Air vs water or both for cooling refrigerant

[ka4wja]

Skip,

1) I agree with Mark....there is something wrong, somewhere....and it is NOT because you're in Vero Beach in the summertime...

I'm just a few miles south of you in Stuart (just inside the inlet), with 5 cu ft freezer and ~ 5 cu ft spill-over frig, running on a Air-Cooled AB CU-100 "Cold Machine" (BD50 system).....and have very cold boxes with half the power consumption that you have...
Frig/Freezer

(and BTW, don't believe the divers that say the fouling has never been worse....'cause it has been worse, actually just 2 years ago it was a lot worse!!)





2) Aside from the other suggestions, regarding what to do / suggestions / directions / etc....

Originally Posted by skipgundlach

Any professionals I've asked (granted, I've not spent yet another boatbuck to have people come out to try to analyze what's happening with hands on) say it's working properly.

So, do you have any suggestions, or directions on how to establish why it is that it's not working properly?

a) Richard Kollmann is "the man" when it comes to marine refrigeration.....he's forgotten more than the rest of us will ever know...
Kollmann Marine
Have you read thru his site??
Asked for his input???
He can be of great help....


b) Beard Marine (Riviera Beach) services your area....and they are truly extraordinary!!!
First off they know their stuff and are HONEST!!! (I've used them for AC work and have been VERY satisfied....and when my AB compressor's cooling fan died after 14 years, they sold me a brand new one for about $22....)

Refrigeration | Beard Marine Group

I understand the aversion to spending money....but the guys at Beard are really top notch and won't steer you wrong...


c) Call Mack Sails in Stuart, FL (yes, they are sailmakers / riggers, but they also have a marine refrigeration and electronics department)
They are not as experienced in marine refrigeration as Beard, but they are cheaper and may be able to help out for less $$$....
Mack Sails Sailmakers for mainsails, headsails, genoas, spinnakers, lazy jacks

Myself and my family have been doing business with Colin and Travis for many years....(my parents did business with their Dad, as Mack-Shaw Sails, back 40 - 45 years ago in Ft. Lauderdale...)
They are good guys!!!



3) Now, I'm not on-board your boat and I'm only a "amateur" when it comes to refrigeration....so, my best advice is to read Richard's site and ask some questions there, and/or bite the bullet and call Beard Marine...





4) Regarding "water-cooling" being better....you can couch it how ever you like, but this is not factual (at least not for > 95% of cruising boats)....

Originally Posted by skipgundlach

Agrees with the above, but cites empirical evidence that water, somehow, is more effective/needed in a marine environment, else there wouldn't be such a proliferation of that modus on boats.

I'm not sure what "such a proliferation" you're referring to....
As, air-cooled BD50 (and BD35) not only proliferate the cruising boat equipment lists, but as so ubiquitous these days, that finding a water-cooled Danfoss system is like finding a needle-in-a-haystack (and they're typically OLD units that someone has been painstakingly maintaining for years and years...)

Please have a look at the SSCA Equipment Survey (as well as research other sites) and you'll see that water-cooled marine refrigeration systems are not only anachronistic, but extremely rare!!
And, they are typically NOT more effective / needed....(assuming, of course, you do allow for good airflow thru, and around, your compressor unit / condenser...)




I hope this helps....

Fair winds..

John
s/v Annie Laurie

[sailorboy1]

have you checked the easy stuff:
- fan is running the right direction
- coils aren't covered with dust/dirt
- air isn't bypassing the condenser due to gaps
- supply line is insulated all the way
- wire size and connections are all good
- thermostats are installed correctly

professionally installed just means someone got paid to do it, not that it is right

[sailorchic34]

Way too much energy being used. How big is your box (fridge/freezer).

People assume water cooling is more efficient, but for small systems it's not that much better. Air cooling is fairly efficient, as its hot gas on one side and cooler air on the other side. Works well till 95 degrees and to a maximum of 105 ish degrees ambient.

In the very best systems and I'm talking 2K to 20k ton industrial water to water chiller systems, there is maybe a 25% savings in energy on a good day over air cooled. The chiller compressor can have very nice part load COP/ kW/ton, maybe to .42kw/ton.

But add in the pumps, cooling tower fans and that overall system efficiency will rise to .8Kw/ton compaired to 1 to 1.1 KW/ton for air cooled systems.

Water cooling is generally not the best option in a small 300-700 BTUH systems with BD50's are. The addition of an extra amp for a small 12V pump, generally increases energy cost / drain for the vast majority of time with little or no real improvement on COP.

Assuming that everything appears to be working fine, but it runs too long, I would check /change out the thermostat to an electronic one with adjustable dead band. Or if you already have one then set the dead band (off time) to 2-3 degrees F and see how it goes. Could be it's slightly overcharged too. Do you have a refrigerant expansion valve in the system. Perhaps the sense bulb, needs to be relocated.

[a64pilot]

I was thinking overcharged too, but I don't know what the low side pressure should be so I kept out of it.

What should the low side be?

[skipgundlach]

Originally Posted by sailorchic34

Way too much energy being used. How big is your box (fridge/freezer).

It's got a top-load freezer and front-load reefer. Both doors are
double-gasketed with a "C" shaped, very soft, 3/8" weatherstripping, with
the 45° angles super-glued together to prevent air movement there, and,
after much fiddling (different style weatherstripping), I'm confident that
the gaskets are efficient. The boxes are, respectively - 16.25"D, 24.5"H and
14.75/28.5"W - 3.4 and 6.56 CF respectively. The spillover is 1/2"
styrofoam, epoxy encased, then sandwiched with two pieces of 1/4" ply, also
epoxy encased, then tabbed into the box bottom and sides. There is a 1" gap
at the top for warm air return, and a 4" box fan centered in the divider;
the circle surface area matches the surface area of the top gap. I made the
spillover relatively thin to enhance the cold on the reefer side; it's where
we keep our drinks.

Originally Posted by sailorchic34

People assume water cooling is more efficient, but for small systems it's not that much better. Air cooling is fairly efficient, as its hot gas on one side and cooler air on the other side. Works well till 95 degrees and to a maximum of 105 ish degrees ambient.

In the very best systems and I'm talking 2K to 20k ton industrial water to water chiller systems, there is maybe a 25% savings in energy on a good day over air cooled. The chiller compressor can have very nice part load COP/ kW/ton, maybe to .42kw/ton.

But add in the pumps, cooling tower fans and that overall system efficiency will rise to .8Kw/ton compaired to 1 to 1.1 KW/ton for air cooled systems.

Water cooling is generally not the best option in a small 300-700 BTUH systems with BD50's are. The addition of an extra amp for a small 12V pump, generally increases energy cost / drain for the vast majority of time with little or no real improvement on COP.

Assuming that everything appears to be working fine, but it runs too long, I would check /change out the thermostat to an electronic one with adjustable dead band. Or if you already have one then set the dead band (off time) to 2-3 degrees F and see how it goes. Could be it's slightly overcharged too. Do you have a refrigerant expansion valve in the system. Perhaps the sense bulb, needs to be relocated.

We have a accumulator/drier with a sight glass. Very occasional (that is, infrequent) bubbles are seen, so I doubt overcharging.

We have a constant pressure valve rather than an expansion valve; I've fiddled with it in one past discussion with SF, because my third plate wasn't fully frosted. I'll save you the details other than it got set so that the bottom was frosted, and the line out of the plate wasn't.

Our system has a 6.5° hysteresis; the probe is located per manufacturer instructions at the bottom upright edge of the evaporator plate. I've elevated the shutoff point from 2.5° - which it never achieved - in steps to, now, 6.5 (13 restart).

That keeps the box at about 10° at the box probe (which shows close to 10 degrees higher with an IR gun). That's cold enough for the short-term stuff we have in there currently, but when we go cruising again, and have to fill it for a more extended time, I'm concerned that it's not really cold enough.

L8R

Skip

[sailorchic34]

Originally Posted by skipgundlach

I'm confident that
the gaskets are efficient. The boxes are, respectively - 16.25"D, 24.5"H and
14.75/28.5"W - 3.4 and 6.56 CF respectively. Skip

Ah, 10 CF of box cooling with one dinky BD-50 compressor. I call that the Genetech problem. They put in two 100 ton york chillers in their process building, turned them on and they went to 100% load and stayed there, all the time. They did not like my answer either.

You sir need another compressor. 10 CF with 3.4 being freezer is a whole lot to ask for with a single 12V DC compressor. You could also add foam inside the boxes to make them smaller.

[sailorchic34]

Ok its a BD80, not a BD50.

Per danfoss data sheet for the BD80, your looking at about 600 BTU's heat rejection at 10 degrees F For a fridge running at 32 degrees it would have roughly 920 BTU's of heat rejection, so could maybe do a 10 CF fridge, but not a 10 CF fridge/freezer. As you drop the temperature of the freezer, the cooling capacity drops and the size of the box it can cool gets smaller and smaller. A 0 F the BD80 does 477 BTU"S. All number at Max RPM...

So either need to cut about about 1/3 of the space out of your box or Pop in a BD50 for the 6.5 fridge section. Not what you want to hear, I know.

Yes the manufacturer is 100% right that the unit is working perfectly. But it will never shut down, as you have found out. Be glad is was not a couple of $50k chillers like my friends at genetech. They had real engineers for that too. Not just professional installers.

Data sheets for the Danfoss BD compressors are available here: Direct Current Compressors - R134a - 12-24V - Danfoss.

[sailorchic34]

Originally Posted by a64pilot

I was thinking overcharged too, but I don't know what the low side pressure should be so I kept out of it.

What should the low side be?

It depends on the ambient air temperature. For 85-90 degrees F and 134A, its 45-55 psig. 80 degrees F would be 40-50 psig

[colemj]

Originally Posted by sailorchic34

You sir need another compressor. 10 CF with 3.4 being freezer is a whole lot to ask for with a single 12V DC compressor. You could also add foam inside the boxes to make them smaller.

For comparison, we have a 4cf freezer with a spillover into a 6cf reefer. It is all cooled by a single air-cooled BD50 running 9-11hrs/day using 50-60Ahr/day.

Ours is not unique - there are 127 other boats like ours with the same system, and many others not like ours. Your old system ran fine with a single BD50, so why is it not possible now?

The BD80 is overkill for your box system - as your previous system showed.

SC, those numbers may make sense to you but they do not reflect reality. The box makes all the difference, of course.

Mark

[sailorchic34]

Originally Posted by colemj

SC, those numbers may make sense to you but they do not reflect reality. The box makes all the difference, of course.

Mark

Oh agree that the box insulation makes a huge difference, which may be part of skips problem.

So I was just wondering what speed Skips BD80 runs at. Is it variable speed or single speed. There is a huge difference in capacity between low and high speed settings. A 1700 ohm resistor will force the compressor to high speed running only.

[skipmac]

Originally Posted by colemj

For comparison, we have a 4cf freezer with a spillover into a 6cf reefer. It is all cooled by a single air-cooled BD50 running 9-11hrs/day using 50-60Ahr/day.

Ours is not unique - there are 127 other boats like ours with the same system, and many others not like ours. Your old system ran fine with a single BD50, so why is it not possible now?

The BD80 is overkill for your box system - as your previous system showed.

SC, those numbers may make sense to you but they do not reflect reality. The box makes all the difference, of course.

Mark

Another system for comparison, I have a 2 cu ft freezer spillover into 7 cu ft fridge. I am in central Florida and have seen daytime highs up to the mid nineties. After initial cool down with a straight air cooled system I'm using under 50 amp hours/day, some days as low as 43 amp hours. With this kind of performance I see no need at all for water cooling.

Air cooled = cheaper, simpler, less maintenance, no salt water with concerns about stray current or galvanic corrosion or critters in the pipes and works fine for me in very hot weather.

[sailorchic34]

Last questions, how long is the heat duct and is there a booster fan on it. That is do you feel lots of warm air coming out of the duct. I assume there is a way for cooler air to reach the unit so that it can be ducted out.

I do agree that Air cooled is the way to go. Gee, we put Air Cooled chillers in Saudi Arabia, so air cooled will work most places, provided adequate air flow reaches the condenser.

[skipgundlach]

Thanks for all the inputs/views/observations.

As much of the questioning I might have answered instead of watching a movie last night have been done by previous readers, I have just a couple of comments.

The ducting for the compressor is perhaps 3' long. It puts out a lot of volume of hot air to the deck right above the compressor. Without my crawling in the ER again, I'm not certain, but I think the vertical rise is probably not more than 2 - 2.5'; the rest of my imputed length is the curvature to accomplish leaving the box and connecting to the vent opening. Note that all of this exercise has been done with the engine off, and an ambient ER; there is no heat load from the engine.

Now that the water is back in operation (see chlorine in cooling water thread), the compressor box is again at near ambient temperatures; when we were working on restoring it last week, and until the pipes opened up, the box was notably warm to the touch.

Our prior Frigoboat keel-cooled BD50 kept our box at a 2° hysteresis of 8-10° in the freezer and 32-34° in the reefer without breaking a sweat. The occasional glance I gave the SSC (in the ER so not readily visible) suggests it ran on medium or low most of the time. And that's with a BD50. A prior poster suggested making the gap 2-3°; SF recommends 6.5 and shipped their controller that way; I've not changed that part (I have played with the cutoff temp). Would I get notably better results with a shorter hysteresis?

While we were battling trying to fix the FB, I redid the gaskets. I believe they're effective.

So, assuming our SF system is working just as it should, and all the others whose systems resemble mine, and in which a BD50 manages to do well with about half the amp load, are accurate in their assertions (and with unknown boxes; I can't imagine any other than vacuum panels exceeding my results without being even more massive than mine) it appears that suddenly (in total time of life, which is now near 10 years) my insulation has taken a dump.

To reiterate, in case it's lost in the mists of the beginning, or was in another thread, it's air, solid, and infrared barriered (aluminum foil, doorskin furring strips, multi-layered and stairstepped panels, all epoxy enclosed, of 2" and 4" extruded polystyrene - Dow blue, I think, though it could have been OC pink - with double gaskets on the doors, which were cut out of the finished box so match reasonably well) 6" foam in a box with no holes other than doors and the dum-dum'ed entry/exit for the piping and electrical.

In our current envrionment (90s air and water), without water cooling, the system will run continuously on low and not reach the setpoints. On medium, in the day, I'm not certain/CRS, but I think that's also right, and the temps slowly climb, as it's not keeping up.

Right now, we're running on medium, and the system cycles well, but that's with the water system apparently working very well (lots of throughput). SF's controller relies on plate, rather than box temps as was the case in FB's. I'm not really happy with that, but I understand that to be the standard in the industry, and FB's was an anomaly. It's also got a huge hysteresis by comparison (FB 2° both boxes, SF 6.5° freezer, by plate temp, rather than box temp - the reefer setup is the same as there were no changes made there; it still uses the Carel electronic thermostat which box contents suggest works well with my circulating fan, as, despite the low temp, other than something right next to the spillover divider, or directly in front of the fan, nothing ever freezes in there, but the beer and coke are icy cold); when I was doing the thousands of recordings, the box averaged 2/3 runtime on medium, and slightly longer on low - but that was before it was a 90s environment, and had water cooling. Despite it being a very impressive (400RPM changes per cycle based on previous history, to get to an ideal 52% runtime - which we've never achieved, nor even come close) unit, SF informs me that medium is less power hungry than automatic. So, the only time I've used high is to chill the box after a defrost, and automatic, after a trial for a while during which time I observed higher overnight total draws, is just a label on the plate. I thus have a multi-hundred $ controller that's no more effective than a few resistors.

To help minimize the volume of the freezer, the bottom (under the shelf) is full of hard-frozen water bottles - about 4 gallons or so. Those provide a thermal flywheel, as well. But that doesn't seem to make any difference in total AH lost overnight when it's dark and still (right now, thank you very much, phew!!, we're getting a breeze and clear weather for the last couple of days; the normal rains and calm will return this evening - but for the last couple of days, our need for the Honda has diminished).

Does the above clarify or obfuscate?

L8R

Skip

[Boatguy30]

Skip,

I know you had the "legendary" marine AC guy at work on it here in St Aug. if you get back this way I'll help you sort it out. I'm right near the Crescent Beach bridge now.

[ka4wja]

Skip,
While this describes things well....

Originally Posted by skipgundlach

Does the above clarify or obfuscate?

I'm left wondering if your earlier question was rhetorical? (if so, my apologies for bothering your with direct answers)....





Earlier you asked do we have any suggestions to establish why it isn't working properly....

Originally Posted by skipgundlach

Any professionals I've asked (granted, I've not spent yet another boatbuck to have people come out to try to analyze what's happening with hands on) say it's working properly.....

So, do you have any suggestions, or directions on how to establish why it is that it's not working properly?

I answered you directly here in post #16, but we never heard if these answers were useful...
http://www.cruisersforum.com/forums/...ml#post1614347

Please advise if these direct answers (as well as real world info, from someone just a few miles from you), were helpful....



Fair winds..

John
s/v Annie Laurie