Dual AC system water

[DWABoat]

For those of you running larger boats with two or three separate AC systems, how is your condenser water supply system designed?
Specifically, does each AC system run a separate water pump/strainer? Do multiple pumps run off one strainer? Does the boat have one water pump/strainer with a proportioning valve to balance the flow due to differences in distance and elevation of each system? Are differing water pipe sizes used to balance per some formula?
Thank you for your responses.

 

[my3sons]

Two AC’s, 1 pump and strainer, lines are Y’d off off pump, no proportioning valves. In our boat the ac units are roughly at the same height above the pump.

 

[Raynard]

41’ boat
One seawater pick-up
One strainer
One pump
Two hoses
Two AC units with individual thermostats

When either thermostat calls for cool, pump is turned on and water flows equally thru both AC units.

 

[Chris-380]

Same for my 380

Two AC’s, 1 pump and strainer, lines are Y’d off off pump, no proportioning valves. In our boat the ac units are roughly at the same height above the pump.

 

[DWABoat]

Two AC’s, 1 pump and strainer, lines are Y’d off off pump, no proportioning valves. In our boat the ac units are roughly at the same height above the pump.

Thank you for the quick response. Do you happen to know the GPH of your pump and BTU’s of your systems?

Reason, I am reconfiguring the AC systems on my 45-foot work boat with two AC systems. I think the builder “low-bid” cheaped us on the design. One system is in the upper cabin where the greater workload is, while one is in the lower cabin with little load. The pump is positioned at the same height as the lower system and only about three feet away. The pump is about ten feet away and four feet below the more loaded of the two systems.
Not only does the water have a lot greater distance to travel, but the at-pump connection has the upper line tee’d up while the lower system passes straight on through. All lines are the same size. As a result, we get continual HPF faults on the upper unit.
As a test, yesterday, we disconnected the lower unit water supply and ran all the water to the upper unit. Ran the upper AC for over two hours, not one HPF all day.
This is why you guys can help by explaining how your multiple AC water systems are balanced out to provide needed flow for different loads/positions in the boat.
Thank you.

 

[DWABoat]

Two AC’s, 1 pump and strainer, lines are Y’d off off pump, no proportioning valves. In our boat the ac units are roughly at the same height above the pump.

Thank you for the quick response. Do you happen to know the GPH of your pump and BTU’s of your systems?

Reason, I am reconfiguring the AC systems on my 45-foot work boat with two AC systems. I think the builder “low-bid” cheaped us on the design. One system is in the upper cabin where the greater workload is, while one is in the lower cabin with little load. The pump is positioned at the same height as the lower system and only about three feet away. The pump is about ten feet away and four feet below the more loaded of the two systems.
Not only does the water have a lot greater distance to travel, but the at-pump connection has the upper line tee’d up while the lower system passes straight on through. All lines are the same size. As a result, we get continual HPF faults on the upper unit.
As a test, yesterday, we disconnected the lower unit water supply and ran all the water to the upper unit. Ran the upper AC for over two hours, not one HPF all day.
This is why you guys can help by explaining how your multiple AC water systems are balanced out to provide needed flow for different loads/positions in the boat.
Thank you.

 

[DWABoat]

Thank you for the quick response. Do you happen to know the GPH of your pump and BTU’s of your systems?

Reason, I am reconfiguring the AC systems on my 45-foot work boat with two AC systems. I think the builder “low-bid” cheaped us on the design. One system is in the upper cabin where the greater workload is, while one is in the lower cabin with little load. The pump is positioned at the same height as the lower system and only about three feet away. The pump is about ten feet away and four feet below the more loaded of the two systems.
Not only does the water have a lot greater distance to travel, but the at-pump connection has the upper line tee’d up while the lower system passes straight on through. All lines are the same size. As a result, we get continual HPF faults on the upper unit.
As a test, yesterday, we disconnected the lower unit water supply and ran all the water to the upper unit. Ran the upper AC for over two hours, not one HPF all day.
This is why you guys can help by explaining how your multiple AC water systems are balanced out to provide needed flow for different loads/positions in the boat.
Thank you.

 

[Henry Boyd]

Four AC units, one strainer and pump. The pump outlet feeds a manifold with four separate lines to each compressor unit.

 

[Henry Boyd]

Four AC units, one strainer and pump. The pump outlet feeds a manifold with four separate lines to each compressor unit.

 

[DWABoat]

Four AC units, one strainer and pump. The pump outlet feeds a manifold with four separate lines to each compressor unit.

How does the water supply to each of your four systems maintain some equal distribution given different distances and elevations working in a shared line?

 

[ttmott]

Four AC units with two thru-hulls, two strainers, and two pumps.
The three for the cabin areas are fed from a single strainer/through-hull, and pump. The pump is a large Obendorfer.
The Bridge 24K BTU is from a separate thru-hull / strainer and pump which is a high lift March unit. The bridge AC raw water thru-hull / strainer is shared with the watermaker via 3 way valve.
The distribution for the three cabin units is a 3/4" pump discharge line to a 3/4" manifold with lines to each unit. The two AC units for the Solon and guest stateroom are 1/2" hose and the forward MSR is 3/4" hose. First picture is Bridge/Watermaker and second is manifold for cabin. In this picture the MSR is disconnected and capped as I was barnacle bustin....

 

[Morgan Jane]

How does the water supply to each of your four systems maintain some equal distribution given different distances and elevations working in a shared line?

I don't think this is something that most boat builders put too much thought into. The way to think about it is that water will always take the path of least resistance. However, choking off one route will not necessarily increase the other routes proportionally and over all just reduces the total water flow running thru the pump. I design Fire Sprinkler Systems for a living. Fire Sprinkler piping configurations mirror boat AC cooling lines. We have to assume from the get go that the pump that is chosen in the first place is not over sized. I would assume the pump sizing is nothing more than the GPM requirements from all your AC systems added together. So assuming that your pump is big enough in the first place, you need to make the route to the problem AC as short, and restrictive free as possible. I don't think elevation differences play a major issue at all. You only loose a 1/2 psi per foot for elevation. The real killer in water flow issues is fittings and non smooth transitions. Any abrupt transition in direction causes non-laminar flow which leads to big pressure loss. Water has mass and therefore moving water has momentum, as soon as it slows down at all, you lose the momentum. For instance, water running straight thru a TEE carries much more momentum then say the water that makes a 90 deg turn at a tee. So if you can reconfigure the TEE that carries water to the bigger unit versus the little unit, that could be a big plus. For instance, Instead of the water coming into the inlet of the TEE and then having to go left or right to either unit, rotate the Tee so that the water going to the bigger unit goes straight thru the tee and the water going to the little unit has to make a turn. And the closer an abrupt turns are to the pump, the more non laminar flow you get because prior to the first TEE off the pump, the water is moving the fastest. Once you hit a tee and water goes in two directions, the speed of the water after the tee slows down. Pressure losses are exponentially related to the speed of the water at the restriction or transition. So the closer you are to the pump, a little tweak here or there can make a huge difference. Hope that helps.

 

[my3sons]

Thank you for the quick response. Do you happen to know the GPH of your pump and BTU’s of your systems?

Thank you.

My pump is the original and rated at 985 gal/hr. I believe the replacements are all generally referred to 1000 gal/hr pumps.
My salon ac is 16k and the forward is 12.

 

[Skybolt]

I have two AC units, 12K in the stateroom for stateroom/Head and 16K for the salon. One raw water pump is a 15 GPM 3/4 feed from one strainer split off into two lines. The pump is a March LC-5C-MD.

EDIT: Corrected GPH to GPM.

 

[Chris-380]

Is that possibly 15 gpm instead of hour?

I have two AC units, 12K in the stateroom for stateroom/Head and 16K for the salon. One raw water pump is a 15 GPH 3/4 feed from one strainer split off into two lines. The pump is a March LC-5C-MD.

 

[Skybolt]

Is that possibly 15 gpm instead of hour?

Nice catch, yes it is GPM. Still having coffee, Thanks Chris!

 

[DWABoat]

Thank you all for your responses.

I believe I can fix this issue with your info and comparative system designs.

Morgan,
I will reconfigure the existing water lines using long radius elbows and hose turns with the most direct route to the upper unit. I will eliminate all the sharp 90 degree turns to ease the flow path.

I will start the process of revamp this way because it is cheap, easy, and, from what I am reading, will likely work.

 

[ttmott]

Thank you all for your responses.

I believe I can fix this issue with your info and comparative system designs.

Morgan,
I will reconfigure the existing water lines using long radius elbows and hose turns with the most direct route to the upper unit. I will eliminate all the sharp 90 degree turns to ease the flow path.

I will start the process of revamp this way because it is cheap, easy, and, from what I am reading, will likely work.

As a suggestion if you keep your boat in the water install nylon hose couplings where a flush system can connect. Another cheap and easy thing that makes maintenance so much more convenient.

 

[Henry Boyd]

How does the water supply to each of your four systems maintain some equal distribution given different distances and elevations working in a shared line?

The compressor units are located side by side. One pair under the helm in the engine bay. These service the air handler in the forward stateroom and the air handler in the salon/guest berth.

The other pair are located in the aft under deck compartment. These service the two air handlers on the helm deck.

Each pair share an outflow through hull. The ER compressor pair are about a foot and a half higher than the stern pair, but the pump/strainer is located in the ER, so they are closer to the pump than the lower pair. Visually the volume of water exiting the through hulls is equal.

 

[ZZ13]

Also there is a shut off valve where each line exits the boat. That way if one unit goes belly up or it’s line gets clogged, you can turn off its water flow and direct the full pump flow to the other unit. Or use the cutoff to flush one line at a time.

 

[stephenm27]

3 AC units (1 x 16k BTU, 2 x 8 BTU units). Single thru hull intake with manifold immediately after pump. Pump is Dometic, 985 GPH at 3 foot of head pressure. All 3 units are located in different area of the boat.