Frigoboat Keel Cooling Refrigeration in Temperate Cold water?

[Frigoboat Info]

Mr Kollmann: I can understand why your estimations are so widly conservative when it seems you deem it neccessary to limit the compressor duty cycle to less than 50%. This is old-school thinking and has absolutely no relevance when using variable speed compressors. In fact, you should know that the most efficient refrigeration system would be one that ran 100% of the time, varying the speed and capacity of the compressor to remove the heat from the box at the same rate as it is entering. This would give the highest COP and the greatest efficiency. With the Frigoboat Merlin Smart Speed Control and it's predeccessor the SSC, we set time limits that result in long duty cycles, and that is why we get such great efficiency with our systems. There is no run cycle time limit imposed by the compressor manufacturer, and no reason that I can think of for limiting the duty cycle as you feel compelled to do. If you ignore your limit, you will see from the numbers that cooling a 20 cu ft refrigerator is indeed feasible and possible with a single BD50 compressor, and in fact we could go larger but are limited by evaporator size.
But please don't just take my word for it. What about the thousands of satisfied Frigoboat (and other manufacturers') owners out there with fridge boxes in the 10 to 15 cu ft range and freezers of 6 cu ft and up? (There are not many boxes larger than those on small/medium boats) The Danfoss/Secop BD50 compressor is a wonderful and incredibly reliable piece of machinery, and when incorporated into a properly and clevery designed system is capable great things, even when operated for long run cycles.

[Richard Kollmann]

Frigoboat has good products but I simply ask salesman to crunch the numbers based on his claim to be able to refrigerate a 20 cu ft box with minimum insulation in a tropical climate with a BD50 at minimum compressor Rpm as if I wanted to buy a unit from him.

What is most important to a cruising boat owner is energy efficiency and variable speed compressors like the BD50 can and do deliver better performance in the right size small refrigerated boxes. Conservative design COP or better yet System Coefficient Of Performance (SCOP) is achieved by compressor lower RPMs and still providing desired refrigerated box temperature while limiting daily amperage consumed. There is a point where reducing speed to improve COP can cause compressor to run too longer and again become energy inefficient. An energy efficient speed can not be determined until that refrigeration is in service. Yes, my 50% projected design duty cycle applies to worst case climate condition for a particular size box.. Of all the engineering skills Mechanical Engineering seems to be the most difficult to project end result performance. Over designing is just as bad as under designing a system.

Selecting size of compressor and its speed for an icebox conversion is only a theoretical calculation because lowering Rpm to improving the SCOP end result depends on how many amp-hrs are consumed per day. Typical example reported by a local boater with a 4 cu ft freezer in Bahamas equipped with a Frigoboat BD50 plus SSC runs at poorest efficiency 6.5 amps at 3500 rpm most of the time. Ten years ago I tested the SSC and was surprised how well it works. The Merlin I tested did not work as well.

Based on 86 degree seawater 90 degree ambient air BD50 compressor in a 20 cu ft box at max rpm 24 hours a day to maintain refrigerator temps with an evaporator temp of +10 degree F would consume as much as 156 amp-hrs per day. If this boat were in cooler sea water amp-hrs can be reduced 2% for each degree reduction of water temperature. One must always remember non active box Btu calculations do not represent personal drinks and other food through put in warm climates my books and web side slide show do include crew and additional people’s impact on refrigeration Btu/amperage.

[Frigoboat Info]

"There is a point where reducing speed to improve COP can cause compressor to run too longer and again become energy inefficient."
I can find no logic in that statement. The lower the speed the higher the COP and the more efficient the system becomes. Danfoss BD 50 specs show that lowest speed always has the highest COP at cycling temperatures.

"a local boater with a 4 cu ft freezer in Bahamas equipped with a Frigoboat BD50 plus SSC runs at poorest efficiency 6.5 amps at 3500 rpm most of the time."
When we get these sort of inquiries in our office we endeavour to determine whether it's application, installation, or operational error that is resulting in such poor performance. Usually it doesn't take too long to identify the source of the problem and have a relieved customer.

"Ten years ago I tested the SSC and was surprised how well it works. The Merlin I tested did not work as well."
In fact, there is absolutely no difference in the operation of the Merlin and the SSC. They both have exactly the same logic.

" Based on 86 degree seawater 90 degree ambient air BD50 compressor in a 20 cu ft box at max rpm 24 hours a day to maintain refrigerator temps with an evaporator temp of +10 degree F would consume as much as 156 amp-hrs per day."
Well now you seem at least to agree that a 20 cu ft refrigerator is indeed possible with a BD 50 compressor! But with a Frigoboat Keel Cooled system we could reduce that daily current draw down to about 60 amp/hrs per day. Maybe you missed a step in your calculations, because working your numbers backwards shows that the insulation in your example must be R5, which is about 1".
So: 20 cuft cube-shaped refrigerator box with R15 (3") insulation, at 90F ambient, will have approx 160 Btu's per hour heat influx.
Capacity of Danfoss BD50 at 5F evap temperature at highest speed is approx. 400 Btu/hr. But that is at 130F condensing temperature, which is the figure used for air cooled condensers, so it will be considerably higher capacity than that at water-cooled condensing temps. Probably more like 450 Btu/hr.
So we have 160 Btu/hr coming in during the heat of the day (and considerably less at night), and we have the capacity to remove 450 Btu/hr with the BD50. There's plenty of excess capacity in hand, so a Merlin speed control would slow the compressor down when it can, but then can use the maximum speed if extra cooling is required. All we need is a well designed and engineered system like a Keel Cooler, with an evaporator that's large enough for the job, and some cold beer to celebrate.

[Richard Kollmann]

Frigoboat info,You are assuming every variable speed Danfoss compressor is going to be equipped with a $100 plus automatic speed control for your COP theory to work, not true. Most systems sold including Frigoboat’s have preset compressor speeds intended to match thermo heat transfer efficiency of evaporator. I was advised by Frigoboat when I purchased their SSC for test purposes that it would not be energy efficient on systems with water pumps because of extended compressor running time. The same thing is true any time slow speed daily amperage is greater than a higher speed’s daily amperage. Fixed speed 12 volt Danfoss compressors in the past meant one size compressor fits all so when installed in a large box with a large evaporator it was reasonable efficient. The true benefit of variable speed is to downsize compressors Btu capacity to achieve improved energy consumption in smaller boxes.

Those with a amp-hr meters on board can monitor daily amps consumed and manually change compressor speed resistors.
For every one else you must rely on the company assembling your unit for correct compressor speed setting. Price wise Danfoss’s AEO at time of system purchase is the better controller with advanced features and module cooling.

My example of 20 cu ft box heat load was based on R21 insulation and maximum BD50 compressor speed.

I ran a number of tests on the Merlin speed control and found it unstable refusing to increase or decrease speed at times. The battery went bad in my temperature data graphics logger so I stopped testing. Will get a new battery and run a final test and send test results and Merlin to you, if you send me a mailing address. If my Merlin has the same circuit board as your SSC it my be mine has a defective board.

[Frigoboat Info]

I do hope this thread is interesting to others out there. I feel it important that the facts are presented clearly, any incorrect statements are challenged, and any misconceptions are analyzed and explained. Please feel free to chime in any time.

Frigoboat info,You are assuming every variable speed Danfoss compressor is going to be equipped with a $100 plus automatic speed control for your COP theory to work, not true. No. Adjusting compressor speed does not have to be done automatically to improve COP. It can be done manually also. Most systems sold including Frigoboat’s have preset compressor speeds intended to match thermo heat transfer efficiency of evaporator. Incorrect. All but the smallest Frigoboat condensing units come with a fully adjustable manually variable speed controller. I was advised by Frigoboat when I purchased their SSC for test purposes that it would not be energy efficient on systems with water pumps because of extended compressor running time. No. Extended PUMP time. Why? Because you are adding at least a 1 amp draw to the system for the pump. The pump keeps going, drawing that 1 amp plus, no matter what the compressor speed, and any gain in compressor COP by lowering compressor speed is negated by the additional pump draw. It is therefore more efficient to keep the run time to a minumum while also reducing the possibility of clogged strainers and pump breakdown. The same thing is true any time slow speed daily amperage is greater than a higher speed’s daily amperage. It will never be unless the box temperature is not kept constant. Fixed speed 12 volt Danfoss compressors in the past meant one size compressor fits all so when installed in a large box with a large evaporator it was reasonable efficient. The true benefit of variable speed is to downsize compressors Btu capacity to achieve improved energy consumption in smaller boxes. No. If possible to do so, lowering compressor speed will increase efficiency and lower energy consumption in all size boxes, as long as it is not a pumped-water cooled system or is using a holding plate.

Those with a amp-hr meters on board can monitor daily amps consumed and manually change compressor speed resistors. The Frigoboat Speed Board has a screwdriver-adjustable potentiometer that is continuously variable between 2,000 and 3,500 RPM. Our Guardian control has a knob on the face-plate that is very easy and convenient for an operator to adjust. An operator can gradually decrease compressor speed until the system is seen to run continuously and the box temperature rise, at which point the speed will need to be increased slightly to be the most efficient. This should be done at the hottest part of the day.
For every one else you must rely on the company assembling your unit for correct compressor speed setting. Price wise Danfoss’s AEO at time of system purchase is the better controller with advanced features and module cooling. The AEO is considerably more expensive than the standard Danfoss module, and involves additional costs if needed to be replaced due to water damage, lightning strike, etc.
My example of 20 cu ft box heat load was based on R21 insulation and maximum BD50 compressor speed. Then I must assume that your methodology is flawed somewhere.

I ran a number of tests on the Merlin speed control and found it unstable refusing to increase or decrease speed at times. Maybe it did not need to change speeds ..... The battery went bad in my temperature data graphics logger so I stopped testing. Will get a new battery and run a final test and send test results and Merlin to you, if you send me a mailing address. If my Merlin has the same circuit board as your SSC it my be mine has a defective board. I believe you were given a Merlin 2 or 3 years ago for your evaluation but we never heard anything from you. There is a slim chance that it was a prototype, but the algorithm should be exactly the same as the old SSC.

[sailorchic34]

[Tortuga's Lie]

Frigoboat,
Not to stray away from such a riveting back-and-forth debate, but I have a question.....

On my unit, I do not have an inline dryer and would like to add one. Can I disassemble the pressure lines and add one without losing refrigerant? How about replacing the O-rings while its apart?

[Richard Kollmann]

I agree let the viewers see fair debate and have opportunity to participate in problem solving and equipment recommendations. It is good to see Frigoboat go from behind in product development to the leader in pleasure boat refrigeration sales. I still believe they have design problems to solve before they can be number one, such as refrigerant flow blockage and line connector leakage. I believe Adler Barbour lost the lead when they added the troublesome Stainless steel electrical box. Low maintenance cost and reliability is what will keep customers satisfied.

[mayball]

Inasmuch as this thread has digressed from "Temperate Cold water", I would like to add my 2 cents. Of the small BD systems that I service here in Puerto Vallarta, I must say that the Frigoboat is the most reliable (with the exception of a small custom builder here in Mexico) and the most efficient. However that said, I believe the keel cooler is just borderline acceptable in these waters except in the Winter. When recharging a system, which had a leak (normally due to the Schrader service tap or a disconnect), there is a fine line between frosting the entire evaporator and a climbing discharge pressure where the keel cooler is not expelling enough heat. Sometimes, I have to stop short of a full charge.

[Frigoboat Info]

Originally Posted by Tortuga's Lie

Frigoboat,
Not to stray away from such a riveting back-and-forth debate, but I have a question.....

On my unit, I do not have an inline dryer and would like to add one. Can I disassemble the pressure lines and add one without losing refrigerant? How about replacing the O-rings while its apart?

Glad to change the subject, Tortuga's Lie!

If you have a Keel Cooled system you already have a filter/drier, and despite what you may have read, it is not absolutely neccessary to add another at this point merely as a precaution. We would only recommend adding a filter/drier if you are experiencing moisture problems or are replacing an evaporator. Nor is it neccessary to change O-rings unless yours are leaking, which is highly unlikely unless you have an older system which you've been running out of the water or with a heavily fouled Keel Cooler. If it ain't broke don't fix it, because you can do more harm than good with uneccessary "fixes". However, we do have a pre-charged filter/drier available with matching couplings so all you need is a couple of wrenches. We have o-rings available too, and it wouldn't hurt to change the one that will be exposed if you ever have to add a filter/drier.
NOTE: In response to numerous customer requests, all Frigoboat Keel Coolers are now supplied with an extra filter/drier installed on the liquid line.

[Frigoboat Info]

Originally Posted by mayball

Inasmuch as this thread has digressed from "Temperate Cold water", I would like to add my 2 cents. Of the small BD systems that I service here in Puerto Vallarta, I must say that the Frigoboat is the most reliable (with the exception of a small custom builder here in Mexico) and the most efficient. However that said, I believe the keel cooler is just borderline acceptable in these waters except in the Winter. When recharging a system, which had a leak (normally due to the Schrader service tap or a disconnect), there is a fine line between frosting the entire evaporator and a climbing discharge pressure where the keel cooler is not expelling enough heat. Sometimes, I have to stop short of a full charge.

Thanks Mayball, and it's good to have a name to pass on if any of our customers are having problems in your area.
I've seen the same symptoms when charging a Keel Cooled system in high water and air temps, but once the box comes down to cycling temp the evap usually shows a full coating of frost or can take a little more charge if needed. We could of course make the Keel Cooler bigger, but then we'd have problems in cold/freezing water.

[s/v Jedi]

Originally Posted by Frigoboat Info

Glad to change the subject, Tortuga's Lie!

If you have a Keel Cooled system you already have a filter/drier, and despite what you may have read, it is not absolutely neccessary to add another at this point merely as a precaution. We would only recommend adding a filter/drier if you are experiencing moisture problems or are replacing an evaporator. Nor is it neccessary to change O-rings unless yours are leaking, which is highly unlikely unless you have an older system which you've been running out of the water or with a heavily fouled Keel Cooler. If it ain't broke don't fix it, because you can do more harm than good with uneccessary "fixes". However, we do have a pre-charged filter/drier available with matching couplings so all you need is a couple of wrenches. We have o-rings available too, and it wouldn't hurt to change the one that will be exposed if you ever have to add a filter/drier.
NOTE: In response to numerous customer requests, all Frigoboat Keel Coolers are now supplied with an extra filter/drier installed on the liquid line.

I would love to see a picture of that extra filter drier and where it is located. My three systems were bought in 2004 and I only have little filter driers on the low side of the compressor.

[Frigoboat Info]

Those filter/dries you have are perfectly adequate Jedi, and adding any now will not accomplish anything unless you have a leak or damage, etc. The pre-charged Filter/Driers we have available are easily installed by undoing the liquid line connection between the Keel Cooler and evaporator and introducing the filter/drier into the system. You'll lose no refrigerant and the charge level will be unaffected if installed in the correct orientation, but that is all explained in the acompanying instructions. You can see one here: Diagnostic aids and maintenance solutions for marine refrigeration systems

[s/v Jedi]

Originally Posted by Frigoboat Info

Those filter/dries you have are perfectly adequate Jedi, and adding any now will not accomplish anything unless you have a leak or damage, etc. The pre-charged Filter/Driers we have available are easily installed by undoing the liquid line connection between the Keel Cooler and evaporator and introducing the filter/drier into the system. You'll lose no refrigerant and the charge level will be unaffected if installed in the correct orientation, but that is all explained in the acompanying instructions. You can see one here: Diagnostic aids and maintenance solutions for marine refrigeration systems

I have a new (spare) evaporator and that charged filter/drier aboard for just in case. The small filter drier does not help for debris coming from the keelcooler which then gets stuck in the evaporator. A filter in between those two would fix that.
I have had this problem, but used some tapping and shaking and evacuating which fixed it long term as this was two years ago. I had not expected that, hence the spare parts.

My point is that it would be great if keelcoolers get a filter on their output.

EDIT: but you said that Frigoboat had listened and added an extra filter. I am confused now, did you add an extra filter? If so, where?

[Frigoboat Info]

Jedi: Who knows where debris may come from, but some it we have found has been foreign material from installation, i.e. foam particles, saw dust, etc. There is a filter between the Keel Cooler and the end of the cap tube, but it is not visible. Any debris will never get as far as the evaporator as it will not get further than the entrance to the cap tube or hopefully caught in the hidden filter before that.
Yes, all new Frigoboat Keel Coolers sold in North America now have a filter/drier permanently installed on the liquid line. This will not prevent problems from debris introduced into the system during installation, i.e. if the dust caps are removed and then left to dangle in the saw dust or the ends are then pushed through holes in foam insulation, but is somethig customers have requested and so Frigoboat has responded.