo of the tiny new compressor compared to the 24 year old compressor and water pump I'm pulling out. Now multiply by two. The old equipment took up two big lockers which are now empty and seem huge. The new compressors now share a well ventilated small locker directly beneath my stove that I never really used for anything, so it feels like the new gear takes up no space. The ice boxes also got bigger in that my old storage plates were huge and heavy, and the new thin evaporators take up much less space. I really can't believe how small the new gear is. Can't wait to fire it up in a few days. Of course amp draw will seem none existent compared to the old beasts. I except happiness will continue.

[IMG][/IMG]

[Richard Kollmann]

There are limits to how cold a condenser cooling medium can be and still allow a refrigerant to perform correctly. Frigoboat’s keel cooler are a simple form of condenser.
Performance of any refrigeration system depends on high pressure/temperature and the low pressure difference inside evaporator. The pressures when using this keel cooler have proven to perform well in seawater temps from 90 degrees to 65 degrees F. There does not seem to be any quantified data on what happens with water cooling temps below 60 degrees or below. Those who engineer boat water cooled refrigeration systems to be used north of Latitude 35 need to control condenser Superheat, Saturated Sub-cool by controlling condenser cooling medium. I would recommend anyone planning on a keel cooler system to be operated in seawater temperatures below 60 degrees to forget the comments that water is a better cooling medium than air and accumulate data from only boaters operating boats with Frigoboat units in the North West cold waters.

[Richard Kollmann]

There are limits to how cold a condenser cooling medium can be and still allow a refrigerant to perform correctly. Frigoboat’s keel cooler are a simple form of condenser.
Performance of any refrigeration system depends on high pressure/temperature and the low pressure difference inside evaporator. The pressures when using this keel cooler have proven to perform well in seawater temps from 90 degrees to 65 degrees F. There does not seem to be any quantified data on what happens with water cooling temps below 60 degrees or below. Those who engineer boat water cooled refrigeration systems north of Latitude 35 need to control condenser Superheat, Saturated Sub-cool. I would recommend anyone planning on a keel cooler system to be operated in seawater temperatures below 60 degrees to forget the comments that water is a better cooling medium than air and accumulate data from only boaters operating boats with Frigoboat units in the North West cold waters.

[senormechanico]

Richard,
Although my system is Vitrifrigo, it looks the same as Frigoboat.
I have a BD35 with a keel cooler in 47 f. water and it has run flawlessly for over a year.
We sailed into 70+ degree water in Canada's inside passage last summer and had HARD ice cream in the freezer.

[Richard Kollmann]

senormechanico To help quantify your systems performance in 47 degree water with a Vesco cooler is your unit consuming 4 amps or less per cubic foot of box size per day? It is box size and ambient temperatures as well as box temperature that will determine projected daily amp-hrs.

It is good information to know that with a keel cooler water cooling medium temp of 47 degrees your unit still function at all. Adler recommended over 20 years ago on their air cooled units to place cardboard in front of 1/2 of condenser fan coil regain good performance. I have one of Vesco's coolers to use on one of my test stands but even in winter seawater at my dock it never gets colder than 75 degrees.

[poiu]

Originally Posted by Richard Kollmann

There are limits to how cold a condenser cooling medium can be and still allow a refrigerant to perform correctly. Frigoboat’s keel cooler are a simple form of condenser.
Performance of any refrigeration system depends on high pressure/temperature and the low pressure difference inside evaporator. The pressures when using this keel cooler have proven to perform well in seawater temps from 90 degrees to 65 degrees F. There does not seem to be any quantified data on what happens with water cooling temps below 60 degrees or below. Those who engineer boat water cooled refrigeration systems north of Latitude 35 need to control condenser Superheat, Saturated Sub-cool. I would recommend anyone planning on a keel cooler system to be operated in seawater temperatures below 60 degrees to forget the comments that water is a better cooling medium than air and accumulate data from only boaters operating boats with Frigoboat units in the North West cold waters.

I am in the process of replacing my old 1hp battleship spec Glacier Bay equipment and was going to go for a keel cooled Frigoboat 50 in both the fridge and freezer (250 and 220lt). I like the advertised low power consumption and in my boat it actually will be easier to install than to duct air to an air cooled system (the compressors have to go in the very hot engine room). I am a bit concerned the keel coolers will work now given your warnings and after having checked the sea temperatures. The buoy information shows above 90 deg near the Florida Keys in summer and similar elsewhere south. I expect a few degrees even higher if in a marina or shallow water. If I were to head up to the far north I would also be out of the operating range on the cool side.

Buoy chart:
NDBC - View Climatic Summary Plots

Will it work, but with reduced efficiency?

It would be good if more people could chime in with their experiences as well.

[Richard Kollmann]

Poiu, First look at the basic figures about replacing one horse power with two BD50 compressor systems in a 250 L (8.8 cu ft) and 220 L (7.7 cu ft) box. The combined horse power of two BD 50 compressors are equal to about ¼ the capacity of the old unit you are removing. A keel cooler system will operate in tropical climates like the keys and Bahamas in summer. Your problem will be the size of on board electrical power grid you will need if one of these boxes is to be a freezer. I would estimate Based on 90 degree seawater over 200 amp-hrs per day in summer tropical weather south on Latitude 36N. In a much cooler seawater of 65 degrees daily amp-hrs are half that of tropical waters.

I helped a friend several years ago install two Frigoboat BD 50 keel cooler SSC systems in a 46 Hylas. Each of the boxes on this boat were smaller than yours and with two engine alternators and a generator he had difficulty in managing his DC power grid even with two 8D batteries. After a couple six week trips to Bahamas the main alternator was replaced with a 160 amp unit.

[Dockhead]

Seawater cooled refrigeration will work better and better, the colder the water, until icing problems appear. I have been using mine in water getting down to +3C for almost 4 years with no issues. If in doubt, cnslt the manufacturer's literature.

[jr_spyder]

I'm learning a lot reading this thread but I'm stumped by something. A lot of traditional systems bring sea water inside the hull to cool the refrigerant, and a keel cooler system brings the refrigerant into the sea water to be cooled outside the hull. In both cases the sea water temp must play a part in the system efficiency. So is the discussion in this thread pretty much universal to sea water cooled (as opposed to air cooled) refrigeration systems?

JR

[poiu]

Richard, thanks for your comments. I should have said the system is designed with big holdover plates. I need to run the pump for maybe 4 hrs a day. It must be oversized as it doesn't pull 1hp. I measured my consumption at 570 watts per day in cooler waters (65 deg F). The boxes are well insulated. 4" and 5" and sit together, which must help. The freezer is a top loader. Frigoboat's information says the BD50 x 2 should be OK:
Consumption Guide

Dockhead. That is reassuring. Alaska should be OK then. The manufacturer mentions limits of 5 to 40 deg C in performance data, but I can't find any conclusive info from them. I must be missing something, but I can't see why the fridge wouldn't work better the cooler the water is.

[Cheechako]

I had a cold machine with the optional sea water cooling. It also had the standard fan. When the raw water pump started acting up I just abandoned it and activated the air cooling circuit. I really could tell no difference in the amount of daily charge time either way. (how do you really ascertain 5 mins extra running without getting real anal about it?) I like the simplicity of the pumpless keel cooled devices, but if you are looking for big electrical gains in a small boat unit, I suspect you wont find them. Maybe different in a big unit.