Hot water tank construction

[Tricolor]

These coca cola tanks cost about nothing, buy one and give your idea a try. I also think that your approach will work better than what I made.

[Franziska]

Originally Posted by GILow

OK, the problem with kegs is that the dimensions are not all that suited to my location, also really hard to get the plumbing into the tank. I need to fit a copper coil in there, which means I need a big opening at the top. Any kind of metal tank is going to be a bugger to reweld, because my MIG will blow holes in anything thin.

Also, this tank is not under any pressure (other than that imposed by the kinetic mass of the water) and the temperature is fair way from engine temperatures. (see note above, 55 - 63 degrees C or 130 - 145 F)

I feel like the plastic tank will be ok if it is well supported... I suppose I could go back to my original thought of making a plywood and fibreglass tank... but I will see how the tank itself behaves without support, should get a chance to fire up the boiler this week.

Edit: Maybe the thing to do will be to support the tank with strapping before I pour the foam.... that and the plywood framework should support it well.

Regarding:"... OK, the problem with kegs is that the dimensions are not all that suited to my location, also really hard to get the plumbing into the tank. I need to fit a copper coil in there, which means I need a big opening at the top..."

Just thinking aloud.

Could you not bend the piping in a helical manor and thread it by "screwing" it through the hole in a keg.

[GILow]

Originally Posted by Franziska

Regarding:"... OK, the problem with kegs is that the dimensions are not all that suited to my location, also really hard to get the plumbing into the tank. I need to fit a copper coil in there, which means I need a big opening at the top..."

Just thinking aloud.

Could you not bend the piping in a helical manor and thread it by "screwing" it through the hole in a keg.

I think you’d end up with a keg full of crushed copper pipe.

Coiling copper pipe takes a lot of care and patience, and is best done with some kind of former to wrap the pipe around. I cannot begin to imagine how you could do it in the keg.

But keep thinking... I’m looking for ideas.

[GILow]

Originally Posted by Tricolor

These coca cola tanks cost about nothing, buy one and give your idea a try. I also think that your approach will work better than what I made.

I think the cola tanks sound great. But John and others have made the observation that the Webasto furnace cokes up if it is not run for a long time. I would rather NOT carry 10 gallons of dead weight around in the boat but it seems like the thing to do if I want to avoid expensive work on the furnace. It’s one of those things where I have to build this thing completely then wait and see how it goes.

John’s five years of no problems is reassuring. And doubly so because of where he lives and the way he has not had the problems many have experienced with the Webasto and the Planar furnaces. Lots of complaints about coking here on CF.

But also some good tips, like running the furnace on kerosene periodically helps prevent coking too.

[Typhoon]

Originally Posted by GILow

Hello again John. I PM’d you on the ColdEh handle, but perhaps you could answer here instead.

I was wondering if you felt the Webasto circulation pump would be adequate in my adaptation of your design, given it is just pumping coolant to/from the buffer tank?

Also, are you still happy with 55 to 63 degrees C coolant temperature?

Yes I think it will be fine , its the long runs around the boat through many finned heat exchangers that tax the pump.

Even the Jabsco pump gave out from the heat and I had to put on a killer pump that has been running for the past 3 years . Its a Gorman Rupp 12v mag drive coolant pump that is designed for this excact application.

In the winter I set the coolant temp to 59 and it flywheels up to 63 . Needs more heat when the water in the tanks is cold . In summer I set it to 55 and it is more then enough for all the hot water I want without running the engines when on the hook for an extended period of time .

Also I had to replace the stainless corrugated steel exhaust, dont use this , it runs noisey and corrodes , it fell apart . I now use copper tubbing and elbows cemented together , this has been much better and I cant here the furnace run at all . It must be the smooth larger interior of the pipe.

Regards John.

[Typhoon]

Originally Posted by GILow

I think the cola tanks sound great. But John and others have made the observation that the Webasto furnace cokes up if it is not run for a long time. I would rather NOT carry 10 gallons of dead weight around in the boat but it seems like the thing to do if I want to avoid expensive work on the furnace. It’s one of those things where I have to build this thing completely then wait and see how it goes.

John’s five years of no problems is reassuring. And doubly so because of where he lives and the way he has not had the problems many have experienced with the Webasto and the Planar furnaces. Lots of complaints about coking here on CF.

But also some good tips, like running the furnace on kerosene periodically helps prevent coking too.

I have no coke problems at all. The furnace runs clean , Keeping the injector nozzle new helps a lot , you can hear when it needs changing the furnace starts to rumble .

I pull fuel from my tanks I have never ran kerosene through it .

Also remember you will need an expansion tank , a point in the system with an air pocket above the coolant to give it room to expand as it heats up otherwise you will blow a hose.

Regards John,

[Tricolor]

Same experience here, used many different Webasto's for my boats and rv's and never had one wish a coke problem. Over 25y experience with them.

[GILow]

Originally Posted by Typhoon

I have no coke problems at all. The furnace runs clean , Keeping the injector nozzle new helps a lot , you can hear when it needs changing the furnace starts to rumble .

I pull fuel from my tanks I have never ran kerosene through it .

Originally Posted by Tricolor

Same experience here, used many different Webasto's for my boats and rv's and never had one wish a coke problem. Over 25y experience with them.

This is really interesting, and reassuring. There are so many here on CF who complain of coking... I wonder what the difference is? Is it simply run times, or is there another explanation? Off the top of my head I don't think there were geographical patterns that would indicate it was a fuel composition issue.

[GILow]

Originally Posted by Typhoon

Yes I think it will be fine , its the long runs around the boat through many finned heat exchangers that tax the pump.

Even the Jabsco pump gave out from the heat and I had to put on a killer pump that has been running for the past 3 years . Its a Gorman Rupp 12v mag drive coolant pump that is designed for this excact application.

In the winter I set the coolant temp to 59 and it flywheels up to 63 . Needs more heat when the water in the tanks is cold . In summer I set it to 55 and it is more then enough for all the hot water I want without running the engines when on the hook for an extended period of time .

Also I had to replace the stainless corrugated steel exhaust, dont use this , it runs noisey and corrodes , it fell apart . I now use copper tubbing and elbows cemented together , this has been much better and I cant here the furnace run at all . It must be the smooth larger interior of the pipe.

Regards John.

This is good news, as I've bought a magnetic drive coolant pump. I expect the duty cycle of the heating pump will be pretty trivial here in Oz when compared to Canada.

Interesting point about the exhaust. I will experiment a little and see what it sounds like without the muffler. My kit came with the muffler so I have it already.

[Franziska]

Originally Posted by GILow

I think you’d end up with a keg full of crushed copper pipe.

Coiling copper pipe takes a lot of care and patience, and is best done with some kind of former to wrap the pipe around. I cannot begin to imagine how you could do it in the keg.

But keep thinking... I’m looking for ideas.

I meant you create like a spiral before inserting it and than feed it in the keg in a screwing type motion by rotating the spiral through the hole.

[AndyEss]

Instead of MIG welding a new SS or Al top to a beer keg (yep, blowing holes through the thin metal is a problem) why not glue in a plastic or plywood cap?
The adhesive would have to have some compliance to accommodate differing expansion rates of the metal keg and cap, but that shouldn't be too tough to spec. Your buffer tank isn't pressurized, so this bond won't be loaded excessively.

[AndyEss]

Originally Posted by Franziska

I meant you create like a spiral before inserting it and than feed it in the keg in a screwing type motion by rotating the spiral through the hole.

I think you are envisioning a double legged spiral.
To get around the very sharp bend at the tank end, solder on a U-fitting made from a 90 elbow and a street elbow (or two elbows and a very short stub in between).
Should work fine - good idea.

[Franziska]

Originally Posted by AndyEss

I think you are envisioning a double legged spiral.
To get around the very sharp bend at the tank end, solder on a U-fitting made from a 90 elbow and a street elbow (or two elbows and a very short stub in between).
Should work fine - good idea.

You nailed it, exactly, that's what I meant.

Important, try to make the u bend as big as you can (depends on the size of your hole in the keg) , that will reduce flowspeed a little less.

In your drum/radiator pipes use a heat retention fluid of some sorts instead of pure water. Water is not the best for keeping heat. You might also think about adding a bit of antifreeze if you do not want to drain in winter (pending if that's an issue in your area).

[sailorchic34]

Well, here I am being a Debby Downer again. Just fyi, I have some experience designing hot water systems to 1200 gpm or so.


Anyway, What the OP is looking at doing is using a 11 gallon tank as a buffer tank, with a copper heating coil and a copper domestic hot water coil.


Lets do a bit of math. Sorry for the imperial units... it's that inbred American thingy.



So lets assume you want to heat one gallon per minute of cold water to hot, say 110f (43c). so 1 gallon x 8.33 (pounds per gallon) X60 degrees (raises 50 degrees F water to 110 degrees F.) = 500 btu per minute. Take that 500 btu x 60 minutes = 30,000 BTU. allow for 80% efficiency in boiler and you need a boiler that produces 37.500 btuh or 10.8kw. This btw is how a formally blonde american engineer might size a heating or domestic hot water boiler.



Of course we can use some of the heat in the 11 gallons. That is the part from 140 degrees F to 110 degrees F (I'm assuming a typical anemic boat shower). So 11x8.33 x30 (140F - 110F) equals 2748 BTU's or enough to heat 5 gallons of water to 110 F ish.



Of course you have to reduce amount of stored water by the area of the two copper loops which will be lots. Probably about 1/3 to 1/2.



I'm betting the OP's unit is maybe 3-4 kw or 10mbh to 13.6 mbh (m for 1000, b for BTU and h for hour). That's about enough for maybe 0.2 gpm which is not a nice shower.



Now if you were using a pressure vessel, you could just take the return heating loop back through the water heater and use 10 degrees F delta to heat the fresh water. It's more or less how the typical marine water heater works. However a plastic pressure vessel as Egon Spengler (ghostbusters) would say, would be bad, as it will not like the 140 degree F working temp and oh say 50 psig working pressure.



So I suspect the OP's system may be less then optimal.

[AndyEss]

Originally Posted by sailorchic34

Well, here I am being a Debby Downer again. Just fyi, I have some experience designing hot water systems to 1200 gpm or so.


Anyway, What the OP is looking at doing is using a 11 gallon tank as a buffer tank, with a copper heating coil and a copper domestic hot water coil.


Lets do a bit of math. Sorry for the imperial units... it's that inbred American thingy.



So lets assume you want to heat one gallon per minute of cold water to hot, say 110f (43c). so 1 gallon x 8.33 (pounds per gallon) X60 degrees (raises 50 degrees F water to 110 degrees F.) = 500 btu per minute. Take that 500 btu x 60 minutes = 30,000 BTU. allow for 80% efficiency in boiler and you need a boiler that produces 37.500 btuh or 10.8kw. This btw is how a formally blonde american engineer might size a heating or domestic hot water boiler.



Of course we can use some of the heat in the 11 gallons. That is the part from 140 degrees F to 110 degrees F (I'm assuming a typical anemic boat shower). So 11x8.33 x30 (140F - 110F) equals 2748 BTU's or enough to heat 5 gallons of water to 110 F ish.



Of course you have to reduce amount of stored water by the area of the two copper loops which will be lots. Probably about 1/3 to 1/2.



I'm betting the OP's unit is maybe 3-4 kw or 10mbh to 13.6 mbh (m for 1000, b for BTU and h for hour). That's about enough for maybe 0.2 gpm which is not a nice shower.



Now if you were using a pressure vessel, you could just take the return heating loop back through the water heater and use 10 degrees F delta to heat the fresh water. It's more or less how the typical marine water heater works. However a plastic pressure vessel as Egon Spengler (ghostbusters) would say, would be bad, as it will not like the 140 degree F working temp and oh say 50 psig working pressure.



So I suspect the OP's system may be less then optimal.

Boo, hiss.

Here we are merrily brainstorming solutions to the OPs question, and some engineer - a blond at that - slaps us up the head with reality.

(I'm a retired engineer)

Excellent analysis, Btw. I'm impressed.