AC unit raw water output, 6 units single or multiple outputs

[sndog]

Hello again.

I was wondering what everyones thoughts are on outputs from AC units. I have 6 units and was wondering if I should use 1 or 2 1.5" or 2" thru hulls with manifolds, or should I have 6 3/4" thru-hulls.

I currently have none, so it is an open canvas.

Thank you

 

[O C Diver]

How many pumps?

Unless you have a manifolded drain system throughout the boat, I would avoid excess plumbing and vent seawater close to each AC unit.

Lot to be said for independent systems (pump, AC, and vent), where a failure only effects one unit.

Ted

 

[slowgoesit]

I have a main seawater manifold off of the sea chest that services two HVAC units. 100% agree with Ted with using separate raw water pumps as well. Coming off of a common seawater manifold will mean less below water penetrations, but longer raw water runs to the self contained HVAC units . . . . Everything is a trade-off.

 

[Comodave]

The more plumbing to more resistant to water flow. And with only one pump that is a single point of failure. One pump goes and all your A/C is gone too. I agree on multiple pumps, how many is something you need to determine due to how the boat is physically setup.

 

[Bmarler]

With six units, I would probably try to double them up if they’re close enough together to make it practical. Three pumps and inlet/outlet fittings. That way you aren’t completely shut down if a pump fails, just inconvenienced.

 

[sndog]

How many pumps?

Unless you have a manifolded drain system throughout the boat, I would avoid excess plumbing and vent seawater close to each AC unit.

Lot to be said for independent systems (pump, AC, and vent), where a failure only effects one unit.

Ted

Two pumps, 4000gph each. They go into a manifold then distribute out to each of the HVAc units via 3/4" ID tubing.

 

[sndog]

I have a main seawater manifold off of the sea chest that services two HVAC units. 100% agree with Ted with using separate raw water pumps as well. Coming off of a common seawater manifold will mean less below water penetrations, but longer raw water runs to the self contained HVAC units . . . . Everything is a trade-off.

I have two seachest as well, so it makes getting water into the ac units the easier part. I do not think I can treat the seachests as outputs though. Correct

 

[sndog]

The more plumbing to more resistant to water flow. And with only one pump that is a single point of failure. One pump goes and all your A/C is gone too. I agree on multiple pumps, how many is something you need to determine due to how the boat is physically setup.

Setup, is left to me, as there is currently no thru-hulls for them.

 

[Comodave]

What I meant is how the units are located in the boat. If you have 2 near each other them maybe 1 pump for them, etc.

 

[O C Diver]

Two pumps, 4000gph each. They go into a manifold then distribute out to each of the HVAc units via 3/4" ID tubing.

Depending on the size of the AC units, 5 to 10 GPM is required.

Note: That's discharge flow from the through hull fitting.

At 66 GPM one pump (with minimal flow loss from properly designed plumbing) could handle all. One other consideration is height above sea level as these pumps suffer greatly from head pressure. At 66 GPM, what is the intake plumbing size, 2" ?

If you're truly planning on using only 2 pumps, I would strongly encourage you to think long and hard about a plumbing strategy. While it might be easiest to plumb all the staterooms off of one pump, losing that pump means no air conditioned sleeping.

Also with that volume of water (whether some AC are running or not), you will find yourself cleaning the strainers far more often.

Ted

 

[SIBERNUT]

Being in freeze prone area, you want to be sure EACH unit gets protected. Last boat with 3 AC's had a common discharge manifold, made it a PITA.

 

[sndog]

Being in freeze prone area, you want to be sure EACH unit gets protected. Last boat with 3 AC's had a common discharge manifold, made it a PITA.

What about it made it a PITA?

 

[sndog]

Depending on the size of the AC units, 5 to 10 GPM is required.

Note: That's discharge flow from the through hull fitting.

At 66 GPM one pump (with minimal flow loss from properly designed plumbing) could handle all. One other consideration is height above sea level as these pumps suffer greatly from head pressure. At 66 GPM, what is the intake plumbing size, 2" ?

If you're truly planning on using only 2 pumps, I would strongly encourage you to think long and hard about a plumbing strategy. While it might be easiest to plumb all the staterooms off of one pump, losing that pump means no air conditioned sleeping.

Also with that volume of water (whether some AC are running or not), you will find yourself cleaning the strainers far more often.

Ted

My design involves one side feeding four AC units: three 18k BTU units and one 24k BTU unit. The other side feeds two units, 2 24k BTU. They are using mag drive pumps. Rated at 4000GPH each, max head of 16.4ft. I have one spare pump that is to be kept on board just in case of failure. Head height for 4 of the units is 0, they will sit about 20" lower than the pump. 3 of the units will sit at about 5' of head height from the pump. The pump sits about 12" below the water line.

The plumbing strategy is straight and as short as possible, as the forward bedroom will have about 50' of line to plumb to it for it to get water.

 

[sndog]

What I meant is how the units are located in the boat. If you have 2 near each other them maybe 1 pump for them, etc.

The aft bedroom has its own discharge. The two units (24k BTU each) feed the salon, galley, and pilot house. The last three units are mostly in a straight line, down the center line of the boat, but with about 15' between them. These are the three that are the most problematic due to the location of the waterline and the location of the units.

 

[SIBERNUT]

PITA- one pump and one discharge. Have to be sure EACH AC unit got protected. Seeing pink from the discharge isnt enough

 

[O C Diver]

My design involves one side feeding four AC units: three 18k BTU units and one 24k BTU unit. The other side feeds two units, 2 24k BTU. They are using mag drive pumps. Rated at 4000GPH each, max head of 16.4ft. I have one spare pump that is to be kept on board just in case of failure. Head height for 4 of the units is 0, they will sit about 20" lower than the pump. 3 of the units will sit at about 5' of head height from the pump. The pump sits about 12" below the water line.

The plumbing strategy is straight and as short as possible, as the forward bedroom will have about 50' of line to plumb to it for it to get water.

To answer your original question:
I wouldn't manifold your outlets together. Someone is going to assume your ship is sinking and a massive trash / bilge pump is trying to keep it afloat.

So, what is the pump rating at around 6' of head? I'm guessing you will likely run loops to about 5' and down to avoid siphoning after shutdown and balance the individual units.

The run that's about 50' should be 1" line. As you push water through a line, you create friction with the static wall of the pipe (frictional line loss). Increasing the line size from 3/4" to 1" almost doubles the cross section of the line. By almost doubling the cross section, you almost half the speed of the water traveling through the line, substantially reducing the frictional line loss. Net result is that the flow through the closest AC unit will match the furthest AC unit.

That's an awful lot of AC, how big is your ship?

Ted

 

[sndog]

To answer your original question:
I wouldn't manifold your outlets together. Someone is going to assume your ship is sinking and a massive trash / bilge pump is trying to keep it afloat.

So, what is the pump rating at around 6' of head? I'm guessing you will likely run loops to about 5' and down to avoid siphoning after shutdown and balance the individual units.

The run that's about 50' should be 1" line. As you push water through a line, you create friction with the static wall of the pipe (frictional line loss). Increasing the line size from 3/4" to 1" almost doubles the cross section of the line. By almost doubling the cross section, you almost half the speed of the water traveling through the line, substantially reducing the frictional line loss. Net result is that the flow through the closest AC unit will match the furthest AC unit.

That's an awful lot of AC, how big is your ship?

Ted

I need to get the pump rating at 6'.

The loops are a good idea, will need to figure out how to loop it up, as the spaces are somewhat height constricted, which is what is causing all of my issues for this.

I thought about going to 1" line. At this point, not easily doable.

The ship is 70' but steel hull. I also sectioned off the areas for HVAC "zones" so at night you can enjoy the bedrooms and not have to condition the other areas, and vice versa during the day. I have substantial battery capacity, and generator capacity, but my goal is to not have to run the gensets at all.

 

[O C Diver]

I need to get the pump rating at 6'.

The loops are a good idea, will need to figure out how to loop it up, as the spaces are somewhat height constricted, which is what is causing all of my issues for this.

I thought about going to 1" line. At this point, not easily doable.

The ship is 70' but steel hull. I also sectioned off the areas for HVAC "zones" so at night you can enjoy the bedrooms and not have to condition the other areas, and vice versa during the day. I have substantial battery capacity, and generator capacity, but my goal is to not have to run the gensets at all.

If the three 18,000 btu units are the staterooms, I would strongly consider separate pumps. In addition to redundancy, from my experience with my charter boat, I found that night time compressor cycling dropped to zero to 20% of day time use. So, with a substantially larger amperage draw pump and less coordinated compressor cycling, you could waste a lot of power pushing water to units that weren't cooling. Not a big issue on a generator or shore power, but significant if you're trying to use batteries. You may also find 3 smaller pumps draw less amps than the large one.

Ted

 

[sndog]

If the three 18,000 btu units are the staterooms, I would strongly consider separate pumps. In addition to redundancy, from my experience with my charter boat, I found that night time compressor cycling dropped to zero to 20% of day time use. So, with a substantially larger amperage draw pump and less coordinated compressor cycling, you could waste a lot of power pushing water to units that weren't cooling. Not a big issue on a generator or shore power, but significant if you're trying to use batteries. You may also find 3 smaller pumps draw less amps than the large one.

Ted

I think that is good info. I think the cycling of the pump, current wise, is negligible for me as it pulls about 200 watts max. And there will be about 140kwh of lithium batteries.

 

[O C Diver]

I think that is good info. I think the cycling of the pump, current wise, is negligible for me as it pulls about 200 watts max. And there will be about 140kwh of lithium batteries.

That's a serious bank.

Ted

 

[Greg QS]

Have you considered a chiller plant system? With 6 units very hard to balance the load on the 220 circuit. A single chiller with a cooling circuit to each room with fans in each room.

If i were starting from scratch I would do the chiller system.

 

[O C Diver]

Have you considered a chiller plant system? With 6 units very hard to balance the load on the 220 circuit. A single chiller with a cooling circuit to each room with fans in each room.

If i were starting from scratch I would do the chiller system.

While a chiller is quieter and gives you the ability to have more than one in series for heavier cooling, they're definitely not efficient for cooling. They do offer the ability to capture heat off the engine for the heat cycle. Usually the loop is running continuously with significant cooling loss in the lines. They also don't work if the lower staterooms need heat and the saloon needs air conditioning.

Ted

 

[psneeld]

Large vessels sometimes plumb all to reach main manifold, sometimes engine exhaust tube, so multiple outlets don't leave stains on side of hull or make splashing sounds that can be annoying.

But without actually seeing the layout of the boat, setting up an AC system, especially run on minimal electric is not something I can recommend.

 

[sndog]

Have you considered a chiller plant system? With 6 units very hard to balance the load on the 220 circuit. A single chiller with a cooling circuit to each room with fans in each room.

If i were starting from scratch I would do the chiller system.

I looked at the chiller plant system, and it is nice, but the issue is if you want to cool just the bedrooms down for sleeping, you are chilling the whole boat, so electrically, it is quite taxing.

For load balancing, the 220V circuits on board, are dedicated to 220v only, though can be swapped to the 110 loads if a system fails, and is a 12kw genset. It runs the 6 AC units, dryer, water maker, and dive compressor.