Any refrigeration experts out there?

I think you'll find it worth the money. It takes you from wanting to have a fridge through each and every step in sizing, design, building, measuring heat loss, cooling requirements depending on water temperature. Just about everything you have been asking about. There is even a step by step overhaul section on most common compressors.

And, the guy is a good enough writer that you can almost read the book for entertainment. He has also written a book on electrical systems that is interesting and factual.

The author has been living aboard and cruising for quite a few years now so everything he recommends is based on experience and I found both the refrigeration and the electrical books worth paying for.

Reply to
Bruce in Bangkok
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"Steve Lusardi" fired this volley in news:g90qd4$842$02$ snipped-for-privacy@news.t-online.com:

That's not nearly enough information. You need to know the heat load at pretty much all operating conditions. You also need to know the condensor operating conditions. For a job of this nature, I doubt you'll ever gather enough good info to do it.

Lacking that information, and doing it simply by 'overkill', you'll have to follow Jon's advice, and keep the compressor running any time either TEV is open.

You can do that by adding a low-side switch that monitors the evaporators' exit pressure, and turning on the compressor any time it goes higher than your desired preset.

LLoyd

Reply to
Lloyd E. Sponenburgh

innews:g90qd4$842$02$ snipped-for-privacy@news.t-online.com:

The problem is that air conditioning suction pressure needs to be much higher then freezer suction pressure. As indicated in my post something like a POA valve is needed so the air conditioning evaporators operate at a higher pressure then the freezer evaporators. You still can use thermostatic expansion valves to control a constant super heat of the refrigerant in each evaporator.

I have not worked this industry since 1977, but my recommendation is to keep the two systems separate down to dual compressors, and condensers. Each sized for the application, and operating temperatures. ignator

Reply to
ignator

Reply to
Steve Lusardi

Not necessarily incorrect, but new technologies available might require a rethink on how you accomplish the task. There's always more than one way to do it, and the alternatives may be better than "that's how we always did it."

"Don't raise the drawbridge, lower the river."

I've seen these big built-up "one compressor" refrigeration systems at supermarkets, and they certainly can be made to work. But consider what happens when that one compressor blows up, or that one massive refrigerant system springs a leak - now you have no refrigeration for the entire boat, and the Chief starts sweating.

Supermarkets can call the local refrigeration service company and have a tech on site in an hour who knows that system inside and out, and with full access to parts and supplies from the local supply house. If you are out in mid ocean...

And supermarkets usually put all the freezers on one combined system and refrigerators on the other, just to simplify the controls. Otherwise they have to start adding check valves and suction regulation everywhere. And it's best to unload the compressor and let it run rather than constant starts and stops - but then you get into run-time wear, and since you have to make your own the power is a lot more expensive on a boat than a building...

Consider that these big systems always have a problem keeping the refrigeration oil in the compressor - it gets carried out into the big accumulator and all the low spots of the lines, and unless you put oil traps and return lines everywhere it never gets back. Then the compressor dies from oil starvation - see "What happens when the one compressor fails" above.

You will be fighting this forever with oil traps and oil makeup tanks and crankcase controls. And trying to keep the velocities in all the return lines right, and getting the slopes and falls right, placing P-traps everywhere to get the oil moving back - and then the boat goes up on plane and all the working angles change...

You do need at least a small accumulator on the compressor suction side as a trap to protect against slugging - gases compress, liquids don't, and you don't want to test the anti-slugging feature on the compressor head too often or it can break the springs. Then refer to "What happens when the one compressor fails" above.

This was my thought too - Danfoss

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the BD Series 1/20 HP and 1/12 HP hermetic brushless motor compressors that run on 12V or 24V internally, and they have several control boxes to run them on 12/24V battery systems OR variable voltage solar or wind systems OR auto-changeover between 120VAC/240VAC world voltages and 12/24 VDC. And the control boxes have integrated temperature controls - just add a thermistor in the conditioned space and an adjustment rheostat.

Even one control box specifically to control EMI/RFI radiation that could rip the navigation and radar systems on a ship to heck.

And if there is enough demand, I'll bet they could build them bigger without too much trouble. 1/2 HP or even 1 HP isn't out of the question for 12VDC battery supplied systems.

It will be a HECK of a lot simpler to make separate systems that run continually from a deep-cycle battery bank, and each one optimized to it's task - freezer, refrigerator, ice-maker, live-well chiller, etc.

And a whole lot simpler to circulate low pressure condenser water around the ship to separate small heat exchangers at each refrigeration device, rather than high pressure refrigerant.

And it WINS hands down on KISS simplicity and redundancy - if one refrigerator fails, you just move everything to the three others that still work. If your battery bank goes flat, start the generator set and they all switch to 120V.

For space cooling in the cabins, consider either a "Mini-Split" refrigeration based heat-pump separate from the freezers (if you plan to run the gen-set or inverters 24/7), or ducted fan coil units and circulating chilled/heated water from the engine room. Keep all the refrigeration in one compact spot, and you could use a large ice-bank tank low in the ship (they are heavy!) to shut down the gen-set at night.

Heat is easy, I'll bet you have lots of excess heat when those two big main propulsion diesels are running - and when they aren't use the same tankless hot water heater you have for the showers. Or an RV-style forced air propane furnace. Many ways, all depends.

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Reply to
Bruce L. Bergman

They CAN be refilled, but that's not for the amateur. Good info. I understand the

OK, I gather the compressor will only be run a couple times a day, and the brine (or whatever state-change fluid) needs to keep it cold between runs? Is that the basic idea?

Very concentrated brine can probably be made up with something like calcium chloride that will freeze out at some really low temperature. I don't know if you can get to -40, but definitely well below 0 F. The cooling capacity of these brines drops as the water content drops, though. Oh, yeah, litium bromide would definitely work! But, it might be way too hazardous to use near food. If there was any leakage, you'd get REALLY mellow on all that lithium.

Anyway, I'm not a pro at this, but I think you will have real trouble making it to -40 with an R-22 system and any appreciable heat load. It will eventually get there if you can keep the doors shut, and there aren't any air leaks.

One other thing I discovered some years ago is that some foam insulations get saturated with ice. You know this has happened when a chunk of foam suddenly weighs about 40 Lbs! It is HELL to get the water back out of the foam, too.

Jon

Reply to
Jon Elson

Absolutely. This will NEVER work with any efficiency. You'd need to have suction throttling valves on the air cond evaporators, or the'd raise the suction pressure preventing the freezer from ever getting cold. Suction throttling valves are used in cars to prevent freezing the evaporator, but having very heavy throttling will MASSIVELY reduce compressor capacity. You'd end up using a 10 Hp compressor to get 1/2 Hp worth of comfort air conditioning - it would be a collosal disaster.

They actually make DIFFERENT compressors for different temperature differentials, or expressing it a different way, specific suction pressures. For many refrigerants that are used in different services, like R-22, you will find low, medium and high-pressure compressors, meant for freezer, refrigerator and air cond use, respectively. If you use a low-pressure compressor for AC, it will overload due to the much higher volume of gas pouring into it. If you use a high-pressure compressor for a freezer, it will not develop rated power as it is not getting as much gas in as it was designed for. I have made the same observation of cold plate performance that

Don't confuse freezing temperature with heat capacity. They are totally different. You want the most heat of solidification per volume, but maybe most H.O.S. by weight should suffice.

Jon

Reply to
Jon Elson

I have the idea that I heard somewhere that the preferred liquid for the cold plates was a mixture of ethylene glycol rather then "brine". I believe that the reason is that by mixing water and E.G. you can control the freezing point which is pretty much what you are trying to do.

Reply to
Bruce in Bangkok

Steve, they must have saw you coming on this one. Just in case the deal falls through and you can try again take a look at this search:

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There were several new copies for under $20 when I visited.

An even better place to go looking for the best price is here:

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Give these places a whirl next time you need an odd book :)

Reply to
Leon Fisk

Bruce, No, it is cold storage capacity by volume, as Jon alluded to (HOS) and there have been several very successful solutions developed recently for the transport of human organs from donor to recipient, which work much better than the conventional fluids like brine and ethylene glycol. These mediums require the -40 temperature to freeze. Steve

Reply to
Steve Lusardi

On Wed, 27 Aug 2008 14:42:54 -0400, with neither quill nor qualm, Leon Fisk quickly quoth:

Don't forget

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and
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. I get lots of 1-cent books shipping for $2.36, the total price essentially covering Media Mail s/h on eBay (and Amazon $4 total.)

-- Smokey the Bear's rules for fire safety should apply to government: Keep it small, keep it in a confined area, and keep an eye on it. --John Stossel in _Myths, Lies, and Downright Stupidity_

Reply to
Larry Jaques

Can you expand on this a bit as my understanding of eutectic systems has always been that you "freeze", or at least get slushy, a medium contained in the plates. The temperature at which the medium "freezes" is controlled in part to match the capacity of the compressor. The volume/mass and initial temperature of the plates then keeps the interior of the fridge below a desired temperature for a period of time depending on the mass of the plate/medium and insulation value of the container (ignoring the number of times you open the door for the moment).

I'm not arguing but trying to correct my understanding if it is not correct.

Reply to
Bruce in Bangkok

It is the phase change i.e. latent heat of fusion (freezing) that is where the energy is stored in the the cold plate. The working fluid needs to have a very large latent heat, BTU/lb.mass, and not have a strange shape change that destroys the container. I have no idea what that fluid is in cold plates. Water alone has 144 BTU/lb. latent heat, just how much better can you get by adding salts or glycol? It must change phase to store and retrieve this energy. ignator

Reply to
ignator

My constant sermon.

Refrigeration only happens effectively when you have intimate thermal contact with a phase-changing medium. Brines or other fluid mediums cannot work as well, because their temperatures rise as they absorb heat, and heat transfer efficiency is all about delta T.

Homebrewers with jockey boxes will never accept that drained ice works better than a water/ice bath, though.

Reply to
Richard J Kinch

I just brought home a 1944 copy of Audell's "Refrigeration and Air Conditioning Guide". That ought to be fun reading this winter. Lots of chapters dealing with marine and commercial units, drinking water coolers, brine systems, and even soda fountain equipment, but no mention of automotive as it hadn't been done yet. Makes me want to restore and old cooling tower. Remember those scenic wonders? I know where two are still standing.

Reply to
Stupendous Man

Automotive had to have been done before 1944, but it would still be somewhere between the "Laboratory Prototype" and "Very expensive and not widely used - which would bring down the cost but we can't get the ball rolling" stage. The only place you would need it back then is the President's bulletproof limousine or other armored car - everyone else can roll down the windows.

The sticking points were probably weight, added horsepower needs in the days when you didn't have a lot to spare, added electrical needs in the days of the DC generator and 6-volt system that was pretty well maxed out already, and the high pressure rubber hoses to put it all together, coming up with a synthetic rubber that would keep the refrigerant on the inside long term.

Water cooled condensers (cooling towers) are still made new and in use, but mostly in commercial settings where they have an on-site maintenance staff. The reason they don't get used more is that added energy efficiency also comes with a lot more maintenance work - you have to clean and descale it, and drain and refill, and keep the chemistry right and the fill valve from sticking, and occasionally rebuild it.

They've got some nifty small fiberglass units, but even though the outer shell doesn't rust and/or corrode the guts still do...

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Reply to
Bruce L. Bergman

Or something like this....

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Reply to
Jim Stewart

R12 mobile refrigeration was developed in the 1930s and used in WWII.

Reply to
Richard J Kinch

Hey, if it works... Looks like someone's 'Last Resort' residence.

Any idea what the white and green "Book" logo on the trunk is? I've seen that around a few times.

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Reply to
Bruce L. Bergman

I once saw a 1940 Packard on a used car lot that had a large evaporator mounted under the rear package shelf. It had a large V-twin compressor and it all appeared to be factory installed. I think several of the luxury car manufacturers were starting to offer air conditioning about that time. It seems to me that Nash was the first to offer it in the lower price cars, around 1952 as I recall. I have owned a 1954 Packard, a 1955 Cadillac, and a 1957 Olds convertible, all with factory air conditioning. It seemed very common at that time in the desert southwest US.

I saw a mid-fifties Chrysler which had the condenser lying nearly horizontal under the front bumper pan. It was also unusual in that it used R-22 refrigerant.

Don Young

Reply to
Don Young

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