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Old 19-03-2016, 17:15   #1
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6000 BTU AC Water Discharge Amount

I have 2 AC units

A 6000 BTU Mermaid in the Vberth, and a 16,000 BTU Cruisair for the rest of the boat.

I Installed a CAL 900 pump to run both units (based on advice from Flagship Marine).

I got the small unit hooked up today, there is a few more things to accomplish before I get the big unit hooked up.

The pump is pushing plenty of water, I get a nice full stream from the 3/4 hose. But as you can see in the photo the output from the small unit seems to only be about 1/2 or even less than a full stream.

I am wondering if that is right and it is just that the small units water coil is that restrictive? The coil looks to only be 1/2 diameter, and of course has the condenser coils running inside that, so perhaps its just that restrictive that is all the water that comes out?

The unit does seem to be working. The water that is coming out is pretty warm and the radiator coils are getting cold. However there is a high pressure switch that says push to reset and it pops out when running, but the unit seems to continue running fine, so not sure what that is about.

So, should I be seeing more water discharging? If so what is my next step to try to solve?

Here's the pic, please don't pick on my for the ugly installation, still cleaning up stuff from the PO (who had everything hooked up with no pump at all!!), one step at a time!




Thanks
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Old 19-03-2016, 17:34   #2
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Re: 6000 BTU AC Water Discharge Amount

You're going to need more water. You've got a restriction somewhere, or too much hose between the pump and the small unit, and too little hose between the pump and the big unit.


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Old 19-03-2016, 17:47   #3
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Re: 6000 BTU AC Water Discharge Amount

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Originally Posted by Sailmonkey View Post
You're going to need more water. You've got a restriction somewhere, or too much hose between the pump and the small unit, and too little hose between the pump and the big unit.
Thanks

The Y you see in the photo is shut off for the back unit, its not hooked up right now as it is being relocated a bit, so right now the only plumbing the pump is using is to the small unit.

Strainer is attached directly to Thru Hull, there is 3 ' of 3/4 " hose to the pump inlet, from the pump outlet to the small units inlet is less than 8 feet. And from the small unit to the outlet shown pumping in the photo is about 6 feet.

I guess my first question should be (since I haven't dealt with these types of pumps before) they don't really have much pressure right? If I let the pump just run it pumps a nice full 3/4 inch stream, but its basically just runs out of the hose its not shooting across the bilge with any pressure or anything. Which I think is correct for these types of pumps?
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Old 19-03-2016, 17:54   #4
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Re: 6000 BTU AC Water Discharge Amount

Forgot to mention the small unit sits about 3 feet above the level of the pump .
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Old 19-03-2016, 18:18   #5
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6000 BTU AC Water Discharge Amount

I have two AC's also, but ran separate pumps.
I assume with one pump going to both units that water flows through both even when only one is on?
If so then I'll hazard a guess that the other unit due to height, length of hose etc is just the path of least resistance?
If so then I'd assume you will have to install a restricted orifice in the other line. I'd go with a cheap plastic ball valve and adjust it closed so that you get good water flow out of both units.
Now that assuming of course your pump is big enough to flow both units and I'm right in how they are set up, as I have no experience, just guessing.
But maybe I'll trigger someone who has two units on one pump to chime in.


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Old 19-03-2016, 18:23   #6
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Re: 6000 BTU AC Water Discharge Amount

From a strictly engineering standpoint your going to need 1.2 GPM for the 6000 btuh unit and 3.2 gpm for the 16000 btuh. That's for a 10 degree F. temperature rise, which is quite conservative.

Of course the issue is head loss. The small pumps for cooling don't have much head. Plus their flow rates are generally at zero head. You have to look at the pump data sheet and more importantly the flow curve to see which pump will work for the head in your system.

A march LC-3CP pump would have 5 gpm at 13 feet of head, which might just be enough, or it might be a tad low. What is the type and model of your pump.

Might check the through hole for obstructions.

Also time the amount of time it takes the discharge to fill a gallon jug. That will give you the gpm flow rate at the discharge.
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Old 19-03-2016, 18:32   #7
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Re: 6000 BTU AC Water Discharge Amount

A/c pumps are about volume/flow not pressure. Do you have good flow through the y-valve? It looks like a pvc/cheap plastic y-valve for a garden hose...unsuitable for marine use in this application. I believe this to be your restriction.

Most a/c condenser tubing is 5/8

I recommend bypassing y-valve to test.

I hope you aren't in salt water with what looks to be brass garden hose fittings.


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Old 19-03-2016, 18:35   #8
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Re: 6000 BTU AC Water Discharge Amount

Cal 900 is 900gph



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Old 19-03-2016, 21:25   #9
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Re: 6000 BTU AC Water Discharge Amount

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Cal 900 is 900gph



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A cal 900 is 900 gph at 0 feet of head, which is great marketing, but quite meaningless in the real world. At 5 gpm or 300 gph, it's 13.8 feet of head.

Water movement through pipe fittings and even at the through hole inlet orifice, cause friction loss. In order to move the water through the system there must be adequate head or pressure that exceeds the system friction losses at the required flow rate.

Every centrifugal pump has a pump curve where the head is highest at zero flow and flow is highest at zero head. You can not flow 900 gpm through any length of pipe as there is always friction losses that will reduce the flow rate to something less then 900 gph, in this case.

I suspect that the head loss in the system exceeds what the cal 900 pump can produce. Note that the vertical lift would be to the highest point of the heat exchanger and not at the inlet or outlet. So that 3 feet might be 4 feet, add hose loss, say 3 feet, heat exchanger pressure loss of 5 feet, inlet loss of .7 feet, maybe .4 feet loss through the valve and if there is a strainer there is another 2 ish feet loss there.

So could easily have over 14 feet of head and the cal pump has zero gpm flow at 15.9 feet of head.

BTW centrifugal bulge pumps have the same "issues" (some engineers call this a feature ) with flow and head....
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Old 19-03-2016, 21:33   #10
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Re: 6000 BTU AC Water Discharge Amount

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I hope you aren't in salt water with what looks to be brass garden hose fittings.
^^^THIS

A very good point. Even more so is dissimilar metals. That is the cheap Y fitting which may be pot metal and the brass hose end will have different galvanic potentials.

two things will happen, well really three. First the zinc in the cheap brass will sacrifice it's self to the galvanic corrosion, that will leave about 70% of the copper remaining which will be weak and brittle.

Second the brass will cause the metal Y valve to corrode away in salt water, to the point the fitting will fail. This would of course happen as the worst possible time which caused the third thing, that is the boat to fill with water.

Strongly recommend redoing that using brass hose barbs and tee.
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Old 20-03-2016, 05:39   #11
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6000 BTU AC Water Discharge Amount

I recommend two bronze full flow ball valves. Full flow y split better than tee. The garden hose Y-valve in pic...has two, restrictive quarter turn ball valves, with at best a 4-5 mm bore.

I am sure Sailorchic34 meant bronze...not brass...in recommendations barbs and tee...

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Old 20-03-2016, 06:56   #12
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Re: 6000 BTU AC Water Discharge Amount

Are these new A/C units or older ones? The plumbing shown indicates perhaps older systems. If older have the coils ever been cleaned?

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Old 20-03-2016, 08:42   #13
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Re: 6000 BTU AC Water Discharge Amount

Yes, I know the Y need replaced, I am just brings systems online, we are going through the entire boat, I was mainly just trying to get the system up yesterday to test the small unit to know if I had any issues with it as I am wrapping up all of the projects in the VBerth where it is installed.

There is plenty of flow through the Y, I can see it being a problem with the final installation, but not with just the small unit connect.

Getting ready to head back over for a day of projects today, I plan to do a few things to test it out. I will bypass the Y, I plan to garden hook a hose to it and see what the flow looks like from that.

Tellie, definitely older units. Last two POs neither did anything "good" with the boat. How do you clean the coils?
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Old 20-03-2016, 08:49   #14
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Re: 6000 BTU AC Water Discharge Amount

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Originally Posted by sailorchic34;2076663.............
Strongly recommend redoing that using brass hose barbs and tee.
Shouldn't they be bronze, not brass? Nylon would work as well.
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Old 20-03-2016, 09:57   #15
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Re: 6000 BTU AC Water Discharge Amount

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Shouldn't they be bronze, not brass? Nylon would work as well.
DOH.....Yes, I was thinking bronze and typing brass. Got to stop with the late night responses.

Agree Nylon would be fine too
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