Hot water tank construction

[Tricolor]

+1 (that's why I have some experience with Webasto's) for cooking, how much I dislike it, there is on a small yacht for me still no alternative for propane gas.

[Franziska]

Originally Posted by Tricolor

Dutch website;
https://www.propaangeiser.nl/nl/prod...ropaan-butaan/

UK website;

https://www.propanegaswaterheaters.c...r-propane-but/
I don't know where you got this wrong info from.

Direct propane/butane water heaters are allowed in the whole of Europe, see the EU Certificates on the website, as they are a closed system, fresh air and exhaust from the oitside, they can be used safe on boats and rv's

Just because it's on the site of someone selling it does not mean it's legal and that the installation can be certified.

Unless it has been allowed since the last info I received (2015) it was not legal to install a closed system with fully externally vented exhaust, intake and burn chamber on the inside of the boat.

I was hoping to be allowed to install one and the Dutch sales person told me the Cointra system would be legal.
Check back with the official bodies in Germany brought to light that it was not certifiable in 2015.

Only existing old systems could be certified with under a "grand-fathering" rule.

The information at the time came from Deutscher Boots- und Schiffbau Verband as well as from Mr. Stöhr @ Deutscher Verband Flüssiggas.

If it would have been allowed I would have installed in no time!

[Tricolor]

I come back on this topic, can't believe this.

[Franziska]

So tricolor,

I'd be very happy if you can show to us on the base of the applicable norms&standarts (recreational craft directive & standarts) that the legislation has been changed by now.

It would be wonderful if that would be the case now and I truly would appreciate to learn that.

[Tricolor]

Franziska I called k.i.i.p bv in the Netherlands and they confirmed that your comments here are NOT true. I advice everyone who is interested in their products to call them. So aa far as for me this subject os closed.

PS. If you want yo learn something then do as I did and call the producer in The Nethwrlands and not scam them without any proof.

[Franziska]

And that was exactly the dealer who claimed it was legal back than.

I double checked with officials (stated above) here in Germany back then and they said you will get the installation not certified and you will get no insurance either without that inspection.

Kiip has every interest to claim its legal as they want you to buy their stuff. I suggest you check with someone who does certify gas installations to standart on BOATS.

I decided not to buy in 2015 after I did exactly that.

By all means buy it if you feel otherwise, your choice & your boat & your risk. Go for it.

But do not put the claim up that the installation is fully legal and that I do give misinformation unless you can point us to the correct official (and not sales info!) information.
I am happy to learn and even buy if the situation has really changed.

Check with an outside source (and not someone outside suggest by Kiip or Cointra or associated with them.) I'm happy to see the relevant standarts and norms showing that a BOAT installation is legal. If that would be the case it would great.

[sailorchic34]

Originally Posted by GILow

Sorry SC, but I really don't think you are describing my system at all. I have read your post a number of times now, and nothing tallies with what I have drawn.

Did you see my diagram? Where is this second domestic hot water coil? How does the heating loop have anything to do with the water heater?

I am VERY confused now.

Sorry, the domestic hot water is the cold water coil from your fresh water tank that heats the domestic/potable water for cooking/ showering. I assumed you would add a second hydronic loop as your break tank is at atmospheric pressure and your hydronic loop will be pressurized just a bit. If nothing else from expanded water and perhaps pump head.

You really don't want to pressurize that plastic tank at all. Why. Well lets have fun. Lets assume the tank is 12" in diameter and is pressurized to 4 PSI (pounds per square inch). This either from pump head pressure or thermal expansion.

So the area of the cap is 113 square inches (6x6xpi). 113 sq inch x 4 psi equals 452 pounds of force trying to push the cap off. Plastic is weak structurally and gets weaker the more it's heated. This is why we don't make pressure vessels from plastic.

Fun fact: steel looses up to 80 percent of it's ultimate strength at 600 degrees F.

That is why I assumed there was a second loop...

Anyway, the break tank is just a wide spot in the piping with a bit of thermal mass.

Your basically heating the potable shower water in a more of less instantaneous way. That is energy intensive. So a 5.2kw heater is equal to 17,742 BTUH or 17.7MBH. (3412 btu's per KW) So your heater puts out 295 btu's per minute. That would heat 0.59 gpm or roughly 2 lpm

Now as I said the tank does offer some storage. Lets assume 9 gallons allows 2 gallons for the copper coil for heating domestic water. So 9 gallons x 8.33 lb's per gal x 30 F (delta between stored water temp at 140f and hot water design temp of 110F). So that gives 2,249 btu's.

Lets assume 4 lpm of hot water for the shower. That's 1.06 gpm. so heating 4 lpm takes 529 btuh (BTU's is a much easier way then Joules which makes huge numbers). So your buffer tank in theory can provide about 4 minutes of hot water.

I say in theory, as in reality it will be less. This as the temperature in the buffer tank approaches the water temp in the pipe the heat transfer rate slows down. LOTS. So lets say that you get 3 minutes of hot water. perhaps a bit less. Still not a bad sailor shower. This assumes you have enough copper surface area to get the heat transfer dialed in.

Now the normal marine water heater, puts the domestic water / fluid in the tank and the hydronic loop in the coil. In this way a 11 gallon tank will give about 9 gallons of hot water, before the entering cold water cools the tank too much.

That is a much better way of doing it, specially when the boiler is too small to provide instant hot water . It just can't be done in plastic as plastic makes a very poor pressure vessel. You will get a much better system overall by using a metal pressure tank.

BTW when I was designing that 1200 GPM instant domestic hot water system, it was fed with 125 lb steam from multiple 700 BHP steam boilers. That was for the Venetian in Las Vegas. That was the biggest system I have designed. I suspect it's the biggest anyone has designed that's not industrial.

[sailorchic34]

Originally Posted by Franziska

Just because it's on the site of someone selling it does not mean it's legal and that the installation can be certified.

Unless it has been allowed since the last info I received (2015) it was not legal to install a closed system with fully externally vented exhaust, intake and burn chamber on the inside of the boat.

Ah... the unit takes combustion air from outside and the burner/heat exchanger is sealed from the inside of the building. In the USA this is called direct vent sealed combustion.

Of course I can see where a unit could be approved in the Netherlands and not approved in Germany.

It's even more fun in the US where codes are set at the state and sometimes City level. So something approved in say Florida might not be approved for use in California. Not at all uncommon and something I had to deal with for way too long. So Happy I'm retired now.

[Franziska]

Originally Posted by sailorchic34

Ah... the unit takes combustion air from outside and the burner/heat exchanger is sealed from the inside of the building. In the USA this is called direct vent sealed combustion.

Of course I can see where a unit could be approved in the Netherlands and not approved in Germany.

It's even more fun in the US where codes are set at the state and sometimes City level. So something approved in say Florida might not be approved for use in California. Not at all uncommon and something I had to deal with for way too long. So Happy I'm retired now.

Actually there is a European legal base by now for that sort of stuff called European Recreational Craft Directive which lists all relevant standarts to be adheard to by boat builders in member states of the EU.

So the flexibility of individual states to deal with such things is very limited.
This serves the aim to create a harmonized market with common safety criteria.

I am not opposed against those instant water heaters, they are used in a lot of places world wide and I really wish we could use them here as well.
Accidents with them are fairly few (but desasterous) when they happen.

After all most boats have Propane driven stoves already on board. (Let's not get into the old discussion on their safety now...).

[RaymondR]

The original question was related to how to construct a container for hot water.

The container to consist of: a fluid barrier constituted of a plastic material, a thermal barrier consisting of pour in expanding foam, structural containment of the foam and plastic constituted by a plywood box.

It is rightly assumed that since there is no functional requirement for the containment to be pressurized that it will be vented to the atmosphere.

Consequently, the only pressures to be considered are those generated by the small head of fluid and those generated by inertial forces acting upon the head of fluid. The design as initially proposed is adequate for it's purpose.

[Franziska]

Thank you Raymond.

Done with this stupid discussion on the other subject now.
May everyone do what they please and feel is right for them.

Back to the by the opener intended subject. Sorry about that degression.

[sailorchic34]

Originally Posted by RaymondR

It is rightly assumed that since there is no functional requirement for the containment to be pressurized that it will be vented to the atmosphere.

Consequently, the only pressures to be considered are those generated by the small head of fluid and those generated by inertial forces acting upon the head of fluid. The design as initially proposed is adequate for it's purpose.

Ah, The pump will develop head probably on the order of 10-12 feet of head or 4.3 to 5.2 psig. This is required to overcome the friction loss in piping and heating coils, etc.

So if the break tank is connected on the discharge side of the pump then the water could exit the atmospheric vent (assuming said vent was less then 10 feet above the pump.

If the break tank was on the suction side of the pump, it might work, specially if a balance valve was added to eat the latent head, but might still be pressurized a pound or two.

Most land side hydronic systems are pressurized to 5-15 psig. You really don't want to operate the pump in the NPSH range (below zero gauge pressure) without doing calculations and checking pump curves to make sure it will work.

I've know professional engineers ( I was one too) who have missed that tiny detail on 30 million dollar systems, when sizing condenser water pumps that can and do operate below zero pressure gauge at the suction inlet.

They told me I did not know what I was talking about, when I pointed out that the pumps would be operating below their required NPSH. I was reviewing their plans as the owners rep. They built it and lo it operated exactly where I said it would and captivated all to hell. This was four 7500 gpm 900 rpm pumps. When I was asked how do we fix it, I said it could not be fixed, as it was a systemic error. I said they could raise the cooling towers ten feet higher (they were already mounted 8 feet above the ground. Alas the pump volute was 5 feet high, so they only had 3 feet of vertical head.. Fun times.

[Tricolor]

Back to the beginning, as far as I still understand Raymond wants to build a approx. 10 gallon box shaped watertank and heat the water directly, without a coil, with a kind of Webasto. In this body of water he wants to put a coil to direct heat his shower. Correct Raymond? If he uses a Webasto +/- 5 kW these have a build in circulation pump and from experience I know that these pumps work perfect with an atmospheric pressure tank.
Then the question is if you can make a coil that generate enough heat by a flow acceptable for a shower.

[GILow]

Originally Posted by Tricolor

Back to the beginning, as far as I still understand Raymond wants to build a approx. 10 gallon box shaped watertank and heat the water directly, without a coil, with a kind of Webasto. In this body of water he wants to put a coil to direct heat his shower. Correct Raymond? If he uses a Webasto +/- 5 kW these have a build in circulation pump and from experience I know that these pumps work perfect with an atmospheric pressure tank.
Then the question is if you can make a coil that generate enough heat by a flow acceptable for a shower.

Well, only my closest friends call me Raymond. The rest call me Matt, or on the forum I am often called GILow. (Raymond did add some good posts though)

I think you have added the word I should have put in right at the start. “Acceptable”. I’m on a 40 year old mono and I just need an “acceptable “ shower and according to Typhoon, (and my calculations) this will do it.

At least there seem to be no concerns about the boat heating side of the system. At least not yet.

[Tricolor]

[emoji35] I am ashamed for missing your name, sorry.