420DB – Bridge A/C and Heat Installation

[douglee25]

I'm not sure where you're going with this?

Doug

 

[Turtlesboat]

Just trying to figure out how many gph that pump will actually draw. How much pressure you have to produce to adequately feed 3 units. Maybe we can calculate how far it'll shoot out the side of the boat. Maybe even calculate how long it'll take to fill the salon full of water when a hose lets loose.

 

[fwebster]

Actually, I think he has more computations to make than that.

Pump volume capacity and pressure aren't the sole determining factors in the cooling system design. Line losses play a significant role in sizing the cooling system because of the added hose length. Bridge air adds about 4 miles of 5/8" hose to the cooling circuit and the system isn't going to cool properly with one pump. The more volume you push thru the system, the closer to sea water temps you keep the compressor and the cooler the compressor, the more effective the temperature change for human comfort. If you can lower the temp 20 degrees with your compressor system design, but your water flow is restricted to the point that your compressor temp is 105 degrees, them the best you can hope for is 85 degrees at the output, but if you can get the cooling water volume high enough to lower the compressor temp to 85 degrees, then your 20 degree temp differential at the output drops the output air to 65 degrees. It will make a difference.

Comparing this installation to other models is also a faulty premise because many larger Sea Ray now dump the cooling water into an exhaust tube molded into the engine exhaust system thus eliminating a fair percentage of the cooling system's small diameter tubing in the cooling circuit which also eliminates some of the systems line loss.

 

[jg300da]

Wow, so many experts and such little knowledge....This thread is filled with alarmists and misinformation. Pay attention, you may accidentally learn something....

Marine A/C, with the exception of some difference in piping materials used, is NO different in design and operation than commercial or residential air conditioning. Water cooled a/c requires 3gpm of cooling water delivered per ton at a design supply water temp of 85deg. That's 180gph per ton. And with a design delta across the condenser coil of 10deg giving you a leaving water temp of 95deg.

If Alex has 6 total tons of cooling on his boat, assuming 2 tons for the bridge, that's a total requirement of 1080gph. Not 1800gph. Now there is some loss due to friction as stated above so the additional piping losses and pressure drop through the unit itself must be carefully calculated when sizing the water pump. The pump manufacturer should be able to provide a pump curve to help with the sizing. Also, balancing valves are necessary to insure proper flow to all systems.

Follow the basic design guidlelines and confirm the specified manufacturers installation requirements and there is no reason an added system cannot deliver the same safe reliable performance of a factory installed system.

 

[Turtlesboat]

Who said I was an expert? Maybe I am an alarmist, I can accept that. I would rather error on the safer side if I had a choice. I also don't recall having to dig out barnacles, sea grass, oysters etc... from my commercial unit. He's also not doing the same upgrades the factory does when adding a bridge unit. And who ever said that because the factory did it, that it's the best or right way to do it? A factory built a Yugo and it didn't have a sticker on it saying "Don't attempt to drive on the freeway" but I still wouldn't try it. His goal is to spend all of this money and be happy and safe, I think we are doing a pretty good job trying to make sure he achieves his goal.

 

[tdschafer]

Goose Frabba, Goose frabba...........

 

[fwebster]

You guys can spout theory all you want. If Alex buys it great, but I'm not going to argue about it. I just attempted to try to save Alex some expense and effort by making him aware of what dealers do and why they do it when they add bridge/cockpit air to a boat that was not originally equipped with it. Could you also be over looking the fact that the ambient air around the pump and manifold is no where near the temperature of the cooling water? It is closer to engine operating temps of something like 125 to 140 degrees, less the cooling effect of vent air in the engine spaces.

 

[douglee25]

So you're telling us that the heat transfer from the ambient engine room temperature is going to heat up the water like it was coming out of a hot water heater when pumped through the circuit?

Science, theory, hydraulics, thermodynamics- whatever you want to call it don't lie. Sure 'real world' conditions can change things slightly, but this stuff isn't made up.

Doug

 

[Turtlesboat]

real world conditions and Ideal conditions meet somewhere in the middle. designing a system must take into account real world conditions. Over engineering a system never hurt nobody.

 

[jg300da]

Could you also be over looking the fact that the ambient air around the pump and manifold is no where near the temperature of the cooling water? It is closer to engine operating temps of something like 125 to 140 degrees, less the cooling effect of vent air in the engine spaces.

This is pure nonsense. At a flow rate of almost 2000 gallons per hour the sea water spends only a second or two in the confines of the engine room. Not nearly enough time to absorb any appreciable heat.

By the way, these are not theories, but proven scientific and engineering facts that are applied everyday in real world applications.

 

[jg300da]

Who said I was an expert? Maybe I am an alarmist, I can accept that. I would rather error on the safer side if I had a choice. I also don't recall having to dig out barnacles, sea grass, oysters etc... from my commercial unit.

Thousand ton open rooftop water towers have to deal with airborne debris, tons of pollen and other contaminants, bird droppings and solid pollutants that YOUR commercial unit does not. Marine environments are much cleaner by comparison.
The factory installed seawater hose on your boat is just as likely to fail as a properly installed aftermarket hose on Alex's boat. Stop sounding the alarm horn simply because you disagree with his decision.
After reading many of Alex's post and seeing how diligent he is, I'm sure he will make certain that each aspect of the installation will be as correct and as safe as possible.

 

[Greg]

... as safe as possible.

There is the problem. After reading through all of this, I don't know if it can be done safely.

I was planning on taking my boat out this weekend, but now I don't think I want to put my family in that kind of danger. Not only is my sea water pump exposed to engine room temps, but my entire condensing unit is.

What the hell was SeaRay thinking? I may try to get some estimates to have my bridge air removed.

In the mean time, do you think it will be safe if I just keep the seacock closed and the breaker turned off?

Alex,
You know I'm your friend. I would hate to see anything happen to you or your family. I can't stand the thought of reading the headlines.

"Yacht erupts into huge fireball when captain turns on air conditioning."


- Friends don't let friends install bridge air.

 

[fwebster]

So you're telling us that the heat transfer from the ambient engine room temperature is going to heat up the water like it was coming out of a hot water heater when pumped through the circuit?

Science, theory, hydraulics, thermodynamics- whatever you want to call it don't lie. Sure 'real world' conditions can change things slightly, but this stuff isn't made up.

Doug

No, my concerns for Alex's approach are the one pump/one strainer for cooling. Computing BTU requirement and sizing units boils down to how cool he wants the bridge to get. The sea water approach everyone seems to be taking is a theoretical one based on volume and pressure. I think there are enough variables involved in this type of installation that it wouldn't hurt to examine a successful bridge air installation done by a Sea Ray dealer and warranted by Sea Ray. I agree, as long as the circulating pump is running, the water isn't in the engine room long enough to make a measurable difference........but what happens with the units cycle off and the pump stops running and water sits in the lines beside hot engines? How much cooling line is added to the system and what are the line losses?

Look, I'm just trying to help Alex with his installation based on real world knowledge after seeing several bridge air systems installed on 42/44DB's by a quality SR dealer. Alex is more than capable of doing his own homework. If he choses to take another approach after studying the facts, great. I don't come to CSR to argue minutiae with folks who come around just for confrontation. Alex can call, PM or email me if he wants further info from the dealer.

 

[Greg]

Line losses play a significant role in sizing the cooling system because of the added hose length. Bridge air adds about 4 miles of 5/8" hose to the cooling circuit

Wow, Alex's boat is big, but 4 miles of additional length? I assume that includes the heat exchanger in the condenser? It's been a while but if my math is right and even if 5/8" was the hose O.D. that works out to about 45 cubic feet. That is impressive that they can pack all that hose into a 3 cubic foot air conditioning unit.

That's also good to know for winterizing, because 4 miles of 5/8" hose is about 336 gallons. Alex, if you plan on winterizing this thing yourself you may want to start buying the antifreeze now.

 

[Alex F]

My understanding is that wear to A/C systems comes from cycling, not running.

Make sure that your through hull and plumbing does not restrict an 1800gph pump.

When I spoke with March tech support the first thing they asked me was the raw water intake size. I told them that it's a 1" hose and that I have about 20' levation. They said it should be fine and advised to use this pump. I did some measuring over last weekend and the actual elevation is only around 12'. The pump they're suggesting is designed for 47'.

....How much pressure can the system tolerate? I mean that's a ton of pressure. A hose clamp lets loose and you're in a world of hurt.

Isn't this an "open" system? The raw water gets in, does few loops and out goes right out of the discharge.

If a hose clamp goes on any currently installaed system you'll have quite of a mess.

As we discussed earlier here, I'll be installing the valves to control the pressure and will measure to make sure that the rate is about the same and not greater (with new pump) to existing A/C units.

Just trying to figure out how many gph that pump will actually draw. How much pressure you have to produce to adequately feed 3 units. ...

Well, isn't this why we have the venders that do all that before producing pumps A, B and C...?

Actually, I think he has more computations to make than that.

Pump volume capacity and pressure aren't the sole determining factors in the cooling system design. Line losses play a significant role in sizing the cooling system because of the added hose length. Bridge air adds about 4 miles of 5/8" hose to the cooling circuit and the system isn't going to cool properly with one pump. The more volume you push thru the system, the closer to sea water temps you keep the compressor and the cooler the compressor, the more effective the temperature change for human comfort. If you can lower the temp 20 degrees with your compressor system design, but your water flow is restricted to the point that your compressor temp is 105 degrees, them the best you can hope for is 85 degrees at the output, but if you can get the cooling water volume high enough to lower the compressor temp to 85 degrees, then your 20 degree temp differential at the output drops the output air to 65 degrees. It will make a difference.

Comparing this installation to other models is also a faulty premise because many larger Sea Ray now dump the cooling water into an exhaust tube molded into the engine exhaust system thus eliminating a fair percentage of the cooling system's small diameter tubing in the cooling circuit which also eliminates some of the systems line loss.

I'm not quite sure why is my installation is any different from what SR does, except generator upgrade? Let's recap, SR upgrades the existing A/C pump from 1000GPH to 1500GPH pump. This simply means that they're using single seacock, seastrainer and the pump to feed 3 units. This means that according to thair calculations the system get enough raw water supply to deliver expected results and do it SAFELY (without blowing up hoses and filling the salon without any kind of pressure controll valves). All I'm doing different is that I'm planning to take MARCH's advice to go for 1800GPH pump and add the valves to control the pressure, simply b/c it makes sense and you just can't fool the physics.

In regards to the hot ER temps, have you guys touched the A/C pump when it's been running for a while? You might burn your hands. So, forget ER temp, b/c the pump's temp is a LOT higher when it's been running for a some time.

 

[jg300da]

...but what happens with the units cycle off and the pump stops running and water sits in the lines beside hot engines?

Besides the water in the lines picking up heat? Nothing. Just like the other tens of thousands of boats of all sizes with A/C where the seawater pump and part of the water tubing resides in the bilge. When the pump starts and cool seawater starts circulating that heat is quickly dissipated by the large volume of entering water. Just as nothing adverse happens to the many dozens of components that share that same hot engine room on the same tens of thousands of boats.

Again, if you have no expertise in this field (which is obvious) why do you continue to post?

 

[douglee25]

I don't come to CSR to argue minutiae with folks who come around just for confrontation. Alex can call, PM or email me if he wants further info from the dealer.

I don't think anyone is here for confrontation. In the end, everyone is here to help Alex get a solid system designed for his needs. With that said, the false claims and misguidance here are huge.

Doug

 

[Turtlesboat]

misguidance? You mean the part where Sea Ray upgrades the Gen? or the part where people with 24kbtu units said 24Kbtu wasn't enough but we're still talking about 18KBTU, or the part where Sea Ray Dealers punch another hole in the boat to feed a bridge unit?

 

[douglee25]

Just because SeaRay does something doesn't mean it's correct or that it couldn't be done a different way.

Doug

 

[jg300da]

I think he was refering to comments like "how much pressure your hoses can take" and "blowing hoses all over the place" as well as "adds about 4 miles of 5/8" hose to the cooling circuit" You know, helpful educated comments like those. Oh, and my favorite "how long it'll take to fill the salon full of water when a hose lets loose".