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Old 25-01-2013, 10:40   #16
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Re: Raw water flow rate for refrigeration heat exchanger?

The short answer is the 1 gpm pump is more then adequate to reject heat off the condenser. Even a 1/2 GPM would be adequate for the typical 500 BTU/hour refrigeration compressor. As Richard indicated a bypass is is really helpful to control heat rejection so that the hot gas is not cooled too far.

The 1 gpm, well I used .75 GPM (allowing for head loss in system) with a 5 degree F delta will give you 1874 btu's of heat rejection. You could double that load and it would still work fine.

IF you also have an air cooled condenser, then when the air temp is below about 85-90 degrees you really don't need the pump. While the water gives a better media to reject heat into, the pump energy usage will impact total system efficiency. So while the compressor may use about 5 amps ish when running, the pump itself may add 2 amps or more. Not so bad with a holding plate, but its energy you really don't need to spend at lower ambient air temperatures.
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Old 25-01-2013, 11:18   #17
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Re: Raw water flow rate for refrigeration heat exchanger?

Microship, The pictures show two separate 110 volt refrigeration compressors the Sea Freeze air cooled is either ¼ or 1/3 horse Power with 3/16 liquid line and ¼ in low pressure line. The larger 110 volt compressor is best guess ½ horse power. It is best if we keep the two systems separate in our review.
  • LARGE STSTEM
Large system is connected to Grunert holding plate. I would assume that other box has a similar plate (Need Picture) and identify freezer and refrigerator box pictures.

The green item above compressor with red button on top is the high pressure safety switch that stops compressor when condenser water flow is low or stopped.

Remove cover from electrical control box above unit and take pictures of inside. Each box’s holding plate is controlled separately as indicated by two solenoids in picture.
There should be a second thermostat in other box. Also there should be a low pressure switch, normally it is a square box with a plastic window in it and two wires going in. And a small refrigerant copper tube connected to it. Need picture of it.

Each thermostat controls refrigerant flow to its box’s holding plate and Low pressure switch controls compressor. When thermostats are satisfied both solenoids are closed excess refrigerant will be stores in the black round container (receiver) and low pressure will cycle compressor of and on based on low pressure. I have described operation common to many systems but need pictures to confirm.
  • SMALL SEA FREEZE SYSTEM
Not much of the small 110 volt air cooled system is visible. I have not seen this type unit before but label lists it as 110 volt AC and draws 5 amps Phone number would indicate manufacturer is located in western Washington State. Most plates I made when I was in business had dual coils so a second hybrid system could be used, your plate picture shows only one coil in plate. The Sea Freeze unit must have an evaporator plate somewhere in boat. Follow those two small lines coming out of Sea Freeze unit all the way to their end. Where ever this evaporator or holding plate is there will be a third thermostat.

This Forum may want us to move this project over to my forum or email your choice.
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Old 25-01-2013, 13:11   #18
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Re: Raw water flow rate for refrigeration heat exchanger?

Just to clarify, assuming both compressors are water cooled, the 1 gpm pump will be adequate, provided you don't have a lot of water piping from inlet to discharge. A 1/2 gallon per minute at 10 degree Delta will give a total heat rejection of about 2500 Btu's.

If we assume that the smaller compressor is 500 BTUH and the larger is 1500 BTUH, which judging by their size is in the ball park, then the combined would still be under the total heat rejection available at 1/2 GPM. So I'm sure that the 1 GPM pump will work provided the head developed by the smaller pump is close to the old 1.5 gpm pump. The head / pressure developed is just as important as the flow rate when considering a pump.

While I look like a Bimbo, I oddly enough have designed 10,000 ton Chiller plants and worked on the design of some plants over twice that size.
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Old 26-01-2013, 12:12   #19
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Re: Raw water flow rate for refrigeration heat exchanger?

Thanks for the flood of excellent info, folks! I'm in Seattle at the boat show as the moment, but will be back aboard tomorrow and look forward to a proper reply. I'll also test the baby pump and, assuming it doesn't vapor lock during the change-over, test its effectiveness.

Cheers!
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Old 10-02-2013, 23:56   #20
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Re: Raw water flow rate for refrigeration heat exchanger?

Hi...

Argh, sorry about the rotated image in my set of photos... how embarrassing. Also, I included some unintended confusing information; the final photo with the big white vent hose is the OTHER fridge, which is a DC front-loader. Richard, you correctly noted that there were two, but until I crawled in to start looking for answers to your questions, I didn't realize that I had mis-identified that image and thrown it in with the others. Oops.

The vendor of both was Sea-Freeze (Bellingham); I just met them at the Seattle Boat Show, although that didn't really translate into anything quite so handy as a manual. But it's good to know who did the install!

Regarding my original pump question: I mentioned in my last post that "I'll test the baby pump" - after some thought (and buying fittings), I'm not sure I should bother.... though I totally agree with you, Sailorchic, that it would move enough water to extract the amount of heat involved. But since it's not self-priming, it may be a pain and end up with a big air bubble... if not during the installation, then perhaps after a haulout (especially if I forget to shut the system off and it quickly clears the hoses of raw water). This hasn't been an immediate problem, as I've been leaving the cabinet door open where the air heat exchanger is located and it's cool weather, but I do need to fix it. Do you folks think I should just replicate the pump that was there and stop tempting fate?

Back to identification, once we ignore the superfluous fifth photo: the big AC refrigeration system is connected to TWO enclosures (are they both cold plates?). One is the photo of the top-loading fridge that I included with the Grunert logo, and the other is a nearby top-loading freezer about 2 feet away, under the nav-station desk. It's a bit icy in there at the moment, so not photographable to reveal any system details... but they are the same system. The pic with the two gauges shows their temps.

Richard, you have me curious now... I'll get in there and take some fresh photos including the inside of the control box. About 3 years ago I had a "maintenance event"... somebody had put a plastic inline fuse-holder unsupported in the middle of the wiring harness to the hinged power panel, and it failed while I was not on board. While trying to figure it out, I opened that box... as I recall, there are just 2-3 open-frame relays in there. Observing the system's cycling, it sometimes runs for just a few minutes, and other times goes for an hour or more... and this is in otherwise steady-state conditions with access and ambient temperature. I'm obsessively geeky about almost everything on the boat and am instrumenting things left and right with a data collection system, yet this has remained a mystery. I really appreciate your helpful insights and pointers to ejumacational resources!

(Again, other than the failed seawater pump, this system has been working just fine... at this point I'm mostly trying to understand it better.)

Cheers,
Steve
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Old 12-02-2013, 19:40   #21
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Re: Raw water flow rate for refrigeration heat exchanger?

Ah interesting. Well if it was me, I would maybe rework the pump location, so it has below the water line and had a flooded suction. That way the pump will not have to pull a prime, which the small pumps do poorly, really not at all. That's a good Idea with any raw water fed pump. That an keeping the pipe runs short as possible. If necessary you could up size the pipe diameter one size, which reduces the system head some.

So short term in the PNW the small pump would be fine. However if you were to spend a lot of time in say mexico then the larger pump would give you a slight bit more efficiency heat rejection wise in the hotter water.

That's a really nice system you have there, BTW.
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Old 26-02-2013, 18:54   #22
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Re: Raw water flow rate for refrigeration heat exchanger?

Thanks, Sailorchic! And intriguing idea about the pump location... I'll look at that. I'm about to remove an old LectraSan and that will really open up some space in the bilge... not to mention improving serviceability. I am not the willowy contortionist that this boat requires (like most boats, I suspect).

I'll do the larger pump... saving the $100 and having problems later is not worth it!

Cheers,
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Old 27-04-2013, 19:25   #23
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Re: Raw water flow rate for refrigeration heat exchanger?

Has anyone used one of the March brushless centrifugal pumps available from RParts? I am currently fitting the reefer box into the boat and prepping to hook up the hardware. I have a spare 1" Groco seacock installed in the galley that I'll use for the reefer cooling pump, and also to the manual galley sink pump. I like the idea of the simple maintenance of the brushless pump, but I don't have anyone who actually has one. I'll be fitting a restrictor valve on the cooling pump to control the flow rate in tropical and PNW water temperature ranges.

Also, if the condensor is above water level, will I need to install a zinc? It will only be wet when pumping.
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